U.S. patent application number 12/959893 was filed with the patent office on 2011-09-15 for pet/mri device, pet device, and image reconstruction system.
This patent application is currently assigned to NATIONAL INSTITUTE OF RADIOLOGICAL SCIENCES. Invention is credited to Takayuki OBATA, Taiga YAMAYA.
Application Number | 20110224534 12/959893 |
Document ID | / |
Family ID | 43733182 |
Filed Date | 2011-09-15 |
United States Patent
Application |
20110224534 |
Kind Code |
A1 |
YAMAYA; Taiga ; et
al. |
September 15, 2011 |
PET/MRI DEVICE, PET DEVICE, AND IMAGE RECONSTRUCTION SYSTEM
Abstract
A PET/MRI device includes an MRI device that has a measurement
port, a PET detector that can be inserted into the measurement
port, and a mechanism that can slide the PET detector into and out
of the MRI measurement port. Thereby, the PET/MRI device allows MRI
measurement during PET measurement.
Inventors: |
YAMAYA; Taiga; (Chiba-shi,
JP) ; OBATA; Takayuki; (Chiba-shi, JP) |
Assignee: |
NATIONAL INSTITUTE OF RADIOLOGICAL
SCIENCES
CHIBA-SHI
JP
|
Family ID: |
43733182 |
Appl. No.: |
12/959893 |
Filed: |
December 3, 2010 |
Current U.S.
Class: |
600/411 |
Current CPC
Class: |
G01T 1/1603 20130101;
G01R 33/56375 20130101; G01R 33/307 20130101; G01R 33/481
20130101 |
Class at
Publication: |
600/411 |
International
Class: |
A61B 5/055 20060101
A61B005/055 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 9, 2010 |
JP |
2010-52389 |
Claims
1. A PET/MRI device comprising: an MRI device that has a
measurement port; a PET detector that is insertable into the
measurement port; and a mechanism that is capable of sliding the
PET detector into and out of the measurement port of the MRI
device, MRI measurement being allowed during PET measurement.
2. The PET/MRI device according to claim 1, wherein the PET
detector has a measurement field of view having a width wider than
that of the MRI device in a longitudinal direction of a measurement
object.
3. The PET/MRI device according to claim 1, wherein the PET
detector is movable through the measurement port with the
measurement object.
4. The PET/MRI device according to claim 1, wherein the PET
detector is attached to a bed of the measurement object for
integral movement.
5. The PET/MRI device according to claim 4, further comprising a
mechanism that is capable of sliding the PET detector in a
longitudinal direction of the bed on which the measurement object
is put.
6. The PET/MRI device according to claim 1, wherein an MRI RF coil
is attached to inside the PET detector.
7. The PET/MRI device according to claim 6, wherein the MRI RF coil
attached to inside the PET detector is a transmitter coil, a
receiver coil, a transmitter-receiver two-way coil, or a coil that
includes both a transmitter coil and a receiver coil.
8. The PET/MRI device according to claim 2, wherein the width of
the measurement field of view of the PET detector is extended to
cover the measurement object at least from a head to a trunk
thereof.
9. The PET/MRI device according to claim 8, wherein the PET
detector is divided in the longitudinal direction of the
measurement object.
10. The PET/MRI device according to claim 8, wherein detector rings
that constitute the PET detector, and/or detector units that
constitute the detector rings, are arranged at nonuniform
intervals.
11. The PET/MRI device according to claim 8, wherein PET detectors
having different resolutions and/or sensitivities are used for a
head and a trunk, respectively.
12. The PET/MRI device according to claim 11, wherein the PET
detector for a head has a resolution higher than that of the PET
detector for the trunk.
13. The PET/MRI device according to claim 8, wherein the PET
detector for a head includes a detector ring that has an inner
diameter smaller than that of a detector ring that constitutes the
PET detector for a trunk.
14. The PET/MRI device according to claim 1, wherein the PET
detector has an opening in at least an eye-covering area near a
head of the measurement object.
15. The PET/MRI device according to claim 1, wherein a detector
ring that constitutes the PET detector near a trunk of the
measurement object has a sectional shape such that a size thereof
in a thickness direction of the measurement object is different
from that in a width direction perpendicular to the thickness
direction so that the detector approaches a surface of the
trunk.
16. The PET/MRI device according to claim 15, wherein the detector
ring that constitutes the PET detector near the trunk of the
measurement object includes an arched upper half portion and an
arched lower half portion in the thickness direction of the
measurement object, the arched upper half portion having a radius
of curvature smaller than that of the arched lower half
portion.
17. The PET/MRI device according to claim 1, wherein the detector
ring that constitutes the PET detector has an arched upper half
portion in the thickness direction of the measurement object, the
arched upper half portion being openable at least in part.
18. The PET/MRI device according to claim 17, wherein the arched
upper half portion is opened in a double-door configuration.
19. The PET/MRI device according to claim 17, wherein the arched
upper half portion is opened in a single-door configuration.
20. The PET/MRI device according to claim 17, wherein the arched
upper half portion and a remaining arched lower half portion are
separable from each other.
21. The PET/MRI device according to claim 3, wherein the detector
ring that constitutes the PET detector has an arched upper half
portion in the thickness direction of the measurement object, the
arched upper half portion being variable in size and/or in shape
according to the measurement object.
22. The PET/MRI device according to claim 9, wherein the PET
detector for a head is movable with respect to and/or detachable
from the PET detector for a trunk.
23. The PET/MRI device according to claim 1, wherein the PET
measurement is started before the PET detector starts being slid
into the measurement port of the MRI device, and ended after the
PET detector ends being slid to a retracted position of the
measurement object after end of the MRI measurement, whereby PET
measurement time is maximized.
