Quality control device

Abstract

A quality control device (QCD) for use in generating a quality control image in a gamma ray medical imaging camera (GRMIC); a kit of parts for making said QCD; and use of said QCD to obtain an image in a GRMIC.

Description

[0001] QUALITY CONTROL DEVICE

[0002] Field of the invention

[0003] This invention relates to a quality control device (QCD). In particular, though not exclusively, the invention relates to a quality control device using gamma rays in medical imaging, as well as methods of using the same.

[0004] Background of the invention

[0005] Gamma ray medical imaging cameras (also called y-cameras, scintillation cameras or SPECT cameras) are used in medical imaging to image gamma radiation being emitted from radioisotopes.

[0006] In gamma ray medical imaging radioisotopes are commonly attached to tracer agents or drugs (radiopharmaceuticals), which travel to specific organs or tissues. In that way those target tissues can be imaged using gamma ray medical imaging cameras (GRMICs). So, this technique can create visual representations of the interior of the target for clinical analysis and medical intervention, as well as visual representation of the function of organs or tissues.

[0007] GRMICs are typically large and expensive and so are usually housed in a bespoke room in a hospital. To be scanned, patients are typically required to go to the location of the GRMIC and are inserted into the body of the device.

[0008] The person skilled in the art is aware of how GRMICs work, and so this will not be detailed here. However, by way of summary, and without wishing to be bound by theory, one way GRMICs work is by converting gamma rays into visible light rays and it is those visible light rays that are detected by a visible light detector.

[0009] A problem faced in gamma ray medical imaging is to ensure that the gamma ray camera is set up correctly when it is first manufactured and / or after it is assembled. Also, there is a need to monitor the performance of gamma ray cameras over time, to ensure that the gamma ray camera continues to operate optimally. If this initial calibration and periodic quality control is not done, images produced would be sub-optimal and any deterioration in image quality over time would not be detected and this could adversely affect patient outcomes.

[0010] GRMIC performance testing typically comprises acquiring test images using a uniform radioactive source material (a 'flood source') to create a 'flood image' which may be inspected for areas of non- uniformity such as 'hot' (more intense) or 'cold' (less intense) regions, and an image of a 'bar phantom' which is created by placing a lead or tungsten mask with regular windows between the flood source and the GRMIC. The bars (windows) of a bar phantom of the prior art are typically arranged in a grid comprising a quadrant pattern with bars of the same size in each quadrant, with precise spacing between them. This pattern allows for the evaluation of the intrinsic resolution, extrinsic resolution and linearity of the gamma camera's imaging capabilities. Flood and bar phantoms are typically large because they are designed such their dimensions match those of the large camera heads employed on large GRMICs.

[0011] Examples of bar phantoms include those available from gamma camera manufacturers such as GE Healthcare and MiE and other suppliers such as Mirion Medical, BritecTechnologies, or Gamma Gurus.

[0012] It is against this background that the present invention has arisen. There remains a need in the art for improved solutions to the problem of reliable gamma ray imaging, and especially in high resolution gamma ray imaging. In particular, there is a need to evaluate and potentially optimise the performance of gamma ray cameras used in medical imaging, especially when the camera is first manufactured, first assembled, first installed and / or first used, and periodically thereafter.

[0013] Summary of the invention

[0014] In a first aspect of the invention, there is provided a quality control device (QCD) for use in generating a quality control image in a gamma ray medical imaging camera (GRMIC) comprising a pinhole collimator, wherein the QCD comprises: a radiation body adapted to receive gamma rays, wherein the radiation body comprises a radiation wall which is substantially opaque to the gamma rays; a plurality of elongate windows in the radiation wall, which permit the gamma rays to travel through the radiation wall; an alignment point which the elongate windows extend radially therefrom, and wherein, in use: when the QCD cooperates with the GRMIC, and gamma rays originate from the radiation body, then the gamma rays are permitted to travel through the elongate windows to the GRMIC, which can then generate the quality control image useful in assessing the imaging performance of the GRMIC.

[0015] As explained further herein below, the present invention provides a quality control device useful in assessing the image quality produced by a GRMIC, in particular one employing a pinhole collimator. The invention may be useful with any GRMIC comprising a collimator with an angular field of view, inclusive of a GRMIC comprising more than one collimator and / or inclusive of a GRMIC comprising diverging or converging collimators. The QCD can help to assess defects in a GRMIC, which might otherwise give rise to sub-optimal images, such as blurred or distorted images.

[0016] In use when the invention contains gamma rays or a gamma ray source (e.g. the gamma rays are generated in situ in the radiation body, or gamma rays pass into the radiation body from another source, such as an external source) and the invention is coupled to a gamma ray camera apparatus, the radiation will exit the radiation body, pass through the elongate windows and illuminate the gamma ray camera with gamma rays. As such, regardless of the ultimate source of the gamma rays, from the perspective of the GRMIC, the gamma rays will originate from the radiation body. If the gamma ray camera is working correctly the image produced in the GRMIC should correspond to the elongate windows of the invention. The image produced by the gamma ray camera can then be assessed by the camera operator (e.g. a technician or medical imaging professional). If the image generated by the camera is acceptable, the camera operator can continue to use the camera as needed. However, if necessary, the camera operator can take the necessary steps to adjust the camera until an acceptable quality control image is produced by the camera, or otherwise subject the camera to maintenance or repair. The camera operator may be provided with a reference image to conveniently compare this to the image generated by the GRMIC when using the invention. The invention may also be provided with instructions for the camera operator to follow when using the invention.

