NL2035925B1 - Collimator part for gamma radiation imaging - Google Patents

Abstract

A collimator part for in a gamma radiation imaging system, for example for scintimammography, comprises a plate with a planar incident surface at a front side and a rear surface at a rear side. 5 A virtual normal plane extends perpendicular to the plate. Multiple inclined first and second holes extend through the plate from a position on the rear surface on a respective first or second side of the normal plane. Each of the first and second holes has a sight line extending along the hole from the rear surface to the planar incident surface and outwards beyond the planar incident surface. For at least one first hole and for at least one second hole a respective 10 crossing position with the normal plane is positioned inward of the planar incident surface, e.g. in a groove at the front side.

Description

P36453NL00

COLLIMATOR PART FOR GAMMA RADIATION IMAGING.

The present invention relates to a collimator part for use in the field of gamma imaging, for example for scintimammography or for imaging another human body part, e.g. an extremity like an arm or a leg, or for imaging an animal body part.

Known systems for scintimammography are described, for example, in WO2010008538,

WO02010/014001, WO2010120836, US2013/0158389, and US105159456.

In gamma imaging, a collimator part is used for forming an image on the detector of a gamma camera.

In a known embodiment, the collimator part is embodied as a plate comprising a planar incident surface at a front side and a rear surface at a rear side. A virtual normal plane extends perpendicular to the plate at a join between a first section of the plate and a second section of the plate. In the first section multiple inclined parallel first holes extend through the plate from a position on the rear surface on a first side of the normal plane. The first holes have an opening in the planar incident surface. In the second section multiple inclined parallel second holes extend through the plate from a position on the rear surface on a second side of the normal plane. The second holes have an opening in the planar incident surface. Each of the first and second holes has a sight line extending along the hole from the rear surface to the planar incident surface and outwards beyond the planar incident surface into an imaging space wherein the body part to be imaged is located. Gamma radiation passes from the body part through the first and second holes onto a detector of the gamma camera when an image is made. In the known collimator part all openings of the first holes are located on the one side of the normal plane and in the planar incident surface. All openings of the second holes are located on the other side of the normal plane and in the planar incident surface. Such a collimator part is known as a dual slant hole collimator. The field of view of this collimator part is the area where the sightlines of the first holes overlap with the sightlines of the second holes.

Because points in the body part to be imaged are covered by two sight lines, each under a different angle, such collimator parts provide good depth resolution. However, their field of view close to the collimator part is not satisfactory. For example, when the known collimator part is used for detecting a region(s) of interest, e.g. A tumorous lesion(s), in a human or animal body part, e.g. in a female breast, shallow lying region(s) are not imaged satisfactory. Herein, in practice, shallow lying means that the region is close to the collimator part during imaging, which commonly corresponds to close to the skin of the body part, e.g. the breast.

It is an object of the invention to provide a collimator part which provides for an enhanced field of view, for example use in scintimammography, e.g. in view of enhanced detection of region(s) of interest in shallow lying region(s).

In order to achieve at least one of the objects, the invention provides a collimator part according to claim 1.

In the inventive collimator part a first sight line of at least one first hole crosses the normal plane on a first crossing position, a second sight line of at least one second hole crosses the normal plane on a second crossing position, and for at least one first hole and for at least one second hole the respective first crossing position and second crossing position is positioned inward of the planar incident surface. So, if the plate has parallel front and rear sides that define a thickness of the plate between them, there are in the collimator part at least one first hole and at least one second hole, in practice a set of multiple first holes and a set of multiple second holes, of which the respective crossing point lies within the thickness of the plate. This in contrast to the known collimator part discussed above, wherein all crossing points of the first and second holes with the normal plane are located outward of the front side of the collimator. In the inventive concept, in practical embodiments, a majority of the first and second holes will still be configured so that their crossing points are located outward of the front side of the collimator part. Yet, some of the first holes and second holes, in a zone which includes the normal plane, will have a crossing point with the normal plane inward of the planar incident surface.

