Device and corresponding method for enhancing determination of the precise location of at least one tracer within a body part of a patient

Abstract

The present invention relates to a method and a device for simultaneously monitoring a body part of a patient by means of high-resolution and high-sensitivity detection techniques that detect radiation emitted by a tracer. The object of the present invention is a device for enhancing the determination of the precise position of at least one tracer within a body part of a patient, the device comprising a first pair of high-resolution detector counterparts and a second pair of high-sensitivity detectors and movable detector counterparts, and the device being configured to determine the position of the second pair of detector counterparts based on a rough position based on signals from the first pair of detector counterparts, and to determine the fine position of the tracer based on signals from the second pair of detector counterparts, thereby allowing the position of the tracer to be determined with high spatial resolution and high sensitivity.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for simultaneously monitoring multiple body parts of a patient by high-resolution and high-sensitivity detection techniques that detect radiation emitted by a tracer, such as by positron emission tomography (PET).

[0002] The apparatus and method according to the present invention can preferably be used in the field of nuclear medicine, particularly for determining the location of a tracer injected into a patient's body.

[0003] Related Art

[0004] Positron emission tomography (PET) has high clinical potential as a functional imaging modality of a patient's body. Herein, simultaneous images of the whole body are particularly promising because organs interact with each other. Herein, one or more tracers, such as a radioactive contrast agent, are injected into the patient's body. These tracers have a higher affinity for certain cells that may be located in more distant parts of the patient's body.

[0005] The radioactive tracer emits positrons, and after a certain range, the positrons annihilate with electrons in the patient's body. After annihilation, a pair of back-to-back photons are emitted and these photons eventually leave the patient's body. Two opposing detectors detect the photon pairs. For a scintillation crystal, there is a certain probability that the photons will interact with the detector, which depends on the density and atomic number of the detector. Optimal signals require high light output and short decay times. For gas detectors such as resistive plate chambers (RPCs), in addition to the probability of interaction, there is also the possibility of extracting electrons from the resistive material. A compromise between the two is desirable for optimal signals.

[0006] Scintillator-based systems are discrete and take the form of pixelated crystals connected to photomultiplier tubes (PMTs) in a one-to-one manner, or a monolithic crystal read out by multiple PMTs. RPC-based systems are continuous because the impact position is determined by the charge deposited between readout channels and the depth of interaction of the impact. The latter detector is essentially parallax-free and thus performs better in terms of spatial resolution. The former detector performs better in terms of sensitivity.

[0007] These two concepts are proposed for PET systems with a large axial field of view (AFOV). Such systems are capable of imaging the whole body with higher sensitivity in a single scan. This can reduce the dose injected into the patient, reduce the total acquisition time, and track the tracer in real time as it passes through the patient's body.

[0008] Scintillator-based systems with large AFOV are quite expensive, and the total cost increases linearly with the number of detectors. RPC-based systems are more cost-effective for such purposes because they are designed to cover large areas. However, these systems have low sensitivity compared to scintillator-based systems.

[0009] On the other hand, scintillator crystals have poor spatial resolution at large acceptance angles because the depth of interaction plays an important role for photons hitting the detector obliquely. However, they are more flexible than RPCs and can adopt different geometries so that photons hit them perpendicularly, thereby reducing the parallax effect and improving the spatial resolution.

[0010] US 9632187 B2 discloses systems and methods for a PET kit. The detector kit can include a gantry, a plurality of PET detector modules, and an event processing device. The PET detector module can include a housing. The housing can include a connecting element configured to detachably and adjustably couple the PET detector module to the gantry. The detector module includes a crystal located within the housing and a photodetector configured to detect light through the crystal. The detector module further includes a communication component configured to transfer data from at least one photodetector to the event processing device to determine coincident events based on the received data. This disclosure also relates to a method for adjusting the position of a PET detector module relative to a first gantry and decoupling the PET detector module from the first gantry via a connecting element. The method further includes coupling the PET detector module to a second gantry.

