Patent Description:
In NM imaging, systems with multiple detectors or detector heads may be used to image a subject, such as to scan a region of interest. For example, the detectors may be positioned adjacent the subject to acquire NM data, which is used to generate a three-dimensional (3D) image of the subject.

Single Photon Emission Computed Tomography (SPECT) systems may have moving detector heads, such as gamma detectors positioned to focus on a region of interest. For example, a number of gamma cameras may be moved (e.g., rotated) to different angular positions for acquiring image data. The acquired image data is then used to generate the 3D images.

The size of the detector heads may limit an available usable area for the placement of detectors, such as Cadmium Zinc Telluride (CZT) wafers. The sensitivity (e.g., the proportion of radiation received relative to the radiation emitted) may be limited by the size of the detector heads and/or the arrangement of CZT wafers. Conventional approaches to improving sensitivity may use thicker detectors, or detectors arranged in generally identical or similar layers stacked directly one on top of each other. Such conventional approaches may not provide a desired or required sensitivity.

<CIT> is directed to a radiation detector assembly is provided including a semiconductor detector, pixelated anodes, and at least one processor. The pixelated anodes are disposed on a surface of the semiconductor detector, and configured to generate a primary signal responsive to reception of a photon and a secondary signal responsive to an induced charge caused by reception of a photon by at least one adjacent anode. The at least one processor is operably coupled to the pixelated anodes, and configured to define sub-pixels for each pixelated anode; acquire primary signals and secondary signals from the pixelated anodes; determine sub-pixel locations for acquisition events using the primary and secondary signals; generate a sub-pixel energy spectrum for each sub-pixel; apply at least one energy calibration parameter to adjust the sub-pixel energy spectra for each pixelated anode; and, for each pixelated anode, combine the adjusted sub-pixel energy spectra to provide a pixelated anode spectrum.

<CIT> is a radiation detector system is provided including a semiconductor detector, plural pixelated anodes, and at least one processor. The plural pixelated anodes are disposed on a surface of the detector. At least one of the pixelated anodes is configured to generate a collected charge signal corresponding to a charge collected by the pixelated anode and to generate a non-collected charge signal corresponding to a charge collected by an adjacent anode to the pixelated anode. The at least one processor is configured to determine a collected value for the collected charge signal in the pixelated anode; determine a non-collected value for the non-collected charge signal in the pixelated anode corresponding to the charge collected by the adjacent anode; use the non-collected value for the non-collected charge signal to determine a sub-pixel location for the adjacent anode; and use the collected value to count a single event in the pixelated anode.

<CIT> is directed to directed to a detector for X-ray and/or gamma radiation, including at least one radiation source and at least one interlayer in the case of an electrode, wherein a neutralization of trap states at the electrode and rise times and decay times in the millisecond range, as are required for the application, can be achieved by the corresponding arrangement. A method for producing the detector is also disclosed.

The invention relates to a detector assembly according to claim <NUM>.

The following detailed description of the invention will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks, the functional blocks are not necessarily indicative of the division between hardware circuitry. For example, one or more of the functional blocks (e.g., processors or memories) may be implemented in a single piece of hardware (e.g., a general purpose signal processor or a block of random access memory, hard disk, or the like) or multiple pieces of hardware. Similarly, the programs may be stand alone programs, may be incorporated as subroutines in an operating system, may be functions in an installed software package, and the like. It should be understood that the invention is not limited to the arrangements and instrumentality shown in the drawings, but has a scope which is defined by the appended claim.

As used herein, the terms "system," "unit," or "module" may include a hardware and/or software system that operates to perform one or more functions. For example, a module, unit, or system may include a computer processor, controller, or other logic-based device that performs operations based on instructions stored on a tangible and non-transitory computer readable storage medium, such as a computer memory. Alternatively, a module, unit, or system may include a hard-wired device that performs operations based on hard-wired logic of the device. Various modules or units shown in the attached figures may represent the hardware that operates based on software or hardwired instructions, the software that directs hardware to perform the operations, or a combination thereof.

"Systems," "units," or "modules" may include or represent hardware and associated instructions (e.g., software stored on a tangible and non-transitory computer readable storage medium, such as a computer hard drive, ROM, RAM, or the like) that perform one or more operations described herein. The hardware may include electronic circuits that include and/or are connected to one or more logic-based devices, such as microprocessors, processors, controllers, or the like. These devices may be off-the-shelf devices that are appropriately programmed or instructed to perform operations described herein from the instructions described above. Additionally or alternatively, one or more of these devices may be hard-wired with logic circuits to perform these operations.

As used herein, an element or step recited in the singular and preceded with the word "a" or "an" should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to "one embodiment" of are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments "comprising" or "having" an element or a plurality of elements having a particular property may include additional elements not having that property.

Various examples not forming part of the presently claimed invention describe systems and methods for improving the sensitivity of image acquisition, for example in Nuclear Medicine (NM) imaging applications.

Various examples not forming part of the presently claimed invention provide one or more different approaches for improving sensitivity and/or other aspects of detector performance. For example, in one approach an array of pinhole openings are used in a collimator for a detector system. In the invention, all events are identified as being absorbed at a location within a range corresponding to an absorption coefficient of the detector (e.g., one over the absorption coefficient of the detector). In an example not forming part of the presently claimed invention, all events are identified as being absorbed at a location and/or within a range that ensures that the energy of the events is measured within the energy window used for imaging. It may be noted that each of the three approaches discussed above in this paragraph may be employed with the use of virtual sub-pixels (or virtual division of the detector) along X and Y directions (or along the width and length of the detector).

