JP2002508505A - Photomultiplier tube transmission time and gain adjustment - Google Patents

Abstract

(57) Abstract: A method is provided for independently adjusting the gain and transmission time of a photomultiplier tube. A method of providing a photomultiplier tube (PMT) having a desired gain and transit time, comprising: a) gain of the photomultiplier tube such that the photomultiplier tube has a desired gain. And b) adjusting the moving time of the photomultiplier so that the photomultiplier has a desired moving time.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to adjustment of a transmission time of a photomultiplier tube (PMT), and particularly to adjustment of a gain and a transmission time of a PMT used in a gamma camera.

BACKGROUND OF THE INVENTION A multi-head gamma camera consists of at least two large detectors. Each detector detects the event (the interaction of the gamma rays with the crystals that form the surface of the detector) and determines the location of the event. In many cases, the detector is an Anger-type gamma detector where a plurality of PMT-like photodetectors capture the crystal and determine the location of the event based on the amount of light detected by the PMT. Since events produce light at the location where the interaction occurs, the magnitude of the signal detected by the various PMTs can be used to determine the location of the event that occurred at the detector.

[0003] In order to accurately determine the location of an event, the gain of the PMT must be the same. During the normal calibration process of the PMT, the gain of the PMT is adjusted by adjusting the voltage of the PMT or by adjusting the voltage distribution between the electrodes of the PMT. This voltage adjustment allows for good gain tracking of the PMT and accurate location of events.

When such a multi-head camera is used as a positron emission tomography (PET) detector, other problems arise. In PET, an event is characterized not only by the detection of an interaction at one of the detectors, but also by the simultaneous detection of two interactions at both gamma detectors. If more than two detectors are used, it is determined by the corresponding interaction at any two detectors.

[0005] However, it is well known that the signal transmission time differs for each PMT.
Thus, the transmission time of PMT is about 65 nanoseconds, but this time is P
It varies up to about 10 nanoseconds between MTs. This spread of transit time results in coincident events at different locations on the same or different detectors being recorded at slightly different times. Since each event is captured by a different PMT, this difference is not constant and depends on the location of the detector surface.

In general, a coincidence (time) window is used for determining coincidence between two detected interactions. If all two interactions occur within the same time window, they are considered to be coincident. Considering the variable transit time of the interaction detection (as well as other variations in the time of flight of the gamma ray at which the interaction is measured), to capture all true coincident events, a relatively large Requires a matching window. However, the use of such large windows also reduces the system's discrimination against non-simultaneous events, such as those associated with irrelevant gamma rays or scattered events.

[0007] Unfortunately, while it is possible to adjust the transmission time of the PMT and to adjust the gain, no method has been disclosed for separately adjusting the gain and the transmission time. Methods that have been used to reduce the size of the match window include reordering the PMTs by characteristics such that a particular set of detectors has the same characteristics. However, in addition to being inaccurate (because there is still a considerable spread between the PMTs), this solution does not tolerate changes in gain or transit time associated with aging of the PMTs, and also makes it easier for the failed PMTs to change. Do not allow replacement.

Another way to reduce the spread between signals generated by the PMT is to use PM
The purpose is to provide various delay lines for each T. This solution has a gain (P
Individual changes in the transmission time (using the delay line) and the transmission time (using the delay line) are allowed. However, this solution is relatively expensive.

SUMMARY OF THE INVENTION One aspect of the present invention relates to the independent adjustment of gain and transit time of individual PMTs. A second aspect of the present invention relates to matching the gain and transmission time of a plurality of PMTs. A third aspect of the present invention relates to the manufacture and calibration of an Anger camera with an internal PMT with matched transit times and gains. Since the outputs of the PMTs are at the same timing, the resulting sum and weighted sum pulses will be shorter and more consistent with respect to their amplitude and timing. According to this aspect of the invention, a non-integrated (or poorly integrated) signal will be used to determine whether an event meets energy criteria. In general, in the prior art, the signal must be at least partially integrated at least partially before an energy decision is made.