[0017] Advantageously, because the invention has a plurality of elongate windows extending radially from the alignment point, this means a pinhole collimator aligned with the alignment point will have a direct line of sight through every elongate window substantially regardless of: (a) the position of the windows on the radiation wall; (b) the proximity to the pinhole to the radiation wall; (c) the angular field of view of the camera; and / or (d) thickness of the radiation wall. Conditions (a) to (d) highlighted above can be particularly problematic in small GRMICs employing a pinhole collimator. This advantage can be seen experimentally if the radiation wall of the QCD is replaced with a prior art mask having quadrants of parallel straight windows, where the lines in each quadrant are orthogonal to the lines in the quadrants adjacent to them. This is discussed herein below with reference to Figure 6. In brief, the image (e.g. Fig. 6(b)) produced using the embodiment of the radiation wall (e.g. Fig. 6(a)) of the invention is superior to the image (e.g. Fig. 6(d)) produced by the prior art mask having quadrants of parallel straight windows (e.g. Fig. 6(c)). The problem associated with the prior art mask with quadrants of parallel straight windows is discussed more with reference to the phenomena shown in Figure 7 herein below.

[0018] In an embodiment, each elongate window comprises a length along its elongate dimension, a width which is substantially perpendicular to its length, and a depth in the radiation wall.

[0019] In an embodiment, the radiation wall is substantially planar, and the depth is substantially perpendicular to the plane of the radiation wall. In an embodiment the plane of the radiation wall is square, rectangular, circular, oval, polygonal (e.g. hexagonal), L-shaped or otherwise irregular. In an embodiment, the radiation wall has a longest dimension of 40 to 120mm, optionally 60 to 100mm, further optionally 70 to 90mm.

[0020] In an embodiment the window comprises a region which is not transparent to light rays but is transparent to gamma rays.

[0021] In an embodiment the length of the windows is in the range 1 to 100mm, optionally 5 to 60mm, and further optionally 10 to 30mm.

[0022] In an embodiment, the windows are substantially the same length. In an embodiment, the windows are spaced away from the alignment point by substantially the same distance.

[0023] In an embodiment the width of the windows is in the range 0.5 to 10mm, optionally 1 to 6mm, and further optionally 2 to 5mm.

[0024] In an embodiment the width of the smallest window is in the range 0.5 to 2mm. In an embodiment the width of the largest window is in the range 3 to 7mm. In an embodiment two windows are 2mm, two windows are 3mm, two windows are 4mm and two windows are 5mm.

[0025] In an embodiment the depth of the windows is in the range 0.5 to 10mm, optionally 1 to 8mm, and further optionally 3 to 5mm. In an embodiment the windows are rectangular or lozenge shaped. In an embodiment, the length of the windows is larger than the width of the windows. In an embodiment, the length is at least 2, 3, 5, 10, 20, 50 or 100 times larger than the width of the window. In an embodiment, the windows comprise equal or less than 30%, 20% 10%, 5%, 1%, 0.5% or 0.25% of the surface area of the plane of the radiation wall.

[0026] In an embodiment, the depth of each elongate window defines a path through the radiation wall. In an embodiment the windows may be fully open, filled or partially filled. In an embodiment the filling material may be different to the material that the radiation wall is made of (e.g. the radiation wall may be made of lead and the windows may comprise a plastic filler material). In an embodiment the windows may be sections etched into, or milled out of, the radiation wall, but optionally where these windows do not pass all the way through the radiation wall. In an embodiment the radiation wall is made without removing material from the radiation wall, such as being cast in one piece or 3D printed.

[0027] In an embodiment, each path through the radiation wall is an angled path through the radiation wall. In an embodiment, the path is angled with respect to the plane of the radiation wall. In an embodiment, each path through the radiation wall is greater than the thickness of the radiation wall.

[0028] In an embodiment, each path through the radiation wall is configured to substantially align with the field of view of the pinhole camera. In an embodiment, the longest dimensions of a window are parallel. In an embodiment, the windows (or the end of the windows) are aligned / chamfered to accommodate the field of view of the pinhole camera. In an embodiment, the path through the radiation wall corresponds to a rectangular prism or a parallelogram prism (parallelepiped).

[0029] It is envisioned that the QCD is for use with a GRMIC that comprises a pinhole collimator and the QCD is adapted to work with the GRMIC. In one embodiment the QCD is constructed to work with a specific GRMIC, or is constructed to work with more than one specific GRMIC. In an embodiment, the QCD comprises an adaptor to work with a specific GRMIC, or various adaptors to work with more than one specific GRMIC.