24. The PET/MRI device according to claim 1, wherein the PET
detector includes a mechanism for sliding inside the measurement
port independent of a sliding movement of the measurement object,
so that the PET detector slides at a moving speed lower than that
at which the measurement object slides.
25. The PET/MRI device according to claim 24, comprising a slide
mechanism that is capable of retracting the PET detector into the
measurement port of the MRI device so as to facilitate loading and
unloading of the measurement object onto/from the bed and setup of
the measurement object.
26. The PET/MRI device according to claim 1, wherein the PET
measurement is started immediately before start of the MRI
measurement and ended immediately after end of the MRI measurement,
or PET data that is collected from immediately before the start of
the MRI measurement to immediately after the end of the MRI
measurement is used for PET image reconstruction processing, so as
to improve simultaneity between the PET measurement and the MRI
measurement.
27. A PET device comprising a PET detector attached to a bed of a
measurement object.
28. The PET device according to claim 27, comprising a mechanism
that is capable of sliding the PET detector in a longitudinal
direction of the bed on which the measurement object is put.
29. The PET device according to claim 27, wherein a width of a
measurement field of view of the PET detector is extended to cover
the measurement object at least from a head to a trunk thereof.
30. The PET device according to claim 29, wherein the PET detector
is divided in the longitudinal direction of the measurement
object.
31. The PET device according to claim 29, wherein detector rings
that constitute the PET detector, and/or detector units that
constitute the detector rings, are arranged at nonuniform
intervals.
32. The PET device according to claim 29, wherein PET detectors
having different resolutions and/or sensitivities are used for a
head and a trunk, respectively.
33. The PET device according to claim 32, wherein the PET detector
for a head has a resolution higher than that of the PET detector
for the trunk.
34. The PET device according to claim 29, wherein the PET detector
for a head includes a detector ring that has an inner diameter
smaller than that of a detector ring that constitutes the PET
detector for a trunk.
35. The PET device according to claim 29, wherein the PET detector
has an opening in at least an eye-covering area near a head of the
measurement object.
36. The PET device according to claim 27, wherein a detector ring
that constitutes the PET detector near a trunk of the measurement
object has a sectional shape such that a size thereof in a
thickness direction of the measurement object is different from
that in a width direction perpendicular to the thickness direction
so that the detector approaches a surface of the trunk.
37. The PET device according to claim 36, wherein the detector ring
that constitutes the PET detector near the trunk of the measurement
object includes an arched upper half portion and an arched lower
half portion in the thickness direction of the measurement object,
the arched upper half portion having a radius of curvature smaller
than that of the arched lower half portion.
38. The PET device according to claim 27, wherein the detector ring
that constitutes the PET detector has an arched upper half portion
in the thickness direction of the measurement object, the arched
upper half portion being openable at least in part.
39. The PET device according to claim 38, wherein the arched upper
half portion is opened in a double-door configuration.
40. The PET device according to claim 38, wherein the arched upper
half portion is opened in a single-door configuration.
41. The PET device according to claim 38, wherein the arched upper
half portion and a remaining arched lower half portion are
separable from each other.
42. The PET device according to claim 27, wherein the PET detector
includes a detector ring at least whose upper portion above a bed
covering the measurement object is variable in size and/or in shape
according to the measurement object.
43. The PET device according to claim 30, wherein the PET detector
for a head is movable with respect to and/or detachable from the
PET detector for a trunk.
44. A PET device comprising a belt-like PET detector that is
composed of detector units connected by links, the detector units
being freely changeable in layout according to a shape of a
measurement object.
45. The PET device according to claim 44, wherein the links has a
function of allowing rotation and a change in distance between the
detector units.
46. The PET device according to claim 44, wherein the links
includes an encoder so that a relationship in spatial position
coordinates between adjoining detector units is obtainable.
47. The PET device according to claim 44, comprising an inner frame
so that the detector units constituting the belt-like PET detector
are located in predetermined positions.
48. The PET device according to claim 47, wherein a plurality of
types of the inner frame are prepared in advance according to size
and/or shape of the measurement object.
49. An image reconstruction system for calculating a system matrix
element for use in an image reconstruction operation by: referring
to a relationship in spatial position coordinates between adjoining
ones of detector units that are connected into a belt-like PET
detector by links, the relationship being acquired from encoders
attached to the links; referring to spatial position coordinates of
the detector units constituting the belt-like PET detector, the
coordinates being determined by an inner frame for locating the
detector units in predetermined positions; or referring to spatial
position coordinates of the detector units, determined by an arched
upper half portion of the PET detector.
50. The image reconstruction system according to claim 49, wherein
system matrices corresponding to respective layout patterns of
detector units are calculated in advance and stored in a storing
device, the layout patterns being uniquely determined by types of
an inner frame or an arched upper half portion of a PET detector.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a PET/MRI device and a PET
device, and more particularly to a PET/MRI device that can obtain a
PET image and an MRI image almost simultaneously in a short time,
and a PET device whose PET detector can be brought close to a
measurement object for improved sensitivity.
[0003] 2. Description of the Related Art
[0004] PET/CT devices such as shown in FIGS. 1A and 1B have been in
widespread use, in which a CT device 100 and a PET device 200 are
combined to provide a functional image of the PET device 200
superposed on a morphological image of the CT device 100 for
diagnosis. In the diagrams, 10 denotes a patient or subject
(hereinafter, referred to generically as a patient) to be measured
(tested); 20 denotes a bed on which the patient 10 is put (lies);
22 denotes a device for moving the bed 20 in a horizontal
direction; 102 denotes an X-ray tube which is the X-ray source of
the CT device 100; 104 denotes an X-ray detector; and 202 denoted
detector rings (hereinafter, also referred to simply as rings)
which constitute the PET detector of the PET device 200. The CT
exposure is typically several times the PET exposure and is
therefore not negligible.
