JP5872241B2 - Positron emission tomography system - Google Patents

Description

  Embodiments described herein generally relate to variable delay devices that adjust the relative delay between analog signals of a PET (Positron Emission Computerized Tomography) sensor and methods for calibrating the devices.

  In PET imaging, or positron emission tomography, a radiopharmaceutical is administered to a subject via infusion, inhalation, and / or food intake. The physical and biomolecular properties of the drug are then concentrated at specific sites in the human body. The actual spatial distribution, concentration of the location and / or area of accumulation, and kinetics of the process from administration and uptake to final elimination are all of clinical importance. In this process, a positron emitter attached to a radiopharmaceutical emits positrons depending on the physical properties of the isotope, such as half-life, branching ratio. Each positron interacts with the electrons of the object and annihilates, producing two gamma rays of 511 keV, which fly substantially 180 degrees apart. The two gamma rays then cause a scintillation event in the scintillation crystal of the PET detector so that the detector detects the gamma rays. By detecting these two gamma rays and drawing a line between them, the “response line”, the estimated position of the actual annihilation is determined. This process only identifies a single straight line with potential interaction, but accumulates many of these lines and estimates the actual distribution with useful accuracy through a tomographic reconstruction process. In addition to the location of the two scintillation events, if accurate timing within a few hundred picoseconds is available, a time-of-flight calculation is also performed to determine the disappearance events along that line. More information about the estimated location can be added. The limit of the scanner's timing resolution determines the accuracy of positioning along this line. The limits of the actual scintillation event positioning determine the ultimate spatial resolution of the scanner. Isotopic intrinsic properties (eg, positron energy) are responsible for determining the spatial resolution of a particular radiopharmaceutical (by the positron range and colinearity of the two gamma rays).

  The above process is repeated for a number of extinction events. In order to determine how many scintillation events are needed to support the desired imaging task, it needs to be analyzed on a case-by-case basis, but traditionally a typical 100 cm long Fluoro-Deoxyglucose (FDG) ) Will accumulate approximately 100 million counts or events. The time required to accumulate this number of counts depends on the injection volume and the sensitivity and count performance of the scanner.

  PET imaging relies on the conversion of gamma rays to light through a fast and bright scintillation crystal that generates the scintillation events described above. Time-of-flight PET further requires sub-nanosecond timing resolution, with a resolution of a few hundred picoseconds also conceivable. Adjusting and adjusting the two channels of the scintillation crystal, the photomultiplier tube (PMT), and the electronics is complex enough, but it becomes more complicated with a large array of crystals and sensors.

  Modern PET systems support timing resolution of 500-600 ps. At this level, even small timing variations of the components are important, and the transition time is the most important variable in this equation. The transition time is the average time between when a photon strikes the PMT photocathode and when the corresponding current pulse is measured at the PMT anode. This amount of variation from one PMT to the other PMT causes the signal to reach the analysis circuit at different times.

  The need for an accurate transition time of the detection chain is often offset by internal or inherent flight differences between the shortest and longest optical paths to the crystal position sensor. This is a complex theoretical estimate to be performed, but the measurements suggest that 25-40 ps is an inherent timing variation for the optical path. Therefore, an accuracy of 25-40 ps with a balanced transition time for all channels of the detector is a reasonable target. It may be more accurate, but the impact on system performance is negligible although it cannot be ignored.

  Conventionally, there are several ways to control or add a time delay to a PMT pulse in a gamma ray detector. Most methods involve active components that reduce the frequency content of the signal and target accuracy that is unnecessary for the synchronization of all signals. Another conventional system does not compensate for the transition of time variation between different PMT assemblies, so timing resolution may be degraded. In addition, circuit techniques that are active in conventional systems are costly, increase circuit complexity, and more importantly, reduce signal quality and integrity.

JP 2007-41007 A

  The problem to be solved by the present invention is to provide a variable delay device, a device adjustment method, and a positron emission tomography system capable of controlling time control with a simple configuration.

The positron emission tomography system according to the embodiment is a positron emission tomography system including a plurality of gamma ray detectors, and each gamma ray detector is adjacent to the plurality of scintillation crystals arranged in an array. A plurality of optical sensors arranged in an array, and a plurality of variable delay devices corresponding to each of the plurality of optical sensors, each variable delay device including a substrate, a plurality of conductive pins, a first Terminal, a second terminal, and a jumper. A plurality of conductive pins are mounted on the substrate. The first terminal is connected to a first conductive pin of the plurality of conductive pins. The second terminal is connected to a second conductive pin of the plurality of conductive pins. A jumper electrically interconnects the plurality of conductive pins at a predetermined distance to the substrate. The time delay introduced by the variable delay device is determined by the electrical path between the first and second terminals formed by the plurality of conductive pins interconnected by the jumpers.

