CN107456235B - Position correction method and system - Google Patents
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Abstract
The application provides a position correction method. The position correction method includes receiving photons through a crystal array and generating an optical signal. The crystal array comprises at least two kinds of crystals with different crystal decay times, and the at least two kinds of crystals are arranged on a receiving surface for receiving photons at intervals. The position correction method further includes converting the optical signal into an electrical signal; determining the position information of the photon incidence to the crystal array and the signal attenuation time of the electric signal according to the electric signal; and comparing the signal attenuation time with the crystal attenuation time, and determining the crystal corresponding to the crystal attenuation time which is accorded with the signal attenuation time to correct the position information. The application also provides a position correction system.
Description
Technical Field
The present application relates to the field of medical imaging, and more particularly, to a method and system for correcting photon location information.
Background
Positron Emission Tomography (PET) is a technique that involves injecting a radionuclide-labeled tracer into a subject, where the tracer is collected by the circulatory system in some tissues of the subject where metabolism is vigorous. Meanwhile, nuclides in the tracer decay to release positrons, and the positrons collide with negative electrons around the positrons to be annihilated, so that photon pairs flying in opposite directions are released. Photon pairs received by a pair of detector units are registered as a coincidence event. When enough photon pairs are received by the PET detector, the distribution condition of the tracer in the detected body can be calculated by utilizing a reconstruction algorithm, so that the metabolic distribution information of the detected body is obtained.
Disclosure of Invention
One aspect of the present application provides a position correction method. The position correction method includes receiving photons through a crystal array and generating an optical signal. The crystal array comprises at least two kinds of crystals with different crystal decay times, and the at least two kinds of crystals are arranged on a receiving surface for receiving photons at intervals. The position correction method further includes converting the optical signal into an electrical signal; determining the position information of the photon incidence to the crystal array and the signal attenuation time of the electric signal according to the electric signal; and comparing the signal attenuation time with the crystal attenuation time, and determining the crystal corresponding to the crystal attenuation time which is accorded with the signal attenuation time to correct the position information.
Another aspect of the present application provides a position correction system. The position correction system includes: a crystal array including at least two kinds of crystals having different crystal decay times, the at least two kinds of crystals being spaced apart on a receiving surface receiving photons, for receiving the photons and generating an optical signal; the photoelectric conversion device is connected with the crystal array and is used for converting the optical signal into an electric signal; the electric signal processing unit is used for determining the position information of the photons incident to the crystal array and the signal attenuation time of the electric signal according to the electric signal; and the correction unit is used for comparing the signal attenuation time with the crystal attenuation time, determining the crystal corresponding to the crystal attenuation time corresponding to the signal attenuation time and correcting the position information.
According to the position correction method and system, the position information of photons incident to the crystal array is corrected by comparing the signal attenuation time with the crystal attenuation time by utilizing the fact that the crystal attenuation time of different crystals is different, and the error rate is reduced.
Drawings
FIG. 1 is a schematic view of one embodiment of a PET detector of the present application;
FIG. 2 shows a front view of the crystal array of the PET detector shown in FIG. 1 from the receiving face;
FIG. 3 is a flow chart illustrating one embodiment of a position correction method of the present application;
FIG. 4 is a two-dimensional position scattergram of an embodiment of the present application;
FIG. 5 is a diagram illustrating a code segmentation table obtained by segmenting the two-dimensional position scattergram shown in FIG. 4;
FIG. 6 is a waveform illustrating the amplitude of an electrical signal as a function of time for one embodiment;
FIG. 7 is a diagram illustrating an embodiment of the present application in which a position correction table and the code segmentation table shown in FIG. 5 are combined;
FIG. 8 is a schematic diagram of another embodiment of the present application in which a position correction table and the code division table shown in FIG. 5 are combined;
FIG. 9 is a schematic block diagram illustrating one embodiment of a position correction system of the present application.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs. The use of "first," "second," and similar terms in the description and in the claims does not indicate any order, quantity, or importance, but rather is used to distinguish one element from another. Also, the use of the terms "a" or "an" and the like do not denote a limitation of quantity, but rather denote the presence of at least one. The word "comprising" or "comprises", and the like, means that the element or item listed as preceding "comprising" or "includes" covers the element or item listed as following "comprising" or "includes" and its equivalents, and does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. As used in this specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.
