U.S. patent application number 09/801005 was filed with the patent office on 2001-12-06 for imaging system and method of constructing image using the system.
Invention is credited to Azemoto, Shogo, Hamada, Seiki, Naito, Hiroaki, Nakamura, Hironobu, Yamamoto, Shuji.
Application Number | 20010048731 09/801005 |
Document ID | / |
Family ID | 18667590 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010048731 |
Kind Code |
A1 |
Nakamura, Hironobu ; et
al. |
December 6, 2001 |
Imaging system and method of constructing image using the
system
Abstract
An imaging system is provided which comprises: a CT scanner; a
first storage unit storing a plurality of transverse images taken
by the CT scanner; an image conversion unit producing a
two-dimensional cross sectional image on the basis of the
transverse images, for which the transverse images are arranged in
a direction perpendicular to a transverse plane; a second storage
unit storing the cross sectional image; a peak detection unit
extracting an outline of the cross sectional image for detecting
peaks or troughs of the outline; a peak interpolation unit carrying
out interpolation on the basis of a specified standard for an
outline between the peaks or between the troughs detected by the
peak detecting unit; and an image construction unit reconstructing
the cross sectional image stored in the second storage unit using
the outline interpolated by the peak interpolation unit. The
imaging system makes it possible to improve a precision and to
increase a speed in peak detection when reconstructing a coronal
image produced from a plurality of transverse images taken by a CT
scanner.
Inventors: |
Nakamura, Hironobu;
(Nishinomiya-shi, JP) ; Naito, Hiroaki; (Osaka,
JP) ; Hamada, Seiki; (Osaka, JP) ; Yamamoto,
Shuji; (Osaka, JP) ; Azemoto, Shogo; (Tokyo,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
18667590 |
Appl. No.: |
09/801005 |
Filed: |
March 8, 2001 |
Current U.S.
Class: |
378/4 ; 378/15;
378/901 |
Current CPC
Class: |
A61B 6/541 20130101;
A61B 6/027 20130101; Y10S 378/901 20130101; A61B 6/032
20130101 |
Class at
Publication: |
378/4 ; 378/901;
378/15 |
International
Class: |
A61B 006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 1, 2000 |
JP |
2000-163899 |
Claims
What is claimed is:
1. An imaging system comprising: a CT scanner; a first storage unit
storing a plurality of transverse images taken by the CT scanner;
an image conversion unit producing a two-dimensional cross
sectional image on the basis of the transverse images, for which
the transverse images are arranged in a direction perpendicular to
a transverse plane; a second storage unit storing the cross
sectional image; a peak detection unit extracting an outline of the
cross sectional image for detecting relative extreme peaks of the
outline; a peak interpolation unit carrying out interpolation on
the basis of a specified standard for an outline between the
relative extreme peaks detected by the peak detecting unit; and an
image construction unit reconstructing the cross sectional image
stored in the second storage unit using the outline interpolated by
the peak interpolation unit.
2. An imaging system as claimed in claim 1 further comprising a
three-dimensional image production unit producing a
three-dimensional image using a plurality of the cross sectional
images reconstructed by the image construction unit.
3. An imaging system as claimed in claim 2 further comprising an
outputting unit outputting the three-dimensional image.
4. An imaging system as claimed in claim 1 further comprising: an
image displaying unit displaying at least the cross sectional
image; and a selection unit provided in the peak detection unit for
allowing a user to select the relative extreme peaks of the outline
of the cross sectional image displayed on the image displaying unit
while the user observing the cross sectional image.
5. An imaging system as claimed in claim 1 wherein the peak
detection unit detects the relative extreme peaks by smoothing
differentiation processing.
6. An imaging system as claimed in claim 1 wherein the CT scanner
is provided with an image pick-up unit rotating around an imaging
object, the image pick-up unit rotating with a rotating speed of
two rotations per minute at least.
7. An imaging system as claimed in claim 1 wherein the relative
extreme peaks are peaks.
8. An imaging system as claimed in claim 1 wherein the relative
extreme peaks are troughs.
9. A method of constructing an image of a heart using the imaging
system as claimed in claim 1 comprising the steps of: when an
imaging object of the CT scanner is a heart, producing a cross
sectional image of the heart with the image conversion unit;
thereafter, detecting peaks with the peak detection unit; carrying
out interpolation for an outline between the detected peaks with
the peak interpolation unit; and reconstructing the cross sectional
image of the heart in a diastolic phase with the image construction
unit using the interpolated outline.
10. A method of constructing an image of a heart using the imaging
system as claimed in claim 1 comprising the steps of: when an
imaging object of the CT scanner is a heart, producing a cross
sectional image of the heart with the image conversion unit;
thereafter, detecting troughs with the peak detection unit;
carrying out interpolation for an outline between the detected
troughs with the peak interpolation unit; and reconstructing the
cross sectional image of the heart in a systolic phase with the
image construction unit using the interpolated outline.
11. A storage medium stored with an image construction program, the
program comprising: an image conversion function for converting
transverse images picked up by a CT scanner into a two-dimensional
cross sectional image for which the transverse images are arranged
in a direction perpendicular to a transverse plane; a peak
detection function extracting an outline of the cross sectional
image for detecting relative extreme peaks; and a peak
interpolation function for carrying out interpolation on the basis
of a specified standard for an outline between the relative extreme
peaks.