  The embodiments described herein and many of the attendant advantages can be more fully appreciated with reference to the following detailed description and considered in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of a gamma ray detection system according to an embodiment of the present invention. FIG. 2A is a schematic diagram (1) of an optical sensor including a variable delay device according to an embodiment of the present invention. FIG. 2B is a schematic diagram (2) of the optical sensor including the variable delay device according to the embodiment of the present invention. FIG. 3 is a schematic diagram of a continuously variable delay device according to an embodiment of the present invention. FIG. 4A is a schematic diagram (1) of delay adjustment of the variable delay device according to the embodiment of the present invention. FIG. 4B is a schematic diagram (2) of delay adjustment of the variable delay device according to the embodiment of the present invention. FIG. 4C is a schematic diagram (3) of delay adjustment of the variable delay device according to the embodiment of the present invention. FIG. 5A is a schematic diagram (1) of delay adjustment of another variable delay device according to the embodiment of the present invention. FIG. 5B is a schematic diagram (2) of delay adjustment of another variable delay device according to the embodiment of the present invention. FIG. 5C is a schematic diagram (3) of delay adjustment of another variable delay device according to the embodiment of the present invention. FIG. 6A is a schematic diagram (1) of a time delay device having a fixed delay after adjustment according to an embodiment of the present invention. FIG. 6B is a schematic diagram (2) of a time delay device with a fixed delay after adjustment according to an embodiment of the present invention. FIG. 7 is a schematic diagram of another photosensor structure including a variable delay device according to an embodiment of the present invention. FIG. 8 is a schematic diagram of a further structure of an optical sensor including a time delay device according to an embodiment of the present invention. FIG. 9 is a schematic diagram of a discontinuous time delay device according to another embodiment of the present invention. FIG. 10 is a schematic diagram of another discontinuous time delay device according to an embodiment of the present invention. FIG. 11 is a schematic diagram of a computer controlled discontinuous time delay device according to an embodiment of the present invention. FIG. 12 is a schematic diagram of another computer controlled discontinuous time delay device according to an embodiment of the present invention. FIG. 13 is a schematic diagram of a calibration circuit for a time delay device according to an embodiment of the present invention. FIG. 14 is a schematic diagram of another calibration circuit for a time delay device according to an embodiment of the present invention. FIG. 15 is a schematic diagram of calibration of a time delay device according to an embodiment of the present invention.

  Generally, in a time-of-flight gamma ray detection system, a variable delay device is connected to a photomultiplier tube or photosensor. The variable delay device includes a substrate and a plurality of conductive pins mounted on the substrate. The variable delay device is connected to the first terminal connected to the first conductive pin of the plurality of conductive pins and to the second conductive pin of the plurality of conductive pins. And a second terminal. Further, a jumper that electrically connects a plurality of conductive pins at a predetermined distance to the substrate is also included in the variable delay device. Here, the time delay introduced by the variable delay device is determined by the electrical path between the first and second terminals formed by a plurality of conductive pins and jumpers.

  In one embodiment for fine timing adjustment, continuous adjustment is possible. In another embodiment, discontinuous adjustments can be made by physically setting jumpers or by electronically selecting various delay circuits. A maximum transition time variation of 400 ps and a 10-step discontinuous delay circuit of 40 ps are provided. However, as will be apparent to those skilled in the art, other maximum transition time variations and delay steps are possible without departing from the scope of the present invention.

  Reference will now be made to the drawings, wherein like reference numerals indicate like or corresponding parts throughout the several views. FIG. 1 is a schematic diagram of a gamma ray detection system according to an embodiment of the present invention. In FIG. 1, the photomultiplier tubes 135 and 140 are arranged on the light guide 130, and the array of scintillation crystals 105 is arranged below the light guide 130. A second array of scintillation crystals 125 is arranged facing the scintillation crystal 105, and a light guide 115 and photomultiplier tubes 195 and 110 are arranged on the second array.

  In FIG. 1, when gamma rays are emitted from a subject (not shown), the gamma rays fly at about 180 ° from each other in opposite directions. In the scintillation crystals 100 and 120, detection of gamma rays occurs simultaneously, and a scintillation event is determined when gamma rays are detected in the scintillation crystals 100 and 120 within a predetermined time limit. In this way, the gamma ray timing detection system detects gamma rays simultaneously with the scintillation crystals 100 and 120. Here, for the sake of simplicity, the detection of gamma rays in the scintillation crystal 100 will be described. However, as will be apparent to those skilled in the art, the description provided herein with respect to scintillation crystal 100 is equally applicable to gamma ray detection in scintillation crystal 120.