Compared to the known collimator part there are now sight lines that cross the normal plane inward of the planar incident surface, which provides a larger and/or more effective field of view when it comes to effectively imaging also region(s) of interest that are located close to the incident surface of the collimator part, such as shallow lying tumours in breast tissue.

In a practical embodiment, the collimator part is provided with an elongated recess at the front side which is recessed relative to the planar incident surface and which extends in the normal plane, wherein at least one first hole and at least one second hole adjoin the elongated recess, wherein for said first hole and second hole the respective first crossing position and second crossing position is positioned in the elongated recess, inward of the planar incident surface.

Preferably, the elongated recess at the front side is symmetrical relative to the normal plane.

In embodiments, the elongated recess is a groove in the front side of the front side of the collimator part, recessed relative to the planar incident surface, e.g. a V-shaped groove.

In a practical embodiment, the elongated recess is delimited by a first recess surface and a second recess surface at the first side and second side of the normal plane, respectively, wherein, preferably, the first recess surface and the second recess surface are flat surfaces, e.g. to define a V-shaped groove, - a first hole defines an opening in the first recess surface, - a second hole defines an opening in the second recess surface, - a first sight line of the at least one first hole is parallel to the second recess surface, - a second sight line of the at least one second hole is parallel to the first recess surface.

Instead of providing an elongated recess, which appears the practically preferred embodiment to implement the inventive concept, one could also arrive at the collimator part of claim 1 without providing the elongated recess. In this alternative design, the planar incident surface remains a continuous surface. In a zone of the collimator part including the normal plane, at least one first hole and at least one second hole are arranged offset from one another in the direction of the intersecting line of the normal plane and the incident surface, wherein each of these holes extends from a location on the rear at one side of the normal plane to a location at the front side on the other side of the normal plane. So, their sight lines have a crossing point with the normal plane that is located inward of the planar incident surface. In practice, this collimator part will have a center zone where first holes and second holes alternate when looking in the mentioned direction along the mentioned intersecting line. This allows for a limited number of first and second holes, compared to the provision of the elongated recess as discussed herein.

In an embodiment, the first sight line of at least one first hole intersects the second sight line of at least one second hole at a point of intersection which is located in the elongated recess, wherein the point of intersection is, preferably, positioned on the normal plane.

In an embodiment, the inclined first holes are parallel to one another to form a first parallel slant hole collimator, and wherein the inclined second holes are parallel to one another to form a second parallel slant hole collimator. In another embodiment, the first holes and second holes are configured in a fan beam arrangement, e.g. with the inclination of the holes increasing as they are further away from the normal plane.

In an embodiment, the sight lines of the inclined first holes are arranged at a first angle with respect to the normal plane and the sight lines of the inclined second holes are arranged at a second angle with respect to the normal plane, wherein the magnitude of the first angle is the same as the magnitude of the second angle. In other embodiments, the first and second angles differ from one another.

In embodiments, the first and second holes each have a uniform cross-section, e.g. diameter, over the length thereof.

The present invention also relates to a gamma camera comprising a detector for gamma radiation and a collimator part as discussed herein.

The present invention also relates to a gamma radiation imaging system, for example for scintimammography, comprising: - a frame supporting a first immobilization plate and a second immobilization plate, which second immobilization plate is arranged or arrangeable to extend parallel to the first immobilization plate, wherein the first and second immobilization plates define an imaging space between them and are configured to clamp a body part to be imaged, e.g. a breast, between the immobilization plates, - a first gamma camera configured and arranged to detect gamma radiation emitted from a volume in the imaging space passing through the first immobilization plate, wherein the first gamma camera comprises: - a first collimator assembly which extends in a plane parallel to the first immobilization plate, which first collimator assembly comprising a first collimator part as discussed herein, - a first gamma sensitive detector arranged to receive gamma radiation passing through the first collimator assembly.

In an embodiment, the first collimator assembly further comprises a second collimator part, wherein the second collimator part is provided with parallel perpendicular holes which extend parallel to the normal plane.