[0005] Instead of the CT device, an MRI device which can obtain
morphological images without radiation exposure is receiving
attention. A PET/MRI device capable of obtaining both PET and MRI
images has been under research and development. In particular,
there has been developed a PET/MRI device of semiconductor light
receiving element type in which all the detector units of the PET
device are arranged within the static magnetic field of the MRI,
using magnetically insensitive avalanche photodiodes (APDs) or
Geiger mode APDs (also referred to as SiPMs) as the light receiving
elements, and this PET/MRI device can be applied to those for small
animals and for the heads (See the following non-patent and patent
documents: Schlyer D et al. "A Simultaneous PET/MRI scanner based
on RatCAP in small animals," IEEE Nuclear Science Symposium
Conference Record, Volume: 5, pp. 3256-3259, 2007; Schlemmer H W at
al. "Simultaneous MR/PET Imaging of the Human Brain: Feasibility
Study," Radiology, 2008: 248, 1028-1035; Judenhofer M S et al.
"Simultaneous PET-MRI: a new approach for functional and
morphological imaging," Net Med 2008, 14(4): 459-65; U.S. Pat. No.
7,626,392 B2; U.S. Patent Application Laid-Open No. 2008/0287772
A1; and U.S. Patent Application Laid-Open No. 2009/0108206 A1).
[0006] Given detectors of the same sensitivity, the PET device
typically increases in sensitivity as the detectors are located
closer to the patient and as the field of view in the direction of
the body axis of the patient (referred to as axial field of view)
is widened. The axial field of view of the PET device as wide as
the effective axial field of view of the MRI device (30 to 40 cm or
so), which is determined by the stable area of the static magnetic
field, has had the problem of insufficient sensitivity of the PET
device, requiring a PET measurement time longer than the MRI
measurement time (typically several minutes).
SUMMARY OF THE INVENTION
[0007] The present invention has been achieved in order to solve
the foregoing conventional problem. It is thus a first object of
the present invention to make it possible to obtain a PET image and
an MRI image almost simultaneously in a short time.
[0008] A second object of the present invention is to improve the
sensitivity of the PET detector.
[0009] The foregoing first object of the present invention has been
achieved by the provision of a PET/MRI device including: an MRI
device that has a measurement port; a PET detector that is
insertable into the measurement port; and a mechanism that is
capable of sliding the PET detector into and out of the measurement
port of the MRI device, MRI measurement being allowed during PET
measurement.
[0010] The PET detector may have a measurement field of view having
a width wider than that of the MRI device in a longitudinal
direction of a measurement object.
[0011] The PET detector may be movable through the measurement port
with the measurement object.
[0012] The foregoing second object has been achieved by the PET
detector being attached to a bed of the measurement object for
integral movement.
[0013] The PET/MRI device may include a mechanism that is capable
of sliding the PET detector in a longitudinal direction of the bed
on which the measurement object is put.
[0014] An MRI RF coil may be attached to inside the PET
detector.
[0015] The MRI RF coil attached to inside the PET detector may be a
transmitter coil, a receiver coil, a transmitter-receiver two-way
coil, or a coil that includes both a transmitter coil and a
receiver coil.
[0016] The width of the measurement field of view of the PET
detector may be extended to cover the measurement object at least
from its head to its trunk.
[0017] The PET detector may be divided in the longitudinal
direction of the measurement object.
[0018] Detector rings that constitute the PET detector, and/or
detector units that constitute the detector rings, may be arranged
at nonuniform intervals.
[0019] PET detectors having different resolutions and/or
sensitivities may be used for the head and the trunk,
respectively.
[0020] The PET detector for a head may have a resolution higher
than that of the PET detector for a trunk.
[0021] The PET detector for the head may include a detector ring
that has an inner diameter smaller than that of a detector ring
that constitutes the PET detector for the trunk.
[0022] The PET detector may have an opening in at least an
eye-covering area near the head of the measurement object.
[0023] A detector ring that constitutes the PET detector near a
trunk of the measurement object may have a sectional shape such
that its size in a thickness direction of the measurement object is
different from that in a width direction perpendicular to the
thickness direction so that the detector approaches a surface of
the trunk.
[0024] The detector ring that constitutes the PET detector near the
trunk of the measurement object may include an arched upper half
portion and an arched lower half portion in the thickness direction
of the measurement object, the arched upper half portion having a
radius of curvature smaller than that of the arched lower half
portion.
[0025] The detector ring that constitutes the PET detector may have
a detector ring that has an arched upper half portion in the
thickness direction of the measurement object, the arched upper
half portion being openable at least in part.
[0026] The arched upper half portion may be opened in a double-door
configuration.
[0027] The arched upper half portion may be opened in a single-door
configuration.
[0028] The arched upper half portion and a remaining arched lower
half portion may be separable from each other.
[0029] The detector ring that constitutes the PET detector may have
an arched upper half portion in the thickness direction of the
measurement object, the arched upper half portion being variable in
size and/or in shape according to the measurement object.
[0030] The PET detector for a head may be movable with respect to
and/or detachable from the PET detector for a trunk.
[0031] The PET measurement may be started before the PET detector
starts being slid into the MRI measurement port, and ended after
the PET detector ends being slid to a retracted position of the
measurement object after end of the MRI measurement, whereby PET
measurement time is maximized.
[0032] The PET detector may include a mechanism for sliding inside
the measurement port independent of a sliding movement of the
measurement object, so that the PET detector can slide at a moving
speed lower than that at which the measurement object slides.
[0033] The PET/MRI device may include a slide mechanism that is
capable of retracting the PET detector into the MRI measurement
port so as to facilitate loading and unloading of the measurement
object onto/from the bed and setup of the measurement object.
