JPH01190337A - X-ray energy difference imaging apparatus - Google Patents

Abstract

PURPOSE:To obtain two images by monochromatic X-rays different in energy within a short time without moving an object, by providing a function as an X-ray shutter to two crystal type spectroscopes by changing the relation between the angles of X-ray diffraction of two crystal type spectroscopes. CONSTITUTION:Two crystal type spectroscopes are used to set spectral diffraction crystals 21, 22 by crystal fine adjustment mechanisms 23, 24 so that the crystal lattice surfaces of said crystals satisfy a Bragg condition not only between continuous X-rays 26 and monochromatic X-rays 27 but also between monochromatic X-rays 27 and monochromatic X-rays by objective monochromatic X-ray energy and an object 13 is irradiated with monochromatic X-rays of about iodine absorption terminal energy and, in the same way, said lattice surfaces are set so as not to satisfy the above mentioned Bragg condition and the irradiation of the object with monochromatic X-rays is prevented and a function as an X-ray shutter is provided to two crystal type spectroscopes. Then, corresponding to the difference between the energies of monochromatic X-rays incident to X-rays II14, the position of a plane mirror is changed over between plane mirrors 4-1, 4-2 by a drive mechanism 12 and two images by monochromatic X-rays are brought to an accumulation state on the photoelectric surface of a imaging tube as charge distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for performing angiography using an energy difference method, and particularly to an energy difference imaging apparatus suitable for reticular arteriography, which is effective in diagnosing heart disease. .

[Prior art] In order to diagnose ischemic heart disease represented by myocardial infarction,
Techniques for imaging the site and degree of stenosis of the LD artery are extremely important, and the development of a less invasive intravenous injection contrast method is desired. For intravenous injection imaging of a complete artery,
The ability to detect dilute iodine contrast agents with high sensitivity, and
It is necessary to take images in a short period of time to eliminate image blurring due to pulsation.

As described in Japanese Patent Application Laid-Open No. 60-249040, conventional equipment simultaneously irradiates fan beam-shaped monochromatic X-rays with different energies to different parts of the subject, and converts each X-ray image into a single X-ray detection system. It was a device that took pictures with a device. This apparatus uses fan-beam X-rays, and scans by moving the subject in order to image the entire target region within the subject.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, when two monochromatic X-ray images with different energies are taken, the time interval between the two images is determined by the difference in the position of the two types of fan beam X-rays in the object scanning direction and the object scanning speed. The difference in position between fan-beam X-rays has a finite value, so in order to capture two images at a time interval where the heart beat can be ignored, the subject must be moved at a very high speed. The above-mentioned conventional technology has the problem that it cannot be used.

An object of the present invention is to provide an apparatus that can take two images using monochromatic X-rays with different energies in a short time when the heartbeat can be ignored without moving the subject.

[Means for solving problems]

The above purpose is achieved by sequentially using a cone-shaped monochromatic X-ray beam that can irradiate the entire target area of the subject, an X-ray image intensifier (hereinafter abbreviated as X-ray II) and a TV camera as detectors. , is achieved by capturing monochromatic X-ray images with different X-ray energies at high speed.

[Effect]

The high-speed sequential imaging method will be explained based on the time chart shown in FIG. In the figure, (1) represents the vertical synchronization signal of the TV camera. (2) is a monochromatic X obtained by a spectrometer
represents the energy switching of a line, in this case the switching between energy above and below the absorption edge energy of iodine in the contrast agent. (3) shows the operation when a two-crystal type spectrometer is used as the spectrometer, and by adjusting the X-ray diffraction conditions between the two crystals, it is given the function of an xi ray shutter. (4) represents the position of the plane mirror in the optical system that forms the output image of X-ray II on the TV camera. Here, when the plane mirror is at position A, as shown in FIG. 3, the X-ray II
The output image is formed on the imaging plane 8-1. In addition, when the plane mirror is at position B, the output image of X-ray II is focused on the imaging plane 8-2, as shown in FIG. 5, and when it is at the plane mirror position C,
The output image of X-ray II is formed at a position other than the imaging planes 8-1 and 8-2. (5) represents image readout by electron beam scanning, and in FIGS. 3 and 5, only the image forming planes 8-1 and 8-2 of the electron beam scanning plane 7 are read out simultaneously. .