In an embodiment, the system further comprises a second gamma camera configured and arranged to detect gamma radiation emitted from a volume in the imaging space passing through the second immobilization plate, wherein the second gamma camera comprises: - a second collimator assembly, which extends in a plane parallel to the second immobilization plate, - a second gamma sensitive detector arranged to receive gamma radiation passing through the second collimator assembly.

In an embodiment, the first and/or the second collimator assembly is movable relative to the respective immobilization plate in said plane in a displacement direction, preferably by collimator motion device configured to controllably move the collimator assembly in the displacement direction.

In an embodiment, at least one of the immobilization plates is provided with a grid of tool apertures each configured to allow for passage of a tool through the first immobilization plate, e.g. a biopsy tool. This allows, for example, taking samples from the body part that has been imaged by inserting a device into the body part through an aperture. For example, a biopsy can be taken from a breast by inserting a hollow needle into the breast directly after imaging the breast. Not only can said tumour candidate or region be imaged accurately, but a biopsy can be taken accurately and fast, minimizing discomfort to the person whose breast is being imaged and increasing accuracy of sampling.

In an embodiment, the first collimator assembly is provided with at least one elongated slot perpendicular to the first immobilization plate, which slot(s) is/are alignable with one or more tool apertures in the first immobilization plate allowing for a tool, e.g. a biopsy tool and/or a marker tool, to be passed through a tool aperture and the slot.

In an embodiment, the system further comprises a marker device, that is configured to pass through a tool aperture and the slot and is adapted to mark the body part.

In an embodiment, the system further comprises a biopsy tool, that is configured to pass through a tool aperture and the slot and is adapted to perform a biopsy of the body part.

In an embodiment, the system is configured, e.g. is provided with a programmed controller, to perform an operation wherein in a first imaging step the first collimator assembly is arranged with the second collimator part thereof between the imaging space and the detector, and wherein, for performing a second imaging step, the first collimator assembly is moved so that the first collimator assembly is arranged with the first collimator part thereof between the imaging space and the detector.

The present invention also relates to a method of gamma imaging of a body part, e.g. of a breast, wherein use is made of a collimator part and/or a gamma camera and/or a system as discussed herein.

The invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts.

In the drawings:

Fig. 1 shows schematically an embodiment of a system according to the invention during a first imaging step, here for scintimammography of a female breast,

Fig. 2 shows schematically in cross-section an example of a collimator part according to the invention.

With reference to the figures an example of a gamma radiation imaging for scintimammography according to the invention will be discussed.

The system comprises a frame 1, only shown highly schematically, supporting a first immobilization plate 10 and a second immobilization plate 110 which extends parallel to the first immobilization plate 10. The plates 10, 110 define an imaging space 200 between them for one breast 250 of a female human person, e.g. standing or sitting.

The system is configured to clamp the breast to be imaged between the plates 10, 110.

In a practical embodiment, the plates 10, 110 are made of plastic material, e.g. visually transparent plastic.

The first immobilization plate 10 is provided with a 2D-grid of tool apertures 15, which are each configured to allow for passage of a tool through the first immobilization plate 10. There may a multitude of such apertures, e.g. apertures being spaced closely to one another, e.g. closer than their individual diameter.

The system further comprises a first gamma camera 50 which is configured and arranged to detect gamma radiation emitted from the breast 250 in the imaging space passing through the first immobilization plate 10.

The system further comprises a second gamma camera 150 which is configured and arranged to detect gamma radiation emitted from the breast 250 in the imaging space passing through the second immobilization plate 110.

The first gamma camera 50 comprises: - a first collimator assembly 60, which extends in a plane parallel to the first immobilization plate 10,

- a first gamma sensitive detector 80 arranged to receive gamma radiation passing through the first collimator assembly 60.

The second gamma camera 150 comprises: -asecond collimator assembly 180, which extends in a plane parallel to the second immobilization plate 110, - a second gamma sensitive detector 180 arranged to receive gamma radiation passing through the second collimator assembly 160.