In various examples, a pinhole collimator includes an array of pinholes that defines multiples cells. Each cell includes or corresponds to only a single physical pixel of the detector and only a single pinhole of the array. In the invention, in contrast to certain conventional approaches, radiation from a given pinhole (also referred to herein as a pinhole opening) only arrives at one particular physical pixel corresponding to the given pinhole. It may be noted that, in the invention, the physical pixel is viewed as including a number of virtual sub-pixels by a processing unit. Each event detected in the physical pixel is counted as related to one of the virtual sub-pixels into which the physical pixel is divided to. The virtual sub-pixel to which the event belongs to is determined by the location of the event within the physical pixel that includes the virtual sub-pixels. There are known methods to derive the location of the event within the physical pixel, such as the method described in <CIT>.

Further, use of a pinhole array instead of a parallel hole array in various examples provides for a smaller area of opening that collects radiation. For example, the size of a pinhole opening may be <NUM>/<NUM> of the width (or <NUM>/<NUM> of the area) of a pixel, whereas an opening of a parallel hole array may be the pixel size less the septa thickness. Accordingly, the opening size in a parallel hole array may be dictated by the pixel size and wall (or septa) thickness; however, in various examples, employing a pinhole array, the opening size may be selected as desired (e.g., to provide a desired sensitivity and/or collimator height). In some examples, physical pixels may be divided in multiple virtual sub-pixels (e.g., an associated processing unit may assign virtual sub-pixels to each physical pixel) along X and Y directions (or length and width of a detector), while having a single layer in the Z direction (or thickness). Alternatively, in other examples, multiple virtual sub-pixels may be employed along the Z direction (or thickness).

Accordingly, various examples provide flexibility to selected collimator height.

Such flexibility is especially advantageous when using a collimator within a swiveling detector head. For example, the collimator height may dictate or influence the radius reserved for each head for swiveling motion. The shorter the collimator is, the smaller is the required radius. Accordingly, for a shorter collimator provided by a pinhole array, more heads may be placed around the object being imaged providing improved sensitivity and image quality in comparison with a taller parallel hole collimator. Additionally, the collimator openings produce solid angles through which the virtual pixels observe the object being imaged, with the smaller size of the pinhole openings providing larger and more separated solid angles for the virtual sub-pixels, with less overlap between the solid angles for the virtual sub-pixels of a physical pixel. Accordingly, the use of such pinhole openings improves spatial resolution, or may be used to maintain a desired resolution with a shorter collimator to increase sensitivity and improve image quality. Further, still, the use of thicker septa or walls helps prevent radiation penetration from a given collimator opening to non-associated pixels (or pixels other than a pixel immediately below the opening), thereby improving image quality. Further still, it may be noted that use of many sub-voxels over the thickness of a detector may reduce the number of events for each volume of interest, thereby increasing statistical noise and degrading image quality. In various examples, using only one location (or range) or layer along the Z direction (or thickness) reduces statistical noise and improves image quality.

It may be noted that in some examples, in connection with sub-pixelization along the X and Y directions, a single Z layer, location, or range may be used to identify events along a thickness of a detector. In the invention, a Z position-range for all events is defined around an average absorption depth of <NUM>/µ, where µ is the absorption coefficient for a specific photon energy for a particular detector material.

In an example not forming part of the presently claimed invention, events may be distributed linearly, as one example, or exponentially, as another example, within a range centered about or otherwise corresponding to distance of <NUM>/µ from the cathode. As another example, a Z position-range for all events may be defined within a range corresponding to energies of the energy window used for imaging. In an example not forming part of the presently claimed invention, in some embodiments, an absorption location for each absorbed photon within the thickness of the semiconductor detector is defined within a range such that ΔL/D = ΔE/E, where ΔL is a distance from the cathode, D is the detector thickness, ΔE is an energy window width, and E is a photopeak energy of an absorbed photon. Again, the events may be distributed linearly, as one example, or exponentially, as another example. Use of such Z position-ranges (in contrast, for example, to multiple virtual sub-pixels along a detector thickness) helps to reduce statistical noise and to improve image quality. Also, it may be noted that use of such Z position-ranges may be accomplished with simpler hardwarde or software (in compariston to, for example, use of multiple virtual sub-pixels along a detector thickness), providing for easier implementation and/or lower cost.

A technical effect provided by the invention may include increased sensitivity of a detector system, such as a NM imaging detector system. The detector system may be provided in a rotating head detector module that may be used as part of a group of similar rotating head detector modules in an imaging system. A technical effect of the invention may include improved image quality and spatial resolution. A technical effect of the described examples includes reduced collimator height allowing for less room needed to allow a detector head to pivot, allowing more detector heads to be placed closely to an object being imaged. A technical effect of the invention may also include reduced penetration by radiation to pixels other than a pixel associated with (e.g., located directly below) a collimator opening. A technical effect of the invention may include reduced statistical noise.