In the time chart of FIG. 6, from one hour t1 to t2, the X-ray shutter is opened and the subject is irradiated with X-rays in a state where the monochromatic X-ray energy is lower than the absorption edge energy. This X-ray image is detected by the X-ray technician I, and is focused at 8-1 on the imaging plane in the imaging plane of the image pickup tube in FIG. 3 by the plane mirror position A. Next, between time t2 and t3, the X-ray shutter is closed, X-ray irradiation is stopped, and the monochromatic X-ray energy is brought into a state higher than the absorption edge energy by the spectrometer. The plane mirror positions are set as position C, and imaging boxes 8-1 and 8
-2 on top, X! It is assumed that the output image of II is not formed.

Between time t3 and t4, the X-ray shutter is opened and the subject is irradiated with X-rays while the monochromatic X-ray energy is higher than the absorption edge energy.

This xm image is detected by X-ray II, and is focused at 8-2 in the imaging plane of the imaging tube in FIG. 5 by the plane mirror position B. Between times t5 and t9, images on the imaging planes 8-1 and 8-2 in the imaging plane are read out by electron beam scanning.

In this way, two images can be captured at a time interval of (ta tl). Further, continuous imaging can be performed in which two energy images are taken as one unit, with time t1 to t7 being one cycle (corresponding to one frame).

By using a two-crystal spectrometer and changing the X-ray diffraction angle relationship between the two crystals, unit X-rays as diffracted X-rays can be emitted.
However, the X-rays scattered from the crystal for spectroscopy are always emitted at a constant rate. Utilizing this performance, by subtracting the captured image when diffracted X-rays are not emitted (X-ray shutter closed) from the captured image when diffracted X-rays are emitted (X-ray shutter open), Purely diffraction
An image can be obtained only by lines.

Next, an image processing method for removing the influence of the X1II afterimage from the captured image will be described. X-ray II has the afterglow characteristic shown in FIG. 9 due to the properties of the phosphors used in the X-ray input phosphor screen and the output phosphor screen of X-ray II. The figure shows the afterglow intensity after the X-ray input to the X-ray controller was stopped at time ○. Because of this afterglow, images taken before the previous time are mixed in as afterimages in each shot image. This afterimage is removed as follows.

First, the ratio of image components at each image capturing time included in each image signal obtained by continuous imaging and afterimage components from before each image capturing time will be explained below. The symbols used in the explanation are defined as follows.

Syl: To the signal component at the time of capturing the nth image m: Afterimage intensity of the image m images before each image capture At this time, the image component intensity and afterimage component intensity at the time of each image capture included in each image signal are as follows. It can be expressed as

Ru.

Here, Arn is obtained by measuring the afterglow characteristics of X-ray II shown in FIG. 9, and as shown in the figure, when the imaging time interval is t, the afterglow intensity at time mXt is Am
be equivalent to.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This embodiment is for performing angiography by injecting a contrast medium into a subject 13. Two images are taken using monochromatic X-rays with energy higher than the absorption edge energy of iodine in the contrast agent and monochromatic X-rays with lower energy. This is an energy difference imaging device that takes the difference between these images and depicts only a blood vessel image.

In the figure, 25 is an X-ray source, which is a synchrotron radiation generating device such as an electron storage device.

26 is a continuous X-ray as synchrotron radiation light.

A spectrometer that converts continuous X-rays into monochromatic X-rays uses a two-crystal type spectrometer consisting of spectroscopic crystals 21 and 22 and crystal fine movement mechanisms 23 and 24 that move them.

Here, the synchrotron radiation light is a fan-beam X-ray, and in order to ensure a sufficient X-ray irradiation area for the subject, the beam is expanded and used as a cone-shaped beam. In the figure, the crystal surface of the spectroscopic crystal 21 is cut out to be a plane non-parallel to the crystal lattice plane 29. Of the continuous X-rays 26 that are incident X-rays, only the monochromatic X-rays 27 with energy satisfying the Black condition are diffracted due to the angle θ formed between the incident X-rays and the crystal lattice plane 29, and at the angle θ with the crystal lattice plane. It is emitted. In this way, the glancing angle of the incident X-ray and the glancing angle of the outgoing X-ray with respect to the crystal lattice plane are equal.

