JP2007136050A - X-ray detector array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that affection the gap influence in a semiconductor detection element is inevitable though a semiconductor detection element with high sensitivity as an X-ray detection element has been desired to be used in an X-ray CT apparatus. <P>SOLUTION: Semiconductor X-ray detection element arrays are arranged in front and back, and arranged deviated by 1/2 pitch of a space between detection elements so as to be arranged to complement the gap positions of each other. By equalizing the directions of pn connection, a difference of detection property is reduced. By this structure, data corresponding to a gap position can be complemented by data of another detection element array. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an array structure of X-ray CT semiconductor radiation detectors using a semiconductor detector with high sensitivity and linearity and a signal processing technique.

In an X-ray CT apparatus using a scintillator, blurring occurs due to the spread of light in the scintillator, and the influence of the detector gap is small.
For this reason, in this type of apparatus, there is no need to consider the gap, and there is no problem even if the detection element groups are arranged in a matrix (see Patent Document 1).
However, a semiconductor detector has recently been used as a detector for X-ray CT.
However, there is no blur in the semiconductor detector, and the influence of the gap occurs clearly.
The semiconductor detector used for the X-ray CT semiconductor radiation detector has the following advantages and disadvantages.
Pros:
1) The semiconductor detector has much higher sensitivity and characteristics than conventional scintillators.
2) A high resolution according to the element size can be obtained.
Cons:
1) A gap (gap) is formed between pixels, and information is lost.
JP 2005-189022 A

FIG. 5 shows an overall view of a computed tomography (CT) imaging apparatus. 4 is a measurement object, 10 is a control device, 11 is a gantry, 12 is an X-ray source, 13 is an X-ray beam, 14 is a rotation center, 15 is a detector array, and 20 is a signal processing device.
FIG. 6 shows a detection element array (1) in which detection elements (5) for conventional X-ray CT are arranged in one row. The detector array (15) is composed of one or a plurality of detector element arrays (1). The incident direction of the X-ray beam (3) is perpendicular to the paper surface and irradiates the entire detection element array (1). There is a structural gap between the detection elements (5). The measurement object (4) is fed downward by an appropriate pitch every time data is acquired.

In the structure shown in FIG. 6, when a measurement object is rotated for X-ray CT imaging to capture a projection image (transmission image) due to the presence of a gap, when the measurement object is small, projection is performed only on the gap at a certain angle. A phenomenon occurs in which an image enters. Further, as shown in FIG. 7, the data obtained is lost and the resolution is lowered. That is, the data obtained by one irradiation (pass1) is data (d11, d12, d13,...) From the detection element corresponding to the angle of the measurement object viewed from the X-ray source. Complementation with data (d21, d22, d23,...) In irradiation (pass2) after being rotated by a small angle is difficult in terms of computation for reconstruction.
The precondition for CT processing is that information from 360 degrees all around is obtained, and lack of information due to gaps occurs in the reconstructed image as linear noise, causing a significant problem.

In the present invention, the detection elements are arranged back and forth with respect to the radiation incident direction, and the pixels are arranged so as to be shifted. With such a structure, the X-rays that have passed through the gap in the first row of detection elements are detected by the second row of detection elements and subjected to charge conversion, thereby preventing the influence of the gap.
For multi-slice CT, a multi-slice imaging is performed by arranging a plurality of arrays in which the detection elements are arranged in two front and rear rows in the moving direction of the measurement object. When multi-slicing is not performed, only one array may be used.
It is desirable to use a photon-charge direct conversion type semiconductor detector containing CdTe as the X-ray detection element.

