JP2011019891A - Multispectral detector for x-ray - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve density resolution of an examination object in a radioparent examination. <P>SOLUTION: X-ray detecting parts (such as combinations of scintillators and photodiodes) different in X-ray transmittance and absorbance are arranged in multiple layers along the traveling direction of X-rays, and X-ray filters using metal plates or the like are put between the respective layers if necessary to detect while changing sensitivity-centered energy for each layer detecting part. Density resolution is improved by the mutual operation of respective layer detection data. This configuration is usable particularly for an X-ray CT apparatus. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

Detailed Description of the Invention

This proposal contributes to the improvement of transmission X-ray detection capability over the entire X-ray inspection field. The effect is particularly great in the medical field.
In the medical field, use with an X-ray CT apparatus seems to be the most prominent use method. Therefore, in the description of the present plan, the use with an X-ray CT apparatus will be mainly described.

The detection unit of the conventional X-ray CT apparatus has a higher intensity (dose) resolution than that of an X-ray film or the like, and its development is in a direction perpendicular to the traveling direction of the detected X-ray. It has been developed by arranging many detectors.
There are two types: the second generation and the third generation, the number of scans in the rotation direction, and the number of scans in the direction perpendicular to the scan direction (rotation axis direction), such as multi-slice. The idea is that a large number of detectors are arranged on the surface where the X-rays to be detected hit.
In X-ray intensity detection, a kind of quantum that improves the scintillator, increases the sensitivity of the photodiode, reduces the noise of the preamplifier, and finely combines the signals from multiple detectors into one signal. Various improvements have been made, including countermeasures against noise, but the method of detecting the total dose regardless of the energy of X-rays has not changed in any of the devices so far.

Problems to be solved by the invention

Although the X-ray CT technique has yielded many results compared to conventional X-ray imaging, there are insufficient parts in the density resolution for lesions in soft tissue and brain tissue.
It is a well-known fact that MRI (NMR-CT) exists to compensate for this.
In addition, although a relatively high X-ray tube voltage is used, X-rays in the diagnosis region have a large amount of energy distributed in the photoelectric effect region, and the influence of the X-ray absorption edge of each element is large (hence, diagnosis). Artifacts caused by X-ray superabsorbents such as bones cannot be wiped out.
This shortcoming is not improved no matter how much multi-slicing progresses.

Means for solving the problem

In the present plan, an element that detects the X-ray such as a scintillator and converts it into light and the like and a photoelectric conversion element such as a photodiode are arranged in multiple layers so as to overlap each other in the traveling direction of the detected X-ray. The elements that detect X-rays must overlap along the direction of travel of the detected X-rays, but the elements that convert light emission or the like into a charge amount (electric signal) or the like do not necessarily overlap. The light emission or the like of the line may be guided by an optical fiber or the like, and photoelectric conversion may be performed at different places.
An X-ray filter using a metal plate or the like is inserted between the X-ray detection elements such as overlapping scintillators, and the X-ray detection elements of each layer including the filter effect by the detection element itself are included. The X-ray energy band to be detected is made different. Naturally, the X-ray generation side (the surface side of the multi-layer detection unit) detects many soft lines with low energy, and the side far from the X-ray generation source (the deep layer as viewed from the surface of the multi-layer detection unit) is hard with high energy. Many X-rays will be detected.
Although soft rays decrease near the surface, the surface X-ray detection layer detects hard X-rays with high energy.
Therefore, it is necessary to consider that the surface X-ray detection layer is thinned or made of a material, and the detection layer on the surface (near the surface) attenuates and detects only the soft line component as much as possible. Further, it is desirable that the energy band of X-rays detected by each layer is separated as much as possible, not just the surface layer.
Since the conditions of X-ray detection sensitivity of each layer are stricter than the conventional one, not only the efficiency of the scintillator, the sensitivity of photoelectric conversion, the low noise of amplification, but also the layout design of each X-ray detection element, The manner of X-ray shielding between the elements is also important.
However, in recent years, semiconductor technology has greatly advanced in the direction of speeding up in the small signal region, and it seems that there is a technical environment in which this proposal can be put into practical use.