[0034] The PET measurement may be started immediately before start
of the MRI measurement and ended immediately after end of the MRI
measurement, or PET data that is collected from immediately before
the start of the MRI measurement to immediately after the end of
the MRI measurement may be used for PET image reconstruction
processing, so as to improve simultaneity between the PET
measurement and the MRI measurement.
[0035] The second object of the present invention has also been
achieved by the attachment of a PET detector to a bed of a
measurement object.
[0036] The present invention also provides a PET device including a
belt-like PET detector that is composed of detector units connected
by links, the detector units being freely changeable in layout
according to a shape of a measurement object.
[0037] The links may have a function of allowing rotation and a
change in distance between the detector units.
[0038] The links may include an encoder so that a relationship in
spatial position coordinates between adjoining detector units is
obtainable.
[0039] The PET device may include an inner frame so that the
detector units constituting the belt-like PET detector are located
in predetermined positions.
[0040] A plurality of types of the inner frame may be prepared in
advance according to size and/or shape of the measurement
object.
[0041] The present invention also provides an image reconstruction
system which calculates a system matrix element for use in an image
reconstruction operation by: referring to a relationship in spatial
position coordinates between adjoining ones of detector units that
are connected into a belt-like PET detector by links, the
relationship being acquired from encoders attached to the links;
referring to spatial position coordinates of the detector units
constituting the belt-like PET detector, the coordinates being
determined by an inner frame for locating the detector units in
predetermined positions; or referring to spatial position
coordinates of the detector units, determined by an arched upper
half portion of the PET detector.
[0042] System matrices corresponding to respective layout patterns
of the detector units may be calculated in advance and stored in a
storing device, the layout patterns being uniquely determined by
types of the inner frame or the arched upper half portion of the
PET detector.
[0043] According to the present invention, it is possible to bring
the PET detector close to the patient and/or make the effective
measurement field of view of the PET detector wider than that of
the MRI device, so that a PET image and an MRI image are obtained
almost simultaneously in a short time.
[0044] The PET detector can be attached to the bed of the
measurement object so that the PET detector comes closer to the
measurement object for even higher sensitivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1A is a perspective view and FIG. 1B is a sectional
view seen from the front, showing the configuration of an example
of a conventional PET/CT device;
[0046] FIG. 2 is a perspective view showing a general configuration
of a first embodiment of the present invention;
[0047] FIG. 3A is a front view and FIG. 3B is a sectional view seen
from a side, showing a detailed configuration of the same;
[0048] FIGS. 4A and 4B are sectional views showing a typical
operation of the same;
[0049] FIGS. 5A and 5B are flowcharts showing operating procedures
of the same;
[0050] FIG. 6 is a time chart of the same;
[0051] FIG. 7 is a time chart of a modification of the same;
[0052] FIG. 8 is a time chart of another modification of the
same;
[0053] FIG. 9A is a perspective view showing a general
configuration of a second embodiment of the present invention, and
FIG. 9B is a sectional view seen from a side, showing a detailed
configuration of the same;
[0054] FIGS. 10A and 10B are cross-sectional views of the same,
showing a state where an RF coil is attached;
[0055] FIG. 11A is a front view and FIG. 11B is a sectional view
seen from a side, showing a detailed configuration of a third
embodiment of the present invention;
[0056] FIG. 12A is a sectional view seen from a side, showing the
configuration of essential parts of a fourth embodiment, and FIG.
12B a fifth embodiment, of the present invention;
[0057] FIG. 13 is a perspective view showing a general
configuration of a sixth embodiment of the present invention;
[0058] FIG. 14 is a sectional view of the same seen from a
side;
[0059] FIG. 15 is a perspective view showing a general
configuration of a seventh embodiment of the present invention;
[0060] FIGS. 16A to 16C are longitudinal sectional views showing
the configuration of essential parts of the seventh embodiment;
[0061] FIGS. 17A, 17B, and 17C are cross-sectional views showing
the layout of the PET detectors for slender type, stout type, and
the head, respectively;
[0062] FIGS. 18A and 18B are cross-sectional views showing the
configuration and operation of an eighth embodiment of the present
invention;
[0063] FIG. 19 is a perspective view of the same;
[0064] FIGS. 20A and 20B are cross-sectional views showing the
configuration and operation of a modification of the eighth
embodiment;
[0065] FIGS. 21A and 21B are perspective views showing the
configuration and operation of essential parts of a ninth
embodiment of the present invention;
[0066] FIG. 22 is a perspective view showing the configuration of
essential parts of a tenth embodiment of the present invention;
[0067] FIG. 23 is a perspective view showing the configuration of
essential parts of a belt-like PET detector used in the tenth
embodiment;
[0068] FIG. 24 is a block diagram showing signal processing and
image reconstruction processing according to the tenth
embodiment;
[0069] FIGS. 25A and 25B are cross-sectional views showing examples
of the layout of the belt-like PET detector;
[0070] FIGS. 26A and 26B are perspective views showing the
configuration and operation of essential parts of an eleventh
embodiment of the present invention;
[0071] FIG. 27 is a perspective view showing the configuration of
joints of the belt-like PET detector used in the eleventh
embodiment;
[0072] FIG. 28 is a perspective view showing the state where the
belt-like PET detector of the eleventh embodiment is being attached
to an inner frame;
[0073] FIGS. 29A and 29B are cross-sectional views showing examples
of the attached state;
[0074] FIG. 30 is a perspective view showing a belt-like PET
detector used in a twelfth embodiment of the present invention;
[0075] FIG. 31 is a perspective view showing the configuration of
joints of the same;
[0076] FIGS. 32A and 32B are cross-sectional views showing examples
of the attached state;
[0077] FIG. 33 is a perspective view showing an inner frame that is
used in a modification of the twelfth embodiment;
[0078] FIG. 34 is a perspective view showing the configuration of a
thirteenth embodiment of the present invention;
[0079] FIGS. 35A and 35B are perspective views showing the
configuration of essential parts of a fourteenth embodiment of the
present invention;
[0080] FIG. 36A is a cross-sectional view and FIG. 36B is a plan
view of the same;
[0081] FIG. 37A is a front view and FIG. 37B is a sectional view
seen from a side, showing the overall configuration of a fifteenth
embodiment of the present invention;
[0082] FIGS. 38A to 38C are sectional views showing the operating
state of the fifteenth embodiment;
[0083] FIG. 39A is a front view and FIG. 39B is a sectional view
seen from a side, showing the overall configuration of a sixteenth
embodiment of the present invention;
[0084] FIGS. 40A to 40C are sectional views showing the operating
state of the same;
[0085] FIGS. 41A to 41C are sectional views seen from a side,
showing the operating state of a seventeenth embodiment of the
present invention;
[0086] FIG. 42A is a front view and FIG. 42B is a sectional view
seen from a side, showing the overall configuration of an
eighteenth embodiment of the present invention;
[0087] FIG. 43 is a perspective view showing the configuration of
essential parts of a nineteenth embodiment of the present
invention;
[0088] FIG. 44 is a perspective view showing the configuration of
essential parts of a twentieth embodiment of the present
invention;
[0089] FIG. 45 is a sectional view seen from a side, showing the
overall configuration of the same; and
[0090] FIGS. 46A to 46C are sectional views showing the operating
state of the same.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0091] Hereinafter, embodiments of the present invention will be
described in detail with reference to the drawings.
