Radiation imaging device comprising array of Cd(Zn)Te detectors

ES 2 625 764 T3

DESCRIPTION

Imaging device comprising a set of Cd (Zn) Te detectors

Background of the invention

1. Field of the invention

The present invention relates to digital radiation imaging. In particular, the invention relates to the effective construction of optimized imaging areas of different sizes and shapes by combining side-by-side separated semiconductor pixel detectors in a mosaic-like manner so that the shape of the active area of ​​the sensor is made to conform as exactly as possible to the shape (or shapes) of the X-ray beam of a specific application.

2, Description of Related Art

A very important problem in the construction of digital X-ray imaging devices is the fabrication of large sensor areas. Today's commercial large area devices generally rely on flat panel technology. Sensors based on other technologies such as scintillation-CCD sensors or especially CMOS semiconductor sensors produce higher quality but suffer from a limitation in the area of ​​active imaging possible to manufacture.

The maximum continuous active area of ​​unit CCD and CMOS continuous detector chip based sensors is typically a few square centimeters (cm²). These unit detector chips can be combined by mounting them side by side in a mosaic-like fashion to form larger areas. Such mosaic constructions have been successfully applied in scanning systems, in which the active imaging area has a groove shape, to form a linear array of imaging elements. Rectangular shaped imaging areas of a few tens of cm have also been successfully fabricated.². Larger rectangular areas of CCD and CMOS-based sensors are limited by the fact that one side of the unit CCD and CMOS chips is always required for external electrical connections and prevents side-by-side mounting on that side. The benefits of building imaging areas from separate small detector elements include flexibility to form irregularly shaped areas and cost effective production. Prior art sensors, however, have not been able to address these needs.

Some applications may demand different sensor areas for different imaging modes. For example, in modern digital extraoral dental X-ray imaging the same imaging system should be capable of performing both fan-beam panoramic scanner acquisition and cone-beam three-dimensional (3D) imaging. In the scanner mode, a relatively long slot-shaped vertical imaging area is preferred in order to match the sensing area with the X-ray fan beam shape and to optimize the speed of data collection. In 3D mode a vertically shorter but horizontally wider sensor area is optimal to provide proper cone beam coverage.

In the prior art, to accommodate these partially contradictory sensor area requirements, manufacturers of modern extraoral dental X-ray systems have either to use two separate digital sensors available in the current art or a larger sensor (typically a flat panel) with a sufficient rectangular area to cover both the fan and cone beam shapes. Both of these options have disadvantages in terms of cost, compactness and effective use. The present invention addresses this issue by featuring a novel digital X-ray sensor with a unique irregular shape of active area optimized for both of the above-mentioned imaging modes. Extraoral dental X-ray imaging is given here only as an example. The invention can be used to benefit any other X-ray imaging application with similar imaging area requirements. The invention can be carried out especially well with CMOS semiconductor detector technology but can also be carried out with other technologies such as scintillation-CCD technology.

Some ideas and methods of constructing larger mosaic-like active imaging areas of unit detector elements have been presented and patented [US Patent Document 6,207,744, US Patent Document 5,812,191, European Patent Document EP0421869, International Patent Document W09708751, European Patent Document EP0138647]. The aim of such methods is generally to realize a sufficiently large regular imaging area of ​​either rectangular or slot shape. Most of the methods presented teach techniques to minimize the inevitable dead space or blind region between the separate detector elements. The minimum gap between the active areas of adjacent detector elements is obviously obtained by mounting the elements in physical contact with each other. Although eliminating or minimizing dead space between multi-element sensor elements is ideal for acquiring uniform X-ray images, it may not be feasible from a manufacturing point of view to assemble the separate sensor elements by physically touching each other. In addition to the optimal irregular shape of the active area mentioned above, the present invention presents an effective manufacturing technique for sensors of

ES 2 625 764 T3 multiple elements. The technique is especially applicable to sensors based on CMOS semiconductor technology and has specific relevance for CdTe-CMOS pixel detectors.

A device according to the preamble of claim 1 has been presented at the 2007 convention of the German Society for Non-Destructive Testing (P. Rost et al: "Ein neues digital Prüfsystem für die radiografishe Prüfung von Rohr-Rohrboden-Verbindungen an Warmetauschern mit computergestützter Auswertung ”, DGZfP-Jahrestagung, Fürth (DE), 14-16, May 2007).