  Each photomultiplier tube (PMT) 110, 135, 140, and 195 is connected to variable gain amplifiers (VGA) 150, 152, 154, and 156, respectively. The VGA acts as a signal buffer so that the acquisition system absorbs fluctuations in PMT gain that occur naturally as part of the PMT manufacturing process and that are caused by aging of the PMTs 110, 135, 140, 195. Can be adjusted. The signal output from each VGA 150, 152, 154, and 156 is split into two separate electronic paths.

  One electron path is used to measure the arrival time of gamma rays. The signal to this path is typically formed by summing two or more signals from the same detector with summing amplifiers 184 and 186. The effect of summing multiple signals from the same detector improves the signal to noise ratio for the timing estimate and reduces the required number of electronic components. After being summed, the signal is passed to discriminators 187 and 188. Typically, a discriminator 187 or 188 having an adjustable threshold generates an electronic pulse that is precisely timed when the summed signal passes the threshold setting. The output of the discriminator 187 or 188 activates time-to-digital converters (TDC) 189 and 190. TDC 189 or 190 generates a digital output that encodes the time of the discriminator pulse relative to a system clock (not shown). In the case of a time-of-flight PET system, the TDC 189 or 190 generates a time stamp with an accuracy of 15-25 ps.

  For each PMT 110, 135, 140, 195, there is an independent electronic path used to measure the amplitude of the signal on each PMT 110, 135, 140, 195. This path includes filters 160, 162, 164, and 166, and analog to digital converters (ADCs) 176, 177, 178, and 179. Filters 160, 162, 164, or 166, for example, bandpass filters, are used to optimize the signal-to-noise ratio of measurements and perform anti-aliasing before conversion to digital signals by ADCs 176, 177, 178, or 179 To do. The ADCs 176, 177, 178, or 179 may operate at 100 MHz, for example, in this case, a free-run type in which a central processing unit (CPU) 170 performs digital integration. Alternatively, the ADCs 176, 177, 178, or 179 may be a peak sensing type. The outputs of the ADC and TDC are supplied to the CPU 170 for processing. The processing step consists of estimating the energy and position from the ADC output and the arrival time from the TDC output for each event, and based on the previous calibration, the accuracy of the energy, position and arrival time estimates is increased. To improve, many correction steps can be applied. As will be apparent to those skilled in the art, the CPU 170 as a discontinuous logic gate, application specific integrated circuit (ASIC), rewritable gate array (FPGA), or other complex type You may implement as a programmable logic device (Complex Programmable Logic Device: CPLD). An FPGA or CPLD implementation may be encoded in VHDL, Verilog, or any other hardware description language. The code may be stored directly in the electronic memory within the FPGA or CPLD, or may be stored as a separate electronic memory. Furthermore, the electronic memory may be non-volatile such as a ROM (Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electronically Erasable and Programmable Read Only Memory), or a flash memory. The electronic memory may also be volatile, such as static or dynamic RAM (Random Access Memory). A processor such as a microcontroller or microprocessor may be provided to manage the electronic memory as well as the interaction between the FPGA or CPLD and the electronic memory.

  Alternatively, the CPU 170 is stored in any or all of the above electronic memories and a hard disk device, a CD (Compact Disc), a DVD (Digital Versatile Disc), a flash drive, or other known storage media. May be implemented as a set of computer-readable instructions. In addition, the computer-readable instructions include processors such as Intel Xeon (registered trademark), or AMDer Opteron (registered trademark), and Microsoft Vista (registered trademark), UNIX (registered trademark), Solaris (registered trademark). , LINUX (registered trademark), Apple's Mac-OS (registered trademark), and other operating systems known to those skilled in the art, utility applications, background daemons, or operating system components, or It may be provided as a combination.

  Once processed by the CPU 170, the processed signal is stored in the electronic storage unit 180 and / or displayed on the display unit 145. As will be apparent to those skilled in the art, the electronic storage unit 180 may be a hard disk device, a CD-ROM device, a DVD device, a flash device, a RAM, a ROM, or any other electronic storage device known in the art. The display unit 145 is an LCD (Liquid Crystal Display) display device, a CRT (Cathode-Ray Tube) display device, a plasma display device, an OLED (Organic Light Emitting Display), an LED (light-Emitting Diode), or well known in the art. It may be implemented as any other display device. As such, the descriptions of the electronic storage unit 180 and the display unit 145 provided in the present specification are merely specific examples, and do not limit the scope of the present invention.

