X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2002-08-06
2004-09-14
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S098800
Reexamination Certificate
active
06792068
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a CT (computed tomography) device of the type having a radiation source which, in order to scan an object to be examined, can be displaced relative to a system axis and emits a beam of radiation, which strikes a detector system formed by an array of lines and columns of detector elements, the measured values obtained in this way being associated with one of a large number of projection angles and being supplied to a computer, which uses them to calculate images of the object to be examined, the signals generated in the detector elements by radiation being supplied to electronic elements to be read and amplified, the number of detector elements of the detector system exceeding the number of electronic elements.
2. Description of the Prior Art
CT devices are known which have a radiation source, for example an X-ray tube, which directs a collimated, pyramidal beam of radiation through the object to be examined, for example a patient, onto a detector system formed by a number of detector elements. The radiation source and, depending on the design of the CT device, the detector system also are mounted to a gantry, which rotates around the object to be examined. A mounting device for the object to be examined can be displaced or moved along the system axis relative to the gantry. The position from which the radiation beam passes through the object to be examined, and the angle at which the beam of radiation passes through the object to be examined, are varied continually as a result of the rotation of the gantry. Each detector element in the detector system that is affected by the radiation produces a signal which constitutes a measure of the overall transparency of the object to be examined for the radiation originating from the radiation source on its path to the detector system. The set of output signals from the detector elements of the detector system, which is obtained for a specific position of the radiation source, is referred to as a projection. A scan is formed by a set of projections, which have been obtained at various positions of the gantry and/or various positions of the mounting device. During one scan, the CT device assumes a large number of projections, in order to be able to build up a two-dimensional sectional image of a layer of the object to be examined. With a detector system constructed from an array of lines and columns of detector elements, a number of layers can be recorded at the same time.
German OS 195 02 574 discloses a CT device of the type mentioned in the introduction having a multi-line detector system, in which, in order to save cost and in order to limit the data rates, the read electronics connected downstream of the detector elements does not have an electronic element for each detector element. Instead, the number of detector lines exceeds the number of lines of electronic elements. Each line of electronic elements can be associated with a number of detector lines via multiplexers and summers.
In this known CT device, a disadvantage is that, as a result of connecting adjacent detector lines together, the thickness of the layers recorded increases, and therefore the resolution in the z-direction is decreased. Another disadvantage is that each detector line is not connected to a line of electronic elements, and therefore it is not possible for the entire detector width in the z-direction to be used for data acquisition.
German OS 198 35 873 discloses a CT device of the type mentioned in the introduction, in which the number of detector elements exceeds the number of electronic elements and, therefore, region by region, a number of detector elements of a detector line are coupled, i.e., are connected to one electronic element, with the coupling of detector elements being omitted in the central region of the detector lines.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a CT device of the type mentioned in the introduction wherein, in spite of a reduced number of electronic elements, as compared with the number of detector elements, a high resolution can be achieved with the detector system and, nevertheless, a high number of individual layers can be recorded at the same time.
According to the invention, this object is achieved by a CT device having a radiation source which, in order to scan an object to be examined, can be displaced relative to a system axis and emits a radiation beam, which strikes a detector system formed by an array of lines and columns of detector elements, the measured values obtained in this way being associated with one of a large number of projection angles and being supplied to a computer, which uses them to calculate images of the object to be examined, signals generated in the detector elements by radiation being supplied to electronic elements to be read and amplified, the number of detector elements of the detector system exceeding the number of electronic elements, and wherein a region of detector columns including at least one detector column can be connected to a larger number of electronic elements, in order to read out the detector elements from this region, than is a different region having the same number of detector columns.
The CT device according to the invention therefore not only has the advantage that the detector system can be implemented more simply and less expensively by means of the number of electronic elements being reduced with respect to the number of detector elements, but also, therefore, region by region a larger number of layers can be recorded at the same time than in the case of detector systems with a reduced number of electronic elements according to the prior art.
Whereas in known CT devices, adjacent detector elements can if required be connected together line by line, and each detector column is associated with a permanently predefined number of electronic elements, the detector system according to the invention can be divided into regions with a different resolution both in the z-direction and in the &phgr;-direction. To this end, different detector columns of the detector system according to the invention can be connected to different numbers of electronic elements. If, for example, a CT device according to the prior art has an 8-line detector system with four lines of electronic elements, then each detector column of the detector system is connected to a maximum of four electronic elements compared to this, a CT device according to the invention, likewise having an 8-line detector system, permits specific detector columns to be connected, for example, to six electronic elements and other detector columns to be connected only to two electronic elements per detector column. A suitable arrangement of multiplexers and summation elements between the detector elements and the electronic elements permits a largely random interconnection of detector elements and the assignment of individual detector elements or interconnected detector elements to individual electronic elements.
A region of the detector system of the CT device according to the invention whose detector columns are assigned an increased number of electronic elements can, for example, be the especially relevant central region of the detector system. Outside the central region, correspondingly fewer measured values are formed as a result of detector elements being combined or not being taken into account. Given the same overall z-length of the collimated layer over the entire detector, many thin individual layers are in this way obtained in one region, but a few wide individual layers in another region. Therefore, in the one region, the number of effective lines, and therefore the resolution in the z-direction, is increased, without additional electronic elements being required for this purpose. In addition, the data rates and amounts of data that can be generated by the detector system do not change with respect to a known detector system having a reduced number of electronic elements.
In the CT device according to the in
Flohr Thomas
Ohnesorge Bernd
Church Craig E.
Schiff & Hardin LLP
Siemens Aktiengesellschaft
Song Hoon
LandOfFree
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