JPH04270986A - X-ray signal processing circuit - Google Patents

Abstract

PURPOSE:To obtain a circuit which does not allow a capacitative load of an amplifier or the number of wire connections between a comparator and a counter to be increased without increase in the number of comparators even if an energy level to be discriminated is increased. CONSTITUTION:A conversion circuit 3 which generates a digital pulse with a pulse width corresponding to a pulse height of an output of an amplifier 2 and a multiplexer 4 which leads the digital pulse to relevant counters 5a and 5b according to the pulse width are provided.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray signal processing circuit based on a photon counting method applicable to medical X-ray imaging devices, industrial non-destructive inspection devices, and the like.

0002

2. Description of the Related Art In X-ray measurement based on the photon counting method, the amount of X-rays is basically measured by counting pulse signals generated by X-rays incident on an X-ray detector. FIG. 3 shows an example of a conventional X-ray signal processing circuit using such a photon counting method.

This conventional example is a circuit that measures the dose of each of the X-rays exceeding two energy levels, and the current pulse output from the X-ray detector 31 is sent to the amplifier 3.
After being converted and amplified into voltage pulses by 2, the voltage pulses are input to comparators 33a and 33b. Comparator 33
A and 33b are provided with different reference voltages VREF1.
and VREF2 are set, and only pulses having a voltage value exceeding each reference voltage are introduced into counters 34a and 34b connected to each comparator 33a and 33b and counted. These counters 34a and 34b
Each count of will represent the dose of x-rays above the energy level specified by VREF1 or VREF2.

0004

[Problems to be Solved by the Invention] In the conventional X-ray signal processing circuit as described above, in order to know the dose of X-rays of different energy levels, multiple comparators and counters are connected to the amplifier as shown in the example. Must be connected in parallel to the output. However, in such a processing circuit,
As the number of energy levels to be separated increases, the capacitive load on the amplifier increases, and when all circuits are configured in a hybrid configuration, the number of connections between the comparator and counter increases, especially. .

The present invention has been made in view of these points, and provides X-ray signal processing in which the load capacity of the amplifier does not increase even when the energy level is increased and the number of connections between the comparator and the counter is reduced. The purpose is to provide circuits.

[0006]

[Means for Solving the Problems] A configuration for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. an amplifier 2 that converts and amplifies current pulses into voltage pulses; a pulse conversion circuit means (for example, a comparator) 3 that outputs a digital pulse with a time width proportional to the pulse height of the output of the amplifier 2; It is characterized by having a multiplexer 4 that switches the signal path depending on the magnitude, and a plurality of counters 5a and 5b that count the pulse signals guided through the multiplexer 4.

[0007]

[Operation] As shown in FIG. 2(A), when comparing the output of the X-ray sensor 1 converted and amplified by the amplifier 2 at a constant voltage level, the width tends to increase as the peak value increases. have Utilizing this feature, for example, one comparator can convert pulse height information of the output of the amplifier 2, and thus information on the energy level of photons incident on the X-ray sensor 1, into digital pulse width information. By guiding a signal to one of a plurality of counters according to the value of this pulse width, it becomes possible to discriminate the energy level of the incident photon.

That is, regardless of the number of energy levels to be discriminated, the output of the amplifier 2 need only be led to one pulse conversion circuit means such as a comparator, and the desired purpose can be achieved.

[0009]

Embodiment FIG. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention, and shows an example in which energy levels are counted separately into two. The current pulse output of the X-ray sensor 1 is converted and amplified into voltage pulses by an amplifier 2 and introduced into one comparator 3. A reference voltage VREF is set in the comparator 3, and the reference voltage VREF
Outputs an H-level digital pulse signal when a signal with a voltage level exceeding .

