JPH01310644A - X-ray ct scanner - Google Patents

Abstract

PURPOSE:To exactly cancel the fluctuation of collecting data due to the change of X-ray intensity without fail and to reduce artifact by calculating the data tor correction of a detector group based on a voltage monitor output and a current monitor output and executing reference correction. CONSTITUTION:A tube voltage, which is the output voltage of a high voltage generator 1, is monitored by a voltage transformer 11 and a voltmeter 12 with a sampling time to be extremely shorter than an integration time DELTAT. The average intensity of an X-ray, which does not pass through a checked body, during a period I0 can be calculated from the output of a Det0. When this average intensity is defined as an X0, Intensity Xi of the X-ray not to pass through the checked body during a period Ii goes to be an expression 1. Concerning respective detectors Deti, the intensity Xi of the X-ray not to pass through the checked body in the peculiar integration time Ii, namely, reference data can be calculated. Then, with using these reference data Xi, as the result of the correction by an expression 2, the data not to depend on the X-ray intensity are given to a re-constituting part 9 and a picture, for which the artifact is reduced, is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an X-ray CT scanner device, and particularly to an X-ray CT scanner device that can reduce artifacts.

(Conventional technology) X! An example of an ICT scanner device will be explained with reference to FIG. 4. That is, an X-ray source 2 driven by the output of a high-voltage generator 1 and a detector 3 are arranged opposite to each other with an imaging area in between, and a subject P is placed within this imaging area. Here, the detector 3 is connected to a reference detector D (3to) arranged so that the X-ray bus does not pass through the imaging area, that is, the X-ray beam does not pass through the subject P. It consists of a group of data collection detectors De line to DeLN arranged to pass through.

For example, by rotating the pair of X-rays M2 and detector 3 while maintaining a facing relationship, projection data based on transmitted X-rays from multiple directions to the subject P can be transmitted to the detector group D e-rays.
= D etNs and e.g. I/V converter 4. Integrator 5
．． The data is collected by a data acquisition unit DAS having a multiplexer 6, an A/D converter 7, etc.
et] ~ DetN and the variations in the characteristics of the data acquisition unit DAS, etc., and the processed data is sent to the reconstruction unit 9 where reconstruction processing is performed to obtain a slice image and displayed on the monitor 10. ing.

With such a configuration, reference correction can be performed to cancel fluctuations in acquired data due to changes in X-ray intensity and obtain an image with reduced artifacts.

Reference correction will be explained below. That is,
Reference correction is performed using the reference detector D in Fig. 4.
et□ and the corresponding elements of the data acquisition unit DAS to which the output of this reference detector DetO is derived (1/V converter 4. Integrator 5. Multiplexer 6, A/D converter 7)
This is carried out in the preprocessing section 8, and its principle will be explained with reference to FIGS. 5 and 6.

That is, as shown in Figure 5, in the X-ray system,
X-rays with an intensity of X are emitted from the radiation source 1, transmit through the subject P, weaken to the intensity of Xl', and become transmitted X-rays, and then transmitted to the detector D.
Enter the e line. The output of the data acquisition unit DAS is an A/D converted signal corresponding to the transmitted X-ray intensity Xl', and this A/D converted signal is used for preprocessing and reconstruction. In this case, since the X-ray intensity X is constantly changing, it is necessary to correct its influence.

In other words, the data required to reconstruct the X-ray CT scanner device is Xi'/X, so in order to realize this,
In the data processing unit DAS, the data collection detector group D
The A/D conversion output (Xi') of the e-line -D etN is converted to the A/D conversion output (X) of the reference detector Det□.
Divide by. This allows data fluctuations due to changes in X-ray intensity to be canceled out. In addition, in actual data collection, as shown in Figure 6, a certain period (integration time ΔT) is required to measure the data x, D
Data X from eto and data collection detector group De
The data XI' from the line to DetN is the average value of the X-ray intensity and the transmitted X-ray intensity that varied during this period.

Here, it will be explained that there are differences in the results of reference correction between a system using pulsed X-rays and a system using continuous X-rays. First, fluctuations in X-ray intensity will be considered with attention to the operation of the high-pressure generator 1. That is, the output voltage of the high voltage generator 1, that is, the tube voltage, fluctuates and ripples at a high frequency during the data collection period, whereas the tube current fluctuates slowly. In a system using pulsed X-rays, as shown in FIG. Since the correction calculation Xi'/X is performed using the output of DaatO and the output of the data collection detector group De line to DctN at the same timing, accurate correction results can be obtained.

Therefore, fluctuations in acquired data due to changes in X-ray intensity are canceled out, and an image with reduced artifacts can be obtained.

On the other hand, in a system using continuous X-rays, as shown in Fig. 8, the integration time ΔT is
This is common to each channel of the data collection detector groups Det1 to DetN, but their timings are shifted by a time d.

Therefore, since the correction calculation Xi'/X is performed on the output of Det(, and the output of the data collection detector group Det1 to DotN at different timings, the correction result becomes inaccurate. (In particular, Xl'/X and
N'/X and Teha thick (different).