<FIG> provides a schematic block view of a detector assembly <NUM> in accordance with the invention, <FIG> provides an exploded view of aspects of the detector assembly <NUM>, and <FIG> provides a sectional view taken along line <NUM>-<NUM> of <FIG>. As seen in <FIG>, the detector assembly <NUM> includes a semiconductor detector <NUM>, a pinhole collimator <NUM>, and a processing unit <NUM>, which for the clarity of the drawings is shown only in <FIG>. Generally, the semiconductor detector <NUM> produces signals in response to absorption events (e.g., photons produced in response to a radiopharmaceutical that has been administered to an object being imaged that impact the semiconductor detector <NUM>). The signals are provided to the processing unit <NUM>, which uses identified events to reconstruct an image of the object being imaged and to derive the location of the event inside the physical pixel as described, for example in <CIT>. The pinhole collimator <NUM> guides photons to the semiconductor detector <NUM>, and limits the angular range of approach of photons to a given pixel or portion of the semiconductor detector <NUM>, helping to allow for accurate determination of the portion of the object being imaged from which a given detected event originated.

As best seen in <FIG>, the semiconductor detector <NUM> has a first surface <NUM> and a second surface <NUM>. The second surface <NUM> is opposed to the first surface <NUM> (and, likewise, the first surface <NUM> is opposed to the second surface <NUM>). The semiconductor detector <NUM> is configured to generate electrical signal in response to photon impacts, and may be made of, for example, Cadmium Zinc Telluride (CZT). The second surface <NUM> includes pixelated anodes <NUM> disposed thereon, and the first surface <NUM> includes a cathode electrode <NUM> disposed thereon. In some examples, the cathode electrode <NUM> may be a monolithic, or single, cathode. The cathode electrode <NUM> collects an opposite electrical charge of the pixelated anodes <NUM>, and the pixelated anodes <NUM> are used to generate signals in response to charges generated by the semiconductor detector <NUM> responsive to photon impacts. The pixelated anodes <NUM> may be arranged in a grid, with the location of one or more pixelated anodes <NUM> at which a signal is generated responsive to a photon impact used to determine a corresponding location in the object corresponding to the photon impact.

As seen in <FIG>, the pinhole collimator <NUM> is interposed between the semiconductor detector <NUM> and an object being imaged (not shown), and is used to control passage of radiation from the object being imaged to the semiconductor detector <NUM> via the pinhole collimator <NUM>. For example, the pinhole collimator <NUM> guides photons to the semiconductor detector <NUM>, limiting an angular range of approach for photons that impact the semiconductor detector <NUM>. The pinhole collimator <NUM> includes an array <NUM> of pinhole openings <NUM> corresponding to the pixelated anodes <NUM> on the second surface <NUM>. In <FIG>, the array <NUM> of pinhole openings <NUM> has a <NUM>:<NUM> correspondence with an array or grid of pixelated anodes <NUM>, with both the pixelated anodes <NUM> and array <NUM> of pinhole openings <NUM> arranged in an <NUM> x <NUM> layout when the projections of openings <NUM> on the second surface <NUM> of the detector <NUM> are centered in the pixelated anodes <NUM>. Accordingly, in the invention, each pinhole opening <NUM> is associated with a single pixelated anode <NUM> of the semiconductor detector <NUM>. Accordingly, radiation that passes through a given pinhole opening <NUM> is confined within a single cell of collimator <NUM> and is absorbed at a location corresponding to one and only one pixelated anode <NUM> that is associated with the given pinhole opening <NUM> (e.g., located directly beneath the pinhole opening <NUM>). Further, each pinhole opening <NUM> defines an area, with the area of each pinole opening <NUM> smaller than a corresponding area of the corresponding pixelated anode <NUM>. For example, as seen in <FIG>, the width of each pixelated anode <NUM> is greater than the width of a corresponding pinhole opening <NUM>. Accordingly, if the pixelated anode <NUM> and pinhole opening <NUM> are generally square-shaped, the area of the pixelated anode <NUM> is greater than the area of the pinhole opening <NUM>. It may be noted that the depicted examples have generally square-shaped cross-sections. Other shapes of opening (e.g., circular, rectangular, or triangular, among others), may be utilized in alternate examples.

As best seen in <FIG> and <FIG>, in various examples the pinhole collimator <NUM> includes a top plate <NUM> through which the pinhole openings <NUM> pass. The top plate <NUM> is mounted to a collimator base <NUM>. The pinhole collimator <NUM> also includes plural septa <NUM> (or walls) extending along a height of the collimator base <NUM> that define collimator cells <NUM> corresonding to the pinhole openings <NUM>. In <FIG>, each pinhole opening <NUM> is associated with a particular collimator cell <NUM> and a particular pixelated anode <NUM>, with photons that pass through the pinhole opening <NUM> passing through the corresponding collimator cell <NUM> toward the corresponding pixelated anode <NUM>. Each collimator cell <NUM> defines a cavity between the corresponding pinhole opening <NUM> and the corresponding pixelated anode <NUM>. The septa <NUM> act to reduce or eliminate passage of a photon through a pinhole opening <NUM> to non-corresponding pixelated anodes (e.g., pixelated anodes adjacent to the particular pixelated anode that corresponds to the particular pinhole opening). A cell width <NUM> defined by the septa <NUM> (e.g., a width between neighboring septa <NUM>) is greater than an opening width <NUM> defined by the pinhole openings <NUM>. For example, the cell width <NUM> is <NUM> times or more greater than the opening width <NUM>. In the example illustrated in <FIG>, the cell width <NUM> is d, and the opening width <NUM> is d/<NUM>, or the cell width <NUM> is <NUM> times greater than the opening width <NUM>. It may be noted that, in contrast, an opening width and width between neighboring walls may be identical for a parallel-hole collimator.