The output of this comparator 3 is introduced into a multiplexer 4 and then sent to a first or second counter 5a.
Or introduced in 5b. A reference clock is introduced into the multiplexer 4, and is configured to guide the input signal to the first or second counter 5a or 5b depending on how many reference clocks are included in the pulse width of the digital pulse signal from the comparator 3. has been done. In addition,
The actual circuit of this multiplexer 4 can be constituted by simple digital circuits such as simple logic gates and counters. That is, by using the output pulse of the comparator 3 as a gate signal and counting the reference clock that passes during that time using a counter or the like, the magnitude of the pulse width is identified, and the pulse signal is guided to the corresponding counter according to the result. This can be achieved by providing such a gate.

Next, the operation of the embodiment of the present invention described above will be described with reference to the signal waveforms of each part shown in FIG. When X-rays enter the X-ray sensor 1, a pulse proportional to the energy value of the X-rays appears at the output of the amplifier 2, as shown in FIG. 2(A). When this pulse is input to comparator 3, (B)
As shown in the figure, the preset reference voltage VR
For those having a peak value exceeding EF, the output of the comparator 3 becomes H level only during the period when the peak value exceeds the reference voltage VREF. Here, the larger the peak value of the output signal from amplifier 2, the longer the period in which it exceeds VREF. Therefore, the pulse width of the digital pulse from comparator 3 is It is a high value, that is, a value that correlates with the energy of incident X-rays.

The pulse width of such a digital pulse from the comparator 3 is determined in the next stage multiplexer 4 based on the number of passages of a reference clock using the digital pulse as a gate signal, as shown in (C). ,
If it is less than a certain value, it is introduced into the first counter 4a, and if it exceeds that value, it is introduced into the second counter 4b for counting. As a result, the first and second counters 4a and 4
From the count value of b, it is possible to know the number of photons of incident X-rays with different energy levels.

[0013] In the above embodiments, the case where the energy level is distinguished into two and counted is shown, but there is no limit to the number of discriminations, and it is possible to expand to a multi-channel, multi-level photon counter. Of course. Furthermore, the pulse width of the digital pulse from the comparator 3 can be determined not only by the number of passages of the reference clock as described above, but also by comparison with a reference pulse width signal using, for example, a one-shot multivibrator. good.

Furthermore, by adding a circuit that accurately converts pulse height into pulse width, more accurate pulse height analysis can be performed. Furthermore, when switching the output destination of the pulse signal by the multiplexer, an appropriate delay element may be inserted in view of the time required to determine the pulse width. Also, based on the pulse width judgment result, in addition to directing the digital pulse itself from the comparator to the corresponding counter as in the example above, other appropriate signals, such as another signal generated based on the judgment result, can be sent to the corresponding counter. It can also be supplied to the counter.

[0015]

Effects of the Invention As explained above, according to the present invention, by guiding the voltage conversion pulse of the current pulse output from the X-ray sensor to one comparator or the like, the pulse width proportional to the pulse height can be changed. The structure is configured so that the signal is converted into a digital pulse signal that has a pulse width and is supplied to the appropriate one of multiple counters according to the value of the pulse width. It is no longer necessary to provide a comparator to supply each amplifier output in parallel, and the capacitive load on the amplifier does not increase even when multiple energy levels are separated.

Furthermore, even if the energy level to be separated is increased, since a large number of comparators are not required, the number of connections between the comparators and the counters does not increase.
At the same time, it consumes less power than conventional circuits.

[Brief explanation of the drawing]

[Fig. 1] Block diagram showing the circuit configuration of an embodiment of the present invention

[Fig. 2] An explanatory diagram of the operation of the embodiment of the present invention shown by signal waveforms of each part

[Figure 3] Block diagram showing a configuration example of a conventional X-ray processing circuit

[Explanation of symbols]

1...X-ray sensor 2...Amplifier 3...Comparator 4...Multiplexer 5a...first counter 5b...Second counter

Claims (1)

[Claims] Claim 1: An amplifier for converting and amplifying current pulses from an X-ray detector into voltage pulses, a pulse conversion circuit means for outputting digital pulses with a time width proportional to the pulse height of the output of the amplifier, and An X-ray signal processing circuit comprising a multiplexer that switches signal paths according to a pulse width value, and a plurality of counters that count pulse signals guided through the multiplexer.