WO1998016852A1

WO1998016852A1 - Rotating small camera for tomography

Info

Publication number: WO1998016852A1
Application number: PCT/US1997/017224
Authority: WO
Inventors: Raymond P. Devito; Guenter Schwierz; Peggy C. Hawman
Original assignee: Siemens Medical Systems, Inc.
Priority date: 1996-10-17
Filing date: 1997-09-25
Publication date: 1998-04-23

Abstract

A gamma camera has a semiconductor-based radiation detector (40, 42) which responds to gamma radiation for generating corresponding detection signals for use in tomographic imaging of a target. The semiconductor-based radiation detector is mounted in a mobile support structure to facilitate transport of the gamma camera. An armature (44) mounts the semiconductor-based radiation detector to the mobile support structure, and the armature is orientable in a plurality of positions for positioning the semiconductor-based radiation detector in a plurality of orientations about the target (16). A rotatable mounting device having a central axis may be included for rotatably mounting the detector to the armature, to allow the semiconductor-based radiation detector to be oriented in a plurality of tilt angles. A slant angle collimator provides an angular window for reception of the gamma radiation. In another embodiment, a parallel-hole collimator is used to provide a window for reception of the gamma radiation. A least one armature is rotatable about an axis, and at least one semiconductor-based radiation detector is connected to an armature and responds to rotation for orbiting about the target and detecting gamma radiation therefrom.

Description

ROTATING SMALL CAMERA FOR TOMOGRAPHY

BACKGROUND INFORMATION

1. Technical Field, This disclosure relates to Single Photon Emission Computed Tomography (SPECT) , and in particular to a rotating camera for use in SPECT applications.

2. Description of the Related Art

SPECT belongs to a group of tomographic imaging techniques which compute three dimensional (3-D) images of an object from a set of projection images. In SPECT a gamma camera having a detector with an imaging window or detection region collects a plurality of projection data from a plurality of projection directions. In limited angle tomography an incomplete range of projections are utilized, and so such techniques suffer from distortions associated with insufficient data stemming from the incomplete range. Ectomography is one reconstruction method that attempts to compensate for incomplete projection data and to produce 3-D images from the incomplete projection data.

In ectomography applied to nuclear medicine, slant hole collimators are typically employed with detectors having a large field of view, in which a slant angle of the slant hole collimator can be increased to reduce the level of distortion. However, increasing the slant angle of the collimator decreases the size of the reconstruction volume, so there is a trade-off between the level of distortion and the size of the reconstruction volume. Conventional SPECT systems employ large (approximately 300 square inch) detectors mounted on a stationary gantry. This gantry facilitates the motion of the system so that the detector is able to travel a path that can orbit the patient. Limited angle tomographic devices normally do not orbit the patient but rather view the object mostly from one direction. For example, as shown in FIG. 1, a gamma camera detector 10 in the prior art is positioned to view the object of interest 16 (such as a heart) in the patient 18 with slant collimation employed on the detector 14. Additional support , structure (not shown in FIG. 1) is provided to rotate the detector around the support axis 12. As shown in FIG. 2, the camera 10 in the prior art typically has the collimator 14 which receives and colli ates radiation, which is passed through a crystal 20, such as an Nal crystal. The incident gamma ray is converted to a scintillation flash, and then passes through a light pipe 22 for amplification by at least one photomultiplier tube (PMT) 24, which generates corresponding signals. The signals are then processed by a pre-amplifier circuit 26 to generate corresponding scintillation detection signals for subsequent processing and imaging.

Due to such relatively large dimensions of the camera 10 and supporting structure, such SPECT systems must be engineered with adequate and often voluminous supporting structure in a facility such as a hospital. A need exists for a generally small and/or compact SPECT system, to economize on space in a facility.

In addition, the patient must be brought to the SPECT system for imaging. Since the patient may be immobile or restricted to an intensive care unit or may experience complications from transport to the SPECT system, such as stroke victims, the use of such large and stationary SPECT systems for diagnosis of the patient may also be detrimental to the patient. Heretofore, due to the large size of the detector and supporting structure, previous SPECT systems have not been able to be mobile.