In the example illustrated in <FIG>, the septa <NUM> are parallel to each other and define square-shaped cross sections for each collimator cell <NUM>; however, it may be noted that different configurations may be employed in alternate examples. As best seen in <FIG> and <FIG>, the top plate <NUM> has a thickness <NUM>, and the septa <NUM> have a thickness <NUM>. In the depicted example, the thickness <NUM> of the top plate <NUM> is greater than the thickness <NUM> of the septa <NUM>. In the example illustrated in <FIG>, the septa <NUM> are parallel to each other and define square-shaped cross sections for each collimator cell <NUM>; however, it may be noted that different configurations may be employed in alternate examples. <FIG> illustrates a cross-section of an example of a top plate <NUM> (e.g., which may be used as top plate <NUM>) that may be used with pinhole collimator <NUM> in various examples. The top plate <NUM> includes a first surface <NUM> configured to be positioned proximate a semiconductor detector (e.g., semiconductor detector <NUM>), or oriented toward an interior <NUM> of a collimator (e.g., pinhole collimator <NUM>) including the top plate <NUM>. The top plate <NUM> also includes a second surface <NUM> that is opposed to the first surface <NUM>. The second surface <NUM> is farther away from the semiconductor detector than the first surface <NUM> is, or the second surface <NUM> is oriented toward an object <NUM> being imaged from which photons <NUM> are emitted. The top plate <NUM> includes pinhole openings <NUM> through which photons <NUM> pass toward the semiconductor detector. The depicted pinhole openings <NUM> each have a first width <NUM> at the first surface <NUM>, and a second width <NUM> at the second surface <NUM>. The first width <NUM> is greater than the second width <NUM>. Accordingly, the pinhole openings <NUM> are tapered, and are larger at the first surface <NUM> than at the second surface <NUM>. It may be noted that the taper orientation of the openings <NUM> in the plate <NUM> of <FIG> is opposite to the taper orientation of the openings <NUM> in the plate <NUM> of <FIG>. The tapered shape in various examples is configured to facilitate passage of photons over a preferred or desired angular range.

Alternatively or additionally, it may be noted that pinhole collimators in various examples may include tapered walls. <FIG> illustrates a cross-section of an example of pinhole collimator septa <NUM> that may be used with pinhole collimator <NUM> in various examples. Septa <NUM> include a first surface <NUM> proximate to a top plate (e.g., top plate <NUM>, top plate <NUM>; top plate not shown in <FIG>), and a second surface <NUM> proximate to a semiconductor detector (e.g., semiconductor detector <NUM>; semiconductor detector not shown in <FIG>). Cells <NUM>, through which photons pass, are defined between neighboring septa <NUM>. The cells <NUM> are a first width <NUM> at the first surface <NUM>, and a second width <NUM> at the second surface <NUM>, with the second width <NUM> greater than the first width <NUM>. Accoridngly, a first width <NUM> of the septa <NUM> at the first surface <NUM> is greater than a second width <NUM> of the septa <NUM> at the second surface <NUM>. In <FIG>, a pitch <NUM> is defined by the septa <NUM>, with the first width <NUM> less than the pitch <NUM>. The tapered septa <NUM> in various examples may cooperate or be complementary with tapered openings (e.g., openings <NUM>). In various examples, the tapered septa <NUM> may be formed by 3D printing a collimator block. The tapered septa <NUM> provide additional thickness (e.g., relative to septa thickness of a parallel hole collimator) for improved reduction of penetration by photons into adjacent collimator cells. The tapered shape in various examples is configured to facilitate passage of photons over a preferred or desired angular range. It may be noted that while the description above includes top plate <NUM> or <NUM>, the pinholes-array collimator of <FIG> may not include a top plate at all when opening <NUM> is in the desired size of the pinholes openings such as the size of openings <NUM> and <NUM> of <FIG> and <FIG>, respectively.

Examples of solid angles corresponding to the pinhole collimator <NUM> may be seen in <FIG>. As seen in <FIG>, the solid angles defined by virtual sub-pixels may vary based on a depth (or depths) within the semiconductor detector <NUM> assigned to events. For example, solid angles 320a, 320b, and 320c result from using a common absorption depth (e.g., <NUM>/µ, where µ is an aborption coefficient) for events from three adjacent virtual sub-pixels <NUM>. As another example, solid angles 330a, 330b, and 330c result from using varying absorption depths for events from three adjacent virtual sub-pixels <NUM>. In <FIG>, the cell width <NUM> between septa <NUM> of the pinhole collimator equals d, a height <NUM> of the pinhole collimator <NUM> is h/<NUM>, and the opening width <NUM> defined by the pinhole openings <NUM> is d/<NUM>.

By way of comparison, examples of solid angles corresponding to use of a parallel hole collimator may be seen in <FIG>. In <FIG>, a detector system <NUM> includes a parallel hole collimator <NUM> that includes walls <NUM> having a common opening width <NUM> therebetween. The opening width <NUM> defines the width of openings <NUM>. The detector system <NUM> also includes a detector unit <NUM> that includes pixelated anodes <NUM> having virtual sub-pixels <NUM> associated therewith (e.g., by a processing unit). As seen in <FIG>, solid angles 660a, 660b, and 660c result from using a common absorption depth (e.g., at the surface of the detector unit <NUM>) for events from three adjacent virtual sub-pixels <NUM>. As seen in <FIG> and <FIG>, the solid angles (solid angles 320a, 320b, and 320c and/or solid angles 330a, 330b, and 330c) for the pinhole collimator <NUM> have noticeably less overlap than the solid angles for parallel hole collimator <NUM> (solid angles 660a, 660b, and 660c). In <FIG>, the width <NUM> between walls (as well as width of openings <NUM>) is d, and the height <NUM> of the parallel hole collimator <NUM> is h.