  FIG. 1 also includes an interface 175 through which the gamma detection system functions in connection with other external devices and / or users. For example, the interface 175 may be a Universal Serial Bus (USB) interface, a Personal Computer Memory Card International Association (PCMCIA) interface, an Ethernet interface, or any other interface known in the art. Interface 175 may also be wired or wireless and may include a keyboard and / or mouse for user interaction, or other human interface devices well known in the art.

  Next, the variable delay device according to the present embodiment will be described. The variable delay device according to the present embodiment is a variable delay device connected to an optical sensor of a gamma ray detection system, and includes a substrate, a plurality of conductive pins, a first terminal, a second terminal, and a jumper. Is provided. A plurality of conductive pins are mounted on the substrate. The first terminal is connected to a first conductive pin of the plurality of conductive pins. The second terminal is connected to a second conductive pin of the plurality of conductive pins. A jumper electrically interconnects the plurality of conductive pins at a predetermined distance to the substrate. The time delay introduced by the variable delay device is determined by the electrical path between the first and second terminals formed by the plurality of conductive pins interconnected by the jumpers.

  In this embodiment, the variable delay device is connected in series with the terminal of the photosensor. The photosensor may be a silicon photomultiplier tube.

  2A and 2B are schematic views of a photomultiplier tube or photosensor incorporating a continuous time delay device according to this embodiment. 2A and 2B, the photomultiplier tube 140 is the same as the photomultiplier tube 140 of FIG. The signal lead 200 from the photomultiplier tube 140 is electrically connected to the time delay device 240. The time delay device 240 includes a substrate on which conductive pins 210 and 215 are mounted, that is, a printed circuit board 205. Jumper 220 is electrically connected to conductive pins 210, 215 to introduce a time delay corresponding to the electrical path formed by conductive pins 210, 215 and jumper 220. A high voltage cable 230 and a signal cable 225 are also connected to the substrate 205. Although not shown in FIGS. 2A and 2B, a voltage divider or a bleeder circuit connected between the high voltage cable 230 and the photomultiplier tube generates a voltage supplied to the dynode of the photomultiplier tube 140. Used to step down to the desired value.

  FIG. 3 is a schematic diagram of the continuous delay device 240 of FIGS. 2A and 2B. As described above, conductive pins 210, 215 are mounted on a circuit board, or substrate 205, and jumper 220 is used to electrically interconnect those conductive pins.

  4A-4C are schematic diagrams of the process of setting a desired delay with continuous delay device 140. FIG. In FIG. 4A, a jumper 220 is slidably connected to the conductive pins 210, 215 to electrically connect the conductive pins 210, 215. The jumper 220 slides up and down the conductive pins 210, 215 to set the desired delay, as indicated by the dotted arrows.

  In FIG. 4B, the conduction path 405 is set by sliding the jumper to a predetermined position of the conductive pins 210 and 215. As such, the total delay from the first conductive pin 210 to the second conductive pin 215 is a function of the length of each conductive pin from the substrate 205 to the jumper 220, as well as the length of the jumper 220 itself. It is. As shown in FIG. 4C, the conduction path 410 is made longer by sliding the jumper 220 on the conductive pins 210 and 215 further away from the substrate 205. Thus, the configuration of FIG. 4C introduces a larger delay than the configuration of FIG. 4B. When the jumper 220 is located farthest from the substrate 205 on the conductive pins 210, 215, the maximum delay of the continuous delay device 140 occurs.

  That is, the maximum time delay is determined by the total length of the plurality of conductive pins.

  As will be apparent to those skilled in the art, conductive pins 210 and 215 may be made of any electrically conductive material, such as copper, aluminum, and / or gold. Further, the jumper 220 may also be made of any electrically conductive material, such as all or any of copper, aluminum, and gold. The conductive pins 210, 215 may also be any shape or length. As such, the shapes, sizes, and material configurations of the conductive pins 210, 215 and jumpers 220 described herein are merely examples and do not limit the scope of the present invention.

  For small delays, the two conductive pin configurations described with reference to FIGS. 3 and 4A-4C are reasonable, but for larger delays, the pin length of the conductive pins increases. It may be too much. Accordingly, as shown in FIG. 5A, a continuous time delay device 500 according to another embodiment of the present invention includes a plurality of conductive pins 501 to 506 mounted on a substrate 510. As described above, the substrate may be a printed circuit board. Jumper 520 includes a plurality of connection points for electrically interconnecting conductive pins 501-506. As shown in FIG. 5B, a jumper 520 is slidably connected to the conductive pins 501-506 to create a conduction path and corresponding delay. As shown in FIG. 5C, the jumper 520 is set at a predetermined distance from the substrate 510 in order to set a conduction path 525 including the length of each conductive pin 501 to 506 and the length of the jumper 520 itself.

