Device and method for computed tomography and positron emission tomography scanning with two rotation axes

Abstract

Imaging device and method for computed tomography, CT, and positron emission tomography, PET, scanning of a subject arranged in an examination region, comprising: a first radiation detector; a second radiation detector; a radiation source which is switchable between, at least, on and off states; wherein the first radiation detector and the second radiation detector are collinear and arranged opposite each other with respect of the examination region and towards the examination region to detect gamma-radiation from the subject; wherein the radiation source and the second radiation detector are arranged opposite each other with respect of the examination region and arranged towards the examination region for the second radiation detector to detect transmitted radiation through the subject from the radiation source; wherein the radiation source, the first radiation detector and the second radiation detector are arranged to rotate together about a first rotation axis which is offset from the examination region centre; wherein the first rotation axis is arranged to rotate about a second rotation axis which is within the examination region.

Description

DESCRIPTIONDEVICE AND METHOD FOR COMPUTED TOMOGRAPHY AND POSITRON EMISSION TOMOGRAPHY SCANNING WITH TWO ROTATION AXESTechnical field

[0001] The present description refers to a device and method of nuclear or medical imaging instrumentation, in particular to a system of X-ray or gamma-ray computed tomography (CT) and positron emission tomography (PET), whereas combining these two imaging modalities, the disclosure is able to produce radiographic transmission and functional images (CT and PET, respectively) using an emission tomography system with two axes of rotation, adapted for this purpose.Background

[0002] Transmission computed tomography is a medical imaging modality that uses a gamma or X-ray radiation source outside the patient and detects the photons transmitted through the body, from different angles, to produce cross-sectional and 3D images. Transmission CT images are essentially maps of the linear attenuation coefficients inside a subject, thus providing morphological information. This technique can be used also for other applications, to assess the characteristics of the internal structure of any object, such as dimensions, shape, internal defects and density, all of which are readily available from CT images.

[0003] Emission tomography is a medical imaging modality that provides functional or metabolic information about an organ, system or tissue, by administering radiolabeled molecules (radiopharmaceuticals) to the patients and imaging the emitted radiation, i.e. the radiation sources are inside the patient. The information of the molecule's 3D biodistribution is useful not only for diagnostic purposes, such as detection of functional abnormalities or early identification of tumors, but can alsobe very helpful in therapy planning and follow-ups. There are two types of emission tomography, depending on the decay mode of the chosen radionuclide: SPECT, Single Photon Emission Computed Tomography, where the nucleus eliminates its energy by emitting one or more photons, and PET, Positron Emission Tomography, where the nucleus emits a positron, antiparticle of the electron. The tomographic images are reconstructed from the external detection of the emitted photons (in SPECT) or the pairs of back-to-back gamma photons in coincidence, which follow positron annihilations (in PET).

[0004] Anatomical images obtained by transmission tomography complement functional images obtained by emission tomography, allowing a precise location of anatomical regions with higher radiopharmaceutical uptake, which is critical in medical applications, for example in the surgical removal of a tumor. In addition, the attenuation map provided by the transmission image is used to correct the emission image, compensating the attenuation effect of the emission photons. For these reasons, PET or SPECT scanners are usually combined with CT scanners in hybrid systems, producing fused PET / CT or SPECT / CT images.

[0005] The typical CT scanner uses a complete set of components: x-ray source and x-ray detectors mounted in a gantry, either in a standalone system or integrated in a hybrid imaging system (e.g., PET / CT or SPECT / CT).

[0006] Document W02016 / 147130 discloses a method and system of positron emission tomography that can have only two detector modules rotating around the object, using two axes of rotation, so as to cover a field of view similar to that of a complete ring of detectors, the so called easyPET scanner technology. This technology allows reducing the number of detectors required to produce a PET image and associated components, while at the same time it can achieve a high spatial sampling and resolution, particularly in the transaxial field of view, where it minimizes parallax errors.

[0007] The high complexity and cost associated with the available CT systems represents a drawback for the implementation of a multimodal imaging system, PET / CT or SPECT / CT.