Returning to <FIG>, the processing unit <NUM> is operably coupled to the semiconductor detector <NUM>, and is configured to identify detected events, deriving the location of events within physical pixels <NUM> and based on their location, assigning them to virtual sub-pixels <NUM> distributed along a length <NUM> and width <NUM> of the semiconductor detector <NUM> to be counted there. In <FIG>, the virtual sub-pixels <NUM> are represented by dashed lines passing through the semiconductor detector correpsonding to the location of the virtual sub-pixels <NUM>. It may be noted that in <FIG>, the semiconductor detector <NUM> includes pixels <NUM>. In <FIG>, there are <NUM> virtual sub-pixels across a width of each pixel <NUM>. Each pixel <NUM> may be understood as including a pixelated anode <NUM>, with each pixelated anode <NUM> smaller (having a smaller area) than the corresponding pixel <NUM>. In <FIG>, there are <NUM> virtual sub-pixels <NUM> per pixelated anode <NUM> or pixel <NUM> (e.g., a grid of <NUM> x <NUM> virtual sub-pixels <NUM> per pixelated anode <NUM> or pixel <NUM>). Each pixel <NUM> includes a plurality of corresponding virtual sub-pixels, with absorbed photons in the semiconductor detector <NUM> counted as events in a corresponding virtual sub-pixel. Additional discussion regarding virtual sub-pixels and the use of virtual sub-pixels, and the use of collected and non-collected charge signals may be found in <CIT> ("the <NUM> Application); <CIT> ("the <NUM> Application"); and <CIT> ("the <NUM> Application).

In various examples the processing unit <NUM> includes processing circuitry configured to perform one or more tasks, functions, or steps discussed herein. It may be noted that "processing unit" as used herein is not intended to necessarily be limited to a single processor or computer. For example, the processing unit <NUM> may include multiple processors, ASIC's, FPGA's, and/or computers, which may be integrated in a common housing or unit, or which may distributed among various units or housings.

It may be noted that operations performed by the processing unit <NUM> (e.g., operations corresponding to process flows or methods discussed herein, or aspects thereof) may be sufficiently complex that the operations may not be performed by a human being within a reasonable time period. For example, the determination of values of collected, non-collected, and/or combined charge signals within the time constraints associated with such signals may rely on or utilize computations that may not be completed by a person within a reasonable time period.

As discussed, herein, signals are generated by one or more pixelated anodes <NUM> in response to a photon impact, with the location of the pixelated anode(s) <NUM> generating a signal used to determine a corresponding location in the object for which an event is counted. In various examples, as also discussed in the <NUM> Application, the <NUM> Application, and the <NUM> Application, signals from adjacent pixels may be used to assign a virtual sub-pixel location within a given pixelated anode <NUM>. In some examples, the processing unit <NUM> is configured to determine an absorption location for a given absorbed phon based on non-collected signals received from pixelated anodes adjancent to a pixelated anode abosrobing the given absorbed photon.

Additionally or alternatively to the use of virtual pixels along a length and/or width of the semiconductor detector <NUM>, in various examples virtual pixels may be employed along a thickness of the semiconductor detector <NUM>. Virtual pixels employed along a thickness of the semiconductor detector <NUM> may be used to represent different depths of absorption of photons. For example, as best seen in <FIG>, the semiconductor detector <NUM> has a thickness <NUM>. Three rows of virtual pixels are distributed along the thickness <NUM> - a first row <NUM>, a second row <NUM>, and a third row <NUM>. The processing unit <NUM> in various examples is configured to identify detector events with the virtual sub-pixels in the first row <NUM>, second row <NUM>, and third row <NUM> distributed alogn the thickness <NUM>. Accordingly, different virtual sub-pixels along a thickness may be used to provide different absorption depths for identifying event locations. For example, as seen in <FIG>, event 331a is shown at a depth corresponding to the first row <NUM>, event 331b is shown at a depth corresponding to the third row <NUM>, and event 331c is shown at a depth corresponding to the second row <NUM>.

However, it may be noted that, in other examples that may or may not include a pinhole-array collimator, a single absorption depth may be employed. In the, invention, the processing unit <NUM> is configured to count absorbed photons as events within the thickness <NUM> of the semiconductor detector <NUM> at a location (e.g., a distance from the cathode <NUM>) corresponding to one over an absorption coefficient of the semiconductor detector <NUM>. For example, with µ as the absorption coefficient, photons (e.g., photons at a given energy corresponding with the absorption coefficient) may be counted as events at a location in the semiconductor detector a distance <NUM> from the second surface <NUM> (and/or cathode <NUM>) along the thickness <NUM>, as shown for event locations 321a, 321b, and 321c of <FIG>. The distance <NUM> in the invention s is <NUM>/µ. It may be noted that µ may vary based on photon energy. It may further be noted that use of a single absorption depth as discussed herein and in the next paragraph may be used in connection with a pinhole collimator (e.g., pinhole collimator <NUM>) in various embodiments, or may be used in connection with a parallel hole collimator (e.g., parallel hole collimator <NUM>) in other embodiments. In the invention , the absorption location for each photon is defined within a range of <NUM>/µ ± <NUM> millimeter.