[0011] WO 2012 / 087171 A1 discloses an apparatus for PET in time-of-flight and whole-body scanning in a single-bed position and a corresponding readout method. The apparatus includes at least four detector modules arranged around an apparatus axis so as to form a polygon. The modules include high-resistivity planar detectors (RPCs) as gamma photon detectors. The apparatus also includes an electronic readout device coupled to both ends of the apparatus inside the modules. This disclosure also relates to the readout method.

[0012] Paulo Martins' 2014 Ph.D. thesis at the University of Coimbra, "Imaging Techniques in RPC-PET," describes an apparatus for PET imaging of small animals. The apparatus includes RPC detectors and a readout system. The thesis also describes a method for determining the exact position of gamma photon hits in the detector. A method for reconstructing whole-body images using a graphics processing unit is also proposed. The reconstruction method includes a time-of-flight-based method for rejecting scattered events in the human body. Clinically relevant reconstruction times are demonstrated.

[0013] The present invention provides a cost-effective solution which also allows determination of the position of a tracer within a patient with high spatial resolution and high sensitivity. Summary of the Invention

[0014] The problem is thus solved by a device and a method for determining the position of a tracer within a patient and by a computer program product comprising executable instructions for performing the method according to the subject matter of the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims, which can be implemented in isolation or in any combination.

[0015] As used in this specification, the term "comprising" or its grammatical variants will be regarded as specifying the presence of the stated features, integers, steps or components or groups thereof, but not precluding the presence or addition of one or more other features, integers, steps, components or groups thereof. The same applies to the term "having" or its grammatical variants, which is used as a synonym of the term "comprising".

[0016] According to an aspect of the present invention, there is provided a device for enhancing determination of the precise position of at least one tracer within a patient (or specifically, within a body part).

[0017] The device may comprise: a first pair of opposing detectors, the opposing detectors in the first pair consisting of high-resolution detectors; and a second pair of opposing detectors, the opposing detectors in the second pair consisting of high-sensitivity detectors and being movable.

[0018] In another aspect, the device may be configured to:

[0019] a) obtain one or more first signals from the first pair of opposing detectors, the one or more first signals comprising spectral information corresponding to radiation emitted by the tracer,

[0020] b) determine a rough position of the tracer based on the one or more first signals,

[0021] c) position the second pair of opposing detectors based on the determined rough position,

[0022] d) obtain one or more second signals from the second pair of opposing detectors, the one or more second signals comprising electromagnetic spectral information corresponding to radiation emitted by the tracer,

[0023] e) determine the precise position of the tracer based on the one or more second signals.

[0024] Accordingly, a device for determining the position of a tracer within a body part can preferably be used to image the function of a body part of a patient, where the body part of the patient includes tumor tissue. In this context, the tumor tissue can include tumor modifiers that may have been introduced into the patient's tissue through cancer.

[0025] When compared to prior art solutions, using a first pair of opposing detectors to determine a coarse position and positioning a second pair of opposing detectors based on this coarse position and thereby determining a fine position reduces the number of detectors (specifically, detectors providing high sensitivity).

[0026] Alternatively or additionally, a device for determining the position of a tracer within a patient's body can also be used to correlate images obtained simultaneously from two body parts, the images corresponding to signals obtained from opposing detector pairs.

[0027] As indicated above, the present invention is for the case of scanning a patient's body after injection of a tracer. As used herein, the term "tracer" refers to a radioactive contrast agent, such as 18F-fluorodeoxyglucose (FDG).

[0028] According to the present invention, the device includes at least two pairs of opposing detectors. The term "opposing detectors" refers to detectors that face each other with the patient's body located therebetween.

[0029] According to the present invention, the device includes detectors with high spatial resolution and detectors with high sensitivity. As used herein, the detectors are designated for determining gamma radiation generated by positron annihilation in the patient's body. As used herein, the term "detector" refers to a device designated for generating a measurable signal from incident gamma radiation. For this purpose, the measurable signal can preferably be selected from electrical signals, particularly voltage or current. Specifically, detector elements can be selected from at least two of the following: resistive plate chambers (RPCs), micro-pattern gas detectors (MPGDs), fast timing MPGDs (FTMs), gas electron multipliers (GEMs), photomultiplier tubes (PMTs), solid-state single-photon sensitive devices (silicon photomultipliers; SiPMs), position-sensitive photomultiplier tubes (PSPMTs), avalanche photodiodes (APDs), charge-coupled devices (CCDs), complementary metal-oxide-semiconductors (CMOS), or quantum image sensor (QIS) chips. However, other types of detector elements are also feasible. Particularly preferably, the opposing detectors have the same type and kind in order to increase the comparability of the measurement signals between the individual detectors.

