Patent Description:
This invention provides practical designs for pixelated-detector based gamma cameras and pixelated-detector-based gamma camera systems. In particular, this invention can be applied beneficially to gamma cameras built from pixelated semiconductor direct conversion CZT (CdZnTe) gamma detectors.

Gamma cameras, previously also known as scintillation cameras or Anger cameras, have been used to image gamma photon emission in a technique known generally as scintigraphy. They are applied in nuclear medicine imaging to view images of a body containing medically injected, inhaled, or ingested radiopharmaceuticals emitting gamma photons. They can also be used in security or astronomy applications to detect and image gamma photons arising from radioactive sources or astrophysical sources. Hal Anger developed the first gamma camera in <NUM> and variations on his design are still widely used today.

<CIT> describes an integrated tomosynthesis/molecular breast imaging device having improved sensitivity includes tomosynthesis imaging components and molecular breast imaging components. <CIT> describes a gamma camera gantry and imaging method. <CIT> describes a PET detection device with a single photon emission computed tomography function. <CIT> concerns an imaging system having a gantry to which several imaging detector columns are attached. The single imaging detector columns are independently positionable along their radial and angular position to facilitate contouring of a region of interest.

A typical scintillation gamma camera consists of a large flat rectangular crystal (typically about <NUM> x <NUM> x <NUM>) of sodium iodide with thallium doping, labelled NaI(Tl), in a sealed container that prevents moisture and visible light from reaching the crystal. One face has a transparent glass window or light guide. The crystal scintillates when a gamma photon strikes it and the scintillation light can escape through the glass window, where an array of optically-coupled photodetectors, such as vacuum photomultiplier tubes (PMTs) or silicon photomultipliers, are typically coupled through optical gel. The location of a gamma photon interaction in the NaI crystal are determined by a center-of-gravity type weighting of the voltage responses of multiple PMTs that detect the scintillation light.

A gamma camera is typically coupled with a collimator (for example: parallel hole, focused, multiple pinhole, or coded aperture) that acts as a lens for forming a planar projection image. In SPECT, used in nuclear medicine, a 3D image is formed by moving the gamma camera to multiple different angular positions around the patient, acquiring planar projections at each position, and then reconstructing a 3D image of the gamma emission source distribution using various techniques, such as filtered back-projection or iterative maximum likelihood estimation reconstruction. Commercial SPECT systems most commonly consist of two scintillator (usually NaI) gamma cameras mounted on a gantry with a patient table positioned between the slowly rotating gamma cameras.

This invention addresses several limitations of current commercial solutions and prior patents. In particular, the basic technology used in gamma cameras has not changed substantially since <NUM>, except that computers have increased the efficiency of the data acquisition and image reconstruction. One significant problem with state-of-the-art systems is that they are usually designed as "general purpose" SPECT systems in which many compromises have been made to accommodate different clinical applications, such as bone, brain, heart, or breast imaging. There are dedicated cardiac SPECT systems on the market, and dedicated planar breast gamma imaging systems, and there have been brain SPECT systems devised.

This invention concerns the introduction of pixelated gamma detectors arrayed as a gamma camera. By way of illustration, pixelated semiconductor Cadmium-Zinc-Telluride (CZT) detectors will be referenced, although similar considerations apply to other semiconductor gamma detectors, such as Cadmium-Telluride (CdTe) and Mercuric Iodide (HgI), or to pixelated scintillator detectors. These pixelated semiconductor detectors have many performance advantages over the monolithic scintillator and PMT prior art, but they also have the disadvantage of having a higher cost than the almost <NUM>-year old prior art. This invention addresses ways to increase the clinical utility and efficiency of pixelated semiconductor gamma cameras by enabling them to adapt and transform to more optimal geometries for various clinical applications.

By way of example, we will discuss a preferred embodiment of a transformable CZT gamma camera consisting of an array of modular pixelated CZT detectors (called D-Matrix™) that we have designed and tested. The basic module is shown in <FIG> and consists of four CZT gamma modules (GM) <NUM> in a 2x2 array comprising one aggregator module (AM) <NUM>. Each AM <NUM> is <NUM> square and provides digital signal output including 2D location (module and pixel numbers or, preferably, x and y) and energy for each gamma photon detection event. Optionally, a 3D location including depth of interaction in the CZT crystal can also be provided by reading the cathode signal as well as the pixelated anode signals. One skilled in the art will appreciate that the AM <NUM> includes ASICs (application-specific integrated circuits), ADCs (analog to digital converters), and FPGAs (field-programmable gate arrays) as well as supporting electronics. Table <NUM> following contains the essential characteristics of each CZT gamma detector aggregator module <NUM>.

