Detector array with pre-focused anti-scatter grid

A radiation sensitive detector array includes a plurality of detector modules (118) extending along a z-axis direction and aligned along an x-axis direction with respect to the imaging system (100). At least one of the detector modules (118) includes a module backbone (124) and at least one detector tile (122). The at least one detector tile (122) is coupled to the module backbone (124) through a non-threaded fastener (142). The at least one detector tile (122) includes a two-dimensional detector (126) and a two-dimensional anti-scatter grid (128) that is focused at a focal spot (112) of an imaging system (100).

The following generally relates to a detector array with an anti scatter grid, and finds particular application to computed tomography (CT). However, it also amenable to other medical imaging applications and to non-medical imaging applications.

Generally, a computed tomography (CT) scanner includes an x-ray tube and a detector array. The x-ray tube emits radiation from a focal spot, and the emitted radiation traverses an examination region. The detector array is disposed across from the x-ray tube on an opposite side of the examination region and detects radiation traversing the examination region. The detector array converts detected radiation into a signal indicative of the detected radiation. A reconstructor reconstructs the signal to generate volumetric image data thereof. An image generator generates one or more images of a scanned subject or object based on the volumetric image data.

With one CT system, the detector array includes a plurality of detector modules, each having a plurality of photosensor blocks. Each photosensor block is a stacked structure consisting of an anti-scatter grid (ASG), a scintillator array, a photosensor array, processing electronics, and a base. The photosensor blocks are first assembled and then used to populate detector modules. The base of each photosensor block includes a threaded recess, and each photosensor block is installed in a detector module by aligning the threaded recess of a photosensor block with a hole machined in the module backbone, inserting a screw through the hole to the recess, and engaging the screw with the threaded recess.

Unfortunately, the alignment of the ASG of a photosensor block with the focal spot depends on the accuracy of the machining of the hole in the module backbone and the accuracy of the assembly of each stacked photosensor block as the stacking of the individual components of each photosensor block may introduce, propagate and/or magnify a stacking error. The foregoing may lead to non-negligible errors in the alignment of an ASG in the detector module and hence with the focal spot, and poor alignment of an ASG with the focal spot can cause detector shadowing, which in turn can cause artifacts such as rings in the CT image.

Aspects of the present application address the above-referenced matters and others.

According to one aspect, a radiation sensitive detector array includes a plurality of detector modules extending along a z-axis direction and aligned along an x-axis direction with respect to the imaging system. At least one of the detector modules includes a module backbone and at least one detector tile. The at least one detector tile is coupled to the module backbone through a non-threaded fastener. The at least one detector tile includes a two-dimensional detector and a two-dimensional anti-scatter grid that is focused at a focal spot of an imaging system.

According to another aspect, a detector array of an imaging system with a focal spot includes a plurality of detector modules aligned along a transverse direction with respect to the imaging system. At least one of the detector modules includes a detector tile. The detector tile includes a two-dimensional anti-scatter grid that is focused with respect to the focal spot of the imaging system before installing the at least one detector module in the imaging system.

According to another aspect, a method aligns an anti-scatter grid of a detector tile with a focal spot of an imaging system prior to installing the anti-scatter grid in the imaging system. The method includes inserting at least one two-dimensional anti-scatter grid in a guide region of an alignment apparatus. The guide region including one or more fiducials that guide the at least one two-dimensional anti-scatter grid in the guide region. The guide region being pre-aligned with the focal spot, and guiding the at least one two-dimensional anti-scatter grid into the guide region focuses the at least one two-dimensional anti-scatter grid with the focal spot.

According to another aspect, an alignment apparatus for focusing anti-scatter grids with a focal spot of an imaging system outside of the imaging system. The alignment apparatus includes at least one guide region configured to receive an anti-scatter grid and focus the anti-scatter grid with respect to the focal spot.

FIG. 1illustrates an imaging system100such as a computed tomography (CT) scanner. The imaging system100includes a stationary gantry102and a rotating gantry104, which is rotatably supported by the stationary gantry102. The rotating gantry104rotates around an examination region106about a longitudinal or z-axis108.

A radiation source110, such as an x-ray tube, is supported by and rotates with the rotating gantry104around the examination region106. The radiation source110emits radiation from a focal spot112. A collimator114collimates the emitted radiation to produce a generally fan, wedge, or cone shaped radiation beam that traverses the examination region106.

A radiation sensitive detector array116detects radiation that traverses the examination region106and generates a signal indicative thereof. The radiation sensitive detector array116includes a plurality of detector modules118aligned in parallel in a transverse (x/y direction) and carried by a module cradle120. A detector module118includes one or more detector mosaics or tiles122aligned along a detector module backbone124in parallel along the z-axis108.

A tile122includes a two-dimensional detector126and a two-dimensional anti-scatter grid (ASG)128. The illustrated detector126includes a scintillator array130, a photosensor array132(with a two-dimensional arrangement of photo sensing pixels such as photodiodes or other optical sensors), a substrate134, processing electronics136, and a base138. As shown inFIG. 2, the ASG128includes a plurality of channels202defined by intersecting walls204and206that extend in the transverse and longitudinal directions. A one-dimensional ASG is also contemplated herein.