However, since the surface of the spectroscopic crystal is non-parallel to the crystal lattice plane, the continuous X-rays 26, which are incident X-rays, are expanded in the vertical direction due to the geometrical relationship shown in FIG. It is reflected as a certain monochromatic X-ray 27. Furthermore, spectroscopic crystal 2
If the same thing as 21 is used as 2, the magnification will be squared, and a sufficient X-ray irradiation area can be secured for the subject.

In order to generate monochromatic X-rays around the absorption edge energy of iodine using a two-crystal type spectrometer, the crystal lattice planes of the spectroscopic crystals 21 and 22 are adjusted by the crystal fine movement mechanisms 23 and 24 to
Settings may be made between the continuous X-rays 26 and the monochromatic X-rays 27, and between the monochromatic X-rays 27 and the monochromatic X-rays 28 so that the desired monochromatic X-ray energy satisfies the Bragg condition. in this way,
By driving the crystal fine movement mechanisms 23 and 24, the subject 13 can be irradiated with monochromatic X-rays around the iodine absorption edge energy.

In addition, in order to have a function as an X-ray shutter using a two-crystal type spectrometer, the crystal lattice planes of the spectroscopic crystals 21 and 22 are adjusted to the continuous
6 and monochromatic X-rays 27, and between monochromatic X-rays 27 and single-image X-rays 28, settings may be made so that the target monochromatic X-ray energy does not satisfy the black condition. As a result, the object is no longer irradiated with monochromatic X-rays, and the two-crystal spectrometer functions as an X-ray shutter.

Here, if a piezo element is used to drive the crystal in the crystal fine movement mechanisms 23 and 24, high-speed energy switching and operation as a high-speed X-ray shutter become possible.

Next, the detector system will be explained. The detector system is
114, an optical system 10, and a TV camera 11. The X-ray image is converted into visible light by X-ray II,
Output from 1IAII. Here, corresponding to the two X-ray images of monochromatic X-rays before and after the iodine absorption edge energy incident on the X-ray II, the output images of the X-ray technician are sequentially placed as two images at different positions on the imaging surface of the TV camera. The image is formed using an optical system. A two-image photographing method using one TV camera will be described below.

In FIG. 2, visible light rays 2 emitted from an X-ray II output image 1 are converted into parallel light by a primary lens 3 in the optical system. This parallel light is θ1 with respect to the optical axis 9 of the primary lens.
It is reflected by a plane mirror 4-1 having an angle of 6-1
imaged as. Then, in the next X-ray image capturing corresponding to another monochromatic X-ray energy, as shown in FIG. The visible light emitted from the line II output image is reflected and condensed by the secondary lens 5 onto the imaging plane 8-2 in the electron beam scanning plane 7 on the TV camera imaging plane shown in FIG. The image is formed as image 6-2. In this way, the position of the plane mirror is adjusted between the plane mirror 4-1 and the plane mirror drive mechanism in the optical system 10 shown in FIG. By switching by 12, two images of monochromatic X-rays before and after the absorption edge energy of iodine can be stored as a charge distribution on the photocathode of the image pickup tube. In image readout, two images can be read out simultaneously by scanning the electron beam of the image pickup tube. Furthermore, if a piezo element is used as the plane mirror drive mechanism of the optical system to switch the position of the plane mirror, high-speed two-image photography becomes possible. In addition, the plane mirror drive mechanism moves the XmII output image to the imaging plane 8-
1 and 5, the plane mirror drive mechanism has a function as a high-speed optical shutter.