By way of further example, we will discuss a gamma camera <NUM> composed of D-Matrix™ aggregator modules <NUM> arrayed in a size compatible with a general-purpose SPECT system as depicted in <FIG>. In the illustration, nine AMs <NUM> are arrayed in each of <NUM> columns, each <NUM> long and <NUM> wide. The <NUM> adjacent columns comprise a camera <NUM> wide. Thus, there are a total of nine x <NUM> = <NUM> AM <NUM>, and <NUM> x <NUM> =<NUM> GM <NUM>. Since each GM <NUM> has <NUM> pixels, the general-purpose gamma camera <NUM> in <FIG> has <NUM>,<NUM> pixels, each two mm square. Some of the advantages of a CZT gamma camera compared to a scintillator gamma camera can be seen in Table <NUM> following.

Table <NUM> shows that CZT detectors can be arrayed in a camera size similar to a typical commercial gamma camera (most are about <NUM> axial x <NUM> transaxial). The <NUM> thickness of CZT is chosen to provide a similar stopping power to a typical <NUM> (<NUM>/<NUM>") thick NaI scintillator. This thickness is adequate for the most common medical isotopes, such as Tc-<NUM> (<NUM> keV), T1-<NUM> (<NUM> keV), Xe-<NUM> (<NUM> keV), Ga-<NUM> (<NUM> keV), and I-<NUM> (<NUM> keV). Increasing the CZT thickness to <NUM> will increase the stopping power and thus the detection efficiency for higher energy medical isotopes, such as In-<NUM> (<NUM> & <NUM> keV) and I-<NUM> (<NUM> keV), although they can be detected with <NUM> thick CZT, albeit less efficiently.

The intrinsic spatial resolution of a CZT gamma camera <NUM> is about <NUM> times better than a typical scintillator gamma camera resulting in <NUM> times more pixels in the same detector area. Moreover, the pixelated CZT gamma camera has no dead edges compared to the scintillation camera which has unusable ("dead") edges about half the diameter of the PMTs wherein the Anger position determination is ineffective. Thus, the edges must be masked off and not used for imaging. Furthermore, a scintillation gamma camera has a nonuniform performance wherein the central field of view CFOV performs significantly better than the peripheral ("useful") field of view UFOV. In a CZT gamma camera the performance is uniform across the full surface, so the CFOV and UFOV performance is equal. Furthermore, the CZT pixels are square and non-overlapping (except for a small amount of charge sharing), while the scintillator pixels are Gaussian with considerable overlap with neighboring pixels. Finally, the energy resolution is typically <NUM> or more times better, resulting in a better discrimination against scattered gamma photons which blur SPECT images.

Another advantage offered by tiled array semiconductor gamma cameras is that they can be advantageously deployed as sparsely populated arrays of detectors, as described in <CIT> and titled "Sparse Acquisition Gamma Cameras".

In regard to the transformable gamma cameras of the present specification, it should be understood that the tiled array of gamma detectors may comprise a sparsely populated tiled array of gamma detectors, as well as the case wherein the tiled array of gamma detectors is fully populated.

One fundamental problem addressed by the present invention is that the gamma cameras for a general-purpose SPECT system are designed for a subset of clinical applications that require large planar projections of the body. This requires that the field-of-view (FOV) be about <NUM> (axial) x <NUM> (transaxial) to enable planar whole-body bone imaging (with patient bed movement to multiple locations), lung ventilation imaging, and cardiac first-pass bolus imaging, for example. All other clinical applications of SPECT would be better served by a different configuration of smaller FOV gamma cameras.

One fundamental characteristic of this invention requires a modular design for pixelated CZT gamma cameras and takes advantage of the fact that there is no dead edge to the CZT detectors. The invention in one aspect is simply that the large FOV camera configuration can be transformed by subdividing the large modular camera into multiple smaller FOV gamma camera modules, independently positioned, and more suited geometrically for optimal SPECT imaging applications. By way of illustration, one embodiment of the present invention is to subdivide the large FOV camera into two equal half-FOV cameras, each about <NUM> (axial) x <NUM> (transaxial). These half-FOV cameras can be positioned around the body in a more optimal configuration for various clinical SPECT imaging applications, as will be discussed.