The embodiment of the application discloses a position correction method, which comprises the steps of receiving photons through a crystal array and generating optical signals, wherein the crystal array comprises at least two kinds of crystals with different crystal decay time, and the at least two kinds of crystals are arranged on a receiving surface for receiving the photons at intervals. And further converting the optical signals into electric signals, and determining the position information of the photons incident to the crystal array and the signal attenuation time of the electric signals according to the electric signals. And comparing the signal attenuation time with the crystal attenuation time, and determining the crystal corresponding to the crystal attenuation time corresponding to the signal attenuation time to correct the position information. "Crystal decay time", or "crystal decay coefficient", is a property of a crystal, and differences in crystal decay time can result in differences in signal decay time of an electrical signal. The position correction method can be used in a PET system and is used for correcting position information of a crystal array of the PET system, which is incident to photons (such as gamma photons), so as to reduce the error rate. "positional information" indicates the position of the crystal in the crystal array at which the photon is incident, i.e., indicates which crystal the photon was received by to generate the optical signal. The "error rate" refers to the fact that a photon enters a certain crystal to generate an optical signal, but due to factors such as optical path transmission omission, device resolution error and circuit identification error, the position of the crystal obtained at the terminal of the system is deviated from the position of the crystal where the actual photon enters, and therefore deviation occurs in the position information of the photon incidence. The position information of the deviation is invalid information or error information, and the correct information identification and reconstruction of the image are influenced.
FIG. 1 shows a schematic view of one embodiment of a PET detector 20. The PET detector 20 includes a crystal array 21 and a photoelectric conversion device 22 connected to the crystal array 21. The crystal array 21 includes at least two kinds of crystals having different crystal decay times, the at least two kinds of crystals being spaced apart on a receiving surface 23 for receiving photons and generating an optical signal. In one embodiment, at least two kinds of crystals are arranged at intervals in the X direction and the Y direction perpendicular to the depth direction (i.e., Z direction) of the crystal array 21. Referring collectively to fig. 2, fig. 2 is a front view of crystal array 21 as viewed from receiving surface 23. In the embodiment of fig. 2, crystal array 21 includes two kinds of crystals 210 and 212 arranged at intervals. The receiving surface 23 of the crystal array 21 is square, and the adjacent crystals of the first crystal 210 in the X direction and the Y direction are the second crystals 212, and similarly, the adjacent crystals of the second crystals 212 in the X direction and the Y direction are the first crystals 210. However, the arrangement of FIG. 2 is not limited thereto, and in other embodiments, the two crystals 210 and 212 may be spaced in other patterns. For example, the two crystals 210 and 212 are arranged at angular intervals to the X-direction and the Y-direction.
In other embodiments, crystal array 21 may include three or more crystals, which may be spaced in a sequence that ensures that two adjacent crystals are of different crystal types. In addition, in some embodiments, the receiving surface 23 of the crystal array 21 may be rectangular, or other shapes, and may be designed according to actual needs. Various crystal arrangements may be designed according to the shape of the receiving surface 23. The above are only some examples and are not limited to the above examples.
The at least two crystals of crystal array 21 have crystal decay times that differ significantly such that the optical signals produced by the different crystals are converted to electrical signals having decay times that differ significantly, however, other properties (e.g., optical output) of the at least two crystals are substantially the same. For example, the crystal array includes a YSO crystal and a lu (y) AP crystal, the optical outputs of the two crystals are substantially identical and thus the amplitudes of the electrical signals are substantially the same, however, the crystal decay time of the YSO crystal is 2.5 times the crystal decay time of the lu (y) AP crystal and thus the decay time of the electrical signals into which the optical signals generated by the two crystals are converted is about 2.5 times. The electrical signal may comprise an analog signal or a digital signal.
In one embodiment, different crystals of crystal array 21 may comprise different materials such that the crystal decay times of the crystals are different. For example, the materials of the different crystals may be completely different. As another example, doping one material in one crystal yields another crystal with a different crystal decay time. In another embodiment, the different crystals may be doped with different concentrations of material, which may result in crystals having different crystal decay times. In yet another embodiment, the shape, surface smoothness, light reflection and transmission, and/or light transmission channels inside the crystal of different crystals are different, so that the decay time of the crystals is different. These different crystals may comprise the same material, or comprise different materials. For example, the crystal can be in different three-dimensional shapes such as a cuboid, a wedge, a cylinder and the like; the different crystals can be obtained by encapsulating the crystals with different light-reflecting materials such as barium sulfate, alumina, titanium dioxide powder, etc., or with a light-reflecting film such as teflon, ESR film, a coating film, etc. The above are merely examples of obtaining different crystals, and one of the above-described ways of changing the decay time of a crystal may be used alone, or two or more of them may be used in combination. However, in other embodiments, the crystal decay time may be varied in other ways to obtain different crystals.
In some embodiments, the crystal array 21 may include BGO crystals, LYSO crystals, LSO crystals, NaI (TI) crystals, CsI crystals, GSO crystals, LaBr crystals3Crystal and BaF2One or more of the crystals. In other embodiments, crystal array 21 may include other crystals that may be used to detect photons.