Accordingly, a need exists for a mobile SPECT system, for providing improved 3-D imaging of patients in diverse locations. Further, using detectors having an imaging window or detection region oriented in one general direction, such limited angle tomography techniques typically have the detector fixed in the single direction relative to the axis of rotation of the detector, thus limiting the angular range of the detectQr. A need exists for increasing the angular range of a detector without increasing the distortion; for example, by increasing the slant angle of the collimator. SUMMARY

A gamma camera is disclosed which has a semiconductor- based radiation detector which responds to reference Fig. 2 gamma radiation from a target for generating corresponding detection signals for use in tomographic imaging of the target. The semiconductor-based radiation detector is mounted in a mobile support structure to facilitate transport of the gamma camera. An armature mounts the semiconductor-based radiation detector to the mobile support structure, and the armature is orientable in a plurality of positions for positioning the semiconductor- based radiation detector in a plurality of orientations about the target.

A rotatable mounting device having a central axis may be included for rotatably mounting the semiconductor-based radiation detector to the armature, to allow the semiconductor-based radiation detector to be oriented in a plurality of tilt angles with respect to a plane. A slant angle collimator is used to provide an angular window for reception of the gamma radiation. In another embodiment, a parallel-hole collimator is used to provide a window for reception of the gamma radiation. At least one armature is provided which is rotatable about an axis, and at least one semiconductor-based radiation detector is operatively connected to a corresponding armature and responds to rotation thereof for orbiting about the target and detecting gamma radiation therefrom. By providing a gamma camera with armatures upon which are mounted a plurality of the semiconductor-based radiation detectors having such relatively small and compact dimensions, _» the detectors may be readily rotated about a portion of the target. For example, the detectors may be rotated about any arbitrary axis, such as an axis passing through the target. The compact size of the detectors also allow the detectors to be positioned relatively near the target and rotatable about an axis and directed to the target. Accordingly, multiple detectors may be focused on the target for improved imaging.

Imaging samples of, for example, the heart may be obtained from a variety of angles, with the angles set to be either large or small. The variable tilt angles allow for smaller viewing angles to be employed by the detectors and/or the collimators, with reduced distortion to provide improved accuracy in the data gathering by the detectors. In addition, the ability to tilt and to rotate the detectors about an axis and directed toward a target provides the disclosed gamma camera with the ability to cover the same or more directional aspects of the target than prior art devices. The amount and quality of the imaging data is thus improved. BRIEF DESCRIPTION OF THE DRAWINGS The features of the disclosed SPECT camera will become more readily apparent and may be better understood by referring to the following detailed description of illustrative embodiments of the present invention, taken in conjunction with the accompanying drawings, in which: FIG. 1 is a schematic drawing of limited angle SPECT system in the prior art;

FIG. 2 is a schematic drawing of the disclosed SPECT system in comparison with the prior art SPECT system of FIG. 1; FIG. 3 is a schematic drawing of the disclosed SPECT camera system in use with a patient; FIG. 4 is a schematic drawing of a multiple camera SPECT system in use with a patient;

FIG. 5 is a schematic drawing of an alternative embodiment of the »pair of cameras of FIG. 4 with the detectors tilted; and

FIG. 6 is a schematic drawing of an alternative embodiment of the pair of cameras of FIG. 4 with the detectors tilted to substantially face each other for SPECT applications with full projection capability.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now in specific detail to the drawings, with like reference numerals identifying similar or identical elements, as shown in FIG. 1-3, the present disclosure describes a SPECT gamma camera 28 illustrated with relative dimensions in comparison with the gamma camera 10 of the prior art. In an illustrative embodiment, the disclosed gamma camera 28 has relatively smaller dimensions than the gamma camera 10 of the prior art, in which the disclosed SPECT gamma camera system of FIG. 3 has improved imaging capabilities and may be configured for mobile applications.