[0010] A fourth aspect of the invention relates to a coincidence camera having a reduced coincidence (time) window width. As shown above, the gain and transit time of the PMT do not match. Therefore,
If the gains of the PMTs of the Anger type detectors are matched with respect to gain (as they must provide accurate location information of the detected interaction)
, The transit time of the PMT will be so different that the coincidence window has to be increased from 15 to 20 nanoseconds. According to a preferred embodiment of the present invention, the coincidence window is reduced to 5-10 nanoseconds.

The present invention provides that both the gain and the propagation delay of the PMT are applied to the PMT,
While relying on the voltage applied to the individual electrodes of T, it is based on the understanding that the voltage dependence is different for the two characteristics.

In a multi-dynode PMT having n dynodes, the gain of the PMT is proportional to [V ₁ * V ₂ *... V _n ] ^0.7 . Here, (V ₁₎ is the voltage difference between the cathode of the first dynode and the tube, V _S is with other subscripts to a voltage between dynodes before and dynodes numbered . That is, the gain is not a function of the grid voltage, but is only a function of the voltage of the individual dynode. Therefore, the gain of the PMT depends on the total voltage applied to the PMT and the distribution of the voltage between the electrodes on the PMT.

[0013] The transit time of the PMT is approximately equal to the sum of the flight times of the electrons between the electrodes. It consists of the time of flight between the cathode and the first dynode, the time of flight between the individual dynodes, and the time of flight from the last dynode to the anode. In general, the time of flight between dynodes depends on the distance between dynodes (a constant value for a particular PMT) and the voltage between dynodes.

[0014] The distance between the cathode and the first dynode is composed of two parts. That is, the portion between the cathode and the grid, and the portion between the grid and the first dynode. The effect of the grid on travel time can be simply understood in the following manner. For the first part of the flight, the time depends on the voltage between the grid and the cathode. Since this distance is relatively large, this voltage has a substantial effect on flight time. Between the grid and the first dynode, the speed of the electrons is further increased due to the voltage between the grid and the dynode. However, the effect of this change in voltage drop is much less than the effect on the photocathode grid voltage, since this distance is relatively small and the electrons already have a substantial velocity. However, in general, the flight time decreases as the voltage from the grid to the cathode increases, while the cathode-first dynode remains constant. However, since the photocathode is current-limited, a voltage change from the grid to the cathode has no significant effect on the PMT gain.

Although equations for gain and time of flight can be established and solved, at least numerically, this is rarely necessary. In practice, the gain and the transit time will depend on the cathode (total) voltage and the grid or, less preferred,
By changing the voltage of the previous dynode, it changes sufficiently. Such changes are measured by measuring the gain and transmission delay for the PMT, and
Is preferably determined empirically by adjusting the parameters to have the same gain and the same transmission delay. Alternatively, the gain and delay are adjusted to have standard gain and travel time for each tube. In particular, changing the single voltage, the overall voltage, which adjusts the gain and then the grid voltage to adjust the transit time, which also changes the voltage of each dynode proportionally By doing so, it is possible to adjust the overall gain.

According to a preferred embodiment of the present invention, a gamma ray source is arranged in close proximity to a detection crystal in front of each of the plurality of PMTs. More preferably, a pulsed light source such as an LED illuminates the PMT directly with light that the PMT can sense. The total voltage (from photocathode to anode) of each PMT, and then the cathode grid voltage, is adjusted so that the signals generated by the PMT are coincident with the same amplitude.

After all PMTs have been adjusted to match their gain and transit time, the PMTs are mounted on the detector. And preferably the PM in the two detectors
This procedure is repeated for the other detectors, using the same standard gain and transit time for T.

After both detectors have been made self-consistent with respect to gain and transit time, the positron annihilation source is preferably at a point equidistant from the two detectors and at the center of the detectors, 2 Placed between two detectors. Ideally, the real coincidence event is when the signals generated by the two detectors are slightly different (on average),
This results in having somewhat different amplitudes.

In one preferred embodiment of the present invention, a match between two interactions is defined based on this timing (or a difference from some fixed timing).
All amplitude differences are corrected in the settings of the electronics associated with the two detectors.