[0030] Advantageously, the path through the radiation wall can be arranged to be at an angle such that the gamma rays are able to pass through substantially the whole width of the window. For example, if the path through the radiation wall is not angled sympathetically, then effectively the depth (i.e. the sides that frame the path through the radiation wall) can partially occlude the free passage of radiation through the full width of the window (e.g. see Fig. 7). In an embodiment, in use the alignment point is configured to be centred relative to the pinhole collimator of the camera. In an embodiment, in use the alignment point is configured to be centred over the pinhole collimator of the camera. Advantageously, this enables the radially aligned elongate windows to be sympathetically aligned with the pinhole. For example, it may be possible for the alignment point not to be centrally located with respect to the radiation wall (the wall may be rectangular), but nevertheless in use, it is envisioned that the alignment point will be arranged to be substantially centred over the pinhole of the GRMIC. Advantageously, this allows for reproducible positioning of the QCD, and so allows for potential automatic assessments.

[0031] In an embodiment, the alignment point is located on the radiation wall. In an embodiment, the alignment point is located centrally on the radiation wall. In an embodiment the alignment point is located in the centre of a substantially circular island area in the radiation wall. In an embodiment the island can be any shape, including but not limited to substantially oval, star-shaped, rectangular, square (or other 4-sided shapes like rhombus, trapezoid etc.) regular or irregular polygonal shapes e.g. pentagonal hexagonal, octagonal etc. In an embodiment, the radiation wall comprises more than one alignment point, wherein each alignment point has a plurality of elongate windows radiating out therefrom.

[0032] In an embodiment, in use the radiation wall is configured to be spaced away from the pinhole of the camera such that all of the elongate windows are substantially within the field of view of the camera. In an embodiment, the windows substantially occupy the whole field of view of the camera. In an embodiment the QCD may comprise a spacing member, such as a lip portion, that can be used to space the radiation wall at a reproducible distance away from the pinhole and at a reproducible orientation. In an embodiment, in use the plane of the radiation wall that is closest to the pinhole is separated from the opening of the pinhole by 2 to 10cm, optionally 3 to 8cm, or further optionally 4 to 6 cm. In an embodiment, in use the plane of the radiation wall that is closest to the pinhole is equal or less than 10, 5, 4, 3, 2, 1 cm from the opening of the pinhole. In an embodiment the lip portion is reversibly removable and / or modular.

[0033] Advantageously, in use the QCD is arranged such that substantially the whole of the sensor of the GRMIC is used to form the image of the QCD. Pinhole collimators tend to produce images fitting within a circular area, whereas the sensors in gamma ray cameras tend to have a square detection area. It is best to optimise the set up such that any image generated fills as much of the sensor as possible, e.g. the square area fits within the circular area mentioned above and the windows fill as much of the 'square' area as possible. As such, the QCD should be optimised such that in use, when coupled with the imaging camera, the QCD is arranged to be suitably spaced away from the pinhole of the camera (e.g. using a spacing lip member), such that the light passing through the windows of the QCD will fill the square area of the sensor mentioned above. Advantageously, using the entire sensor preserves the most information and best possible image resolution.

[0034] In an embodiment, each elongate window is spaced apart from an adjacent elongate window by a spacing distance which is smaller, equal to, or greater than its width. In an embodiment, each elongate window is spaced apart from an adjacent elongate window by a spacing distance which is equal to, or greater than its width. In an embodiment, where adjacent windows are not the same width, the windows are spaced apart by a spacing distance which is equal to, or greater than the smaller width.

[0035] It should be noted that as the elongate windows approach the alignment point the separation between adjacent windows narrows. Advantageously, to ensure each window is distinctly detected by the imaging camera, adjacent windows should be spaced apart along their full length. In an embodiment, the elongate windows do not merge together.

[0036] In an embodiment, the QCD comprises 2 to 20, 3 to 18, optionally 4 to 12, further optionally 6 to 10 elongate windows. In an embodiment, the QCD comprises at least 2, 3, 4 or 5 elongate windows.

[0037] In an embodiment, at least two elongate windows have different widths. Advantageously, having windows of different widths allow the generation of a more complicated image and this can allow the performance of the imaging camera to be better tested. For example, the images of the windows should remain distinct and should not be seen to merge together.

[0038] In an embodiment, each elongate window has the same width as another elongate window (e.g. a pair, triplet or quartet of identically sized windows), and optionally the elongate windows sharing the same width are adjacent to each other. Advantageously, having adjacent windows of the same size and separated by a distance equal to their width allows the performance of the imaging camera to be assessed, where the image generated from each window should be the same. In an embodiment, the windows have the same width, but the distance separating each window may vary.

[0039] In an embodiment, at least 3, 4, 5, 6 or 7 elongate windows extend radially from the alignment point. In an embodiment, substantially all the elongate windows extend radially from the alignment point.

[0040] In an embodiment, at least 3, 4, 5, 6 or 7 elongate windows are not parallelly arranged. In an embodiment, substantially all of the elongate windows are not parallelly arranged. In an embodiment, at least 3, 4, 5, 6 or 7 elongate windows are not perpendicularly arranged. In an embodiment, substantially all of the elongate windows are not perpendicularly arranged.