The most significant performance advantage for the smaller FOV gamma cameras is that the imaging efficiency can be increased, leading to either shorter imaging times, or lower injected radiation doses, or a combination of both lower time and dose. Although this advantage will be apparent to those skilled in the art, an illustration will illuminate this conclusion. Consider heart imaging with standard <NUM> x <NUM> gamma cameras. At any time during the acquisition, two planar projection images of the heart are being acquired, one on each of the two gamma cameras deployed in a standard SPECT system. In an embodiment of the present invention, these two full-FOV cameras will subdivide into four half-FOV cameras. At any time during the SPECT acquisition, there will now be four planar projection images of the heart being acquired simultaneously. This will essentially double the efficiency of the imaging, enabling use of lower time and/or dose without any other changes required.

In one embodiment, general purpose SPECT imaging can be optimized by subdividing two large-FOV gamma cameras into four half-FOV cameras and orbiting these four cameras around the body in a step-and-shoot or continuous acquisition sequence, while each camera individually can approach the body outline as closely as possible ("body contouring") to enhance spatial resolution.

In another embodiment, brain SPECT can be optimized by subdividing two large-FOV gamma cameras into four half-FOV cameras and orbiting these four cameras around the head in a step-and-shoot or continuous acquisition sequence, while each camera individually can approach the head outline as closely as possible to enhance spatial resolution.

In another embodiment, heart SPECT can be optimized by subdividing two large-FOV gamma cameras into four half-FOV cameras and orbiting these four cameras around the body in a step-and-shoot or continuous acquisition sequence, while each camera individually can approach the body outline as closely as possible to enhance spatial resolution and at the same time pointing toward the heart to increase efficiency.

In another embodiment, breast planar imaging (also known as molecular breast imaging) can be optimized by subdividing two large-FOV gamma cameras into four half-FOV cameras and placing a pair of half-FOV cameras in opposition next to each breast. Mild, nonpainful compression between the two cameras will immobilize the breast. Multiple planar views can be acquired: for example, the two views most often used in mammography are the CC (cranial-caudal) and MLO (medial-lateral oblique) views. By imaging both breasts simultaneously, the clinical imaging time can be cut in half.

In a further embodiment of this present invention, the smaller-FOV gamma cameras can each wobble about their mechanical support axis to acquire projection data from a fan of angles. This acquisition strategy can reduce image reconstruction artifacts due to truncated views.

Another embodiment of the present invention is to separate the large FOV gamma camera into individual tiles (<NUM> x <NUM> for D-Matrix™, by way of illustration), each with its own collimator and each positioned to optimize the efficiency and spatial resolution for the clinical application being addressed.

Another embodiment of this present invention is a method for employing a SPECT scanner with transformable gamma cameras designed and manufactured according to any of the mechanical embodiments described herein.

These embodiments are provided for illustration and those of ordinary skill in the art will understand that each large-FOV camera could favorably subdivide into three or more smaller-FOV cameras, each mechanically supported by the gantry and positioned around the patient. Furthermore, the use of three or more large-FOV transformable gamma cameras is possible, as are embodiments which combine standard non-transformable scintillator or semiconductor gamma cameras with transformable semiconductor gamma cameras.

The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying non-scale drawings, wherein like reference numerals identify like elements in which:.

While the invention may be subject to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, specific embodiments with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein.

