U.S. patent application number 09/854647 was filed with the patent office on 2001-10-11 for multi-slice detector array.
Invention is credited to Dafni, Ehud, Feldman, Andre, Freundlich, David, Nahaliel, Ehud, Ruimi, David.
Application Number | 20010028697 09/854647 |
Document ID | / |
Family ID | 11069168 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010028697 |
Kind Code |
A1 |
Nahaliel, Ehud ; et
al. |
October 11, 2001 |
Multi-slice detector array
Abstract
Apparatus for producing multiple image slice data responsive to
incident radiation, comprising: a detector array, comprising at
least a first detector element and a second detector element
disposed in a lateral direction, which detector elements generate
signals responsive to radiation incident thereon, wherein each
detector element is characterized a width in the lateral direction,
wherein each detector element is characterized by an effective
detector width, defined by the portion of the width of the detector
element that is exposed to the radiation, and wherein the second
detector element is shifted in the lateral direction relative to
the first detector element, so as to overlap and mask a portion of
the first detector, thereby altering the first detector's effective
width.
Inventors: |
Nahaliel, Ehud; (Lower
Galilee, IL) ; Dafni, Ehud; (Caesarea, IL) ;
Feldman, Andre; (Haifa, IL) ; Ruimi, David;
(Netanya, IL) ; Freundlich, David; (Haifa,
IL) |
Correspondence
Address: |
Wm Dippert
c/o Cowan, Liebowitz & Latman
1133 Avenue of the Americas
New York
NY
10036-6799
US
|
Family ID: |
11069168 |
Appl. No.: |
09/854647 |
Filed: |
May 14, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09854647 |
May 14, 2001 |
|
|
|
09242079 |
Feb 4, 1999 |
|
|
|
6243438 |
|
|
|
|
09242079 |
Feb 4, 1999 |
|
|
|
PCT/IL97/00267 |
Aug 6, 1997 |
|
|
|
Current U.S.
Class: |
378/19 ; 378/207;
378/4 |
Current CPC
Class: |
G01T 1/1647 20130101;
G01N 23/04 20130101; G01N 23/046 20130101; A61B 6/032 20130101;
A61B 6/5205 20130101; G01T 1/2985 20130101; A61B 6/4085
20130101 |
Class at
Publication: |
378/19 ; 378/4;
378/207 |
International
Class: |
G01N 023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 7, 1996 |
IL |
119033 |
Claims
1. Apparatus for producing multiple image slice data responsive to
incident radiation, comprising: a detector array, comprising at
least a first detector element and a second detector element
disposed in a lateral direction, which detector elements generate
signals responsive to radiation incident thereon, wherein each
detector element is characterized a width in the lateral direction,
wherein each detector element is characterized by an effective
detector width, defined by the portion of the width of the detector
element that is exposed to the radiation, and wherein the second
detector element is shifted in the lateral direction relative to
the first detector element, so as to overlap and mask a portion of
the first detector, thereby altering the first detector's effective
width.
2. Apparatus in accordance with claim 1, and comprising an
adjustable slit or aperture, which masks a portion of the second
detector, thereby altering the second detector's effective
width.
3. Apparatus in accordance with claim 1, wherein the effective
widths of the first and second detectors are substantially
equal.
4. Apparatus in accordance with claim 1, wherein the detector array
is planar in shape.
5. Apparatus in accordance with claim 1, wherein the detector array
is arcuate in shape.
6. Apparatus for producing image slice data responsive to incident
radiation, comprising: a detector array, comprising one or more
rows of detector elements, which generate signals responsive to
radiation incident thereon; and at least one mechanical tilting
device, which controllably tilts at least one of the one or more
rows about a tilt axis thereof, which tilt axis is substantially
parallel to the long dimension of the at least one row, wherein the
one or more rows are characterized by a width, measured in a
direction perpendicular to the tilt axis thereof, and wherein an
effective width of the at least one row, defined by a geometrical
projection of the width thereof onto a plane that is substantially
perpendicular to a direction of propagation of the radiation
incident on the row, is varied by controlling the at least one
mechanical tilting device.
7. Apparatus in accordance with claim 6, wherein the one or more
rows comprises a plurality of rows, and wherein the mechanical
tilting device tilts all of the plurality of rows in the array.
8. Apparatus in accordance with claim 7, wherein the at least one
mechanical tilting device tilts all the rows of the array by a
common angle.
9. Apparatus in accordance with claim 7, wherein the at least one
mechanical tilting device tilts the entire array about a common
tilt axis.
10. Apparatus in accordance with claim 7, wherein the at least one
mechanical tilting device comprises a plurality of such devices,
which tilt about different, respective axes.
11. Apparatus in accordance with claim 10, wherein each row of the
array is tilted about its own respective axis.
12. Apparatus in accordance with claim 10, and comprising a motion
control mechanism, which controls a distance between adjoining rows
of the array when they are tilted, so that geometrical projections
of the rows onto the plane that is substantially perpendicular to
the direction of propagation of the radiation incident on the array
are substantially contiguous.
13. Apparatus in accordance with claim 1, and including one or more
logarithmic amplifiers, to which signals generated by the detector
elements are applied.
14. Apparatus in accordance with claim 13, wherein the one or more
logarithmic amplifiers comprise a plurality of logarithmic
amplifiers, each of which is coupled to a respective one of the
detector elements.
15. Apparatus in accordance with claim 13, wherein the one or more
logarithmic amplifiers receive output data from the signal
processing circuitry.
16. Apparatus in accordance with claim 1, and including a data
acquisition system, which receives the plurality of channels of
output data.
17. Apparatus in accordance with claim 16, and including a
reconstructor, which receives data from the data acquisition system
and reconstructs a multiple-slice image therefrom.
18. Apparatus in accordance with claim 17, wherein the
multiple-slice image comprises image slices, characterized by a
variable slice thickness, and wherein the slice thickness is
determined by the effective widths of the channels of output
data.
19. Apparatus in accordance with claim 17, and including a display,
which displays the multiple-slice image.
20. Apparatus in accordance with claim 19, and including a
processor, which prints the multiple-slice image.
21. A CT scanner, for producing images of multiple sectional slices
through an object, comprising: a radiation source, which irradiates
the object from a first side thereof; and apparatus for producing
image slice data in accordance with claim 1, wherein the detector
array is positioned on a second side of the object, opposite to the
first side.
Description
RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. application
Ser. No. 09/242,079, which was filed in the U.S. Patent and
Trademark Office on Feb. 4, 1999 as a national application of
PCT/IL97/00267, filed Aug. 6, 1997.
FIELD OF THE INVENTION
[0002] The present invention relates generally to transmission
computerized tomographic (CT) systems, and specifically to
segmented array detectors for use in such systems to simultaneously
acquire data from multiple axial slices.
BACKGROUND OF THE INVENTION
[0003] CT scanning systems and methods are well known in the art,
particularly for medical imaging and diagnosis, but also in other
fields of imaging, for example, industrial quality control.
[0004] CT scanners generally create images of one or more sectional
slices through a subject's body. A radiation source, such as an
X-ray tube, irradiates the body from one side thereof. A
collimator, generally adjacent to the X-ray source, limits the
angular extent of the X-ray beam, so that radiation impinging on
the body is substantially confined to a planar region defining a
cross-sectional slice of the body. At least one detector (and
generally many more than one detector) on the opposite side of the
body receives radiation transmitted through the body substantially
in the plane of the slice. The attenuation of the radiation that
has passed through the body is measured by processing electrical
signals received from the detector.
[0005] Typically, in commonly-used third- and fourth-generation CT
scanners, the X-ray source (or multiple sources) is mounted on a
gantry, which revolves about a long axis of the body. In
third-generation scanners, the detectors are likewise mounted on
the gantry, opposite the X-ray source, while in fourth-generation
scanners, the detectors are arranged in a fixed ring around the
body. Either the gantry translates in a direction parallel to the
long axis, or the body is translated relative to the gantry. By
appropriately rotating the gantry and translating the gantry or the
subject, a plurality of views may be acquired, each such view
comprising attenuation measurements made at a different angular
and/or axial position of the source. Commonly, the combination of
translation and rotation of the gantry relative to the body is such
that the X-ray source traverses a spiral or helical trajectory with
respect to the body. The multiple views are then used to
reconstruct a CT image showing the internal structure of the slice
or of multiple such slices, using methods known in the art.
[0006] The lateral resolution of the CT image, or specifically, the
thickness of the slices making up the image, is generally
determined by the angular extent of the radiation beam or of the
individual detectors, whichever is smaller. The use of thick slices
is advantageous in increasing the signal/noise ratio, and thereby
reducing the time needed to acquire the data needed to reconstruct
an image. But images reconstructed using thick slices have poor
resolution in the axial direction and are more susceptible to
partial volume artifacts, i.e., imaging errors that are introduced
when a single volume element (voxel) within a slice contains two
types of tissue having different attenuation coefficients.
[0007] Smaller detectors are generally used, therefore, to improve
axial resolution and reduce partial volume artifacts. Excessive
reduction of the extent of the detector, however, leads to
degradation of the signal/noise ratio and decreases the throughput
of the imaging system. Using very small detectors can also reduce
the system's dose efficiency, i.e., increase the relative amount of
radiation to which the portion of the body being imaged is exposed,
because the angular extent of the X-ray beam irradiating the body
will typically extend somewhat beyond the bounds of the detectors.
