JPH01299535A - Data collecting device - Google Patents

Abstract

PURPOSE:To enable a dynamic range, provided in a device itself, to be effectively utilized despite a length of the integration time by providing an offset correcting voltage adjusting means which enables the offset correction voltage to be adjusted corresponding to switching the integration time by an integration time switching means. CONSTITUTION:A data collecting device 2, which collects an X-ray projection data of a detected body by fetching a detecting output of a detector 1, has an integrator 11, data collecting control part 8, sample holding circuit 9 and an analog/digital converter 10. An operational amplifier 3 functions serving as one part of the integrator or as an offset correction circuit 7. Further offset correction voltage Vof is adjusted in an offset correction voltage adjusting means 6. This adjusting means 6 consists of switches 61 to 6n enabling voltages from voltage sources V01 to V0n to be selectively transmitted to an non-inversion input end of the operational amplifier 3, and by controlling the data collecting control part 8, the switch is alternatively closed being associated with switching the integration time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a data convergence device that collects data by taking in the output of a detector that detects, for example, X-rays.

(Conventional technology) The XIICT scanner is an X-ray scanner consisting of an X-ray tube that emits fan-beam X-rays with a flat fan-shaped spread angle, and a plurality of X-ray detection cells that detect the X-rays. The X-ray tube and the X-ray detector are placed opposite to each other with the subject P in between, and the X-ray tube and the X-ray detector are rotated in the same direction and at the same angular velocity around the subject, so that the X-ray tube and the After collecting enough X-ray projection data,
This data is analyzed by a computer to calculate the X-ray absorption rate corresponding to each position in the cross section of the object, and the image information in the cross section of the object is reconstructed by giving a gradation according to the absorption rate. This allows almost clear tomographic images of everything from soft tissue to hard tissue to be obtained.

The above X11 projection data acquisition was performed using a data acquisition device (DA).
(abbreviated as S). The data acquisition device has a function of integrating the output of the X-ray detector for a predetermined period of time and converting this integrated output into a digital signal.

In the X-ray scanner that uses continuous X-rays,
Since the offset voltage of the X-ray detector and data acquisition device increases in proportion to the integration time due to the integration operation in the data acquisition device, a positive offset is set on the data acquisition device side to prevent the offset voltage from underflowing during the maximum integration time. I try to have it.

(Problem to be Solved by the Invention) However, if an offset is provided in consideration of the maximum integration time, for example, if the offset up to the previous stage of the integrator is negative, the minimum integration time will be Since the dynamic range that can actually be used out of the dynamic range of the data acquisition device (DAS) itself will be significantly narrowed, the density resolution in the reconstructed image will deteriorate. Invite.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks, and its purpose is to provide a data acquisition device that can effectively utilize the dynamic range of the device itself, regardless of the length of the integration time.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides an integrator that integrates the detection output of a detector, an integration time switching means that switches the integration time in this integrator, and an offset correction voltage. offset correction means for correcting the offset of the detector based on the offset correction means for adjusting the offset correction voltage in response to integration time switching by the integration time switching means; It has been established.

(Function) According to the above configuration, the offset correction voltage is adjusted in response to the switching of the integration time, thereby making it possible to effectively utilize the dynamic range of the data acquisition device itself regardless of the length of the integration time.

(Example) Hereinafter, the present invention will be specifically explained with reference to Examples.

FIG. 1 shows an embodiment of the invention.

1 is a detector for detecting X-rays transmitted through a subject in, for example, an Xl1CT scanner; 2 is a detector 1 for detecting X-rays transmitted through a subject;
This is a data acquisition device (DAS) that takes in the X-ray detection output of the object and collects the X-ray projection data of the subject.

This data collection device 2 includes an integrator 11. Data collection control unit 8. S/H (sample and hold) circuit9. and A/
It has a D (analog-to-digital) converter 10.

The integrator 11 integrates the detection output of the detector 1. An integrating capacitor 4 is connected between the inverting input terminal (-) and the output terminal of the operational amplifier 3, and a switch 5 is connected to the integrating capacitor 4. Consists of parallel connections. The output terminal of the detector 1 is connected to the inverting input terminal of the operational amplifier 3. After this integrator 11, there is an S/H circuit 9 which samples and holds the integrated output of the integrator 11 at a predetermined timing. An A/D converter 10 is arranged to convert the output (analog signal) of this S/H circuit 9 into a digital signal.