[0092] As shown in FIG. 2 (a perspective view for overview), FIG.
3A (a front view), and FIG. 3B (a sectional view seen from a side),
a first embodiment of the present invention includes an MRI device
300 and a PET detector 210. The MRI device 300 has a measurement
port (here, a patient port) 302. The PET detector 210 has an outer
diameter smaller than the inner diameter of the patient port 302,
and can move through the patient port 302 with a measurement object
(here, a patient) 10. The PET detector 210 has an effective
measurement field of view (referred to as a PET field of view) P
wider than the effective measurement field of view (referred to as
MRI field of view) M of the MRI device 300, thereby allowing MRI
measurement during PET measurement. In the diagrams, 24 denotes a
cushion for protecting the patient 10, and 304 denotes an RF coil
for the MRI device 300. The RF coil 304 may be integrated with the
cushion 24 at the back side of the patient.
[0093] The MRI field of view M is determined by the area where the
static magnetic field is stable, which is typically 30 to 40 cm or
so. The PET field of view P can be extended to improve the
sensitivity of the PET measurement. A PET image of sufficient image
quality can thus be obtained in a PET measurement time comparable
to the MRI measurement time.
[0094] The PET detector 210 is capable of stable operation in the
MRI magnetic field environment. Examples include APD-bottomed
scintillator blocks, and a Depth-of-Interaction (DOI) detectors
having a three-dimensional array of semiconductor light receiving
elements on the surface of a three-dimensional array of small
scintillator elements, which has been proposed by the inventors in
Japanese Patent Application Laid-Open No. 2009-121929 and in Y.
Yazaki, H. Murayama, N. Inadama, A. Ohmura, H. Osada, F. Nishikido,
K. Shibuya, T. Yamaya, E. Yoshida, T. Moriya, T. Yamashita, and H.
Kawai, "Preliminary study on a new DOI PET detector with limited
number of photo-detectors," The 5th Korea-Japan Joint Meeting on
Medical Physics, Sep. 10-12, 2008, Jeju, Korea, YI-R2-3, 2008. DOI
detectors can be used to suppress a drop in resolution even in
close proximity. The closer access can also reduce resolution
degradation due to angular deviations, as well as increase the
solid angle to improve the sensitivity even with a relatively small
number of detectors.
[0095] In the present embodiment, the PET detector 210 is
integrated with a bed 20. That is, part of the PET detector 210
also functions as a bed. Since the PET detector can be brought
closest to the patient, the solid angle increases for improved
sensitivity and fast measurement.
[0096] The RE coil 304 is installed so as to cover the PET field of
view P and most of the axial field of view. The RE coil 304 is
arranged inside (within the inner diameter of) the PET detector 210
since the closer the RF coil 304 is to the patient 10, the higher
the signal S/N ratio becomes. Another reason is to prevent
electrical noise and the like from the PET detector 210. The RF
coil is highly transparent to annihilation radiations. The presence
of the RF coil 304 thus has only a limited impact on the PET
measurement.
[0097] The bed 20 may be moved by a bed moving device 22 at
constant speed or step by step.
[0098] FIG. 4A shows the state at the start of the MRI measurement.
FIG. 4B shows the state at the end of the MRI measurement. In FIGS.
4A and 4B, the moving speed Vb of the bed, if constant, is given by
Vb=(P-M)/Tm. Tm is the MRI measurement time.
[0099] FIG. 5A shows a procedure in which the PET measurement time
Tp is maximized to increase the data collection time for improved
PET image quality. FIG. 5B shows a procedure in which the PET
measurement is started immediately before the start of the MRI
measurement and ended immediately after the end of the MRI
measurement, or PET data that is collected from immediately before
the start of the MRI measurement to immediately after the end of
the MRI measurement is used for PET image reconstruction
processing. Such a procedure makes the PET measurement time and the
MRI measurement time almost equal, thereby ensuring simultaneity
between the PET measurement and the MRI measurement. For a
breath-held shot, the procedure of FIG. 5B is preferred.
[0100] FIG. 6 shows the time chart. For the bed position, the
positions of the front and rear ends of the bed are plotted.
Suppose that the PET medicine has been administered to the patient
in advance. In FDG-PET, it is typically administered an hour
earlier.
[0101] In FIG. 6, the maximum value Tpmax of the PET measurement
time shows a difference in time between when the PET detector 210
is attached in place and when the PET detector 210 is detached or
moved.