Radiation outside these bounds is "wasted," since it is not used in
forming the CT image
[0008] In order to improve throughput, as well as increase axial
resolution and utilize the X-ray source more efficiently, various
inventors have described the use of differently configured detector
arrays. Such arrays typically include a plurality of radiation
detectors, such as scintillator-photodiodes, which receive
radiation simultaneously from a radiation source and are thereby
used to acquire multiple views and/or multiple slices
simultaneously. Spiral modes of translation and rotation, as
mentioned above, are frequently combined with multi-slice image
acquisition to cover a greater volume of the body in less time with
improved axial resolution.
[0009] For example, U.S. Pat. No. 4,965,726, to Heuscher, et al.,
whose disclosure is incorporated herein by reference, describes a
CT scanner with a plurality of segmented detector arrays. Each
array includes a plurality of rows of radiation-sensitive cells.
The rows may have different dimensions in a lateral direction,
perpendicular to the long dimension of the rows, and the effective
lateral dimensions of the rows may be varied by moving collimators
adjacent thereto, so as to provide slices of the same or different
lateral thicknesses. Multiple detectors may be grouped together in
the lateral direction to provide thicker slices, so as to improve
the signal/noise ratio and throughput of the scanner, while
reducing partial volume artifacts relative to slices of comparable
thickness that are acquired using a single detector having an
equivalent lateral dimension.
[0010] U.S. Pat. No. 5,241,576, to Lonn, whose disclosure is
likewise incorporated herein by reference, similarly describes a CT
scanner including an array of detector elements for the purpose of
acquiring thick-slice images with reduced partial volume artifacts.
The array includes a plurality of detector elements, wherein each
such element includes a set of sub-elements disposed along the
slice thickness (lateral) dimension. The signal output of each
sub-element is processed individually, generally by taking the log
of the signal and applying a weighting factor thereto. The
processed outputs of the plurality of sub-elements belonging to a
single element are then summed together to form a combined
thick-slice signal.
[0011] U.S. Pat. No. 5,430,784 to Ribner, et al., whose disclosure
is also incorporated herein by reference, describes a CT scanner
and detector array having a plurality of rows of identical
detectors, which are connected together by a controllable switching
matrix. This switching matrix is controlled to interconnect a
predetermined number of successive detector sub-elements, in order
to produce combined signals corresponding to one or more slices of
a desired thickness.
[0012] U.S. Pat. No. 4,417,354, to Pfeiler, whose disclosure is
incorporated herein by reference, describes a CT scanner including
a detector array that is mounted to pivot about a lateral axis,
perpendicular to an image slice acquired by the array. The array is
pivoted in order to increase the effective resolution within the
image slice, but only a single image slice is provided, and no
suggestion is made of changing the slice thickness by pivoting the
array about a transverse axis.
[0013] Similarly, U.S. Pat. No. 5,493,593, to Muller et al., whose
disclosure is incorporated herein by reference, describes a scanner
for CT microscopy including a tiltable detector array, which is
also shifted horizontally in order to maximize the utilization of
the array. Only a single image slice is provided, however, without
suggestion of changing the slice thickness.
SUMMARY OF THE INVENTION
[0014] It is an object of the present invention to provide detector
arrays for simultaneous acquisition of multiple image slices of
variable thickness. Preferably, at a given time all the slices are
of substantially equal thickness, and the thickness may be
accurately and conveniently controlled.
[0015] In one aspect of the present invention, the thickness is
controlled in successive steps of increasing thickness.
[0016] In another aspect of the present invention, the number of
switching and summation elements needed for combining adjacent
elements of such detector arrays to form slices of a desired
thickness is minimized.
[0017] In another aspect of the invention, the outputs of the
elements are combined to provide slices of variable thickness.
Preferably, one or two thick slices are provided together with one
or two thin slices wherein the ratio between the thickness of the
two types of slices is greater than 2:1, more preferably, greater
than 3:1 and most preferably greater than 5:1. In a preferred
embodiment of the invention, the ratio of the thicknesses is 9:1 or
10:1.
[0018] Preferably, the detector arrays comprise radiation detectors
and are used in CT scanner systems.
[0019] In preferred embodiments of the present invention, a
detector array, for use in an imaging system, comprises a plurality
of rows of detectors, each row characterized by a width in a
lateral dimension perpendicular to the long axis of the row, which
long axis is typically aligned in the imaging system in a generally
circumferential direction relative to a body being imaged. The
detectors in each row receive radiation from a corresponding slice
of an object being imaged and generate signals in response to the
radiation. Preferably the array includes rows having different
widths, more preferably at least four different widths. A minimum
slice thickness is defined by a lateral dimension of a slice, i.e.,
a dimension of a slice measured in a direction parallel to the
lateral dimension of the rows, corresponding to a row of the array
having the smallest width. Switching circuitry associated with the
array selectively combines signals generated by adjacent detectors
in different rows, so as to produce sum signals corresponding to
multiple slices having a common thickness, which is a selectable
value equal to or greater than the minimum slice thickness.
[0020] Preferably the switching circuitry produces sum signals
corresponding to at least four laterally-adjacent, substantially
contiguous slices, all of which have a common thickness. Acquiring
multiple, contiguous image slices simultaneously, as described
herein, generally increases the throughput and/or resolution of the
imaging system. In general, multi-slice imaging also increases the
dose efficiency of the system, i.e., reduces the relative amount of
radiation to which the body is exposed in producing a CT image,
particularly when thin image slices are acquired, since using
multiple rows of detectors reduces the relative amount of "wasted"
radiation falling outside the bounds of the detectors.
[0021] In preferred embodiments of the present invention, the
switching circuitry may combine the signals using any appropriate
circuit elements and computational algorithms known in the art.
Preferably, the signals undergo a log operation, as is known in the
art, and are digitized and summed. However, other suitable
operations may similarly be used, and the order of performing the
operations may be varied, as desired to reduce the cost and/or
number of components in the imaging system, subject to the
requirement that the system produce images of a desired quality. It
will be understood that image quality includes measures of
resolution, signal/noise ratio, artifacts, particularly partial
volume artifacts, and other measures known in the art.
[0022] In some preferred embodiments of the present invention, the
detector array comprises four adjacent central rows, having a
common lateral width, which is the smallest width of rows in the
array, and a plurality of peripheral rows, symmetrically arranged
on both sides of the four central rows. The widths of the
peripheral rows are preferably integer multiples of the width of
the central rows, wherein the widths of the rows preferably
generally increase with the lateral distance of the rows from the
central rows.
[0023] In some preferred embodiments of this type, the fifth and
sixth rows, which are peripherally adjacent to the four central
rows on either side thereof, have a common width generally twice
that of the central rows. The seventh and eighth rows, which are
peripherally adjacent to the fifth and sixth rows, respectively,
have a common width generally twice that of the fifth and sixth
rows. Ninth, tenth and additional pairs of rows, if desired, are
similarly added peripherally as desired, each additional row having
width generally twice that of its inner neighbor.
[0024] In accordance with such preferred embodiments, when four
slices of the minimum thickness are desired, switching circuitry
selects signals only from the four central rows. To produce four
slices of a greater thickness, approximately twice the minimum
thickness, the switching circuitry selects signals from the fifth
and sixth rows to produce two such slices, and combines signals
generated by mutually adjacent first and second rows of the four
central rows and by mutually-adjacent third and fourth rows
thereof, to produce two more such slices. To produce four slices of
approximately four times the minimum thickness, the switching
circuitry selects signals from the seventh and eighth rows to
produce two such slices, and combines signals from the first,
second and fifth rows (the fifth row being adjacent to the first
row) to produce a third such slice, and from the third, fourth and
sixth rows to produce a fourth slice. Four slices of thickness
corresponding to the width of any of the rows of the array, up to
the largest such width, may similarly be produced.
[0025] In this and other preferred embodiments of the present
invention, the slice thicknesses are generally measured at the
location of the object being imaged. These thicknesses depend
primarily upon the width of the corresponding row or combined rows
of detectors, but are also affected by other elements of the
imaging system in which the detector array is used. Such elements
typically include a radiation source and beam-control optics, such
as collimator slits. Therefore, while the slice thicknesses are
approximately proportional to the row widths, other aspects of the
system must be taken into account to determine the slice
thicknesses accurately.
[0026] Thus, in the context of the present invention, it will be
understood that the use of the term "substantially" or
"approximately" in stating a detector width dimension, for example
to say that the width of rows of detectors are substantially equal,
or that the thickness of one row is substantially an integer
multiple of another row, means that the detector thickness is such
that the slices traversed by the radiation beam has approximately
the stated dimension or ratio. This includes any correction to the
detector width which might be required, for example to correct for
the difference between the effective thickness a.sub.eff and the
thickness that would be obtained if focal point 78 were
infinitesimal or for other geometrically caused variation between
the effective slice width and the detector width. Such correction
is generally very small compared to the detector and slice
dimensions of interest.
[0027] It will be appreciated that the preferred embodiments
described above allow a wide range of choices of slice thickness to
be produced by the detector array and switching circuitry, relative
to the number of rows in the array. For example, an array having
ten rows of detectors, in accordance with a preferred embodiment of
the present invention of the type described above, will be capable
of producing four slices having a common thickness, which is
variable from a minimum slice thickness up to a maximum thickness
approximately eight times the minimum slice thickness. By
comparison, an array composed of rows of detectors having equal row
widths would require 32 rows of detectors in order to produce such
an 8:1 range of slice thicknesses, and would also require
considerably more complex and costly switching circuitry to
accomplish this purpose. In other, analogous preferred embodiments
of the present invention, arrays having greater or lesser numbers
of rows may be used to similar advantage.