12. A storage medium stored with an image construction program as
claimed in claim 11 wherein the relative extreme peaks are
peaks.
13. A storage medium stored with an image construction program as
claimed in claim 11 wherein the relative extreme peaks are
troughs.
14. A storage medium stored with an image construction program as
claimed in claim 11 wherein the program further comprises: an image
construction function for reconstructing the cross sectional image
by using the outline interpolated by the peak interpolation
function; and a three-dimensional image production function for
producing a three-dimensional image from a plurality of the cross
sectional images reconstructed by the image construction function,
and when an object of image pick-up of the CT scanner is a heart,
producing the three-dimensional image of the heart in a diastolic
phase from the cross sectional images reconstructed by carrying out
interpolation for an outline between the detected peaks.
15. A storage medium stored with an image construction program as
claimed in claim 11 wherein the program further comprises: an image
construction function for reconstructing the cross sectional image
by using the outline interpolated by the peak interpolation
function; and a three-dimensional image production function for
producing a three-dimensional image from a plurality of the cross
sectional images reconstructed by the image construction function,
and when an object of image pick-up of the CT scanner is a heart,
producing the three-dimensional image of the heart in a systolic
phase from the cross sectional images reconstructed by carrying out
interpolation for an outline between the detected troughs.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is related to Japanese Patent Application
No. 2000-163899 filed on Jun. 1, 2000, whose priority is claimed
under 35 USC .sctn. 119, the disclosure of which is incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an imaging system in a
medical field, particularly to an imaging system which can
construct an image from transverse images (tomograms) taken by a CT
scanner about an imaging object having a periodically changing
shape like a heart.
[0004] 2. Description of the Related Art
[0005] An X-ray computer tomography system (hereinafter referred to
as a CT scanner) has been used for taking medical images in a
medical field.
[0006] The CT scanner is a system which irradiates a diagnosing
subject with X-ray to collect projection data of the X-ray
transmitted through the diagnosing subject. On the basis of the
projection data, an image processing is carried out to reconstruct
a transverse image (also referred to as a tomogram) of visceral
organs of the diagnosing subject.
[0007] Furthermore, by processing a number of the reconstructed
transverse images so as to be arranged in the direction
perpendicular to the transverse plane at uniform intervals to form
a stack, a cross sectional image (herein after referred to as an
MPR (multi-planer reconstruction) image) is reconstructed. With
three-dimensional information further collected on the basis of the
MPR image, production of a three-dimensional image of the
diagnosing subject is also carried out.
[0008] For producing such a three-dimensional image, a large amount
of the transverse images must be collected with a high speed and
high precision. For this purpose, a helical type CT scanner
(hereinafter referred to as a helical scanning CT) has been
recently used which collects data of a helical cross sectional
plane.
[0009] The helical scanning CT is used for producing a transverse
image or a three-dimensional image used for examining and
diagnosing a function of a heart. The image of the heart is
obtained as being in a diastolic phase or systolic phase. However,
a heart repeats a diastole and systole with a certain personally
different characteristic period (about 60 beats/minute). Therefore,
no plurality of transverse images can be obtained about the heart
in the diastolic phase, for example, only at one time scanning.
[0010] Thus, in general, an electrocardiograph is provided to
select the transverse images supposed to be those in the diastolic
or systolic phase in synchronism with data signal obtained from the
electrocardiograph. From thus selected transverse images, there are
produced the MPR images or the three-dimensional images in the
diastolic or systolic phase.
[0011] FIG. 1 is a block diagram showing an outline of a
configuration of a related synchronization system of an
electrocardiograph with a helical scanning CT system.
[0012] The synchronization system comprises a helical scanning CT
130, an electrocardiograph 141 outputting data of an
electrocardiogram of a diagnosing subject, an electrocardiogram
synchronization unit 140 analyzing electrocardiogram data of a
diagnosing subject to transmit a synchronization signal to the
helical scanning CT, and a computer carrying out an image
processing.
[0013] In addition, the computer comprises a control unit 100
comprising a CPU and associated units, a storage unit 110, a
displaying unit 120, and an inputting unit 121.
[0014] In the storage unit 110, there are stored collected signals
111, transverse images 112, MPR images 113, and three-dimensional
images 114. The collected signals 111 are those of projection data
obtained by the helical scanning CT, transverse images 112 are
constructed from the collected signals 111, MPR images 113 are
produced from the transverse images 112, and three-dimensional
images 114 are produced on the basis of the MPR images 113.
[0015] The control unit 100 is provided with various functions such
as a signal collection function 101, a transverse image
construction function 102, an MPR image production function 103,
and a three-dimensional image production function 104. The signal
collection function 101 is for driving the helical scanning CT 130
and storing the collected signals 111 of the projection data in the
storage unit 110. The transverse image construction function 102 is
for constructing the transverse images 112 using the stored
collected signals 111. The MPR image production function 103 and a
three-dimensional image production function 104 are for producing
the MPR images 113 and the three-dimensional images 114 using the
transverse images 112 and the MPR images 113, respectively.