In some embodiments, different crystals may be encapsulated, bonded or fixed by the same light reflective material or reflective film, and the surface of the crystal array 21 may be wrapped by aluminum film to enhance the light reflective performance of the crystals.
The photoelectric conversion device 22 is used to convert an optical signal generated by the crystal array 21 into an electrical signal. The photoelectric conversion device 22 may include a PMT (Photomultiplier Tube) or a SiPM (Silicon Photomultiplier Tube) that multiplies and converts an optical signal into an electrical signal. The PET detector 20 may include a plurality of photoelectric conversion devices 22 connected to a crystal array 21, as shown in fig. 1, including 4 photoelectric conversion devices 22, but is not limited thereto.
The plurality of PET detectors 20 may form an annular ring of detectors arranged along an axis to form a detector arrangement defining an interior space. Pairs of photons generated by positron annihilation events occurring within this interior space are detected by a pair of PET detectors 20 when incident upon the pair of PET detectors 20 in opposite directions.
FIG. 3 is a flow chart illustrating one embodiment of a position correction method 30. The position correction method 30 includes steps 31-34. Wherein the content of the first and second substances,
in step 31, photons are received by the crystal array and an optical signal is generated.
The crystal array comprises at least two kinds of crystals with different crystal decay times, and the at least two kinds of crystals are arranged at intervals on a receiving surface for receiving photons. The crystal array may be the crystal array 21 of the embodiment shown in fig. 1 and 2, or the crystal arrays of the other embodiments described above, and will not be described herein again. The incident of photons to the crystals of the crystal array excites visible light, i.e. an optical signal.
In step 32, the optical signal is converted to an electrical signal.
The optical signal may be converted into an electrical signal by a photoelectric conversion device. The electrical signal converted by the photoelectric conversion device is an analog signal, and the analog signal can be further converted into a digital signal. The analog signals may be converted to digital signals by signal processing circuitry, such as circuitry including analog-to-digital conversion (a/D) chips.
In step 33, the position information of the photon incident on the crystal array and the signal attenuation time of the electrical signal are determined from the electrical signal.
The position coordinates (X, Y) of the photons incident into the crystal array can be determined using a centroid method, and position information can be determined from the position coordinates. In one example, the crystal array includes a plurality of photoelectric conversion devices, and an optical signal generated by a photon incident on the crystal array reaches the plurality of photoelectric conversion devices in a certain proportion, is multiplied and converted into an electrical signal, and signal energy can be obtained according to the electrical signal.
For example, the four photoelectric conversion devices 22 in fig. 1 respectively output signal energies EA、EB、EC、EDIn which EASignal energy output from a photoelectric conversion device at the upper left corner, EBSignal energy outputted from a photoelectric conversion device at the upper right corner, ECSignal energy output from a photoelectric conversion device at the lower left corner, EDThe signal energy output by the photoelectric conversion device at the lower right corner. The total energy E of signals output by the four photoelectric conversion devices can be expressed as formula (1):
E＝EA+EB+EC+ED (1)
the total signal energy E may be the signal energy E output by multiple photoelectric conversion devicesA、EB、EC、EDAnd performing analog addition or digital addition calculation. Signal energy EA、EB、EC、EDThe acquisition can be performed digitally by using a high-speed a/D chip, or the analog signal is saturated by using a TOT (Time over threshold) method, and the signal energy is acquired by using the digital chip to acquire the saturation Time.
The position coordinates (X, Y) of the photons incident into the crystal array are obtained by calculation through a gravity center method and are expressed as formulas (2) and (3):
in this way, the position coordinates (X, Y) of the photons incident in the crystal array can be determined, for each photon its position coordinates can be determined. The above description has been given only with four photoelectric conversion devices as an example, but is not limited thereto, and calculation of the position coordinates is similar to the above example for other numbers of photoelectric conversion devices.
And further determining position information according to the position coordinates, namely determining the position of the crystal on which the photons are incident in the crystal array. In one embodiment, a coded partition table is constructed and the location information is determined using the coded partition table. The code division table includes a number of code regions corresponding to the crystals of the crystal array. The coding regions correspond to the crystals of the crystal array one by one, and the coding regions are coded according to a certain sequence, so that each crystal of the crystal array is coded. In one embodiment, several block regions may be coded one by one, such that the coding of a coded region is one coding of that region. In another embodiment, the boundary line dividing several regions may be encoded such that the encoding of a region is the encoding of a plurality of boundary lines surrounding the region. The positional information includes a code of a corresponding code region of the crystal upon which the photon is incident, from which code the corresponding crystal in the array of crystals can be located.