[0028] Furthermore, in the preferred embodiments of the present
invention described above, the selection of slice thicknesses is
accomplished without the use of any additional mechanical aperture,
collimator or beam optics.
[0029] In other preferred embodiments of the present invention,
however, a linear aperture whose width is variable in a lateral
direction, i.e., the direction parallel to the lateral dimension of
the rows of the array, is used in conjunction with the detector
array and switching circuitry to produce slices having desired
thicknesses. In one preferred embodiment of this sort, two central
rows of the array have the smallest width, and peripheral rows
having greater widths are symmetrically arranged on both sides of
these two central rows. The aperture is constructed and aligned so
that when it is fully open, all rows of the array are exposed to
radiation from the object. When the aperture is narrowed, however,
it masks all or portions of successive peripheral rows in the
array, preventing radiation from impinging thereon. The aperture
thus controls the effective widths of the peripheral rows by
covering or exposing desired portions thereof.
[0030] Signals from mutually-adjacent detectors in different,
selected rows of the array are combined by the switching circuitry,
as described above, to produce multiple image slices having a
common, desired thickness. By appropriately varying the aperture
from a minimum to a maximum opening dimension, while controlling
the switching circuitry, the thickness of the multiple slices is
increased approximately by multiples of the minimum slice
thickness, as defined by the smallest row width and/or minimum
aperture. The addition of the aperture allows a wider variety of
thickness multiples to be produced, for a given number of rows,
than in the preferred embodiments described above in which only the
detector array and switching circuitry are used to determine the
slice thicknesses.
[0031] In some preferred embodiments of the present invention, the
linear aperture may be narrowed sufficiently to mask all peripheral
rows of the array and portions of the two central rows. In this
configuration, signals from the two central rows are selected by
switching circuitry to produce two thin image slices.
[0032] It will be appreciated that by producing two adjoining, thin
image slices rather than a single slice of comparable thickness,
the dose efficiency of the imaging system is generally enhanced. To
maximize this efficiency, the aperture is adjusted so as to
generally match a minimum lateral extent of a beam of radiation
that is irradiating the object and impinging on the array. This
minimum lateral extent is generally determined by the geometry of a
radiation source irradiating the object. In this case, the minimum
slice thickness is approximately equal to half the lateral extent
of the beam of radiation. If only a single slice of this minimum
thickness were produced, then only about half of the radiation
irradiating the subject would be used in creating the image, so
that the dose efficiency would similarly be about 50% less.
[0033] Preferably, when the linear aperture is opened to its
maximum opening dimension, the switching circuitry combines signals
from selected rows of the array to produce four slices having a
common thickness, corresponding to the width of outermost rows of
the array. Additionally or alternatively, signals from each of the
two central rows may be combined with signals from all other,
peripheral, rows on its respective side of the array, out to and
including the outermost row, so as to produce two slices have a
maximum possible thickness.
[0034] In one such preferred embodiment of the present invention,
the array comprises eight rows of detectors, wherein the two
central rows have the smallest width, and the peripheral rows,
having greater widths, are symmetrically arranged on both sides of
the central rows. The array is coupled to a switching network
comprising fourteen switches, which may be of any suitable type
known in the art. The array and the switches are coupled to four
adders, whose outputs are used to produce two or four image slices
of desired thickness, as described above.
[0035] In still other preferred embodiments of the present
invention, the detector array is mounted on a movable base, which
shifts the array laterally, relative to the object being imaged,
along an axis perpendicular to the long axes of the rows of the
array. In such preferred embodiments, rows of different widths may
be arranged asymmetrically relative to a central axis of the array
defined by one or more rows of the smallest width, unlike the
preceding embodiments, in which the array is generally symmetrical
about such an axis. Preferably the movable base is used in
conjunction with switching circuitry and a variable aperture, as
described above, to produce multiple slices of varying thicknesses,
while keeping the slices commonly centered on a central plane, in a
fixed relation to the object, regardless of the thickness of slices
that is chosen.
[0036] The use of the movable base in conjunction with other
aspects of the present invention allows an array having a reduced
number of rows to be used in producing a desired combination of
slice widths. In other words, the use of the movable base allows a
greater variety of slice thicknesses to be produced, relative to
the number of rows in the detector.
[0037] In some preferred embodiments of the present invention, a CT
imaging system includes a detector array, as described above,
wherein an X-ray tube irradiates the body of a subject, and the
detector array is positioned on the opposite side of the body to
the tube, so that the detectors receive radiation that has been
transmitted through the body. The detector array preferably
comprises scintillators and photodiodes or other suitable X-ray
detectors known in the art and produces a plurality of sectional
image slices, preferably four such slices, although different
numbers of slices may similarly be produced. Preferably a
collimator is associated with the X-ray tube so as to limit the
extent of the X-ray beam irradiating the body to a region of the
body containing the slices.
[0038] In some of these preferred embodiments, the detector array
is planar, i.e., all the detectors are substantially in a single
plane. In other preferred embodiments, however, the detector array
is arcuate, having a radius of curvature approximately equal to the
distance of the array from the X-ray tube, which preferably emits a
fan-shaped beam whose angular extent generally corresponds to the
angle subtended by the arcuate array. In still other preferred
embodiments, in which the CT imaging system preferably comprises a
fourth-generation CT scanner, the detector array generally
describes a ring, substantially surrounding the body. It will be
appreciated that the various arrangements of rows having different
widths, as described above, as well as the accompanying switching
circuitry, aperture, movable base and other aspects of the present
invention, may equally be applied to planar and arcuate detector
arrays.
[0039] Preferably, the X-ray tube is mounted on a gantry or other
suitable apparatus, which revolves about an axis passing through
the body. In preferred embodiments of the present invention in
which the detector array is planar or arcuate, the array is
preferably mounted on the gantry, opposite the X-ray tube, so as to
revolve around the body, as is known in the art with regard to
third-generation CT scanners. Alternatively, in preferred
embodiments of the present invention in which the detector array
describes a ring, the array preferably remains rotationally
stationary, and only the X-ray tube revolves around the body. In
either of these cases, the position of the gantry and detector
array translates laterally relative to the body in a direction
parallel to the axis, preferably by translational motion of the
body relative to the gantry and array. The revolution of the gantry
and the translation of the gantry and the detector array relative
to the body allow multiple angular views and multiple sectional
slices to be acquired.
[0040] In alternative preferred embodiments of the present
invention, a tiltable, planar detector array comprises a plurality
of rows of detectors, all such rows having generally equal widths.
The array is coupled to a mechanical tilting device, which
controllably tilts the array about a tilt axis substantially
parallel to the long axes of the rows. A normal orientation of the
tiltable array is defined by a plane that is perpendicular to a
line passing through a focal point of the radiation source and
perpendicularly intersecting the tilt axis of the array. An
effective row width, common to all the rows, is defined by
geometrical projection of the lateral dimension of the row onto the
plane of the normal orientation. It will thus be understood that as
the array tilts away from the normal orientation, the effective
widths of the rows decrease, substantially in proportion to the
cosine of a tilt angle thereof.
[0041] The detectors in each row of the array receive radiation
from a corresponding slice of an object being imaged. When the
array is substantially in the normal orientation, the detectors
have effective widths equal to the fill widths of the rows, and
thus receive radiation from equal, relatively thick slices of the
object. When the array is tilted relative to this direction,
however, the effective widths of the detectors are smaller, and
therefore, the detectors receive radiation from equal, relatively
thinner slices. By tilting the array to various tilt angles,
multiple slices having a plurality of different thicknesses are
defined.
[0042] In still other preferred embodiments of the present
invention, a detector array comprises a plurality of rows of
detectors having substantially equal widths (and providing
substantially equal slice widths), wherein each such row may be
controllably tilted about its respective long axis. Preferably all
the rows in this preferred embodiment are co-planar and contiguous
with their immediate neighbors, when the rows are in a normal
orientation, as described in reference to the preceding
embodiments. Preferably all rows are tilted to substantially equal
angles, so that they define multiple slices having equal, variable
thicknesses.
[0043] In one such preferred embodiment of the present invention,
the rows are moved laterally relative to one another, in a
direction perpendicular to their long axes. When the rows are
tilted, they are then also moved closer together, so as to maintain
substantial contiguity of the thinner slices defined by this tilted
orientation.
[0044] In still further preferred embodiments of the present
invention, a detector array comprises four parallel rows of
detectors, including two outer rows and two inner rows, preferably
all of equal width, each row corresponding to a respective image
slice. The outer rows are adapted to act as a linear aperture with
respect to the inner rows, i.e., the outer rows are mounted so that
they may be translated laterally to overlap and thus mask portions
of the widths of the inner rows. In this way, the thicknesses of
the two slices corresponding to the two inner rows are controlled.
Preferably, an adjustable aperture or collimator slit masks
portions of the widths of the outer rows, so that all four of the
outer and inner rows may have any desired effective widths,
preferably equal effective widths.
[0045] It will be understood that while the above preferred
embodiment is described in terms of four rows of detectors,
generating four image slices of preferably equal thicknesses, the
principle of using one or more rows of the detector array to
variably overlap and mask one or more other rows may similarly be
applied in other, different preferred embodiments of the present
invention, as well. For example, the array may include more than
four rows of detectors, so as to produce more than four image
slices. The effective widths of these more than four rows of
detectors may be controlled by the above principle of overlapping
and masking rows, or by other means as described above with
reference to other preferred embodiments of the invention.
