JPS5950683A - X-ray tv signal processor - Google Patents

Abstract

PURPOSE:To form a subtraction image of an X-ray TV signal with less effect of movement of a personnel to be inspected, by providing a mask image memory before and after the injection of a contrast medium with an image pickup tube output to be switched. CONSTITUTION:A switch 12 is connected to other terminal than those shown in Figure, and a mask image of an X-ray pulse train 1 is obtained at a memory 16. Then, the switch 12 is changed over to a live image memory 14 with a pulse 2 to obtan a live image and each picture element of the mask image is subtracted from that of the live image at a comparator 30. When the result is zero, it is taken that no contrast medium is injected and the live image by the pulse 2 is replaced into the mask image. Then, the similar operation is done with pulses 3-5. When the contrast medium is injected at a pulse 6, the added value of each picture element on the subtracted plane is discriminated as negative at the comparator 30 and no replacement of the mask images is performed. The subtraction image obtained at succeeding pulse trains taken the image just before the application of contrast medium as the mask image, allowing to reduce the effect of movement of a personnel to be inspected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray TV signal processing device having a subtraction function.

X-ray TV equipment subtracts images before and after contrast agent injection,
The so-called subtraction method, which displays a difference image using only a contrast agent, has been frequently used in recent years. As the image before this contrast agent injection, an image (mask image) taken at a fixed time in a series of X-ray sequences was used, so from that point on, the contrast agent actually begins to flow in. The patient's movements during the same period of time are displayed as motion artifacts, superimposed on the contrast agent-only image.
This made reading the image difficult. For this reason, a subtraction image with fewer motion artifacts was desired. Conventionally, processing to obtain such an image was performed manually by recording and reproducing on a VTR, 5VDR, etc., which caused a lot of noise and was troublesome.

The purpose of the present invention is to automatically obtain an image immediately before contrast medium inflow, which is considered to be the best mask image, regardless of whether the subject moves or not after contrast medium injection, and to create a subtraction image with few motion artifacts. An object of the present invention is to provide an X-ray TV signal processing device that can be obtained.

The subject matter and embodiments of the invention are explained with reference to the drawings.

FIG. 1 shows an example of currently used subtraction processing. The image obtained with the first pulse 1 of a series of X-ray pulse trains is fixed as the image before contrast agent inflow (mask image) and stored in the image memory, and the image obtained with the next pulse (live image) is The mask image is subtracted from the image, the image is appropriately emphasized, and then displayed. For example, assume that a contrast medium flows in at the time of the sixth pulse 6. In this case, if the subject moves at the 6th note "i!" (right image in Figure 2), a motion artifact (
(right side image in Figure 2) will appear, and this will also be displayed overlapping the images of the contrast medium from the 6th and subsequent shots. To remove such motion artifacts, specifically:
It is proposed that the image immediately before the contrast agent flows into the mask image may be used.

According to the present invention, detecting the point in time when the contrast medium has flowed in,
If within that point, replace the live image with a mask image,
Once that point is detected, the replacement is interrupted and a difference image immediately before that point is obtained.

A schematic block diagram illustrating one embodiment of the invention is shown in FIG. 10 is an image pickup tube, 12 is a switch, 14 is a live image memory, 16 is a mask image memory, 18 is a subtraction circuit that subtracts mask image data from live image data, 20 is an AND circuit, 22 is a Fi address comparison circuit, and 24 is a 28 is an adder circuit, 3o is a comparator, 32 is a preset,
34 is an OR circuit, which controls the write operation of the mask image memory 16 based on the output of the comparison circuit 3o. 36 is a monitor. 26 is a circuit that selects an arbitrary region of the image subtracted by the subtraction circuit I8, and the preset 24 has the address set in advance to limit the region into which the contrast agent will flow. . The subtracted pixels in the arbitrary area of the image are averaged by the adding circuit 28.