[0030] Preferably, the opposing detectors in the first pair are continuous detectors, and the opposing detectors in the second pair are discrete detectors.

[0031] In a preferred embodiment, the device may include at least one pair of first opposing detectors and / or at least one pair of second opposing detectors. More preferably, two, four, eight, twelve, sixteen, twenty or more pairs of first and second opposing detectors. In the present context, each pair of detectors is spaced apart from one another, and thus the closer they are to the patient's body, the higher the spatial resolution at which determination can be made.

[0032] Additionally, the device may further include an evaluation device. As is commonly used, the term "evaluation device" refers to a device designated for determining the first and second signals obtained, where the first and second signals include information regarding gamma radiation that has been obtained by the first and second pairs of opposing detectors, and specifically may be based on measurable signals provided to the evaluation device by the first and second pairs of opposing detectors. For this purpose, a wire-based connection may be provided, or alternatively or additionally, a wireless connection may be provided between the first and second pairs of opposing detectors and the evaluation device.

[0033] The evaluation device according to the present invention may in particular be designed for determining the position of a tracer within a patient's body, where this type of information may be based on measurable signals provided to the evaluation device by at least two detectors. For this purpose, the evaluation device may include a fast analog-to-digital converter, which preferably has a sampling rate of 10 ns, more preferably 4 ns, even more preferably 1 ns or lower. In the present context, the fast analog-to-digital converter may preferably be selected from at least one of the following: flash analog-to-digital converter (FADC), field-programmable gate array (FPGA), application-specific integrated circuit (ASIC), versatile module eurocard (VME) digitizer, time readout board (TRB), or oscilloscope. However, other types of fast analog-to-digital converters are also conceivable.

[0034] Additionally, the evaluation device may further include a clock for assigning time stamps to each detector signal and providing time synchronization of the detector signals, which preferably has a nanosecond or picosecond level of accuracy, more preferably having an accuracy of 100 ps or lower.

[0035] Additionally, the evaluation device may further include a motion sensor for monitoring motion (such as object motion). The motion sensor may include monitoring physiological parameters, such as cardiac and respiratory motion.

[0036] In another aspect of the present invention, there is provided a method for enhancing the determination of the precise position of a tracer within a body part of a patient, where the tracer emits radiation.

[0037] The method according to the invention comprises at least the following steps, however, additional steps may also be performed. In a preferred embodiment, the indicated steps may be performed in a sequential method, however, subsequent steps may be performed at least partially simultaneously with the previous step. In an alternatively preferred embodiment, the steps may be performed in an integrated method or a hybrid method by combining a sequential method and an integrated method, specifically for minimizing the time and / or storage space required for performing the method of the invention. Additionally, other steps not indicated herein may also be performed.

[0038] It should be understood that the method of the invention is implemented by the device of the invention in any embodiment of the invention, and the method comprises the following steps:

[0039] a) Obtaining one or more first signals sequentially from a first pair of opposing detectors, the one or more first signals comprising spectral information corresponding to radiation emitted by a tracer,

[0040] b) Determining a rough position of the tracer based on the one or more first signals,

[0041] c) Positioning a second pair of opposing detectors based on the determined rough position,

[0042] d) Obtaining one or more second signals from the second pair of opposing detectors, the one or more second signals comprising electromagnetic spectral information corresponding to radiation emitted by the tracer,

[0043] e) Determining an exact position of the tracer based on the one or more second signals.