The data collection control unit 8 receives input signals from a keyboard (not shown), etc., and a graticule pulse signal generated from the graticule system of the X-ray CT scanner in accordance with the rotation of the gantry rotating unit. It controls the entire operation of the embodiment device @2. Switch 5° S/H circuit 9 in the integrator 11. and A/D converter 10 are placed under the control of this data collection control section 80. Here, the integration time of the integrator 11 is equal to the duration of the open state of the switch 5, and by controlling this duration of the open state by the data collection control section 8, the integration time can be switched. Therefore, the integration time switching means in the present invention is functionally realized by this data collection section 8.

Further, an offset correction voltage Vof is applied between the non-inverting input terminal (+) of the operational amplifier 3 forming the integrator 11 and the ground line, and based on this offset correction voltage The offset of the detector 1 is corrected.

That is, in this embodiment, the operational amplifier 3 functions as a part of the integrator 11 and also functions as an offset correction circuit. Here, the offset correction means 7 in the present invention is functionally realized by this operational amplifier 3.

Further, the offset correction voltage Vof is adjusted by an offset correction voltage adjustment means 6. This offset correction voltage adjusting means 6 includes voltage sources VO1, V
O2, VO3,..., Van (however, VCl2
It is composed of switches 61, 62, 63, . The switches 61 to 6n are under the control of the data collection control section 8, and are selectively closed in conjunction with the switching of the integration time.

Incidentally, in the X-ray CT scanner, integrator 11, S/H circuit 9, etc. are actually arranged corresponding to the number of channels of detector 1.

Next, the operation of the embodiment device configured as described above will be explained.

It is assumed that each of the voltage sources V'01 to Von is set to the optimum value in consideration of each integration time switched by the data collection control unit 8.

When performing scanography of a subject with an X-ray CT scanner (integration time is the longest), only the switch 6n is closed under the control of the data acquisition control unit 8, and the voltage from the voltage source Von (highest voltage) is It is applied to the non-inverting input terminal of operational amplifier 3. In other words, in this case, vof=Von. In this state, the X-ray detection output from the detector 1 is integrated by the integrator 11, this integrated output is sampled and held by the S/H circuit 9, and this sampled and held output is A/D converted by the A/D converter 10. D-converted.

Further, each time the integration time is changed according to the X-ray CT scan, the switch forming the offset correction voltage adjustment means 6 is selectively closed, and the voltage source corresponding to the integration time is selected. Become.

In this way, in the device of this embodiment, by selectively closing the switches 61 to 6n in conjunction with switching of the integration time, offset correction is performed using an offset correction voltage suitable for the integration time. Because
Even when the integration time is short, unlike conventional devices, there is no unnecessary offset (see FIG. 2), and the dynamic range of the data acquisition device itself can be fully utilized. Therefore, the output (A
The image formed based on the X-ray projection data output from the /D converter 10 has excellent density resolution.

Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above embodiment, and various modifications can be made.

For example, in the above embodiment, the offset correction means 7 is formed by the operational amplifier 3 which is a part of the integrator 11, but an operational amplifier is added before or after the integrator 11, and the added operational amplifier has an offset. A correction voltage Vof may also be applied. in this case,
The newly added operational amplifier forms the offset correction means 7.

Further, in the above embodiment, the offset correction voltage adjusting means 6 is explained using switches 61 to 6n that selectively select the voltage sources VOl to Von, but a plurality of voltage dividing resistors that divide a predetermined voltage are used. and suitable means (for example, a switch) capable of changing the voltage dividing ratio of this voltage dividing resistor.
The offset correction voltage adjusting means may be formed by including the above. The point is that the offset correction voltage V is adjusted according to the integration time switching.
Any circuit that changes of and 1q may be used, and the circuit for this purpose may have any configuration.

Further, in the above embodiment, the offset correction voltage vOf is automatically adjusted under the control of the data collection control section 8, but it may be directly adjusted by manual operation.

Further, the data collection device according to the present invention can be applied to devices other than X-ray CT scanners.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to provide a data acquisition device that can effectively utilize the dynamic range of the device itself, regardless of the length of the integration time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a data acquisition device according to the present invention, and FIG. 2 is a characteristic diagram showing limitations due to offsets in the dynamic range of the data acquisition device (DAS) itself. 1...Detector , 2... data collection device, 6...
- Offset correction voltage adjustment means, 7... Offset correction means, 8... Data collection control section (integration time switching means), 11
...Integrator, Vof...Offset correction voltage. Figure 2

Claims (1)

[Claims] The detector has an integrator that integrates the detection output of the detector, an integration time switching device that switches the integration time in the integrator, and an offset correction device that corrects the offset of the detector based on an offset correction voltage. In the data collection device that collects data by taking in the detection output of the detector, an offset correction voltage adjustment means is provided that can adjust the offset correction voltage in response to integration time switching by the integration time switching means. A data collection device featuring: