RU93547U1 - MATRIX X-RAY RECEIVER FOR SCANNING X-RAY APPARATUS - Google Patents

Abstract

 1. A matrix X-ray detector (MCI) for a scanning X-ray apparatus, comprising a series of planar crystals connected in a line, each of which includes a photodetector in the form of a matrix of photocells optically coupled to an input scintillation layer, characterized in that the crystals are made in the form of parallelograms connected into the line with its sides, while the width of the gap between the photodetector zones of neighboring crystals does not exceed the value determined by the expression! d = H ! 2. The receiver according to claim 1, characterized in that the number of cells in any column of the MCI is the same. ! 3. The receiver according to claim 1, characterized in that in the areas of the crystal, free of photocells, control circuits and read information from this crystal are installed.

Description

The utility model relates to X-ray technology, in particular, to matrix X-ray receivers (MRI), and is intended for use in medical scanning x-ray devices with high spatial resolution, for example, mammographs, as well as in industrial introscopes for obtaining large-size images through the use of composite matrices.

Currently, digital x-ray machines are widely used in medical diagnostics, allowing direct digital registration and processing of x-ray images with subsequent output to a computer screen or solid media.

For example, the primary radiological signs of breast cancer are the presence of microcalcifications several tens of micrometers in size. To obtain x-ray images that allow the determination of artifacts of 50 microns in size, the dimensions of the element of the recording matrix must be at least two times smaller, i.e. 25 microns. Therefore, the main task in obtaining high-resolution and large-size images in mammography is the availability of affordable matrix X-ray detectors with a matrix size of 240 × 300 mm and a resolution element size of about 20 μm. Experimental samples of matrices of this size have a very low technological yield of suitable devices, and the dimensions of the matrix element exceed 100 microns. The cost of such a matrix is many times higher than the price of currently available film mammographs.

An attempt to manufacture a prefabricated structure from small-sized matrices leads to the fact that insensitive zones are present in the prefabricated matrix in the gaps between adjacent crystals, as a result, information in these image areas is lost.

This is due to the fact that it is impossible to place the photodetector zones of electronic circuits close to the edge of the semiconductor crystal, because the minimum technological fields at the edges of the crystal, ensuring the performance of the matrices after cutting semiconductor washers, amount to several hundred micrometers.

Known matrix X-ray detector containing a single scintillation layer, optically coupled through fiber optic plates (FOP) with spaced apart photodetector crystals arranged in two rows (see technical description FOS (Fiber Optic Plate with Scintillator) for Digital X-ray Imaging, Hamamatsu Photonics, pp. 19-20, www.procon-x-ray.de/downloads/FOS.pdf).

Due to the spacing of the crystals from each other in the direction perpendicular to the axis of the input plane, the technological fields of the crystals do not interfere with their placement in the assembly, i.e. an attempt was made to eliminate gaps in the x-ray receiver.

However, this design is applicable only for receivers with a resolution not exceeding 200 microns, and, therefore, unsuitable for obtaining x-ray images with a high spatial resolution of about 20 pairs of lines per mm. To avoid gaps, tolerances for deviation of the optical fiber from parallelism to the faces of adjacent VOP modules should be less than the size of the matrix element. The side faces of the FOP modules must be strictly perpendicular to the input plane, and the optical fibers must be strictly parallel to these faces. The smaller the detector element, the stricter these tolerances. Meanwhile, it is known that the manufacturing process of VOP does not give the desired degree of control over the parallelism of the optical fibers in the washer. So, for example, the general Hamamatsu specification for GPs indicates a “Gross Distortion” parameter (fiber deflection) of up to 100 microns, thus an insensitive zone up to 200 microns in size may appear at the junction of two GPs.

Closest to the claimed technical solution is a multi-channel X-ray detector for scanning x-ray apparatus, taken as a prototype, described in patent SU No. 1808215, class. G01T 1/20, 1991, (the embodiment is shown in FIG. 2), consisting of n flat rectangular semiconductor crystals stacked into a ruler by the side ends, each of which includes a photodetector zone in the form of a matrix of photocells optically coupled via a fiber optic scintillation transducer x-ray radiation.

Thanks to the use of VOP, it is possible to protect crystals from degradation due to direct x-ray radiation. In addition, using a single GP, it is possible to eliminate the disadvantages of the above analogue, in particular the appearance of insensitive zones at the joints of the GP modules.