[0044] Thus, this method provides that a rough position is determined based on signals obtained from a first pair of opposing detectors, and a second pair of opposing detectors is positioned based on this rough position and thereby an exact position is determined, thus reducing the number of detectors (specifically, detectors providing high sensitivity) when compared to prior art solutions.

[0045] Another object of the invention is a computer program product comprising executable instructions for performing the method of the invention in any embodiment of the invention. Description of the Drawings

[0046] Other optional details and features of the invention may preferably be derived from the following description of the preferred embodiments in conjunction with the dependent claims. Among them, the corresponding features may be implemented in isolation or in any combination. The invention is not limited to the preferred embodiments. Identical reference numerals in the figures refer to identical elements, or elements having the same or similar functions, or elements corresponding to each other in terms of their functions.

[0047] Figure 1A preferred embodiment of a device for determining the position of a tracer in a patient is shown in a side view, wherein the device includes two opposite flat panel detectors with high spatial resolution and two adjustable opposite detectors with high sensitivity.

[0048] Figure 2 A preferred embodiment of a device for determining the position of a tracer in a patient is further shown in a perspective view, wherein the parallel high-resolution detectors are fixed, and the high-sensitivity detectors are moved to the region of interest in the axial, horizontal, and vertical transverse directions by means of a mechanical unit and can be positioned in a certain way around the axis passing through the tracer such that gamma rays impinge on them perpendicular to the front face of the high-sensitivity detectors. The device also includes an actuator along the radial axis passing through the approximate position of the tracer such that the distance of the second pair of opposite detectors to the approximate position of the tracer is minimized. The device can also adopt a configuration in which the entire device rotates by ±90 degrees, wherein the high-resolution detectors are located below and above the patient platform, and the high-sensitivity detectors are moved laterally to the patient.

[0049] Figure 3 Another preferred embodiment of a device for determining the position of a tracer in a patient is shown in a perspective view, wherein the device includes a pair of detectors that can be used to image one region of the body (e.g., the brain) and another pair of detectors for imaging another region of the body (e.g., the pelvis);

[0050] Figure 4 Another preferred embodiment of a device for determining the position of a tracer in a patient is shown in a perspective view, wherein the device includes a pair of detectors that cover the entire body and are capable of tracking the position of the tracer in the body. Once the region of interest is determined, the high-sensitivity detectors are moved to these regions in order to acquire a large amount of statistical data.

[0051] Figure 5A and Figure 5B A preferred embodiment of a method for determining the position of a tracer in a Figure 2 patient is further shown in a side view, wherein the high-sensitivity detectors move between Figure 5A and Figure 5B to adjust the spatial resolution according to the region of interest provided by the parallel high-resolution detectors. Detailed Description

[0052] In an embodiment of the device (110) of the present invention, the opposite detectors in the first pair (116) are fixed.

[0053] In another aspect of the device of the present invention, the device further includes a patient platform (124) adapted to receive a recumbent patient, and the first pair of opposed detectors and the second pair of opposed detectors are positioned to be able to detect radiation (123) emitted by a tracer within a body part (112) of a patient (114) lying in the patient platform (124).

[0054] In an advantageous embodiment of the device of the present invention, the opposed detectors in the second pair are movable at least around a rotation axis (126) parallel to the patient platform (124) and / or in a plane perpendicular to the patient platform (124).

[0055] In another advantageous aspect of the device of the present invention, the first pair of opposed detectors (116) and the second pair of opposed detectors (118) are positioned such that a plane perpendicular to the patient platform (124) intersects the first pair of opposed detectors (116) and the second pair of opposed detectors (118), thereby allowing enhanced alignment between the detectors.

[0056] In another aspect of the device of the present invention, the first pair of opposed detectors (116) and the second pair of opposed detectors (118) are positioned to cover the entire patient platform (124), thereby enabling tracking of the position of the tracer throughout the body of the patient (114).

[0057] In a preferred embodiment, the device of the present invention includes a plurality of first pairs of opposed detectors (116) positioned along the patient platform (124) and a plurality of second pairs of opposed detectors (118) positioned along the patient platform (124), thereby allowing coverage of the entire body of the patient (114) by moving along the patient platform (124), preferably the entire patient platform (124).