[0046] In yet a further alternative embodiment of the invention a
plurality of rows of detectors having equal widths is provided. The
outputs of the detectors are summed such that a single wide slice
and a single thick slice are produced. Alternatively, one wide
slice, flanked by two narrow slices are produced. Further
alternatively, a single thin slice flanked by two thin slices are
produced. Preferably, these slice widths are produced without
masking the detectors. Furthermore, the thicker slices are
preferably produced by adding the outputs of a plurality of equal
sized detectors while the thinner slices are produced by utilizing
the output of a single row of detectors or a sum of a lesser number
of detectors than that utilized for producing the thicker
slice(s).
[0047] In yet another preferred embodiment of the invention, a
plurality of rows of different widths is provided, with a thin row
or rows at the center and wider rows on one side of or preferably
flanking the thin row or rows. In this embodiment of the invention
one or more thin slices are provided at the center of the group of
rows and thick are provided by combining the outputs of detectors
of adjoining wider rows. The thin slices may be provided by the
detectors of a single row or by combing signals from detectors of
adjacent thin rows. In a preferred embodiment of the invention,
ratios of 3:1, 5:1, 8:1 or more, such as 10:1 are provided between
the thin slices and the thicker slices.
[0048] There is therefore provided, in accordance with a preferred
embodiment of the present invention, apparatus for producing
multiple image slice data responsive to incident radiation passing
through an object, including:
[0049] a detector array, including a plurality, p, of parallel rows
of detector elements, which receive the incident radiation and
generate signals in response thereto, each of which rows is
characterized by a width, measured in a direction perpendicular to
a long dimension thereof; and
[0050] signal processing circuitry, which receives signals from the
detector elements and which combines the signals in a first
combination mode to form a set of n groups of rows, each such group
of rows having an effective group width substantially equal to the
effective group width of each of the other groups, and which
further combines the signals in at least m additional combination
modes to form different sets of n groups of rows, each such set
having a different effective group width common to all groups in
the set, wherein p.ltoreq.n+2(m-1).
[0051] Preferably, in at least one of the combination modes, at
least one of the n groups of rows includes at least one row having
a width different from all the rows in at least one other of the n
groups of rows.
[0052] Preferably, each group of rows includes mutually adjoining
rows, and the n groups of rows in each of the combination modes are
mutually exclusive.
[0053] There is further provided, in accordance with a preferred
embodiment of the present invention, apparatus for producing
multiple image slice data responsive to incident radiation,
including:
[0054] a detector array, including a plurality of parallel rows of
detector elements, which generate signals responsive to radiation
incident thereon, each of which rows is characterized by a width,
measured in a direction perpendicular to a long dimension thereof;
and
[0055] signal processing circuitry, coupled to the array, which
receives signals from at least four of the rows of the array and
produces four or more channels of output data, each such channel
including data derived from signals generated by detector elements
in one or more rows of the array selected by the circuitry for
inclusion of data therefrom in said channel,
[0056] wherein each row is characterized by an effective row width,
defined by a geometrical projection of the portion of the width of
the row that is exposed to the radiation, onto a plane that is
substantially perpendicular to a direction of propagation of the
radiation incident on the array, and
[0057] wherein each channel of output data is characterized by an
effective channel width, defined by the sum of the effective widths
of the one or more rows selected by the circuitry for inclusion of
data therefrom in the channel, and
[0058] wherein the effective channel widths of all of the four or
more channels are substantially equal, and
[0059] wherein the number of different effective channel widths
that may be selected by the signal processing circuitry is equal to
at least half the number of rows in the array, less one.
[0060] Preferably, the signal processing circuitry includes
switching circuitry, which alternately selects different rows for
inclusion of data therefrom in each of the four or more channels,
thereby varying the effective channel widths thereof; and two or
more adders, each respectively associated with one of the four or
more channels, and each of which sums the signals generated by
adjacent detectors in two or more respective, adjoining rows of the
array that are selected by the circuitry for inclusion of data
therefrom in the channel.
[0061] Preferably, the array includes two central rows having a
common width smaller than or equal to the widths of all the other
rows, and the widths of all the rows are substantially equal to
integer multiples of the width of the central rows.
[0062] Additionally or alternatively, the apparatus includes an
adjustable slit or linear aperture, having an aperture that is
variable in a direction perpendicular to the long dimension of the
rows, which may be variably closed to mask portions of the widths
of the rows, thereby varying the effective row widths.
[0063] Additionally or alternatively, the apparatus includes a
movable base on which the detector array is mounted, which base
moves the array in a direction perpendicular to the long dimension
of the rows.
[0064] Additionally or alternatively, the apparatus includes at
least one mechanical tilting device, which controllably tilts a row
of the array about a tilt axis substantially parallel to the long
dimension of the rows, wherein the effective row width is varied by
controlling the at least one tilting device.
[0065] There is moreover provided, in accordance with another
preferred embodiment of the present invention, apparatus for
producing multiple image slice data, responsive to incident
radiation, including:
[0066] a detector array including at least three detector elements
disposed in a lateral direction, which detector elements generate
signals responsive to radiation incident thereon, wherein each
detector element is characterized by a width, measured in the
lateral direction, and wherein at least two of the at least three
detector elements have substantially different widths; and
[0067] circuitry, coupled to the array, which selects a first
exclusive group including one or more detector elements and sums
the signals generated by the detector elements in the first group
to produce a first channel of output data, and which selects a
second exclusive group including at least two detector elements and
sums the signals generated by the detector elements in the second
group to produce a second channel of output data,
[0068] wherein each detector element is characterized by an
effective detector width, defined by the portion of the width of
the detector element that is exposed to the radiation, and
[0069] wherein each channel is characterized by an effective
channel width, defined by the sum of the effective detector widths
of the one or more detector elements in the group that is selected
to produce the channel, and
[0070] wherein the effective channel widths of the first and second
channels are substantially equal.
[0071] Preferably, the widths of all of the at least two detector
elements having substantially different widths are integer
multiples of the width of the one of the at least two detector
elements having the smallest width.
[0072] There is also provided, in accordance with a preferred
embodiment of the present invention, apparatus for producing
multiple image slice data responsive to incident radiation,
including:
[0073] a detector array, including at least a first detector
element and a second detector element disposed in a lateral
direction, which detector elements generate signals responsive to
radiation incident thereon, wherein each detector element is
characterized a width in the lateral direction,
[0074] wherein each detector element is characterized by an
effective detector width, defined by the portion of the width of
the detector element that is exposed to the radiation, and
[0075] wherein the second detector element is shifted in the
lateral direction relative to the first detector element, so as to
overlap and mask a portion of the first detector, thereby altering
the first detector's effective width.
[0076] Preferably, the apparatus includes an adjustable slit or
aperture, which masks a portion of the second detector, thereby
altering the second detector's effective width.
[0077] There is additionally provided, in accordance with a
preferred embodiment of the present invention, apparatus for
producing image slice data responsive to incident radiation,
including:
[0078] a detector array, including one or more rows of detector
elements, which generate signals responsive to radiation incident
thereon; and
[0079] at least one mechanical tilting device, which controllably
tilts at least one of the one or more rows about a tilt axis
thereof, which tilt axis is substantially parallel to the long
dimension of the at least one row,
[0080] wherein the one or more rows are characterized by a width,
measured in a direction perpendicular to the tilt axis thereof,
and
[0081] wherein an effective width of the at least one row, defined
by a geometrical projection of the width thereof onto a plane that
is substantially perpendicular to a direction of propagation of the
radiation incident on the row, is varied by controlling the at
least one mechanical tilting device.
[0082] Preferably, the one or more rows include a plurality of
rows, and the mechanical tilting device tilts all of the plurality
of rows in the array, more preferably tilting all the rows of the
array by a common angle, and most preferably tilting the entire
array about a common tilt axis.
[0083] Alternatively or additionally, the at least one mechanical
tilting device includes a plurality of such devices, which tilt
about different, respective axes, wherein each row of the array is
preferably tilted about its own respective axis.
[0084] Preferably, the apparatus includes a motion control
mechanism, which controls a distance between adjoining rows of the
array when they are tilted, so that geometrical projections of the
rows onto the plane that is substantially perpendicular to the
direction of propagation of the radiation incident on the array are
substantially contiguous.
[0085] There is further provided, in accordance with still another
preferred embodiment of the present invention, a CT scanner, for
producing images of multiple sectional slices through an object,
including:
[0086] a radiation source, which irradiates the object from a first
side thereof; and
[0087] apparatus for producing image slice data, as described
above,
[0088] wherein the detector array is positioned on a second side of
the object, opposite to the first side.
[0089] There is also provided, in accordance with yet another
preferred embodiment of the present invention, a detector array
switching network, including:
[0090] a plurality of detector elements, which generate signals
responsive to incident radiation;
[0091] a plurality of switches; and
[0092] two output channels,
[0093] wherein a first detector element is connected to a first
output channel, and
[0094] wherein a second detector element adjacent to the first
detector element, is connected by a first switch to the first
output channel and alternatively by a second switch to a second
output channel, and
[0095] wherein a third detector element adjacent to the second
detector element, is connected by a third switch to the first
output channel and alternatively by a fourth switch to the second
output channel, and
[0096] wherein a fourth detector element adjacent to the third
detector element, is connected by a fifth switch to the second
output channel, and
[0097] wherein the switches are controlled so that one of the
second, third and fourth detector elements is connected to the
second output channel, and other detector elements, if any, between
the first detector element and the detector element connected to
the second output channel are connected to the first output
channel, together with the first detector element.