[0016] In such a related system used for constructing the image of
a heart in a diastolic or systolic phase, data collection
processing and imaging processing in the control unit 100 were
generally carried out by either one of the following.
[0017] (1) Processing of driving the helical scanning CT in
synchronism with a data signal of the electrocardiograph and
obtaining projection data when the heart shows a little motion.
[0018] FIG. 2 is a waveform diagram showing a typical data signal
of an electrocardiograph.
[0019] In general, in a waveform of the data signal of the
electrocardiograph, it is well known that a wave form in the range
between the T wave and the R wave exhibits a little variation.
Here, for allowing the projection data to be obtained within the
range, the electrocardiogram synchronization unit 140 transmits a
trigger signal to the helical scanning CT 130 at a specified
timing. The helical scanning CT 130 receiving the signal carries
out a series of processing for obtaining projection data in a
followed certain period.
[0020] Therefore, in the storage unit 110, only the projection data
in the range with a little variation from the T wave to the R wave
are stored as the collected signals 111.
[0021] After the scanning of the helical scanning CT 130 is over,
the control unit 100 constructs a plurality of the transverse
images 112 on the basis of the collected signals 111.
[0022] Furthermore, there is carried out processing of selecting
the transverse images from a plurality of the transverse images 112
in synchronism with the data signal of the electrocardiograph. The
selected transverse images 112, for example, those in a period
corresponding to the systolic phase of the heart (a specified
period after the T wave). On the basis of the selected images 112,
processing is further carried out for producing the MPR images 113
or 3 dimensional images 114.
[0023] Also about the transverse images 112 in the diastolic phase,
processing is carried out for selecting transverse images in a
period corresponding to the diastolic phase (a specified period
before the R wave).
[0024] (2) Processing of obtaining the projection data by the
helical scanning CT without in synchronism with a data signal of
the electrocardiograph, constructing transverse images on the basis
of the obtained data, and selecting images corresponding to those
in the diastolic or systolic phase of the heart with a measurer
comparing the constructed transverse images and the waveform of the
data signal of the electrocardiograph.
[0025] Here, the electrocardiogram synchronization unit 140 is not
used. Namely, the control unit 100 separately stores the data
signal obtained from the electrocardiograph 141 and the projection
data obtained from the helical scanning CT 130 in the storage unit
110 as the collected signals 111.
[0026] After this, the control unit 100 constructs the axial CT
images (transverse images) on the basis of the projection data. The
constructed axial CT images include those in both the diastolic and
systolic phases.
[0027] There, the axial CT images and the waveform of the data
signal of the electrocardiograph are displayed on a displaying unit
or printed out. From thus displayed or printed out images and
waveform, images corresponding to those in the diastolic or
systolic phases within the range from the T wave to the R wave are
manually selected in order by the measurer with correspondence of
each image with time made ascertained.
[0028] On the basis of a number of thus manually selected axial CT
images, processing is carried out by the control unit 100 for
producing the MPR images 113 or 3 dimensional images 114.
[0029] The helical scanning CT is a system in which linear movement
of a table with a diagnosing subject mounted thereon and rotation
of an X-ray tube and detectors are combined to collect the spiral
projection data. The path of the X-ray always passes through a
certain fixed range within the diagnosing object to provide
continuous projection data in the direction of the table
movement.
[0030] Namely, when transverse images with a certain thickness are
constructed with the table position gradually shifted, the time at
which the image is obtained becomes a little different depending on
the table position. Therefore, each of the transverse images is
constructed so as to include projected data obtained at times a
little different from each other.
[0031] For example, when a whole heart is scanned in 37.5 sec with
a helical scanning CT which has an axial resolution (slice
thickness) of 2 mm, takes 0.5 sec for one rotation (scanning time
0.5 sec) and reconstructs 10 images per rotation, an image is
reconstructed at 0.05 sec time intervals and 750 transverse images
are obtained in total.
[0032] In general, the period of the diastole and systole of a
heart of R-R 60 (60 beats/min) is about 1 sec (60 beats/60 sec).
Thus, the 750 transverse images include images for the diastolic
phase and those for systolic phase.
[0033] Therefore, in the case that MPR images are produced with the
750 transverse images arranged in the direction perpendicular to
the transverse plane (axial plane), the MPR images is provided with
a wavy outline because of mixed transverse images obtained in both
the diastolic and systolic phases. Namely, although an MPR image of
a heart would be obtained to have originally a smoothly varying
outline when the heart was at rest, the image is obtained to have
an indistinct outer shape with the outline thereof having small
"peaks (maximum peaks)" and "troughs (minimum peaks). This is
because the images are taken while the heart is periodically
moving.
[0034] Therefore, in order to produce the MPR image in the
diastolic (or systolic) phase from the transverse images, either
one of the above described two kinds of processing was used to
select the transverse images in the diastolic (or systolic) phase
among a large number of transverse images.
[0035] Both of the two kinds of processing, however, requires the
measurer to work for visually ascertaining a large number of
transverse images and data of electrocardiogram, for which a long
period of several days was necessary.