[0008] These facts are described in order to illustrate the technical problem solved by the realizations of the present document.General Description

[0009] The present disclosure refers to a radiation instrumentation / imaging, in particular to a system of x-ray or gamma ray computed tomography, CT, which produces morphologic / anatomic images of a subject, more particularly a CT system which comprises, in one side, a radioactive source and, in the other side and in front of it, detector modules rotating around the subject, so as to cover a field of view similar to that of a complete ring of detectors.

[0010] Through the CT system and its acquisition method with two axes of rotation, the achievements of the present disclosure aim to further reduce the number of detectors needed to obtain a CT image.

[0011] It is therefore, one of the aims of the present description to obtain CT images in two or three dimensions, using detectors in solidarity (i.e. moving together) with the radioactive source, that also moves together, and perform two independent scans around two axes of rotation, so as to cover a cylindrical field of view between the detectors and the radioactive source, defined by the amplitude of one of the scans. The radioactive source and the detectors remain collinear and always aligned during all scans, eliminating aberration effects due to misalignments.

[0012] It is disclosed an imaging device for computed tomography, CT, and positron emission tomography, PET, scanning of a subject arranged in an examination region, comprising: a first radiation detector; a second radiation detector; a radiation source which is switchable between, at least, on and off states; wherein the first radiation detector and the second radiation detector are collinear and arranged opposite each other with respect of the examination region and towards the examination region to detect gamma radiation from thesubject; [PET scanning involves the subject receiving a small amount of a radioactive substance, a tracer, which - as it decays - emits two gamma rays in opposite directions] wherein the radiation source and the second radiation detector are arranged opposite each other with respect of the examination region and arranged towards the examination region for the second radiation detector to detect transmitted radiation through the subject from the radiation source; [The radiation source and the first detector are thus near each other or jointly mounted together.] wherein the radiation source, the first radiation detector and the second radiation detector are arranged to rotate together about a first rotation axis which is offset from the examination region centre; [This way, a first scanning degree of freedom is obtained by the rotation about the first rotation axis] wherein the first rotation axis is arranged to rotate about a second rotation axis (i.e. at a predetermined distance, from said second rotation axis) which is within the examination region. [This way, a second scanning degree of freedom is obtained by the rotation about the second rotation axis, in order to substantially scan a 2D section of the subject arranged in the examination region]

[0013] As first and second detectors for PET scanning, and the radioactive source and the second detector for CT scanning, remain collinear and aligned during the scans, being arranged opposite in respect of the examination region, and the first and second axis of rotation being fixed, this eliminates aberration effects and enables the acquisition of positron emission tomography images and also radiographic transmission images through alternating or simultaneous rotations of the first axis and second axis of rotation.

[0014] The arrangement allows to focus on a specific area and also allows for "subpixel" movement, i.e. movements smaller than detector size between radiation acquisition in order to improve the overall resolution of the system.

[0015] In an embodiment, the first radiation detector comprises a first stack of detectors stacked along a stacking direction parallel to the first rotation axis, and thesecond radiation detector comprises a second stack of detectors stacked along a stacking direction parallel to the first rotation axis, wherein each of the detectors of the first stack of detectors is arranged collinear and arranged opposite a corresponding detector of the second stack of detectors with respect of the examination region to detect gamma radiation from the subject.

[0016] In an embodiment, the radiation source is arranged at a central position of the first stack of detectors along the stacking direction.

[0017] In an embodiment, the radiation source is arranged on a lateral side of the first radiation detector, in particular arranged on a lateral side of the first stack of detectors.

[0018] In an embodiment, the radiation source, the first radiation detector and the second radiation detector are collinear.

[0019] Preferably the radiation source, the first radiation detector and the second radiation detector are collinear, i.e. lying in a same straight line. In this case, the radiation source may be arranged directly in front of the first detector.

[0020] In an embodiment, the first rotation axis and the second rotation axis are arranged parallel to each other.

[0021] Nevertheless, a small acute angle or an adequately small angle between the first and second rotation axis can be taken into account by software configured to recover 3D information from the detected radiation.

[0022] In an embodiment, each detector comprises a photodetector and a scintillator, thus defining, respectively, a back of the detector and a front of the detector, the front of the detector being arranged towards radiation to be detected.

[0023] wherein the first rotation axis is coincident with a front of the first detector.

[0024] By having the first rotation axis coincident, or as close as possible, with a front of the first detector (or a front of the first stack of detectors), the calculations to be carried out to recover 3D information from the detected radiation are simpler to carry out.