Summary of the invention

The present invention provides a sensor structure that leaves a finite physical gap between adjacent detector elements. This structure is a departure from the prior art teachings of eliminating dead space between individual detector chips. This brings definite advantages in terms of production performance and long-term resistance of the sensor. Since solid state semiconductors are generally brittle crystals, mounting them in physical contact greatly increases the risk of damaging the crystal edges with cracks or fractures during production. It also leaves the sensing elements much more vulnerable to damage caused by thermal expansion or mechanical shock compared to the method of mounting the elements with an intermediate physical gap. Furthermore, physical contact between semiconductor detector crystals can lead to distortions in the signal collected by the electric field applied to the crystals. The gap between the detector elements can be simply an empty space or the gap can be created by placing some material such as mylar film between the detector elements. The size of the gap is defined by the characterization portion of claim 1.

The invention applies to X-ray imaging sensors made from CdTeCMOS pixel detectors.

The invention is to be used in particular in extraoral dental X-ray imaging but is beneficial in other applications as well.

Brief description of the drawings

Figure 1 illustrates different options of irregular shapes of the active area of ​​the invented X-ray sensor.

Figure 2 illustrates a preferred form of the invented X-ray sensor active area designed for extraoral dental X-ray imaging.

Figure 3 illustrates preferred forms of the active area of ​​the invented X-ray sensor designed for extraoral dental X-ray imaging.

Figure 4 illustrates a preferred form of the active area of ​​the invented X-ray sensor designed for extraoral dental X-ray imaging.

Figure 5 illustrates various views of a detector element.

Figure 6 illustrates a slot sensor with three separate sensor elements, which is an embodiment of the present invention.

Figure 7 illustrates two identical sensor substrates populated with sensor elements to form different active sensor areas.

Figure 8 illustrates a sensor constructed of two separate sensor substrates.

Figure 9 is a schematic of an extraoral dental X-ray imaging system.

Description of preferred embodiments

A radiation imaging device includes several individual detectors that define an X-ray sensitive and irregular rectangular active area with different widths along a length of the active area. The individual detectors can be of different rectangular shapes and be mounted on a base plate. The base plate can be formed by a first module that mounts a first of two individual detectors and a second detachable module connected to the first module and mounts a second of two individual detectors.

A preferred form 5 of the active area of ​​the X-ray sensor is shown in Figure 2. Form 5 is constructed, in this example, from nine individual detector elements 8 and is designed for X-ray imaging needs. modern extraoral dental in which a fan beam 3 is, at the same time, used for panoramic scan imaging and a rectangular conical beam 4 is used for 3D tomographic imaging. Typical dimensions of the preferred active area are given in Figure 2. As can be seen from Fig. 2, the beam coverage of the irregularly shaped preferred active sensor area 5 is much better than that of a large conventional rectangular area 6. Rectangular shape 6 leaves much more sensor area 3

ES 2 625 764 T3 useless both in panoramic mode (fan beam) and in 3D mode (cone beam).

As illustrated by Figures 1-2, in each case, the radiation imaging device includes an X-ray sensitive active area. The active area has an irregular rectangular shape with a total length y (150mm in the figure 2) and a total width x (50 mm in figure 2). Advantageously, each imaging device has different local widths (50mm, 6mm in Figure 2) for corresponding different ranges along the length (respectively the lower and upper halves of the device of Figure 2).

Figure 3 shows three other preferred forms 19, 20 and 21 of active sensor area in the extraoral dental X-ray imaging application. Many other similar shapes can also be used in extraoral dental imaging. The choice of shape depends on the X-ray beam shapes of the application. Shape 19 provides coverage for a large cone beam which may be desired to acquire image data from a large area for more comprehensive cross-layering (tomographic) or 3D imaging. Shapes 20 and 21 provide less cone beam coverage resulting in a more economical sensor solution. In shape 21 the cone beam area 22 is raised higher than in shape 20. Shape 21 is a desirable sensor shape if the conical X-ray beam is centered higher above the chin to more efficiently cover the tooth region.

Figure 4 shows another preferred shape 9 of the active area optimized not only for tomographic and dental panoramic imaging but also for cephalometric imaging. In cephalometric imaging, an image of the entire human skull is acquired, and therefore the vertical dimension of the short part of the active sensor area has to be longer.

Figure 5 shows a drawing of a detector element 10 used to construct larger imaging areas in a radiation imaging device in accordance with the present invention. Top and side views 23 and 24, respectively, of element 10 are shown. The structure of element 10 reflects the structure of a CdTe-CMOS detector which comprises a CdTe crystal 16 connected to a CMOS data reading circuit 17. Element 10 has electrical connections 11 (typically ultrasonic wire junctions) on one side that prevent side-by-side mounting of elements on this side. Other elements can be mounted very close or in physical contact to this element 10 on all other sides 12.