  5A-5C, the continuous time delay device 500 is shown as including six conductive pins 501-506, but as will be apparent to those skilled in the art, the continuous time delay device 500 is not limited thereto. Not. More or fewer conductive pins can be added to achieve the desired maximum delay. The continuous time delay device 500 of FIGS. 5A-5C allows greater delay than the continuous time delay device of FIG. 3 as long as the pin length of the conductive pins is kept relatively short.

  The variable delay device may include fixing means for mounting the jumper on the plurality of conductive pins at predetermined positions.

  Also, as shown in FIGS. 6A and 6B, once the continuous time delay device 500 is adjusted to the desired delay, the jumper 520 may be held in place using a fixative 600 such as an adhesive. In FIGS. 6A and 6B, the fixing agent 600 shows an example in which the jumper 520 is mounted on the outermost conductive pins 501 and 506, but other configurations are possible. For example, the fixative 600 may mount the jumper 520 on each conductive pin 501-506, on one conductive pin, or any other possible conductive pin combination. Further, the jumper 520 may be soldered to the conductive pins or may be crimped. Thus, FIG. 6 is merely an example and will be apparent to those skilled in the art, but other methods of securing the jumper 520 to the conductive pins 501-506 are possible without departing from the scope of the present proposal. is there.

  FIG. 7 is a schematic diagram of another configuration of a photomultiplier tube 140, or photosensor, in which the continuous delay device 500 is connected to the photomultiplier tube 140 via a signal lead 700. FIG. In FIG. 7, the conductive pins 501 to 506 of the continuous delay device 500 face the photomultiplier tube 140 with the jumper 520 therebetween. However, as will be apparent to those skilled in the art, such a configuration is merely an example and does not limit the present proposal. For example, the continuous delay device 500 may be arranged so that the direction of the conductive pins 501 to 506 deviates from the photomultiplier tube 140. FIG. 7 also shows a signal cable 705 connected to the continuous delay device 500 and a high voltage cable 710 connected to the substrate 510. These cables can include a voltage divider as described above.

  In addition, the substrate of the variable delay device may be disposed away from the optical sensor.

  Further, FIG. 8 is a schematic diagram of another configuration of continuous delay device 240. In FIG. 8, the continuous delay device 240 is mounted on a first printed circuit board 800 that is disposed apart from the photomultiplier tube 140. A signal cable 805 interconnects the second printed circuit board 810 to a continuous delay device on the circuit board 800. A signal conductor 815 connects the photomultiplier tube 140 to the printed circuit board 810. The high voltage cable 820 is also connected to a printed circuit board 810 that includes the voltage divider described above.

  As will be apparent to those skilled in the art, a continuous delay device having two conductive pins is shown in FIG. 8, but such an embodiment is not limited to a continuous delay device having two conductive pins. . In fact, a continuous delay device incorporating any number of conductive pins and corresponding jumpers can be used without departing from the scope of the proposal.

  In another embodiment, the variable delay device comprises a plurality of delay elements and at least one jumper. The plurality of delay elements introduce a time delay that is fixed by the length of the delay element. The jumper interconnects at least two delay elements of the plurality of delay elements. The total delay of the variable delay device is determined by the total conduction path length formed by at least one jumper and at least two delay elements. In the conduction path, signals are transmitted by propagation of changes in the electric field in the conductor.

  In another embodiment of the proposal, a delay device is described having pre-set discrete delay elements. FIG. 9 illustrates a discontinuous delay device 900. In FIG. 9, the preset delay elements 905-950 each achieve a delay of 40 picoseconds. However, as will be apparent to those skilled in the art, delay elements 905-950 can achieve delays greater than 40 picoseconds or less than 40 picoseconds without departing from the scope of the proposal. Similarly, although FIG. 9 shows ten discontinuous elements 905-950, it will be apparent to those skilled in the art that any number of discontinuous delay elements can be used in the proposal.

  For example, in the example of FIG. 9, the time delay introduced by the variable delay device ranges from 0 to 400 picoseconds.

  In FIG. 9, the first conductor 960 is connected to the first element 905 of the delay elements. The second conductor 955 is connected to the second element 925 of the delay elements. Additional jumpers 965-980 provide all delay elements between delay element 905 and delay element 925 to form a conduction path whose total length is the sum of the lengths of delay elements 905-925 and jumpers 965-980. Are interconnected. The delay sum is obtained by this conduction path length.

