CN113116371B

CN113116371B - PET device and calibration method

Info

Publication number: CN113116371B
Application number: CN202011601735.1A
Authority: CN
Inventors: 李晓莉; 强翼; 肯特·布尔; 彭鹏
Original assignee: Canon Medical Systems Corp
Current assignee: Canon Medical Systems Corp
Priority date: 2019-12-30
Filing date: 2020-12-30
Publication date: 2024-04-19
Anticipated expiration: 2040-12-30
Also published as: CN113116371A

Abstract

The embodiment provides a PET device and a calibration method capable of performing calibration with good precision. The detector detects simultaneous event pairs, which are made up of a plurality of processing units. Circuitry corrects for relative timing offsets within the set of processing units based on data acquired via the radiation source, corrects for timing offsets between the set of processing units using inherent radiation, and performs a calibration of the detector based on the corrected relative timing offsets within the set of processing units and the corrected timing offsets between the set of processing units.

Description

PET device and calibration method

Reference to related applications

The present application enjoys the benefit of priority of U.S. patent application Ser. No. 62/9557270 to the 30 th month of 2019, U.S. patent application Ser. No. 16/907972 to the 22 th month of 2020, and Japanese patent application Ser. No. 2020-211197 to the 21 st month of 2020, the entire contents of which are incorporated herein by reference.

Technical Field

Embodiments disclosed in the present specification and drawings relate to a PET apparatus and a calibration method.

Background

As a method for performing timing calibration OF a detector in a TOF (time OF flight) PET (Positron Emission Tomography: positron emission computed tomography) apparatus, there is a method using an external radiation source such as a phantom (phantoms). However, methods of timing calibration of detectors using external radiation sources such as phantom are subject to large, difficult to handle, or require complex mechanical movements of the phantom.

As other methods of timing calibration of the detector in the TOF PET apparatus, methods of using the inherent radiation (INTRINSIC RADIATION) of the detector are also contemplated. However, methods of timing calibration of detectors using the inherent radiation of the detector generally require very long times.

Disclosure of Invention

One of the technical problems to be solved by the embodiments disclosed in the present specification and the drawings is to perform calibration with good accuracy. However, the technical problems to be solved by the embodiments disclosed in the present specification and the drawings are not limited to the above technical problems. The technical problems corresponding to the effects of the respective configurations described in the embodiments described below can be also located as other technical problems.

The PET device of the embodiment is provided with a detector and a circuit. The detector detects a pair of simultaneous events generated by annihilation (annihilation) of positrons emitted from a radiation source disposed within a field of view (FOV) of the detector. Circuitry corrects for relative timing offsets within the set of processing units based on data acquired via the radiation source, corrects for timing offsets between the set of processing units using inherent radiation, and determines a total timing offset based on the corrected relative timing offsets within the set of processing units and the corrected timing offsets between the set of processing units, thereby performing a calibration of the detector.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the PET apparatus of the embodiment, calibration with good accuracy can be performed.

Drawings

Fig. 1 is a schematic diagram of a PET scanner according to an embodiment.

Fig. 2A is a schematic diagram showing an exemplary position of an external radiation source with respect to each of the opposing detectors.

Fig. 2B is a diagram showing a TOF difference histogram between the 2 detectors of fig. 2A.

FIG. 3 is a schematic diagram showing another exemplary position of an external radiation source pair relative to opposing detectors.

Fig. 4 is a schematic diagram showing another exemplary position of an external radiation source relative to opposing detectors.

Fig. 5 is a schematic diagram showing another exemplary position of an external radiation source with respect to each of the opposing detectors.

Fig. 6A is a schematic diagram illustrating various embodiments of an external positron emission source within a detector ring.

Fig. 6B is a schematic diagram illustrating various embodiments of an external positron emission source within a detector ring.

Fig. 6C is a schematic diagram illustrating various embodiments of an external positron emission source within a detector ring.

Fig. 6D is a schematic diagram illustrating various embodiments of an external positron emission source within a detector ring.

Fig. 7A is a schematic diagram illustrating various embodiments of an internal radiation source within a detector ring.

Fig. 7B is a schematic diagram illustrating various embodiments of an internal radiation source within a detector ring.

Fig. 8A is a diagram showing an internal radiation timing distribution before the correlation offset correction obtained from the external radiation source is applied.

Fig. 8B is a diagram showing a distribution relating to the same data after the application of the walk correction including the nonlinear walk correction (non-LINEAR WALK correction).

Fig. 9 is a schematic diagram showing an exemplary configuration of various stages of timing calibration.

Fig. 10 is a diagram showing another exemplary configuration of various stages of timing calibration.

Fig. 11 is a diagram showing a rising discriminator used in the TOF PET system.

Fig. 12A is a graph representing a histogram of TOF differences between DU14 and DU33 from lutetium background radiation data (Lutetium background radiation data).

Fig. 12B is a graph representing a histogram of TOF differences between DU14 and DU33 from lutetium background radiation data.

Fig. 13 is a graph showing a histogram of TOF differences between DU14 and DU33 from lutetium background radiation data.

Fig. 14 is a diagram showing a TOF difference histogram between DU14 and DU33 from the Ge source and background radiation data.

Fig. 15A is a diagram showing timing offset between pairs of DUs before short-time timing calibration.

Fig. 15B is a diagram showing timing offset between pairs of DUs after short-time timing calibration.

Fig. 16 is a diagram showing the difference between the count when the energy window is applied to limit the count in order to avoid the influence of walking (walk) and the count when the whole count is accepted by performing walking correction.

Detailed Description

Embodiments of a PET apparatus and a calibration method are described in detail below with reference to the drawings.

In PET, an image of a living body is produced. PET scanners produce images representing various biological processes and functions. Typically, in a PET scan, a radioactive substance called a PET isotope is initially administered to a patient. The administered PET isotope sometimes functions as a tracer if it is related to a standard (japanese: a physical process) in the patient. Typical positron emission PET isotopes include ¹¹C、¹³N、¹⁵ O and ¹⁸ F. If a positron (and neutron) is emitted from an unstable nucleus in the body, it combines with an electron in adjacent tissue to annihilate. A pair of gamma photons (gamma photons) emitted in opposite directions are generated by the annihilation event. The gamma photons are detected by the detector ring as shown in fig. 1. The detector ring 300 may be composed of a plurality of detectors (for example, 101) each including a scintillator block and a photon sensor. For example, the detector 101 is constituted by a scintillator block 102 and a photon sensor 103.

One way of PET detection is TOF PET, which measures the arrival time of a pair of simultaneous photons. In TOF PET, if a radiation event (e.g., a gamma photon) is detected, a scintillator block at the detection site immediately records the time of the detected radiation event. By acquiring the arrival time, more weight is given to a place where the probability of the radiation position of each event is higher, thereby reducing the uncertainty of the statistics of the reconstructed image.