[0025] In an embodiment, the first rotation axis is coincident with a front of the radioactive source.

[0026] By having the first rotation axis coincident, or as close as possible, with a front of the radioactive source, the calculations to be carried out to recover 3D information from the detected radiation are simpler to carry out.

[0027] In an embodiment, the second rotation axis is centred halfway between the first and second detectors, and the second rotation axis is preferably substantially centred within the examination region.

[0028] By having the second rotation axis centred halfway between the first and second detectors, the calculations to be carried out to recover 3D information from the detected radiation are simpler to carry out.

[0029] In an embodiment, the radiation source, the first radiation detector and the second radiation detector are arranged to move together (in particular, smaller rotation movements, i.e. oscillate, fan or swing) about the first rotation axis.

[0030] Preferably, the first rotation axis is used for smaller rotation movements whereas the second rotation axis is used for larger rotation movements

[0031] An embodiment comprises a computer data processor configured for actuating a motor or motors for rotating the radiation source, the first radiation detector and the second radiation detector.

[0032] A motor may be used to rotate the first axis and second axis, or separate motors may be used each for rotating the first axis and second axis.

[0033] In an embodiment, the computer data processor is further configured for acquiring radiation detector data, when the radiation source, the first radiation detector and the second radiation detector are not being rotated.

[0034] Radiation acquisition is preferably carried out when not rotating.

[0035] In an embodiment, the computer data processor is further configured for acquiring CT scanning data from the second detector when the radiation source is in the on state and configured for acquiring PET scanning data from the first and second detectors when the radiation source is in the off state, in particular the computer data processor is further configured for the first detector being inactivated when the radiation source is in the on state.

[0036] CT and PET scanning data may be acquired separately and non-overlapping periods of time.

[0037] In an embodiment, the computer data processor is further configured for biasing the second detector for a lower energy level of detection when acquiring CT scanning data and configured for biasing the first and second detectors for a higher energy level of detection when acquiring PET scanning data.

[0038] In an embodiment, the computer data processor is further configured for acquiring CT scanning data from the second detector, and configured for acquiring PET scanning data from the first and second detectors, and configured for telling apart detected CT and PET radiation based on an energy level of a detected photon.

[0039] CT and PET scanning data may be acquired simultaneously or in overlapping periods of time. In this case, the detectors may be biased for the PET higher energy level of detection which may have the disadvantage of increasing noise for the CT lower energy level of detection.

[0040] In an embodiment, the computer data processor is further configured for acquiring radiation detector data: when not actuating the motor or motors to not rotate the radiation source, the first radiation detector and the second radiation detector; or when actuating the motor or motors to not rotate the radiation source, the first radiation detector and the second radiation detector.

[0041] Certain types of motors may require to be specifically actuated in order not to have rotation movement, that is a continuous energization to maintain a stationary position, like stepper motors or servo motors, whereas other motors may simply require a lack of actuation in order not to have rotation movement, that is a continuous lack of energization to maintain a stationary position, like motors with worm gear mechanisms, permanent magnet synchronous motors with passive locking, or synchronous reluctance motors with frictional locking.

[0042] In an embodiment, the radiation source is a radioactive source emitting in particular gamma-ray or x-ray photons.

[0043] In an embodiment, each detector comprises a photodetector and a scintillator, and the scintillator comprises faces coated with an optical reflective material except for a scintillator face coupled to the photodetector which is optionally coated with an optical transmissive material.

[0044] In an embodiment, the photodetector is a photomultiplier.

[0045] In an embodiment, the radiation source, the first radiation detector and the second radiation detector are arranged to rotate together about the first rotation axis with a rotation angle of up to 180°.

[0046] In an embodiment, the first rotation axis is arranged to rotate about the second rotation axis with a rotation angle of up to 360°.

[0047] In an embodiment, the computer data processor is further configured for an alternating rotation about the first rotation axis and about the second rotation axis, repeated a predetermined number of times.

[0048] In an embodiment, the computer data processor is further configured for acquiring and transmitting the angular positions of the two rotation axes and the number of radiation events detected at each angular position, for 3D image reconstruction.

[0049] In an embodiment, the computer data processor is further configured for a predetermined stopping time at each angular position of the two axes to count the number of radiation events detected.