[0041] In an embodiment, at least 3, 4, 5, 6 or 7 elongate windows are not perpendicularly and / or parallelly arranged. In an embodiment, substantially all of the elongate windows are not perpendicularly and / or parallelly arranged.

[0042] In an embodiment, at least 3, 4, 5, 6 or 7 elongate windows are not orthogonally arranged. In an embodiment, substantially all of the elongate windows are not orthogonally arranged.

[0043] In an embodiment, the elongate windows are not arranged in quadrants where the lines (elongate windows) in each quadrant are orthogonal to the lines (elongate windows) in the quadrants adjacent to them.

[0044] In an embodiment, substantially all of the elongate windows are arranged radially like spokes in a wheel. In an embodiment, substantially all of the elongate windows are arranged radially like spokes in a wheel and substantially all of the 'spokes' pass through the alignment point.

[0045] In an embodiment, none of the elongate windows pass through the alignment point.

[0046] In an embodiment, the angle between two adjacent elongate windows (e.g. the angle formed when comparing the longest direction of two adjacent windows; with reference to Figure 6(a) the angle formed between the two top-most elongate windows is about 60 degrees ) is greater than about 1 degree and less than about 89 degrees. In an embodiment, the angle between two adjacent windows is greater than about 5 degrees and less than about 85 degrees. In an embodiment, the angle between two adjacent windows is greater than about 15 degrees and less than about 70 degrees. In an embodiment, the angle between two adjacent windows is greater than about 25 degrees and less than about 60 degrees. In an embodiment, the angle between two adjacent windows is greater than about 35 degrees and less than about 55 degrees.

[0047] In an embodiment, the angle between every adjacent elongate window is greater than about 1 degree and less than about 89 degrees. In an embodiment, the angle between every adjacent elongate window is greater than about 5 degrees and less than about 85 degrees. In an embodiment, the angle between every adjacent elongate window is greater than about 15 degrees and less than about 70 degrees. In an embodiment, the angle between every adjacent elongate window is greater than about 25 degrees and less than about 60 degrees. In an embodiment, the angle between every adjacent elongate window is greater than about 35 degrees and less than about 55 degrees.

[0048] In an embodiment, the elongate windows are substantially straight. In an embodiment, the elongate windows do not substantially bend, kink and / or merge into and / or interconnect with other elongate windows. In an embodiment the elongate windows are distinct.

[0049] In an embodiment, the radiation body and / or radiation wall of the QCD may comprise or consist of any material that prevents gamma rays from substantially passing through it. In an embodiment the material can be a material of suitable density and / or thickness to prevent gamma rays from substantially passing through it. In an embodiment, the material may comprise tungsten, lead or gold.

[0050] In an embodiment the radiation body and / or radiation wall comprises a material with a density of greater than llg / cm3, and optionally greater than 19 g / cm3. In an embodiment the radiation body and / or wall material is arranged to attenuate more than 90, 95%, 98%, 99% or 99.99% of gamma rays having an energy of about 122 keV or about 141 keV.

[0051] In an embodiment, the radiation body comprises tungsten and / or lead. In an embodiment, the radiation wall comprises tungsten and / or lead. In an embodiment, the radiation wall consists of tungsten and / or lead.

[0052] In an embodiment the QCD is small. In an embodiment, the radiation body defines a volume that does not exceed 0.2m3, optionally it does not exceed 0.03m3, further optionally it does not exceed 0.003m3. In an embodiment the QCD has a mass equal or less than 0.5, 0.4, 0.3 or 0.2kg.

[0053] Advantageously, the QCD is of a small size and so this makes it portable. This ensures that the QCD can be carried by hand to the various locations where GRMICs are being used, which might be different rooms in a hospital, or even in a room in a different hospital.

[0054] In an embodiment, the QCD comprises a coupling which in use is configured to attach / align the QCD to / with a GRMIC, and in particular this is done in a fixed and reproducible manner. Advantageously, the QCD is adapted to (or has an adaptor or jig to) work with a specific GRMIC.

[0055] In an embodiment, the QCD has a cup-shaped profile and in use is adapted to fit around the imaging parts of a GRMIC. In an embodiment the QCD may take on any convenient shape (cylinder, cone, halfsphere, cube, oblong, etc.) that is adapted to couple or attach with a GRMIC. Advantageously, the QCD is adapted to fit around the imaging parts of a GRMIC. This can be used to shield the GRMIC from any other sources of gamma rays or other high energy rays, and to protect the user from radiation originating from the QCD when in use. Advantageously, the QCD is ergonomic and easy to hold in one hand.

[0056] In an embodiment, the radiation body is adapted to receive gamma rays, wherein the gamma rays may originate from within the body, e.g. from a gamma ray source housed in the body; and / or from a gamma ray source making up all of (or part of) the radiation body; and / or from radiation from a radiation source introduced into the radiation body; and / or the radiation body may be a body arranged to receive radiation from an external radiation source, e.g. the radiation body is a radiation conduit for radiation originating outside of the QCD. So, from the perspective of the GRMIC, the gamma rays will originate from the radiation body.