<FIG> shows a modular semiconductor direct conversion CZT gamma detector called D-Matrix™. This aggregator module (AM) <NUM> is composed of four CZT crystal detectors <NUM>, each designated a gamma module (GM), each measuring about <NUM> x <NUM> x <NUM> thick. Each GM <NUM> may comprise a monolithic crystal or may comprise multiple tiles of CZT mounted in an abutting composite with small gaps between the tiles. The top GM <NUM> surface in <FIG> is the metallic cathode, which is typically monolithic but which can also be pixelated. Gamma photons generally enter the GM from the cathode side of the CZT crystal. The lower surface of the GMs <NUM> has metallic anode pixels with a pitch of about two mm in an <NUM> × <NUM> pixel pattern for each CZT detector. The CZT is bonded to a substrate that provides mechanical stability and electrical connections to the read-out electronics boards, which include ASICs, one or more ADCs, and an FPGA. Negative DC bias voltage (about -<NUM> V for <NUM> thick CZT) is provided for the cathodes and an optional capacitive decoupling circuit allows reading the induced cathode signal as well as the anode signals. The overall dimension of the D-Matrix™ aggregator module (AM) <NUM> with <NUM> GMs <NUM> (CZT detectors, <NUM> thick) and readout electronics is about <NUM> x <NUM> x <NUM> thick. This AM <NUM> can be tiled to comprise various sized arrays to constitute flat panels, curved panels, rings, ellipses, or other structures as will be disclosed in this specification. Some of the features of the AM <NUM> are listed in Table <NUM>.

One of the advantages of CZT gamma detectors is that they occupy a smaller volume than scintillators and PMTs, so that CZT gamma cameras can be shielded by far less volume and weight of heavy metal, such as lead (Pb) or tungsten (W). Thus a SPECT system gantry designed specifically for a CZT gamma camera can be smaller and lighter than a conventional SPECT gantry. It may have a smaller footprint and fit into a smaller examination room.

Furthermore, the energy resolution of a CZT gamma camera, as tabulated in Table <NUM>, is much better (about <NUM>% vs about <NUM>% for NaI). Practically, this means that a narrower energy window can be used to for the photopeak planar projection images that are reconstructed into 3D SPECT images. This narrower energy window will discriminate against scattered gamma photons which blur the SPECT image. Thus, the final image contrast should significantly improve in a CZT camera compared to a scintillation gamma camera.

<FIG> depicts one such array <NUM> of AMs <NUM> (only two of <NUM> are labelled) in a size typical of flat panel gamma cameras used in general purpose medical SPECT. The illustrative array <NUM> comprises nine rows and <NUM> columns of AMs <NUM> forming a flat panel gamma camera <NUM> with dimensions of about <NUM> x <NUM>. This illustrative arrangement comprises nine x <NUM> = <NUM> AMs and (nine x <NUM>) x (<NUM> x <NUM>) = <NUM> x <NUM> = <NUM>,<NUM> pixels, as tabulated in Table <NUM>.

The original gamma camera built by Hal Anger in <NUM> was a flat panel detector with a circular field of view. All commercial clinical gamma cameras have been derivatives of the original flat panel, although the field of view became rectangular in the <NUM> when 3D tomographic image reconstruction from SPECT became practical. There have been several attempts to use curved scintillation cameras for brain or heart imaging applications, but none have been commercially successful. Several small-animal preclinical SPECT systems were built using CZT modules in a ring, but these have not been sold in any successful quantities. Nevertheless, modular detector assemblies, such as the Aggregator Module, AM <NUM>, of <FIG> and <FIG> are amenable to forming a curved arcuate surface, or ring, or ellipse of detectors.

<FIG> illustrate this design option for a curved detector surface. <FIG> illustrates a transaxial cross-section (view from the patient's feet) of a dual-detector SPECT system with a human body <NUM> as the example object being imaged by gamma emission. Both detector arrays <NUM> in <FIG>, as in <FIG>, are shown in cross-section with <NUM> columns <NUM> illustrated by gray boxes. By reference to <FIG>, it is apparent that each column <NUM> comprises nine AMs <NUM> with length about <NUM>. Not shown explicitly are collimators, radiation shielding, and readout electronics, but these elements are well known by those of skill in the art. <FIG> illustrates curved arcuate surface detectors <NUM> that could be formed by placing the columns <NUM> of AMs <NUM> along a curved surface that roughly follows the contour of a typical human body.

A gamma camera could be designed to mechanically transform between the flat panel configuration of <FIG> and the curved panel configuration of <FIG>. It is anticipated that the curvature could be fixed or variable. The reconstruction would be easier for a fixed curvature, but if the position of each detector is tracked mechanically or by other means, then the iterative reconstruction software could accommodate "body contouring" with variable curve panels. As will be apparent to those skilled in the art, the hinge points for such a transformation would depend upon the collimation scheme employed. For example, if parallel hole collimators were attached to each CZT detector column <NUM>, then the hinge points would be at the front face of the collimator columns. However, if multiple-pinhole collimation were employed, the hinge points would be at the front face of the CZT detectors <NUM> of <FIG>.