As another example of use of a single absorption depth, in some examples , the processing unit <NUM> is configured to count absorbed photons as events within the thickness <NUM> of the semiconductor detector <NUM> at a distance corresponding to an energy window width used to identify the events as photon impacts. For example, in some examples, an absorption location for each absorbed photon within the thickness <NUM> of the semiconductor detector <NUM> is defined within a range such that ΔL/D = ΔE/E, where ΔL is the distance <NUM> from the first surface <NUM> (and/or the cathode <NUM>), D is the detector thickness (e.g., thickness <NUM>), ΔE is an energy window width, and E is a photopeak energy of an absorbed photon. The energy window width in various examples is a range of energies around the photopeak energy which are considered as true events.

<FIG> is a schematic illustration of a NM imaging system <NUM> having a plurality of imaging detector head assemblies mounted on a gantry (which may be mounted, for example, in rows, in an iris shape, or other configurations, such as a configuration in which the movable detector carriers <NUM> are aligned radialy toward the patient-body <NUM>). In particular, a plurality of imaging detectors <NUM> are mounted to a gantry <NUM>. Each detector <NUM> may include, for example, collimators and detectors arranged generally similarly to the arrangements discussed in connection with <FIG>. In <FIG>, the imaging detectors <NUM> are configured as two separate detector arrays <NUM> and <NUM> coupled to the gantry <NUM> above and below a subject <NUM> (e.g., a patient), as viewed in <FIG>. The detector arrays <NUM> and <NUM> may be coupled directly to the gantry <NUM>, or may be coupled via support members <NUM> to the gantry <NUM> to allow movement of the entire arrays <NUM> and/or <NUM> relative to the gantry <NUM> (e.g., transverse translating movement in the left or right direction as viewed by arrow T in <FIG>). Additionally, each of the imaging detectors <NUM> includes a detector unit <NUM> (which may include collimator and/or detector assemblies as discussed herein in connection with <FIG>), at least some of which are mounted to a movable detector carrier <NUM> (e.g., a support arm or actuator that may be driven by a motor to cause movement thereof) that extends from the gantry <NUM>. In some examples, the detector carriers <NUM> allow movement of the detector units <NUM> towards and away from the subject <NUM>, such as linearly.

Thus, in <FIG> the detector arrays <NUM> and <NUM> are mounted in parallel above and below the subject <NUM> and allow linear movement of the detector units <NUM> in one direction (indicated by the arrow L), illustrated as perpendicular to the support member <NUM> (that are coupled generally horizontally on the gantry <NUM>). However, other configurations and orientations are possible as described herein. It should be noted that the movable detector carrier <NUM> may be any type of support that allows movement of the detector units <NUM> relative to the support member <NUM> and/or gantry <NUM>, which in various examples allows the detector units <NUM> to move linearly towards and away from the support member <NUM>.

Each of the imaging detectors <NUM> in various examples is smaller than a conventional whole body or general purpose imaging detector. A conventional imaging detector may be large enough to image most or all of a width of a patient's body at one time and may have a diameter or a larger dimension of approximately <NUM> or more. In contrast, each of the imaging detectors <NUM> may include one or more detector units <NUM> coupled to a respective detector carrier <NUM> and having dimensions of, for example, <NUM> to <NUM> and may be formed of Cadmium Zinc Telluride (CZT) tiles or modules. For example, each of the detector units <NUM> may be 8x8 cm in size and be composed of a plurality of CZT pixelated modules (not shown). For example, each module may be 4x4 cm in size and have 16x16=<NUM> pixels. In some examples, each detector unit <NUM> includes a plurality of modules, such as an array of <NUM> x <NUM> modules. However, different configurations and array sizes are contemplated including, for example, detector units <NUM> having multiple rows of modules.

It should be understood that the imaging detectors <NUM> may be different sizes and/or shapes with respect to each other, such as square, rectangular, circular or other shape. An actual field of view (FOV) of each of the imaging detectors <NUM> may be directly proportional to the size and shape of the respective imaging detector.

The gantry <NUM> may be formed with an aperture <NUM> (e.g., opening or bore) therethrough as illustrated. A patient table <NUM>, such as a patient bed, is configured with a support mechanism (not shown) to support and carry the subject <NUM> in one or more of a plurality of viewing positions within the aperture <NUM> and relative to the imaging detectors <NUM>. Alternatively, the gantry <NUM> may comprise a plurality of gantry segments (not shown), each of which may independently move a support member <NUM> or one or more of the imaging detectors <NUM>.

The gantry <NUM> may also be configured in other shapes, such as a "C", "H" and "L", for example, and may be rotatable about the subject <NUM>. For example, the gantry <NUM> may be formed as a closed ring or circle, or as an open arc or arch which allows the subject <NUM> to be easily accessed while imaging and facilitates loading and unloading of the subject <NUM>, as well as reducing claustrophobia in some subjects <NUM>.

Additional imaging detectors (not shown) may be positioned to form rows of detector arrays or an arc or ring around the subject <NUM>. By positioning multiple imaging detectors <NUM> at multiple positions with respect to the subject <NUM>, such as along an imaging axis (e.g., head to toe direction of the subject <NUM>) image data specific for a larger FOV may be acquired more quickly.