[0057] In an embodiment, the gamma ray source is a flood or point source. In an embodiment the gamma ray source comprises substantially an evenly distributed density of a radioisotope or isotopes.

[0058] In an embodiment, the radiation body comprises a radiation housing to house a gamma ray source.

[0059] Advantageously, it is useful to use a radiation source with known and hence controlled properties. This ensures that the image that the QCD will produce in the imaging camera is controllable. In an embodiment, the radiation housing is adapted to hold the gamma ray source.

[0060] In an embodiment, the radiation housing is adapted to receive a liquid gamma ray source, optionally the radiation housing is reversibly fillable with the liquid gamma ray source. In an embodiment, the radiation housing is a sealed unit and comprises a liquid gamma ray source. In an embodiment the radiation housing comprises a reservoir that may be reversibly filled with a liquid gamma ray source. In an embodiment the reservoir may be substantially rectangular. In an embodiment the reservoir may reversibly sealed with a plug or water-tight screw. In an embodiment the reservoir has a volume of equal or less than 30, 20, 10, 5, 2, 1, or 0.5 or 0.25ml.

[0061] Advantageously, a liquid gamma ray source can be stored and / or reversibly inserted into the QCD with relative ease. For example, the liquid gamma ray source could be inserted and / or removed from an internal reservoir using a syringe. In an embodiment, the gamma ray source is solid. Advantageously, the reservoir is a modular sealed cassette unit that may be easily inserted and / or removed from the QCD. In an embodiment, the QCD is adapted to work with a gamma ray source that produces gamma ray photons having an energy of 35 to 750KeV. In an embodiment the gamma ray source comprises one or more of Tc-99m, 1-123, 1-131, Lu-177, In-111, Y-90, Sc-47, Ga-67, Cr-51, Sn-177m, Cu-67, Tm-167, Ru-97, Re-188, Au-199, Pb-203, Ce-141, Co-57, F-18, Ga-68, C-ll, 0-15, N-13, Zr-89, Rb-82, Cu-64.

[0062] In an embodiment the QCD is adapted to work with a gamma ray source comprising an amount of radioactivity that allows a 'phantom image' to be collected in less than 30 minutes, optionally less than 10 minutes.

[0063] In an embodiment the QCD is adapted to work with a gamma ray source comprising 10 - 1000 MBq, optionally 50-500 MBq and preferentially 150-350MBq of radioactivity. In an embodiment the gamma ray source is liquid and comprises Tc-99m. In an embodiment the gamma ray source is solid and comprises Co-57.

[0064] In an embodiment, the radiation housing is reversibly removable from the QCD, optionally the radiation housing is a reversibly removable cassette. In an embodiment, the radiation wall is reversibly removable from the QCD, optionally the radiation wall is a reversibly removable cassette.

[0065] Advantageously, various parts forming the QCD may be modular and so removed and replaced (e.g. modular cassettes). This might be done to change the nature of the radiation source, or to change the nature of the image to be generated. For example, the radiation wall could be easily removed and replaced with a different radiation wall having a different arrangement of windows, and / or having a different thickness of lead. This might be done when testing different isotopes (higher energy gamma rays may require a radiation wall that is made of a thicker or more dense material), or if testing a different GRMIC that has different requirements. The QCD could be supplied with a set of different radiation walls, a set of cassettes that can be removed and inserted to suit need. The QCD might be adapted to hold more than one cassette at a time to form a combined cassette radiation wall. For example, a cassette radiation wall could have no windows at all, and this modular radiation wall could be used to simply increase the opacity of the combined cassette radiation wall where too much radiation is reaching the sensor. The radiation wall module could even be swapped out for a radiation wall module which is substantially transparent to gamma rays or omitted. In that way the whole sensor area would be fully illuminated by gamma rays so that the same QCD can be easily configured by the use to acquire images of either flood or bar phantoms. This can be useful in identifying any 'hot' or 'cold' spots in the sensor. This is because sensors sometimes contain small defects when they are manufactured. Once hot / cold spots are identified using the QCD, a digital correction to the GRMIC sensor can be made to compensate for these hot / cold spots.

[0066] In an embodiment, the radiation wall is held in place by a reversibly removable retaining (end) wall. In an embodiment, the QCD is modular and reversibly assemblable. A reversibly removable retaining wall can be used to hold the radiation wall in place and to ensure that in use it is held in good optical alignment with a GRMIC. For example, to prevent the radiation wall from inadvertently sliding, tilting or rotating.

[0067] Advantageously, various parts forming the QCD may be modular, and so having a reversibly removable retaining wall can allow the QCD to be put together and / or taken apart to suit need in a modular way. The retaining wall may have means to attach the QCD to the GRMIC. The retaining wall may have means to align the QCD to the GRMIC. The retaining wall may be modular and so can be swapped with a retaining wall of a different configuration to suit need. The means to attach the retaining wall to a GRMIC may be via a frictional grip (e.g. a rubber seal that cooperates with a projection on the GRMIC), clip, hook, or portion that can be reversibly screwed to the GRMIC. The means to align the retaining wall to the GRMIC may be one or more protrusions or recesses which mate with one or more recesses or protrusions on the GRMIC. The means to align the retaining wall may be a clip or comprise a magnetic attachment.