The main disadvantage of the known solution is that the technological fields of crystals interfere with the tight adjacency of their photodetector zones. Even the use of special measures does not allow to reduce the technological fields of the crystal less than 200 microns. Therefore, at the junction of the two crystals there will be an insensitive zone of 400 microns in size. In the same patent (the embodiment of FIG. 3), an attempt was made to use GPs with zooming (focons) in order to create additional space for placing crystal fields and eliminating insensitive zones in the image. However, when replacing a single VOP with an assembly of individual focons, the aforementioned problem of uncontrolled joints between individual VOP modules arises.

The objective of the proposed technical solution is to eliminate this drawback, namely, to eliminate the influence of end gaps when docking flat crystals with photo cells when creating an MCI, suitable for obtaining large images on x-ray scanning devices with high spatial resolution, for example, for mammography.

The indicated problem in the MCI for a scanning X-ray apparatus containing a series of plane crystals connected in a line, each of which includes a photodetector zone in the form of a matrix of photocells optically coupled to the input scintillation layer, is solved by the fact that the crystals are made in the form of parallelograms connected by their lateral sides, the width of the gap between the photodetector zones of neighboring crystals does not exceed the value determined by the expression

d = H ctgα, (1)

where d is the width of the gap between the photodetector zones of neighboring crystals in a row, Н is the column height of the photocell matrix of the photodetector zone of the crystal, α is the acute angle between the base and the side of the parallelogram.

Due to the indicated shape of the crystals, it is possible to reduce the influence of gaps between the sensitive zones at the junction of the crystals on the quality of the resulting image partially or completely due to the fact that photo cells of one or two adjacent crystals always participate in the formation of the integral image element obtained from the matrix column.

To completely eliminate the effect of gaps between the sensitive zones at the junction of the crystals on image quality, the number of photo cells in any column of the MCI should be the same. At the same time, a part of the crystal area free of photocells can be used for control and reading information from a given crystal.

Figure 1-6 presents drawings explaining the essence of the proposed technical solution.

Figure 1 presents a figure showing one of the possibilities of obtaining x-ray images of the investigated object using the inventive MCI, where: 1 - x-ray source; 2 - collimator; 3 - U-shaped scanning frame; 4 - an object of study mounted on an x-ray transparent table 5; 6a and 6b are adjacent crystals of MCI, 7 is a scintillation layer (phosphor); 8 - photosensitive zones of crystals 6; 9 - element of the investigated object corresponding to one element of the x-ray image; 10 - matrix column, according to which the WZN - summation occurs (the formation of the integral image element of the column by time delay with accumulation).

Figure 2 presents a figure explaining the loss of information in the prototype in the WZN - summed signal due to the presence of insensitive zones at the edges of the crystals in the docking area, where: 6a and 6b are adjacent crystals of MCI; 11 - a single photocell of the crystal; 12 - columns WZN - summation passing through the sensitive zones of the crystals; 13 - columns WZN - summation passing through insensitive zones of crystals in which information is lost.

Figure 3 presents a drawing of the inventive MCI with a decrease in the influence of insensitive zones in the area of coupling of crystals on the WZN - summed signal, where: 14 - columns WZN - summation with partial loss of information; 15 - sections of columns WZN - summation, in which there are no photo cells.

Figure 4 presents a picture of the connected crystals with the parameters taken into account when excluding insensitive zones, where: 6a and 6b are the adjacent MCI crystals, 8a and 8b are the photodetector zones of the crystals.

Fig. 5 is a drawing explaining the principle of connecting into a line of crystals with the same number of photo cells in the columns of the WZN - summation at any point of the MCI, where: 16 - columns of the WZN - summation columns that are the same in the number of photo cells; 17 - released part of the crystal.

Figure 6 presents the pattern of the crystal with the released part of the area for installing the polling circuit information from the crystal.

