WO2016050631A1

WO2016050631A1 - Angle-sensitive gamma camera with a rotary obstruction

Info

Publication number: WO2016050631A1
Application number: PCT/EP2015/072103
Authority: WO
Inventors: Matjaz VENCELJ; Larisa HOSNAR; Klemen BUCAR; Janez BURGER
Original assignee: Jozef Stefan Institute
Priority date: 2014-09-29
Filing date: 2015-09-25
Publication date: 2016-04-07
Also published as: GB2530574A; GB201417153D0; SI24818A; GB2530574B

Abstract

The present invention provides an angle-sensitive camera for detecting radiation, including a stationary detector (1) and a set of simultaneously rotating gamma-ray absorbent obstructions (3) of specific shape and placement such that the detection of the radiation incident from a given direction is hindered twice per device revolution and that the azimuthal and elevation angle of the radiation direction translate uniquely into the exact times of detection hindrance during each revolution.

Description

Angle-sensitive gamma camera with a rotary

obstruction

The present invention belongs in the field of radiation measurement technology. It is particularly, but not

exclusively, concerned with devices for determining the incident direction of gamma rays or other penetrating

radiation, an apparatus for carrying out such a determination and methods of determining the incident direction.

Devices, apparatuses and methods of this type find use in the fields of medical radiotherapy, nuclear industry and homeland security. A specific medical use for such devices is in High Dose Rate brachytherapy in clinical oncology where catheters are

surgically positioned through a malignant lesion, followed by the temporary insertion of a gamma-radioactive source into the catheters in order to locally deposit a therapeutic radiation dose over a volume of the lesion.

Current practices suffer from an absence of real-time feedback on the actual deposited radiation dose. A camera, sensitive to the incoming direction of gamma radiation would sense, in real time, the position of the radiation source inside the treated patient and could therefore introduce a quality-control component to described radiotherapy.

Other examples of use are in detection and localization of radioactive contaminations in nuclear medicine environments and in nuclear power installations as well as in real-time control of inventory and transportation of special nuclear material, localization of potentially harmful radioactive sources, such as so-called "dirty bombs", etc. Several angle-sensitive gamma-ray imaging devices are known, as set out below. CN201637854U, WOl 994029748A1 and RU2138832C1 all propose the localization of a radiation source by variants on the "camera obscura" apparatus, predominantly by combining a position- sensitive sensor with an absorbing wall having a small hole through which the radiation source illuminates a portion of the detector.

RU2300784C2 describes a method based on a quadrant-readout of the gamma interaction loci in a multi-layered scintillation detector to determine by extrapolation the direction of incident gamma rays.

DE10318416A1 is another multi-layered approach comprising a number of stationary detection plates with corresponding individual read-out channels.

GB2293742A comprises a sensor head with a coded aperture mask and sensors. To provide an extended field of view the complete

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mask in relation to the sensor.

US20050029461A1 comprises a rotary arrangement of collimators that restrict gamma rays entry to one incident plane at every given time. US6100530A describes a rotary scintillation system that is coupled optically to a stationary photomultiplier tube. It provides azimuthal information on the incoming radiation direction . US 6847838 Bl comprises a single pinhole or a plurality of pinholes collimator, through which passing gamma rays reach one or several PSPMT detectors. Detector may be stationary or it might change its position and thereby receive gamma rays from different angles.

US 20120132814 Al is an omnidirectional sensor device where a three-dimensional structure is formed of a plurality of walls, which comprise detector arrays and determines the incident direction of gamma rays from the ratio of signals in these detectors .

Some of the abovementioned solutions use multi-channel

detectors which considerably complicates the readout and the interpretation of data, and adds complexity and cost to the design. Some, in addition, severely limit the detection efficiency and thus angular sensitivity by blocking most of the radiation flux. All of the others only provide one spatial coordinate of the flux direction, such as the azimuth.

At their broadest, devices of the present invention are angle- sensitive cameras for detecting radiation, with rotating obstructions or obstruction elements which uniquely obscure or permit incident radiation from substantially all paths to the detector at certain times during their rotation.