The apparatus shown in this embodiment is driven by the sequence controller 30 shown in FIG. 1 in accordance with the vertical synchronization signal of the TV camera, and takes two images using monochromatic X-rays before and after the iodine absorption edge energy. The driving sequence will be explained with reference to FIG. In the figure, (1) is T
V camera vertical synchronization signal, time t1 to t7 is 1
It is a frame. (2) represents monochromatic X-ray energy switching by a spectrometer, and the crystal microtremor mechanism 23 shown in FIG.
and 24 are driven to represent a state in which energy higher than the absorption edge energy is generated in iodine, or a state in which energy lower than the absorption edge energy is generated. (3) represents the operating state of the X-ray shutter; when it is open, the X-ray diffraction conditions are satisfied for a specific monochromatic X-ray energy between the two crystals of the two-crystal spectrometer, and monochromatic X-rays are It is emitted. Further, when it is closed, it means that the X-ray diffraction conditions are not satisfied between the two crystals, and no X-rays are emitted. (4
) represents the plane mirror position, that is, the imaging position of the X-ray II output image on the imaging tube. The plane mirror position A is a state in which the X-ray ■I output image is focused on the imaging plane 8-1 in the electron beam scanning plane in FIG. -2 represents the state where the image is formed. Position C is a state in which the X-ray II output image is formed at a position other than the imaging planes 8-1 and 8-2, and corresponds to a state in which the optical shutter is closed so that no image is input to the TV camera. . (5) represents image reading from the image pickup tube by electron beam scanning, and is a time chart in which only the image information of the imaging planes 8-1 and 8-2 in the electron beam scanning plane is read out. , between times t1 and t2, the X-ray shutter is opened and the subject is irradiated with X-rays in a state where the monochromatic X-ray energy is lower than the absorption edge energy of iodine. This X-ray image is detected by X-ray II, focused on the imaging plane 8-1 of the image pickup tube by the plane mirror position A, and accumulated as a charge distribution on the photoelectric film. Between time t2 and t3, energy switching is performed by the spectrometer. During this time, the X-ray shutter is closed, and the optical shutter is kept closed at the plane mirror position C so that the afterglow of XIII does not enter the TV camera. Between time t3 and t4, the X-ray shutter is opened and the subject is irradiated with X-rays in a state where the monochromatic X-ray energy is higher than the absorption edge energy of iodine. This X-ray image is detected by X-ray II, focused on the imaging plane 8-2 of the imaging tube by the plane mirror position B, and accumulated as a charge distribution on the photoelectric film. As a result, at time t5, two images before and after the absorption edge energy of iodine are accumulated as a charge distribution on the imaging planes 8-1 and 8-2 in the electron beam scanning plane. Here, the electron beam scanning of the image pickup tube is to sequentially scan the electron beam scanning surface shown in FIG. 3 from top to bottom in the horizontal direction one scanning line at a time, and up to 1 hour t5, The electron beam scan does not reach the imaging planes 8-1 and 8-2.

Between time t5 and t6, the image forming planes 8-1 and 8-2 are scanned by the electron beam, and the two images accumulated on the photoelectric film are simultaneously read out and sent to the image recording processing device 3 as image data.
to be recorded.

As a result of the above, two images of monochromatic X-rays before and after the absorption edge energy of iodine can be taken at a time interval of (t3 tl). This (t4-11) is 174 or less time compared to the time of one frame (tfut1). For example, if one frame is 33.3 milliseconds,
Two images can be captured at a time interval of about 8 milliseconds. Also,
Continuous photography is possible with one frame being one synchronization and two images being photographed as one unit.

The two images obtained here include image components due to scattered X-rays generated from the two-crystal spectrometer. remove this component,
A method of obtaining an image using purely monochromatic X-rays will be described below. For this purpose, in the two-crystal spectrometer, the crystal lattice planes of the spectroscopic crystals 21 and 22 must be aligned with the continuous X-ray 26 and the monochromatic
Settings are made such that the black condition is not satisfied for a specific monochromatic X-ray energy between the line 27 and the single X-ray 27 and the monochromatic X-ray 28, and an image is taken in this state.

This image is created only by X-rays scattered by the spectroscopic crystal, and by inputting this image into an image recording processing device and subtracting it from the two images created by monochromatic X-rays,
Two images are obtained using purely monochromatic X-rays.

The two images subjected to the above processing are then subjected to another image processing in the image recording processing device.

First, processing is performed to remove the influence of afterglow, but in this case two images are taken consecutively, and the image taken between time t1 and t2 is better than the image taken between time t3 and t4 (high energy image). It is sufficient to remove the afterimage component due to the afterimage of X-ray II (low energy image). FIG. 8 shows an image recording processing apparatus. The configuration of the afterimage removal processing section is shown. In the figure, 33 is an image memory that records one image, 34 is a subtracter that performs subtraction for each corresponding pixel in processing between two images, and 35 is a multiplier that multiplies all pixels of the image memory by a certain coefficient. 36 is a coefficient holding register that holds constant coefficients.