It is intended that the concept of arcuate detector panels should be applied to other possible embodiments, such as those in <FIG>, <FIG>, and <FIG>. Wherever a flat panel gamma camera is illustrated, an arcuate panel gamma camera can be substituted.

The smaller square pixels of a CZT gamma camera can also be used to advantage compared to the overlapping Gaussian pixels of a scintillation gamma camera. Collimators can be designed (not the subject of the present invention) to optimize the spatial resolution and efficiency of the detector-collimator system, again improving the image contrast. By way of illustration, Table <NUM> shows a comparison of typical hexagonal parallel-hole collimators, as used in typical SPECT systems, and some possible pixel-registered square-hole collimators. These design concepts have not been optimized, but are illustrative of the performance achievable with such pixelated CZT specific collimators.

<FIG> shows graphically the comparison of the four collimators shown in Table <NUM>. The dashed curves represent the system resolution for typical LEGP (Low Energy General Purpose, short dash) and LEHR (Low Energy High Resolution, longer dash) hexagonal parallel-hole lead (Pb) collimators. By way of illustration, the solid lines represent the system resolution for two potential designs for pixel-registered square-parallel-hole lead (Pb) collimators. The thinner solid line with open circle markers represents the LEGP-CZT collimator response; the thicker solid line with open square markers represents the LEHR-CZT collimator response. The system resolution at <NUM> distance from the face of the collimator was matched for the two LEGP and two LEHR collimators, as an example of a possible design. Of course the resolution as a function of distance from the collimator can be traded off for system efficiency (sensitivity). For the particular choice illustrated in <FIG> and TAB. <NUM>, the registered LEGP-CZT is <NUM>% more efficient than the typical clinical hexagonal hole LEGP collimator. Likewise, the LEHR-CZT is <NUM>% more efficient than the typical clinical hexagonal hole LEHR collimator. The optimization of the design depends on the application task and could be accomplished by Monte Carlo modeling simulation of the system response coupled with iterative reconstruction employing a full physics description of the detector-collimator response.

As will be apparent to one skilled in the art, a pixel-registered collimator response has no significant dependence on the detector spatial resolution, hence the system resolution response function is approximately a straight line. In contrast, for a scintillator with Gaussian pixels, the system resolution is a quadrature summation of the detector and collimator resolutions, hence the resolution response function is approximately parabolic. The advantage for closer distances belongs to the CZT gamma camera with pixel-registered collimator. It will be apparent to one skilled in the art that the spatial resolution for a square-hole collimator is not isotropic in the plane. In our experience with such collimators as used in Molecular Breast Imaging (MBI), this off-axis resolution is not a significant issue.

As will be apparent to one skilled in the art, pixelated CZT detectors are a preferred embodiment of the present invention, but some of the advantages can be obtained with pixelated scintillator gamma cameras. The pixels may be made of NaI, CsI, or LaBr, for example, and the scintillation light readout may be achieved by optically-coupled photodetectors, such as vacuum PMTs, avalanche photodiodes, position-sensitive photomultiplier tubes, or Silicon photomultipliers, for example. None of these alternative pixelated cameras can match CZT in energy resolution, spatial resolution, and compactness of form. Nevertheless, it is possible to beneficially apply the principles disclosed in the present specification to such alternative pixelated gamma cameras.

<FIG> illustrates an embodiment of the present invention as a cross-sectional view of gamma cameras and a body for various clinical SPECT imaging applications. In <FIG> the approximately ellipsoidal cross-section of the torso of a body <NUM> is being imaged by multiple gamma cameras <NUM> and <NUM>. In <FIG> the head and brain <NUM> is being imaged, while in 5d) the heart <NUM> and in 4e) the breasts <NUM> are being imaged. The gamma cameras <NUM> and <NUM> (and <NUM>, 14R, <NUM>, 18R) comprise pixelated gamma sensors, readout electronics, radiation shielding, and collimation, as will be discussed in <FIG> and <FIG> below.

In <FIG> the dashed lines <NUM> represents a plane bisecting the transaxial width of the full-FOV gamma cameras <NUM> and <NUM>. It is at this plane that each of the two pixelated gamma cameras <NUM> and <NUM> have been configured to separate into two smaller FOV cameras (<NUM> and 14R, <NUM> and 18R). In a special case, both smaller FOV cameras are equal in width. One with skill in the art will recognize that such subdivisions can occur in multiple locations and that the resulting smaller FOV cameras need not all be the same size. In <FIG>, the smaller FOV cameras are shown, by way of illustration, as four half-FOV cameras <NUM>, 14R, <NUM>, 18R with left and right halves.