A first aspect of the present invention provides an angle- sensitive camera for detecting radiation, the camera

comprising: a detector, and an elongate obstruction made from a material which strongly attenuates the radiation, wherein the obstruction is rotatable about an axis of rotation which passes through the detector so as to sweep through a spheroid or cylindroid centred on the detector such that substantially all paths to the detector are uniquely obscured for an identical period of time by the obstruction on at least two instances in each full revolution of the obstruction.

The camera of the present aspect provides a very simple device which can be used to determine the incident angle of radiation using a radiation detector with no directional capability. The inherent symmetry of this device and the fact that it need only comprise one sensor can allow it to be essentially free of directional bias, even when averaged over long exposure times.

Rotating the obstructions (which do not require electrical connections for power or signal purposes) rather than the sensor further simplifies the device.

It is preferable that the obstructions sweep a complete sphere as this ensures that all paths to the detector are equally obscured during the rotation of the obstructions as the obstructions will be the same distance from the detector at the point where they block each path to the detector.

However, the skilled person will appreciate that it may not be possible, for example for practical construction reaso s, to arrange the obstruction or obstructions such that a complete perfect sphere is swept. In particular, it may be necessary for a small gap to be present at the "top" and/or "bottom" of the sphere along the axis of rotation to allow for support for the detector and rotation of the obstructions. In these cases, the camera will not be useful in the detection of incident radiation coming through these gaps, but these gaps will preferably account for a very small proportion (e.g. less than 10%, more preferably less than 5%) of the total range of possible incident directions, and this limitation will be known in advance of the use of the camera. Therefore, the term spheroid is used to include nearly

complete spheres as well as shapes which are approximately, but not exactly spherical in their dimensions.

A similar effect to a sphere with gaps at the top and bottom can be achieved where the volume swept is a cylinder (or cylindroid) . Preferably there are a plurality of said obstructions and the obstructions are connected so as to always be in the same relative position and orientation to each other. The

obstructions may be connected by being mounted on a common support which is rotated.

The obstruction or obstructions preferably lie substantially in a plane which intersects the axis of rotation at the detector . Preferably the plane intersects the axis of rotation at an angle of between 40 and 50 degrees to the axis of rotation, more preferably at substantially or exactly 45 degrees to the of the obstructions reguired to substantially sweep through a spheroid or cylindroid are minimised. However, the skilled person will appreciate that angles other than 45 degrees could easily be used and the advantages of the invention achieved.

Preferably, when viewed along the axis of rotation, the obstructions lie substantially on a circle or ellipse centred on the axis of rotation.

Preferably the obstruction or obstructions are eguidistant from the director at all, or substantially all, points. This means that the attenuation effect of the obstruction ( s ) is the same from every direction.

The camera may further comprise one or more counterweights mounted to balance the weight of the obstructions, and thereby reduce periodic strain and vibration of the camera. As the obstructions will typically be formed from dense metal in order to have the greatest attenuation effect on the

radiation, their asymmetrical arrangement around the axis of rotation may place considerable period strain on their

supports and the motor (s) which drive the rotation. The asymmetry may also result in vibration as the obstructions rotate. By providing counterweights which balance out this asymmetry, the strain and vibration can be reduced, preferably significantly so.

The camera of this aspect may include some, all or none of the above described preferred and optional features, in any combination .

A second aspect of the present invention provides an angle- sensitive camera for detecting radiation, the camera

comprising: a detector, and a substantially cylindrical obstruction element which is rotatable about an axis of rotation that passes through the detector, the obstruction element being primarily made from a material which strongly attenuates the radiation, wherein the obstruction element contains at least one elongate window and is arranged such that said window sweeps through a spheroid or cylindroid centred on the detector such that substantially all paths to the detector are uniguely open to the passage of radiation at least twice for an identical period of time in each full revolution of the obstruction element. It will be appreciated that the camera according to the second aspect essentially operates in mirror image to the camera according to the first aspect, with the windows replacing the obstructions and detection being based on the times when the intensity is increased, rather than decreased.