It will be appreciated that the above procedure particularly simplifies the replacement of old and defective PMTs. Since all PMTs are set to the same standard (or at most a limited number of standards), only little, if any, adjustment is needed to match the gain and transmission time of the new PMT to the old PMT Not necessary for This is done by centering the source on the new PMT and adjacent PMTs and adjusting the new PMT until the new PMT's amplitude and transmission time match the old one.

It should be noted that an additional benefit of the calibration process of the present invention is that when the outputs of the PMTs are summed for energy and position determination, they have a summed form (and thus a maximum) per pulse. Are matched so as to be more uniform. This advantage is also available if the gain and transit time of one of the Anger detectors is calibrated and adjusted as in the above procedure.

In a further preferred embodiment of the invention, the gain is essentially PM
It changes by changing the overall voltage of the PMT without changing the transmission time of T. To compensate for the change in transit time, a delay line is inserted after at least some of the PMTs to compensate for the change in transit time. These delay lines may be fixed delay lines that are selected from delay lines having different delays to best match the required delay. Alternatively or additionally, they may be tapped delay lines that are selected to provide the required delay.

Alternatively or additionally, a continuously variable or electronically adjustable delay line may be used, and the delay then varies in a manner similar to the variation of the delay with the grid voltage described above. Let me do.

When more than one delay line is used for each PMT, an overall transit time correction is achieved using a fixed delay line or a tapped delay line, and fine transit time correction is achieved with tapped, continuous This is accomplished using either an adjustment or an electronic adjustment delay line. Alternatively, a tapped delay line may be used for overall correction and a continuously adjusted delay line may be used for fine adjustment. The use of two or more delay lines results in lower cost and / or finer adjustment capabilities than the use of one delay line.

Accordingly, provided by a preferred embodiment of the present invention is a method for providing a photomultiplier tube (PMT) having a desired gain and transit time, wherein (a) the photomultiplier tube is And (b) adjusting the moving time of the photomultiplier so that the photomultiplier has a desired moving time.

Preferably, the adjustment of the gain includes an overall voltage adjustment of the photomultiplier tube such that the photomultiplier tube has a desired gain. Preferably, adjusting the transit time comprises adjusting the voltage on the grid or the first dynode of the photomultiplier so that the photomultiplier has a desired transit time. Preferably, the voltage of the grid or the first dynode is adjusted without substantially changing the voltage for the other electrodes. Alternatively, adjusting the voltage for the grid comprises changing the overall gain of the photomultiplier tube and repeating steps (a) and (b) at least once.

[0027] Further provided is a method of producing a gamma detector, comprising: providing a scintillator crystal; providing a plurality of photomultiplier tubes for capturing a surface of the crystal; and gaining the photomultiplier tube. And adjusting the transit time so that they are substantially the same for the plurality of photomultiplier tubes.

Preferably, said gain and travel time are adjusted according to the method of the present invention.

Further, provided by a preferred embodiment of the present invention is a multi-detector P
An ET camera, wherein a plurality of Anger gamma camera detectors produced according to the method of the present invention that generate a timing signal when an event is detected, and a time between the timing signals generated by the gamma camera. A match circuit that determines the presence of a valid event based on the difference between

Details of the Preferred Embodiment FIG. 1 schematically shows a PMT 10. PMT 10 includes a cathode 12, a grid 14, and a series of dynodes 16-23. PMT 10 further includes a final collector electrode 26 (anode) where the signal is generated. In addition,
FIG. 1 is a schematic representation, and the actual configuration of the PMT may vary between many available configurations.

In operation, each of the cathode 12, the grid 14, and the dynodes 16 to 23 have their cathode 12 at the lowest (most negative) voltage and each successive electrode having a more positive voltage. , Voltage is supplied. Preferably, cathode 12 is a photocathode. That is, it emits electrons in response to the light impinging on it, and the number of electrons is approximately proportional to the total impinging light flux for a given light wavelength.

When light of a certain intensity strikes the cathode 12, a large number of electrons having substantially zero momentum are generated at the cathode. Under the influence of the electric field created by the voltage difference between the cathode 12 and the grid 14, the electrons are accelerated towards the grid and then
Pass through the grid towards the first dynode. In general, in order to maintain a proportional relationship between light and the number of electrons passing through the grid, the cathode and grid voltages should be such that for light impinging on the photocathode, all electrons are intercepted from the cathode and space charge does not develop. Selected.