[0102] The actual Tp is determined by the following formula:
Tm.ltoreq.Tp.ltoreq.Tpmax. (1)
[0103] According to the procedure of FIG. 5A, Tp approaches Tpmax.
With the procedure of FIG. 5B, Tp approaches Tm.
[0104] The MRI measurement start position and the MRI measurement
end portion need not necessarily be set at the respective ends of
the MRI field of view M. For example, as in a modification shown in
FIG. 7, the MRI measurement start position and the MRI measurement
end position both may be at the center of the MRI field of view
where a favorable magnetic field is formed.
[0105] During the MRI measurement, the bed may be slid step by
step, not at constant speed.
[0106] In FIGS. 6 and 7, the MRI measurement is performed while the
bed is moving on one way. However, as in another modification shown
in FIG. 8, the MRI measurement may be performed on both ways of the
reciprocating movement. In such a case, MRI measurement 1 onward
and MRI measurement 2 on the return may be performed by the same
sequence. Different sequences may be combined, for example, so that
MRI measurement 1 is T1-weighted and MRI measurement 2 is
T2-weighted.
[0107] The foregoing first embodiment has dealt with the case where
the PET detector 210 has a uniform configuration in the
longitudinal direction of the measurement object, or the direction
of the body axis of the patient 10 here. As in a second embodiment
shown in FIG. 9A, the PET detector 210 may be divided into a head
PET detector 212 and a trunk or body PET detector 214. FIG. 9B
shows a sectional view of a concrete example of the second
embodiment seen from a side. FIGS. 10A and 10B show cross-sectional
views of the body and head portions of the PET detector. The body
PET detector has an elliptical cross section, whereas it may be
circular.
[0108] In the present embodiment, the head PET detector 212 and the
body PET detector 214 are fixed to the bed 20 so that they can be
horizontally moved with the patient 10 by the bed moving device
22.
[0109] Coincidence measurement between the head PET detector 212
and the body PET detector 214 can prevent a drop in the accuracy of
the reconstructed image near the border between the head PET
detector 212 and the body PET detector 214.
[0110] The head PET detector 212 and the body PET detector 214 may
be spaced apart by using the technology of the open PET device that
the inventors have proposed in WO 2009/133628 A1. In the absence of
the space as in FIGS. 9A and 9B, the PET field of view P equals to
the head field of view H+the body field of view B.
[0111] The RE coil may be a transmitter-receiver two-way coil, a
transmitter coil, or a receiver coil. The RF coil and the PET
detector may be formed as separate members. When the RF coil and
the PET detector are integrated as shown in FIGS. 10A and 10B, the
following combinations are possible:
[0112] A transmitter-receiver two-way RE coil is integrated into
inside the PET detector.
[0113] Only a transmitter RE coil is integrated into inside the PET
detector, and a receiver RF coil is separately arranged so as to
cover the patient.
[0114] A transmitter RF coil is built in the main unit of the MRI
device, and only a receiver RE coil is integrated into inside the
PET detector.
[0115] In FIGS. 10A and 10B, 218 denotes a cover, 312 denotes a
head RE coil, and 314 denotes a body RE coil.
[0116] FIG. 11A is a front view showing a concrete example of a
third embodiment which is a modification of the second embodiment.
FIG. 11B is a sectional view seen from a side.
[0117] In the present embodiment, the head PET detector 212 is
fixed to the bed 20. The body PET detector 214 can be horizontally
moved by a PET detector moving device 220, independent of the bed
20. In the diagrams, 320 designates rollers that support the PET
detector 214 in the patient port 302.
[0118] The head PET detector 212 and the body PET detector 214 have
different center positions in the patient port 302 of the MRI
device 300. The bed moving device 22 may include a bed up-down
mechanism 26 so that the head PET detector 212 and the head RF coil
312 can be slid and moved up and down with the patient 10. The body
PET detector 214 and the body RE coil 314 are only moved to slide
horizontally, without up and down movements.
[0119] The PET detector may be made of a combination of detectors
of different resolutions depending on the locations. FIG. 12A shows
a fourth embodiment in which high-resolution detectors are arranged
in the vicinity of the head where high resolution is needed. FIG.
12B shows a fifth embodiment with a reduced number of detectors, in
which the detectors are spaced wider, instead of the sensitivity
being lowered, for the lower body or the legs in particular where
not so high sensitivity is needed.
[0120] As in a sixth embodiment shown in FIG. 13 (a perspective
view) and FIG. 14 (a sectional view seen from a side), the
technology of the open PET device may be used to form an open area
in the head PET device 212 in the vicinity of the field of view so
as to alleviate the sense of confinement on the head.
[0121] As in a seventh embodiment shown in FIG. 15, the body PET
detector 214 may be made of noncircular (in the diagram,
elliptical) rings so that the PET detector comes closer to the
patient's body.
[0122] FIGS. 16A to 16C show the configuration of essential parts
where the detector rings can be changed in size according to the
body type of the patient 10. FIG. 16A shows an example where
normal-sized detector rings 214a are used.
[0123] FIG. 16B shows an example where large-diametered detector
rings 214b are used for the abdomen. FIG. 16C shows an example
where the large-diametered detector rings 214b are used not only
for the abdomen but for the entire body.
[0124] FIGS. 17A to 17C show the cross sections of FIGS. 16A to
16C. FIG. 17A shows a PET detector layout for slender type, FIG.
17B shows a PET detector layout for stout type, and FIG. 17C shows
a PET detector layout for the head. In the PET detector layout for
stout type of FIG. 17B, the arched half portion of the detector on
the bed side (lower side in the thickness direction) and that on
the opposite side (upper side in the thickness direction) are
arranged along the curves of respective different curvatures.
[0125] The cells in the diagrams represent scintillator blocks or
detector units.