The drawings in <FIG> show a snapshot in time of a SPECT data acquisition. Multiple projection views must be acquired to reconstruct a 3D SPECT image and the required orbital motion of the gamma cameras <NUM> and <NUM> (or <NUM>, 14R, <NUM>, and 18R) is not illustrated here, because it is well-known to those of skill in the art. Further, the drawings show the front surface of the gamma cameras <NUM> and <NUM> in contact with the body <NUM>, head <NUM>, or breasts <NUM>. This is a preferred geometry in which the gamma camera is positioned as close as possible to the volume of interest. However, when the gamma cameras <NUM> and <NUM> are moved to the next imaging view, they must first back away from the body <NUM>. head <NUM>, or breasts <NUM>, then move to the new viewing position, and then move to close proximity to the body <NUM>, head <NUM>, or breasts <NUM>. This procedure is known by those skilled in the art as "body contouring" and for safety reasons with large gamma cameras <NUM> and <NUM>, the closest approach to the body <NUM>, head <NUM>, or breasts <NUM> (as detected by infrared beams, for example) may be limited to several cm. With smaller FOV gamma cameras <NUM>, <NUM> R, <NUM>, and 18R it will be safer to approach the body <NUM>, head <NUM>, or breasts <NUM> more closely, thus improving the reconstructed spatial image resolution.

<FIG>) illustrates an embodiment of the present invention as a cross-sectional view of a pixelated gamma camera <NUM> that is configured to subdivide at the plane <NUM> into two smaller gamma cameras <NUM> and 14R as illustrated in <FIG>). The gamma camera <NUM> comprises a pixelated detector with readout electronics <NUM>, radiation shielding <NUM>, and collimation <NUM>, shown by way of example as a parallel hole collimator. In a preferred embodiment, the detector <NUM> comprises pixelated CZT direct conversion semiconductor modules, such as the D-Matrix <NUM> shown in <FIG>. The readout electronics associated with the pixelated detector <NUM> comprises ASICs, ADCs, and digital communications that transmit to a data acquisition computer (<NUM>, <FIG>) a list of gamma photon detection event packets containing at least 2D position and energy. As in <FIG>, the dashed line <NUM> marks a plane of potential separation where the detector <NUM>, shielding <NUM>, and collimator <NUM> can subdivide to form two smaller FOV gamma cameras <NUM> and 14R.

As will be apparent to those skilled in the art, a subdivided detector requires additional radiation shielding <NUM> and 13R to cover the edge of the exposed detector <NUM> and 10R. This additional shielding <NUM> and 13R can be emplaced robotically or manually. Of course, this additional shielding <NUM> and 13R must be removed before the subdivided gamma cameras <NUM> and 14R can be rejoined into a full-FOV gamma camera <NUM>. <FIG>) shows this additional edge shielding attached to the large-FOV general-purpose gamma camera <NUM> in a position where it can be deployed when the transformable camera <NUM> is subdivided. <FIG>) illustrates the case in which the two small-FOV cameras <NUM> and 14R formed by subdividing the full-FOV camera <NUM> are separated completely and form independent gamma cameras. The additional radiation shielding <NUM> and 13R has been moved (preferentially automated) to cover the exposed ends of the subdivided gamma cameras. A different case is illustrated in <FIG>) in which the two small-FOV cameras <NUM> and 14R are not completely separated, but are held together at a hinge line to keep some dependence on location and orientation between the two small-FOV cameras. In this case, the additional shielding <NUM> and 13R would cover the wedge-shaped space between the two small-FOV cameras.