[0050] In an embodiment, immediately successive angular positions are spaced at a distance smaller than a pixel size of the first and second detectors.

[0051] In an embodiment, the computer data processor is further configured for a predetermined stopping time at alternating angular positions of the two axes to count the number of radiation events detected, alternatingly, for CT scanning by the second detector, and for PET scanning by the first and second detectors.

[0052] It is also disclosed an x- or gamma-ray computed tomography system comprising:two axes of rotation, where the second axis is fixed and the first axis is movable within a circumference defined by the second axis and is mechanically coupled to a support; one or more detectors fixed to the support, and aligned along the same longitudinal axis with the radioactive source; one or more scintillator detectors fixed to the support that are integral parts of the rotation system; a photodetector attached to each scintillator crystal or covering all scintillators; in alternative, any type of x- or gamma-ray detectors; a support, fixed to the first axis of rotation, with a free region between the radioactive source-detector pair, the region where the subjects of which the images are to be produced, are placed; an electronic system for reading detector signals consisting of individual or group of amplifier circuits and circuits for detecting events recorded in the photodetector coupled to scintillator crystals or other x-ray or gamma ray detectors; a controller unit consisting of one or more microcontrollers, for system control and communication between a computer and the other parts of the system described above.

[0053] In an embodiment the fixed second axis of rotation of the imaging system for radiographic transmission computed tomography is centered halfway between detectors and the radioactive source and the movable first axis of rotation is parallel and coincident with the front face of the radioactive source.

[0054] In an embodiment, the one or more scintillator detectors of the imaging system for radiographic transmission computed tomography are coupled to the photodetectors by means of gel or optical cement.

[0055] In an embodiment, the faces of the one or more scintillator detectors of the imaging system for radiographic transmission computed tomography, except the face coupled to the photomultiplier, are coated with an optical reflective material.

[0056] In an embodiment, the integration of the CT system into a PET system is used in the imaging system for radiographic transmission computed tomography, using the same detectors used by the PET system, now for detecting the radiation, x-ray or gamma-ray, from the external source to produce the CT images.

[0057] In an embodiment, the imaging system further comprises a power supply unit and an integrated electronic reading system mounted on the same support as the radioactive source and detector modules.

[0058] In an embodiment, the imaging system achieves the acquisition of radii and response views at different angular positions of the two rotation axes.

[0059] In an embodiment, the fixed second axis of the imaging system sweeps an angle of up to 360 degrees and, for each position of the fixed second axis, the first axis sweeps an angle of up to 180 degrees, defining the field of view.

[0060] In an embodiment, the alternating rotation of the second axis of rotation and the first axis of rotation of the imaging system is repeated a predefined number of times to improve image resolution.

[0061] In an embodiment, the imaging system further comprises a predefined stopping time at each angular position of the two axes to count the number of rays detected.

[0062] In an embodiment, the controller unit of the imaging system communicates the angular positions of the two axes of rotation and the number of rays detected at each position to the computer for real-time image reconstruction.Brief description of the drawings

[0063] The following figures provide preferred embodiments for illustrating the disclosure and should not be seen as limiting the scope of invention.

[0064] Fig. 1: Schematic representation (transaxial) of an embodiment of the CT / PET image acquisition method with two axes of rotation, where one axis is fixed and the other axis is movable on a circumference centered on the fixed axis, in order toacquire several response views at different angular positions covering a field of view between the source and detectors.

[0065] Fig. 2: Schematic orthogonal representation (axial) to the plane shown in Fig. 1 of an (3D) embodiment of the CT / PET system, consisting of two axes of rotation (associated with two motors, for example stepper motors), with a free examination region between the radioactive source and the opposed detectors, that are an integral part of the PET system, wherein the radiation source has a disc-shaped support / container.

[0066] Fig. 3: Schematic orthogonal representation (axial) to the plane shown in Fig.1 of an axial (3D) embodiment of the CT / PET system, wherein the radiation source has a smaller support / container.

[0067] Fig. 4: Schematic orthogonal representation (axial) to the plane shown in Fig.1 of an axial (3D) embodiment of the CT / PET system, wherein the radiation source is located closer to the detector front.