In PET, each detector assigns an energy and time stamp to each gamma ray detected. An energy window is applied to select energy in a range around 511keV, while a count time window (coincidence timing window) is applied to determine the simultaneous pairs of gamma rays. By each simultaneous pair, a coincidence Line (LOR) connecting 2 detector elements that detect gamma rays is defined. To generate an image from the detected LOR, a reconstruction method is applied.

In TOF PET, a difference in time stamps of gamma rays of simultaneous pairs is used to give priority to a place where the probability of annihilation position of each event is higher, thereby reducing statistical uncertainty of a reconstructed image. In order to provide a significant improvement to the reconstructed image, the measurement time difference (TIME DIFFERENCE) for each LOR record must be very accurate, typically in the range of hundreds of picoseconds. Calibration is required to adequately ensure accuracy of the measured time differences due to unavoidable manufacturing tolerances, such as cable lengths of different photon sensors within the detector, or differences in timing response.

As one method, it is considered to individually calibrate the time difference of each LOR in the system. PET scanners typically have tens of thousands of detector elements, with the number of LORs being on the order of hundreds of millions, and therefore this approach is not practical. The common approach of the prior art is to offset correct each detector element. An offset correction value is applied to the measurement time stamp of each detector element before determining whether the detected gamma ray is part of a simultaneous pair. Offset correction values for the 2 gamma rays for the simultaneous pairs are also applied to calculate the TOF difference for the pair used in reconstruction. Typically, the timing offset value is a "signed" value, which means that there is a positive or negative case.

In a TOF PET system for measuring a timing difference (TIMING DIFFERENCE), when there are N detector elements in the system, it is necessary to determine (N-1) timing offset values in order to be able to accurately measure the timing difference. For example, the timing offset value with respect to a certain element may be arbitrarily set to zero, and the other (N-1) offset values may be determined based on the element arbitrarily set to zero. Or with an additional condition (again meaning only (N-1) independent values) that the average offset value is zero with respect to all of the N detector elements, N offset values are sometimes calculated. In this way, when the same additional timing offset value is given to all the measured values, any measured timing difference does not change.

The following illustrates several non-limiting examples described above. These examples are merely illustrative and do not necessarily represent a preferred embodiment of a clinical PET system.

As shown in fig. 2A, an example of annihilation radiation sources 50 disposed between 2 detector elements D10 and D30 is examined. By the simultaneous occurrence of events, 1 LOR60 is generated between the detector elements. In this example, annihilation radiation sources 50 are positioned equidistant from D10 and D30 (alternatives other than equidistant are equally effective). The time measured by D10 is denoted by t _D10 and the time measured by D30 is denoted by t _D30. From the noise or uncertainty in the time measurement, a distribution of time differences (t _D10-t_D30) is made, which is sometimes plotted as a histogram as shown in fig. 2B.

Prior to calibration, the measured histogram 70 has an intermediate value of t _measured (which is sometimes calculated as a simple average or determined, for example, by least squares fit to the gaussian function of the measured histogram). Since the radiation source is equidistant from the 2 detectors, the time difference of flight with respect to the 2 detectors is equal and the expected time difference is zero.

By measuring the time difference distribution, a single equation can be written, (t _D10+t_OffsetD10)-(t_D30+t_OffsetD30)＝t_measured+t_OffsetD10-t_OffsetD30 =0).

In the equation, t _OffsetD10 and t _OffsetD30 are offset correction values of D10 and D30, respectively. Since there are only 1 equation and 2 unknowns, other conditions need to be applied in order to be able to determine t _OffsetD10 and t _OffsetD30.

As 1 example, a case where t _OffsetD10 =0 is selected, and as a result, t _OffsetD30＝t_measured can be considered. As another example, (t _OffsetD10+t_OffsetD30)/2=0 is selected, and as a result, t _OffsetD10＝-t_measured/2 and t _OffsetD30＝t_measured/2 may be obtained.

By selecting any one of these 2 (or other possible choices of conditions), as a result, the corrected timing histogram 80 centered on the expected value (zero) is obtained. In this simple example, 2 detectors (i.e., n=2) are used, 1 of which can determine 1 (i.e., N-1) independent offset values, and the system can be calibrated for accurately measuring timing differences (i.e., TOF).

In the case where the number of detectors is increased to 4 and annihilation radiation sources are placed equidistantly from each other between the detectors, 2 LOR's are generated, and as a result, 2 equations relating the measured average time differences for the respective LOR's are made. With a detector of n=4, 3 (N-1=3) independent offset values need to be determined for full timing calibration. It is clearly impossible to determine 3 unknowns from 2 equations. This means that it is a substantial problem to perform timing calibration using a single limited range of radiation sources at a single fixed location.

One method for solving this problem is shown in fig. 3. The second radiation source 55 is placed equidistant from the detectors D30 and D40 between them (again, equidistant options are used to simplify the illustration and are not necessarily options). With this second radiation source, an additional LOR65 is generated, so a third equation relating the timing offset values relative to each other can be written. By deriving 3 equations with 3 unknowns, 3 (N-1 = 3) independent offset values required to fully calibrate the timing response of the system can be solved. Here, the respective pairs of detector elements can be paired by a series of LORs (with 4 detector elements, there being 6 possible combinations of detector elements), i.e.,

D10 is directly paired with D30 by LOR60,

D20 is directly paired with D40 by LOR62,

D30 is directly paired with D40 by LOR65,

D10 is paired indirectly with D40 by LOR60 and LOR65 (via D30),

D10 is paired with D20 indirectly through LOR60, LOR65 and LOR62 (via D30 and D40),

D20 is indirectly paired with D30 by LOR62 and LOR65 (via D40), and therefore, the overall timing difference of the timing differences required for the system can be determined.

This example means that, when there are 3 or more detectors, a certain degree of "one-to-many" pairs of elements are necessary for measurement. In this case, the detector D30 and D40 are brought into a plurality of pairs by the additional radiation source.

Fig. 4 and 5 show 2 examples of one-to-many pairs in a group (group) of detectors, which can determine a required independent offset value in the group (group) accompanied by an additional pair. For example, in fig. 5, LOR67 connecting the first group of detectors can calculate 5 independent offset correction values. Similarly, LOR69 connecting the second group (set) of detectors can calculate additional 5 independent offset values, and the total number of determined offset values becomes 10. This total number 10 is missing 1 from the 11 individual offset values required. This lack occurs because there are no crossing pairs between the 2 sets (sets) of LOR's based on a single limited range radiation source 50. This example means that one-to-many pairs within a group (group) or group (set) can determine the relative offset values within that group, but crossing pairs of groups (set) are also necessary to calibrate the timing response of the system in its entirety. The requirements for the one-to-many pairs and the pair-crossing pairs between the groups (sets) of detector elements are handled by several methods in the related art as described below.