  Although FIG. 9 shows that each delay element 905-950 has a fixed delay of the same length, the present invention also includes a discontinuous time delay device having discontinuous delays of different lengths. In FIG. 10, the time delay device 1000 includes four discontinuous delays 1005, 1010, 1015, and 1020, each having a different delay. For example, 40 ps, 80 ps, 160 ps, and 320 ps delays are shown. As will be apparent to those skilled in the art, other delay values are possible without departing from the scope of the present invention.

  In FIG. 10, the first conductor 1025 is connected to the delay element 1005. Second conductor 1030 is connected to delay element 1015. Jumper 1035 interconnects delay elements 1005 and 1015 except for delay element 1010. As such, the composite delay realized by the discontinuous delay device 1000 of FIG. 10 is determined by the length of the delay element 1005, the length of the delay element 1015, and the length of the jumper 1030. Further, although not shown in FIG. 10, additional jumpers can be used to configure various delays. Thus, a discontinuous delay device 1000 that includes a plurality of discontinuous delay elements 1005-1020, each having a different preset delay, can be used to implement a wide range of delay values.

  Further, the step of setting the desired delay in the delay device 1000 can be performed manually or by computer control. As shown in FIG. 11, in a further embodiment of setting the delay under computer control, both 900 and 1000 jumpers are connected to electronic control switches 1101, 1102, 1103, connected to the controller 1105. 1104 is replaced. Accordingly, the control unit 1105 sets the delay of the delay device 1000 by not closing any of the switches 1101, 1102, 1103, and 1104, or by closing some or all of them. Each switch 1101, 1102, 1103, 1104 is arranged to bypass a portion of an impedance controlled conductive trace made of, for example, copper. Thus, electronic switches (1101, 1102, 1103, 1104) allow signals to selectively bypass long conductor paths 1107, 1108, 1109, 1110, thereby allowing PMTs in impedance controlled conductive traces. The effective transition length of the signal path can be adjusted incrementally. Based on the switches 1101, 1102, 1103, 1104 that are activated, several relatively long paths 1107, 1108, 1109, 1110, each having a different length, are impedance controlled to allow a wide range of adjustments. It can be arranged along the conductive trace 1100. The effective transition times for each of the long paths 1107, 1108, 1109, 1110 are defined as a predetermined minimum value that represents the granularity of the adjustment. In order to minimize the detrimental effect of the shorted stub on the portion of the signal having the highest importance, the effective shorted stub length of each of the bypassed relatively long paths 1107, 1108, 1109, 1110 is reduced. Choose.

  FIG. 11 includes four relatively long paths 1107, 1108, 1109, 1110, but can include any number of longer paths without departing from the invention. The switches 1101, 1102, 1103, and 1104 can also be either normally open or normally closed switches, and the controller can use either positive logic or negative logic to control the switches. As such, FIG. 11 is merely an example and does not limit the invention.

  Thus, for example, the variable delay device is connected to a predetermined length of conductive trace, a first terminal connected to the first end of the conductive trace, and a second end of the conductive trace. A second terminal, a plurality of switches that bypass a portion of the conductive trace, and a control unit that controls the plurality of switches to set the total delay of the variable delay device. And the total delay of the variable delay device is the conduction path length formed between the first terminal and the second terminal by the non-bypassed portion of the conductive trace and any of the plurality of closed switches. Determined by.

  For example, the controller closes at least one subset of the plurality of switches to bypass a portion of the conductive trace.

  Note that the variable delay device may include a nonvolatile memory that stores setting values for each of the plurality of switches.

  For example, as shown in FIG. 12, a nonvolatile memory such as an EEPROM 1106 may be connected to the control unit 1105 to store switch settings. Then, the control unit 1105 can rewrite the switch setting in the EEPROM 1106 when a component change affecting the signal delay or other system change is made. Obviously, other non-volatile memories such as flash memory, EPROM, PROM (Programmable Read Only Memory), and battery backup RAM can also be used without departing from the scope of the present invention. The non-volatile memory may also be incorporated into the control unit 1105 or may be a separate device as shown in FIG.

  Next, a method for adjusting the delay device will be described. The method described below applies to the calibration of both continuous and discontinuous delay devices. All or any of the delay devices 240, 500, and 1000 are incorporated into each stage of the PMT, such as an electronic substrate that also includes a voltage divider to supply the proper voltage to the detector or PET system PMT or to the electronic substrate. be able to. If an adjustment mechanism is incorporated into each PMT individually, the fine delay can be set using a pulsed laser, a co-gamma source, and a scintillator crystal.

