JPH06289140A - Positron ct device - Google Patents

Abstract

PURPOSE:To prevent the reduction of the image precision by grasping the existence of the quantitative performance of the obtained data, i.e., the existence of the data reliability by taking account of the counting loss as the cause for deteriorating the quantitative performance of the counting value of the PET of a positron CT device, and previously knowing the region where the correction of the counting loss is impossible in theoretical aspect, when the concentration of the radioactivity applied to an inspected body exceeds a certain value. CONSTITUTION:A positron CT device is equipped with a counter 37 for monitoring the counting rate which measures the output counting rate of the single counting circuit 31, comparison circuit 38 which compares the counting rate measured by the counter 37 and the previously set reference counting rate and outputs an alarm signal when the counting rate of the counter becomes larger than the reference counting rate, and an alarm circuit 39 which receives the alarm signal and transmits alarm through the visual or auditory method or both.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positron CT apparatus (also referred to as PET) used for nuclear medicine diagnosis, and more particularly to a PET capable of monitoring the quantitativeness of measurement data.

[0002]

2. Description of the Related Art In PET, the output from a group of detectors closely arranged in a ring around a subject is simultaneously counted, and the obtained projection data is used in an image similar to that obtained by an X-ray CT apparatus. A diagnostic image is created using a reconstruction technique.

FIG. 3 shows that in a conventional PET, the detector (group) output becomes projection data and is recorded in a memory.
It is a block diagram which shows the circuit part transferred to a data processing apparatus. In FIG. 3, the detector (group) output SD is output from the coincidence counting circuit 31 as a coincidence counting pair signal (i, j) when a coincidence counting event is detected by the coincidence counting circuit 31. Here, i and j are i arranged to face each other.
The th detector and the jth detector are shown. Thus (i, j) will represent coincidence counting events occurring at the i and j detectors.

The (i, j) output (also referred to as (i, j) data) from the coincidence counting circuit 31 is a +1 circuit 32 in the subsequent stage.
Is input to. The +1 circuit 32 has a function of adding 1 to the data at the address (i, j) of the addresses of the memory 33 at the next stage. That is, (i, j) data is written in the memory 33 by a method called a histogram mode. The data sequentially written in the memory 33 and accumulated within a certain measurement period are appropriately sent to a data processing device (not shown) in the subsequent stage to be imaged. On the other hand, the detector output SD
Is also input to the single detection circuit 34, and the address of the detector i or j
The count value such as is recorded in the memory 36 through the +1 circuit 35.

[0005]

In the conventional device shown in FIG. 3, when the concentration of radioactivity to be administered into a subject (not shown) becomes high, it is measured (i, j) accordingly.
The count value or count rate of the data becomes high, and so-called counting-down occurs due to the dead time of the circuit system.

FIG. 4 is a graph showing the relationship between the radioactivity concentration showing the counting loss characteristic and the measured counting rate, and simply shows the above counting. In an ideal circuit system without counting down, a measurement value such as a straight line a is obtained in proportion to the radioactivity concentration. On the other hand, in a normal circuit system, measured values showing a tendency like curves b and c are obtained. In particular, it is well known in the field of radiation measurement that a circuit system showing a tendency like a curve b has a saturation type dead time and a case like a curve c has a choking type dead time. These characteristics impair the proportional relationship between the administered radioactivity concentration and the measured count value, here the (i, j) data recorded in the memory, and as a result, the quantitative evaluation of the count value becomes impossible. Means to become.

The characteristic of PET is that it can be quantitatively evaluated. Therefore, the degree of non-linearity due to the above counting is important as a factor that impairs the characteristics of PET. Usually, even if such a counting-down occurs, a non-linearity correction, that is, a counting-down correction can be performed by a mathematical process.

However, the saturation value or maximum value P shown in FIG.
The above-mentioned correction is not possible in the range of radioactivity concentration exceeding the above range. In this case, the dose must be limited in advance so that the radioactivity concentration does not exceed the value P. In clinical settings, there are individual differences in the uptake of radioactivity at the test site, and it is often difficult to manage. Therefore, the quantitativeness of the measurement data is impaired, the reliability of the data is reduced,
There was a problem that the accuracy of the image was reduced.

An object of the present invention is to provide a positron CT apparatus which can prevent the quantitativeness of measurement data from being impaired and the reliability of data to be prevented from being lowered, and the deterioration of image accuracy to be prevented.

[0010]

SUMMARY OF THE INVENTION The above object is to provide a counter for counting rate monitor which measures an output counting rate of a single counting circuit,
A comparison circuit that compares the count rate measured by this counter with a preset reference count rate and outputs a warning signal when the count rate of the counter is larger than the reference count rate; And / or audibly, or both, to provide a warning circuit.

[0011]

The comparator circuit compares the output count rate of the single counting circuit measured by the count rate monitor counter with a preset reference count rate, and when the count rate of the counter is larger than the reference count rate. Output a warning signal. The warning circuit receives the warning signal from the comparison circuit and issues a warning visually or audibly or both.

This allows the operator or the like to know whether or not the output of the coincidence counting circuit system is in the region in which the counting loss can be corrected, and the operator or the like can take appropriate measures to reduce the reliability of the data. Will be prevented.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the drawings. Prior to that, the principle of the present invention will be described. In a positron CT apparatus (PET), whether the measured data is due to a saturated region or a radioactivity concentration that has already exceeded the maximum value P is usually a saturated type circuit system including a coincidence counting circuit, a +1 circuit and a memory. It cannot be judged from the count rate of the data unless it has a counting loss of.