The invention's effect

Since the effect of this plan changes with embodiments, the effect will be described for each embodiment.
First, there are some of the current CT devices that have effects close to some of the effects of the present plan, depending on how they are used.
Some of today's CT apparatuses have two sets of X-ray tubes and detectors, and can perform high voltage and normal voltage imaging simultaneously. Since each image is mechanically photographed at the same position, artifact reduction processing and the like are performed using two types of images.
The difference between the above apparatus and the present plan is that the above two types of images are taken at the same slice position at the same time, and they do not exactly overlap each other.
In this proposal, it can be said that the detectors in each layer detect the same transmitted X-rays. (The detectors in each layer detect the same X-rays with different centers of energy to obtain sensitivity. ) Images constructed for each layer of detectors can be completely overlaid.
In addition, even if an image configuration in which data of each layer is mixed is performed, positional unreasonableness does not occur in the configuration image.
Based on the above differences, there are many effects that can only be obtained with this proposal.
Example 1 Image configuration equivalent to soft-line imaging Soft-line imaging is not possible with a normal X-ray CT apparatus. This is because soft rays do not transmit X-rays throughout the body.
Using the data photographed with the detector of the present plan, and performing image composition calculation with emphasis on the image composition near the body surface to the data of the detector of the soft line detection layer, it is equivalent to soft radiation imaging in the tissue near the body surface An image can be generated.
This means that imaging equivalent to soft line imaging such as mammography can be performed with a CT apparatus.
Example 2 Reduction of Artifact by X-ray High Absorption Object This is an application example that is energetically opposite to the image generation equivalent to soft-line imaging in Example 1 above.
X-ray CT is imaged with a relatively high tube voltage, but when viewed with bones or metal, the influence of photoelectric effect absorption is great and artifacts due to highly absorbing objects cannot be avoided.
If there is a high-absorption object, use the detector of the present plan and place emphasis on the detection data of the high-energy band detection layer so that the X-ray absorption value by the high-absorption object does not become excessive, and image composition calculation Can generate an image with few artifacts.
Such a method is currently performed in a CT apparatus having a plurality of X-ray tubes and detectors, but since the present method detects the same X-ray, an image with a higher degree of completeness can be obtained.
Example 3 A contrast agent can be sensitized.
The contrast agent used for the X-ray examination has an X-ray absorption edge unique to the element in the component, and absorbs X-rays having a specific energy or less and greatly attenuates.
By using this proposal and providing a detector layer that sensitively detects the energy band attenuated by the contrast agent, and performing image composition calculation with emphasis on the data of that layer, an image with enhanced contrast agent effect can be obtained. Can do.
In the past, an attempt was made to obtain an image equivalent to a contrast using an arterial catheter by contrast-enhanced intravenous injection using synchrotron radiation X-rays. It can be expected that an image equivalent to synchrotron radiation X-ray imaging will be obtained.
Example 4 High-accuracy electron density measurement by ultra high voltage imaging X-rays as well as radiotherapy using protons, heavy ions, and other radiations, the electron density distribution of the human body is calculated from the CT values of the X-ray CT This is an important task in treatment planning.
However, in the present X-ray CT apparatus, although a relatively high X-ray tube voltage is used, the influence of the photoelectric absorption region is large, and the electron density conversion from the CT value is far from ideal.
However, CT using a proton beam or the like has been studied and experimental at present, and its practicality has not been seen so far.
In contrast to this, the present proposal proposes a CT apparatus using ultrahigh-pressure X-rays in a therapeutic area such as linac.
However, just using ultra-high pressure X-rays as it is does not give a decent medical image like linacography. Therefore, if the X-ray filter is used in the same manner as a normal CT device, and the detector of this proposal is provided with a detection layer for detection of an ultrahigh energy band, it can be used for calculating electron density from the data of the detection layer of the ultrahigh energy band. CT images for diagnosis can be constructed, and CT images for diagnosis can be constructed from the data of the medical zone energy band detection layer.
Since these two types of images overlap completely, the treatment plan is input as a diagnostic image, and the dose distribution is calculated using the electron density converted from the CT value of the CT image for electron density calculation, and the calculation result is diagnosed. What is necessary is just to display on an image.
Note that the purpose of this ultra-high pressure imaging is to shoot in the Compton region suitable for electron density calculation. Therefore, the energy of X-rays is not necessarily high. This is because electron pair generation also occurs when the energy is high.
That is, any energy that can sufficiently avoid the influence of the X-ray absorption edge specific to each atom in the photoelectric region is sufficient.
Here, let us touch on the behavior of X-rays and the basic idea of this proposal.
X-rays cannot be spectrally separated by a prism or the like like visible light. In addition, there is a phenomenon in which diffraction, photoelectric effect, Compton scattering, and electron pair generation greatly differ depending on the energy, so that even if each energy region can be detected completely separated, transmission X From the line information, it is difficult to completely analyze the transmitted object.
Also, in the generation of X-rays, it is extremely difficult to obtain monochromatic X-rays (radiated light) that can be used for taking medical images with the size of a hospital apparatus.
Then, instead of forcing the impossible, change the energy center of the sensitivity of the X-ray to detect the transmission image of continuous X-rays (meaning which energy band X-ray is detected with the highest sensitivity). The idea is to detect in many energy bands.
Change how the detected intensity for each energy band is converted to light and shade. (Change of Gamma Value) Various special images that could not be obtained by the conventional X-ray inspection can be created by adding and reducing a specific energy band and then forming an image.
This is not possible with a combination of simple high-pressure imaging and low-pressure imaging, and is possible because it is a proposal in which X-ray intensities can be independently detected simultaneously at a plurality of energy centers at the same position.
Example 5 Multi-layering of flat panel X-ray detector The example of Example 1-4 can be similarly applied even if the flat panel X-ray detector is multi-layered into a multi-spectral type.
There is an experimental example based on the same principle as the present plan of taking a metal plate on the imaging plate in the past, and this plan may seem to be only a sensor, but if it is not sensorized, it cannot be used for CT equipment. In view of the fact that the image processing in the above example is virtually impossible, there is no doubt that new progress has been made by this proposal.
Example 6 Non-destructive inspection of huge objects Although there are already X-ray CT systems for large structures using ultra-high pressure X-rays, it is expected that larger objects can be inspected more closely by using the detector of this proposal. it can.
In order to realize this, it is necessary to deal with scattered radiation in the scintillator section and expand the sensitivity range of the photoelectric conversion section.
This is a common problem because the X-ray detection conditions are severe in the present plan.
To increase the sensitivity range, a countermeasure such as attaching a plurality of photoelectric conversion units having different sensitivities to one scintillator can be considered.

  It is a fundamental structure figure of this plan.   It is a principle structure figure of a conventional type sensor.

DESCRIPTION OF SYMBOLS 1 X-ray tube focus 2 X-ray 3 Photoelectric conversion element 4 Metal plate layer for X-ray filter 5 Low energy scintillator 6 Medium energy scintillator 7 High energy scintillator 8 Total energy scintillator

Claims (1)

  A multi-layer arrangement is made so that a plurality of detectors overlap in the traveling direction of the X-ray to be detected, and an X-ray filter using a metal plate or the like is inserted between the layers as necessary to pass through the inspection object. A compound detector that detects the intensity of a line in different energy bands.

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