In the drawings, the detectors are shown to be rather far from the corresponding collimator assembly. This is done for reason of clarity of the figures. In practical embodiments, the detector is in close proximity to the corresponding detector.

The first and the second collimator assemblies 60, 180 are each movable in the plane of the corresponding plate 10, 110 in a displacement direction Y relative to the respective immobilization plate.

Each collimator assembly 60, 180 is linearly driven in Y-direction by a corresponding collimator motion device 95, 195 which configured to controllably move the collimator assembly in the displacement direction Y.

The X-direction extends in the plane of the plates 10, 110, perpendicular to the Y-direction.

As shown, the first collimator assembly 60 has a first collimator part 61 according to the invention which is shown in more detail in figure 2.

The first collimator comprises a plate 62 with a planar incident surface 63 at a front side and a rear surface 64 at a rear side. Here, as preferred, the surfaces 63, 64 are parallel to one another, defining a thickness of the plate.

A virtual normal plane 65 extends perpendicular to the plate in the center thereof.

Multiple inclined first holes 66 extend through the plate from a position on the rear surface 64 on a first side of the normal plane 65.

Multiple inclined second holes 67 extend through the plate from a position on the rear surface on a second side of the normal plane 65.

The first and second holes 66, 67 each have a uniform cross-section, e.g. diameter, over the length thereof.

It is noted that in practical embodiments, there is a multitude of holes 66, 67, closely spaced from one another. The limited number of holes in the drawings are shown to increase clarity of the drawings.

Each of the first holes 66 and second holes 67 has a sight line extending along the hole from the rear surface 64 to the planar incident surface 83 and outwards beyond the planar incident surface into imaging space 200 where the body part 250 to be imaged is located.

The first collimator part 61 is provided with an elongated recess 70 at the front side which is recessed relative to the planar incident surface 63 and which extends in the normal plane 65.

As shown, at least one first hole 66 and at least one second hole 67 adjoin the elongated recess 70, so have an opening at the end of the hole that adjoins the recess 70.

In the embodiment shown, the elongated recess 70 forms a groove, here a V-shaped groove in the front side of the collimator part. Here the V-shaped groove is symmetrical relative to the normal plane 65.

As is illustrated, a first sight line 66a of at least one first hole 66 crosses the normal plane 65 on a first crossing position and a second sight line 67a of at least one second hole 67 crosses the normal plane 65 on a second crossing position. As shown, for example, these crossing points coincide and are located on the normal plane, here indicated with reference numeral 68.

As is illustrated, for at least one first hole and for at least one second hole the respective first crossing position and second crossing position, here the common point 88, is positioned inward of the planar incident surface 63, here in the elongated recess or groove 70.

In this example, the first sight line 66a of at least one first hole 66 intersects the second sight line 67a of at least one second hole 67 at a point of intersection 68 which is located in the elongated recess 70. As shown, the point of intersection 68 is, preferably, positioned on the normal plane 65.

As follows from figure 2 the sight lines of the first and second holes in proximity of the normal plane 65 provide an enhanced field of view, in particular close to the collimator part 61. As explained, this enhanced field of view allows for more effective imaging of regions of interest in the body part that are located close to the collimator part 61 during imaging. This, for example,

allows for improved detection of tumorous lesion(s) close to the skin.

As shown, by way of example, the groove 70 is delimited by a first recess surface 70a and a second recess surface 70b at the first side and second side of the normal plane, respectively.

The first recess surface 70a and the second recess surface 70b are flat surfaces as preferred.

A first hole 66 defines an opening in the first recess surface 70a, a second hole 67 defines an opening in the second recess surface 70b. As shown, the first sight line 66a is parallel to the second recess surface 70b, and the second sight line 67a is parallel to the first recess surface 70a. A more diverging arrangement of the surfaces 70a, b is not practical as it would not further enhance the field of view and would further reduce the thickness of the plate locally.

The second collimator assembly has a first collimator part 161 of the prior art design addressed in the introduction. This is done to allow for a better understanding of the inventive concept as implemented in the first collimator part 61. The enhanced field of view as explained above is absent in this prior art design of collimator part 161.