[0098] There is further provided, in accordance with an additional
preferred embodiment of the present invention, a detector array
switching network, including first and second sub-networks, each
such sub-network substantially in accordance with the switching
network described above,
[0099] wherein the respective first detector elements of the first
and second sub-networks are mutually adjacent, and
[0100] wherein the network is substantially symmetrical about a
central axis, defined by a border between the respective first
detector elements.
[0101] There is also provided, in accordance with a preferred
embodiment of the present invention, a method for producing
multiple-slice images of an object, including: irradiating the
object;
[0102] receiving and processing signals generated in response to
radiation transmitted through a volume of the object;
[0103] dividing the volume into a plurality of substantially
contiguous, parallel object slices, each of which slices has a
thickness approximately determined by the width of a respective
detector that generates signals responsive to radiation transmitted
therethrough;
[0104] producing four or more substantially contiguous sectional
image slices having a common thickness, each such image slice
corresponding to one or more adjoining object slices; and
[0105] reconstructing an image of the volume, said image including
at least the four or more sectional image slices,
[0106] wherein the object slices comprise at least two central
slices of substantially equal thickness, which thickness is less
than the thickness of each the other object slices, and at least
two peripheral slices whose thickness is greater than the thickness
of the central slices, and
[0107] wherein producing four or more image slices having a common
thickness comprises producing at least four image slices of
thickness substantially equal to the thickness of the two central
slices.
[0108] There is further provided, in accordance with a preferred
embodiment of the invention, a method for producing multiple-slice
images of an object, comprising:
[0109] radiating the object;
[0110] receiving and processing signals generated in response to
radiation transmitted through a volume of the object;
[0111] dividing the volume into a plurality of substantially
contiguous, parallel object slices, each of which slices has a
thickness approximately determined by the width of a respective
detector that generates signals responsive to radiation transmitted
therethrough;
[0112] producing two or more substantially contiguous sectional
image slices having at least two different thicknesses, each such
image slice corresponding to one or more adjoining object slices;
and
[0113] reconstructing an image of the volume, said image including
at least the two or more sectional image slices,
[0114] wherein the thickness of the widest reconstructed slice and
the thickness of the thinnest image slice have a ratio of at least
3:1.
[0115] In preferred embodiments of the invention the ratio is at
least 5:1 or 8:1. In a preferred embodiment of the invention, the
ratio is about 10:1.
[0116] There is further provided, in accordance with a preferred
embodiment of the invention, a method for producing multiple-slice
images of an object, comprising: irradiating the object;
[0117] receiving and processing signals generated in response to
radiation transmitted through a volume of the object;
[0118] dividing the volume into a plurality of substantially
contiguous, parallel object slices of equal width, each of which
slices has a thickness approximately determined by the width of a
respective detector that generates signals responsive to radiation
transmitted therethrough;
[0119] producing two or more substantially contiguous sectional
image slices having at least two different thicknesses, each such
image slice corresponding to one or more adjoining object slices;
and
[0120] reconstructing an image of the volume, said image including
at least the two or more sectional image slices.
[0121] There is further provide, in accordance with a preferred
embodiment of the invention a method for producing multiple-slice
images of an object, comprising: irradiating the object;
[0122] receiving and processing signals generated in response to
radiation transmitted through a volume of the object;
[0123] dividing the volume into a plurality of substantially
contiguous, parallel object slices, each of which slices has a
thickness approximately determined by the width of a respective
detector that generates signals responsive to radiation transmitted
therethrough;
[0124] producing two or more substantially contiguous sectional
image slices having at least two different thicknesses, at least
one such image slice corresponding to a plurality of adjoining
object slices; and
[0125] reconstructing an image of the volume, said image including
at least the two or more sectional image slices.
[0126] In a preferred embodiment of the invention, the object
slices are of substantially the same thickness.
[0127] In various preferred embodiments of the invention, the image
slices comprise a single thin slice and a single thick slice or a
single thin slice and two thick slices or a single thick slice and
two thin slices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0128] The present invention will be more fully understood from the
following detailed description of the preferred embodiments
thereof, taken together with the drawings in which:
[0129] FIG. 1 is a schematic, partly sectional representation of a
CT scanner, in accordance with a preferred embodiment of the
present invention;
[0130] FIG. 2 is a schematic representation of a detector array, in
accordance with a preferred embodiment of the present
invention;
[0131] FIG. 3A is a cross-sectional view of the CT scanner shown in
FIG. 1;
[0132] FIG. 3B is a cross-sectional view of a CT scanner similar to
that shown in FIG. 3A, but including a detector array in accordance
with an alternative preferred embodiment of the present
invention;
[0133] FIG. 3C is a cross-sectional view of a CT scanner in
accordance with still another preferred embodiment of the present
invention;
[0134] FIGS. 4A-4D are sectional representations of the detector
array of FIG. 2, together with schematic representations of
switching circuitry associated therewith, in accordance with a
preferred embodiment of the present invention;
[0135] FIGS. 5A-5D are sectional representations of a detector
array and a mechanical aperture associated therewith, in accordance
with a preferred embodiment of the present invention;
[0136] FIGS. 6A-6D are sectional representations of a detector
array, together with an associated mechanical aperture and movable
base, in accordance with a preferred embodiment of the present
invention;
[0137] FIGS. 7A-7B are sectional representations of a tiltable
detector array, in accordance with a preferred embodiment of the
present invention;
[0138] FIGS. 8A-8B are sectional representations of an array of
tiltable rows of detectors, in accordance with another preferred
embodiment of the present invention;
[0139] FIGS. 9A-9E are sectional representations of a detector
array and a mechanical aperture associated therewith, in accordance
with a preferred embodiment of the present invention;
[0140] FIG. 10 is a schematic representation of switching circuitry
associated with the detector array shown in FIGS. 9A-9E, in
accordance with a preferred embodiment of the present
invention;
[0141] FIG. 11 is a schematic representation of a detector array
and a mechanical aperture associated therewith, in accordance with
still another preferred embodiment of the present invention;
and
[0142] FIG. 12 shows two ways in which the outputs of detectors
having the same width may be combined in accordance with a
preferred embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0143] FIG. 1 shows a schematic side view of a CT scanner 20 in
accordance with a preferred embodiment of the present invention. An
X-ray tube 22 irradiates a region of the body 24 of a subject being
imaged. The angular extent of a beam of radiation 26 is preferably
restricted by an adjustable collimator 28. X-rays transmitted
through body 24 are received by a multi-slice detector array 30, as
will be described below. The lateral dimension of array 30, i.e.,
the dimension parallel to long axis 25 of body 24, is exaggerated
in FIG. 1 for the purpose of clarity in the explanation that
follows below. Array 30 may be mounted as shown to a movable base
32, which moves and aligns the array relative to an axis defined by
X-ray tube 22. In some preferred embodiments of the present
invention, collimator 28 and/or a mechanical aperture 34 limits the
angular extent of the radiation beam striking array 30. Preferably,
collimator 28 is adjusted so as to limit the angular extent of beam
26 to the region of body 24 being imaged by array 30, and minimize
irradiation of other regions of the body. Base 32 and/or aperture
34 are particularly useful in conjunction with certain preferred
embodiments of the present invention, such as those shown in FIGS.
5A-5D, 6A-6D and 9A-9E and described hereinbelow. The base and the
aperture are not essential to the operation of array 30, but are
shown in FIG. 1 by way of illustration.
[0144] Reference is now made additionally to FIG. 2, which is a
schematic view of array 30, viewed from above in the perspective of
FIG. 1. As shown in FIG. 2, array 30 comprises a plurality of rows
50, 52, 54, 56, 58, 60, 62, 64, 66 and 68, each such row comprising
a plurality of detector elements 70. Detector elements 70 may
comprise any suitable type of radiation-sensitive detectors, for
example photodiodes or other detectors known in the art.
Preferably, multiple elements 70 are fabricated and/or mounted
together on a common substrate, although alternatively elements 70
may be discrete elements, without a common substrate.
[0145] Along a direction parallel to the long axis 72 of array 30,
detector elements 70 preferably all have a substantially equal
dimension, or pitch, as shown in FIG. 2. In the direction
perpendicular to axis 72, however, some of the rows have different
widths. Central rows 58 and 60 have the smallest width, while
peripheral rows have widths equal to or greater than this smallest
width, and exterior rows 50 and 68 have the greatest widths. In the
preferred embodiment of the present invention shown in FIG. 2, all
rows have widths that are integral multiples of the width of the
central rows, wherein if the width of rows 58 and 60 is taken to be
equal to 1, the remaining rows have the following widths:
[0146] Rows 56, 62--width=1
[0147] Rows 54, 64--width=2
[0148] Rows 52, 66--width=4
[0149] Rows 50, 68--width=8
[0150] The reasons for this choice of proportions will be explained
below.
[0151] FIG. 3A is a cross-sectional view of the scanner shown in
FIG. 1. Array 30 is mounted in CT scanner 20 with its long
dimension, indicated by axis 72, transverse to long axis 25 (shown
in FIG. 1, and perpendicular to the plane of FIGS. 3A and 3B) of
body 24. Each element 70 of array 30 receives radiation that has
traversed body 24 along a linear path from a focal point 78 of
X-ray tube 22 to the element, and generates an electrical signal
indicative of the attenuation of tissue in the body intercepted by
this path. Array 30 and X-ray tube 22, along with ancillary
apparatus, such as collimator 28, are mounted on gantry 74. The
gantry revolves around an axis substantially parallel to axis 25,
so that array 30 can capture views from different angles with
respect to this axis. Body 24 is further translated laterally
relative to gantry 74, in a direction substantially parallel to
axis 25, so that different cross-sectional portions of body 24 may
be imaged.
