JP2772667B2 - Radiation dose adjusting device in radiation imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation (generally, X-ray) imaging apparatus, and more particularly, to a technique for adjusting exposure to various portions of a subject to compensate for exposure.

<Prior Art> A radiation imaging apparatus generally includes a radiation source using an X-ray tube, a radiation-sensitive film that detects and records an amount of radiation from the radiation source that has passed through an object to be irradiated, and a radiation-sensitive film. And imaging means such as a luminescent phosphor.

Meanwhile, for example, in chest imaging using an X-ray examination apparatus used for medical purposes, there is a problem that anatomical thickness shows a large variation due to a difference in thickness or radiation absorbability in an imaging part.

That is, a region with a large thickness is underexposed and becomes too thin, and a region with a small thickness is overexposed and becomes too dark to reduce the latitude.

For this reason, a slit is provided in front of the radiation source, and an aperture member made of a radiation shielding material (for example, lead) is moved in and out so as to variably control the opening area of each of the slits divided in the longitudinal direction. While scanning the radiation beam obtained by passing the radiation beam in the direction perpendicular to the longitudinal direction and irradiating the subject with an image, recording and recording the radiation dose of each part on the imaging surface while capturing and recording on the imaging surface provided behind the subject. There is a configuration in which a detector for detection is provided, and a radiation amount is adjusted by controlling a diaphragm amount by the diaphragm member so as to obtain an appropriate exposure amount based on a detection signal from the detector (Japanese Patent Laid-Open No. Sho 62-62). No. 129034).

<Problem to be Solved by the Invention> However, such a conventional radiation dose adjusting device is configured to adjust the dose in each of the regions divided in the longitudinal direction by changing the irradiation area, so that the required dose is required. It is difficult to irradiate the image in such a manner that the image is accurately matched with the corresponding portion, resulting in a false image, and there is a problem in imaging accuracy that the image is easily affected by the scattering of radiation in the adjacent region.

The present invention has been made in view of such a conventional problem, and solves the above problem by forming a radiation beam having a small irradiation area and variably controlling a scanning speed thereof, thereby improving imaging accuracy. It is an object of the present invention to provide a radiation irradiation amount adjusting device in a radiation imaging apparatus having an increased radiation irradiation amount.

<Means for Solving the Problems> For this reason, the present invention provides a plurality of slit members having fine slits that transmit radiation in a part of the longitudinal direction between the radiation source and the subject, Scanning means for scanning radiation transmitted through the slit by moving the slit of each slit member at a variable speed in the longitudinal direction of the slit member.

<Operation> The scanning unit controls the moving speed of the slit of each slit member based on a detection signal such as the amount of radiation transmitted through each part of the subject. Thereby, the scanning speed of the radiation beam obtained through each slit is independently controlled, and the radiation dose of the corresponding portion is adjusted according to the speed.

<Example> Hereinafter, an example of the present invention will be described with reference to the drawings.

1 and 2 showing the configuration of the first embodiment, a modulator 2 having a radiation dose adjusting function according to the present invention is arranged between a radiation source (generally, an X-ray tube) 1 and a subject 3. Is established.

The modulator 2 includes a window member 21 having a rectangular opening 21a corresponding to an imaging surface formed in the center of a plate made of a radiation shielding material such as lead, tungsten, tantalum, and the like. A slit member 22 provided, and a drive unit 23 for moving each of these slit members 22 in the longitudinal direction (horizontal direction) at a variable speed.
And is provided.

As shown in FIG. 2, the slit member 22 is made of lead (or tungsten W, molybdenum Mo) which is a radiation shielding material except for a part in the longitudinal direction on one surface of a PET (polyethylene terephthalate) tape 22a made of a radiation transmitting material. It is formed by laminating the Pb tapes 22b formed by the above. It should be noted that one of the adjacent side surfaces of the PET tape 22a and the Pb tape 22b is formed to be convex and the other is formed to be engaged in the longitudinal movement freely. The portion where the Pb tape 22b is not laminated is a minute slit 22c that transmits radiation.

Then, the movable end of the drive unit 23 is connected to one longitudinal end of each slit member 22. The drive unit 23 is composed of, for example, a linear solenoid, and has a stroke amount that allows the minute slit 22c to cross the opening 21a of the window member 21.

A subject 3 is located behind the modulator 2, and a bucky grid 4, a plane detector 5, and an imaging surface 6 such as a screen / film are disposed behind the subject 3. The bucky grid 4 is provided for directing a radiation beam to the surface detector 5 at a right angle. The surface detector 5 has each slit 22
By detecting the radiation dose on the imaging surface 4 of the pencil beam PB that has passed through c, the radiation transmission amount of each part of the subject 3 is detected. The moving speed of the movable end of each drive unit 23 is controlled by a control signal from the control circuit 7 in accordance with a detection signal from the surface detector 5.

Then, imaging / recording is performed by changing the irradiation time for each part according to the moving speed of the pencil beam PB obtained by passing through the slit 22c on the imaging surface 6. In the case of a screen / film, radiation is applied to a phosphor layer (fluorescent screen) to be converted into visible light, and this variable light is exposed to a film coated with a silver salt photosensitive material. However, the imaging surface 6 is not limited to this, and may be a recording medium containing a stimulable phosphor. For example, image information can be stored by using a stimulable phosphor detector, scanned and extracted by a semiconductor laser, and this digital image information can be stored in an external memory and reproduced on a CRT.

 Next, a series of operations will be described.