In a full timing calibration, one-to-many pairs of all detector elements to be calibrated are required. Previous calibration methods generally used external and/or internal radiation sources.

Several methods of using external sources of radiation are shown in fig. 6A-6D. These methods all implement the required one-to-many pairs including crossing pairs across groups (sets) of detector elements. For example, the detector elements within a group (set) are sometimes individual scintillator elements within a scintillator array of a single detector module. In this case, the cross-pair means that the described external radiation source method provides pairs across the gaps between modules, i.e. LOR based on several scintillator elements paired with scintillators in 2 or more detector modules on opposite sides of the detector ring.

Hereinafter, the term "phantom" refers to a specially designed object placed in the field of view of a scanner's detector for purposes of scanner calibration or scanner performance evaluation. In PET, the phantom typically contains a positron emitting source (e.g., ge-68, F-18, or Na-22), and in most cases an enclosed material, the emitted positrons are reliably converted to back-to-back (back-to-back) 511keV photons in a short time by annihilation with electrons within the enclosed material. The phantom is sometimes as simple as a simple mount or mount (mount) for the radiation source. The phantom sometimes also contains a material intended to scatter or partially absorb the emitted radiation. For example, in PET, a cylinder mold is often used. The fillable cylinder mold is sometimes composed of an acrylic cylinder with a central void and a closable port. In use, the central void is filled with a radioactive liquid such as Fluorodeoxyglucose (FDG) mixed with water (labeled F-18). Or sometimes a cylindrical mold body that seals the radiation source. In this case, the plastic cylinder shell is sometimes filled with Ge-68 equivalent elements and then cured with cured epoxy. The cylindrical mold body emits radiation, and the material of the cylindrical object also scatters and attenuates the radiation. The phantom includes movable parts for calibration purposes or to simulate the motion of an organ such as the beating or respiratory motion of the heart.

Fig. 6A shows a method of using a large cylindrical phantom 51. For example, the phantom is sometimes about 20cm in diameter, the same length as the scanner's field of view in the body axis direction, and is the case with a cylinder filled with Ge-68 containing epoxy. As shown by representative LOR61, each scintillator element within scintillator block 102 is paired with a plurality of other scintillator elements, including those within several different detector modules 101, via each LOR of the phantom. The method shown in fig. 6A has disadvantages in that it is difficult to handle since the mold itself has a weight of 20kg, and in addition, strict shielding (for example, about 150kg of lead) is required for protecting staff and patients when the mold is not used.

Fig. 6B illustrates a method of using the movable mold body 52. In this case, the phantom may be composed of a rod-shaped radiation source (e.g., ge-68 in a steel sleeve) that annihilates radiation, and a device that moves on an endless track in the field of view of the scanner detector. As the radiation source rotates, the representative LOR61 pairs each scintillator element within the scintillator block 102 with a plurality of other scintillator elements including those within several different detector modules 101. The complexity cost and maintenance of the apparatus that brings the radiation source to move is a disadvantage of this approach.

Fig. 6C shows a method of using a phantom composed of a cylindrical annihilation target 53 and a respective radiation source (for example, ge-68, not shown) of positrons, which are not shielded from each other, and as a result, positrons are separated from the radiation source and annihilated together with electrons in the annihilation target 53, thereby generating back-to-back annihilation radiation of 511 keV. For example, the annihilation target may be a plastic cylinder housing having a diameter of about 20cm and a length equal to the field of view of the scanner in the body axis direction. As in the method described above, each scintillator element in the scintillator block 102 is paired with a plurality of other scintillator elements including the scintillator elements in several different detector modules 101 via the LOR denoted by 61 of the phantom. Larger size annihilation targets are sometimes difficult to handle and thus become a disadvantage for this approach. The larger size may be inconvenient to store when not in use.

Finally, fig. 6D shows a method in which a pair of annihilation radiation sources are surrounded by a large block of scattering medium. In this case, the phantom 54 sometimes contains a Ge-68 rod radiation source surrounded by a steel cylinder from an inner diameter to about 10 cm. There are several disadvantages to this approach. First, the die body is quite heavy and sometimes difficult to handle. Then, since only a very small number of gamma rays emitted from the radiation source can be actually used to form one-to-many pairs due to the inefficiency in attenuation and scattering of the gamma rays of 511keV, the data collection time is long and the convergence of the iterative method of estimating the offset may take time. Further, due to uncertainty in scattering sites, accuracy is reduced, especially in time-axis resolution (200 ps) that can be achieved with the latest systems.

A prior art method of using an internal radiation source is shown in fig. 7A-7B.

Fig. 7A illustrates a method of pairing elements within scintillator block 102 with elements around a detector ring using inherent radiation, as illustrated by representative LOR 61. In general, in order to achieve sufficient accuracy, the time for data collection is required. In addition, since the inherent radiation from Lu-176 forms a very broad energy spectrum, the energy range of the identified event is limited to 2 fairly narrow windows (1 is about 511keV and another 1 is about 307 keV), at which time there is a stronger radiation of Lu-176, 1. As a result of the application of these energy windows, the available counts are extremely reduced.

The results are shown in fig. 16. The data shown in this figure are data obtained from a PET system using a scintillator crystal (crystal) containing Lu-176. The simultaneous occurrence spectrum of all Lu-176 is represented by 900. In the full spectrum 900, the counts are 78, 416, 224. The simultaneous energy spectrum after 2 energy windows are applied is indicated by 950. The width of the energy spectrum 950 is significantly reduced because the probability of simultaneous occurrence of a pair of 1 event being a 511keV window (in this case 435 to 625 keV) and another 1 event being a 307keV window (in this case 250 to 350 keV) is lower. In the energy window spectrum 950, the counts are 10, 241, 786. Thus, the application of 2 energy windows functions to reduce the result of the walk of the measured timing offset, but also reduces the available counts to about 13% of the full spectrum 900.

Fig. 7B shows other methods of using the inherent radiation. In this method, LOR's joining adjacent scintillator blocks 102 as shown by representative LOR61 are used. In addition to the difficulty of long data collection times, limiting LOR to contiguous modules presents another significant disadvantage. All scintillator elements need to be connected to the scintillator elements of the neighboring blocks by LOR, but the transmittance of the emitted intrinsic radiation is limited (mainly 202keV and 307keV gamma rays, which are quite low energies than the 511keV gamma rays detected by PET). Thus, the method is limited to calibration of blocks smaller than approximately 20mm in width.

In summary, the drawbacks of the existing TOF PET technology are roughly described in terms of 2 methods. With respect to methods using external radiation sources, the phantom is large, difficult to handle, or requires complex mechanical movements of the phantom. On the other hand, methods using inherent radiation are generally very time consuming.