[0152] FIG. 3B shows an alternative preferred embodiment of the
present invention, wherein array 76 is arcuate, rather than planar.
The arrangement of rows and detector elements in array 76, however,
is identical to that of array 30, and in all other respects, the
preferred embodiment shown in FIG. 3B is substantially identical to
that shown in FIGS. 1, 2 and 3A. The radius of curvature of array
76 is generally equal to the distance from the array to focal point
78. Thus, all elements 70 in array 76 subtend substantially equal
angles of beam 26 in the transverse direction. As is known in the
art, this equality of angles is useful in reducing angular
distortion in the image of body 24 that is produced by CT scanner
20. Although the following preferred embodiments of the present
invention will be described with reference to planar detectors
arrays, it will be appreciated that arcuate arrays may similarly be
used in such embodiments.
[0153] FIG. 3C shows still another, alternative, preferred
embodiment of the present invention, wherein array 77 describes a
ring shape, substantially surrounding body 24. In this preferred
embodiment, scanner 20 is preferably a fourth-generation CT
scanner. As in the embodiment of FIG. 3B, the arrangement of the
rows and detector elements 70 in array 77 is substantially
identical to that of array 30. In other respects, array 77 is used
in system 20 in a manner substantially similar to that shown in
FIGS. 1 and 2 and described herein, except that whereas arrays 30
and 76 preferably revolve around body 24 on gantry 74, array 77 is
preferably substantially stationary.
[0154] Referring again to FIG. 1, the signals generated by elements
70 are processed by pre-processing circuitry 80 and then
transferred via a switching network 82 to a data acquisition system
(DAS) 84. A reconstructor 86 receives data from DAS 84 and applies
algorithms, as are known in the art, to reconstruct images showing
internal structures within body 24. These images are preferably
displayed by a display unit 87. A processor 88 receives these
images and, optionally, records them in mass memory, prints them on
hard-copy media and performs other data and display processing
functions known in the art. Processor 88 preferably includes a
computer, which controls other components of CT scanner 20,
including collimator 28, aperture 34, movable base 32 and gantry
74.
[0155] Pre-processing circuitry 80 may be of any type known in the
art, and may be integrated on a common substrate with array 30, or
contained on a separate substrate or circuit board. Preferably the
pre-processing circuitry includes analog pre-amplifiers.
[0156] Switching network 82 preferably selects the rows of array 30
from which data are to be acquired, and adds together signals
generated by elements in selected, adjacent rows. The switching
network may be integrated with array 30 on a common substrate or
contained on a separate substrate or circuit board.
[0157] Although in the preferred embodiment shown in FIG. 1,
switching network 82 receives signals from array 30 after
processing by pre-processing circuitry 80, in other preferred
embodiments of the present invention, the switching network may
select and add together signals from adjacent rows before the
signals are pre-processed. Such embodiments may generally be
advantageous in reducing the number of components in the system,
and thus reducing the system's cost, particularly if switching
network 82 is integrated on a common substrate with array 30.
Switching of signals before pre-processing, however, may also tend
to introduce a greater degree of noise into the signals.
[0158] In still other preferred embodiments of the present
invention, switching network 82 may be eliminated, and instead
signals from all the rows of array 30 may be acquired separately by
DAS 84, and then signals from adjacent rows may be selected and
added together by software processing.
[0159] DAS 84 preferably digitizes signals received from switching
network 82, using analog-to-digital (A/D) conversion circuitry
known in the art. Preferably a logarithm operation is then
performed on the digitized signals, for example using look-up
tables.
[0160] The foregoing order of operations, wherein signals generated
by elements 70 are first summed, then digitized and then undergo a
logarithm operation, is advantageous in that it reduces the number
of electronic components required in the system, and thus reduces
the cost of the system, as well. In other preferred embodiments of
the present invention, however, the order of these operations may
be different.
[0161] For example, in one such preferred embodiment,
pre-processing circuitry 80 also includes a logarithmic amplifier
for each active detector, which results in reduced partial volume
artifacts, as is known in the art. Switching network 82 then
serializes, selects and adds together signals, and network 82
digitizes the signals, as described above.
[0162] In other preferred embodiments of the present invention,
pre-processing circuitry 80 may include analog-to-digital (A/D)
conversion circuitry. Switching network 82 includes digital
circuitry, as is known in the art, which serializes, selects and
sums the signals. A logarithm operation may be performed by
logarithmic amplifiers included in pre-processing circuitry 80, as
described above, or alternatively may be performed digitally, for
example by look-up table. Such preferred embodiments will tend to
be costly to produce, since they must generally include multiple
A/D conversion circuits, but they will generally have the advantage
of improved signal/noise ratio.
[0163] As illustrated by FIG. 1, by way of example, the rows and/or
combinations of rows selected by switching network 82 define
substantially parallel image slices 102, 104, 106 and 108 within
the angular extent of X-ray beam 26. Slice 102 is reconstructed, by
reconstructor 86, using data derived from row 52; slice 104 is
reconstructed using data from rows 54, 56 and 58; slice 106 from
rows 60, 62 and 64; and slice 108 from row 66. Data from rows 50
and 68 are not used in this case. Preferably collimator 28 and
aperture 34 are adjusted so as to limit the angular extent of beam
26 to an angle subtended by slices 102, 104, 106 and 108, so as to
reduce unwanted radiation dosage, but this adjustment is not
necessary to the operation of the preferred embodiment shown here,
as long as radiation traversing body 24 can reach all the rows
selected by the switching network.
[0164] It will be understood that the thickness of each of the
image slices, i.e., its lateral dimension measured along axis 25,
is generally determined approximately by the width of the row or
the sum of the widths of the multiple rows defining the slice.
Thus, thinner or thicker slices may be produced by appropriate
selection of the rows of the array. Preferably all four slices 102,
104, 106 and 108 are of substantially equal thicknesses.
[0165] The actual slice thicknesses are determined only
approximately by the row widths, because the thicknesses also
depend on optical qualities of other elements of scanner 20, such
as X-ray tube 22 and collimator 28. Generally, however, these other
elements have only minor effect on the slice thicknesses, as will
be illustrated by the following example:
[0166] Assuming focal point 78 of X-ray tube 22 to have a dimension
f, and rows 56 and 62, the narrowest rows of array 30, to have
width w, the effective thickness a.sub.eff of an image slice
defined by row 56 or 62 will typically be given (neglecting the
generally insignificant effect of collimator 28) by:
a.sub.eff=1/M*SQRT[w.sup.2+(M-1).sup.2f.sup.2]
[0167] where a.sub.eff is measured at the center of rotation of
gantry 74, and M, the magnification, is the ratio of the distance
from focal point 78 to array 30, over the distance from the focal
point to the center of rotation. Taking typical values of w=2 mm,
f=1 mm and M=2, we find that a.sub.eff=1.1 mm, rather than 1 mm,
which would be the slice thickness if focal point 78 were
infinitesimal. It will be appreciated that when wider rows of the
array are used, the effect of the other elements of scanner 20 on
the slice thickness will be even less significant.
[0168] As noted earlier, it will be understood that the use of the
term "substantially" or "approximately" in stating a detector width
dimension, for example to say that the width of rows of detectors
are substantially equal, or that the thickness of one row is
substantially an integer multiple of another row, means that the
detector thickness is such that the slices traversed by the
radiation beam has approximately the stated dimension or ratio.
This includes any correction to the detector width which might be
required, for example to correct for the difference between the
effective thickness a.sub.eff and the thickness that would be
obtained if focal point 78 were infinitesimal or for other
geometrically caused variation between the effective slice width
and the detector width. Such correction is generally very small
compared to the detector and slice dimensions of interest.
[0169] The size of focal point 78, together with other geometrical
factors, such as the position of collimator 28 and the size of its
aperture, also determines a minimum extent of beam 26 at the center
of rotation, as is known in the art. In typical CT system
geometries, such as that shown in FIG. 1, this minimum extent is
significantly larger than the dimension f of the focal point. Thus,
if only a single slice of a minimum thickness, for example 1 mm, is
acquired by scanner 20, substantial radiation will pass through
body 24 outside the bounds of this single slice. The system in this
case will have a relatively low dose efficiency. On the other hand,
when multiple slices are acquired simultaneously, as described
herein, more or substantially all of the radiation incident on body
24 is captured by detector array 30 and used in creating the CT
image, so that dose efficiency is increased.
[0170] FIGS. 4A-4D schematically illustrate the row-adding function
of switching network 82 with respect to array 30, which is shown in
cross-section in the figure. In these figures, switching network 82
includes two adders 90 and 92 and four output channels, 94, 96, 98
and 100, corresponding to four image slices, labeled slice A
through slice D, respectively. Adders 90 and 92 may be of any
suitable type known in the art, for example multi-input analog
operational amplifiers or digital adder circuits (in the case that
the signals received by network 82 have first been digitized).
Pre-processing circuitry 80 is omitted in these figures, for
simplicity of illustration (and, as described above, because
pre-processing may be performed after switching). As described
above, switching network 82 may receive the signals from elements
70 before they are pre-processed.
[0171] In FIG. 4A, channels 94, 96, 98 and 100 receive signal data
from rows 56, 58, 60 and 62, respectively. In this case, image
slices A through D have the smallest possible thickness,
corresponding to detector row width=1, where the width of rows 58
and 60 (as well as 56 and 62) has been taken to be equal to 1, as
described earlier. In this case, CT scanner 20 will produce images
having the highest available resolution in the lateral direction,
although possibly at the expense of lower volume coverage for a
given scanning duration and/or reduced signal/noise ratio.