Therefore, fluctuations in collected data due to changes in X-ray intensity cannot be accurately canceled out, resulting in images with artifacts.

(Problem to be Solved by the Invention) In this way, in the conventional technology, especially when using continuous X-rays, correction calculations are performed without using data that follows the fluctuating X-ray intensity. There is a problem in that it is not possible to accurately cancel out fluctuations in collected data due to changes in the image quality, resulting in images with artifacts.

Therefore, an object of the present invention is to perform reference correction calculations using data that follows the fluctuating X-ray intensity, thereby accurately canceling fluctuations in collected data due to changes in X-ray intensity, and creating images with reduced artifacts. An object of the present invention is to provide an XICT scanner device that can obtain the following information.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a structure in which the following means are taken to solve the above problems and achieve the objects.

That is, in the present invention, an X-ray source and a group of detectors are arranged opposite to each other through an imaging area, and a subject placed in the imaging area is exposed to radiation from the X-ray source and transmitted from multiple directions. In an X-ray CT scanner device, transmitted X-rays are detected by the detector group, and the detected signals are passed through a data acquisition section and a preprocessing section, and then subjected to reconstruction processing in a reconstruction section. a reference detector is provided on a bus that does not have a reference detector, and means for monitoring the output voltage of a high voltage generator for driving the X-ray source is provided, and the detector group A configuration in which correction data for each channel is calculated and reference correction is performed in the preprocessing section using the calculated value, or an output voltage and an output voltage of a high voltage generator that drives the X-ray source are calculated. A means for monitoring is provided, and correction data for each channel of the detector group is calculated based on the voltage monitor output and current monitor output by this means, and reference correction is performed in the preprocessing section using the calculated value. The structure is such that it can be carried out.

(Function) According to such a configuration, reference correction calculation is performed using X-ray intensity data that does not pass through the object and follows the varying X-ray intensity, whether it is pulsed X-ray or continuous X-ray. Therefore, fluctuations in acquired data due to changes in X-ray intensity can be accurately canceled out, and images with reduced artifacts can be obtained.

(Embodiment) An embodiment of the X-ray CT scanner device according to the present invention will be described below with reference to FIG. 1, in which the same parts as in FIG. 4 are denoted by the same reference numerals. In this embodiment, a voltage transformer 11 is provided on the line between the high voltage generator 1 and the X-ray source 2.
1 is led to the voltmeter 12, where the tube voltage detection signal is sampled at a period of ΔT/(N+1), and the sampling data is digitized by the A/D converter 13, and the result is as shown in FIG. is introduced into a preprocessing section 8' having a predetermined calculation procedure. This preprocessing unit 8' corrects the A/D conversion output (X) of the reference detector Det□ using the sampling tube voltage signal that reflects the X-ray intensity fluctuation, and performs the reference correction calculation on the We are trying to do this using data that follows.

Hereinafter, a specific correction procedure will be explained in detail. In other words, as mentioned earlier, rapid fluctuations in X-ray intensity are mainly caused by
This is due to changes in the voltage supplied to the line tube. and,
Measuring voltage is much easier than measuring X-rays, and can be measured one after another in a much shorter time than the integration time ΔT. That is, the tube voltage, which is the output voltage of the high voltage generator 1, can be monitored by the voltage transformer 1 and the voltmeter 12 in a sampling time that is much longer than the integration time ΔT.

Now, assuming that the X-ray radiation, tube voltage, X-ray intensity, and detector output are at the timing shown in FIG. 3, each data collection period 1o, 11. ..., the measured value of the tube voltage at IN is as follows. However, in Figure 3, N
−6, and generally ΔT≦(N+1)d, m−4
It is.

The measured value of the tube voltage corresponding to the period Io is vo,...
The measured value of the tube voltage corresponding to the period of Vm-1■ is vl
,..., the ill constant value of the tube voltage corresponding to the period of VlIN is VN,..., Vm+N-1 Here, since the change in the tube current is gradual, the current can be kept constant here, and under this condition Below, measure the X-ray intensity at voltage V,
Let this be p (v). Furthermore, the ratio of P (v) at the reference voltage V to p (v) at the voltage V is defined as a function Qv (V).

Qv (V)-P (Vn /P (v)Qv
(V) can generally be approximated with sufficient accuracy by a polynomial (l
1-V/v l=Q, because the fluctuation is on the order of 01. ). Let this polynomial be Rv (V).

However, the system is VT-for example 100KV.

Assuming that the voltage can be set to 3g class such as 120KV and 140KV, polynomials as many as the number of voltage ratings are prepared in advance.

Therefore, the average voltage V corresponding to the period IO. becomes as follows.

Similarly, the average voltage V1 corresponding to period 11 is as follows.

Therefore, the average intensity of X-rays that do not pass through the subject during period IO can be calculated from the output of DetO. Assuming that this is Xo, the X-ray intensity X1 that does not pass through the subject during period 11 is as follows.

Xl ”1X(1-Rv (Vl) /Rv (Vo
) In this way, for each detector De line, the X-ray intensity X1 that does not pass through the object at its unique integration time 11, that is, the reference data, can be calculated, and using this reference data XI, the reference correction is performed as follows. Do the following.