The camera of the present aspect provides a very simple device which can be used to determine the incident angle of radiation using a radiation detector with no directional capability. The inherent symmetry of this device and the fact that it need only comprise one sensor can allow it to be essentially free of directional bias, even when averaged over long exposure times . Rotating the windows and the cylindrical obstruction element (which do not require electrical connections for power or signal purposes) rather than the sensor further simplifies the device . Whilst it is preferable that the windows sweep a complete sphere as this ensures that all paths to the detector are equally opened during the rotation of the obstructions, this l a n n†^~ n r a p l- i' a l †^~ n n r nwi H p a n n P i n nn H i ri n oh o f n i r t" ! nn element. A substantially cylindrical obstruction element is therefore provided and a small gap will therefore be present at the "top" and/or "bottom" of the sphere along the axis of rotation to allow for support for the detector and rotation of the obstruction element. In these cases, the camera will not be as useful in the detection of incident radiation coming through these gaps, but these gaps will preferably account for a very small proportion (e.g. less than 10%, more preferably less than 5%) of the total range of possible incident directions, and this limitation will be known in advance of the use of the camera.

Therefore, the term spheroid is used to include nearly

A similar effect to a sphere with gaps at the top and bottom can be achieved where the volume swept is a cylinder (or cylindroid) .

The window or windows preferably lie substantially in a plane which intersects the axis of rotation at the detector.

Preferably the plane intersects the axis of rotation at an angle of between 40 and 50 degrees to the axis of rotation, more preferably at substantially or exactly 45 degrees to the axis of rotation. When the plane is at 45 degrees, the size of the windows required to substantially sweep through a spheroid or cylindroid are minimised. However, the skilled person will appreciate that angles other than 45 degrees could easily be used and the advantages of the invention achieved.

Preferably, when viewed along the axis of rotation, the windows lie substantially on a circle or ellipse centred on the axis of rotation.

In particular embodiments of the above aspects, the radiation is gamma-ray radiation and the detector is a gamma-ray detector. Detection of gamma-ray radiation has significant utility in the fields of medical physics and radioactive localization as described above.

A third aspect of the present invention provides an apparatus for determining the incident direction of radiation, the apparatus including a camera according to either of the above first or second aspects, including some, all or none of the optional and preferred features of those aspects, and a processor which is arranged to determine the incident

direction of the radiation from the intensity of radiation incident on the detector and the position of the obstructions or windows.

The apparatus preferably further includes a detector which is arranged to detect the rotational position of the obstructions or windows and supply information on said position to the proces sor .

At their broadest, methods of the present invention provide methods of determine the incident direction of radiation which use reductions or increases in the incident radiation caused by rotation obstructions which allow uniquely identification of the incident direction.

A fourth aspect of the present invention provides a method of determining the incident direction of radiation, the method including the steps of: rotating an elongate obstruction made from a material which strongly attenuates the radiation about an axis of rotation which passes through a detector so as to sweep through a spheroid or cylindroid centred on the detector such that substantially all paths to the detector are uniquely obscured for an identical period of time by the obstruction on at least two instances in each full revolution of the

obstruction; measuring the intensity of radiation incident on the detector during said rotation; determining the positions of obstruction at the times when the intensity of radiation is reduced; and determining the incident direction of radiation from said positions. The method of this aspect preferably, but not necessarily, makes use of a camera according to the above first aspect, including some, all or none of the optional and preferred features of that aspect. A fifth aspect of the present invention provides a method of determining the incident direction of radiation, the method including the steps of: rotating an elongate cylindrical obstruction element, made primarily from a material which strongly attenuates the radiation and containing at least one elongate window, about an axis of rotation which passes through a detector so that said window sweeps through a spheroid or cylindroid centred on the detector such that substantially all paths to the detector are uniquely open to the passage of radiation for an identical period of time by the obstruction on at least two instances in each full revolution of the obstruction; measuring the intensity of radiation incident on the detector during said rotation;

the positions of obstruction at the times when the intensity of radiation is increased; and determining the incident direction of radiation from said positions.

The method of this aspect preferably, but not necessarily, makes use of a camera according to the above second aspect, including some, all or none of the optional and preferred features of that aspect.