[0058] In an embodiment of the device of the present invention, each first pair of opposed detectors (116) corresponds to a single second pair of opposed detectors (118).

[0059] In an advantageous embodiment of the device of the present invention, each first pair of opposed detectors (116) corresponds to more than one second pair of opposed detectors (118), and each first pair (118) has a length such that it covers a section of the patient platform (124) corresponding to more than one second pair of opposed detectors (116) along the same plane. This solution allows reduction in the number of the first pair of opposed detectors (116), thereby taking advantage of the continuous condition of such high-resolution detectors.

[0060] In an embodiment of the device of the present invention, the first pair of opposed detectors (116) and the second pair of opposed detectors (118) are composed of positron emission tomography detectors.

[0061] In an advantageous aspect of the device according to the invention, the device further comprises an evaluation device (128), which consists of a computing device (129), the evaluation device (128) being configured to determine a rough position (121) according to step c) and to determine an exact position according to step e).

[0062] In an aspect of the device according to the invention, the device further comprises a mechanical unit (130), which is configured to move and thereby position a second pair of opposing detectors (118). The evaluation device (128) is preferably also configured to provide the rough position (121) to the mechanical unit (130) in order to move and thereby position the second pair of opposing detectors (118). The evaluation device (128) may also comprise motion sensors, which are also configured to provide the patient motion to the mechanical unit (130) in order to move and thereby move the second pair of opposing detectors (118) in a manner synchronized with the patient motion.

[0063] In another advantageous aspect of the device according to the invention, the device further comprises a first communication module (132) associated with the first pair of opposing detectors (116) and a second communication module (134) associated with the second pair of opposing detectors (118), each communication module being configured to transmit one or more first signals (120) and one or more second signals (122) to the evaluation device (128) respectively, the communication modules optionally being configured to operate by means of wired or wireless communication.

[0064] In a creative aspect of the method according to the invention, step a) comprises determining a detector gap (136) in the horizontal transverse axis direction (133), in which radiation is detected in the first pair of opposing detectors (116), and thereby step b) comprises determining a rough position (121) of the radiation emitted by the tracer hitting the first pair of opposing detectors (116) in the axial (131) and horizontal (133) and vertical (140) transverse axis directions. A disadvantage of scintillation detectors is the lack of depth of interaction (DOI). Apart from complex solutions based on multi-crystals organized in two or three layers and algorithms allowing the measurement of the rough position of impacts in the transverse axis direction in a monolithic scintillator, scintillation detectors do not provide information about the transverse axis direction. Furthermore, the more inclined the incident photons are, the higher the probability of depositing energy in more than one detector. This is the so-called parallax effect. Since the spacing of most detectors is small (0.25 mm - 6 mm), but the thickness is large (1 mm - 30 mm), the higher the chance of photons passing through multiple crystals, the greater the angle of incidence of the photons entering the detector.

[0065] In another creative aspect of the method according to the invention, the positioning of the second detector in step c) is such that the detector is movable along the axial (131) and horizontal (133) and vertical (140) transverse axis directions.

[0066] In another inventive aspect of the method of the present invention, step e) comprises determining the time difference between the radiation emitted by the tracer at each detector of the first pair (116) and the radiation arrival time, and reconstructing one or more second signals with a low-statistics time-of-flight reconstruction routine. The time difference in the arrival times of photons at opposite detectors (also known as the time of flight (TOF)) confines the so-called line of response (LOR) between the two detectors to a line segment. Thus, TOF is related to accelerating the reconstruction routine and increasing the signal-to-noise ratio.

[0067] In an aspect of the method of the present invention, the detectors in the second pair of opposite detectors (118) are positioned in step c) relative to the axis of rotation (126) passing through the approximate position (121) of the tracer such that the radiation emitted by the tracer impinges on the detectors in the second pair of opposite detectors perpendicular to the front face (135) of such detectors. Events impinging on the detectors perpendicularly with high resolution and high sensitivity will provide a more reliable way of measuring the true activity in the tracer, since only the activity emitted from the tracer will be detected.