Each of the imaging detectors <NUM> has a radiation detection face, which is directed towards the subject <NUM> or a region of interest within the subject.

In the invention, a multi-bore collimator is constructed to be registered with pixels of the detector units <NUM>, which in one example are CZT detectors. However, other materials may be used. Registered collimation may improve spatial resolution by forcing photons going through one bore to be collected primarily by one pixel. Additionally, registered collimation may improve sensitivity and energy response of pixelated detectors as detector area near the edges of a pixel or in-between two adjacent pixels may have reduced sensitivity or decreased energy resolution or other performance degradation. Having collimator septa directly above the edges of pixels reduces the chance of a photon impinging at these degraded-performance locations, without decreasing the overall probability of a photon passing through the collimator. As discussed herein, in various examples parallel-hole and/or pin-hole collimation may be employed.

A controller unit <NUM> may control the movement and positioning of the patient table <NUM>, imaging detectors <NUM> (which may be configured as one or more arms), gantry <NUM> and/or the collimators <NUM> (that move with the imaging detectors <NUM> in various examples, being coupled thereto). A range of motion before or during an acquisition, or between different image acquisitions, is set to maintain the actual FOV of each of the imaging detectors <NUM> directed, for example, towards or "aimed at" a particular area or region of the subject <NUM> or along the entire subject <NUM>. The motion may be a combined or complex motion in multiple directions simultaneously, concurrently, or sequentially as described in more detail herein.

The controller unit <NUM> may have a gantry motor controller <NUM>, table controller <NUM>, detector controller <NUM>, pivot controller <NUM>, and collimator controller <NUM>.

The controllers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be automatically commanded by a processing unit <NUM>, manually controlled by an operator, or a combination thereof. The gantry motor controller <NUM> may move the imaging detectors <NUM> with respect to the subject <NUM>, for example, individually, in segments or subsets, or simultaneously in a fixed relationship to one another. For example, the gantry controller <NUM> may cause the imaging detectors <NUM> and/or support members <NUM> to move relative to or rotate about the subject <NUM>, which may include motion of less than or up to <NUM> degrees (or more). The table controller <NUM> may move the patient table <NUM> to position the subject <NUM> relative to the imaging detectors <NUM>. The patient table <NUM> may be moved in up-down directions, in-out directions, and right-left directions, for example. The detector controller <NUM> may control movement of each of the imaging detectors <NUM> to move together as a group or individually as described in more detail herein. The detector controller <NUM> also may control movement of the imaging detectors <NUM> in some examples to move closer to and farther from a surface of the subject <NUM>, such as by controlling translating movement of the detector carriers <NUM> linearly towards or away from the subject <NUM> (e.g., sliding or telescoping movement). Optionally, the detector controller <NUM> may control movement of the detector carriers <NUM> to allow movement of the detector array <NUM> or <NUM>. For example, the detector controller <NUM> may control lateral movement of the detector carriers <NUM> illustrated by the T arrow (and shown as left and right as viewed in <FIG>). In various examples, the detector controller <NUM> may control the detector carriers <NUM> or the support members <NUM> to move in different lateral directions. Detector controller <NUM> may control the swiveling motion of detectors <NUM> together with their collimators <NUM>.

The pivot controller <NUM> may control pivoting or rotating movement of the detector units <NUM> at ends of the detector carriers <NUM> and/or pivoting or rotating movement of the detector carrier <NUM>. For example, one or more of the detector units <NUM> or detector carriers <NUM> may be rotated about at least one axis to view the subject <NUM> from a plurality of angular orientations to acquire, for example, 3D image data in a 3D SPECT or 3D imaging mode of operation. The collimator controller <NUM> may adjust a position of an adjustable collimator, such as a collimator with adjustable strips (or vanes) or adjustable pinhole(s).

It should be noted that motion of one or more imaging detectors <NUM> may be in directions other than strictly axially or radially, and motions in several motion directions may be used in various examples. Therefore, the term "motion controller" may be used to indicate a collective name for all motion controllers. It should be noted that the various controllers may be combined, for example, the detector controller <NUM> and pivot controller <NUM> may be combined to provide the different movements described herein.

Prior to acquiring an image of the subject <NUM> or a portion of the subject <NUM>, the imaging detectors <NUM>, gantry <NUM>, patient table <NUM> and/or collimators <NUM> may be adjusted, such as to first or initial imaging positions, as well as subsequent imaging positions. The imaging detectors <NUM> may each be positioned to image a portion of the subject <NUM>. Alternatively, for example in a case of a small size subject <NUM>, one or more of the imaging detectors <NUM> may not be used to acquire data, such as the imaging detectors <NUM> at ends of the detector arrays <NUM> and <NUM>, which as illustrated in <FIG> are in a retracted position away from the subject <NUM>. Positioning may be accomplished manually by the operator and/or automatically, which may include using, for example, image information such as other images acquired before the current acquisition, such as by another imaging modality such as X-ray Computed Tomography (CT), MRI, X-Ray, PET or ultrasound. In some examples, the additional information for positioning, such as the other images, may be acquired by the same system, such as in a hybrid system (e.g., a SPECT/CT system). Additionally, the detector units <NUM> may be configured to acquire non-NM data, such as x-ray CT data. In some examples, a multi-modality imaging system may be provided, for example, to allow performing NM or SPECT imaging, as well as x-ray CT imaging, which may include a dual-modality or gantry design as described in more detail herein.