Embodiments of the invention will now be described with reference to the accompanying Figure which illustrates a camera according to an embodiment of the present invention. An embodiment of the present invention is shown in Figure 1 and comprises a simple single stationary gamma-ray sensor 1, such as a scintillation detector in counting mode, which is mounted on a structural support beam 2, such that both lie centrally along the rotation axis 5 of the apparatus.

Further, the device comprises two opposing ribbon-shaped obstructions 3 made of a gamma-ray absorbing material such as lead, that are simultaneously rotated along the common

rotational axis 5. The obstructions 3 are predominantly positioned in a geometrical plane that intersects the

rotational axis 5 at the position of the gamma-ray sensor 1 at an angle of 45°. The obstructions 3 are also predominantly shaped and positioned such that most of their material is placed at the same given radius from the axis 5, i.e., when viewed along the axis 5, the obstructions 3 lie on the

circumference of a circle. Because of the specific shape and placement of the rotating obstructions 3, the radiation intensity sensed by the

radiation detector 1 changes over time. Specifically, the signal measured by the detector 1 temporarily becomes smaller each time when the obstructions 3 cross the line-of-sight path between the radiation source and the sensor 1. Because there are two obstructions 3, this occurs exactly twice per full revolution of the obstructions.

The exact times when the two signal reductions occur over each full revolution, depend uniquely both on the azimuth and the elevation angle of the radiation source with respect to the device of the invention. This makes it possible, by

continuously measuring the detector signal and the angular position of the obstructions 3 (or of the rotor assembly that supports the obstructions 3), to determine in real time the incoming direction of the radiation, or equivalently, the angular position of the radiation source. The apparatus may also comprise two additional weights 4 that serve as counter-weights to stabilize the rotating part of the apparatus by balancing the weight of the obstructions 3.

The obstructions 3 and the counter-weights 4 are mounted on a structural support member 6 in the shape of a cylinder wall whose symmetry axis coincides with the apparatus rotation axis 5.

In an alternative embodiment, the obstructions 3 and said structural cylindrical support 6 exchange roles such that the cylinder 6 is made of gamma-ray absorbing material and that holes or windows are cut in place of obstructions 3. In this case, the radiation intensity changes by increasing at the times when the direct path from the radiation source to the sensor 1 passes through the holes or windows, which occurs exactly twice for every revolution of the cylindrical support 6.

Again, the exact times when the two signal increases occur over each full revolution, depend uniquely both on the azimuth and the elevation angle of the radiation source with respect to the device of the invention. This makes it possible, by continuously measuring the detector signal and the angular position of the obstructions 3 (or of the rotor assembly that supports the obstructions 3), to determine in real time the incoming direction of the radiation, or equivalently, the angular position of the radiation source.

The device may further comprise an optical device which is arranged to measure or detect the current rotational position of the rotor, or some other form of position detector may be used, for example the positional information from a stepper motor driving the obstruction or cylindrical support.

In a further embodiment, the apparatus also includes a

processor which is arranged to receive intensity data from the sensor 1 and information regarding the position of the

obstructions 3 (or the corresponding holes or windows) and to determine the incident direction of the radiation from that data and information.

The processor determines the incident direction of the

radiation by determining, from the position of the

obstructions 3 (or the corresponding holes or windows) the single direction along which radiation is either attenuated, or permitted, by the device at both of the times when the reduced or increased intensity of radiation is received at the sensor 1.

The systems of the above embodiments may be implemented in a computer system (in particular in computer hardware) in

†-^~ n t h p s—l—r—i—i r—f—n—ra l mmnnn pn t_s_ ΛΠΗ n—s p—r i n t p ra r.H nn s described. In particular the processor may be a computer processor, suitably controlled by computer software.

The term "computer system" includes the hardware, software and data storage devices for embodying a system or carrying out a method according to the above described embodiments. For example, a computer system may comprise a central processing unit (CPU), input means, output means and data storage.

Preferably the computer system has a monitor to provide a visual output display. The data storage may comprise RAM, disk drives or other computer readable media. The computer system may include a plurality of computing devices connected by a network and able to communicate with each other over that network . The methods of embodiments of the invention may be provided as computer programs or as computer program products or computer readable media carrying a computer program which is arranged, when run on a computer, to perform the method (s) described above .