In one embodiment, a two-dimensional position scatter diagram displaying the distribution of a plurality of photons is generated according to the position coordinates of the photons, a plurality of areas which are the same as the number of crystals of a crystal array and contain the distribution center of gravity are segmented on the two-dimensional position scatter diagram according to the distribution center of gravity of the photons on the two-dimensional position scatter diagram, and the areas are coded to obtain a code segmentation table. As shown in fig. 4, fig. 4 is a two-dimensional position scattergram of an example. The photons are marked on the two-dimensional position scatter diagram according to the position coordinates of the photons, and the black dots in fig. 4 represent the photons. The plurality of photons are distributed on a two-dimensional position scatter diagram, the two-dimensional position scatter diagram displays distribution centers 41 of the plurality of photons, and the number of the distribution centers 41 is equal to the number of crystals of the crystal array. As shown in fig. 5, fig. 5 is a code division table obtained by dividing the two-dimensional position scattergram of fig. 4. Each region 42 in the coded partition table contains a distribution center of gravity 41, and the distribution center of gravity 41 is located substantially at the center of the coded region 42. The code segmentation table in fig. 5 corresponds to the 8 x 8 crystal array shown in fig. 1 segmented into 8 x 8 code regions. The position information of the incident photon can be obtained from the code division table, and the position information obtained in this step includes the code of the code region where the photon is located, which is the initial position information.
In one embodiment, determining the signal decay time as the time during which the absolute value of the amplitude of the electrical signal exceeds the amplitude threshold may facilitate determining the signal decay time. The amplitude threshold is a positive number. As shown in fig. 6, fig. 6 is a waveform diagram of the amplitude of the electric signal with time. In fig. 6 the amplitude threshold T is set to 0.2V and the duration during which the absolute value of the amplitude of the electrical signal exceeds the amplitude threshold T (i.e. the amplitude of the electrical signal is below-0.2V) is L, which is the signal decay time. Fig. 6 is only an example, and the amplitude threshold value may be set according to practical applications. In one embodiment, the signal decay time acquisition is performed digitally. Specifically, a digital signal is obtained, signals of which the absolute value of the amplitude of the digital signal exceeds an amplitude threshold value are counted to obtain the number of sampling points, and the number of the sampling points is multiplied by the sampling interval time to obtain the signal attenuation time. In another embodiment, the signal decay time acquisition is implemented in an analog manner. Specifically, a comparator may be used, the threshold of the comparator is set as an amplitude threshold, a pulse is formed when the absolute value of the electrical signal exceeds the amplitude threshold, and the pulse length or pulse interval is identified as the signal attenuation time. In other embodiments, the above-described signal decay time may be determined in other ways.
In another embodiment, the duration of time for which the absolute value of the amplitude of the electrical signal rises to a first threshold and falls to a second threshold is determined to be the signal decay time, the first threshold and the second threshold being positive numbers. For example, the first threshold is 90% of the absolute value of the initial amplitude of the electrical signal, and the second threshold is 10% of the absolute value of the initial amplitude, so the duration from when the absolute value of the amplitude of the electrical signal rises to 90% of the absolute value of the initial amplitude of the electrical signal to when the absolute value of the amplitude of the electrical signal falls to 10% of the absolute value of the initial amplitude is the signal decay time. In other examples, the first and second thresholds may be set to other values. The above are only two examples of determining the signal decay time and are not limited to the above examples.
With continued reference to fig. 3, in step 34, the signal decay time is compared with the crystal decay time to determine the crystal corresponding to the crystal decay time to which the signal decay time corresponds, and the position information is corrected.
When the signal decay time of the electrical signal coincides with the crystal decay time of the crystal, it indicates that the optical signal converted into the electrical signal is generated by the crystal, i.e., photons are incident on the crystal. The signal attenuation time of the electric signal corresponding to the photon and the crystal attenuation time of the crystal corresponding to the coding region where the photon is located can be compared, if the two are consistent, the coding region where the photon is located is consistent with the position of the crystal where the photon is actually incident, and the incident position information of the photon is correct position information. If the two are not consistent, the coded region where the photon is located is not consistent with the position of the crystal where the photon is actually incident, and the incident position information of the photon is invalid information or error information. The signal attenuation time and the crystal attenuation time of the crystal corresponding to the adjacent coding region can be further compared, the crystal attenuation time is different from the crystal attenuation time of the crystal corresponding to the coding region where the photon is located, if the two are consistent, the crystal position where the photon is actually incident is the position of the crystal corresponding to the adjacent coding region, the position information is corrected to include the position information of the coding of the adjacent coding region, namely the photon is drawn into the adjacent coding region, and thus the initial position information is corrected to obtain the corrected position information. In one embodiment, if the signal attenuation time is consistent with the crystal attenuation time of the crystal corresponding to two or more adjacent coding regions, according to the position coordinates of the photon, one adjacent coding region closest to the photon is selected as the coding region corresponding to the crystal on which the photon is actually incident, and the position information includes the code of the adjacent coding region. In one embodiment, if the signal attenuation time is not consistent with the crystal attenuation time of the crystal corresponding to the adjacent coding region, the position information may be invalid position information, and may be discarded and not used for subsequent processes such as determining the coincidence response line and reconstructing the image. Therefore, the wrong position information is corrected, and the invalid position information is abandoned, so that the error rate is reduced, the accuracy of the line obtained according to the position information is improved, and the accuracy of the information identification of the image is improved. The method can reduce the error rate caused by factors such as optical path transmission omission, device resolution errors, circuit identification errors and the like, and can also reduce the error rate caused by dividing photons close to the boundary of the coding region into wrong coding regions when the coding region is divided.