In the illustrative embodiment, the disclosed camera

28 has a collimator 30 for collimating radiation, and for applying the collimated radiation to a semiconductor-based radiation detector 32. Such semiconductor-based radiation detectors 32 are known in the art, as described in G.F. Knoll, "Radiation Detection and Measurement, Second Edition", John Wiley & Sons: New York, pp. 465-469. In one illustrative embodiment, the disclosed camera 28 has the semiconductor-based radiation detector 32 composed of cadmium telluride (CdTe) or cadmium zinc telluride (CZT or CdZiTe) which are from 1 mm to over 1 cm in diameter, with such semiconductor-based detectors being rugged and stable in field use, and operable routinely at temperatures up to 30° C without excessive thermal noise. Accordingly, in using, for example, a CdTe based detector 32, the disclosed camera 28 may be portable, and is well-suited for field use; i.e. for transport to diverse environments, inclμding relatively warm environments without thermal noise impairing the functioning of the detector 32.

In addition, the height of the radiation detector 32 in conjunction with the collimator 30 may be reduced to have an overall height of about 1 inch, to provide a more compact configuration.

Upon receiving the gamma radiation from the collimator 30, the radiation detector 32 generates corresponding signals which are processed by a pre-amplifier circuit 34 to generate corresponding detection signals for subsequent processing and imaging. In an illustrative embodiment, the pre-amplifier circuit 34 may be an application specific integrated circuit (ASIC) which permits the pre-amplifier circuit 34 to have relatively small dimensions as well. Accordingly, the overall camera 28, having the collimator 30, the radiation detector 32, and the pre-amplifier circuit 34, may be constructed to be not only compact and small but also lightweight, relative to detectors in the prior art such as camera 10.

With such a compact and lightweight construction, the camera 28 may be mounted on a relatively lightweight arm 36 using a mounting device 38. The arm 36 may be composed of aluminum and/or other lightweight materials, and thereupon connected to additional support structure (not shown in FIGS. 2-3) which may include mechanisms for mobility such as wheels, casters, and/or handles for pushing, pulling, carrying, or otherwise transporting the camera 28 and associated support structure to a patient.

The compact and lightweight construction of the camera 28 also facilitates the ability of the support structure and arm 36 to rotate the camera 28 for SPECT applications. In addition, such compactness and lightweight construction also provide^' advantages in control of the orientation and rotation of the camera 28. For example, during rotation, the camera 28 would provide less torque on the support structure than the camera 10 in the prior art, and so may be controlled by servomechanisms with less deviation in the distance from the target 16 during operation. Alternatively, more sensitive servomechanisms may be used to provide increased accuracy in the control of the camera 28. In addition, rotation speeds may be increased without wear and tear on the support structure to provide a greater number of samples per unit of time.

As shown in FIG. 3, in an illustrative embodiment, a single tomographic camera 28 having a slant angle collimator 30 may be used to receive radiation from the target; i.e. the heart 16. In alternative embodiments, multiple cameras 28 may be used.

In the alternative embodiment shown in FIG. 4, a plurality 40, 42 of the disclosed SPECT gamma cameras 28 of FIG. 2 are used, which are mounted upon a common armature 44. In a cross-sectional view of the patient 18, the heart 16 is imaged from radiation along overlapping projections to the plurality 40, 42 of cameras. In the illustrative embodiment, a pair of cameras are employed. However, as the disclosed camera 28 of FIG. 2 may be of relatively compact and lightweight construction, it is contemplated that more that two cameras may be used, which may be mounted in various configurations on one or more armatures and support structures. For example, as shown in FIG. 4, the cameras 40, 42 may be oriented about 180° apart about the axis 50 of rotation of the common armature 44, although it is contemplated that the plurality of cameras may be in any angular configuration with respect to the rotation axis 50 to allow the cameras to be rotated or to orbit about the axis 50. As shown in FIGS. 3-4, each camera may be mounted on a corresponding armature by a mounting device. For example, in FIG. 3, the mounting device 38 connects the camera 28 to the arm 36, and in FIG. 4, each camera 40, 42 is mounted to the common armature 44 by a corresponding mounting devices 46, 48. In one embodiment, the mounting devices 46, 48 may be a welding seam, a pin and socket engagement, etc., or other commercially available mechanisms, for fixedly mounting the camera to the associated armature and thence to the supporting structure. In alternative embodiments, the mounting devices 38, 46, 48 may be rotatable and optionally mechanically and/or electronically controllable mechanisms, such as commercially available rotating mounting mechanisms, for tilting the corresponding cameras 28, 40, 42 about a central axis of the corresponding mounting devices to different angles, and so to control the focussing of the cameras on the target for improved imaging thereof. Thus, the use of tiltable cameras provides an added degree of freedom to the imaging of targets such as the heart of a patient. By providing a gamma camera with armatures upon which are mounted a plurality of the semiconductor-based radiation detectors having such relatively small and compact size, the detectors may be readily rotated about a portion of the target. For example, the detectors may be rotated about any arbitrary axis, such as an axis passing through the target, as shown in FIG. 4. The compact size of the detectors also allow the detectors to be positioned relatively near the target and rotatable about an axis and directed to the target. Accordingly, multiple detectors may be focused on the target for improved imaging and less distortion.