[0036] In particular, in the above processing (1), the
electrocardiogram synchronization unit 140 was necessary for the
synchronization with the data signal of the electrocardiograph,
which further required complicated preprocessing for the
synchronization including adjustment and parameter setting of the
units shown in FIG. 1.
[0037] In the processing (2), the work for selecting transverse
images required the measurer to have a high expert knowledge and to
spend a lot of time. Furthermore, the work of selection was carried
out subjectively without flexible applicability.
SUMMARY OF THE INVENTION
[0038] Accordingly, it is an object of the present invention to
provide an imaging system which can construct sharp images with a
high speed, high precision and easiness without requiring any
electrocardiogram synchronization unit and any image selection
processing by a measurer having expert knowledge, even for an
imaging object moving periodically such as a heart.
[0039] The above object can be accomplished by an imaging system
which comprises a CT scanner; a first storage unit storing a
plurality of transverse images taken by the CT scanner; an image
conversion unit producing a two-dimensional cross sectional image
on the basis of the transverse images, for which the transverse
images are arranged in a direction perpendicular to a transverse
plane; a second storage unit storing the cross sectional image; a
peak detection unit extracting an outline of the cross sectional
image for detecting peaks or troughs of the outline; a peak
interpolation unit carrying out interpolation on the basis of a
specified standard for an outline between the peaks or between the
troughs detected by the peak detecting unit; and an image
reconstruction unit of the cross sectional image stored in the
second storage unit using the outline interpolated by the peak
interpolation unit.
[0040] With the system, the cross sectional image of the diagnosing
subject can be constructed with higher speed, higher precision, and
more easiness.
[0041] In addition, according to the present invention, when an
imaging object of the CT scanner is a heart, the image conversion
unit produces a cross sectional image of the heart; thereafter, the
peak detection unit detects peaks; the peak interpolation unit
carries out interpolation for an outline between the detected
peaks; and the image reconstruction unit reconstructs the cross
sectional image of the heart in the diastolic phase by using the
interpolated outline.
[0042] Similarly, by using the detected troughs, the cross
sectional image of the heart in the systolic phase can be
reconstructed.
[0043] It is also possible for the system to detect the peaks or
troughs with nonuniform intervals. This makes it possible to
produce the cross sectional image of the heart in the diastolic or
systolic phase with a high speed, high precision, and easiness
without visual ascertaining work of the measurer.
[0044] In the present invention, the cross sectional image means a
so-called MPR (Multi Planar Reconstruction) image. Therefore, the
MPR image includes tomograms in all directions which are
reconstructed from the projection data obtained by the CT scanner.
In the present invention, however, coronal images or sagittal
images are to be mainly reconstructed as the MPR images.
Particularly in the following embodiments, the coronal image is
explained as the MPR image. However, the present invention is not
limited to this, but can be applied all kinds of cross sectional
images.
[0045] In the present invention, the CT scanner may be of any type
of scanning method used in the medical field such as T/R method,
R/R method, SIR method, N/R method, and helical scanning method.
However, since the imaging object of the present invention is a
diagnosing subject with a periodical movement, a high speed and
high precision CT scanner is required. Thus, it is preferable to
use the helical scanning type CT scanner which can finish
image-taking of whole diagnosing subject with a high precision
while the subject is holding breath.
[0046] For the first storage unit and second storage unit, a
rewritable storage unit of a semiconductor device (RAM) or a hard
disk can be used. In the present invention, a remarkable amount of
storage capacity is necessary for both the transverse images stored
in the first storage unit and the cross sectional images (MPR
images) stored in the second storage unit. Thus, it is preferable
to use a mass storage and quick access type storage device such as
a hard disk or a magneto-optical disk.
[0047] The image conversion unit according to the present invention
comprises a control program executing MPR images producing
function. Specifically, the unit is a section in which a
microcomputer with a CPU executes a specified algorithmic operation
on the basis of the control program to thereby output the cross
sectional images.
[0048] The peak detection unit according to the present invention
comprises a control program executing a so-called peak detection
function which extracts the outline of the cross sectional image
and detects the peaks or troughs of the outline.
[0049] The control program is executed with the data of the cross
sectional image inputted and data of the positions of the peaks or
those of the troughs outputted.
[0050] An algorithm for detecting positions of the peaks and the
troughs is realized by a difference operation (See "Kagakukeisoku
no tame no Hakei Data Shori (Waveform Data Processing in Scientific
Measurement)", ed. by Shigeo Minami, CQ Publication Co., Ltd., Apr.
30, 1986 (in Japanese)).
[0051] The peak interpolation unit according to the present
invention comprises a control program executing a function (peak
interpolation function) of interpolating between the obtained two
peaks (or two troughs). The control program is executed with the
peaks and the troughs inputted and an interpolated value between
the peaks outputted.
[0052] For example, the interpolation algorithm is realized by
linear interpolation method (See Yasuzo Sudou, "Igaku ni okeru
Sanjigen Gazoshori (Three Dimensional Image Processing in Medical
Science)", CORONA PUBLISHING CO., LTD., Mar. 10, 1995 (in
Japanese)).
[0053] The image construction unit according to the present
invention comprises a control program executing a function of
reconstructing cross sectional images, in which approximately the
same algorithm as that used for the image conversion unit can be
used. The control program is executed with transverse images
corresponding to the interpolated outline inputted and the cross
sectional images outputted.