  In one method, the output of the pulse laser 1300 is divided by the beam splitter 1315 and sent to two detectors 1305 and 1310 as shown in FIG. Laser 1300 generally generates picosecond pulses, but femtosecond or nanosecond pulsed lasers can also be used without departing from the scope of the present invention. The combination of one detector 1305 and the cable is a “reference detector”. All devices to be calibrated are calibrated against the same reference detector 1305. A fixture (not shown) is used to ensure that both detectors 1305, 1310 are always in the same location. Both the output of the reference detector 1305 and the detector under test 1310 are sent to an oscilloscope 1320 or other suitable electronic measurement device. The variable delay device 240, 500, or 1000 is then adjusted to produce the desired relative delay between the pulse from the reference detector 1305 and the pulse from the detector 1310 under test.

  Thus, for example, in the device adjustment method for adjusting the time delay device, the scintillator is irradiated with simultaneously generated gamma rays and the scintillation event is detected by the reference detector. Further, the scintillation event is detected by a plurality of optical sensors, and an arrival time corresponding to a time at which the scintillation event is detected is measured for each of the plurality of optical sensors. A time delay device jumper is then adjusted for a plurality of conductive pins on the time delay device based on each measured arrival time.

  In another method shown in FIG. 14, a scintillator crystal is coupled to a reference detector 1405 and a detector 1410 under test. Both detectors 1405, 1410 are placed on either side of a simultaneous gamma source 1400 (eg, 511 keV annihilation photons from 22Na or 68Ge). All devices to be calibrated are calibrated against the same reference detector 1405. A fixture (not shown) is used to ensure that both detectors are always in the same location. Both the output of the reference detector 1405 and the detector under test 1410 are sent to an oscilloscope 1415 or other suitable electronic measurement device. The variable delay element is then adjusted to produce the desired relative delay between the pulse from the reference detector and the pulse from the detector under test.

  In either method described above, the delay adjustment can be performed manually or by computer control. In the case of manual adjustment, the position of the slidable element of the continuously variable delay device could be set by hand or by a manually moving stage with a micrometer connected to the slidable element. Or for a delay device that can be adjusted discontinuously, the jumper position could be set manually. For computer controlled adjustment, the slidable element of the continuously variable delay device could be set by a computer controlled moving stage using a stepper motor. Or, in an embodiment with an electronically controlled switching element, the computer could select the setting of the electronic switch. The advantage of these methods is that these adjustments are performed during PMT manufacturing. The laser method in particular requires a short set-up and measurement time, resulting in a lower overall cost. Alternatively, if the adjustment mechanism is individually incorporated into each PMT, or if the adjustment mechanism is incorporated into one or more separate electronic boards, then each PMT / cable for each PMT / cable after incorporation of the PMT into the detector. A desired delay can be set. As will be apparent to those skilled in the art, the above adjustment method is similar for discontinuous delay devices such as apparatus 1000 and continuous delay devices having two or more conductive pins such as devices 240 and 500. Applicable to.

  If adjustment is performed after detector assembly, all PMTs are connected to the delay board 1600 as shown in FIG. 15 prior to calibration. The delay board 1600 is connected to a scanner (not shown) and a pre-analog circuit of the oscilloscope. Although a four channel oscilloscope is shown in FIG. 15, it will be apparent to those skilled in the art that more or fewer than four channels can be used. As such, the number of oscilloscope channels in FIG. 15 is merely an example. All jumpers on the delay board 1600 are set to default positions.

  The source is arranged so that the gamma rays are incident on the center point 1501 of the first trigger zone 1500 (to balance the light flight delay). By physical collimation (for example using a lead or tungsten collimator) or by an electron (using a properly positioned reference detector to trigger acquisition of signals from the detector under test) Collimation of gamma rays to the region near the center of the trigger zone is achieved by collimation or by using the detector position detection function to select events that are incident only on the center of the detector. Next, each of the PMTs 1 to 4 included in the first trigger zone is connected to the delay chain substrate 1600. Light pulses from each PMT are visualized, for example, as pulses 1505-1520 on an oscilloscope (not shown), and delay devices 1525-1540 are adjusted until pulses 1505 and 1545-1555 are aligned to the same time delay t1. . The process is then repeated for the remaining trigger zones 2-5.