In the coincidence counting circuit 31 system as shown in FIG. 3, the dead time is generally longer than that in the single counting circuit 34 system, and accordingly, the counting loss occurs in the region where the radioactivity concentration is high. It will be noticeable. FIG. 5 is a graph showing the relationship between the radioactivity concentration showing the count loss characteristic and the measured count rate, and conveniently shows the count rate characteristics of the two circuits 31 and 34. In FIG. 5, the curve c is related to the coincidence counting circuit 31 system, and the curve d is related to the single counting circuit 34 system. Points P and P ″ indicate the maximum values of the curves c and d.

Now, by monitoring the output of the single counting circuit 34 system, that is, the output counting rate Cp of the single counting circuit 34 system at the radioactivity concentration which gives the maximum value P of the counting rate of the simultaneous counting circuit 31 system. If there is an output count rate exceeding Cp, the coincidence counting circuit 31
We can see that the system has already exceeded its maximum. Therefore, if this is notified and warned by voice or lighting of a light emitting diode (LED), the operator or the like can know that the count rate cannot be corrected, and the operator or the like can take a measure of the data. This will prevent the reliability from decreasing.

FIG. 1 is a block diagram showing a main part of an embodiment of a positron CT apparatus according to the present invention. In FIG. 1, 31 to 36 and SD are the same as in FIG.
37 is a counter for monitoring the count rate for measuring the output count rate of the single counting circuit 31, 38 is the counter rate measured by the counter 37 and a preset reference count rate, and the count rate of the counter 37 is the reference rate. A comparator circuit that outputs a warning signal when the count rate is higher than the count rate, and a warning circuit 39 that receives the warning signal and issues a warning visually or audibly or both. The warning circuit 39 is
Here, the audio output circuit 39a and the light emitting diode (LE
D) It comprises a lighting circuit 39b.

In the above-mentioned device of the present invention, the single counting circuit 3
The output of 1 is input to the counting rate monitor counter 37.
The counter 37 counts down the input count rate to 1 / N (N is a positive integer) to prevent the count rate from increasing in advance. The value of N is the single counting circuit 31.
Is arbitrarily selected according to the processing speed of.

The output of the counting rate monitor counter 37 is n
It is expressed and output as a signal of bits (for example, n = 8 or n = 16). The n-bit counter output is input to the comparison circuit 38. As the value of the reference signal of the comparison circuit 38, a value Cp that satisfies the curves c and d in FIG. 5 is selected.

It is assumed that the output level of the comparator circuit 38 becomes 1 when the input signal (output signal of the counter 37) value thereto exceeds the reference signal value Cp. When the output level is 1, the warning circuit 39 at the next stage is driven. That is, the audio output circuit 39a and the light emitting diode (LE
D) The lighting circuit 39b is driven. Audio output circuit 39a
A voice for warning is recorded in the internal ROM, and P
The ET operator is warned by voice information that the radioactivity concentration is in a region exceeding the maximum value P shown in FIG. The light emitting diode lighting circuit 39b is a light emitting diode (LED).
A similar warning is given visually by sequentially illuminating. The warning circuit 39 may be either the voice output circuit 39a or the light emitting diode (LED) lighting circuit 39b, and the warning circuit 39 may be configured to issue a warning visually or audibly or both of them. Good.

FIG. 2 is a block diagram showing the essential parts of another embodiment of the device of the present invention. As shown in FIG. 2, in the PET, the coincidence counting circuit 34 system has a plurality of series (or channels).
It generally consists of In such a configuration, each detector output SD is processed by the common single counting circuit 31. The counting rate counter 37 is provided for each channel and measures a single counting rate for each channel. The input to each counter 37 is counted down to 1 / N as in the embodiment of FIG.

In the comparison circuit 38, if any of the outputs of the counter 37 of each channel exceeds the Cp value, the sound is output and the light emitting diode is turned on by the same method as described in the embodiment of FIG. Illuminates and alerts visually and / or audibly.

[0022]

As described above, according to the present invention, a warning is issued when RI is administered to a subject at a radioactive concentration that makes counting loss correction in principle impossible.
It is possible to prevent the operator from starting the PET measurement during this period. Also, when the RI intake is increased during measurement and the radioactivity concentration becomes higher than a predetermined value, the operator is similarly warned.
It is possible to inform that the quantitativeness of the measurement data is impaired. Therefore, whether or not the data is reliable can be taken into consideration at the time of data processing, and there is an effect that deterioration of image accuracy can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of an embodiment of a device of the present invention.

FIG. 2 is a block diagram showing a main part of another embodiment of the device of the present invention.

FIG. 3 is a block diagram showing a main part of a conventional device.

FIG. 4 is a graph showing the relationship between the radioactivity concentration showing the counting loss characteristic and the measured counting rate.

FIG. 5 is a graph showing the relationship between the radioactivity concentration showing the counting loss characteristic and the measured counting rate.

[Explanation of symbols]

 31 Single Counting Circuit 32 +1 Circuit 33 Memory 34 Simultaneous Counting Circuit 35 +1 Circuit 36 Memory 37 Counting Rate Monitor Counter 38 Comparison Circuit 39 Warning Circuit 39a Voice Output Circuit 39b Light Emitting Diode Lighting Circuit SD Detector (Group) Output

Claims (1)

[Claims] 1. A counter for monitoring a count rate for measuring an output count rate of a single counting circuit, and a count rate measured by this counter and a preset reference count rate are compared, and the count rate of the counter is the reference rate. A positron CT apparatus comprising: a comparator circuit that outputs a warning signal when the count rate is greater than the count rate; and a warning circuit that receives the warning signal and issues a warning visually or audibly or both. .