[0068] Fig. 5: Schematic orthogonal representation (axial) to the plane shown in Fig. 1 of an axial (3D) embodiment of the CT / PET system, wherein the radiation source is located in front of the detector front and transaxially collinear with the detector.Detailed description

[0069] The present description refers to a device and method of nuclear or medical imaging instrumentation, in particular to a system of X-ray or gamma-ray computed tomography (CT) and positron emission tomography (PET), whereas combining these two imaging modalities, the disclosure is able to produce radiographic transmission and functional images (CT and PET, respectively) using an emission tomography system with two axes of rotation, adapted for this purpose.

[0070] It is disclosed an imaging device for radiographic transmission computed tomography, comprising: a radioactive source; one or more detector modules aligned with the radioactive source along the same longitudinal axis; a first axis of rotation; a second fixed axis of rotation, wherein the first axis of rotation is movable within acircumference defined by the fixed second axis of rotation; a support for the radioactive source and one or more detector modules; a controller unit for coordinating the movement of the first and second axes of rotation and for communicating with a computer for image reconstruction; an electronic system for reading signals from the one or more detector modules, comprising individual amplifier circuits and event detection circuits; wherein the support comprises a free region between the radioactive source and one or more detector modules for placing the subject to be imaged; wherein the radioactive source and one or more detector modules remain collinear and aligned during all scans, being in the opposite direction to the first and second fixed axis of rotation, eliminating aberration effects and enabling the acquisition of radiographic transmission images through alternating rotations of the first axis and second fixed axis of rotation.

[0071] In an embodiment, the imaging system further comprises one or more scintillator detectors fixed to the support that are integral parts of the rotation system, for better results.

[0072] In an embodiment, the one or more scintillator detectors of the device are coupled to the photodetectors by means of gel or optical cement, for better results.

[0073] In an embodiment, the fixed second axis of rotation of the device is centered halfway between detectors and the radioactive source and the first axis of rotation is parallel and coincident with the front face of the radioactive source, for better results.

[0074] In an embodiment, the faces of the one or more scintillator detectors of the imaging system, except the face coupled to the photomultiplier, are coated with an optical reflective material, for better results.

[0075] In an embodiment, the device further comprises a power supply unit and an integrated electronic reading system mounted on the same support as the radioactive source and one or more detector modules, for better results.

[0076] In an embodiment, the fixed second axis of the device sweeps an angle of up to 360 degrees and, for each position of the fixed second axis, the first axis sweeps an angle of up to 180 degrees, defining the field of view, for better results.

[0077] In an embodiment, the alternating rotation of the fixed second axis of rotation and the first axis of rotation of the device is repeated a predefined number of times to improve image resolution, for better results.

[0078] In an embodiment, the controller unit of the imaging communicates the angular positions of the two axes of rotation and the number of rays detected at each position to the computer for real-time image reconstruction, for better results.

[0079] In an embodiment, the device further comprises a predefined stopping time at each angular position of the two axes to count the number of rays detected, for better results.

[0080] In an embodiment, the device further comprises integration with a positron emission tomography (PET) system, wherein the same detectors are used for PET imaging and for detecting radiation from the external source to produce CT images, for better results.

[0081] In an embodiment, the one or more detector modules and radioactive source of the device are configured to perform radiographic acquisitions at different angular positions of the two axes of rotation, for better results.

[0082] In an embodiment, the device further comprises a photodetector attached to each of the one or more scintillator detectors, for better results.

[0083] In an embodiment, the radioactive source of the device emits in the frequency of an X-ray or gamma-ray, for better results.

[0084] In an embodiment, CT / PET image acquisition device and method, whose is represented in Fig. 1, comprises: two axes of rotation represented by 1 and 2, which are associated to two step motors. Axis 1 is fixed and centered at half distance between the detectors (3 and 5). Axis 2 is mobile within the circumference drawn by axis 1 and coincident with the frontal face of detector 5 below the radioactive source 4;axis 1 and axis 2 rotate alternatively, in which axis 1 scans an angle a, up to 360 degrees, and for each axis 1 position, axis 2 describes an angle 0 between 0 and 180 degrees, defining the transaxial field of view of the system; at each position of axes 1 and 2, detector 3 receives an amount of photons coming from radioactive source 4,which are attenuated in the scanned object / patient, to perform a CT image acquisition.