[0172] In FIG. 4B, channels 94 and 100 receive signal data from
rows 54 and 64, which have width=2. Channel 96 receives data
derived by summing signals using adder 90, wherein the signal from
each element in row 56 is summed with that from an adjacent element
in row 58, so that channel 96 corresponds to an effective row
width=2, i.e., the sum of the widths of rows 56 and 58; and channel
98 similarly receives data summed by adder 92 from rows 60 and 62.
In this case, slices A through D have a common thickness that is
approximately twice that of the slices produced in the
configuration shown in FIG. 4A.
[0173] FIG. 4C shows still another configuration, in which each of
channels 94, 96, 98 and 100 receives data corresponding to an
actual or effective row width=4, producing image slices as
illustrated by slices 102, 104, 106 and 108 in FIG. 1.
[0174] FIG. 4D shows another configuration, in which all the rows
of array 30 are used to produce slices having a maximal thickness,
approximately eight times as thick as the slices defined by the
configuration of FIG. 4A. The configuration of FIG. 4D will
generally enable CT scanner 20 to operate at its highest throughput
rate and highest signal/noise ratio.
[0175] It will be appreciated that detector array 30 as illustrated
by FIG. 2, operating in accordance with FIGS. 1, 3A and 4A-4D,
enables CT scanner 20 to acquire four image slices, of equal
thickness, simultaneously. The slice thicknesses may be varied
electronically, without the use of moving parts, over a range of
approximately 1:8. Array 30, however, includes only ten rows of
detector elements 70, so that the complexity and cost of
pre-processing circuitry 80 and switching network 82 may be reduced
relative to comparable circuitry that must be used for producing
multiple slices of similarly variable thicknesses in conjunction
with other detector arrays known in the art.
[0176] It will further be appreciated that although the preceding
preferred embodiment, as well as other preferred embodiments of the
present invention described below, is shown to produce four image
slices with four alternative choices of slice thickness, the
principles of the present invention may similarly be applied to
produce a greater number of slices and a greater or smaller range
of thicknesses. The number of slices and the thicknesses thereof,
in such embodiments of the present invention, are generally
dependent on the number of rows in the detector array and the
construction and function of a switching network associated
therewith.
[0177] FIGS. 5A-5D illustrate an alternative preferred embodiment
of the present invention, wherein a detector array 102 has
structure and function generally similar to those of array 30, but
the rows of array 102 have different relative widths,
specifically:
1 Central rows 112, 114 - width = 1 Rows 110, 116 - width = 2 Rows
108, 118 - width = 4 Rows 106, 120 - width = 3 Rows 104, 122 -
width = 10.
[0178] In the preferred embodiment shown in FIGS. 5A-5D, mechanical
aperture 34 is controlled to selectively mask some of the rows in
array 102. Preferably, collimator 28 is also adjusted so as to
limit the angular extent of beam 26 to the extent of aperture 34
shown in the figures. Collimator 28 may, alternatively, be used
instead of aperture 34 for this purpose. As shown in FIGS. 5A-5C,
this selective masking may include limiting the effective widths of
some of the rows. Switching circuitry similar to network 82, as
illustrated in FIGS. 4A-4D, selects and adds together signals from
adjacent rows of array 102, so as to produce four slices labeled
slice A, B, C and D, as above.
[0179] Thus, in FIG. 5A, aperture 34 is narrowed laterally so as to
mask substantially one half of the widths of rows 110 and 116, and
the effective widths of these rows are then substantially equal to
1, like rows 112 and 114. In this case, four relatively thin slices
A-D are produced, corresponding to row width=1.
[0180] In FIG. 5B, aperture 34 is opened so that rows 110 and 116
are fully exposed, and substantially one fourth of the widths of
rows 108 and 118 are masked, so that these rows have effective
width=3. Signals from rows 110 and 112 are combined in slice B,
thus producing a similar effective width=3, and likewise rows 114
and 116 in slice C.
[0181] In FIG. 5C, aperture 34 is opened still further, so as to
mask substantially 60% of the widths of rows 104 and 122, and
expose all other rows fully. In this case, the four slices have
thickness corresponding to effective row width=7.
[0182] Finally, in FIG. 5D, aperture 34 is fully open, and the four
slices have thickness corresponding to effective row width=10.
[0183] It will be appreciated that preferred embodiments of the
present invention that make use of a variable aperture, such as
collimator 28 or mechanical aperture 34, in the manner described
here can typically generate a wider range of choices of slice
thicknesses than can embodiments that use electronic switching
alone, such as that shown in FIGS. 4A-4D.
[0184] FIGS. 6A-6D illustrate an alternative preferred embodiment
of the present invention, using a detector array 130, which has
structure and function generally similar to those of arrays 30 and
122, but having rows of different relative widths, which vary
asymmetrically about a central axis of the array parallel to the
rows. Specifically:
2 Rows 138, 140 - width = 1 Row 136 - width = 2 Row 134 - width = 4
Rows 132, 142, 144 - width = 8.
[0185] In the preferred embodiment shown in FIGS. 6A-6D, as in the
preceding embodiment, mechanical aperture 34 is controlled to mask
some of the rows in array 130, so as to limit their effective
widths. Movable base 32 further controls the lateral position of
array 130, relative to an axis 146 perpendicular to the surface of
the array and passing through focal point 78. Switching circuitry
similar to that illustrated in FIGS. 4A-4D selects and adds
together signals from adjacent rows of array 130, so as to produce
four slices labeled slice A, B, C and D, as above.
[0186] In FIG. 6A, mechanical aperture 34 masks portions of rows
136 and 142, so that these two rows have effective width=1, and
four image slices are produced having a minimum thickness
corresponding to this width.
[0187] In FIG. 6B, movable base 32 shifts the position of array
130, so that a common edge of adjoining rows 136 and 138 is
substantially aligned with axis 146. Mechanical aperture 34 opens
asymmetrically, so as to mask portions of rows 134 and 142. Four
image slices corresponding to effective row width=2 are thus
produced.
[0188] In FIG. 6C, movable base 32 shifts array 130 still further,
so that a common edge of adjoining rows 134 and 136 is
substantially aligned with axis 146, and aperture 34 opens so as to
mask portions of rows 132 and 142. Four image slices are produced
corresponding to effective row width=4.
[0189] In FIG. 6D, aperture 34 is filly opened, and movable base 32
shifts array 130 back to align a common edge of adjoining rows 140
and 142 with axis 146. Four image slices are produced corresponding
to effective row width=8.
[0190] It will be appreciated that array 130, as shown in FIGS.
6A-6D, achieves the same range and values of slice thicknesses as
does array 30, as illustrated by FIGS. 4A-4D; but array 130
includes only seven rows of detector elements, while array 30 has
ten rows. Thus, array 130 can achieve resolution that is comparable
to that of array 30, but with substantially fewer detector elements
in the array, and a correspondingly simpler switching network.
[0191] FIGS. 7A and 7B show an alternative preferred embodiment of
the present invention, in which a planar detector array 150
comprises a plurality of detectors 70 arranged in four rows 152,
154, 156 and 158 of equal widths. Array 150 may be used in CT
scanner 20 in place of detector array 30 shown in FIG. 1. Array 150
is mounted on a pivot 160, which rotates about an axis parallel to
the long axes of the rows, preferably under the control of
processor circuitry, such as processor 88. The array is coupled to
pre-processing, DAS and reconstructor circuitry similar to that
illustrated in FIG. 1, but switching network 82 may be
eliminated.
[0192] As shown in FIG. 7A, when array 150 is oriented so that the
plane of the array is substantially perpendicular to axis 146 (as
described in reference to FIGS. 6A-6D), CT scanner 20 will produce
four image slices having a common thickness T, determined by the
width of the rows. As FIG. 7B shows, however, when array 150 is
tilted, due to rotation of pivot 160, the thickness of the slices
is reduced to a value approximately equal to Tcos.theta., where
.theta. is the angle of rotation of the array relative to its
starting position. By rotating array 150 through an angle
.theta.=82.8.degree., the slice thickness may be reduced to
approximately T/8. Provision must be made, for example in
reconstructor 86, for small differences that will arise in the
relative strengths of the signals among the four rows and in the
corresponding slice thicknesses, due to rows 156 and 158 being
closer to focal point 78 than rows 154 and 152.
[0193] FIGS. 8A and 8B show still another preferred embodiment of
the present invention, wherein a detector array 170 comprises a
plurality of tiltable rows 172, 174, 176 and 178, each of which
comprises a plurality of detector elements 70. Array 170 may be
used in CT scanner 20 in place of detector array 30 shown in FIG.
1. Rows 172, 174, 176 and 178 have substantially equal widths. Each
row is independently fixed to a pivot 180, which allows the row to
tilt about a row axis substantially parallel to the row's long
dimension. Preferably, pivots 180 are mounted on movable pivot
mounts 184, and are rotated about the respective row axes by
transmission belts 182, or other suitable rotation transmission
devices. Mounts 184 and belts 182 are coupled to a motion control
mechanism 186, which is preferably controlled by a computer, such
as processor 88.
[0194] As shown in FIG. 8A, when rows 172, 174, 176 and 178 are
oriented so as to define a plane that is substantially
perpendicular to axis 146 (as described above), CT scanner 20 will
produce four image slices having a common thickness, determined by
the width of the rows. As FIG. 8B shows, however, when rows 172,
174, 176 and 178 are tilted, due to rotation of pivots 180, the
thicknesses of the slices are reduced, as was described above with
reference to FIG. 7B. Preferably all the rows are tilted by a
common angle, so that the thicknesses of the slices are
substantially equal.