Returning toFIG. 1, the scintillator array130is optically coupled to the photosensor array132, and the photosensor array132is electrically coupled to the processing electronics136on the substrate134. The processing electronics136includes an application specific integrated circuit (ASIC) and/or other integrated circuit. An input/output (I/O) contact(s) (not shown) is in electrical communication with the processing electronics136. The ASG128is affixed to the scintillator array130on a side of the incoming radiation.

The ASG128allows transmission radiation to pass through and illuminate the scintillator array130and attenuates a substantial amount of scatter radiation that would otherwise illuminate the scintillator array130. The scintillator array130detects the radiation traversing the channels of the ASG128and generates a light signal indicative thereof. The photosensor array132detects the light signal and generates an electrical signal indicative of the detected radiation. The processing electronics136process the electrical signal. The processed signal (and/or the unprocessed electrical signal) is conveyed off the tile detector122via the I/O contact(s). Note that the I/O contact(s) is also used to convey a signal(s) to the tile detector122.

The module backbone124includes one or more tile receiving regions140. In the illustrated embodiment, tiles122are affixed to the tile receiving regions140with a fastener142such as an adhesive like a thermally conductive epoxy or the like. Another suitable fastener includes a low melting point metal or alloy. Before affixing the tiles122to the module backbone124, the ASGs128are focused (or pre-focused) with respect to the focal spot112and aligned with respect to each other. As described in greater detail below, the ASGs128are focused and aligned as such and the tiles122are affixed to the module backbone124using an alignment apparatus.

Tile-populated modules118are affixed to the scanner100. In the illustrated embodiment, the module118includes a fastening region144with a material free region146. An example fastener148is shown extending through the material free region146. In one instance, the module118is affixed to the cradle120using the fastener148or other fastener and the material free region146. By way of example, where the fastener148is a screw or the like, the screw engages a threaded recess (with threads complementary to the threads of the screw) in the cradle120and removably secures the module118to the cradle120.

As noted above, the radiation sensitive detector array116detects radiation and generates a signal indicative thereof. A reconstructor150reconstructs the signal and generates volumetric image data indicative thereof. A patient support154, such as a couch, supports the patient in the examination region106for the scan. A general purpose computing system152serves as an operator console. Software resident on the console allows the operator to control the operation of the system100, such as select a scan protocol, initiate and/or terminate a scan, etc.

FIG. 3illustrates an example alignment apparatus300. The apparatus300includes one or more module backbone mounting regions302. The module backbone mounting regions302are configured to be physically substantially similar to the module mounting regions of the cradle120and are configured for mechanically interfacing the fastening regions144(FIG. 1) of the module backbone124.

The above allows for focusing the ASGs128at the focal spot112while installing tiles122in the apparatus300and affixing the tiles122to the module backbone124. The illustrated backbone mounting region302include recesses306, which are adapted to engage the fasteners148(FIG. 1). An alignment fiducial304facilitates aligning the module backbone124with the module backbone mounting region302. In another embodiment, the alignment fiducial304is omitted.

The apparatus300further includes one or more guide regions308. A guide region308includes one or more alignment fiducials, including one or more alignment features310and an alignment surface312. The alignment fiducials310and312support and guide an anti-scatter grid128in the apparatus300. The alignment features310are configured to guide an outside surface of the sidewalls of an ASG128as the ASG128or the corresponding tile122is inserted in the apparatus300.

Note that the dashed lines between the pairs of features310are for illustrative purposes and are not part of the alignment features310. In addition, note that the number of illustrated alignment features310is for explanatory purposes and not limiting.

The tile alignment surface312is adapted to contact a side of the ASG128facing the incoming radiation. The alignment surfaces312are configured with respect to the module backbone mounting region302, and hence the cradle120, and facilitate orienting the ASGs128with respect to the module backbone mounting region302to focus the ASGs128at the focal spot112. As a result, installing an ASG128into the region308pre-focuses the ASG128with respect to the focal spot112.

FIG. 4illustrates an example method.FIGS. 5-8graphically illustrate acts of the method.

Initially referring toFIGS. 4 and 5, at402tiles122are installed in the guide regions308of the alignment apparatus300. As noted above, the alignment fiducials310and312guide the tile122in the guide regions308, aligning the ASGs128of the tiles122with respect to each other and with respect to the module backbone mounting regions302, which focuses the ASGs128of the tiles122at the focal spot112. The alignment of the ASGs128can be tested as described in greater detail below.

With respect toFIGS. 4 and 6, at404the fastener142is applied to the bases138of the tiles122. In the illustrated embodiment, the fastener142is a screw-less fastener such as a thermally conductive adhesive or other screw-less fastener.

With respect toFIGS. 4 and 7, at406the module backbone124is mounted to the alignment apparatus300. In the illustrated embodiment, the backbone124is mounted thereto utilizing the fastener148. Mounting the module backbone124as such brings the fastener142into physical contact with the tile fastening regions140of the backbone124.