[0054] The image conversion unit, peak detection unit, peak
interpolation unit, and image construction unit can be realized by
single control unit as will be explained later, for example, a
personal computer or workstation.
[0055] The control program realizing the above described functions
can be stored in a fixed storage medium such as a hard disk. In
addition to this, the program can be stored in a portable storage
medium such as a CD-ROM, MO, or DVD-ROM. Alternatively, the control
program can be also stored in a server for being transferred to a
personal computer at a remote location through a network.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1 is a block diagram showing an outline of a
configuration of a related synchronization system of an
electrocardiograph with a helical scanning CT system;
[0057] FIG. 2 is a waveform diagram showing a typical data of a
cardiogram;
[0058] FIG. 3 is a block diagram showing an embodiment of an
imaging system according to the present invention;
[0059] FIG. 4 is a flowchart showing whole processing carried out
in a control unit in the imaging system according to the present
invention;
[0060] FIG. 5 is a schematic illustration showing a flow of
constructing an MPR image;
[0061] FIG. 6 is a schematic diagram showing MPR images of a heart
produced by the processing according to the present invention;
and
[0062] FIG. 7 is a block diagram showing another embodiment of an
imaging system according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0063] The present invention will be explained in detail on the
basis of embodiments. However, the present invention is not limited
to the embodiments.
[0064] FIG. 3 is a block diagram showing an embodiment of an
imaging system according to the present invention.
[0065] The system of the embodiment can be applied to a
periodically moving diagnosing subject, and construction of an
image of a heart in the diastolic and systolic phases will be
explained below.
[0066] The system according to the present invention, compared with
the related system shown in FIG. 1, is different from the related
one in that it necessitates no electrocardiogram synchronization
unit 140 and no electrocardiograph 141.
[0067] In FIG. 3, a helical scanning CT 130 may be one which has
been conventionally used. However, for constructing an image with a
high resolution, one with an X-ray tube rotated at a high speed and
detectors with high resolution is preferable.
[0068] For example, a helical scanning CT with a performance of a
rotation speed of 2 rps and a slice thickness (resolution) of about
0.5 mm can be used ("Aquilion" supplied from Toshiba Corp.).
[0069] For a control unit 100, a so-called personal computer or
workstation can be used. Namely, a microcomputer can be used which
comprises ROM, RAM, various I/O interfaces, a timer, and associated
peripheral equipment with CPU centered. In addition, control
programs for realizing various functions according to the present
invention are stored in storage media in the control unit 100 such
as semiconductor storage devices such as ROM and RAM, or a hard
disk.
[0070] A storage unit 110 is for storing the control programs and,
in addition thereto, obtained collected signals, data of
constructed images, setting parameters and intermediate status data
while various functions are being executed. For the unit 110,
various storage media can be used such as rewritable semiconductor
memories (RAM), hard disks (HD), MO, MD, PD, DVD-RAM.
[0071] In the storage unit 110 according to the present invention,
there are stored, for example, collected signals 111 obtained from
the helical scanning CT 130, transverse images 112 constructed from
the collected signals 111, coronal images (MPR images) 113 produced
on the basis of the transverse images 112, three-dimensional images
114 of the diagnosing subject, outline images 115 of extracted
outlines of the MPR images 113, and positional data of peaks 116
and troughs 117 of the outlines of the outline images 115.
[0072] A displaying unit 120 is for displaying the transverse
images, MPR images, and three dimensional images constructed by
imaging processing, for which various kinds of displaying units
such as CRT, LCD, and PDP can be used depending on
applications.
[0073] An inputting unit 121 is for operation of inputting setting
parameters, inputting indication of various operations, starting
and stopping of various functions. For the inputting unit 121, in
addition to a keyboard, various pointing devices such as a mouse
and a track ball can be used.
[0074] Details of processing carried out in the control unit 100
will be explained in the following.
[0075] FIG. 4 is a flowchart showing whole processing carried out
in the control unit 100 according to the present invention.
[0076] The processing carried out in the control unit 100 comprises
those mainly carried out by eight function blocks shown in FIG.
3.
[0077] Here, a signal collection function block 101 is a part
carrying out processing for obtaining the collected signals 111 by
the helical scanning CT 130 (step S1 in FIG. 4). A transverse image
construction function block 102 is a part carrying out processing
for constructing the transverse images 112 by using the obtained
collected signals 111 (step S2 in FIG. 4). An MPR image production
function block 103 is a part carrying out processing for producing
the MPR images 113 by using the constructed transverse images 112
(step S3 in FIG. 4). A three-dimensional image production function
block 104 is a part carrying out processing for producing the
three-dimensional images 114 of the diagnosing subject (a heart,
for example) from the obtained MPR images 113 (step S12 in FIG.
4).
[0078] The four function blocks can be processed by using the same
processing as that realized in the related imaging system shown in
FIG. 1.
[0079] In FIG. 3, four function blocks of a peak detection function
105, an image at peak position selection function 106, a between
peaks interpolation function 107, and an MPR images reconstruction
function 108 are those characteristic to the system according to
the present invention.