At the time when no contrast medium is flowing in, the added value (average value) is zero. Even if there is a motion artifact, as shown in Figure 3, images of the same size and opposite signs are produced on both edges, so the average of each pixel is zero. Next, when a contrast agent flows in, the contrast agent has high X-ray absorption, so the video level becomes low, and when the mask image is subtracted from the live image, a negative value is detected. In other words,
The summed value (average value) of each pixel in the subtracted image is always negative. Therefore, the comparator 30 determines whether the added value of the pixel in the subtracted image is zero or negative. Based on the output, an image at the time of contrast medium inflow can be detected.

Referring to FIG. 1, switch 12 is connected to a different terminal than shown, and a mask image is obtained in memory 16 with pulse 1. Next, after pulse 2, the switch 12 is switched to obtain a live image in the memory 14, and pulse 2
The mask image is subtracted from the live image by , the added value of each pixel is determined, and a zero/negative determination is made. If it is detected as zero by the output of the comparator 30, it means that no contrast agent has flowed in. As a result, a write signal is output from the OR circuit 34, and the live image based on pulse 2 is replaced with a mask image. The same operation occurs for the live images of pulses 3 to 5, and after pulse 5 ends, the live image data of pulse 5 is stored in the mask image memory 16.
It is written from 4 to 1 and stored. If the contrast agent flows in with the X-ray pulse 6, the sum value of each pixel of the subtracted image is detected as negative by the comparator 30. Due to this detection, the write signal is not output from the OR circuit 34, and the above-mentioned mask image is not replaced, and the subtraction image obtained with the subsequent pulse train uses the image immediately before the contrast medium inflow as the mask image. , motion artifacts due to the movement of the subject up to the inflow of the contrast agent are removed.

In reality, zero-negative determination is sensitive to noise, so a certain level is set, this is set in the preset 32, a noise margin is taken, and when that level is exceeded, it is detected that the contrast agent has flowed. Also, when taking the sum of each pixel of the subtracted image, rather than taking the average of the entire screen, is it better to limit it to the area where the contrast agent will flow in, or to use information about the contrast agent inflow? Since it appears prominently, it becomes resistant to noise. At this time, if you specify a narrow area, as shown in Figure 4,
This means that only one side of the motion artifact will be adopted, resulting in a deviation from zero in the addition*W equation. Therefore, it is necessary to take such a case into account and set the level of the zero-negative determination described above.

It was explained that the contrast agent image is negative on the upper side.
It can also be made positive by subtraction, in which case the determination will be zero pressure.

Another embodiment of the present invention is constructed by means of switching the data in the mask image memory to the minuend side instead of rewriting data from the live image memory to the mask image memory. Other modifications, such as installing buffer memory, are also possible. Furthermore, instead of setting a region of interest and taking the average, each pixel of the image may be multiplied by a weight and then added.

When adding pixels that are 1, it is not necessary to add all the pixels in the area selected by the circuit 26, but it is also possible to sample the pixels appropriately and add them.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a fixed mask image according to a conventional example, FIG. 2 is a display image according to a conventional example, FIG. 3 is an explanatory diagram of the operation according to the present invention, and FIG. 4 is a subtraction FIG. 5 is a block diagram showing an embodiment of the present invention. 14 is a live image memory, 16 is a mask image memory, 18 is a subtraction circuit, 2G is a circuit for selecting an arbitrary area of the subtraction image,
28 is an adder circuit, and 30 is a comparator.

Claims (1)

[Scope of Claims] 2. In an X-ray TV signal processing system having a subtraction function, a mask image memory before contrast agent injection, a live image memory after injection, and a circuit for subtracting mask image data from live image data. , in this case the subtracted image data is
On the one hand, it is transmitted to the monitor, and on the other hand, it is input to a circuit where that arbitrary region is selected, a circuit that adds each pixel of the region image, a circuit that compares the added value with a preset value, and a comparison. An X-ray TV signal processing device comprising a circuit that controls writing of data from a live image memory to a mask image memory based on an output signal of the circuit. 1. The X-ray TV signal processing device according to claim 1, characterized in that instead of writing data from the live image memory to the mask image memory, there is a means for switching the data in the mask image memory to the minuend side. .