After the imaging detectors <NUM>, gantry <NUM>, patient table <NUM>, and/or collimators <NUM> are positioned, one or more images, such as three-dimensional (3D) SPECT images are acquired using one or more of the imaging detectors <NUM>, which may include using a combined motion that reduces or minimizes spacing between detector units <NUM>. The image data acquired by each imaging detector <NUM> may be combined and reconstructed into a composite image or 3D images.

In one example, at least one of detector arrays <NUM> and/or <NUM>, gantry <NUM>, patient table <NUM>, and/or collimators <NUM> are moved after being initially positioned, which includes individual movement of one or more of the detector units <NUM> (e.g., combined lateral and pivoting movement) together with the swiveling motion of detectors <NUM>. For example, at least one of detector arrays <NUM> and/or <NUM> may be moved laterally while pivoted. Thus, in various examples, a plurality of small sized detectors, such as the detector units <NUM> may be used for 3D imaging, such as when moving or sweeping the detector units <NUM> in combination with other movements.

In various examples, a data acquisition system (DAS) <NUM> receives electrical signal data produced by the imaging detectors <NUM> and converts this data into digital signals for subsequent processing. However, in various examples, digital signals are generated by the imaging detectors <NUM>. An image reconstruction device <NUM> (which may be a processing device or computer) and a data storage device <NUM> may be provided in addition to the processing unit <NUM>. It should be noted that one or more functions related to one or more of data acquisition, motion control, data processing and image reconstruction may be accomplished through hardware, software and/or by shared processing resources, which may be located within or near the imaging system <NUM>, or may be located remotely. Additionally, a user input device <NUM> may be provided to receive user inputs (e.g., control commands), as well as a display <NUM> for displaying images. DAS <NUM> receives the acquired images from detectors <NUM> together with the corresponding lateral, vertical, rotational and swiveling coordinates of gantry <NUM>, support members <NUM>, detector units <NUM>, detector carriers <NUM>, and detectors <NUM> for accurate reconstruction of an image including 3D images and their slices.

It should be noted that the various examples may be implemented in hardware, software or a combination thereof. The various examples and/or components, for example, the modules, or components and controllers therein, also may be implemented as part of one or more computers or processors. The computer or processor may include a computing device, an input device, a display unit and an interface, for example, for accessing the Internet. The computer or processor may include a microprocessor. The microprocessor may be connected to a communication bus. The computer or processor may also include a memory. The memory may include Random Access Memory (RAM) and Read Only Memory (ROM). The computer or processor further may include a storage device, which may be a hard disk drive or a removable storage drive such as a solid-state drive, optical disk drive, and the like. The storage device may also be other similar means for loading computer programs or other instructions into the computer or processor.

As used herein, the term "computer" or "module" may include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC), ASICs, logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term "computer".

The computer or processor executes a set of instructions that are stored in one or more storage elements, in order to process input data. The storage elements may also store data or other information as desired or needed. The storage element may be in the form of an information source or a physical memory element within a processing machine.

The set of instructions may include various commands that instruct the computer or processor as a processing machine to perform specific operations such as the methods and processes of the various examples which do not form part of the presently claimed invention. The set of instructions may be in the form of a software program. The software may be in various forms such as system software or application software and which may be embodied as a tangible and non-transitory computer readable medium. Further, the software may be in the form of a collection of separate programs or modules, a program module within a larger program or a portion of a program module. The software also may include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to operator commands, or in response to results of previous processing, or in response to a request made by another processing machine.

Instead, the use of "configured to" as used herein denotes structural adaptations or characteristics, and denotes structural requirements of any structure, limitation, or element that is described as being "configured to" perform the task or operation. For example, a processing unit, processor, or computer that is "configured to" perform a task or operation may be understood as being particularly structured to perform the task or operation (e.g., having one or more programs or instructions stored thereon or used in conjunction therewith tailored or intended to perform the task or operation, and/or having an arrangement of processing circuitry tailored or intended to perform the task or operation). For the purposes of clarity and the avoidance of doubt, a general purpose computer (which may become "configured to" perform the task or operation if appropriately programmed) is not "configured to" perform a task or operation unless or until specifically programmed or structurally modified to perform the task or operation.

As used herein, the terms "software" and "firmware" are interchangeable, and include any computer program stored in memory for execution by a computer, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and nonvolatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program.

Claim 1:
A detector assembly (<NUM>) including:
a semiconductor detector (<NUM>) having a first surface (<NUM>) and a second surface (<NUM>) opposed to each other, the first surface (<NUM>) including pixels (<NUM>) containing pixelated anodes (<NUM>), and the second surface (<NUM>) comprising a cathode electrode (<NUM>);
a collimator (<NUM>) including openings (<NUM>), each opening associated with a single corresponding pixel (<NUM>) of the semiconductor detector (<NUM>); and
a processing unit (<NUM>) configured to identify detected events within virtual sub-pixels (<NUM>) distributed along a length (<NUM>) and width (<NUM>) of the semiconductor detector (<NUM>),
wherein each pixel (<NUM>) comprises a plurality of corresponding virtual sub-pixels (<NUM>),
characterized in that the processing unit (<NUM>) is configured to assign absorbed photons as events in a corresponding virtual sub-pixel (<NUM>),
wherein absorbed photons are counted as events within a thickness (<NUM>) of the semiconductor detector (<NUM>) defined within an average absorption depth of <NUM>/µ±<NUM>, where µ is the absorption coefficient for a specific photon energy for a particular detector material.