[0080] The peak detection function block 105 is a part carrying out
processing for extracting an outline of an MPR image 113 obtained
by the MPR image production function block 103, producing the
outline image 115, and detecting tops and bottoms of the edge of
the outline image 115, namely, peaks and troughs.
[0081] Here, for the processing for extracting the outline, various
methods can be used such as an automatic tracing used in computer
graphics for drawing an outline.
[0082] Also for the processing for detecting peaks, various methods
can be used. Typical one of such is a method in which slopes of the
waveform of a signal are successively obtained to find the peaks
and the troughs by the difference operation. Another is a smoothing
differentiation method in which a smoothing processing of the
extracted outline is carried out with a moving-average method or a
frequency region method before being processed by the difference
operation.
[0083] By the peak detection function 105, data are obtained about
positions of a number of the peaks and the troughs on the edge of
the targeted outline image.
[0084] Instead of the peak position detection with the specified
automatic processing programmed in the control unit as above, the
detection of the peaks and the troughs may be carried out as
follows. In the detection, the obtained MPR image 113 is displayed
on the displaying unit 120, with the outline part enlarged in some
cases, and the positions of the tops and bottoms on the edge of the
outline are inputted by indication of the measurer.
[0085] The indicated positions of the peaks can be more easily
inputted with the use of a pointing device such as a mouse.
[0086] The image at peak position selection function 106 is a part
carrying out processing for selecting transverse images 112
corresponding to those at a number of positions of, for example,
the peaks.
[0087] Interpolation between two peaks is carried out with the
transverse images at the peak positions used by the between peaks
interpolation function 107 that will be described later. This
provides a reconstructed MPR image constructed only with the
transverse images corresponding to those in the so-called diastolic
phase.
[0088] The processing for selecting the transverse images 112 can
be carried out by selecting from the storage unit 110 the
transverse images 112 which are made in correspondence in time to
the positions of the peaks or the troughs. That is, the selection
can be made by carrying out some kind of flagging indicating
selection of the above transverse images 112 in the diastolic (or
systolic) phase.
[0089] The between peaks interpolation function 107 is a part
carrying out processing for estimating positions of edges between
two selected peaks and producing transverse images equivalent to
those to be between the transverse images at the positions of the
above two peaks (referred to as an interpolated image).
[0090] For interpolation between peaks, in addition to the
so-called "linear interpolation method", the "nonlinear
interpolation method" can be used. In the "linear interpolation
method", a linear interpolation is carried out with a ratio of the
distance of the interpolated image from one of the peak to the
distance between the two peaks. In the "nonlinear interpolation
method", the images are once converted into images called as
distance images before being processed by general interpolation
processing such as linear interpolation.
[0091] The MPR images reconstruction function 108 is a part
carrying out reconstruction of the MPR image 113 by using the
transverse images at the position of the peaks and the interpolated
images produced by the between peaks interpolation function 107.
This can be carried out by the same processing as that of the MPR
image production function 103 only with difference in used
transverse images.
[0092] With such processing, MPR images can be produced as
corresponding to those in the diastolic or systolic phases of a
heart.
[0093] Each of the above functions can be realized by the control
unit 100 executing control programs in a specified order.
[0094] An example of processing carried out by the control unit in
the embodiment of the imaging system according to the present
invention will be explained on the basis of the flowchart shown in
FIG. 4.
[0095] Here, a heart of a human body is taken as a diagnosing
subject.
[0096] First, the projection data of the diagnosing subject are
collected by the helical scanning CT 130 and the collected signals
111 of the projection data are stored in the storage unit 110 (step
S1).
[0097] Here, a present helical scanning CT 130 can be used with a
performance of a rotation speed of 2 rpm, axial resolution (slice
thickness) of 0.5 mm, spatial resolution of 0.5 mm, and gray level
value (CT value) indication with 16 bit code.
[0098] Let the length of the heart in the axial direction be 70 mm,
for example. If we let the helical scanning CT 130 be moved by 2.5
mm per one rotation, the rotation speed of taking 0.5 sec per
rotation provides a moving speed of 2.5 mm/0.5 sec=5 mm/sec. Here,
the moving distance per one rotation to the slice thickness is
called as a helical pitch. The above moving distance per rotation
of 2.5 mm is equivalent to five times the slice thickness (0.5 mm).
Thus, the helical pitch in the above case is called as a helical
pitch 1:5 or a helical pitch 5. Therefore, for the helical pitch 5,
a scanning of the whole heart (70 mm in length) takes 70/5=14
sec.
[0099] This shows that the scanning of the whole heart can be
completed in a comparatively short time of the order of 14 sec.
[0100] Following this, on the basis of the collected signals 111,
the transverse images are constructed by the normally carried out
image processing (step S2). For example, the whole heart (70 mm in
length) is constructed with the transverse images 112 of the number
of 70 mm/0.5 mm=140.
[0101] As described above, the scanning time for the whole heart is
14 sec. While, the period of the beat of a heart is generally about
1 sec. Therefore the constructed transverse images 112 mixedly
include those in the diastolic phases of the heart and those in the
systolic phases.
[0102] FIG. 5 is a schematic illustration showing a flow of
constructing an MPR image.