The embodiments presented in this specification are a significant new approach, utilizing a single stationary "limited range" external source of radiation in combination with inherent radiation. The calibration method divides the timing calibration into 2 steps. In a first step, a single stationary limited range external radiation source is used to obtain a "relative timing offset" within a group (group) of processing units. In a second step, the "natural radiation" is used to obtain the offset between groups (groups) of processing units. In this case, the total offset is the sum of the "relative timing offset" and the "processing unit offset".

The major drawbacks of the external radiation source method in the existing TOF PET method are eliminated by using a single external radiation source that rests in a limited range. Further, by dividing the processing into 2 steps, the total amount of data required for the intrinsic radiation processing can be greatly reduced, and thus the main drawbacks of the conventional intrinsic radiation method in TOF PET can be eliminated.

The number of counts required for the intrinsic irradiation step is significantly reduced for 2 reasons. First, by determining the relative offset in the external radiation source step, the offset determined in the intrinsic radiation step is thus only the "processing unit offset". This means that all counts from all scintillator crystals within the processing unit can be pooled, thereby reducing the collection time. As an example, in the case of a scintillator array of 1 processing unit having crystals of 10×10=100, the number of counts required to achieve the desired accuracy at the processing unit level is reduced to 100 times as compared to the number of counts achieving the same accuracy in the external radiation source step at the crystal level. Further, by correcting in advance the use of the intrinsic radiation timing data based on the result of the external radiation source step, the width of the distribution of the intrinsic radiation data is greatly reduced. This effect is further increased in the case where the relative offset correction obtained in the external emission source step includes an walk-behind correction and in particular a nonlinear walk-behind correction.

The offset values described above are associated with variations in delays of various components of the detector system. The 1 source of such fluctuation may be a source of energy in a timing discriminator depending on the generation timing signal. Fig. 11 shows the use of more, rising discriminators in a TOF PET system. The time t is given when the signal level exceeds the value of the threshold. Fig. 11 shows an example of signals generated simultaneously by 3 different energy gamma rays interacting with detector elements. The 3 different signals correspond to energies E ₁、E₂ and E ₃(E₁＞E₂＞E₃). Although 3 gamma rays arrive at the same time, the times (t ₁、t₂ and t ₃, respectively) at which the threshold values are exceeded are different. This phenomenon is often referred to as time-stamping.

The correction of the walk before the "natural radiation" step, as compared to the event-limited analysis (in the prior art) in a narrow energy window as shown in fig. 16, can also use the full count acquired. This further reduces the required collection time.

Fig. 8A shows the inherent radiation timing distribution before the application of the relative offset correction obtained from the external emission source, and fig. 8B shows the distribution related to the same data after the application of the timing correction (including the nonlinear walk correction) from the first step. In this case, the width of the timing distribution is reduced by 2 times or more. The effect of this reduction in distribution width is approximately equivalent to increasing the number of counts by more than 4 times in order to achieve the same statistical uncertainty by the processing unit offset. Thus, the data is pre-corrected by the second step before the process is divided into 2 steps and before the calculation is performed, whereby in the example suggested (compared to the case where the intrinsic radiation of the crystal grade (THE CRYSTAL LEVEL) is used, but the data is not pre-corrected), the amount of data (or collection time) required in the intrinsic radiation step is reduced to approximately 100×4=400. Thus, the collection time was changed from several hours when the intrinsic radiation was used for all calibration to about 1 minute in the method described in the present specification, and the collection time was performed without using a large or movable external radiation source.

In timing offset calibration, it is necessary to pair all of the processing units being calibrated by the simultaneous occurrence of events. Sometimes 1 processing unit is 1 element in any stage of the electronic device structure of fig. 9 and 10. The processing units being calibrated sometimes pair directly by the simultaneous occurrence of events. The calibrated processing units are sometimes also paired indirectly by the simultaneous occurrence of events. For example, processing unit 1 is paired with unit 2, unit 2 is paired with unit 3, and unit 1 is indirectly paired with unit 3.

To calibrate relative crystal shifts and walks within the processing unit, a small and lightweight limited-range external emission source (e.g., a smaller limited-diameter line source) can be used (without movement of the radiation source or multiple radiation sources).

The intrinsic radiation (even at low activity levels) can also be used (after correction of relative crystal shifts and walk-in) to determine the processing unit shift. The preliminary correction of the relative crystal shift and walk narrows the initial timing distribution, as a result of which the number of counts required to achieve a particular processing unit shift accuracy is reduced, making the collection time for the intrinsic radiation appropriate. Further, for example, instead of a narrow range of energy limited to around 511keV, all events from the intrinsic radiation can be used by walk-behind correction.

In this case, the total offset is the sum of the relative crystal offset and the processing unit offset.

Advantages include reduced necessity for a large limited range of radiation sources, movement of radiation sources, or multiple radiation sources. The radioactive source with smaller limited range has simple treatment and shielding and lower replacement cost. Furthermore, the processing unit offset can be periodically recalibrated using only the inherent radiation.

During an initial full-timing calibration, the timing offset and time walk within the opposing pair of processing units are calibrated, for example, by centering annihilation radiation, such as a positron emission source, on the scanner. The radiation source needs to have a sufficient thickness in order to pair each stage of the crystal with 2 or more stages of the crystal in the opposing processing unit. After correcting for relative timing offset and time drift within the opposing pair of processing units, the timing offset between the processing units is calibrated using the inherent radiation within the crystal.

Here, the intrinsic radiation is radiation caused by decay (decay) of a radioactive material (within a crystal, a surface of a crystal, within a reflector material, or the like) that is part of the scintillator array. Typical intrinsic radiation is background radiation from the naturally occurring isotopes of the scintillator material. LYSO Lu-176 is an example of background radiation. The intrinsic radiation sometimes intentionally adds or dopes the scintillator material. As another example, co-60 is a material that can be added to scintillator materials.

Regarding the necessary conditions related to the inherent radiation, there are: the decay process comprises at least 2 (substantially) simultaneous emissions (e.g. beta immediately after gamma) of sometimes occurring coincidence events, or the decay process comprises 1 emission of sometimes occurring coincidence events due to compton scattering within the detector due to radiation, a half-life of more than 10 years and thus having a natural activity that has an effect over the life of the scanner, an activity in the range of 100 to 1000Bq per 1cm ³ and thus a data collection time is practical and the occurrence of occasional events is excessive, the energy of the emissions is several hundred keV to 1MeV, and among the candidates Lu-176 and Co-60, etc.