The electrons accelerated by the electric field between the cathode and the grid, and further accelerated by the electric field between the grid and the first dynode, have their surface formed of a material having a high secondary emission ratio. Collision with the first dynode. In general, the ratio of the number of electrons emitted by the dynode to the number of electrons striking the dynode is proportional to the 0.7 voltage of the voltage between which the electrons fall (cathode-first dynode voltage).
Thus, the ratio for the first dynode, ie, its electronic gain, is (V ₁ -V _k ) ^0.7 . Similarly, the gain for the other dynodes _{are ^{(V i -V i-1)}} 0.7. Therefore, the overall PMT gain is

(Equation 1) Where i is the number of dynodes and the cathode voltage is defined by V ₀ . This gain is not a function of the grid voltage, but only of the individual dynodes.

The transmission time of the PMT is substantially equal to the sum of the flight times of the electrons between the electrodes. It consists of the time of flight between the cathode and the first dynode and the time of flight between individual dynodes. In general, the time of flight between dynodes depends on the distance between dynodes (which is constant for a particular PMT) and the voltage between dynodes. In general, the flight time between the dynode i-1 and i to two consecutive _is represented by ^{_{t i = k i * (V}} i) -0.5. Here, k _i is a constant that depends on the distance between the two dynode i-1 and i, V _i is the voltage between dynode i-1 and i.

The distance between the cathode and the first dynode is composed of two parts, a part between the cathode and the grid and a part between the grid and the first dynode.
The effect of the grid on travel time can be easily understood in the manner described below.
For the first part of the flight, the time depends on the voltage between the grid and the cathode, with the time decreasing in proportion to the 0.5 power of the voltage. The speed of electrons between the grid and the first dynode further increases due to the voltage difference between the grid and the dynode. In general, this leads to a complex formulation of the time of flight that decreases with increasing grid voltage. While the grid voltage affects the time of flight, the first dynode 1
It should be noted that as long as the voltage of 6 is not changed, it does not affect the gain of the PMT.

That is, the transit time can be represented by f (V _i , V _g ), where V _i is the voltage of the cathode or dynode with respect to the preceding dynode, and V _g is This is the voltage difference between the cathodes.

Although these equations can be solved at least numerically, this is not necessary in the preferred embodiment of the present invention. In fact, the gain and transit time are
It can be varied satisfactorily by changing the overall voltage and the grid voltage (or one of the previous dynodes) respectively. Such changes are preferably performed empirically by measuring the gain and transmission time of the PMT and adjusting the voltage so that all PMTs have the same gain and the same transmission time. In particular, by changing one voltage, the overall voltage to change the gain, which also changes the voltage at each dynode in proportion, and then by changing the grid voltage to adjust the transit time , It is possible to adjust the overall gain.

Generally, electrode voltages are supplied to individual dynodes using a continuous voltage drop resistor. FIG. 2 shows one configuration of a resistor, a variable resistor, and a potentiometer used to supply voltage to a dynode for independent adjustment of PMT gain and transmission time. The high voltage source 30 supplies a high voltage to fixed resistors 32 to 38 and a potentiometer 40 in series with an electronic gain control circuit 42 shown schematically in FIG. Details of the configuration of such a gain control are described below. A variable high voltage is applied to the variable resistor 44 from the high voltage bus that fills all PMTs in the gamma camera
It is preferably supplied via

In a preferred embodiment of the present invention, grid 14 is connected to a wiper of potentiometer 40. One end of potentiometer 40 is connected to the high voltage (and to the cathode), and the other end is connected to the first dynode. The other dynodes are connected in sequence to the connections of fixed resistors 32-38. Typically, the anode 26, which collects the charge generated at the last dynode, is virtually grounded at the input of the current towards the voltage converter 46.

In practice, all the electronic circuits shown in FIG. 2 are preferably located on a PC board connected to the PMT. After adjusting the potentiometer 40 and the variable resistor 44 to set the PMT gain and travel time, the PMT is ready for mounting in a gamma camera, as described below.