[0085] In an embodiment a simple schematic of the CT system is represented in Fig. 2, comprising: two sets of detectors, one activated (represented by 3) and the other one deactivated (represented by 5). are composed of scintillator crystals coupled with a silicon photodetector, one to one. The radioactive source 4 is placed above and centered with detectors group 5.

[0086] In an embodiment, detectors are supported by a board or support, fixed to the mobile axis of rotation 2. Each group of detectors, 3 and 5, is aligned front to front, presenting a free region between them where the objects intended to be imaged are placed.

[0087] Fig. 1 shows the schematics of the acquisition method for CT acquisition with two axes of rotation 1 and 2, in which axis 1 is fixed and axis 2 is mobile within circumference defined by axis 1; a represents the angle step described by axis 1, and 0 represents the angle range scanned by axis 2 for each axis l's position. The two axes are used to move the groups of detectors (3 and 5) together with the radioactive source 4, in order to acquire photons from 4, covering a cylindrical field of view between the detectors 3 and the source 4.

[0088] Fig. 2 represents a simple schematic of the CT system, being an orthogonal representation of Fig. 1. The group of detectors activated during CT acquisition are represented by 3, and the radioactive source 4 is placed above and centered with the deactivated group of PET detectors 5.

[0089] Fig. 3-5 show alternative arrangements of the radiation source.

[0090] Fig. 1-5 thus show an embodiment where the imaging device for computed tomography, CT, and positron emission tomography, PET, scanning of a subject arranged in an examination region, comprising: a first radiation detector 5; a second radiation detector 3; a radiation source 4 which is switchable between, at least, on and off states;wherein the first radiation detector and the second radiation detector are collinearand arranged opposite each otherwith respect of the examination region and towards the examination region to detect gamma-ray decay radiation from the subject; wherein the radiation source 4 and the second radiation detector 3 are arranged opposite each otherwith respect of the examination region and arranged towards the examination region for the second radiation detector to detect transmitted radiation through the subject from the radiation source; wherein the radiation source, the first radiation detector and the second radiation detector are arranged to rotate together about a first rotation axis 2 which is offset from the examination region centre; wherein the first rotation axis is arranged to rotate about a second rotation axis 1 which is within the examination region.

[0091] The term "comprising" whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0092] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof. The above-described embodiments are combinable.

[0093] The following dependent claims further set out particular embodiments of the disclosure.

Claims

C L A I M S1. Imaging device for computed tomography, CT, and positron emission tomography, PET, scanning of a subject arranged in an examination region, comprising: a first radiation detector; a second radiation detector; a radiation source which is switchable between, at least, on and off states; wherein the first radiation detector and the second radiation detector are collinear and arranged opposite each other with respect of the examination region and towards the examination region to detect gamma radiation from the subject; wherein the radiation source and the second radiation detector are arranged opposite each other with respect of the examination region and arranged towards the examination region for the second radiation detector to detect transmitted radiation through the subject from the radiation source; wherein the radiation source, the first radiation detector and the second radiation detector are arranged to rotate together about a first rotation axis which is offset from the examination region centre; wherein the first rotation axis is arranged to rotate about a second rotation axis which is within the examination region.

2. Imaging device according to the previous claim wherein the first radiation detector comprises a first stack of detectors stacked along a stacking direction parallel to the first rotation axis, and the second radiation detector comprises a second stack of detectors stacked along a stacking direction parallel to the first rotation axis, wherein each of the detectors of the first stack of detectors is arranged collinear and arranged opposite a corresponding detector of the second stack of detectorswith respect of the examination region to detect gamma radiation from the subject.

3. Imaging device according to any of the previous claims wherein the radiation source is arranged at a central position of the first stack of detectors along the stacking direction.

4. Imaging device according to any of the previous claims wherein the radiation source is arranged on a lateral side of the first radiation detector, in particular arranged on a lateral side of the first stack of detectors.

5. Imaging device according to any of the previous claims wherein the radiation source, the first radiation detector and the second radiation detector are collinear.

6. Imaging device according to any of the previous claims wherein the first rotation axis and the second rotation axis are arranged parallel to each other.