As shown in the alternative embodiments in FIGS. 5-6, the cameras 40, 42 are tilted at an angle 52 of about 25° below a plane 54 in FIG. 5, and titled about 90° below the plane 54 in FIG. 6. The configuration of cameras 40, 42 to substantially face each other provides complete angular sampling for SPECT applications.

Referring to FIGS. 4-6, by tilting the cameras 40. 42, the level of distortion cause by the limited angle tomography techniques is reduced, and the size of the reconstruction volume is increased. The tilt angle 52 can vary to allow the cameras 40, 42 to be positioned as close to the patient as possible. It is also contemplated that each camera 40, 42 may be rotated independently and/or rotated to distinct tilt angles. By using a plurality 40, 42 of cameras rotated to distinct tilt angles, a greater range of projections are utilized, and so distortions associated with insufficient data are minimized and system sensitivity is increased.

In the embodiment shown in FIG. 5, the cameras 40, 42 are in two positions about 180° degrees apart, and with each camera 40, 42 having a corresponding tilt angle 52 of about 25°. In the case that each of cameras 40, 42 has a slant angle collimator having a slant angle of about 45°, the configuration of cameras 40, 42 in FIG. 5 produces an effective slant angle of about 70° for scans of the target.

Accordingly, imaging samples of, for example, the heart may be obtained from a variety of angles, with the angles set to be either large or small. The variable tilt angles allow for smaller viewing angles to be employed by the detectors and/or the collimators, with reduced distortion to provide improved accuracy in the data gathering by the detectors. In addition, the ability to tilt and to rotate the detectors about an axis and directed toward a target provides the disclosed gamma camera with the ability to cover the same or more directional aspects of the target than prior art devices. The amount and quality of the imaging data is thus improved.

As shown in FIG. 6, the configuration of cameras 40, 42 allows for scans and imaging of objects which can be completely enclosed by the orbit of the cameras. For example, improved imaging of the brain as well as of individual breasts in mammography may be performed, in which the cameras 40, 42 may function as a SPECT device with complete angular sampling. For example, using parallel hole colli^mators for the cameras 40, 42, brain imaging with such cameras 40, 42 having tilt angles set to about 90° may be performed using SPECT.

While the disclosed tomographic camera and method of use have been particularly shown and described with reference to the preferred embodiments, it is understood by those skilled in the art that various modifications in form and detail may be made therein without departing from the scope and spirit of the invention. Accordingly, modifications such as those suggested above, but not limited thereto, are to be considered within the scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A gamma camera comprising: a radiation detector, responsive to gamma radiation from a garget, for generating corresponding detection signals for use in tomographic imaging of the target, wherein the radiation detector is mounted in a mobile support structure to facilitate transport of the gamma camera.

2. The gamma camera of claim 1 wherein the radiation detector is a semiconductor-based radiation detector.

3. The gamma camera of claim 2 further comprising: a collimator for colli ating received gamma radiation; and the semiconductor-based radiation detector is responsive to the collimated gamma radiation for generating the detection signals.

4. The gamma camera of claim 2 wherein the semiconductor-based radiation detector includes a cadmium telluride (CdTe) based radiation detector.