The collimator part 161 is embodied as a plate comprising a planar incident surface at a front side and a rear surface at a rear side. A virtual normal plane 162 extends perpendicular to the plate at a join between a first section 165 of the plate and a second section 170 of the plate. In the first section multiple inclined parallel first holes 166 extend through the plate from a position on the rear surface on a first side of the normal plane. The first holes 166 each have an opening in the planar incident surface. In the second section the multiple inclined parallel second holes 171 extend through the plate from a position on the rear surface on a second side of the normal plane. The second holes 171 each have an opening in the planar incident surface. Each of the first and second holes 166, 171 has a sight line extending along the hole from the rear surface to the planar incident surface and outwards beyond the planar incident surface into the imaging space 200 wherein the body part 250 to be imaged is located. Gamma radiation passes from the body part through the first and second holes onto detector 180 of the gamma camera 150 when an image is made. In the known collimator part 161 all openings of the first holes 166 are located on the one side of the normal plane and in the planar incident surface. All openings of the second holes 171 are located on the other side of the normal plane and in the planar incident surface. Such a collimator part is known as a dual slant hole collimator.

It will be appreciated that for the collimator part 161 the crossing points where a sight line crosses the plane 162 all lie outward of the collimator part 161, effectively in the imaging space 200. As explained, a drawback thereof is that the imaging of the portion of the body part 250 close to the immobilization plate 110 is not satisfactory.

In a preferred embodiment of the system, the collimator part 161 is also of the design as shown for first collimator part 61.

As shown by way of example, all first holes 66 are parallel to one another and all second holes 67 are parallel to one another. As explained, this is not a necessity in the context of the present invention. The holes 66, 67 could also, for example, be arranged in a fan beam arrangement.

As preferred, the first collimator assembly 80 further comprises a second collimator part 75. The second collimator part is provided with parallel third perpendicular holes 76 which extend parallel to the normal plane 85, so perpendicular to the first immobilization plate 10.

The second collimator assembly further comprises a second collimator part 175. The second collimator part is provided with parallel third perpendicular holes 176 which extend parallel to the normal plane 65, so perpendicular to the second immobilization plate 110.

In both of the first and the second collimator assembly 60, 160, the second collimator part 75, 175 adjoins the first collimator part 60, 160 in the displacement direction Y.

The collimator assemblies 60, 160 here each are embodied as one component that is slidable in

Y-direction along a side of the respective immobilization plate 10, 110 that faces away from the imaging space 200. So, as shown, the first and second parts of each assembly are connected to one another. In another embodiment, these parts adjoin one another without being interconnected.

For example, where the first collimator part 61 adjoins the second collimator part 75 a linear array of elongated slots 90 may be present through the first collimator, the slot(s) being perpendicular to the assembly and the immobilization plate. The line of slots is alignable with one or more tool apertures 15 in the first immobilization plate 10 allowing for a tool, e.g. a biopsy tool and/or a marker tool, to be passed through a tool aperture and the slot.

In embodiments, the system further comprises a comprising a marker device, that is configured to pass through a tool aperture 15 and the slot 90 and is adapted to mark the breast.

As shown in figures 1 in a first imaging step the first and second collimator assemblies 60, 160 are each arranged with the second collimator part 75, 175 thereof between the imaging space 200 and the detector 80, 180. As the holes 76, 176 are perpendicular to the plates 10, 110, this generally allows for localization of regions of interest, e.g. a tumorous lesion, in the X,Y plane, so parallel to the plates 10, 110.

For performing a second imaging step, the first and second collimator assemblies 60, 160 are moved by the respective drives 95, 195 to the second imaging configuration, so that each collimator assembly 60, 160 is arranged with the first collimator part 61, 161 thereof between the imaging space 200 and the respective detector 80, 180.

Preferably, the XY location of a region of interest in the breast which has been determined in the first imaging step is used for positioning the collimator parts 61, 161 for performing the second imaging step. Herein, the first and second collimator assemblies 61, 161 are moved so that the region of interest determined in the first imaging step is located in the normal plane of the first collimator part of each of the first and second collimator assemblies.

