JPH03258249A - X-ray ct apparatus - Google Patents

Abstract

PURPOSE:To obtain the title apparatus capable of preventing an increase in a reconstituting time by mounting a means for collecting X-ray data cut off according to the sampling frequency determined by a sampling determining means. CONSTITUTION:When X-ray data is detected by a detector 1, the X-ray data is sent to a filter circuit 3 and a scanning condition is also applied to a scanning control part 9 from a reconstitution apparatus 7 and sampling frequency is determined. Cut-off frequency is guided according to the sampling frequency and a sampling signal 101 is outputted to an ADC 5 from the scanning control part 9 and, at the same time, a selection signal 103 selecting the cut-off frequency is outputted to the filter circuit 3 to determine the cut-off frequency and analogue X-ray data is cut off to be outputted to the ADC 5 and analogue data is sampled to be converted to digital data and a definite number of X-ray data are collected to reconstitute a tomographic image. As a result, a data bundling time becomes unnecessary and, therefore, the time reconstituting the tomographic image can be shortend.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention (Industrial Application Field) The present invention relates to an xmcT device that can change the sampling frequency of X-ray data according to the X-ray scan time.

(Prior Art) In an X[CT apparatus, X-ray data obtained by imaging a subject is collected by a data collection system. The collected data is then reconstructed to obtain a tomographic image of the subject.

A low pass filter is used in the data acquisition system, and the cutoff frequency is set by this filter. Then, X-ray data is collected according to a sampling frequency determined based on the cutoff frequency.

Conventionally, the cutoff frequency is fixed at a constant frequency, so the sampling frequency is also fixed. Because X-ray data is collected at regular intervals regardless of the X-ray scan time, if the scan time is long, the number of collected data (hereinafter referred to as the number of views) will increase in proportion to the time. Stop. As a result, when reconstructing a tomographic image, an averaging process is performed to bundle these data as preprocessing.

(Problems to be Solved by the Invention) As described above, time is wasted by averaging a large amount of data, and as a result, there is a drawback that it takes time to reconstruct a tomographic image.

The present invention was made in view of the conventional circumstances, and its purpose is to increase the number of collected data by changing the cutoff frequency according to the X-ray scan time. X-ray C that can be kept constant regardless of the ray scan time and prevent increase in reconstruction time
The objective is to provide a T device.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a sampling method that determines the sampling frequency of X-ray data detected by an X-ray detector according to the X-ray scan time. a determining means; a filter circuit capable of selecting a plurality of types of cutoff frequencies for the X-ray data; a selecting means for selecting a cutoff frequency based on the sampling frequency determined by the sampling determining means from the filter circuit; According to the sampling frequency determined by the determining means, the pre-gc! and a collection means for collecting X-ray data.

(Operation) In the above configuration, the present invention determines the sampling frequency of X-ray data detected by the X-ray detector.

A cutoff frequency based on the determined sampling frequency is selected from the filter circuit. This filter circuit allows selection of a plurality of types of cutoff frequencies, and sets the selected cutoff frequency. Then, X-ray data cut off by the set cutoff frequency is collected at a constant number of views, which is independent of the scan time, according to the sampling frequency. Furthermore, the collected data is reconstructed to obtain tomographic images.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the X&lCT apparatus of the present invention.

In the figure, a detector 1 detects X-ray data obtained by X-ray imaging of a subject (not shown) and sends the X-ray data to a filter circuit 3.

The filter circuit 3 receives X-ray data and sets the cutoff frequency of this data.

This filter circuit 3 is capable of selecting a plurality of types of cutoff frequencies as shown in FIG. 2, and has a function of switching to a cutoff frequency according to the X-ray scanning time. Further, the filter circuit 3 converts the cut-off analog X-ray data into an ADC (Analog to D).
ldigital Converter) 5.

The ADC 5 samples the analog X-ray data output from the filter circuit 3 according to a sampling frequency determined according to the scan time.

Further, the ADC 5 converts analog data into digital data and collects a certain number of data (hereinafter referred to as the number of views). Furthermore, the ADC 5 provides the collected X-ray data to the reconstruction device 7.

The reconstruction device 7 receives the collected data given from the ADC 5 and reconstructs the photographed tomographic image. Furthermore, the reconstruction device 7 provides scan conditions such as scan time to the scan control section 9.

The scan control section 9 determines a sampling frequency according to the scan time instructed by the reconstruction device 7, and supplies this frequency to the ADC 5. Further, the scan control unit 9 derives a cutoff frequency from the determined sampling frequency, and selects the derived frequency from a plurality of types of cutoff frequencies of the filter circuit 3.

One embodiment of the present invention is thus constructed, and will now be described in detail.

When X-ray data is detected by the detector 1, this X-ray data is sent to the filter circuit 3.

At this time, the reconstruction device 7 provides scan conditions such as scan time to the scan control unit 9.

The scan control unit 9 given the scan conditions determines the sampling frequency according to the scan time.

Furthermore, a cutoff frequency is derived based on the determined sampling frequency.

Once the sampling frequency and cutoff frequency are determined, the scan control unit 9 outputs a sampling signal 101 instructing the sampling frequency to the ADC 5. At the same time, a selection signal 103 for selecting a cutoff frequency is output to the filter circuit.

In the filter circuit 3, a cutoff frequency selected from a plurality of types of cutoff frequencies by the selection signal 103 is set. As a result, the analog X-ray data is cut off by this cutoff frequency, and the AD
Output to C5.

Analog data input to the ADC 5 is sampled at a sampling frequency indicated by a sampling signal 101. Furthermore, the sampled analog data is converted to digital data. This allows a fixed number of X-ray data to be collected regardless of the scan time.

The collected X-ray data is output to the reconstruction device 7, and the reconstruction device 7 reconstructs a tomographic image.

Here, the operation of the scan control section 9 will be specifically explained.

For example, regardless of scan time, always set the number of views to 1.
Let us consider the case of 000 views. When the scan time is 1 second, the sampling frequency is set to IKHz, and the cutoff frequency at this time is selected to be a frequency smaller than 500 Hz according to the sampling theorem.

When the scan time is 2 seconds, the number of views is 1000 views/2S, the sampling frequency is determined to be 500 Hz, and a frequency smaller than 250 Hz is selected as the cutoff frequency.

Similarly, when the scan time is 4 seconds, it is 1000 views/4S, the sampling frequency is 250 Hz, and the cutoff frequency is selected to be a frequency smaller than 125 Hz.

In this way, since the sampling frequency is determined according to the scan time, a constant number of views of X-ray data are always collected.

Note that the filter circuit is not limited to that shown in FIG.

[Effects of the Invention] As explained above, in the X-ray CT apparatus according to the present invention, the sampling frequency of X-ray data is switched according to the X-ray scan time, so the number of collected data can be reduced. The number is constant regardless of the scan time. This eliminates the need for time to bundle data as pre-processing, so it is possible to shorten the time to reconstruct a tomographic image.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is a circuit diagram showing an example of a filter circuit. 3... Filter circuit 5-ADC (^nalogue to Digital
Converter) 7... Reconfiguration device 9... Scan control unit

Claims (1)

[Scope of Claims] Sampling determining means for determining a sampling frequency of X-ray data detected by an X-ray detector according to an X-ray scan time, and a filter capable of selecting a plurality of types of cutoff frequencies of the X-ray data. circuit; selection means for selecting a cutoff frequency based on the sampling frequency determined by the sampling determination means from the filter circuit; An X-ray CT apparatus comprising a collection means for collecting the X-ray data.