During daily clinical use, timing offset corrections based on pre-determined timing corrections and time walk corrections are applied prior to recalibration of timing offset at the processing unit level. The timing offset for each processing unit is sometimes calculated together using the intrinsic radiation and annihilation radiation, e.g., a central positron emission source, or is sometimes calibrated using the intrinsic radiation during periods when the scanner is not in use. Sometimes 1 processing unit is 1 element in an arbitrary stage (stage) of the electronic device structure of fig. 9 and 10.

Reference throughout this specification to "1 embodiment" and "one embodiment" means that a particular location, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the application, but does not mean that they are present in all embodiments.

Therefore, the phrase "in 1 embodiment" or "in one embodiment" expressed in various scenes throughout this specification does not necessarily refer to the same embodiment of the present application. Further, specific locations, constructions, materials, or characteristics may be combined in any suitable manner in 1 or more embodiments.

The PET scanner in the embodiment of the present invention sometimes has a different electronic device structure. A non-limiting exemplary configuration is shown in fig. 9 and 10.

In this case, the PET scanner, that is, the entire scanner is generally in the form of a ring.

The area is a relatively large portion of a scanner such as a four-partition section constituted by high-level data processing, data transfer, clock control, signal processing, and the like. The scanner may also have several regions. The timing offset/drift based on the clock distribution is sometimes a regional basis.

The Detector Unit (DU) is a relatively independent module, and is composed of data transmission, clock control, signal processing and the like. One region may have 10 to 20 DUs. The timing offset/drift based on the clock distribution is sometimes the DU-base.

A circuit Board (Board) is an electronic device circuit Board, consisting of several signal processing circuits for channels. The DU may also have 5 to 20 circuit boards. Timing offset/drift based on the power supply device is sometimes a circuit board substrate.

An ASIC is the smallest signal processing unit, typically consisting of 1 timing processing channel and several energy processing channels. The Circuit board may also have 1-10 Application SPECIFIC INTEGRATED Circuits (ASIC). Timing offset/drift is sometimes the ASIC body.

The crystal is the smallest element in the scanner. The ASIC may also perform signal processing on tens of crystals.

As described above, in the embodiment, the detector 300 is constituted by a plurality of processing units, and the circuit (processing circuit) of the embodiment corrects the relative timing offset within the group (set) of processing units based on the data acquired via the radiation source, and then corrects the timing offset between the groups (set) of processing units using the inherent radiation. Next, the circuit of the embodiment calculates the total timing offset by adding up the corrected relative timing offset in the group (set) of processing units and the calibrated timing offset between the groups of processing units, thereby performing calibration of the detector 300.

Here, as the "processing unit", various embodiments can be considered. As an example, as shown in fig. 9, the processing unit may have a plurality of detectors of the electronic device circuit board, respectively. That is, the circuitry of the embodiments may also first correct for the relative timing offset within the set (set) of detectors using the radiation source, and then correct for the timing offset between the sets (set) of detectors using the inherent radiation. As another example, as shown in fig. 10, the group (set) of processing units may include a plurality of detector units in one area (for example, a relatively large portion of a scanner such as a four-partition section configured by high-level data processing, data transfer, clock control, signal processing, and the like). In this case, the circuitry of the embodiments may also first correct for relative timing offset within an area using the radiation source, and then correct for timing offset between areas using the inherent radiation. As another example, the processing unit according to the embodiment may be an electronic device circuit board having a plurality of ASICs. In addition, as another example, the group (set) of processing units of the embodiment may be one detector unit. That is, the group (set) of processing units may be a detector unit.

Timing calibration is typically performed at different stages (stages). The number of components in each stage of the electronic device structure is expanded and contracted by approximately 1 order of magnitude. The collection time and analysis time for calibrating the timing offset in each stage varies greatly for the same statistical uncertainty. For example, since a DU sometimes contains 500 to 1000 crystals, the collection time required for calibration of the DU offset is approximately ∈ (500 to 1000) or 20 to 30 times shorter than that for calibration of the crystal offset (this is the case when the calculation time is ignored).

However, timing calibration is sometimes required only at a certain stage (stage). After an initial timing calibration, timing drift occurs at a certain level depending on the cause of the timing drift. Therefore, maintenance timing calibration needs to be performed only at the stage where timing drift occurs, and thus is sometimes performed very quickly.

The time walk can be corrected by including an energy-dependent condition in the offset correction. By correcting the time drift, a better time resolution (i.e., a distribution in which the measurement timing difference is narrower) can be obtained. Typically, in PET, imaging is performed using only gamma rays around 511keV that are detected through a narrow window. In the case of using only events in a narrow energy window, linear ambulation correction (i.e., linear and energy dependent ambulation correction) is typically sufficient. For example, an offset containing a linear walk correction can be written at t _offset＝t_offset(E＝511)+W₁ (E-511). Where W ₁ is a linear walk correction factor. The walk correction can be extended to t_offset＝t_offset(E＝511)+W₁(E-511)+W₂(E-511)²+…+W_n(E-511)ⁿ et al, which contain nonlinear conditions. Where W ₁ to W _n are walk correction coefficients.

Here, the method suggested in this specification uses events that span a very large range of energy in the "natural radiation" part of the calibration (in order to reduce the total collection time to a practical range), thus substantially improving performance through nonlinear walk-around correction. An arbitrary function used for the walk correction can be expressed by taylor series expansion, and therefore, this is equivalent to the case where f is set as a function to t _offset =f (E), but the functional type of f may become nonlinear.

During an initial full timing calibration, the timing offset of each crystal and the time walk of each crystal are calibrated. The source needs to have sufficient thickness in order for each stage of the crystal to pair with more than 2 stages of the crystal within the opposing DU. Data using the positron emission source and the intrinsic radiation are sometimes acquired separately or simultaneously.

In one embodiment, data using a positron emission source and intrinsic radiation are acquired separately. The positron emission source may be at least 1 of a Ge-68, F18-FDG, or Na-22 source.

In particular, during data collection using positron emission sources, a method is disclosed in which the positron emission sources are placed in the center Of the Field Of View (FOV) Of the scanner detector, and coincidence count data using the positron emission sources is acquired. Standard clinical data collection FOV and coincidence counting time windows are sometimes used. The number of simultaneous count events using a positron emission source needs to be a number sufficient to be calibrated from the peak positions of the TOF difference histograms for the individual crystals.

During data collection using intrinsic radiation, the disclosed method is to remove all sources of radiation from the scanner and use the intrinsic radiation to acquire coincidence count data. The FOV is sometimes collected using standard clinical data. In order to cope with the movement of the radiation particles such as gamma particles on the whole scanner, the count time window needs to be sufficiently large. The number of simultaneous counting events using the inherent radiation needs to be a number sufficient to calibrate from the peak positions of the TOF difference histograms associated with the respective DUs.

In yet another embodiment, data using both a positron emission source and intrinsic radiation may be acquired.