[0068] In another aspect of the method, the detectors in the second pair of opposite detectors (118) are positioned in step c) along the radial axis (146) passing through the approximate position (121) of the tracer by means of an actuator (144) such that the distance between the second pair of opposite detectors (118) and the approximate position (121) of the tracer is minimized and the sensitivity of the second pair of opposite detectors (118) is increased.

[0069] In an embodiment, step e) comprises reconstructing one or more second signals with a maximum a posteriori (MAP) estimation algorithm based on the determined approximate position (121) of the tracer. PET-MR is used to utilize the prior knowledge of the exact position of the anatomy provided by MRI and model it in PET image reconstruction. This is the so-called maximum a posteriori (MAP) estimation. MAP can be used to obtain a point estimate of the observables from empirical data. It is similar to the maximum likelihood (MLEM) algorithm, but employs an optimization objective that incorporates a prior distribution over more than the quantity to be estimated. It is regarded as a regularization of MLEM. So far, MAP has not been used for PET data based on a previous PET distribution. It is mainly used in conjunction with a previous MRI distribution. The advantage is that MRI is not required, since the high-resolution detectors already provide prior knowledge. The process can be iterative, where the PET distributions from the high-resolution detectors and the high-sensitivity detectors are fed to each other alternately.

[0070] In another inventive aspect of the method of the present invention, it is allowed to correlate signals obtained from at least two body parts (112) of a patient (114), and it further includes correlating the positions of a tracer at at least two body parts (112) of the patient (114), this correlation including:

[0071] - determining the exact position of the tracer at a given time point during an uptake period in one region of the body,

[0072] - determining the exact position of the tracer at the same time point during an uptake period in another region of the body,

[0073] - measuring the standardized uptake values in the two regions during a predefined period, and

[0074] extracting the temporal correlation between the uptakes in the two regions.

[0075] An associated advantage is the spatial tracking of the tracer and its kinetics (activity over time) simultaneously at different parts of the body. Quantification techniques require blood sampling as an input related to the activity of the brain, heart, tumors, etc. Therefore, the object of the present invention is to simultaneously evaluate the position and kinetics of the tracer at different parts of the body. One or several tracers may exhibit different kinetics, having a higher uptake time in some organs than in others. This can be quantified in a single scan without moving the patient and without blood sampling to estimate the true activity in the body. The metabolism of tumors can be imaged with FDG, while myocardial perfusion of the heart is imaged with 82 rubidium imaging. This is so-called parametric imaging: simultaneously monitoring multiple organs and correlating their uptakes with each other.

[0076] In an advantageous aspect of the method of the present invention, the method further includes correlating the position of the tracer throughout the body of the patient (114), this correlation including:

[0077] - determining the exact position of the tracer at a given time point during an uptake period throughout the body of the patient (114),

[0078] - measuring the uptake throughout the body and in the region of interest, and

[0079] - correlating the standardized uptake values throughout the body and in the region of interest.

[0080] Some tumors will not be detected because the normal procedure is to image the body from the eyes to the thighs to reduce scan time. The brain, legs, and feet are not usually scanned. However, the detection of tumors in these areas provides an assessment of disease progression. Metastatic tumors of melanoma in the legs will change the staging and treatment process. If a person can detect tumors in unexpected areas through an affordable full-body scan, a second pair of detectors can confirm and enhance the precise location of the tumor.

[0081] In addition, unexpected activity in a certain part of the body may trigger the second pair of detectors to move to that area. Suppose we want to evaluate a person's sexual response. Higher uptake may be obtained in different parts of the body, such as the heart, brain, and pelvic regions, etc. A full-body scan will identify the area of interest, and a specific tracer with an affinity for that area can be correlated with a tracer with an affinity for whole-body metabolism (e.g., FDG).

[0082] In an embodiment, the patient can see the functions of their body in real time, thus mimicking other neurofeedback therapies.

[0083] Other modifications and variations will also be apparent to those skilled in the art.