[0126] In an eighth embodiment shown in FIGS. 18A and 18B, an
arched half PET detector 224 on the upper side in the thickness
direction is openable, for example, in a double-door configuration
so as to facilitate setting up the patient 10. In the diagrams, 222
denotes the lower (bed-side) PET detector, and 226 denotes
hinges.
[0127] Since the PET detector is heavy in weight, it may be divided
into several sections as shown in FIG. 19 (six sections in FIG.
19).
[0128] As in a modification shown in FIGS. 20A and 20B, the PET
detector may be formed in a single-door configuration.
[0129] Alternatively, as in a ninth embodiment shown in FIG. 21,
the PET detector may be configured so that it is divided into an
arched half detector 222 on the bed side (lower side in the
thickness direction) and an arched half detector 224 on the
opposite side (upper side in the thickness direction). Various
sizes of upper detectors 224 may be provided according to the body
type.
[0130] As in a tenth embodiment shown in FIG. 22, detector units
204 may be connected into a belt-like configuration by links 232.
The same belt-like PET detectors 230 can be used to form various
sizes of detector rings according to the body type. In the lower
half, or the bed portion, the detector units 204 are fixed by
fixing wires 234, for example.
[0131] As shown in FIG. 23, encoders 236 for acquiring angular
information are attached to the joints of the detector units 204 on
the upper side in the thickness direction. As shown in FIG. 24,
relative positions between the detector units 204 (the relationship
in spatial position coordinates between adjoining detector units)
can thus be acquired to obtain a tomographic image by image
reconstruction calculations.
[0132] With reference to FIG. 24, a description will be given of
the relationship between the encoders 236 and an image
reconstruction workstation (WS) 400 when the layout pattern of the
PET detector is changed according to the subject's body type. Pairs
of annihilation radiations detected by the PET detector 204 are
processed into measurement data by a data collection system 500
through coincidence processing, data collection processing, etc.
The measurement data is transmitted to the image reconstruction WS
400 for image reconstruction processing before output as a
tomographic image. The image reconstruction needs accurate detector
positions, or it is not possible to calculate the system matrix.
The encoders 236 are then used to grasp the relationship in spatial
position coordinates between the adjoining detector units, thereby
grasping the positions of the respective detectors.
[0133] Specifically, the encoders 236 provide relative angular
information on the joints between the detectors. The information is
transmitted to the image reconstruction WS 400. The detector
coordinates are initially determined by detector coordinate
calculation processing. The system matrix is then calculated based
on the detector coordinates. For the image reconstruction
processing, a whole system matrix calculated may be read at a time.
Or, necessary system matrix elements may be calculated by
on-the-fly processing when needed.
[0134] FIG. 25A shows a case with small detector rings according to
the tenth embodiment. FIG. 25B shows a case with large detector
rings.
[0135] As in an eleventh embodiment shown in FIGS. 26A and 26B,
large and small inner frames 30 attachable to the bed 20 may be
prepared for respective body types. This makes it possible to
accurately and easily grasp the spatial position coordinates
(detector positions) of the belt-like PET detector 230 having no
encoders such as shown in FIG. 27. Such inner frames 30 are formed
to have high rigidity as well as high transparency to radiation.
For example, the inner frames 30 are made of reinforced
plastic.
[0136] FIG. 28 shows the state where the belt-like PET detector 230
is being attached to an inner frame 30 according to the eleventh
embodiment. FIGS. 29A and 29B show attached states. FIG. 29A shows
an example of small ring size, and FIG. 29B shows an example of
large ring size.
[0137] The belt-like PET detector 230 may not only allow free
rotations of the detector units 204, but also make the distances
between the detector units 204 variable as in a twelfth embodiment
shown in FIG. 30. FIG. 31 shows the joints in detail.
[0138] FIG. 32A shows the state of attachment of small ring size
according to the twelfth embodiment. FIG. 32B shows the state of
attachment of large ring size. Rings of different sizes can be
formed by using the same number of detectors (in FIGS. 32A and 32B,
eight movable detector units) without redundant detectors as in
FIG. 29A.
[0139] As in a modification of the twelfth embodiment shown in FIG.
33, positioning recesses 30a may be formed in the inner frame 30 so
as to fix the detector positions.
[0140] Now, a description will be given of the image reconstruction
processing when various sizes of arched upper half detectors 224
and inner frames 30 are prepared in advance and appropriate ones
are selected according to the patient's body type (size and shape)
as in the ninth embodiment shown in FIGS. 21A and 21B or the
eleventh embodiment shown in FIGS. 26A and 26B. Since the layout of
the detector units is uniquely determined by the size and shape of
the upper detector 224 or inner frame 30 selected, it is possible
to acquire the spatial position coordinates of the detector units
without encoders. Specifically, the type of the upper detector 224
or inner frame 30 selected may be entered by the user from a
console. Identification tags may be attached to the upper detectors
224 or inner frames 30 so that the type used is automatically
detected on the side of the bed 20.
[0141] As shown in FIG. 24, the system matrix may be calculated
each time based on the detector coordinates. Since the types of the
upper detectors 224 or inner frames 30 for use are limited, system
matrices corresponding to the respective patterns of detector
layout may be calculated in advance and stored into a storing
device in the image reconstruction WS as a data set.
[0142] The belt-like PET detectors may be used not only for the
head and body, but also for some specific areas. FIG. 34 shows a
thirteenth embodiment which shows another application example of
the belt-like PET detectors. Here, a belt-like PET detector 230 for
arms is wound around the arm. The reference numeral 40 denotes a
table on which the belt-like PET detector is placed.