[0103] The transverse images 112 are obtained as axial images for
which a heart 10 of a diagnosing subject 11 is cut transversally
along transverse planes 12 as shown in the figure.
[0104] Returning to FIG. 4, as a next step, processing for
producing an MPR image is carried out (step S3).
[0105] With reference to FIG. 5, the MPR image 113 is a coronal
image on a two-dimensional cross sectional plane A. For the image,
all of the transverse images 112 obtained in step S2 are arranged
in the direction perpendicular to the transverse planes 12 to be
cut along a plane perpendicular to the transverse planes 12.
[0106] Since the MPR image 113 is produced on the basis of the
transverse images mixed with those in the diastolic and systolic
phases, the outline thereof is made to have minute
irregularity.
[0107] For example, in the MPR image 113 in FIG. 5, the outline has
"tops" at line segments c1 and c2. This shows that the portions are
constructed on the basis of the transverse images 112 in the
diastolic phase.
[0108] Furthermore, the outline has "bottoms" at line segments d1
and d2. This shows that the portions are constructed on the basis
of the transverse images 112 in the systolic phase.
[0109] Next, processing for extracting the outline of the MPR image
113 is carried out (step S4).
[0110] To the extraction processing, there can be applied the
processing that is normally carried out with an application
software for image processing.
[0111] With the extraction processing, an outline image 115 having
only an outline is produced as shown in FIG. 5.
[0112] Following this, there is carried out processing for
detecting peaks and troughs of the outline image 115 (step S5).
[0113] The processing for the detection can be carried out by the
difference operation as described before. The positions of the
detected peaks 116 and troughs 117 are stored in the storage unit
110.
[0114] FIG. 6 is a schematic diagram showing MPR images of a heart
produced by the processing according to the present invention.
[0115] The outline image 115 of the MPR image 113 extracted at step
S4 has tops and bottoms as shown in FIG. 6. With the extraction
processing in step S5, positions shown with transverse planes c are
detected as those of tops (peaks), while positions shown by
transverse planes d are as those of bottoms (troughs).
[0116] Here, even for nonuniform intervals between the positions of
the transverse planes c and d, the positions can be detected easily
and surely.
[0117] The transverse images corresponding to the respective
transverse planes c or d can be easily selected by retrieving the
transverse images 112 stored in the storage unit 110.
[0118] In step S6, processing is carried out for selecting from the
storage unit 110 transverse images in the diastolic phase
corresponding to the positions of the obtained peaks (transverse
planes c).
[0119] For example, for a helical pitch of 3 (the moving distance
for one rotation becomes three times the slice thickness of 0.5 mm,
i.e. 0.5.times.3=1.5 mm), the moving distance in one second becomes
3 mm. For a heart of a human body with 60 beats/min, the period
between diastoles is one second. Thus, images in the diastolic
phase can be selected with 3 mm intervals. The 3 mm interval
includes 6 images with 0.5 mm slice thickness. Thus, of the 140
transverse images constructed in step S4, there are selected the
order of 140/6=23 transverse images in the diastolic phases.
[0120] Furthermore, in step S7, processing is carried out for
selecting from the storage unit 110 transverse images in the
systolic phase corresponding to the positions of the obtained
troughs (transverse planes d).
[0121] Next to this, in step S8, processing is carried out for
interpolating the peaks.
[0122] With the 23 transverse images in the diastolic phases
selected in step S6, an MPR image in the diastolic phase is
reconstructed. However, since transverse images between the two
transverse images in the diastolic phase are thinned out,
processing for interpolating between the peaks is carried out for
interpolating the thinned out transverse images as will be
described later. For the interpolation processing, the previously
described linear or nonlinear interpolation processing can be
used.
[0123] For example, in FIG. 6, instead of the trough at a position
d between positions of two transverse planes c (peaks), a point, an
intersection point of a straight line connecting the two peaks, is
taken as an interpolation point of the outline.
[0124] Then, processing is carried out for producing a transverse
image corresponding to the above interpolation point from the two
transverse images in the diastolic phases corresponding to
positions of the two peaks, respectively.
[0125] Following this, in step S9, processing is carried out for
interpolating the troughs. The processing is carried out in the
same way as that for interpolating the peaks in step S8 with only
difference therefrom being use of troughs instead of the peaks.
[0126] Thus, there are formed transverse images in the systolic
phase between the troughs.
[0127] Next, in step S10, an MPR image is reconstructed by using
the transverse images in the diastolic phases selected in step S6
and those produced in step S8. The reconstruction processing is
carried out in the same way as carried out in step S3. The
reconstruction processing provides an MPR image in the diastolic
phase 113-1 as shown in FIG. 6.
[0128] Further, reconstruction of an MPR image using the transverse
images in the systolic phases selected in step S7 and those
produced in step S9 (step S11) provides an MPR image in the
diastolic phase 113-2 as shown in FIG. 6.
[0129] With the processing as described above, from an indistinct
MPR image with a wavy outline due to mixed images in both the
diastolic and systolic phases, an MPR image corresponding to the
diastolic phase and an MPR image corresponding to the systolic
phase could be separately obtained.