Claims

1. An apparatus (110) for enhancing the determination of the precise location of at least one tracer within a body part (112) of a patient (114), wherein the apparatus comprises: A first pair of opposing detectors (116), the first pair of opposing detectors consisting of high-resolution detectors, A second pair of opposing detectors (118), the second pair of opposing detectors consisting of high-sensitivity detectors and being movable, and The apparatus (110) is configured to: a) Obtain one or more first signals (120) from the first pair of opposing detectors, the one or more first signals including electromagnetic spectrum information corresponding to radiation (123) emitted by the tracer, b) Determine a rough location (121) of the tracer based on the one or more first signals (120), c) Locate the second pair of opposing detectors (118) based on the determined rough location (121) of the tracer, d) Obtain one or more second signals (122) from the second pair of opposing detectors (118), the one or more second signals (122) including electromagnetic spectrum information corresponding to radiation (123) emitted by the tracer, e) Determine the precise location of the tracer based on the one or more second signals (122).

2. The apparatus (110) according to claim 1, wherein the first pair of opposing detectors (116) is fixed.

3. The apparatus (110) according to claim 1, wherein the apparatus further comprises a patient platform (124), the patient platform (124) being adapted to receive a lying patient, and the first pair of opposing detectors (116) and the second pair of opposing detectors are positioned to be able to detect radiation (123) emitted by a tracer within a body part (112) of a patient (114) lying in the patient platform.

4. The apparatus (110) according to claim 1, wherein the second pair of opposing detectors (118) is movable at least around a rotation axis (126) parallel to the patient platform and / or in a plane perpendicular to the patient platform (124).

5. The apparatus (110) according to claim 3, wherein the first pair of opposing detectors (116) and the second pair of opposing detectors (118) are positioned such that a plane perpendicular to the patient platform (124) intersects the first pair of opposing detectors (116) and the second pair of opposing detectors (118).

6. The apparatus (110) according to claim 1, wherein the first pair of opposing detectors (116) and the second pair of opposing detectors (118) are positioned such that they cover the entire patient platform (124), thereby enabling tracking of the location of the tracer throughout the body of the patient (114).

7. The apparatus (110) according to claim 5, wherein the apparatus comprises a plurality of first pairs of opposing detectors (116) positioned along the patient platform (124) and / or a plurality of second pairs of opposing detectors (118) positioned along the patient platform (124).

8. The device (110) according to claim 1, wherein each first pair of opposed detectors (116) corresponds to a single second pair of opposed detectors (118).

9. The device (110) according to claim 7, wherein each first pair of opposed detectors (116) corresponds to more than one second pair of opposed detectors (116), each first pair of opposed detectors (116) having a length such that it covers a section of the patient platform corresponding to more than one second pair of opposed detectors (118) along the same plane.

10. The device (110) according to claim 1, wherein the first pair of opposed detectors (116) and the second pair of opposed detectors (118) are composed of positron emission tomography detectors.

11. The device (110) according to claim 1, wherein the device further comprises an evaluation device (128), the evaluation device being composed of a computing device (129), the evaluation device being configured to determine the approximate position (121) of the tracer according to step c) and the precise position according to step e).

12. The device (110) according to claim 1, wherein the device further comprises a mechanical unit (130), the mechanical unit (130) being configured to move in the axial (131) or horizontal (133) or vertical (140) transverse axis direction and thereby position the second pair of opposed detectors (118).

13. The device (110) according to claim 11, wherein the evaluation device (128) is further configured to provide the determined approximate position (121) of the tracer to the mechanical unit (130) to move in the axial (131) or horizontal (133) or vertical (140) transverse axis direction and thereby position the second pair of opposed detectors (118).

14. The device (110) according to claim 11, wherein the device further comprises a first communication module (132) associated with the first pair of opposed detectors (116) and a second communication module (134) associated with the second pair of opposed detectors (118), each communication module being configured to transmit the one or more first signals (120) and the one or more second signals (122) to the evaluation device respectively, the communication module optionally being configured to operate by wired or wireless communication.

15. The device (110) according to any one of claims 1 to 14, wherein the device comprises at least one pair of first pairs of opposed detectors (116) and / or at least one pair of second pairs of opposed detectors (118).