FIG. 1 shows an arrangement example of the detector array (15).
The detector array (15) is composed of two rows of parallel detector element arrays (1, 2). The detection elements (5, 6) are arranged in front and back over two rows. The incident direction of the X-ray beam (3) is from the top to the bottom of the page, and irradiates the entire detection element array (1, 2). The detection element (5) in the front row and the detection element (6) in the rear row have a structure in which a detection element in the rear row is provided in the gap in the front row in order to complement each gap. The measurement object moves in a direction perpendicular to the paper surface.
FIG. 2 shows a structure in which the orientation of the pn structure is adjusted. When aligned in this manner, the difference in detection characteristics due to the difference in the traveling properties of electrons and holes generated by X-rays is reduced. Although two substrates are used in FIG. 2, a structure in which a two-layer structure is created on one substrate as shown in FIG. 1 may be adopted.
Many detection elements have not only pn junctions but also Schottky junctions. Even in this case, the difference in detection characteristics is reduced by unifying the orientations of the joint surfaces. Generally speaking, in a detection element having a laminated structure composed of different types of semiconductors and an insulator provided as desired, it is clear that the difference in detection characteristics is reduced if the orientations of the joint surfaces are unified. The term “junction” as used herein includes not only a structure in which different types of semiconductors have a clear boundary surface but also a stepwise transition structure due to a doping concentration gradient or the like.
In order to align the characteristics of each element as a CT device, it is desirable that the first and second rows have the same size.

Making the detection element in two layers on the substrate involves manufacturing difficulties. In this case, as shown in FIG. 3, by disposing the detection element arrays on both sides of the base, the difficulty during manufacture is reduced. Furthermore, a two-layer detection element array structure may be formed by attaching a detection array in which only one layer is formed on a substrate back to back. Here, the back-to-back structure may be a structure in which the base surfaces are bonded together or a structure in which the detection element surfaces are bonded together, and is not limited to either.
When adopting this structure, it is important to use a substrate with low X-ray absorption.

If the detector array is moved to the left and right by 1/2 pitch of the element spacing, it can be regarded as if the detection elements are substantially doubled, and the resolution can be improved. Furthermore, if the data is collected at each position by moving the element interval by 1/3 pitch and 2/3 pitch, the resolution can be substantially tripled. In general, if the element spacing is detected a plurality of times at n equal positions, n times the resolution can be obtained.
An example is shown in FIG.
Reference numeral 15 denotes a detector array. Here, the detector array (15) is composed of two rows of detector element arrays (1, 2). Up to this point, the technique is the same as that shown above.
The detector array (15) is movable by the actuator (16) by a 1/2 pitch in the lateral direction. Reference numeral 17 denotes a fixed end. As an actuator, a piezoelectric element can be miniaturized. In addition, a solenoid, a small motor, an ultrasonic motor, a linear motor, or the like can be used.

  The problem of the gap that occurs when a semiconductor detector with high sensitivity and good characteristics is used in an X-ray CT apparatus can be solved, and a high-resolution CT image can be obtained.

The figure which shows the example of an arrangement | sequence of X-ray detector array (15) The figure which shows the structure which aligned the direction of a pn junction and arranged the detection element array (1, 2) in two rows The figure which shows the structure which arranged the detection element (5, 6) back to back Diagram showing movement of detector array by actuator Diagram showing the overall image of a computed tomography (CT) imaging device The figure which shows the X-ray detector array by the conventional 1 line arrangement | sequence for X-ray CT Conceptual diagram showing missing information due to existing gaps

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Detection element array 3, 13 X-ray beam 4 Measurement object 5, 6 Detection element 10 Control apparatus 11 Gantry 12 X-ray source 14 Rotation center 15 Detector array 16 Actuator 17 Fixed end 20 Signal processing apparatus

Claims (3)

Similarly to the first detection element array (1) in which the first semiconductor X-ray detection elements (5) are arranged in one column, the second semiconductor X-ray detection element (6) is also arranged in one column. X which consists of a 2nd detection element array (2), arrange | positions the said 1st detection element array (1) ahead, and passes the gap in the said 1st detection element array (1) behind it. An X-ray detector array in which the detection elements (6) of the second detection element array (2) are arranged corresponding to the gaps of the first detection element array in order to detect lines.
The first semiconductor X-ray detection element (5) and the second semiconductor X-ray detection element (6) have different types of semiconductor junctions, and the directions of the different types of semiconductor junctions as light receiving surfaces are unified. The X-ray detector array according to claim 1. Actuator for moving the first detection element array (5) and the second detector array (6) in the column direction by m / n (m, n are natural numbers and m <n) between detection elements. The X-ray detector array according to claim 1, further comprising (16).

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