[0130] By using the MPR images obtained in steps S10 and S11,
precision of image extraction can be ascertained about the
diastolic phase and systolic phase of the heart.
[0131] All of the processing from step S2 to step S11 can be
carried out by single control unit 100. Furthermore, this can be
executed within a short time of several minutes until the MPR
images 113-1 and 113-2 are reconstructed after the collected
signals 111 from the helical scanning CT are stored in the storage
unit 110.
[0132] As a next step, three-dimensional images in the diastolic
and systolic phases are produced with the transverse images
obtained in the processing from step S6 to step S9 (step S12).
[0133] The three-dimensional image can be produced by well-known
technique for which such a method as the volume rendering method,
geometric model method, or voxel method can be employed.
[0134] Namely, a three-dimensional image in the diastolic phase is
produced by, for example, the volume rendering processing with the
transverse images selected in step S6 and those produced by
interpolation processing in step S8 (step S12-1). The transverse
images selected in step S6 are those in the diastolic phases at the
positions of the peaks, and those produced in step S8 also
correspond to the diastolic phase. In the same way, a
three-dimensional image in the systolic phase is produced by, for
example, the volume rendering processing with the transverse images
selected in step S7 and those produced by interpolation processing
in step S9 (step S12-2). The transverse images selected in step S7
are those in the systolic phases at the positions of the troughs,
and those produced in step S9 also correspond to the systolic
phase.
[0135] For producing the three-dimensional image, it is preferable
for the axial resolution of the CT scanner to be less than about
0.7 mm, for which isotropic voxels are formed each having equal
spatial resolution and axial resolution.
[0136] The MPR images obtained in steps S10 and S11 are sharp ones
each having a sharp outline without irregularity. Thus, each of the
three-dimensional images obtained in step S12 also has a sharp
outer shape.
[0137] Following this, in step S13, processing for analyzing
various functions of a heart is carried out as follows.
[0138] The analyses are, for example:
[0139] 1) processing for calculating out the volume of a heart in a
diastolic phase from the three-dimensional image in the diastolic
phase;
[0140] 2) processing for calculating out the volume of a heart in a
systolic phase from the three-dimensional image in the systolic
phase;
[0141] 3) processing for producing a moving image of a heart
repeating diastole and systole from a plurality of
three-dimensional images; and
[0142] 4) processing for detecting abnormal portions on the surface
of a heart from three-dimensional images.
[0143] Any of the above processing can be carried out by combining
control programs realized at present.
[0144] Here, the images obtained in steps S10 to S12, being more
sharply provided than previous ones, can improve accuracy of
various kinds of analyses carried out in step S13.
[0145] In the processing in step S5 in FIG. 4, the peaks and the
troughs can be detected even they are positioned at nonuniform
intervals. The peaks, however, may be also detected by selection of
a measurer who actually carries out visual observation of the peaks
and troughs of the outline of an MPR image produced in step S3. At
this time, the MPR image is displayed on the display unit 120 with
the outline partially enlarged.
[0146] The operation for the selection can be carried out by using
various kinds of inputting units 121 such as a mouse.
[0147] In this way, with a manual operation allowed to be carried
out by a measurer, an image of a local part in the diastolic or
systolic phases can be easily obtained as desired by the
measurer.
[0148] Also in the present invention, as shown in FIG. 3, it is not
always necessary for the system to be in synchronism with a signal
of an electrocardiogram. However, for more improved precision, an
electrocardiograph 141 and electrocardiogram synchronization unit
140 may be added as shown in FIG. 7 so as to drive the helical
scanning CT in synchronism with the electrocardiogram like in a
related system.
[0149] In the present invention, in step S1 the inputted image
signals of the diagnosing subject are those obtained by the helical
scanning CT. In addition to this, the image signals may be those
obtained by MRI (Magnetic Resonance Imaging) system or PET
(Positron Emission Tomography).
[0150] In the embodiments, a heart was explained as the diagnosing
subject. However, the present invention can be also applied to
other visceral organs exhibiting periodical movement (such as
lungs).
[0151] According to the present invention, even for a periodically
moving imaging object such as a heart, a sharp coronal image and
three dimensional image can be constructed from images obtained by
a helical scanning CT with a high speed, high precision and
easiness.
[0152] In addition, when obtaining images with the helical scanning
CT, no unit is necessary for synchronization with an
electrocardiograph and no image selection is also necessary which
is processed by a measurer having expert knowledge.
[0153] Furthermore, when a heart is examined with the helical
scanning CT, no special device is necessary to be attached to the
examinee. Moreover, it takes only 20 to 30 sec for scanning the
whole heart, so that the examination can be completed only by
forcing the examinee to hold breath one time. This can reduce an
amount of X-ray irradiation compared with an examination with the
related system that necessitates synchronization with an
electrocardiograph. Therefore, the examination can be made
noninvasive and remarkably time saving to make it possible to
construct an examination system causing no pain to patients.
[0154] In addition, after the signals of the projection data are
collected by the helical scanning CT, a series of processing, from
the construction of the transverse image to the analyses of the
function of the heart, can be carried out by single control unit
without any intervention of manual operation. Thus, the series of
operations can be easily carried out without requiring any special
knowledge of image processing.
* * * * *