The inventive device operates as follows. The radiation of the X-ray source 1 is formed using a collimator 2 into a flat fan beam, which scans the object of study 4, located on the X-ray transparent table 5, by moving the U-shaped frame 3. The X-ray radiation transmitted through the object of study 4, is perceived by MCI, consisting of a number of crystals 6, the photosensitive regions of which are optically coupled to the phosphor 7. In the figure, the optical connection is shown in the form of a direct adjacency of the phosphor 7 to the crystals 6. Photosensitive zones 8 of the crystal 6 formed from the photoelectric devices 11, forming a multi-line array of M rows, which produces a series of continuous image acquisition. The speed of movement is chosen such that during one registration, the MCI is shifted by a distance equal to the size h (see figure 4) of a single photo cell 11 in the direction of movement, with each element 9 of the investigated object 4 is recorded M times at successive times with further summation of the images obtained from the MCI taking into account its movement. This summation is known as WZN summation (see Technical Description Characteristics and use of back-thinned TDI-CCD, Hamamatsu Photonics, p. 3, TDI Time Delay Integration mode, http://sales.hamamatsats.com/assets/applications/ SSD / tdi-ccd_kmpd9004e01.pdf). At the end of each registration, the next line of integrated elements of the resulting image is digitally generated based on the signals read from the MCI photo cells.

In the formation of the signal value of each integral element of the resulting image, all the photo cells located on the WZN - summation column for the corresponding element 9 of the studied object are involved. If on some column of the WZN summation 14 some of the cells are missing (see FIG. 3), this does not lead to loss of information in this integral image element, but only to a decrease in the useful signal proportional to the missing cells.

At the junction between the crystals, the WZN summation columns 14 intersect the photocells of both adjacent crystals 6a and 6b, as well as the intercrystal gap 15. In this case, the photocells of both the left 6a and right 6b crystals will participate in the formation of the integrated signal. The size of the plot 15, in which there are no photo cells, is: d · tg α and can be minimized by choosing geometric parameters. So, for example, with a photodetector zone height H = 10 mm, an angle α = 45 ° and a gap d = 0.5 mm on the WZN - summation column 14, section 15, in which there are no photocells, is only 5% of the total height H of the photodetector zone column 12 In this case, the signal-to-noise ratio at the interface will become worse only by (1-√0.95) ≈2.5%, which is visually indistinguishable in the image.

The maximum value of the gap value is defined as: d = H · ctg α. When the gap exceeds this value, overlapping photodetector zones 8 of neighboring crystals along the columns will not occur.

In cases where even a slight deterioration of the signal at the junction area is unacceptable, it is possible to modify the shape of the photodetector zone of the crystals so that for any column of the WZN - summation 16 the number of photo cells in it becomes the same (see Fig. 5). signal for each integral element of the resulting image, but also use the freed region of the crystal 17 to accommodate electronic circuit servicing the crystal.

Example. For the scanning mammograph was made a prototype MCI with the following characteristics:

- the total crystal size in the form of a parallelogram is 25 × 10 mm;

- angle α = 63 °;

- the step of installing crystals in the line is 20 mm;

- clearance d = 0.5 mm;

- the number of crystals in the line - 12 pcs .;

- the number of lines MCI - 500 pcs .;

- the number of columns MCI - 12000 pcs .;

- sizes of the photocell - 20 × 20 microns;

- step of photocells - 20 microns.

Characteristics of the resulting image:

- image size - 240 × 300 mm;

- spatial resolution - 18 pairs of lines / mm throughout the image field;

- There are no visible joints in the image.

Thus, the claimed device allows one to create prefabricated MCIs for scanning X-ray machines from the same flat semiconductor crystals, in which the insensitive zones on the crystals do not affect the quality of the resulting image, and with their help obtain large x-ray images with high spatial resolution, for example, for general radiography, mammography, or technical introscopy.

Claims (3)

1. A matrix X-ray detector (MCI) for a scanning X-ray apparatus, comprising a series of planar crystals connected in a line, each of which includes a photodetector in the form of a matrix of photocells optically coupled to an input scintillation layer, characterized in that the crystals are made in the form of parallelograms connected in the line with its sides, while the width of the gap between the photodetector zones of neighboring crystals does not exceed the value determined by the expression d = H · ctg α, where d is the width of the gap between the photodetector zones of neighboring crystals in a row, Н is the column height of the photocell matrix of the photodetector zone of the crystal, α is the acute angle between the base and the side of the parallelogram. 2. The receiver according to claim 1, characterized in that the number of cells in any column of the MCI is the same. 3. The receiver according to claim 1, characterized in that in the areas of the crystal free of photocells, control circuits and read information from this crystal are installed.