5. The gamma camera of claim 2 wherein the semiconductor-based radiation detector includes a cadmium zinc telluride (CdZiTe) based radiation detector.

6. The gamma camera of claim 1 further comprising: a pre-amplifier for processing the detections signals.

7. The gamma camera of claim 6 wherein the preamplifier includes: an application specific integrated circuit.

8. The gamma camera of claim 1 further comprising: an armature for mounting the radiation detector to the mobile support structure.

9. The gamma camera of claim 8 wherein the armature is orientable in a plurality of positions for positioning the radiation detector in a plurality of orientations about the target.

10. The gamma camera of claim 8 further comprising: a rotatable mounting device having a central axis for rotatably mounting the radiation detector to the armature, thereby allowing the radiation detector to be oriented in a plurality of tilt angles with respect to a plane.

11. The gamma camera of claim 8 further comprising: a slant angle collimator for providing an angular window for reception of the gamma radiation.

12. The gamma camera of claim 8 further comprising: a parallel hole collimator for providing a window for reception of the gamma radiation.

13. The gamma camera of claim 10 further comprising: at least one armature rotatable about an axis; and at least one radiation detector operatively connected to a corresponding armature and responsive to rotation thereof for orbiting the target and detecting gamma radiation therefrom.

14. A gamma camera comprising: a plurality of the semiconductor-based radiation detectors, responsive to gamma radiation from a target, for generating corresponding detection signals for use in tomographic imaging of the target; and a plurality of armatures for mounting the plurality of semiconductor-based radiation detectors thereupon and for rqtating the plurality of semiconductor- based radiation detectors about a portion of the target.

15. The gamma camera of claim 14 wherein each of the plurality of armatures rotates the plurality of semiconductor-based detectors about at least one axis to orbit the plurality of semiconductor-based radiation detectors about the portion of the target.

16. The gamma camera of claim 14 wherein each of the plurality of semiconductor-based detectors is rotatably mounted on the plurality of armatures for tilting each semiconductor-based detector in a particular direction.

17. The gamma camera of claim 16 wherein each of the plurality of semiconductor-based detectors is tiltable at an angle of less than 90° with respect to a predetermined plane.

18. The gamma camera of claim 16 wherein the plurality of semiconductor-based detectors are tiltable at an angle of about 90° with respect to a predetermined plane.

19. A method for performing tomographic imaging comprising the steps of: providing a gamma camera having a semiconductor- based radiation detector mounted in a mobile support structure to facilitate transport of the gamma camera; receiving gamma radiation from a target at the semiconductor-based radiation detector; generating detection signals using the semiconductor-based radiation detector corresponding to the gamma radiation for use in tomographic imaging of the target.

20. The method of claim 19 further comprising the step of: collimating the gamma radiation using a collimator; and the step of receiving includes the step of receiving the collimated gamma radiation at the semiconductor-based radiation detector.

21. The method of claim 19 further comprising the steps of: mounting the semiconductor-based radiation detector on an armature connected to the mobile support structure; and orienting the armature in a plurality of positions for positioning the semiconductor-based radiation detector in a plurality of orientations about the target.

22. The method of claim 19 further comprising the steps of: providing a plurality of the semiconductor-based radiation detectors, each being mounted to a plurality of armatures for mounting the plurality of semiconductor-based radiation detectors thereupon; and rotating the plurality of semiconductor-based radiation detectors about a portion of the target.

23. The method of claim 22 wherein the step of rotating includes the step of: rotating the plurality of semiconductor-based detectors about at least one axis to orbit the plurality of semiconductor-based radiation detectors about the portion of the target.

24. The method of claim 22 wherein the step of providing a plurality of the semiconductor-based radiation detectors includes the step of: rotatably, mounting the plurality of semiconductor-based radiation detectors to the plurality of armatures for tilting each semiconductor-based detector in a particular direction.

25. The method of claim 24 further comprising the step of: tilting at least one of the plurality of semiconductor-based radiation detectors at an angle of less than about 90° with respect to a predetermined plane.

26. The method of claim 24 further comprising the step of: tilting the plurality of semiconductor-based radiation detectors at an angle of about 90° with respect to a predetermined plane.