In particular, methods are disclosed for acquiring coincidence count data using positron emitting sources and intrinsic radiation. The FOV is sometimes collected using standard clinical data. In order to cope with the movement of the radiation particles over the scanner as a whole, the count time window needs to be sufficiently large. The number of coincidence events using the positron emission source needs to be a number sufficient to be calibrated from the peak positions of the TOF difference histograms for the respective crystals, and the number of coincidence events using the intrinsic radiation needs to be a number sufficient to be calibrated from the peak positions of the TOF difference histograms for the respective DUs.

In the case of acquiring data using both a positron emission source event and an intrinsic emission event during data analysis, the events may be separated by a TOF difference. The FOV can also be used to separate the source events from the intrinsic radiation events when the source events are centered in a narrow FOV while the intrinsic radiation events have a wider effective range.

During data analysis, the timing correction is divided into 3 different elements, i.e., an energy-independent relative timing shift for each crystal in the opposing DU pair, a time-shift correction coefficient for each crystal, and an energy-independent timing shift between DUs. The non-energy dependent relative timing offset for each crystal within the subtended pair of DUs, and the time walk correction coefficient for each crystal, are calculated from positron source data, but the non-energy dependent timing offset between DUs is calculated from intrinsic radiation data. In the following description, the relative timing offset in the opposing pair of DUs and the timing offset between DUs mean non-energy dependent conditions.

Regarding timing calibration within opposing pairs of DUs, the method is to divide coincidence count data using positron emission sources into N/2DU pairs for a PET scanner having N DUs. The relative timing offset and time-walk correction coefficients within opposing pairs of DUs are sometimes calibrated simultaneously for different pairs of DUs. In the case where the source is not perfectly centered, annihilation position correction is applied to the TOF differences for all events. The relative timing offset for each crystal within an opposing pair of DUs is repeatedly calculated by: i) Calculating a timing offset by finding the peak position of the timing histogram for each crystal; ii) correcting the TOF difference for the timing offset of each crystal after the calibration, and then repeating steps i) and ii) until the sequence converges; iii) The last timing offset for each crystal within the DU pair is the aggregate of the timing offsets for each crystal calibrated by all repetitions.

After correction of the relative timing offset of each crystal within the opposing pair of DUs, i) plotting the timing versus energy curve for each particular crystal taking into account the LOR that the particular crystal is linked to any of the crystals on the opposite side; ii) applying an appropriate fit (e.g. a linear fit or an exponential function fit) to the timing-energy curve of the crystal, whereby the walk correction coefficient for each crystal can be calculated, and the time walk correction coefficient for each crystal can be calculated.

Regarding timing offset calibration between DUs, the method is to apply timing offset correction and time walk correction within the DU pair to the radiation coincidence count data. For event location correction of TOF differences, it is not necessary, as the TOF difference histogram of the DU pair is symmetrical. But to achieve a narrower timing histogram, event location correction can be applied to the TOF difference for all events. The timing offset of each DU can be repeatedly calculated by: i) Calculating a timing offset by finding the peak position of the timing histogram for each DU; ii) correcting the TOF difference for the timing offset of each DU after the calibration, and then repeating steps i) and ii) until the sequence converges; iii) The last timing offset of each DU is the aggregate of the timing offsets of each DU calibrated by all repetitions.

In another embodiment, the timing offset of each DU is sometimes calculated analytically. In particular, a TOF difference histogram is calculated for each DU pair covered by the data collection FOV. The timing center for each DU pair is calculated by finding the peak position of the TOF difference histogram. The set (set) of equations is sometimes formed from the timing center per DU pair. The variable is the timing offset of each DU. The rank (rank) of the coefficient matrix of the equation needs to be equal to the number of DUs. The timing offset for each DU can be calculated by solving the above equation. The timing offset of each DU can be calculated from the timing center of each DU pair using a neural Network (Neutral Network).

In yet another embodiment, the timing offset of each DU can be calculated using a neural network. In particular, the input to the neural network may be, for example, an arrangement in which each column corresponds to a timing histogram for a single DU. The output is an offset for each DU. The neural network can be trained using target offset data that is generated using any of the conventional timing offset calibration methods. Training requires data from multiple systems. When the network must be trained in a state where only a small number of systems can be built, a large number of additional training data sets may be generated using data enhancement (described later).

In particular, the data enhancement is to acquire data from any of the existing systems (for example, 3 to 4), calibrate each system using the conventional timing offset calibration, generate corrected timing histograms for each DU pair using the calibration, generate random timing offsets for each DU in order to realize a plurality of systems (hundreds or thousands), and apply the random timing offsets to the corrected timing histograms to construct an enhanced data set for DUs in the realization of each system. The target offsets associated with these enhanced data sets are known offsets derived from the random timing offsets generated for each DU.

Neural network designs are sometimes convolutional neural networks (to reduce the number of parameters required). In this case, the convolutional layer is one-dimensional and functions only when the histogram from a single DU (for example, when each column corresponds to the histogram from a single DU as described above, the column of the input matrix).

By the disclosed method, a short time timing calibration using intrinsic radiation can be performed.

In particular, the timing offset of each processing unit is calculated. In this specification, the processing unit is sometimes a DU or an electronic device processing unit within a DU. Data collection using the intrinsic radiation removes all sources from the scanner, and acquires simultaneous count data using the intrinsic radiation. The FOV is sometimes collected using standard clinical data. In order to cope with the movement of the radiation particles throughout the scanner, the count time window must be sufficiently large. The number of simultaneous counting events using the inherent radiation needs to be sufficient to be calibrated from the peak positions of the TOF histograms for each processing unit.

In data analysis, timing offset correction from initial timing correction and time-lapse correction are applied before short-time timing correction is performed. The data analysis order of the timing offset calibration for each processing unit in the short-time timing calibration is the same as the data analysis order of the timing offset calibration for each DU in the initial full-time timing calibration.

In another embodiment, short time timing calibration using intrinsic radiation and positron source can be performed by the disclosed methods. In the case where calibration is required for the timing offset of the processing unit smaller than DU, the short-time timing calibration can be calculated in the same manner as the initial timing calibration.

Regarding data collection, the number of coincidence counting events using positron emission sources needs to be a number sufficient to calibrate from the peak positions of the TOF difference histograms for the respective processing units, and the number of coincidence counting events using intrinsic radiation needs to be the same as the initial timing calibration except for the number sufficient to calibrate from the peak positions of the TOF histograms for the respective processing units.

Data interpretation is similar to initial timing calibration.

The timing offset correction and the time walk correction from the initial timing calibration are applied before the short time timing calibration is performed. The timing offset for each processing unit within an opposing pair of DUs is calculated using a positron emission source in the central data as in the initial full timing calibration. The timing offset between DUs is calibrated using the inherent radiation as in the initial full timing calibration.