Due to the sets of holes, here parallel slant holes with opposite signs in each of the collimator parts 61, 161, the second imaging step is performed to also, or in particular, locate the region of interest in a direction normal to the first and second immobilization plates 10, 110, which is referred to as the Z-direction.

For example, a person, e.g. a medical doctor or technician, may study the image obtained in the first imaging step and then select one or more regions of interest in said image, e.g. using suitable graphic image processing software in conjunction with a digital version of the image, e.g. that allows to select an item (such as a suspect region in the object) and then create a contour line or other graphical indicator thereof, e.g. a localization of maximum emitted gamma radiation. Then the collimator assemblies 60, 160 can be positioned, possibly automatically based on instructions derived from the selection that has been made, as discussed above.

When it is determined that a biopsy of the region of interest is desired, the breast 250 remains immobilized by the plates 10, 110. The slot(s) 90 are then aligned with the region and with one or more apertures 15 in the plate 10. Part of the first gamma camera 50, at least including the detector 80 in practice also including a housing between the detector 80 and the collimator assembly 60, is repositioned away from the operative position thereof to provide space for the tool 300. The tool 300 is then passes through the slot 90 and an aperture 15 so as to penetrate into the breast 250.

Repositioning of the first gamma camera 50, at least the detector 80, in order to provide access for the tool is done by camera drive 85.

The plates 10, 110 may be fairly thin as the collimator assemblies 60, 160, here effectively embodied as collimator plates 60, 160, remain in contact with the plates 10, 110 and provide support against bending of the plates 10, 110 due to the compression of the breast.

The collimator plates 60, 160 are guided by guide rails 5, 6 of the frame of the system.

Claims (20)