The radiation emitted from the radiation source 1
A plurality of pencil beams PB are transmitted through the minute slits 22c of each slit member 22 traversing 21a, and each pencil beam PB is transmitted through the subject 3 and hits the surface detector 5 via the bucky grid 4, where each pencil beam PB is transmitted. The amount of transmission of the pencil beam PB through the subject 3 is detected.

The detection signal of the transmission amount is input to the control circuit 7, and the control circuit 7 outputs a control signal to each of the drive units 23 corresponding to the respective detection signals, and each of the drive units 23 outputs a speed corresponding to the control signal. To move and scan the slit member 22. That is, each drive unit 23 and the control circuit 7 constitute a scanning unit.

Specifically, in places where the amount of transmission is large, increase the moving speed to shorten the irradiation time per unit area, suppress overexposure, and in places where the amount of transmission is small, reduce the moving speed and lengthen the irradiation time. Appropriate exposure compensation is performed by suppressing underexposure. As a result, the exposure is adjusted according to the anatomical thickness, and a clear image with a wide latitude can be obtained.

When the exposure adjustment is controlled by the moving speed of the pencil beam PB in this way, compared to the case of controlling by the irradiation area, the required irradiation amount can be almost exactly matched with the corresponding portion, and irradiation can be performed. So that fake images can be prevented,
Since the effect of the scattering of radiation in the adjacent area can be prevented,
More accurate imaging can be obtained.

FIG. 3 shows a second embodiment in which mercury 31 which is a radiation absorbing fluid is mixed with a radiation transmitting fluid 32 such as oil or water.
Small diameter portion 33a of a plurality of tubes 33 filled with a small amount of
Are arranged in the vertical direction without any gap in the same manner as in the first embodiment so as to face the opening 21a of the window member 21.

Each of the pipes 33 is formed of a radiation-transmissive material, and the lower portion thereof is expanded in diameter to form a pressure chamber 33b. Inside the pressure chamber 33b, a piezoelectric element 34 having flexibility capable of radially contracting a peripheral wall is provided. The peripheral wall is deformed to a large extent by energization and the volume of mercury 31 filled in the pressure chamber 33b is reduced, so that the mercury 31 filled in the pressure chamber 33b is pushed out to the small-diameter portion 33b and radiation is applied. The configuration is such that the permeated fluid 32 crosses the opening 21a. Here, the filled portion of the radiation transmitting fluid 32 is
A minute slit capable of transmitting radiation is formed. And
A piezoelectric element 34 is connected via a drive circuit 35 connected to each piezoelectric element 34.
The moving speed of the radiation-transmitting fluid 32, that is, the minute slit, can be controlled by controlling the amount of current flowing through the slit. The drive circuit 35 is connected to a control circuit 36, and the control circuit 36 uses the radiation transmission amount detection signal from the surface detector 5 similar to the first embodiment to move the radiation transmitting fluid 32 in accordance with the magnitude of the transmission amount. Is controlled to change the driving circuit. Therefore, each piezoelectric element 34, a driving circuit 35 for driving the same, and a control circuit 36 constitute a moving scanning unit. Note that the end of the tube 33 on the side opposite to the pressure chamber 33b is spherical and serves as a mercury storage chamber 33c for storing mercury. With such a configuration, since the piezoelectric element 34 has a high response speed, the radiation transmitting fluid 32 is extremely The movement can be controlled with good responsiveness, whereby the exposure is controlled so as to maintain the exposure of each part properly as in the above-described embodiment. An image is obtained.

Furthermore, each tube 33 is sufficiently small (need to be small in order to improve responsiveness), and the control circuit of the piezoelectric element 34 is also an LSI, as compared with a device using a drive mechanism such as a solenoid.
Therefore, the modulator 2 as a whole can be significantly reduced in size.

In the embodiment described above, each pencil beam is used.
Although the mechanism for moving and scanning the PB in the horizontal direction is shown, it is a matter of course that these mechanisms may be rotated by 90 ° to move and scan the pencil beam PB in the vertical direction. Also,
The present invention can also be applied to a device in which a weak radiation beam is once irradiated by a detector or a stimulable phosphor, and then the irradiation amount at the time of main imaging is corrected and controlled based on the detected value of the radiation transmission amount.

<Effects of the Invention> As described above, according to the present invention, since the control of the radiation dose is performed by controlling the moving speed of the minute slits, a wide latitude without influence of spurious images and scattering can be obtained. The result is a unique image.

[Brief description of the drawings]

FIG. 1 is a plan view showing the overall configuration of a first embodiment of the present invention, FIG. 2 (A) is a longitudinal sectional view of a main part of the embodiment, and FIG. 2 (B) is FIG. (C) of FIG.
FIG. 3A is a cross-sectional view of FIG.
FIG. 4B is a plan view of a main part of the second embodiment, and FIG. 1 ... radiation source, 2 ... modulator, 3 ... subject,
7: control circuit, 22: slit member, 22c: minute slit, 31: mercury, 32: radiolucent fluid, 33:
Tube, 34 Piezoelectric element, 35 Drive circuit, 36 Control circuit, PB Pencil beam

Claims (1)

(57) [Claims] 1. A plurality of slit members each having a minute slit for transmitting radiation in a part of a longitudinal direction between a radiation source and a subject are arranged side by side in a direction perpendicular to the longitudinal direction. A radiation irradiation amount adjusting apparatus in a radiation imaging apparatus, comprising: a scanning unit configured to scan radiation transmitted through a slit by moving a slit of the member at a variable speed in a longitudinal direction of the slit member.