To calibrate the PMT and its associated circuitry, the electronic gain 42 is set in the middle of the range and the high voltage supply 30 is set to the standard high voltage used in the system. Cathode 12 is illuminated with a short burst of light having standard brightness from an LED or the like. A pulse length of one nanosecond or similar is appropriate. The amplitude of the output signal is adjusted by changing the resistance of variable resistor 44 until the output signal matches the standard output where all PMTs are matched. The time delay between the burst of light and the appearance of the signal at output 48 of converter 46 is measured and grid 1 is adjusted so that the time delay matches the desired standard time delay.
4 (by adjusting the position of the wiper of potentiometer 40). Adjustment of potentiometer 44 with little or no P
It does not affect the gain of the MT, but additional repetitions may be performed if necessary.

FIG. 2B shows an alternative method for adjusting the gain and time delay of the PMT. In this way, resistors 51 and 52 replace potentiometer 40 of FIG. 2A.
The gain is adjusted by changing the resistance of resistor 44 as in FIG. 2A. The time delay is changed by changing the resistance of the variable resistor 50. In general, the resistor 50 is made much smaller than the sum of the resistors 51, 52 and 53 to avoid a troublesome effect on tube gain when the time delay is adjusted. However, there is an interaction between gain and time delay associated with this method, and some repetition of adjustment may be required to achieve both the desired gain and time delay.

FIG. 2C shows a configuration of a resistor whose overall gain is affected by transfer time adjustment. In this configuration, the cathode-grid resistance is a variable resistance 53 and the fixed resistance 55 connects the grid 14 to the first anode 16. A resistor 54 having a resistance much smaller than the sum of the resistances of the resistors 53 and 55 connects the cathode 12 and the first dynode 16. The presence of the resistor 54 fixes the voltage at the first dynode (and hence the overall gain) to a large degree, regardless of the value of the variable resistor 53 used to set the time delay.

FIG. 2D illustrates yet another method of controlling the gain and transit time of a PMT substantially independently in accordance with a preferred embodiment of the present invention. In this embodiment of the invention, the transit time is substantially controlled by changing the relative voltage of the grid, and the gain is set by setting the resistor 39 and by changing the variable resistor 4.
1 by changing the overall resistance of the tube. Resistance 4
A reasonable change of 1 does not have a noticeable effect on the transit time of the PMT, but does make a sufficient change to the change in tube gain for the purposes of the present invention.

Although the configuration shown in FIGS. 2A-2D is preferred, those skilled in the art will recognize that many different combinations of variable resistors, potentiometers, and various voltage changing methods can be used in the calibration and standardization of PMTs according to the present invention. It will be clear that it is also good.
Further, while it is usually more convenient to provide a variable resistor as shown in FIGS. 2A-2D, the same effect is achieved by determining the resistance value after the value has been determined or by replacement or trial and error. This is achieved by replacing the variable resistance element with a given resistance. This method is usually less convenient and often less accurate than other methods. Also, while some adjustment methods according to preferred embodiments of the present invention require a gridded PMT, other methods may use gridless tubes.

FIG. 2E shows a circuit 56 that helps achieve a variable electronic gain of the PMT, according to a preferred embodiment of the present invention. In operation, the gain is changed by applying a changing voltage to terminal 58. While this circuit varies gain by adjusting the effective resistance between dynodes 21-23, at least in part, the rate of time delay due to the transfer of electrons between these dynodes is relatively small, so that the overall The effect on the typical time delay is small. However, as described below,
This electronic adjustment allows adjustment of the gain in situations where there is little degradation of the PMT match in the detector according to the age of the tube.

FIG. 3 shows an Anger camera head 70 useful in a coincidence-detecting gamma camera. Portion 70 includes a scintillation crystal 72, such as a NaI crystal. Crystal 72 emits a faint flash whenever gamma rays interact with it and are absorbed thereby. PMTs 74, which are preferably arranged in a hexagonal configuration, are located on the rear side and each SMT captures the scintillation crystal to detect a portion of the light generated by the interaction, and is proportional to the brightness of the light it captures. To generate a signal. A high voltage is supplied from a common high voltage source 30 to each PMT, each PMT including circuitry shown at one or more of FIGS. 2A-2D, and preferably being adjusted and calibrated as described above. .

As is usual in such a camera, the output of the PMT is
6 (after amplification and optional partial integration). The output of the adder 76 includes information about the time of occurrence of the interaction of the gamma ray with the crystal 72 and information about the gamma ray energy. This information is used to trigger an event detector 80 that sends a timing signal to the Anger electronics 78 and the match unit 90, as described below. Many variations are known in the art for anger electronics 78 and the present invention may be adapted for use with all such systems. Generally, the Anger electronic circuit 78 responds to the output of the PMT by:
Generate position and energy signals as well as other signals well known in the art.

FIG. 4 is a block diagram of a coincidence camera 88 according to a preferred embodiment of the present invention. In particular, the camera 88 incorporates a plurality of detectors 70, for example as described in conjunction with FIG. 3, and a matching unit 90 that receives an event detection trigger signal from the event detector 80 shown in FIG. When a trigger is received within a small, typically preset time delay, the match unit 90 outputs its output 9
2 generates a valid match output. The valid match output signal controls a pair of switches 94 and 96 that receive information from the detector's Anger electronics 78. If the match detector does not determine that a match event was generated by the detector, generally no information is transmitted from the detector to the rest of the matching camera.

Once a valid match signal has been generated, the information from the detector is transmitted to the Anger processor 98.
Supplied to Such anger processors are well known in the art, and this unit, as well as the host computer, display, user interface, and storage, may be of any design and configuration known in the art. good.

FIG. 5 shows a more detailed block diagram of the matching unit 90 according to a preferred embodiment of the present invention. The coincidence unit 90 receives trigger signals from the two detectors and provides a variable delay for each by the delay circuits 100 and 102. The two delayed signals arrive at the variable pulse generators 104 and 106, and if the trigger arrives within a certain delay of the coincidence unit, respectively, the pulsed AND gate 108 receives signals from both of them simultaneously. Such pulses having different pulse widths are generated. For example, if a valid coincidence output is desired whenever the trigger is less than 10 nsec apart, one of the signals will be delayed by 10 nsec from the other. The pulse width of the faster channel is one pulse wider than that of the slower channel.
Made 0nsec longer. AND gate 108 preferably triggers one-shot 110 to produce a constant length match output. However, if the width of the shorter pulse is sufficient for the desired time interval to switch switches 94 and 96, one shot can be omitted.

[0052] Alternatively, the trigger signal may be digitized and a digital coincidence unit may be used. 6A and 6B illustrate a method of adjusting a gain and a travel time of a PMT assembly according to a preferred embodiment of the present invention. As shown in FIG. 6A, the calibration device provides a very short light pulse to the pulse generator 124 and the PMT 10 for the LE.
D126. Associated with PMT 10 is a resistive electronic circuit 121, preferably as shown in FIGS. 2A-2E. The electronic circuit 121 includes two voltage sources, a high voltage source 3
0 and amplifier 46 which is part of electronic circuit 121 (and element 42 if present)
Is supplied using a power supply 128 for The electronic circuit 10 preferably includes two knobs 120 and 122 used to change the resistance, potentiometer, or voltage as appropriate in the various embodiments of FIGS. 2A-2D. Alternatively, an external driver may be used to drive these variable elements.

The light pulses cause the PMT 10 and the electronics 121 to generate short pulses that are viewed using a high speed scope 126, which is preferably a digital sampling scope. The scope trigger is provided by the same pulse that drives the LED 126. The signal appears on the scope similar to that shown in FIG. 6B. FIG.
B shows two traces. One of these is a reference trace representing the desired pulse amplitude and timing for the PMT. The other pulse is the actual output of the PMT. The operator changes the positions of knobs 120 and 122 until the two traces match to the extent possible.