Specifically, in one embodiment, a position correction table is constructed and the position information is corrected using the above-described coded partition table and position correction table. The position correction table includes a number of sub-regions within a number of encoding regions. The edges of the position correction table coincide with the edges of the coded partition table. Fig. 7 is a diagram showing a combination of a position correction table and a code division table. In the figure, the region divided by the thick solid line (for example, the line indicated by LX1, LX2, LY1, LY 2) is the coding region (for example, the region indicated by a11, a12, a21, a 22) in the code division table, and the thin solid line (for example, the line indicated by LX1, LX2, LY1, LY 2) divides the coding region into a plurality of sub-regions (for example, the sub-regions indicated by 1-16) of the position correction table. In the figure, one coding region is divided into 4 sub-regions, but the invention is not limited thereto, and a plurality of sub-regions can be divided according to practical application. For the purpose of explanation, only parts of the boundary lines and regions are denoted by reference numerals in fig. 7.
In one embodiment, the sub-regions may be encoded. Similarly to encoding the encoded regions in the encoding partition table, encoding the sub-regions in the position correction table may be implemented by encoding each block region or encoding boundary lines surrounding the sub-regions. In one embodiment, the sub-regions in the entire table may be encoded one by one in a certain order. In another embodiment, the sub-regions in each encoded region may be encoded, and the sub-regions in different encoded regions may be encoded with the same code, the encoding of the sub-regions in combination with the encoding of the encoded regions to distinguish the different sub-regions. The above are just some examples, however in other embodiments, other encoding schemes may be used for encoding. The reference number shown in fig. 7 can be used as a code, but is not limited thereto, and the code can be designed as required in practical application.
With combined reference to fig. 4 and 5, in the present embodiment, the position correction table may be obtained by dividing a plurality of sub-regions on the two-dimensional position scattergram through connecting lines of distribution centers 41 of a plurality of photons on the two-dimensional position scattergram. In the embodiment shown in fig. 7, the distribution centers of gravity 41 are connected in the X direction and the Y direction, and a line connecting in the X direction and the Y direction, i.e., a thin solid line, is obtained, thereby dividing several sub-regions.
In one embodiment, the signal attenuation time of the electric signal generated by the photon in the sub-region is compared with the crystal attenuation time of the crystal corresponding to the coding region in which the sub-region is located and/or the adjacent coding region, and the coding region corresponding to the crystal attenuation time corresponding to the signal attenuation time is determined, so as to correct the position information. The sub-region in which the photon is located can be determined from the position coordinates (X, Y), and the position information can include the coding of the sub-region. In one embodiment, when the signal attenuation time of the electrical signal is not consistent with the crystal attenuation time of the crystal corresponding to the coding region where the electrical signal is located, the position information may be corrected by comparing the signal attenuation time of the electrical signal with the crystal attenuation time of the crystal corresponding to the coding region adjacent to the sub-region where the electrical signal is located.
As illustrated in fig. 7, after a photon is incident on the crystal, an electrical signal is obtained, and position information is determined according to energy distribution of the electrical signal, which is initial position information. For example, the position information is directed to the encoding region a11 in the upper left corner of fig. 7, and it can be understood that the electrical signals and photons fall into the encoding region a 11. The signal attenuation time of the electric signal and the crystal attenuation time of the crystal corresponding to the code region a11 are compared, and if both are matched, the position information is correct position information, and the electric signal is the signal of the code region a 11. If they do not match, the electrical signal may be the signal of the adjacent code area of the code area a11, and the position information is corrected.
In one embodiment, the crystal corresponding to coding region a11 is the same as the crystal corresponding to coding region a22 and has the same crystal decay time, and the crystal corresponding to coding region a12 is the same as the crystal corresponding to coding region a21 and has the same crystal decay time, whereas the crystals corresponding to coding regions a11, a22 are different from the crystals corresponding to coding regions a12, a21 and have different crystal decay times, such as the embodiment shown in fig. 2. In the case that the signal attenuation time of the electrical signal does not coincide with the crystal attenuation time of the crystal corresponding to the coding region a11, the electrical signal may be the crystal error corresponding to the adjacent coding region a12 or a21 to the coding region a 11.