The term "computer readable media" includes, without

limitation, any non-transitory medium or media which can be read and accessed directly by a computer or computer system. The media can include, but are not limited to, magnetic storage media such as floppy discs, hard disc storage media and magnetic tape; optical storage media such as optical discs or CD-ROMs; electrical storage media such as memory, including RAM, ROM and flash memory; and hybrids and combinations of the above such as magnetic/optical storage media.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent

modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

Claims

1. An angle-sensitive camera for detecting radiation, the camera comprising:

a detector , and

an elongate obstruction made from a material which strongly attenuates the radiation, wherein

the obstruction is rotatable about an axis of rotation which passes through the detector so as to sweep through a spheroid or cylindroid centred on the detector such that substantially all paths to the detector are uniquely obscured for an identical period of time by the obstruction on at least two instances in each full revolution of the obstruction.

2. A camera according to claim 1, wherein there are a plurality of said obstructions and the obstructions are connected so as to always be in the same relative position and orientation to each other.

3. A camera according to claim 1 or claim 2, wherein the obstruction or obstructions lie substantially in a plane which intersects the axis of rotation at the detector.

Drding to claim 3 wherein the plane intersect the axis of rotation at an angle of between 40 and 50 degrees to the axis of rotation.

5. A camera according to any one of the preceding claims wherein, when viewed along the axis of rotation, the

obstructions lie substantially on a circle or ellipse centred on the axis of rotation.

6. A camera according to any one of the preceding claims, further comprising: one or more counterweights mounted to balance the weight of the obstructions, and thereby reduce periodic strain and vibration of the camera.

7. An angle-sensitive camera for detecting radiation, the camera comprising:

a detector , and

a substantially cylindrical obstruction element which is rotatable about an axis of rotation that passes through the detector, the obstruction element being primarily made from a material which strongly attenuates the radiation, wherein

the obstruction element contains at least one elongate window and is arranged such that said window sweeps through a spheroid or cylindroid centred on the detector such that substantially all paths to the detector are uniquely open to the passage of radiation at least twice for an identical period of time in each full revolution of the obstruction element .

8. A camera according to claim 7, wherein the window or windows lie substantially in a plane which intersects the axis of rotation at the detector.

9. A camera according to claim 8 wherein the plane intersects the axis of rotation at an angle of between 40 and 50 degrees to the axis of rotation.

10. A camera according to any one of claims 7 to 9 wherein, when viewed along the axis of rotation, the windows lie substantially on a circle or ellipse centred on the axis of rotation .

11. A camera according to any one of the preceding claims, wherein the radiation is gamma-ray radiation and the detector is a gamma-ray detector.

12. An apparatus for determining the incident direction of radiation, the apparatus including a camera according to any one of the preceding claims and a processor which is arranged to determine the incident direction of the radiation from the intensity of radiation incident on the detector and the

position of the obstructions or windows.

13. An apparatus according to claim 12, further including a detector which is arranged to detect the rotational position of the obstructions or windows and supply information on said position to the processor.

14. A method of determining the incident direction of

radiation, the method including the steps of:

rotating an elongate obstruction made from a material which strongly attenuates the radiation about an axis of rotation which passes through a detector so as to sweep

through a spheroid or cylindroid centred on the detector such that substantially all paths to the detector are uniquely obscured for an identical period of time by the obstruction on at least two instances in each full revolution of the

obstruction;

measuring the intensity of radiation incident on the detector during said rotation;

determining the positions of obstruction at the times when the intensity of radiation is reduced; and

determining the incident direction of radiation from said positions .

15. A method of determining the incident direction of

radiation, the method including the steps of:

rotating an elongate cylindrical obstruction element, made primarily from a material which strongly attenuates the radiation and containing at least one elongate window, about an axis of rotation which passes through a detector so that said window sweeps through a spheroid or cylindroid centred on the detector such that substantially all paths to the detector are uniquely open to the passage of radiation for an identical period of time by the obstruction on at least two instances in each full revolution of the obstruction;

determining the positions of obstruction at the times when the intensity of radiation is increased; and

determining the incident direction of radiation from said positions .