[0068] In an embodiment, the radiation wall, radiation housing, any retaining wall and any fixings needed to hold the radiation wall, radiation housing and retaining wall in place have a uniform density and thickness. Advantageously, to help prevent the generation of artifacts in any generated image in the GRMIC the parts of the QCD that interact with gamma rays can be of uniform density and thickness. That is, an unnaturally brighter area can be generated on the GRMIC sensor if the radiation wall has an area which is of lower density / thickness. This could give misleading results.

[0069] In a further aspect of the invention, there is provided a kit of parts for making a QCD as defined in any one of the aspects and / or embodiments disclosed herein. In an embodiment, the QCD kit comprises, a radiation body, reversibly removable radiation housing, reversibly removable radiation wall and a reversibly removable retaining wall. Advantageously, the supply of the QCD as a kit of parts allows easy transportation and saves on assembly costs.

[0070] In a further aspect of the invention, there is provided the use of a QCD as defined in any one of the aspects and / or embodiments disclosed herein, to obtain an image in a GRMIC. Aspects, embodiments and / or disclosures disclosed herein may be independently combined with any other embodiment, embodiments, aspect or aspects of the invention.

[0071] Brief description of the drawings

[0072] The present invention will now be further described with reference to the following non-limiting examples and the accompanying illustrative drawings, of which:

[0073] Figure 1 is an exploded perspective view of an embodiment of the invention.

[0074] Figure 2 is a cross-section side view of the embodiment shown in Fig. 1.

[0075] Figure 3 is a cross-section view of an assembled embodiment shown in Fig. 2

[0076] Figure 4 is an end view of an assembled embodiment shown in Fig. 3

[0077] Figure 5 shows alternative representations of the radiation housing (30) shown in Fig. 3.

[0078] Figure 6 shows: (a) a radiation wall embodiment shown in Fig. 1; (b) the resultant image produced when gamma rays pass through the windows shown in Fig. 6(a); (c) a prior art mask having quadrants of parallel straight windows; and (d) the resultant image produced when gamma rays pass through the windows shown in Fig. 6(c).

[0079] Figure 7 shows a schematic representation of a pinhole collimator interacting with two apertures in a wall section, where the apertures in the wall are at different distances from the pinhole.

[0080] Like features have been given like reference numerals.

[0081] Detailed description of the invention

[0082] Figure 1 is an exploded perspective view of an embodiment of the invention (l). The QCD embodiment (1) comprises a retaining wall (10), radiation wall (20), radiation housing (30) and radiation body (40).

[0083] The retaining wall (10) is made up of a substantially plastic circular plate (11), having three screw holes (12) and an aligning projection (13), which in use is used to align the plate and hence the QCD to the GRMIC. The plate is 76mm in diameter. The radiation wall (20) is made up of a substantially square tungsten plate (21), with dimensions of 56 x 56 x 5mm. The tungsten plate (21) has eight elongate windows (22) which extend radially from an alignment point which is located substantially at the centre of the tungsten plate (21).

[0084] The radiation housing (30) comprises a hollow plastic container (31) that holds an internal reservoir (34) to receive a radioactive fluid via an inlet port (33). The container (31) has external dimensions 56 x 56 x 11mm. The spacer (32) extends this to 56 x 56 x 19.5mm and the internal reservoir (34) has dimensions 50 x 50 x 5mm.

[0085] The radiation body (40) has a plastic cup-shaped body part (41) which has an external diameter of 126.5mm at the wider end and a diameter of 114mm at the narrower end, where the circular ends are separated by a cup depth of 45.6mm. The cup-shaped body part (41) has a pocket-like recess area that is arranged to hold and align the radiation housing (30) and radiation wall (20). The cup-shaped body part (41) is equipped with three projections that each have a screw hole (42).

[0086] When the QCD embodiment (1) is assembled the radiation housing (30) is first placed into the pocketlike recess in the cup-shaped body part (41). Second, the radiation wall (20) is also placed in the pocket, where the radiation wall plate (21) substantially covers the exposed face of the radiation container (31). Third, the end piece (10) is placed over the radiation wall (20), where the circular plate (11) of the retaining wall covers the exposed face of the radiation wall lead plate (21). The aligning projection (13) is arranged so it is not in contact with the radiation wall (20). Finally, three screws (or other similar fixings; not shown) are inserted into the screw holes (12) in the circular plate (11) of the retaining wall, and then screwed to mate with the holes (42) in the cup-shaped body part (41), to reversibly hold the QCD assembly together. The screws do not contact the radiation wall (20) or radiation housing (30). In an embodiment, the screws are kept away from the source because these may give an area of non- uniform material (e.g. of a higher density). The radiation housing can contain a radioactive fluid and so should not be damaged by a screw as this may cause a radioactive leak.

