JPS61199841A - X-ray ct apparatus - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an X-ray CT device that can obtain a constant A/D conversion input level regardless of changes in the amount of X-rays incident on the X-ray detector. .

[Background of the invention]

An X-ray CT device irradiates a subject with X-rays through a collimator installed on the X-ray irradiation side of an X-ray source, and a detection system converts the transmitted X-rays into electrical signals that are detected and amplified. , and then performs A/D conversion and reconstructs the image by combinator processing to obtain a tomographic image.

By the way, conventionally, there is an X-ray CT device that uses a variable X-ray width collimator, but in this conventional device, the gain of a preamplifier buffer circuit in the detection system is changed depending on the X-ray width of the collimator. In particular, a constant A/D conversion input level can be obtained regardless of changes in the amount of X-rays incident on the X-ray detector.

However, this alone is not sufficient to stabilize the A/D conversion input level; The A/D conversion input level changes depending on the radiographing conditions. In particular, when the A/D conversion input level decreases, the SAJ becomes smaller, which isometrically manifests as an increase in quantization noise in A/D conversion, which deteriorates the image quality. Improvements in these points are required. was requested.

[Purpose of the invention]

The present invention was made in view of the above-mentioned demands, and it is possible to obtain a constant A/D conversion input level not only by the X-ray width of the collimator but also by setting the image reconstruction area and X-ray imaging conditions. It is an object of the present invention to provide an X1aCT device that has a high S/N ratio and can improve image quality.

[Summary of the invention]

The device of the present invention changes the A/D conversion input level by changing the gain of the amplifier circuit in the detection system according to the X-ray width of the collimator, the image reconstruction area corresponding to the size of the subject, and the X-ray imaging conditions. The objective is to achieve the above-mentioned purpose.

[Example of Haimei]

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing essential parts of an embodiment of an X-ray CT apparatus according to the present invention, and numeral 11 in the figure is an X-ray source. A collimator 12 is arranged on the X-ray irradiation side of the X-ray source 11 and is capable of varying the X-ray width in multiple stages. 13 is a subject; 14 is an X-ray detector that detects transmitted X-rays from the subject 13; and 15 is an integrator that integrates the output signal of the detector 14. Reference numeral 16 denotes a multi-blephr, and 17 denotes a prior/gupanopha circuit. The multi-brephther 16 sequentially sends the output signals of each detection element of the detector 14 to the buffer circuit 17, and the buffer circuit 17 has a gain ( (hereinafter referred to as buffer dine) can be switched to multiple stages. 18 is an A/D converter that A/D converts the output signal of the buffer circuit 17; 19 is an image reproduction unit that receives the signal from the A/D converter 18 and reconstructs the image through computer processing to obtain a tomographic image; It is a circuit. 2
0 is an X-ray generation circuit for generating X-rays from the X-ray source 11, which controls X-ray imaging conditions such as voltage and current (tube voltage, tube current) to the X-ray source 11, and pulse width. is possible. 21 is an X-ray width control circuit that controls the X-ray width of the collimator 12. 22 is a CT device operation control circuit, and when measurement conditions are set by the operator, the corresponding F
Signals are sent to each circuit 19, 20, and 21 so that the OV, X-ray width, and X-ray imaging conditions are given, and each circuit is controlled to a set value.

Although not shown, the image reproducing circuit 19 includes amplification gain control means for switching and controlling the graph add-in. In this case, the amplification gain control means changes the buffer dyne according to the FOV, X-ray width, and X-ray imaging conditions (hereinafter collectively referred to as set measurement conditions) set as described above, and Regardless of changes such as the incidence xii on A
The input signal level to the /D converter 18 is kept constant, and the buffer dyne for the set measurement conditions is set using a ROM chisol or the like that has a correspondence relationship determined in advance by calculation or experiment. It consists of For example, assume that the buffer dyne is 1 when the X-ray width is 10 m5, the voltage and current are 120 kV, 300 mA, and FOV is 200 as the X-ray imaging conditions, and this is used as the reference value. Under these measurement conditions, X
When the line width is changed to 5-, the amount of X-rays incident on the X-ray detector 14 becomes 2, so the buffer dyne is set to 2, and
If the current is also changed to 150 mA along with this change, the incident X-ray dose will be further halved, so the buffer dyne will be set to 4, and in addition to these changes, the FOV will also be set to 4.
If the buffer dyne is changed to 00, the buffer dyne is set to 5. Thus, the correspondence between the values is made into a table and the buffer dyne is changed in proportion to changes in the amount of X-rays incident on the X-ray detector 14. Make it.

That is, in the apparatus of the present invention, when measurement conditions are set in the operation control circuit 22, the FOV, X-ray width, and X-ray imaging conditions (set measurement conditions) are applied to the amplification gain control means provided in the image reproduction circuit 19. The gain of the preamplifier buffer circuit 17 is selectively switched so that a constant A/D converter input signal level can be obtained irrespective of changes in the set values.

In the above embodiment, the case where the preamplifier/47 fur circuit 17 is selected as the gain-controlled amplifier circuit in the detection system from the X-ray detector 14 to the input end of the A/D converter 18 is described. However, the present invention is not limited to this, and the gain of an X-ray detector output amplifier group (not shown) provided between the X-ray detector 14 and the multiplexer 16 may be controlled. In this case, the gain is similarly controlled for each of the output amplifiers provided corresponding to each detection element of the X-ray detector 14, which constitutes the output amplifier group.

Further, it goes without saying that the amplification gain control means is not limited to being provided in the image reproduction circuit 19.

〔Effect of the invention〕

As described above, according to the present invention, the input level of A/D conversion does not change depending on the settings of F'OV, X-ray width, and X-ray imaging conditions, so the S/N is higher than that of conventional devices.
This has the effect of isometrically reducing quantization noise in A/D conversion and improving image quality. This means that in conventional equipment, when measurement conditions are set such that the amount of X-rays incident on the X-ray detector is reduced, at the same time the X-ray source and
The input level of the A/D conversion can be kept constant without increasing the load on the X-ray generation system such as the ray generation circuit, which can reduce the cost and improve the reliability of the X-ray generation system. Become.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main parts of an embodiment of the apparatus of the present invention. 11... X-ray source, 12... X-ray width variable collimator, 1
3... Subject, 14... X-ray detector, 17... Preamplifier/fuss circuit, 18... A/D converter, 19
...Image reproduction circuit, 20...X-ray generation circuit, 21.
...X-ray width control circuit, 22...CT device operation control circuit.

Claims (1)

[Claims] 1. A collimator with variable X-ray width is provided at the irradiation port of the X-ray source,
The subject is irradiated with X-rays through this collimator, and the transmitted X-rays are converted into electrical signals in the detection system, which are detected and amplified. After that, A/D conversion is performed, and the image is reconstructed by computer processing. In an X-ray CT apparatus that obtains a tomographic image by An X-ray CT apparatus, comprising an amplification gain control means for changing the gain of the amplifier circuit to keep the input level of the A/D conversion constant. 2. The amplifier circuit according to claim 1, wherein the amplifier circuit is a group of X-ray detector output amplifiers or a preamplifier buffer circuit provided between this group of amplifiers and the A/D conversion means. X-ray CT device.