16. The device (110) according to claim 15, wherein the device comprises two, four, eight, twelve, sixteen, twenty or more pairs of first pairs of opposed detectors (116) and / or second pairs of opposed detectors (118).

17. The device (110) according to any one of claims 1 to 14, wherein the first pair of opposed detectors (116) are continuous detectors and the second pair of opposed detectors (118) are discrete detectors.

18. A method for enhancing the determination of the precise position of a tracer within a body part (112) of a patient (114), the tracer emitting radiation (123), the method being implemented by the device (110) according to any one of the preceding claims, and the method comprising the following steps: a) Obtaining one or more first signals (120) successively from the first pair of opposing detectors (116), the one or more first signals (120) comprising electromagnetic spectrum information corresponding to the radiation (123) emitted by the tracer; b) Determining a rough position (121) of the tracer based on the one or more first signals (120); c) Positioning the second pair of opposing detectors (118) based on the determined rough position (121) of the tracer; d) Obtaining one or more second signals (122) from the second pair of opposing detectors (118), the one or more second signals (122) comprising electromagnetic spectrum information corresponding to the radiation (123) emitted by the tracer; e) Determining the precise position of the tracer based on the one or more second signals (122).

19. The method according to claim 18, wherein step a) comprises determining a detector gap (136) in the horizontal (133) transverse axis direction, wherein the radiation (123) is detected in the first pair of opposing detectors (116), and whereby step b) comprises determining the rough position (121) of the tracer in the axial (131), horizontal (133) and vertical (140) transverse axis directions of the first pair of opposing detectors (116) at which the radiation (123) emitted by the tracer impinges.

20. The method according to claim 18, wherein the positioning in step c) enables the second pair of opposing detectors to be movable along the axial (131), horizontal (133) and vertical (140) transverse axis directions.

21. The method according to claim 18, wherein step e) comprises determining the time difference between the time at which the tracer emits radiation at each detector of the second pair of opposing detectors (118) and the arrival time of the radiation (123), and reconstructing the one or more second signals (122) with a low-statistics time-of-flight reconstruction routine.

22. The method according to claim 18, wherein the positioning in step c) positions the detectors in the second pair of opposing detectors (118) relative to a rotation axis (126) passing through the determined rough position (121) of the tracer such that the radiation (123) emitted by the tracer impinges on the second pair of opposing detectors (118) perpendicular to the front face (135) of the second pair of opposing detectors (118).

23. The method according to claim 18, wherein the positioning in step c) positions the detectors in the second pair of opposed detectors (118) along a radial axis (146) passing through the rough position (121) of the determined tracer by means of an actuator (144), such that the distance of the second pair of opposed detectors (118) to the rough position (121) of the determined tracer is minimized and the sensitivity of the second pair of opposed detectors (118) is increased.

24. The method according to claim 18, wherein step e) comprises reconstructing the one or more second signals (122) using a maximum a posteriori probability (MAP) estimation algorithm based on the rough position (121) of the determined tracer.

25. The method according to any one of claims 19 to 24, wherein the method further comprises correlating the positions of the tracer within at least two body parts (112) of a patient (114), the correlation comprising: - determining the exact position of the tracer at a given time point during an uptake period in one region of the body part (112), - determining the exact position of the tracer at the same time point during an uptake period in another region of the body part (112), - measuring the standardized uptake values in the two regions during a predefined period, and extracting the temporal correlation between the uptakes in the two regions.

26. The method according to any one of claims 19 to 24, wherein the method further comprises correlating the positions of the tracer throughout the body of a patient (114), the correlation comprising: - determining the exact position of the tracer at a given time point during an uptake period throughout the body of the patient (114), - measuring the uptake throughout the body and in the region of interest, and - correlating the standardized uptake values throughout the body and in the region of interest.

27. The method according to any one of claims 19 to 24, wherein the tracer comprises 18F-fluorodeoxyglucose (FDG).

28. The method according to claim 27, wherein the tracer consists of 18F-fluorodeoxyglucose (FDG).

29. A computer program product comprising executable instructions for performing the method according to any one of claims 19 to 28.

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