[0087] The assembled QCD can then be attached to a GRMIC, to cooperate with the GRMIC, and a quality control image generated as necessary. Typically the body lip (43) will fully surround the imaging part of the GRMIC. The aligning projection (13) is used to help align the QCD with the GRMIC. In particular, in use the aligning projection (13) can be used to substantially locate the alignment point of the QCD assembly over the camera of the GRMIC. Beneficially, this allows the QCD to properly and reliably and relatively quickly locate onto the GRMIC. A quality control image can then be generated by the GRMIC. In an embodiment the QCD cooperates with (e.g. connects to / attaches with / locates on the GRMIC, either directly or indirectly. In an embodiment the radiation body (e.g. see 40 in Fig. 2) of the QCD cooperates with the front end of the GRMIC.

[0088] Figure 2 is a cross-section side view of the embodiment shown in Fig. 2. In this view the internal reservoir (34) can be seen.

[0089] Figure 3 is a cross-section view of an assembled embodiment of the invention shown in Fig. 2. In this view, it can be seen that the radiation housing (30) and radiation wall (20) fit within the pocket in the cup-shaped radiation body (40), and that the retaining wall (10) holds these two parts in place via three screws that fit into screw holes (12 and 42). The radiation body (40) has a lip portion (43) that extends past the radiation housing (30), radiation wall (20) and the retaining wall (10).

[0090] Figure 4 is an end view of an assembled embodiment of the invention shown in Fig. 3.

[0091] Figure 5 shows alternative representations of the radiation housing (30) shown in Fig. 3. In particular, in this embodiment the substantially + shaped spacer section (32) and fluid inlet port (33) can be seen.

[0092] Figure 6(a) shows an embodiment of the radiation wall (20') of the invention. The radiation wall has 8 lozenge-shaped elongate holes in a substantially square tungsten plate (21'). In this embodiment the 8 windows are arranged into four pairs (22(a)-(d)). The windows are all the same depth, but each pair has a different width and different lengths to occupy as much of the visible area as possible. In the embodiment, the windows are in 2, 3, 4, and 5mm wide pairs and are 12.5, 12.0, 11.5, and 11.0mm in length respectively, when measured from their centre points (i.e. the centre of the circle at each end of the window). The elongate windows radiate out from a substantially centrally located alignment point.

[0093] In use, when the radiation wall (20') is exposed to gamma rays, the gamma rays pass through the 8 windows and generate the image shown in Fig. 6(b). The bright areas correspond to the detection of gamma rays. The brighter areas correspond to the detection of more gamma rays. The darker areas correspond to the detection of fewer gamma rays.

[0094] Figure 6(c) shows a mask (90) that has windows arranged into quadrants of parallel lines (bar phantom). In use, when the plate (91) is exposed to gamma rays, the gamma rays pass through the quadrant of windows and generate the image shown in Fig. 6(d). If the images in Fig. 6(b) and 6(d) are compared, it can be seen that the image in Fig. 6(b) is superior. In particular, it can be seen that the corners of the image in Fig. 6(d) do not correspond well to the windows in the plate (91) in Fig. 6(c). These corner areas (shown in white dashed boxes) are faint and indistinct. That is, in the top and bottom righthand corners the lines are missing altogether. In the bottom lefthand corner (which corresponds to the location of two lozenge-shaped windows), the bottom most lozenge image is much fainter than the lozenge image above it. Likewise, in the top lefthand corner the left most lozenge area is fainter than the lozenge to the right of it. This means that the plate (91) in Fig. 6(c) would not give a true / fair representation of how well the camera is performing. For example, if one of the corners of the GRMIC being tested had a fault, then this may not be detected when using the plate (91) in Fig. 6(c). This problem, wherein the regions furthest from the centre of the phantom are faint or features are even altogether absent from the image, is exaggerated as the phantom is brought closer to the pinhole collimator of the GRMIC.

[0095] In the prior art, bar phantoms are located sufficiently far away from the pinhole (e.g. about 20cm), and in this way this problem becomes less significant and in practice is not observed. However, to fill the field of view of the camera, the phantom must be made much larger. This has resulted in slotted lead or tungsten plates with dimensions of around 40cm x 40cm which are heavy (e.g. 5-10kg) and so are unwieldy. So, the deficiencies seen in Figure 6(d) result when attempting to miniaturize the bar phantom and when trying to get it closer to the pinhole in the GRMIC.

[0096] By comparison, in Fig. 6(b) it can be seen that the lozenge-shaped images are uniform and distinct. On very close inspection of Fig. 6(b), it may be noticed that the very ends of each lozenged-shaped 'bar' is slightly less bright than the rest of the bar. This is not a significant problem, but this could be improved / rectified if the end of each elongate window was slightly chamfered to match the angular field of view of the collimator, and this is an embodiment which is considered within the scope of the present invention.