<FIG>) illustrates an embodiment of the present invention as a plan view of a pixelated gamma camera <NUM> that is configured to subdivide at the plane <NUM> into two smaller gamma cameras <NUM> and 14R as in <FIG>). The additional radiation shielding <NUM> and 13R covers the exposed edges of the detectors <NUM> and 10R. One further essential mechanical feature is illustrated in <FIG>, namely the mechanical supports <NUM> and 16R. These mechanical supports can take various forms in the contemplated embodiments of this present invention. In one embodiment, the mechanical supports <NUM> and 16R would connect to a standard SPECT system gantry ring <NUM> and would be capable of radial and azimuthal (rotating) motions in addition to providing pivoting motion along the mechanical support axis <NUM> or 16R to aim the camera away from the system gantry axis of rotation. In another embodiment, the mechanical supports <NUM> and 16R would comprise articulated arms to enable manual or robotic positioning of the gamma cameras (<NUM> or <NUM> and 14R) in many positions surrounding the body, as illustrated in <FIG> for a sampling of potential clinical applications.

As one skilled in the art will understand, a standard SPECT system is required to support the transformable gamma cameras and there are multiple geometric forms for such systems. In essence, such systems contain a stand <NUM> that supports a rotor <NUM> and gantry <NUM>. The transformable gamma cameras <NUM> or <NUM> and 14R are supported by mechanical supports <NUM> and 16R. All motions of the system (rotations, translations, robotic positioning) including a patient bed (not shown) are controlled by a computer <NUM>, which also acquires digital data from the gamma cameras <NUM> or <NUM> and 14R, reconstructs 2D planar and 3D SPECT images, and displays the resulting images for medical interpretation.

In summary, this invention provides in one embodiment an innovative design for a SPECT system that robotically transforms into an adaptable geometry that is more optimized for various clinical applications than the state-of-the-art SPECT systems with two large-FOV flat panel scintillator gamma cameras. This embodiment provides means to subdivide the large full-FOV gamma cameras <NUM> and <NUM> into at least four smaller FOV gamma cameras <NUM>, 14R, <NUM>, and 18R, and to position these around the body in more efficient geometries for SPECT imaging. The most apparent advantage is that the efficiency of acquisition can be approximately doubled. Also, the spatial resolution of reconstructed images can be improved by placing more of the detector volume closer to the imaged volume of interest.

<FIG> is a process flow diagram depicting an illustrative method for applying any of the embodiments of the present invention in a clinical setting. Assuming that a SPECT system with one or more transformable gamma cameras has been designed, built, and installed in a nuclear medicine ("molecular imaging") clinic, then the steps illustrated in <FIG> would be followed to utilize such an innovative system. The first step <NUM> for each patient examination is to choose a clinical application. Typically, one application is employed for each patient, but it is possible to conduct two or more sequential studies in the same patient during a single examination. If that is the case, this process flow is repeated for each clinical application, such as brain blood flow, lung perfusion/ventilation, myocardial perfusion, or whole-body bone (planar or SPECT).

The next step <NUM> is to match the clinical application with an optimal configuration for the gamma cameras and collimators. Choices must be made such as flat or curved panels, number of gamma cameras, and type of collimation. Typically, such choices will be entered into a graphical user interface which will associate preferred configurations provided by the manufacturer for each clinical application. After selection of a desired configuration, the scanner will transform automatically into the desired configuration, subdividing the large general-purpose gamma camera into smaller subsets of the large tiled array, as shown in step <NUM>. This transformation process may be entirely robotic or it may be manually assisted. For example, collimators may need to be exchanged and additional radiation shielding may need to be attached or removed.

The next step <NUM> is patient preparation. This step may, of course, be performed before or in parallel with the previous steps. After the scanner is properly configured (step <NUM>) and the patient has been prepared with an injection of a radiotracer, then the patient will be positioned on the scanner bed and moved into position for the first of multiple projection images.

Claim 1:
A transformable gamma camera (<NUM>, <NUM>) comprising:
groups of tiled arrays of gamma detectors (<NUM>), a collimator (<NUM>) and radiation shielding (<NUM>);
the transformable gamma camera being configured to subdivide at a plane (<NUM>) bisecting the transaxial width of the camera into a plurality of subdivided gamma cameras (<NUM>, 14R, <NUM>, 18R), each of the subdivided gamma cameras having at least one of the groups of tiled arrays of gamma detectors and corresponding collimator,
wherein the radiation shielding comprises additional shielding (<NUM>, 13R) configured to cover the exposed edges of the subdivided gamma cameras (<NUM>, 14R, <NUM>, 18R);
wherein the plurality of subdivided gamma cameras (<NUM>, 14R, <NUM>, 18R) can be independently positioned to facilitate contouring with a region of interest for a spatial resolution.