After assembling the PMTs in the detector, the detector is provided by supplying coincident optical signals to adjacent PMTs and by adjusting the gain so that they each provide a signal of the same amplitude. Fine tuning of the PMTs within may be achieved. Such a coincident optical signal is used to define the area between (and equidistant from) the PMT in the crystal 7
2 will be produced by irradiation by a source of collimated radiation that interacts with the two. Light generated in the crystal by the interaction results in equal signals being generated by adjacent PMTs. Of course, the signals should also match. An electronic fine gain control is then adjusted to provide the required equal gain. This adjustment may be performed automatically by the gamma camera.

Additionally or alternatively, any overall difference in the time delay of the two detectors and the time delay of the cables, electronics and other components can be attributed to the delay circuit 1
It may be compensated by adjusting the 00 delay.

Although the present invention has been described with respect to manual adjustment of PMT gain and transit time, in a preferred embodiment of the present invention, the potentiometer and the variable resistor can be externally controlled. If such a device is used, the adjustment will be performed automatically.

In a further preferred embodiment of the invention, the gain is itself a PMT
By changing the overall voltage of the PMT without changing the transmission time of the PMT. To compensate for the change in transit time, a delay line is inserted after at least some PMTs to compensate for the change in transit time. These delay lines may be fixed delay lines such that each delay line is selected from delay lines having different delays to best match the required delay. Alternatively or additionally, they may be tapped delay lines, where the taps are chosen to provide the required delay.

FIG. 7 shows three tapped delay lines 130, 132 and 13 used to compensate for the propagation time variations of the three PMTs 136, 138 and 140.
4 is shown. The output of the PMT is preferably connected to three amplifiers 14
Preferably, it is amplified by one of the two. Optionally, the gain of the amplifier is made variable to provide at least part of the compensation for gain variation between PMTs, especially part of the electronic control. Alternatively, the amplifier is a simple charge converter and the gain of the PMT is made uniform in the manner described above.

Alternatively or additionally, a continuously variable or electronically adjustable delay line may be used, and the delay is then reduced in a manner similar to the variation of the delay using the grid voltage described above. It may be changed.

When more than one delay line is used per PMT, an overall transmission time correction is achieved using a fixed delay line or a tapped delay line, and fine transmission time correction is tapped, continuous adjustment Achieved using either possible or electronically adjustable delay lines. Alternatively, a tapped delay line may be used for the overall correction and a continuously adjustable delay line may be used for fine adjustment. The use of more than one delay line will result in lower cost and / or fine tuning capability than using one delay line.

The present invention has been described with reference to those embodiments having a significant number of different features. Obviously, these features can be combined in various ways,
It is clear that certain features can be omitted in preferred embodiments of the invention, as set forth in the claims.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of one PMT.

FIG. 2A illustrates a configuration suitable for independently adjusting the gain and transmission time of a PMT according to a preferred embodiment of the present invention.

FIG. 2B illustrates a configuration suitable for independently adjusting the gain and transmission time of a PMT according to a preferred embodiment of the present invention.

FIG. 2C illustrates a configuration suitable for independently adjusting the gain and transmission time of a PMT according to a preferred embodiment of the present invention.

FIG. 2D illustrates a configuration suitable for independently adjusting the gain and transmission time of a PMT according to a preferred embodiment of the present invention.

FIG. 2E is a circuit diagram of a circuit that provides a PMT with an electronically variable gain.

FIG. 3 is a diagram of a portion of an Anger detector, according to a preferred embodiment of the present invention.

FIG. 4 is a block diagram of a coincidence Anger camera utilizing two Anger detectors of FIG. 3;

FIG. 5 is a block diagram of a matching unit according to a preferred embodiment of the present invention.

FIG. 6A illustrates a method of calibrating and adjusting a PMT according to a preferred embodiment of the present invention.

FIG. 6B illustrates a method of calibrating and adjusting a PMT according to a preferred embodiment of the present invention.