[0097] Without wishing to be bound by theory, Fig. 7 provides an explanation of why the plate (91) in Fig. 6(c) has the noted defects. Fig. 7 shows a schematic representation of a pinhole collimator interacting with two apertures in a wall section that substantially correspond to the plate (91) shown in Fig. 6(c). It can be seen that the pinhole (100) is illuminated with more radiation by the aperture on the right, as compared to the aperture on the left. This is because the depth of the aperture blocks out some of the radiation. The aperture on the right is closer to the pinhole and so this results in less radiation being blocked out by the sides of the aperture. So, because the windows located towards the corners of the plate (91) in Fig. 6(c) are furthest from the pinhole, less radiation will reach the sensor in the GRMIC, and so the resultant image of those windows will be faint. The present invention substantially overcomes this problem experienced in the prior art by aligning the longest dimension of the windows (22) sympathetically with the pinhole and so this negative effect experience by the plate (91) of the prior art is substantially overcome.

Claims

Claims1. A quality control device (QCD) for use in generating a quality control image in a gamma ray medical imaging camera (GRMIC) comprising a pinhole collimator, wherein the QCD comprises: a radiation body adapted to receive gamma rays, wherein the radiation body comprises a radiation wall which is substantially opaque to the gamma rays; a plurality of elongate windows in the radiation wall, which permit the gamma rays to travel through the radiation wall; an alignment point which the elongate windows extend radially therefrom, and wherein, in use: when the QCD cooperates with the GRMIC, and gamma rays originate from the radiation body, then the gamma rays are permitted to travel through the elongate windows to the GRMIC, which can then generate the quality control image useful in assessing the imaging performance of the GRMIC.

2. A quality control device according to claim 1, wherein each elongate window comprises a length along its elongate dimension, a width which is substantially perpendicular to its length, and a depth in the radiation wall.

3. A quality control device according to claim 2, wherein the depth of each elongate window defines a path through the radiation wall.

4. A quality control device according to claim 2 or 3, wherein each path through the radiation wall is an angled path through the radiation wall.

5. A quality control device according to any one of the claims 2 to 4, wherein each path through the radiation wall is greater than the thickness of the radiation wall.

6. A quality control device according to any one of the preceding claims, wherein each path through the radiation wall is configured to align with the field of view of the pinhole.

7. A quality control device according to any one of the preceding claims, wherein in use, the alignment point is configured to be centred over the pinhole of the camera.

8. A quality control device according to any one of the preceding claims, wherein in use, the radiation wall is configured to be spaced away from the pinhole of the camera such that all of the elongate windows are substantially within the field of view of the camera, and optionally substantially occupy the whole field of view of the camera.

9. A quality control device according to any one of the preceding claims, wherein each elongate window is spaced apart from an adjacent elongate window by a spacing distance which is equal to or greater than its width.

10. A quality control device according to any one of the preceding claims, wherein the QCD comprises 3 to 18, optionally 4 to 12, further optionally 6 to 10 elongate windows.

11. A quality control device according to any one of the preceding claims, wherein at least two elongate windows have different widths.

12. A quality control device according to any one of the preceding claims, wherein each elongate window has the same width as another elongate window, and optionally the elongate windows sharing the same width are adjacent to each other.

13. A quality control device according to any one of the preceding claims, wherein the radiation body comprises tungsten and / or lead.

14. A quality control device according to any one of the preceding claims, wherein the radiation wall comprises tungsten and / or lead.

15. A quality control device according to any one of the preceding claims, wherein the radiation body defines a volume that does not exceed 0.2m3, optionally not more than 0.03m3, further optionally not more than 0.003m3.

16. A quality control device according to any one of the preceding claims, wherein the QCD comprises a coupling which in use is configured to attach / align the QCD to / with a GRMIC.

17. A quality control device according to any one of the preceding claims, wherein the QCD comprises a cup-shaped profile and in use is adapted to fit around the imaging parts of a GRMIC.

18. A quality control device according to any one of the preceding claims, wherein the radiation body comprises a radiation housing to house a gamma ray source.

19. A quality control device according to claim 18, wherein the radiation housing is adapted to receive a liquid gamma ray source, optionally the radiation housing is reversibly fillable with the liquid.

20. A quality control device according to any one of the claims 18 or 19, wherein the radiation housing is reversibly removable from the QCD, optionally the radiation housing is a reversibly removable cassette.

21. A quality control device according to any one of the preceding claims, wherein the radiation wall is reversibly removable from the QCD, optionally the radiation wall is a reversibly removable cassette.

22. A quality control device according to any one of the preceding claims, wherein the radiation wall is held in place by a reversibly removable retaining wall.

23. A quality control device according to any one of the preceding claims, wherein the radiation wall, radiation housing, retaining wall and any fixings needed to hold the radiation wall, radiation housing and retaining wall in place have a uniform density and thickness.

24. A kit of parts for making a QCD as defined in any one of the preceding claims, wherein the QCD kit comprises, a radiation body, reversibly removable radiation housing, reversibly removable radiation wall and reversibly removable retaining wall.

25. Use of a QCD as defined in any one of claims 1 to 24 to obtain an image in a GRMIC.

Images