(Dell's A/D conversion output) /Xi As a result of this correction, data independent of X-ray intensity is given to the reconstruction unit, and an image with reduced artifacts is generated.

The arithmetic procedure described above is performed by the preprocessing section 8 as shown in FIG.
', the average value of the measured voltage vO+V1. . . . block 8A, and block 8B to obtain the X-ray intensity X1 that does not pass through the subject.

Block 8C for determining rl = DI /Xi, pi −
is executed in block 8D which determines the noogrl.

Next, another embodiment of the present invention will be described. In the above-mentioned embodiment, in order to obtain X-ray intensity data that does not pass through the object that follows the fluctuating X-ray intensity, the reference detector Det□ is provided on the bus that does not pass through the imaging area, and the output of the high-voltage generator 1 is A voltage transformer 11 as a means for monitoring voltage. Voltmeter 12
etc., but the reference detector D et
(Without providing a means for monitoring the output voltage, a means for monitoring the output current, such as a current transformer, a voltmeter, etc., is provided,
Correction data can be calculated using the voltage monitor output and the current monitor output.

The X-ray intensity at voltage V when the current value is a (a is assumed to be constant) is measured in advance, and this is defined as P (v).

Data VO+ measured by a voltmeter during sample period d
``1 + ... Data measured by the ammeter in the sample period d AO + A1 r ... From this, is obtained, and the data X1 of the X-ray intensity that does not pass through the object is calculated using the following formula.

Xi −P (Vi) ・A1 /a The present invention is not limited to the above embodiments, but can be implemented with various modifications without departing from the gist of the present invention.

[Effects of the Invention] As described above, in the present invention, a reference detector is provided on a path that does not pass through the imaging area, and a means for monitoring the output voltage of the high voltage generator that drives the X-ray source is provided, and the reference detector A configuration in which correction data for each channel of the detector group is calculated based on the output of Means for monitoring the output voltage and output voltage of a high-voltage generator that drives the radiation source is provided, and correction data for each channel of the detector group is calculated based on the voltage monitor output and current monitor output by this means. , by using a configuration in which reference correction is performed in the preprocessing section using the calculated value,
Pulsed X-ray.

Regardless of the type of continuous X-ray, reference correction calculations can be performed using X-ray intensity data that does not pass through the subject and follows the fluctuating X-ray intensity. Fluctuations can be accurately canceled and images with reduced artifacts can be obtained.

Therefore, according to the present invention, reference correction calculations are performed using data that follows changing X-ray intensity, thereby accurately canceling fluctuations in acquired data due to changes in X-ray intensity, and producing images with reduced artifacts. It is possible to provide an XnCT scanner device that makes it possible to obtain the following.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of an X-ray CT scanner device according to the present invention, FIGS. 2 and 3 are diagrams showing the operation of the same embodiment, and FIG. 4 is a diagram showing a conventional example. Figures 5 and 6 are diagrams explaining the principle of reference correction, Figure 7 is a diagram explaining reference correction in a system using pulsed X-rays, and Figure 8 is a diagram explaining reference correction in a system using continuous X-rays. This is a diagram. DESCRIPTION OF SYMBOLS 1... High pressure generator, 2... X-ray source, 3... Detector, Dat□... Reference detector, Data,...
.... D OtN...detector group, DAS...data collection unit, 8'...preprocessing unit, 9...reconstruction unit, 10...
monitor. Applicant's Representative Patent Attorney Takehiko Suzue 1st Ward, Rehobe Hez 2nd Ward, Figure 3, 4th Ward, Figure 6, Figure 7, Figure 8

Claims (2)

[Claims] (1) An X-ray source and a group of detectors are arranged facing each other through an imaging area, and transmitted X-rays are emitted from the X-ray source and transmitted from multiple directions for a subject placed in the imaging area. is detected by the detector group, and the detected signal is passed through a data acquisition unit and a preprocessing unit, and is subjected to reconstruction processing in a reconstruction unit.
In the X-ray CT scanner device, a reference detector is provided on a path that does not pass through the imaging area, and means for monitoring an output voltage of a high voltage generator that drives the X-ray source is provided, and the output of the reference detector and the means are provided. An X-ray CT scanner apparatus characterized in that correction data for each channel of the detector group is calculated based on a voltage monitor output from the detector group, and reference correction is performed in the preprocessing section using the calculated value. (2) An X-ray source and a group of detectors are arranged opposite to each other through an imaging area, and transmitted X-rays are transmitted from the X-ray source and transmitted from multiple directions for a subject placed in the imaging area. is detected by the detector group, and the detected signal is passed through a data acquisition unit and a preprocessing unit, and is subjected to reconstruction processing in a reconstruction unit.
In the X-ray CT scanner device, means for monitoring the output voltage and output voltage of the high-voltage generator that drives the X-ray source is provided, and each channel of the detector group is detected based on the voltage monitor output and current monitor output by this means. An X-ray CT scanner apparatus, characterized in that the preprocessing unit performs reference correction using the calculated values.