Further, if the electrical signal falls into the sub-region 2, the signal attenuation time of the electrical signal is determined by comparison to conform to the crystal attenuation time of the crystal corresponding to the coding region a12 adjacent to the sub-region 2, and then the electrical signal is regarded as the signal of the coding region a 12. If the electric signal falls into the subregion 3, the signal attenuation time is determined to be consistent with the crystal attenuation time of the crystal corresponding to the coding region A21 adjacent to the subregion 3 through comparison, and then the electric signal is regarded as the signal of the coding region A21. If the electric signal falls into the sub-region 4, the adjacent coding region A12 or A21 in the two coding regions A12 and A21, which is closer to the photon position in the sub-region 4, is determined according to the position coordinates (X, Y) of the photon, and the signal attenuation time is determined by comparison to be consistent with the crystal attenuation time of the crystal corresponding to the closer coding region A12 or A21, the electric signal is regarded as the signal of the closer coding region A12 or A21. If the electrical signal falls into sub-region 1, because sub-region 1 has no coding region adjacent to it, the electrical signal is discarded and considered as an invalid signal. Other electrical signals that do not meet the above-mentioned decision rule are also regarded as invalid signals and discarded. Photons falling within the other encoding regions in fig. 7 can be referred to the above-described rule to determine and correct the position information.
In another embodiment, the crystals corresponding to the coding region a22 are different from the crystals corresponding to the coding regions a11, a12, a21, respectively, and thus the crystal decay time of the crystals corresponding to the coding region a22 is different from the crystal decay time of the crystals corresponding to the coding regions a11, a12, a21, respectively. In the case where the signal attenuation time of the electrical signal falling into the coding region a11 is not consistent with the crystal attenuation time of the crystal corresponding to the coding region a11, the electrical signal may be a crystal error corresponding to the adjacent coding region a12, a21, or a22 in the coding region a 11. If the electric signal falls in the sub-area 1, 2 or 3, the position information is corrected similarly to the determination rule in the above embodiment in which the electric signal falls in the corresponding sub-area 1, 2 or 3.
If the electrical signal falls into sub-region 4, further, in one example, the crystal corresponding to encoding region a12 is different from the crystal corresponding to encoding region a21, and has different crystal decay times. And comparing the signal attenuation time with the crystal attenuation time of the crystal corresponding to the coding region A12, A21 and/or A22 adjacent to the sub-region 4, and if the signal attenuation time is consistent with one of the crystal attenuation times, regarding the electric signal as the coding region corresponding to the consistent crystal attenuation time. In another example, the crystals corresponding to the encoding regions a12 and a21 are the same, with the same crystal decay time. Comparing the signal attenuation time with the crystal attenuation time of the crystal corresponding to the coding regions A12 and A21 adjacent to the subregion 4, and/or the crystal attenuation time of the crystal corresponding to the adjacent coding region A22. If the signal decay time of the electrical signal falling into the sub-region 4 coincides with the crystal decay time of the crystals corresponding to the encoding regions a12 and a21, the adjacent encoding region a12 or a21 of the two encoding regions a12 and a21, which is closer to the position of the photon in the sub-region 4, is determined from the position coordinates (X, Y) of the photon, and the electrical signal is regarded as the signal of the closer encoding region a12 or a 21. If the signal attenuation time matches the crystal attenuation time of the crystal corresponding to the code region a22, the electric signal is regarded as the signal of the code region a 22. This corrects the position information.
The above is merely an example, but not limited thereto, and in other embodiments, the coding region into which the electrical signal falls may be determined by other determination rules, so as to correct the position information.
Fig. 8 is a diagram showing another embodiment in which a position correction table and a code division table are combined. Connecting the distribution centers 41 of photons in fig. 4 obliquely results in the position correction table in fig. 8, the edge of which overlaps with the edge of the code division table similarly to fig. 7. In fig. 8, the connecting lines (for example, lines denoted by reference numerals 81 and 82) connecting the distribution centroids in the position correction table overlap with the diagonal lines of the code region of the code division table, thus dividing the code region into a plurality of sub-regions in the diagonal direction. The connecting line connecting the distribution centers of gravity in fig. 8 divides each coding region into two sub-regions in the diagonal direction from the upper left to the lower right. Similar to the method of fig. 7 for determining the coding region into which a photon falls, the position information may be corrected by comparing the signal decay time and the crystal decay time and determining the coding region into which an electrical signal should fall according to the position of the sub-region into which the electrical signal falls.
In another embodiment, the line connecting the distribution centers of gravity may be in a diagonal direction from top right to bottom left. In yet another embodiment, the connecting lines connecting the distribution centers of gravity may include a connecting line in a diagonal direction from top left to bottom right and a connecting line in a diagonal direction from top right to bottom left, dividing each encoding region into four sub-regions. The above are only some examples of the position correction table, but not limited thereto, and in other embodiments, the position correction table may be divided into sub-regions by other forms or rules.
The corrected position information can be used for generating a coincidence response line, and an image is reconstructed according to the coincidence response line, so that the generated coincidence response line is more accurate, the identification information of the image is more accurate, and diagnosis and treatment can be better assisted.
The actions of the position correction method 30 are illustrated in the form of modules, and the sequencing of the modules and the division of the actions within the modules shown in fig. 3 are not limited to the illustrated embodiments. For example, the modules may be performed in a different order; actions in one module may be combined with actions in another module or split into multiple modules. In some embodiments, there may be additional steps before, after, or in between the steps of the position correction method 30.
In correspondence with the aforementioned embodiment of the position correction method 30, the present application also provides an embodiment of a position correction system. FIG. 9 is a schematic block diagram illustrating a position correction system 90, according to one embodiment. The correction system 90 comprises a detector 91, an electrical signal processing unit 92 and a correction unit 93. Several detectors 91 form a detector ring, the detectors 91 may be the PET detectors 20 shown in fig. 2, including the crystal array 21 and the photoelectric conversion devices 22. The detailed description of the crystal array 21 and the photoelectric conversion device 22 is referred to above and will not be repeated here.
The electrical signal processing unit 92 is used to determine the position information and signal decay time of the photons incident on the crystal array according to the electrical signals. The electrical signal processing unit 92 is further configured to construct a code division table, and determine the position information using the code division table. The code division table includes a number of code regions corresponding to the crystals of the crystal array. In one embodiment, the electrical signal processing unit 92 is further configured to generate a two-dimensional position scattergram showing the distribution of the photons according to the position coordinates of the photons, and segment a plurality of regions, which are the same as the number of crystals of the crystal array and include the distribution center of gravity, on the two-dimensional position scattergram according to the distribution center of gravity of the photons on the two-dimensional position scattergram, and encode the regions to obtain an encoded segmentation table. In one embodiment, the electrical signal processing unit 92 is configured to determine the time during which the absolute value of the amplitude of the electrical signal exceeds the amplitude threshold as the signal decay time.
The electrical signal processing unit 92 receives the electrical signal generated by the photoelectric conversion device of the detector 91, and may convert the analog signal into a digital signal. The electric signal processing unit 92 may include a processing circuit, an a/D conversion chip, a digitizing chip, and/or an FPGA (Field-Programmable Gate Array), and the like.
The correcting unit 93 is configured to compare the signal attenuation time with the crystal attenuation time, and determine a crystal corresponding to the crystal attenuation time corresponding to the signal attenuation time, so as to correct the position information. The correction unit 93 is further used to construct a position correction table, and correct the position information using the coded partition table and the position correction table. The position correction table includes a number of sub-regions within a number of encoding regions. In one embodiment, the correction unit 93 is further configured to obtain the position correction table by dividing a plurality of sub-regions on the two-dimensional position scattergram through a connecting line of distribution centers of the plurality of photons on the two-dimensional position scattergram. The correcting unit 93 is further configured to compare the signal attenuation time of the electrical signal generated by the photon in the sub-region with the crystal attenuation time of the crystal corresponding to the coding region in which the sub-region is located and/or the adjacent coding region, and determine the coding region corresponding to the crystal attenuation time to which the signal attenuation time corresponds, so as to correct the position information. The correction unit 93 may comprise a processor, a memory and/or a comparator etc.
The electric signal processing unit 92 and the correction unit 93 of the position correction system 90 may be implemented by software, or may be implemented by hardware, or a combination of hardware and software. The functions and functions of the elements of the position correction system 90 are specifically realized by the steps and sub-steps of the position correction method 30, and are not described herein again.
In one embodiment, the position information corrected by the correction unit 93 may be provided to a coincidence processor (not shown) for generating a coincidence line. The resulting line of coincidence may be provided to an image reconstruction unit (not shown) for reconstructing an image from the several lines of coincidence. The reconstructed image may be provided to a display device (not shown) for display. In other embodiments, the position correction system 90 may also include other elements not shown, and the corrected position information may be provided to other elements in addition to the above elements for further processing, etc.
For the device embodiments, since they substantially correspond to the method embodiments, reference may be made to the partial description of the method embodiments for relevant points. The above-described embodiments of the apparatus are merely illustrative, and the units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the components can be selected according to actual needs to achieve the purpose of the scheme of the application. One of ordinary skill in the art can understand and implement it without inventive effort.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the scope of protection of the present application.
Claims (6)
1. A position correction method characterized by: it includes:
receiving photons through a crystal array and generating an optical signal, wherein the crystal array comprises at least two kinds of crystals with different crystal decay times, and the at least two kinds of crystals are arranged on a receiving surface for receiving the photons at intervals;
converting the optical signal into an electrical signal;
determining the position information of the photon incidence to the crystal array and the signal attenuation time of the electric signal according to the electric signal; and
comparing the signal attenuation time with the crystal attenuation time, and determining the crystal corresponding to the crystal attenuation time which is accorded with the signal attenuation time to correct the position information;
the determining the position information of the photon incident to the crystal array and the signal attenuation time of the electric signal according to the electric signal comprises:
constructing a coding segmentation table, wherein the coding segmentation table comprises a plurality of coding regions corresponding to the crystals of the crystal array; and determining the location information using the coded partition table;
the comparing the signal attenuation time with the crystal attenuation time, and determining the crystal corresponding to the crystal attenuation time to which the signal attenuation time corresponds, so as to correct the position information, includes:
constructing a position correction table, wherein the position correction table comprises a plurality of sub-regions in the plurality of encoding regions; and correcting the position information using the code division table and the position correction table;
the correcting the position information using the code division table and the position correction table includes:
and comparing the signal attenuation time of the electric signal generated by the photon in the sub-region with the crystal attenuation time of the crystal corresponding to the coding region where the sub-region is located and/or the adjacent coding region, and determining the coding region corresponding to the crystal attenuation time which is accorded with the signal attenuation time to correct the position information.
2. The position correction method according to claim 1, characterized in that: the constructing of the coding partition table includes:
generating a two-dimensional position scatter diagram for displaying the distribution of the photons according to the position coordinates of the photons; and
according to the distribution centers of gravity of the photons on the two-dimensional position scatter diagram, dividing a plurality of areas which are the same as the number of crystals of the crystal array and contain the distribution centers of gravity on the two-dimensional position scatter diagram, and coding the areas to obtain the coding division table.
3. The position correction method according to claim 2, characterized in that: the constructing of the position correction table includes:
and segmenting the plurality of sub-regions on the two-dimensional position scatter diagram through the connecting line of the distribution centers of gravity of the plurality of photons on the two-dimensional position scatter diagram to obtain the position correction table.
4. A position correction system characterized by: it includes:
a crystal array including at least two kinds of crystals having different crystal decay times, the at least two kinds of crystals being spaced apart on a receiving surface receiving photons, for receiving the photons and generating an optical signal;
the photoelectric conversion device is connected with the crystal array and is used for converting the optical signal into an electric signal;
the electric signal processing unit is used for determining the position information of the photons incident to the crystal array and the signal attenuation time of the electric signal according to the electric signal; and
the correction unit is used for comparing the signal attenuation time with the crystal attenuation time, determining a crystal corresponding to the crystal attenuation time corresponding to the signal attenuation time, and correcting the position information;
the electrical signal processing unit is further configured to:
constructing a coding segmentation table, wherein the coding segmentation table comprises a plurality of coding regions corresponding to the crystals of the crystal array; and determining the location information using the coded partition table;
the correction unit is further to:
constructing a position correction table, wherein the position correction table comprises a plurality of sub-regions in the plurality of encoding regions; and correcting the position information using the code division table and the position correction table;
the correction unit is further used for comparing the signal attenuation time of the electric signal generated by the photon in the sub-region with the crystal attenuation time of the crystal corresponding to the coding region where the sub-region is located and/or the adjacent coding region, and determining the coding region corresponding to the crystal attenuation time corresponding to the signal attenuation time to correct the position information.
5. The position correction system according to claim 4, characterized in that: the electrical signal processing unit is further configured to:
generating a two-dimensional position scatter diagram for displaying the distribution of the photons according to the position coordinates of the photons; and
according to the distribution centers of gravity of the photons on the two-dimensional position scatter diagram, dividing a plurality of areas which are the same as the number of crystals of the crystal array and contain the distribution centers of gravity on the two-dimensional position scatter diagram, and coding the areas to obtain the coding division table.
6. The position correction system according to claim 5, characterized in that: the correction unit is further configured to obtain the position correction table by dividing the plurality of sub-regions on the two-dimensional position scattergram through a connection line of distribution centers of the plurality of photons on the two-dimensional position scattergram.
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| CN101806912A (en) * | 2010-03-18 | 2010-08-18 | 清华大学 | High-energy ray laminated type crystal module detector |
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