[0143] For example, dynamic function measurement on the head, using
a head PET device (not shown in the diagram), is not easy to
perform since arterial blood needs to be sampled at time intervals
of several seconds to several minutes. The combined use of the head
PET device and the belt-like PET detector wound around the arm can
facilitate the dynamic function measurement since it is possible
without arterial blood sampling to measure the concentration and
flow rate of RI flowing through the arteries in the arm. Aside from
arterial blood sampling, the belt-like PET detector also allows
area-specific high-precision diagnostic imaging. Examples of the
area include the arms as well as the feet, joints, neck, and
breast.
[0144] In a fourteenth embodiment shown in FIGS. 35A and 35B, the
head PET detector 212 can be slid over guide rails 21 of the bed 20
in the direction of the body axis so as to facilitate setting up
the patient 10. FIG. 36 shows the slide mechanism in detail. The
head PET detector 212 may be detachable.
[0145] As in a fifteenth embodiment shown in FIGS. 37A and 37B, the
bed 20 and the PET detector 210 may be independently slidable when
the PET field of view P lies between the field of view F of the RF
coil and the MRI field of view M.
[0146] According to the present embodiment, the bed 20 and the PET
detector 210 can be slid at different speeds so that a wider field
of view corresponding to the width of the field of view F of the RF
coil can be measured by PET and MRI.
[0147] FIGS. 38A to 38C show the states from the start to the end
of the examination according to the present embodiment. Assuming
that the bed moving speed Vb and the PET detector moving speed Vp
both are constant, Vp and Vb are given by the following
equations:
Vp=(P-M)/T, and (2)
Vb=(F-M)/T, (3)
where T=the MRI measurement time=the PET measurement time.
[0148] The fifteenth embodiment has dealt with the case where the
PET detector is integrated in the direction of the body axis. As in
a sixteenth embodiment shown in FIGS. 39A and 39B, the head PET
detector 212 and the body PET detector 214 may be separated from
each other. The head PET detector 212 and the bed 20 are integrated
with each other, and slide at a speed of Vb. The body PET detector
214 slides at a speed of Vp.
[0149] FIGS. 40A to 40C show the states of movement from the start
to the end of the examination according to the sixteenth
embodiment. Assuming that the bed moving speed Vb and the PET
detector moving speed Vp both are constant, Vp and Vb are expressed
by the following equations:
Vp=(B+H-M)/T, and (4)
Vb=(F-M)/T, (5)
where T=the MRI measurement=the PET measurement time.
[0150] As in a seventeenth embodiment shown in FIGS. 41A to 41C,
the PET detector (or at least the body PET detector 214) may have a
mechanism for making a movement independent of the movement of the
bed 20. In such a case, the PET detector 214 can be moved into the
MRI detector 300 for easy patient setup without a contrivance to
open the PET detector.
[0151] More specifically, for patient setup, as shown in FIG. 41A,
the PET detector 214 is moved into the MRI patient port 302 so that
the patient 10 can easily get on the bed 20. The head PET detector
212, if used, is moved to the left in the diagram.
[0152] Next, the RF coils 312 and 314 and the head PET detector 212
are attached as shown in FIG. 41B. Specifically, the head and body
RF coils 312 and 314 are initially attached. The head PET detector
212, if used, is slid for attachment. The head RE coil 312 may be
integrated with the head PET detector 212.
[0153] Finally, as shown in FIG. 41C, the bed 20 and the PET
detector 214 are slid to a predetermined MRI measurement start
position.
[0154] After the examination, the patient can be evacuated in order
reverse to the foregoing.
[0155] While the diagrams show the configuration where the patient
enters the MRI patient port 302 head first, the MRI patient port
302 may be entered feet first.
[0156] As in an eighteenth embodiment shown in FIGS. 42A and 42B, a
transmitter RE coil 304S may be integrally arranged inside the PET
detector 210. A receiver RE coil is arranged closer to the patient.
A head RF coil 312R and a body RF coil 314R of different sizes may
be used.
[0157] FIG. 43 shows a nineteenth embodiment for measuring a local
area, not the whole body, by PET and MRI at the same time. The PET
detector 210 is slidable along the guide rails 21 on the bed 20, so
that the PET detector 210 can be freely moved to the position of
the area to measure. The PET detector 210 can be accurately and
safely mounted on the measurement area when outside of the MRI
patient port 302. Since the PET detector 210 mounted is slid with
the patient on the bed 20, there is no danger of displacement. The
difference in level between the bed 20 and the PET detector 210 is
eliminated by the provision of cushions 24. The cushions 24 need to
be adjusted in length depending on the position of the PET detector
210.
[0158] FIG. 44 is a perspective view showing the configuration of
essential parts of a twentieth embodiment which is a modification
of the nineteenth embodiment. The bed 20 is composed of a base 20B
which includes the guide rails 21, and supports 20S and a cover
20C. The PET detector 210 is arranged so that part of the ring is
interposed between the base 20B and the cover 20C. Such a
configuration eliminates a difference in level on the cover 20C
which makes contact with the patient. In addition, the PET detector
210 can conveniently be slid to an appropriate position where to
cover the measurement point with the patient put on the bed.
[0159] FIG. 45 is a sectional view seen from a side, showing the
overall configuration of the twentieth embodiment. Here, the RF
coil 304 is integrally arranged inside the PET detector 210.
[0160] FIGS. 46A to 46C show the operating state of the twentieth
embodiment. When setting a patient on the bed, as in FIG. 46A, the
bed is located away from the MRI patient port 302 and the PET
detector 210 is moved to the bed end. After the patient is laid on,
as in FIG. 46B, the PET detector 210 is slid so that the
measurement point (in the diagram, chest) is covered by the PET
detector 210. After the completion of the patient setup, the PET
detector 210 is inserted into the MRI patient port 302 and the MRI
measurement is started.
[0161] According to the present invention, it is possible to
perform PET and MRI concurrent examinations and a whole-body
PET/MRI examination with extremely high utility.
* * * * *