[0195] Preferably, as shown in FIG. 8B, motion control mechanism
186 reduces the distance between mounts 184 when the rows are
tilted. In this way, the slices may be maintained in substantial
contiguity, i.e., without intervening spaces that are not imaged in
between the image slices, regardless of changes in the thickness of
the slices.
[0196] It will be appreciated that in the preferred embodiments of
the present invention shown in FIGS. 7A, 7B, 8A and 8B and
described above, image slices may be produced having substantially
any desired thickness, by appropriately tilting the array or rows
in the array, as long as the desired thickness is less than or
equal to a maximum thickness, determined by the width of the rows
of the array. Furthermore, although all the rows of array 150 in
FIGS. 7A and 7B and of array 170 in FIGS. 8A and 8B are shown as
having substantially equal widths, in other preferred embodiments
of the invention, rows of different widths may be provided so as to
produce slices of different thicknesses.
[0197] It will further be appreciated that in the preferred
embodiment of the present invention shown in FIGS. 8A and 8B, the
rows of array 170 need not all be tilted by an equal angle, as
illustrated in FIG. 8B, but may rather be tilted by different
angles, so as to produce slices of different thicknesses. Such
varying slice thicknesses are useful in certain CT imaging
modalities, for example, in CT imaging of the lungs, in which high-
and low-resolution slices may be interspersed so as to reduce the
radiation dose to which the body is exposed.
[0198] Furthermore, while tilting the detectors allows for a wide
range of variation in the width of the slices, this range can be
further increased by utilizing, in addition to such tilting,
combination of rows as shown in FIGS. 4-6 and 9-11. One way these
two methods could be combined is for the combination of rows to
provide a first, coarser slice width and for the tilting to provide
a finer variation on the combination width.
[0199] FIGS. 9A-9E show still another preferred embodiment of the
present invention, wherein a detector array 190 has structure and
function generally similar to those of arrays 30 and 102, and
operates in conjunction with mechanical aperture 34, in a manner
similar to that described above with reference to the preferred
embodiment shown in FIGS. 5A-5D. The rows of array 190, however,
have the following relative widths:
3 Central rows 198, 200 - width = 1 Rows 196, 202 - width = 1.5
Rows 194, 204 - width = 2.5 Rows 192, 206 - width = 5
[0200] FIG. 10 schematically shows a switching network 210 that
receives signals from array 190 and selectively combines these
signals to produce the slices shown in FIGS. 9A-9E. It will be
appreciated that the network comprises two substantially identical
and independent portions: a first portion coupled to rows 192, 194,
196 and 198, and a second portion coupled to rows 200, 202, 204 and
206. Network 210 is configured so that either two or four image
slices may be simultaneously produced.
[0201] Thus, as shown in FIG. 9A, aperture 34 is narrowed laterally
so as to mask substantially one half of the widths of rows 198 and
200, and the effective widths of these rows are then substantially
equal to 0.5. Switches S1, S2, S8 and S9, shown in FIG. 10, are
held in an open position, and two thin slices, A and B, are
produced and acquired respectively by receiving an output from row
198 via adder Al and an output from row 200 via adder A3. The
remaining switches are closed, and the outputs of adders A2 and A4
are not used.
[0202] In FIG. 9B, aperture 34 is opened so that rows 198 and 200
are fully exposed, and substantially one third of the widths of
rows 196 and 202 are masked, so that these rows have effective
width=1. Switches S3, S6, S7, S10, S13 and S14 are closed, while
the remaining switches are held open. Four slices having thickness
corresponding to width=1 are thus produced and acquired via adders
A1-A4.
[0203] In FIG. 9C, aperture 34 is opened still further, so as to
expose substantially all of rows 194 and 204 (as well as rows 196,
198, 200 and 202 in between them). Switches S1, S4, S7, S8, S11 and
S14 are closed, while the remaining switches are held open. The
outputs of rows 196 and 198 are combined by adder Al, and those of
rows 200 and 202, by adder A3. Four slices having thickness
corresponding to effective row width=2.5 are thus produced and
acquired via the adders.
[0204] In FIG. 9D, aperture 34 is fully open. Switches S1, S2, S5,
S8, S9 and S12 are closed, while the remaining switches are held
open. Four slices having thickness corresponding to effective row
width=5 are thus produced.
[0205] Finally, FIG. 9E illustrates a configuration in which two
slices, having thickness corresponding to effective row width=10,
are produced. In this case, the switches are maintained in the same
positions as were described above with reference to FIG. 9D. The
outputs of adders A1 and A2 are combined, preferably by means of a
software operation carried out by DAS 84, for example, to produce
slice A, and the outputs of adders A3 and A4 are similarly combined
to produce slice B.
[0206] It will thus be appreciated that array 190, having eight
rows, together with switching network 210, is capable of producing
two or four slices simultaneously, having an available range of
five different slice thicknesses. Other preferred embodiments of
the present invention, similar to that illustrated in FIGS. 9A-D
and 10 but generally including detector arrays having a greater
number of rows than array 190, can similarly produce more than four
slices simultaneously.
[0207] FIG. 11 illustrates schematically yet another preferred
embodiment of the present invention, in which a detector array 220
comprises four parallel rows of detectors: inner rows 222 and 224,
and outer rows 226 and 228, each row corresponding to a respective
image slice. Preferably all four rows have equal widths. As shown
in the figure, outer rows 226 and 228 are mounted and positioned
relative to inner rows 222 and 224 so that the outer rows may be
translated laterally to overlap and mask portions of the widths of
the inner rows. Preferably, aperture 34 and/or collimator 28 (as
shown in FIG. 1) similarly masks portions of the widths of outer
rows 226 and 228.
[0208] It will thus be appreciated that by translating rows 226 and
228 and correspondingly opening or closing aperture 34 (and/or
collimator 28), the four image slices may be adjusted to
substantially any desired thickness, up to a maximum corresponding
to the full width of the rows. Preferably, outer rows 226 and 228
and aperture 34 and/or collimator 28 are positioned so that all
four of the outer and inner rows have substantially equal effective
widths. However, the principle described here of using one or more
rows of the array to overlap and mask, and thus control the
effective width of, one or more other rows, may similarly be used
in other preferred embodiments of the present invention in which
the array includes a greater or lesser number of rows, and produces
image slices having equal or different thicknesses.
[0209] Although the above preferred embodiments have been described
with reference to detector elements having substantially equal
pitch sizes, wherein pitch is measured in a direction substantially
parallel to long array axis 72, it will be appreciated that the
principles of the present invention may similarly be applied to
arrays of detectors having two or more different pitch sizes.
Signals from adjacent detectors within a row of the array may also
be combined, using switching circuitry and/or methods similar to
those described above, or other circuitry and methods known in the
art.
[0210] FIG. 12 shows a first combination of detectors in different
rows to produce composite slice widths especially suitable for lung
imaging. In a preferred embodiment of the invention, 10 small
detectors rows 300 each having a row width of 1-2 mm are utilized.
In a preferred embodiment of the invention, the outputs of
corresponding detectors in 9 of the rows are added together to form
data for a thick slice while the data for the 10th row is used to
form a thin slice. Alternatively, the outputs of all the rows are
added together to form a thick slice and the outputs of one row is
used to provide a thin slice. Alternatively, two thin slices may be
provided in this manner, which thin slices can be either adjacent
slices or formed of the outputs of rows at the ends of the group of
rows. Further, alternatively, a single thin slice may be either at
the center of the group of rows or at the edge of the group.
[0211] In a further alternative embodiment of the inventions
non-uniform slices are produced using combinations of the outputs
of detectors in non-uniform rows. In these embodiments for example,
the row configurations of FIGS. 1, 2, 4, 5, 6 or 9 may be utilized.
For example, in these configurations, signals from detectors in the
two central thin rows may be combined to form a single relatively
thin slice and signals from detectors in a plurality of adjacent
outer detector rows may be combined to form two (or more) thick
slices. These thin and thick slices may have any ratio, consistent
with the available widths, but preferably a large ratio, as
described above, is provided as required, for example, for lung
images. Alternatively, two (or four) thin slices are provided
utilizing the separate outputs of the detectors of the central two
(or four) rows and thick slices are provided by summing the outputs
of the detectors in the outside rows. Of course, if the ratio
between the width of detectors in the various rows is large enough
for the application, no summing is necessary.
[0212] Alternatively, only detectors on one side of the center of
the row grouping are irradiated and only a single thin slice and a
single thick slice is formed. Alternatively, the detectors on one
side of the center line of the row configurations of FIGS. 1, 2, 4,
5, 6 or 9 may be omitted.
[0213] In a further preferred embodiment of the invention, a
greater or lesser number of rows may be provided, such that the
ratio between the slices is less than the 9:1 or 10:1 described
above. For example, if 6 equal rows are provided, then ratios of
6:1, 5:1 or less can be achieved. If a larger number of rows is
provided, then more than one wide grouping of rows and more than
one narrow grouping of rows may be achieved.
[0214] Preferred embodiments of the present invention have been
described with reference to CT scanners and CT imaging of the human
body, and are preferably used in the context of third- and
fourth-generation CT scanners. The inventive principles of the
present invention may be similarly applied, however, to CT scanners
applied to industrial quality control and other applications, as
well as to other imaging systems and methods.
[0215] It will be appreciated that the preferred embodiments
described above are cited by way of example, and the full scope of
the invention is limited only by the claims.
* * * * *