Stacking errors present in the tiles122can be compensated for through the fastener142. By way of example, as the fastener142engages a tile fastening regions144, the fastener142is compressed and excess fastener142is squeezed out from between the tile122and the tile fastening region144. As such, differences in thickness of the stacked tiles122will result in difference thickness of the fastener142. In addition, the fastener142also mitigates mechanical errors due to machining inaccuracies in the module backbone124as with configurations in which a screw is used to mount the tiles122to the backbone124. As such, detector shadowing and artifacts such as rings in the CT image can be mitigated.

With respect toFIGS. 4 and 8, at408the assembled module118is removed from the alignment apparatus300. With respect toFIG. 4, at410the assembled module118can be installed in the scanner100.

Variations and/or alternatives are discussed.

In the illustrated embodiment, the detector126is a scintillator/photosensor type detector. In another embodiment, the detector126includes a direct conversion material such as Cadmium Telluride (CdTe), Cadmium Zinc Telluride (CZT), etc.

FIG. 9shows another non-limiting embodiment of the alignment apparatus300. In this embodiment, at least one of the guide regions308includes at least one alignment feature902, and the alignment features310are omitted. Unlike the alignment features310, the at least one alignment features902is configured to contact an inner portion of the ASGs128such as one or more of the walls204or206of the ASGs128. In another embodiment, both of the alignment features310and902and/or other alignment fiducials are used. In yet another embodiment, other alignment fiducials can be used.

In the embodiments of the module118illustrated in connection withFIGS. 1,3,7and8, the tiles122are permanently affixed to the module backbone124through the fastener142.FIGS. 10 and 11illustrate alternative configurations in which the tiles122are removably affixed to the module backbone124. With respect toFIG. 10, the tile receiving region140of the module backbone124includes a recess1002followed by a material free region1004. The base138of the tile122includes first and second sub-portions1381and1382, having generally planar inner sides1008and1010that face each other and mate together. The second sub-portion1382includes a threaded recess1006on a side opposite of the inner side1010.

The second sub-portion1382is secured to the module backbone124utilizing the recess1002, the material free region1004, and the threaded recess1006. By way of example, the fastener148can be a screw or the like, and can be used to secure the second sub-portion1382to the module backbone124by extending though the recess1002and material free region1004and engaging the threaded recess1006.

With this embodiment, the second sub-portion1382is affixed to the module backbone124via the fastener148. The first sub-portion1381is then affixed to the second sub-portion and1382, thereby affixing the tile122to the module backbone124and forming the module118. A particular tile122can be removed from the module backbone124via removing the fastener148.

FIG. 11is similar toFIG. 10except that inner sides1008and1010are non-planar and have a greater surface area. The larger surface area allows for greater heat transfer and therefore the temperature drop across the adhesive. In the illustrated embodiment, the surface area is increased by making interlocking fins on the upper and lower base sections1381and1382. Other shapes are also contemplated herein.

With bothFIGS. 10 and 11, the upper and lower sections1381and1382can be formed from a metal such as aluminum or from another material. Since module accuracy is achieved with the fastener148, the upper and lower sections1381and1382need not be highly accurate. The upper and lower sections1381and1382can therefore be made by lower cost methods such as casting, extrusion or the like.

FIG. 12illustrates an apparatus1200for testing the alignment of the ASGs128installed in the alignment apparatus300. In this example, the ASGs128are installed in the alignment apparatus300as described herein using the alignment fiducials310,312and/or902. Before affixing the detectors126to the ASGs128, an ASG alignment test fixture1200is mounted to the module backbone mounting regions302.

The alignment test fixture1200includes a moveable detector1202, which can be selectively positioned with respect to a particular installed ASG128, for example, ASG1281in the illustrated embodiment. Radiation is projected through the corresponding ASG128to the detector1202. The focal spot112can be moved during testing, and ASG shadowing can be evaluated based on the signal output of the detector1202.

In another embodiment, the apparatus1200is used to test tiles122(rather than just ASGs128) installed in the alignment apparatus300. Likewise, the tiles122are installed in the alignment apparatus300as described herein using the alignment fiducials310,312and/or902. Radiation is similarly projected through the corresponding tile122to the detector1202, and ASG shadowing can be evaluated based on the signal output of the detector1202.

In another embodiment, a film1204is additionally or alternatively used in place of the detector1202.

Being able to pre-test an ASG128before mounting it to a detector126and/or pre-test a tile122before mounting the tile122to a module backbone124can reduce costs as faulty parts can be detected before the tile122and/or the module118are fully assembled.

The apparatus1200can be formed from a reasonably x-ray transparent material such as aluminum.

The detector array116described herein is applicable to various imaging applications, including CT scanners and/or other modality scanners. More particularly, it is well suited for applications in which each tile122of the detector array116has its own ASG128and is separately mounted to the module backbone124.

The invention has been described herein with reference to the various embodiments. Modifications and alterations may occur to others upon reading the description herein. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.