  Although certain embodiments have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the invention. Indeed, the novel methods, apparatus and systems described herein can be embodied in a variety of other forms. In addition, various omissions, substitutions, and modifications in the form of the methods, apparatuses, and systems described herein can be made without departing from the spirit of the invention. The appended claims and their equivalents are intended to cover the forms or modifications that would fall within the scope and spirit of the present invention.

  For example, the methods, apparatus, and systems described herein can be applied to positron emission tomography systems that include a plurality of gamma ray detectors. In that case, each gamma ray detector includes a plurality of scintillation crystals arranged in an array, a plurality of photosensors arranged in an array adjacent to the scintillation crystal, and a plurality of variable corresponding to each of the plurality of photosensors. A delay device. Each variable delay device includes a substrate, a plurality of conductive pins mounted on the substrate, a first terminal connected to a first conductive pin of the plurality of conductive pins, and a plurality of conductive pins. A second terminal connected to the second conductive pin of the conductive pins, and a jumper that electrically interconnects the plurality of conductive pins at a predetermined distance from the substrate. The time delay introduced by the variable delay device is then determined by the electrical path between the first and second terminals formed by a plurality of conductive pins interconnected by jumpers.

  The methods, apparatus, and systems described herein can also be applied to, for example, positron emission tomography systems that include multiple detector modules. In that case, each detector module receives a plurality of scintillation crystals arranged in an array, a plurality of photosensors arranged in an array adjacent to the scintillation crystal, and a signal corresponding to each of the plurality of photosensors. And a means for generating a variable time delay.

  The methods, apparatus, and systems described herein can also be applied to positron emission tomography systems that include multiple gamma detectors, for example. In that case, each gamma ray detector includes a plurality of scintillation crystals arranged in an array, a plurality of photosensors arranged in an array adjacent to the scintillation crystal, and a plurality of variable corresponding to each of the plurality of photosensors. A delay device. Each variable delay device includes a plurality of delay elements that introduce a time delay fixed by the length of the delay element, and at least one jumper that interconnects at least two of the plurality of delay elements. Is provided. The total delay of the variable delay device is then determined by the total conduction path length formed by at least one jumper and at least two delay elements.

205 substrate 210, 215 conductive pin 220 jumper 240 time delay device

Claims (10)

A positron emission tomography system comprising a plurality of gamma ray detectors,
Each gamma ray detector
A plurality of scintillation crystals arranged in an array;
A plurality of photosensors arranged in an array adjacent to the scintillation crystal;
A plurality of variable delay devices corresponding to each of the plurality of optical sensors;
With
Each variable delay device
A substrate,
A plurality of conductive pins mounted on the substrate;
A first terminal connected to a first conductive pin of the plurality of conductive pins;
A second terminal connected to a second conductive pin of the plurality of conductive pins;
A jumper that electrically interconnects the plurality of conductive pins at a predetermined distance to the substrate;
With
The time delay introduced by the variable delay device is determined by an electrical path between the first and second terminals formed by the plurality of conductive pins interconnected by the jumpers. Positron emission tomography system. The positron emission tomography system according to claim 1, further comprising a fixing unit that mounts the jumper on the plurality of conductive pins at a predetermined position. The positron emission tomography system according to claim 1, wherein the time delay is in a range of 0 to 400 picoseconds. The positron emission tomography system according to claim 1, wherein a maximum delay of the time delay is determined by a total length of the plurality of conductive pins. The positron emission tomography system according to claim 1, wherein the substrate is attached to the optical sensor. The positron emission tomography system according to claim 4, wherein the variable delay device is connected in series with a terminal of the photosensor. The positron emission tomography system according to claim 1, wherein the substrate is disposed apart from the optical sensor. The positron emission tomography system according to claim 1, wherein the photosensor is a photomultiplier tube. A positron emission tomography system comprising a plurality of detector modules,
Each detector module is
A plurality of scintillation crystals arranged in an array;
A plurality of photosensors arranged in an array adjacent to the scintillation crystal;
Means for generating a variable time delay for signals corresponding to each of the plurality of photosensors;
A positron emission tomography system characterized by comprising: A positron emission tomography system comprising a plurality of gamma ray detectors,
Each gamma ray detector
A plurality of scintillation crystals arranged in an array;
A plurality of photosensors arranged in an array adjacent to the scintillation crystal;
A plurality of variable delay devices corresponding to each of the plurality of optical sensors;
With
Each variable delay device
A plurality of delay elements that introduce a time delay fixed by the length of the delay element;
At least one jumper interconnecting at least two delay elements of the plurality of delay elements;
With
A positron emission tomography system, wherein the total delay of the variable delay device is determined by the total conduction path length formed by the at least one jumper and the at least two delay elements.

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