Figure 6 illustrates the invented radiation imaging device with detector elements 13 side by side with a finite physical gap 14 between the elements 13. The gap 14 between the outermost edges of the detector elements may be empty or it may be filled by placing an electrical insulating material 15 such as a mylar film between the elements 13. The width of the gap 14 is relative to the size of the pixel dimension of the detector and may be less than the pixel size as long as electrical isolation is maintained and physical contact is avoided. This is important since the edges can be "roughened" or trimmed with some acceptable degree of "chipping" and therefore the distance between the edges can be more appropriately referred to as the mean distance. A typical pixel size can be 0.1mm.

However, the invention also applies to pixels of size from 0.05mm to 0.1mm. For the 0.1mm pixel, the gap is within the range of 0.005mm to 0.10mm, since it offers adequate spacing but also a sufficiently small gap compared to the pixel size.

In one embodiment, the inventive radiation imaging device is made up of individual Cd (Zn) Te detectors juxtaposed side by side with a mean physical gap of 0.005mm - 0.10mm between the edges of the Cd detectors ( Zn) Te. This gap can be provided by film, for example by a 0.005mm - 0.10mm thick mylar, or alternatively by precisely positioning the Cd (Zn) Te detectors using a microscope that has a mean gap in the previous range.

Figure 7 shows how two different active sensor area shapes 32 and 33 can be constructed on identical sensor substrates 34 (also referred to as detector module (s)). In this illustration, the detector / substrate module 34 is a printed circuit board (PCB). The same substrate can accommodate a variable number of detector elements of different or identical size and shape to form a desired active sensor area. The benefit of this is cost-effective and time-efficient production.

Figure 7 shows, for each of the identical detector modules / sensor substrates 34, a plurality of individual detectors defining an X-ray sensitive active area. The active areas each have a rectangular shape with a total length yy a total width x. In each case, the detector / substrate module 34 serves as a common base plate with the active area comprising individual detectors of different rectangular shape commonly mounted on the base plate. As shown, a first of the detectors has a first active length y1 and a first active width x1, and a second of the two detectors has a second active length y2 and a second active width x2. Since the two types of individual detectors have different rectangular shapes, at least one of the first active length y1 and the second active length y2 are different or the first active width x1 and the second active width x2 are different. This allows the construction of the active area to be such that the active width x varies along the active length y (for example, see the active width x and x 'in Figure 7).

ES 2 625 764 T3

Figure 8 shows how a desired sensor area can be constructed by combining two different sensor substrates 35 and 36 side by side in a separable manner. In this example, substrate 35 accommodates a slot-shaped linear array sensor and substrate 36 accommodates a square-shaped sensor. The benefit of this is, as above, effective product development and production. Using multiple substrates allows separate substrates to be used independently and flexibly in applications where an irregular shape of the sensor area is not required or in combination to form an active area shape in accordance with the present invention.

Figure 8 shows a radiation imaging device comprising a first module 35 (ie, first detector substrate) mounting a first individual detector 37 and a second module 36 (ie, second detector substrate) detachable connected to the first module. 35 and mounting a second individual detector 38. Together, the first and second detectors define the active X-ray sensitive area. As shown, the first and second detectors are of different rectangular shape with at least one of their lengths and widths being different.

Figure 9 illustrates the application to extraoral dental X-ray imaging. A patient 25 is positioned between an X-ray source 26 and an X-ray imaging sensor 27. Image acquisition is performed as a rotational scan around the patient's head. The shape 28 of the X-ray beam is, in this illustration, optimized for simultaneous acquisition of a panoramic image and a tomographic image. Tomographic image data is collected by the lower and widest portion 29 of the sensor area while the entire narrowest slot-like length 30 of the active area is used to collect the panoramic image data.

Data is acquired at a predetermined rate as image frames with each frame corresponding to a certain position of the X-ray source and sensor along the rotational path of the scan. The data is sent to a computer 31 for image reconstruction and display. A complete panorama layer or a local part of a panoramic layer as well as a transverse slice or 3D image corresponding to a local part of a panoramic layer can be reconstructed from the data frames.

The system of Figure 9 thus provides an extraoral dental X-ray imaging system. X-ray source 26 generates X-rays for exposure of such X-rays to the patient to be imaged. X-ray imaging devices 28, as described above, are used to produce multiple frames during at least part of the exposure. At least one of the X-ray source and the imaging device rotate about at least one axis of rotation 37 defined by a groove 38, the axis being located between the focal point of the X-ray source and the imaging device. X-ray imaging and changing position along directions 39 and 40 during scanning.

Computer 31, a processor, processes single exposure frames to selectively compose at least two of a group of elements, the elements comprising (a) a predetermined dental panoramic layer image, (b) a local part of a layer image non-predetermined dental panoramic, (c) a slice transverse to a local part of a dental panoramic layer image; and (d) a 3D reconstruction of a volume corresponding to some local part of a dental panoramic layer.