The coefficients held in the coefficient holding register are obtained by the following method. FIG. 9 shows the afterglow characteristics of X-ray II. On the horizontal axis, if the incident X-ray is stopped at a time of 0 milliseconds, the intensity of the output visible light image (the vertical axis is normalized with the intensity during X-ray irradiation as 1) will attenuate as shown in the figure. . In this example,
The imaging time interval between the two images is (ta-t□), which corresponds to m-t in the figure, and the afterglow intensity An at this time is
is the afterimage component of the low energy image mixed in the high energy image. Therefore, the coefficient value held in the coefficient holding register is m- corresponding to the time (ta tl).
This is the relative value Am of the afterglow intensity at time t, which is normalized by setting the intensity during X-ray irradiation to 1, and this Am is measured and stored in a coefficient holding register.

In the image processing process, first, image data of a low energy image is recorded in an image memory. Next, all pixels of this image data are multiplied by the coefficient Am of the coefficient holding register using a multiplier, and this result is compared with the image data of the input high energy image for each image and subtracted using a subtracter. By doing so, it is possible to remove the afterimage of the low energy image more than that of the high energy image.

After performing afterimage removal processing, by taking the difference between a high energy image and a low energy image that are not affected by afterimages,
The desired energy difference image is obtained.

Here, the monochromatic X-ray energies before and after the absorption edge energy of iodine are close to each other. For this reason, the X-ray absorption rate of living tissue other than the contrast agent hardly changes between these two energies, so the contrast of living tissue is almost the same between high-energy images and low-energy images. However, regarding the contrast agent, since the absorption edge energy is sandwiched between the iodine and the contrast agent, the contrast differs greatly between the two images. As a result, in the energy difference image, the image components of the living tissue are erased, and a high-contrast image containing only the blood vessel image is obtained. In addition, the shooting time interval (t3 tl
) can be set to a short time that the movement of living tissue can be ignored.
No artifacts occur in the energy difference image due to movement of the living tissue.

〔Effect of the invention〕

According to the present invention, it is possible to capture multiple images in a short time without being affected by the afterimage of X-ray II and the movement of the living body is negligible, and it is possible to take a plurality of images in a short period of time without being affected by the afterimage of X-ray II. This has the advantage that it is possible to obtain a high-contrast energy difference image without artifacts that occur as a result of .

[Brief explanation of the drawing]

Claims (1)

[Claims] 1. An X-ray image capturing apparatus, which includes an X-ray source, a means for changing X-ray energy, an X-ray shutter, an X-ray image intensifier, a TV camera, and an X-ray image intensifier. It consists of an optical system that focuses the output image of the shifter on the imaging surface of the TV camera, and by using a two-crystal spectrometer as a means to change the X-ray energy,
By changing the X-ray diffraction angle relationship between the two crystals, it functions as an X-ray shutter, and the output images of the X-ray image intensifier are sequentially focused on different positions on the imaging surface of the TV camera. An X-ray energy difference imaging device characterized by having an optical system that allows a TV camera to simultaneously capture a plurality of images. 2. The optical system includes an optical lens and a plane mirror, and by changing the reflection angle of visible light by the plane mirror, the T
The X-ray energy differential imaging device according to claim 1, characterized in that the imaging position on the imaging surface of the V camera is changed. 3. The optical system includes an optical lens and a plane aperture, and by changing the angle of reflection of visible light by the plane mirror, the output image of the X-ray image intensifier is adjusted to a region other than the image detection area on the imaging surface of the TV camera. The X-ray energy difference imaging device according to claim 1, having a function as an optical shutter by forming an image at the position. 4. It further has an image processing device that reads out the image signal of the TV camera, records and processes the image signal, and the image processing device extracts the image signal of the X-ray image intensifier from the image signal read out from the TV camera. The X-ray according to claim 1, characterized in that it has a function of subtracting image signals corresponding to residual components of the previous and previous captured images due to afterimages and calculating only the image captured this time. Energy difference imaging device. 5. An X-ray energy differential imaging apparatus characterized in that the synchrotron radiation light according to claim 1, which is emitted from a high-energy electron storage ring, is used as the X-ray source. 6. A two-crystal spectrometer is used as a means for changing the X-ray energy, and the relationship between the X-ray diffraction angles between the two crystals is changed to take images of diffracted X-rays and only scattered X-rays, and both 1. The X-ray energy difference imaging apparatus according to claim 1, further comprising calculation means for calculating only images free from the influence of scattered X-rays by taking a difference between images.