7. Imaging device according to any of the previous claims wherein each detector comprises a photodetector and a scintillator, defining, respectively, a back of the detector and a front of the detector, the front of the detector being arranged towards radiation to be detected from the subject.

8. Imaging device according to the previous claim wherein the first rotation axis is coincident with a front of the first detector.

9. Imaging device according to any of the claims 7-8 wherein the first rotation axis is coincident with an emission front of the radioactive source.

10. Imaging device according to any of the previous claims wherein the second rotation axis is centred halfway between the first and second detectors, and the second rotation axis is substantially centred within the examination region.

11. Imaging device according to any of the previous claims wherein the radiation source, the first radiation detector and the second radiation detector are arranged to move together about the first rotation axis.

12. Imaging device according to any of the previous claims comprising a computer data processor configured for actuating a motor or motors for rotating the radiation source, the first radiation detector and the second radiation detector.

13. Imaging device according to the previous claim wherein the computer data processor is further configured for acquiring radiation detector data, when the radiation source, the first radiation detector and the second radiation detector are not being rotated.

14. Imaging device according to any of the claims 12-13 wherein the computer data processor is further configured for acquiring CT scanning data from the second detector when the radiation source is in the on state and configured for acquiring PET scanning data from the first and second detectors when the radiation source is in the off state, in particular the computer data processor is further configured for deactivating the first detector when the radiation source is in the on state.

15. Imaging device according to any of the claims 12-14 wherein the computer data processor is further configured for biasing the second detector for a lower energy level of detection when acquiring CT scanning data, and configured for biasing the first and second detectors for a higher energy level of detection when acquiring PET scanning data.

16. Imaging device according to any of the claims 12-13 wherein the computer data processor is further configured for acquiring CT scanning data from the second detector, and configured for acquiring PET scanning data from the first and second detectors, and configured for telling apart detected CT and PET radiation based on an energy level of a detected photon.

17. Imaging device according to any of the previous claims wherein the computer data processor is further configured for acquiring radiation detector data: when not actuating the motor or motors to not rotate the radiation source, the first radiation detector and the second radiation detector; orwhen actuating the motor or motors to not rotate the radiation source, the first radiation detector and the second radiation detector.

18. Imaging device according to any of the previous claims wherein the radiation source is a radioactive source or a high energy electromagnetic source, in particular a gamma-ray source or an x-ray source.

19. Imaging device according to any of the previous claims wherein each detector comprises a photodetector and a scintillator, and the scintillator comprises faces coated with an optical reflective material except for a scintillator face coupled to the photodetector.

20. Imaging device according to any of the previous claims wherein the photodetector is a photomultiplier.

21. Imaging device according to any of the previous claims wherein the radiation source, the first radiation detector and the second radiation detector are arranged to rotate together about the first rotation axis with a rotation angle of up to 180°.

22. Imaging device according to any of the previous claims wherein the first rotation axis is arranged to rotate about the second rotation axis with a rotation angle of up to 360°.

23. Imaging device according to any of the previous claims comprising a computer data processor configured for an alternating rotation about the first rotation axis and about the second rotation axis, repeated a predetermined number of times.

24. Imaging device according to any of the previous claims comprising a computer data processor configured for acquiring and transmitting the angular positions of the two rotation axes and the number of radiation events detected at each angular position, for 3D image reconstruction.

25. Imaging device according to any of the previous claims comprising a computer data processor configured for a predetermined stopping time at each angular position of the two axes to count the number of radiation events detected.

26. Imaging device according to any of the previous claims comprising a computer data processor configured such that immediately successive angular positions are spaced at a distance smaller than a pixel size of the first and second detectors.

27. Imaging device according to any of the previous claims comprising a computer data processor configured for a predetermined stopping time at alternating angular positions of the two axes to count the number of radiation events detected, alternatingly, for CT scanning by the second detector, and for PET scanning by the first and second detectors.

28. Method for operating the imaging device of any of the previous claims, comprising, sequentially or simultaneously: rotating together about a first rotation axis the radiation source, the first radiation detector and the second radiation detector; and rotating the first rotation axis about the second rotation axis; wherein the method also comprises, sequentially or simultaneously: acquiring, by the first radiation detector and the second radiation detector, gamma- or x-ray radiation from the subject; and acquiring, by the second radiation detector, transmitted radiation through the subject from the radiation source.

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