FIG. 7 schematically illustrates a system using an external delay line for compensating for variations in PMT transmission time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 PMT 12 Cathode 14 Grid 16-23 Dynode 26 Anode 40 Potentiometer 42 Electronic gain control circuit 44 Variable resistance 72 Scintillation crystal 78 Anger electronic circuit 80 Event detector 90 Matching unit 98 Digital anger processor 100, 102 Delay circuit 104, 106 Variable pulse Generator 124 pulse generator 126 high-speed scope

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] July 17, 2000 (2000.7.17)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

17. A multi-detector PET camera, each of which generates a timing signal when an event is detected.
A plurality of Anger gamma camera detectors according to claim 6 or produced by the method of claim 11 or claim 12, and the presence of a valid event based on a time difference between timing signals generated by said gamma camera. A multi-detector PET camera, comprising: a matching circuit that determines:

[Procedure amendment]

[Submission date] October 11, 2000 (2000.10.11)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 2B

[Correction method] Change

[Correction contents]

FIG. 2B

Claims (18)

[Claims] 1. A method for providing a photomultiplier tube (PMT) having a desired gain and transit time, comprising: (a) said photomultiplier tube having a desired gain; And (b) adjusting the transit time of the photomultiplier so that the photomultiplier has a desired transit time. 2. The method of claim 1, wherein adjusting the gain includes adjusting the overall voltage of the photomultiplier so that the photomultiplier has a desired gain. The described method. 3. The method of claim 2, wherein adjusting the transit time comprises adjusting a voltage on a grid or an initial dynode of the photomultiplier such that the photomultiplier has a desired transit time. 3. The method according to claim 1 or claim 2, wherein 4. The method according to claim 3, wherein the voltage of the grid or the first dynode is adjusted without substantially changing the voltage of the other electrodes. 5. The method of claim 1, wherein adjusting the voltage for the grid comprises changing the overall gain of the photomultiplier and repeating steps (a) and (b) at least once. The method according to claim 3, wherein 6. A method for providing a photomultiplier tube (PMT) system having a desired gain and transit time, comprising: (a) the photomultiplier tube system having a desired gain. Adjusting the gain of the multiplier system; and (b) adjusting the transit time of the photomultiplier system such that the photomultiplier system has a desired transit time. 7. The photomultiplier tube system includes a photomultiplier tube, and adjusting the gain comprises adjusting a total voltage for the photomultiplier tube such that the photomultiplier tube has a desired gain. 7. The method of claim 6, comprising adjusting. 8. The photomultiplier tube system includes an amplifier for amplifying the output of the photomultiplier tube, and adjusting the overall gain of the amplifier so that the photomultiplier tube system has a desired gain. The method of claim 7, comprising: 9. The photomultiplier tube system includes a photomultiplier tube, wherein adjusting the transit time comprises delaying the output of the photomultiplier tube such that the photomultiplier tube has a desired transit time. 7. The method of claim 6, comprising: 10. The photomultiplier tube according to claim 1, further comprising a delay of an output of the photomultiplier tube so that the photomultiplier tube has a desired moving time. The method according to any one of claims 1 to 8. 11. The method according to claim 9, wherein the delay comprises a delay of the output using a delay line. 12. A method of producing a gamma detector, comprising: providing a scintillator crystal; providing a plurality of photomultiplier tubes for capturing a surface of the crystal; and adjusting a gain and a transit time of the photomultiplier tube. Adjusting them to be substantially identical for the plurality of photomultiplier tubes. 13. The method according to claim 6, wherein the gain and the transit time are adjusted according to the method according to one of the preceding claims. 14. A photomultiplier tube (PMT) system comprising: a plurality of photomultiplier tubes; and a plurality of delaying outputs of respective ones of the photomultiplier tubes with substantially the same delay. A photomultiplier tube system comprising: a delay line; 15. The photomultiplier tube system according to claim 14, wherein said photomultiplier tubes have substantially the same gain. 16. The photomultiplier tube system according to claim 15, further comprising means for varying a voltage on said photomultiplier tube to produce said substantially identical gain. 17. A method for producing a gamma detector, comprising: providing a scintillator crystal; and providing a photomultiplier tube system according to any one of claims 14 to 16, which captures a surface of the crystal. A method for producing a gamma detector, comprising: 18. A multi-detector PET camera, wherein the plurality of angers are produced according to the method of claim 12, 13 or 13, generating a timing signal when an event is detected. A multi-detector comprising: a gamma camera detector; and a matching circuit that determines the presence of a valid event based on a time difference between timing signals generated by the gamma camera. PET camera.