JPS59122295A - Digital subtraction system - Google Patents

Abstract

PURPOSE:To obtain a clear picture having reduced influence of noise even if the reading-out speed from an image pickup tube is reduced to narrow a frequency band by sampling a reading signal and A/D converting the sampled signal during the interruption time of reading beams from the image pickup tube. CONSTITUTION:When the video signal reading-out speed from the image pickup tube 14 is set up to 1/2 the usual speed, the time scanning an area corresponding to one picture element on the target surface of the image pickup tube is doubled and the size of a video signal from the image pickup tube is reduced by about a half. Therefore, the reading-out beam from the image pickup tube is interrupted by a half of one picture element period during the time of horizontal scanning and reading is executed only at the remaining half period. Consequently, the period reading out a video signal from an area corresponding to one picture element is the same as the usual speed and the video signal is almost the same as the video signal read out at a normal speed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital subtraction system for an X-ray TV apparatus that can display differential images before and after injection of a contrast medium.

In the digital subtraction system, in order to improve the signal-to-shape ratio of the TV left camera video signal, a method was adopted in which the readout speed from the image pickup tube was lowered, the frequency bandwidth of the video signal was narrowed, and a stain filter was inserted. . However, in this case, when the read speed decreases, the absolute value of the signal current entering the preamplifier also decreases, which causes a problem in that the S/- ratio decreases by this amount.

An object of the present invention is to reduce the readout speed from the image pickup tube and narrow the frequency band of the video signal, while improving the S//N ratio and preventing a decrease in the output of the video signal.
Digital subtraction that allows you to obtain good subtraction images with less influence of V-system noise.
The goal is to provide a system.

The purpose of this is to reduce the readout speed of the video signal from the image pickup tube and time-divide the time width for writing each pixel into the frame memory into the signal readout time and the time to cut off the readout beam of the image pickup tube. This is achieved by sampling the read signal and performing A/D conversion within the same period.

In other words, the video signal readout speed from the image pickup tube is changed to 1 when scanning an area equivalent to 1 pixel, and the remaining 4 The video processor is controlled to sample the video signal of the pixel and perform A/D conversion during the period in which the video signal is output within one pixel period.

Next, preferred embodiments of the present invention will be described with reference to the drawings.

In Figure 1, the left side shows the waveforms of each signal when the video signal is read out at normal speed, and the right side shows the waveforms of the same signals when the speed is set to /2. It shows. FIG. 2 is an overall block diagram of the digital subtraction system with the flow of control signals according to the present invention added.

In Figure 1, (a) is an output waveform diagram of the image pickup tube, (b)
shows an example of the pixel configuration (image matrix) of the frame memory, and the shaded area indicates that horizontal scanning is in progress. (c
) is a horizontal deflection signal, (d) is a cathode blanking signal of the image pickup tube, (e) is a U sample and hold signal, and (f) is a conversion timing signal. Also, in Figure 2, 11
is an X-ray tube, 12 is a subject, 13 is an image intensifier (1,]), 14 is an image pickup tube, 15 is a camera control unit, 16 is a video processor section, 17
is a system controller, 18 is a logarithmic converter, 19 is a sample and hold circuit, 20 is an N converter, 21 is an arithmetic unit, 22 and 23 are frame memories, 24 is an enhancement circuit, 25 is a D/A converter, 26 is a monitor TV.

In the case of normal speed, as shown on the left side of FIG. 1, the cathode blanking signal (d) does not operate at all during horizontal scanning and is at H level. On the other hand, in the tree invention, as shown on the right side, when reading at a speed of 4, the horizontal deflection signal (C) rises at a slope of 1/. Therefore, the time it takes to scan an area equivalent to one pixel of the image matrix (b) on the target surface of the image pickup tube is doubled, so the video signal (a) from the image pickup tube is Bo1/
becomes the size of Therefore, during the horizontal scanning period, the readout beam of the image pickup tube is blocked for only 1 period out of 1 pixel period, and readout is performed only for the remaining 1/1 period. .

As a result, the period for reading out the video signal from the area equivalent to one pixel is the same as in the case of normal speed, so the video signal (
As shown by the dotted line, a) is obtained as a video signal of approximately the same size as readout at normal speed. However, during the blanking period, that is, at the L level of signal (d), the video signal is obtained. Therefore, the sampling of video data and the conversion of N must be performed in synchronization with the blanking signal (d), as shown in signals (e) and (f). This is controlled by a video processor section 16, ie, a system controller 7, as shown in FIG.

In the illustrated embodiment of FIG. 1, the blanking period is set to % for reading at a false speed, but the division ratio is not necessarily limited to this.

According to the present invention, the charge on the target of the image pickup tube is intermittently read out as a signal current, but if residual charge is generated due to this, the diameter of the electron beam is increased to the minimum necessary range. do.

[Brief explanation of drawings]

FIG. 1 is a time chart showing one embodiment of the present invention, and FIG. 2 is an overall block diagram showing an example of control according to the present invention. (a) is a video signal, (b) is an image matrix, (C) is a horizontal deflection signal, (d) is a cathode blanking signal,
(e) is sample & hold signal, (f) is milk [F]
This is a conversion timing signal. Figure 1 1 (1-1 503-

Claims (1)

[Claims] The video signal readout speed from the image pickup tube is reduced, and the time width for writing each pixel into the frame memory is time-divided into the signal readout time and the time for cutting off the readout beam of the image pickup tube.
During the cut-off time, sample the read signal and
A digital subtraction system characterized by D conversion.