Fig. 12A and 12B show examples of TOF difference histograms of DU pairs from lutetium background radiation data in the case of calculating timing offset between DUs. The TOF difference is calculated as the timestamp of the (first hit (THE FIRST HIT) -the timestamp of the second hit).

The timing center of DU to TOF difference histogram can be found by gaussian fitting to a full curve, or parabolic fitting to the peak region. The timing center of the TOF difference histogram of DU pairs can also be found using a Neural Network (NN).

As an equation for determining the timing offset of each DU, the following equation holds.

Tcenter_14-33＝Toffset₁₄–Toffset₃₃-Tdiff_distance

Tcenter_33-14＝Toffset₃₃–Toffset₁₄-Tdiff_distance

Toffset₁₄–Toffset₃₃＝(Tcenter_14-33–Tcenter_33-14)/2

Here, tdiff _distance is event position correction for the TOF difference, and the event position correction is canceled by each other when calculating the timing offset difference between DU14 and DU 33.

Fig. 13 shows another way of TOF difference histogram calculation of DU pairs from lutetium background radiation data in the case of calculating timing offset between DUs. The TOF difference is calculated as (timestamp of DU 14-timestamp of DU 33). The timing center of DU to TOF difference histogram can be found by gaussian fitting to a full curve, or parabolic fitting to the peak region. The timing center of the DU versus TOF difference histogram can also be found using Neural Networks (NN).

As an equation of the timing offset of each DU, the following equation holds.

Tcenter_left＝Toffset₁₄–Toffset₃₃–Tdiff_distance

Tcenter_right＝Toffset₁₄–Toffset₃₃+Tdiff_distance

Toffset₁₄–Toffset₃₃＝(Tcenter_right+Tcenter_left)/2

Fig. 14 shows an example of a TOF difference histogram of DU pairs from lutetium background radiation data and Ge radiation source data acquired simultaneously. The TOF difference is calculated as (timestamp of DU 14-timestamp of DU 33). Positron source data and lutetium intrinsic radiation data are sometimes separated by a time of flight (TOF) difference.

The timing offset between pairs of DUs is substantially reduced after a short time timing calibration. For example, fig. 15A shows timing offset between pairs of DUs before short time timing calibration, and fig. 15B shows timing offset between pairs of DUs after short time timing calibration. According to one embodiment disclosed herein, an accurate, simple, and rapid method for timing calibration of a TOF PET scanner is provided.

In order to effectively reduce statistical noise of reconstructed images and improve image quality for TOF PET scanners, the various embodiments discussed in this specification provide good temporal resolution and are used in order to maintain accurate timing correction between daily clinical use, enabling images with a reduced number of artifacts of the TOF PET scanner.

According to one embodiment, timing offset calibration is performed by aggregating and pairing all processing units calibrated by simultaneous events.

According to another embodiment, the timing offset calibration is performed by: until the simultaneous occurrence of gamma photons between a sufficient number of groups (groups) brings about a sufficient timing offset calibration for all of the crystals, the overlapping groups (groups) of crystals caused by the simultaneous occurrence of gamma photons are summarized and performed in pairs.

According to one embodiment, during an initial full timing calibration, (1) the timing offset and time walk within the or each DU are calibrated by disposing a limited range positron emission source in the scanner FOV, and (2) after correction of the timing offset and time walk within the or each DU, the inherent radiation (e.g., lutetium) is used to calibrate the timing offset between the or each DU pair.

According to one embodiment, in step (1), the limited range radiation source preferably has a thickness sufficient for the crystals to pair with a plurality of crystals within the other DU.

According to another embodiment, during daily clinical use, (1) a timing offset correction from an initial timing calibration and a time walk correction are applied prior to the timing calibration during daily clinical use; (2) The timing offset of each processing unit is calculated using the inherent radiation (e.g., lutetium) together with a limited range positron emission source within the scanner FOV; and/or (3) the timing offset of each processing unit is calibrated using inherent radiation (e.g., lutetium) during periods when the scanner is not in use.

According to 2 different implementations, (1) data is acquired using a limited range positron emission source and intrinsic radiation (e.g., lutetium), respectively; (2) While data is acquired using a limited range of positron emitting sources and intrinsic radiation (e.g., lutetium).

Advantageously, if at least the embodiments disclosed herein are used, then (1) there is no need to move the source during the initial full-time calibration, or a large limited range source is used; (2) A short time timing calibration can be performed without using an external radiation source during daily clinical use; (3) The simplified method is performed without position dependent timing correction; (4) Calibration is performed relatively quickly due to simultaneous processing and simple methods.

The method and system described in this specification can be performed in some techniques, but can be adapted to the processing circuit in general for performing the calibration described in this specification. In one embodiment, the processing circuitry is implemented alone or through an Application Specific Integrated Circuit (ASIC), a field programmable gate array (Field Programmable GATE ARRAY:FPGA), a general purpose logic array (GENERIC ARRAY of logic: GAL), a programmable logic array (Programmable Array of Logic:PAL), a 1-time-limited programmable circuit of logic gates (e.g., using fuses), or a combination of reprogrammable logic gates.

Furthermore, the processing circuit includes a computer processor having an embedded and/or external nonvolatile computer readable memory (e.g., RAM, SRAM, FRAM, PROM, EPROM and/or EEPROM) storing a computer program (binary executable command and/or interpreted computer command) for controlling the computer processor to perform the processing described in the present specification. Computer processor circuits sometimes support single or multi-threading, respectively, and install a single processor or multiple processors each having a single or multiple cores.

In one embodiment using a neural network, the processing circuitry for training the artificial neural network need not be the same as the processing circuitry for installing the artificial neural network for training for calibration as described herein. For example, the processing circuitry and memory are used to make a trained artificial neural network (e.g., defined by interconnections and weights), and the FPGA may also be used to install the trained artificial neural network. In addition, in order to improve the training and use of the trained artificial neural network, a serial installation method or a parallel installation method (for example, by installing the trained neural network in a parallel processor architecture such as a graphics processor architecture) may be used to improve the performance.

According to at least one embodiment described above, calibration with good accuracy can be performed.

Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other modes, and various omissions, substitutions, modifications, and combinations of the embodiments can be made without departing from the spirit of the invention. These embodiments and modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

As for the above embodiments, as one aspect and optional features of the invention, the following supplementary notes are disclosed.

(Additionally, 1)

In one aspect of the present invention, a PET apparatus includes a detector and a circuit. The detector detects a pair of simultaneous events generated by annihilation of positrons emitted from a radiation source disposed within a field of view (FOV) of the detector. The circuit corrects the relative timing offset in the set (set) of processing units based on the data acquired via the radiation source, corrects the timing offset between the set (set) of processing units using the inherent radiation, and determines a total timing offset based on the corrected relative timing offset in the set (set) of processing units and the corrected timing offset between the set (set) of processing units, thereby performing the calibration of the detector.