CONCLUSIONS 1. A collimator portion (61) for collimating gamma radiation in a gamma radiation imaging system, for example for scintimammography, the collimator portion comprising: - a plate comprising a planar incident surface (63) at a front side and a rear surface (64) at a rear side, - a virtual normal plane (85) perpendicular to the plate, - a plurality of inclined first holes (66) extending through the plate from a position on the rear surface on a first side of the normal plane (65), - a plurality of inclined second holes (67) extending through the plate from a position on the rear surface on a second side of the normal plane (65), wherein: - each of the first and second holes (66, 67) has a line of sight (66a, 67a) extending along the hole from the rear surface (64) to the planar incident surface (63) and outside the planar incident surface, - a first line of sight (66a) of at least a first hole (66) crosses the normal plane (65) at a first cross position (68), - a second sight line (67a) of at least one second hole (67) crosses the normal plane at a second cross position (68), - for at least one first hole (67) and for at least one second hole (67), the respective first cross position (68) and second cross position (68) are located inwardly with respect to the plane incident surface (63). 2. The collimator member of claim 1, wherein the collimator member comprises an elongated recess (70) at the front side which is recessed relative to the planar incident surface (83) and extends into the normal plane, at least one first hole (66) and at least one second hole (67) adjoining the elongated recess (70), for said first hole and second hole the respective first cross position (68) and second cross position (68) being located in the elongated recess (70), inwardly relative to the planar incident surface (83). 3. A collimator part according to claim 2, wherein the elongated recess (70) at the front side is symmetrical with respect to the normal plane (65). 4. The collimator plane of claim 3, wherein the elongated recess (70) is a V-shaped groove. A collimator member according to any one of the preceding claims 2 to 4, wherein: - the elongated recess (70) is defined by a first recess surface (70a) and a second recess surface (70b) on a first side and on a second side of the normal plane (85), respectively, wherein, preferably, the first recess surface (70a) and the second recess surface (70b) are planar surfaces, - a first hole (66) defines an opening in the first recess surface (70a), - a second hole (67) defines an opening in the second recess surface (70b), - a first line of sight (66a) of at least one first hole is parallel to the second recess surface (70b), - a second line of sight (67a) of at least one second hole is parallel to the first recess surface (70a). 6. A collimator member according to any one of claims 2 to 5, wherein the first line of sight of at least one first hole intersects the second line of sight of at least one second hole at an intersection point (68) located in the elongated recess, the intersection point (68) preferably being located in the normal plane (65). A collimator member according to any preceding claim, wherein the inclined first holes (66) are parallel to each other to form a first collimator arrangement having parallel inclined holes, and wherein the inclined second holes (67) are parallel to each other to form a second collimator arrangement having parallel inclined holes. 8. The collimator member of claim 7, wherein the lines of sight of the inclined first holes (66) are disposed at a first angle relative to the normal plane and the lines of sight of the inclined second holes (67) are disposed at a second angle relative to the normal plane, the magnitude of the first angle being the same as the magnitude of the second angle. 9. A collimator member according to any preceding claim, wherein the first and second holes (66, 67) each have a uniform cross-section, e.g. a diameter, over their length. 10. Gamma camera comprising a gamma radiation detector and a collimator part (61) according to one or more of the preceding claims. 11. A gamma-ray imaging system, for example for scintimammography, comprising: - a frame supporting a first immobilization plate (10) and a second immobilization plate (110), the second immobilization plate being arranged or being arranged to extend parallel to the first immobilization plate, the first and second immobilization plates defining an imaging space therebetween and being arranged to sandwich a body part being imaged, for example a breast, between the immobilization plates, - a first gamma camera (50) arranged and configured to detect gamma radiation emitted from a volume in the imaging space passing through a first immobilization plate, the first gamma camera comprising: - a first collimator assembly (60) extending in a plane parallel to the first immobilization plate, the first collimator assembly comprising a first collimator portion (61) according to any one or more of the preceding claims 1 to 9, - a first gamma-sensitive detector (80) arranged to receive gamma radiation passing through the first collimator assembly. The system of claim 11, wherein the first collimator assembly further comprises a second collimator portion (75), the second collimator portion having parallel perpendicular holes extending parallel to the normal plane (65). The system of claim 11 or 12, wherein the system further comprises a second gamma camera (150) configured and arranged to detect gamma radiation emitted from a volume in the imaging space passing through a second immobilization plate (110), the second gamma camera comprising: - a second collimator assembly (160) extending in a plane parallel to the second immobilization plate, - a second gamma-sensitive detector (180) arranged to detect gamma radiation passing through the second collimator assembly. A system according to any one or more of the preceding claims 11-13, wherein the first and/or second collimator assembly (60, 160) is movable relative to the immobilization plate in said plane in a direction of displacement, preferably by a collimator movement device arranged to controllably move the collimator assembly in a first direction of displacement. 15. A system according to any one or more of the preceding claims 11-14, wherein at least one of the immobilization plates (10) is provided with a grid of tool openings each adapted to allow the passage of a tool through the first immobilization plate, for example a biopsy tool. The system of claim 15, wherein the first collimator assembly includes at least one elongated slot perpendicular to the first immobilization plate (10), the slot(s) being alignable with one or more of the tool openings in the first immobilization plate to provide a tool, e.g., a biopsy tool and/or a marking tool, for passage through the tool opening and the slot. 17. The system of claim 18, wherein the system further comprises a marking tool configured to pass through a tool opening and the slot and configured to mark the body part. 18. The system of claim 16, wherein the system further comprises a biopsy tool configured to pass through a tool opening and the slot and configured to perform a biopsy of a body part. A system according to claim 12, wherein the system is arranged, for example comprising a programmable controller, to perform an operation in which, in a first imaging step, the first collimator assembly is disposed with a second collimator portion (75) thereof between the imaging space and the detector, and wherein, for performing a second imaging step, the first collimator assembly is moved such that the first collimator assembly is disposed with the first collimator portion (61) thereof between the imaging space and the detector. 20. Method of gamma imaging a body part, for example a breast, using a collimator part (61) according to one or more of the following claims 1-9, and/or a gamma camera (50) according to claim 10, and/or a system according to one or more of the preceding claims 11-19.