(Additionally remembered 2)

The circuit may determine a total timing offset as a sum of the relative timing offset and the calibrated timing offset, thereby performing the calibration of the detector.

(Additionally, the recording 3)

The circuit may further correct time drift within the set (set) of processing units based on data acquired via the radiation source.

(Additionally remembered 4)

The time shift may be a nonlinear time shift.

(Additionally noted 5)

The intrinsic radiation may be radiation generated by decay of a radioactive material that is part of a scintillator array of the PET apparatus.

(Additionally described 6)

It is also possible that the decay process of the intrinsic radiation comprises at least 2 substantially simultaneous emissions that produce a coincidence count due to the decay process.

(Additionally noted 7)

The intrinsic radiation may be radiation generated by decay of a radioactive material that is part of a scintillator array of the PET apparatus,

The decay process of the intrinsic radiation contains radiation within the detector that causes this counting phenomenon due to radiation, sometimes due to compton scattering.

(Additionally noted 8)

The inherent radiation may be radiation emitted from at least one of the scintillator, an adhesive holding the reflector in place, the reflector itself, or the detector housing.

(Additionally, the mark 9)

The inherent radiation may also be Lu-176 or Co-60.

(Additionally noted 10)

The radiation source may be a limited-range annihilation radiation source within the field of view of the detector, the limited-range annihilation radiation source including a range in which each crystal in the scanner is paired with a plurality of crystals in at least one other group (set) of processing units.

(Additionally noted 11)

The source may be a limited range annihilation source within the field of view of the detector,

The narrowest cross-sectional extent of the limited-range annihilation radiation source is less than 10mm.

(Additional recording 12)

The limited-range annihilation radiation source may be a radiation source.

(Additional recording 13)

The limited-range annihilation radiation source may be a positron radiation source.

(Additional recording 14)

The circuit may also use a neural network to calculate the timing offset for each processing unit.

(Additional recording 15)

The limited range annihilation radiation source may be at least 1 of a Ge-68, F18-FDG, or Na-22 radiation source.

(Additionally remembered 16)

The group (set) of processing units may be a pair of processing units.

(Additionally noted 17)

The group (set) of processing units may be at least one of a pair of processing units and a group (set) of processing units that are paired based on simultaneous counting by the radiation source.

(Additional notes 18)

The circuit may acquire a part of data from the intrinsic radiation and the radiation source, respectively.

(Additionally, a mark 19)

The circuit may acquire a part of the data from the inherent radiation and the radiation source at the same time.

(Additionally noted 20)

The processing unit may be a detector unit having a plurality of electronic device circuit boards, respectively.

(Additionally, the recording 21)

The group (set) of processing units may be a plurality of detector units included in one region.

(With 22)

It is also possible that the set (set) of processing units is one detector unit.

(Additionally note 23)

The processing unit may be an electronic device circuit board having a plurality of ASICs, respectively.

(Additionally noted 24)

The calibration method provided in one aspect Of the present invention is a method Of performing timing calibration in Time Of Flight (TOF) positron emission tomography (Positron Emission Tomography: PET), by configuring a radiation source within the FOV Of a PET scanner, obtaining a relative timing offset within a set (set) Of processing units, correcting the relative timing offset within the set (set) Of processing units, calibrating the timing offset between the set (set) Of processing units using intrinsic radiation, and performing calibration Of a detector based on the corrected relative timing offset within the set (set) Of processing units and the calibrated timing offset between the set (set) Of processing units.

Claims

1. A PET device, namely a positron emission tomography device, comprises:

A detector configured to detect a pair of simultaneous events generated by annihilation of positrons emitted from a radiation source disposed within a field of view (FOV) of the detector, the detector being configured to detect the pair of simultaneous events; and

A circuit configured to correct a relative timing shift in the group of the processing units based on data acquired via the radiation source, calibrate a timing shift between groups of the processing units using inherent radiation, and determine a total timing shift based on the corrected relative timing shift in the group of the processing units and the calibrated timing shift between groups of the processing units, thereby performing calibration of the detector, each group of the processing units having two or more detector units.

2. The PET device of claim 1, wherein,

The circuit determines a total timing offset as a sum of the relative timing offset and the calibrated timing offset, thereby performing calibration of the detector.

3. The PET device of claim 1, wherein,

The circuitry further corrects for time walk within the set of processing units based on data acquired via the radiation source.

4. The PET device of claim 1, wherein,

The intrinsic radiation is radiation generated by the decay of radioactive material, which is part of the scintillator array of the PET device,

The decay process of the intrinsic radiation involves radiation that sometimes occurs with simultaneous counting events due to compton scattering within the detector due to the radiation.

5. The PET device of claim 1, wherein,

The source is a finite range annihilation source within the field of view of the detector,

The limited-range annihilation radiation source includes a limited-range radiation source having a range in which each crystal in the PET apparatus is paired with a plurality of crystals in at least one other group of processing units.

6. The PET device of claim 1, wherein,

7. The PET device of claim 1, wherein,

The circuit uses a neural network to calculate the timing offset for each processing unit.

8. The PET device of claim 1, wherein,

The set of processing units is at least one of a pair of simultaneous processing units, and a set of processing units, paired according to simultaneous counting via the radiation source.

9. The PET device of claim 1, wherein,

The circuitry obtains a portion of the data from the intrinsic radiation and the radiation source, respectively.

10. The PET device of claim 1, wherein,

The circuitry simultaneously acquires a portion of data from the intrinsic radiation and the radiation source.

11. The PET device according to any one of claims 1 to 10, wherein,

The processing unit is a detector unit having a plurality of electronic device circuit boards, respectively.

12. The PET device according to any one of claims 1 to 10, wherein,

The set of processing units is a plurality of detector units comprised by one area.

13. The PET device according to any one of claims 1 to 10, wherein,

The set of processing units is one detector unit.

14. The PET device according to any one of claims 1 to 10, wherein,

The processing unit is an electronic device circuit board having a plurality of ASICs, i.e. application specific integrated circuits, respectively.

15. A calibration method is a method for performing timing calibration in time-Of-flight (TOF) positron emission tomography (Positron Emission Tomography: PET),

A radiation source is configured within a detector field of view (FOV) of a PET scanner to obtain a relative timing offset within a group of processing units, the relative timing offset within the group of processing units is corrected, the timing offset between the groups of processing units is calibrated using intrinsic radiation, the calibration of the detector is performed based on the corrected relative timing offset within the group of processing units and the calibrated timing offset between the groups of processing units, each group of processing units having more than two detector units.