X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-10-28
2001-09-18
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S098200, C250S370090, C250S363020, C250S367000
Reexamination Certificate
active
06292528
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a computer tomograph detector for the detection of electromagnetic radiation transmitted by an object, which detector includes at least one detector row which consists of a plurality of detector elements, each detector element including a scintillator for converting radiation of a first energy level into radiation of a second energy level, as well as a photosensor for converting the radiation into an electrical current, an amplifier element being associated with each photosensor.
2. Description of Related Art
Computer tomographs serve to form planar images of imaginary slices of an object, for example a body. A computer tomograph generally consists of a circular portal frame or gantry in which a scanning device with an X-ray source is integrated. The scanning device rotates about an imaginary longitudinal axis extending through the body. After having traversed the body, the X-rays are incident on an oppositely situated detector which rotates together with the scanning device. The reconstruction of a single image requires a set of images which correspond to different protection angles, each image having radiation intensities which are detected by individual detector elements.
Detectors comprising one or more rows are known. EP 0 819 406 A1 discloses a computer tomograph with a plurality of parallel detector rows, i.e. a so-called multi-line detector. The detector consists of a two-dimensional array of detector elements, i.e. a plurality of detector rows, which are arranged parallel to one another in the direction of the axis of rotation (z direction). A multi-line detector offers the advantage that during a rotation of the gantry a plurality of cross-sectional images can be simultaneously picked up in dependence on the extent of the detector in the z direction.
In the case of a computer tomograph with a one-dimensional detector, i.e. single-line detector, only the cross-sectional image of a fan-shaped beam is picked up. In order to obtain a volume image, the body, i.e. the patient, must be moved through the computer tomograph. When a multi-line detector is used, however, a pyramid-like beam or cone beam is used, so that a volume image can be picked up already during a single rotation of the gantry, said volume image consisting of a number of cross-sectional images in conformity with the number of rows of the array.
The body is scanned helically or spirally in the case of single-line detectors as well as in the case of multi-line detectors. The gantry is then rotated about the body while at the same time the patient is moved along the axis of rotation relative to the gantry. Using a multi-line detector, the execution of such a spiral scan is significantly faster than when use is made of a single-line detector, because the patient can be transported over the full width of the detector during one revolution of the gantry. Such a reduction of the scanning time by using multi-line detectors minimizes the detrimental image artefacts due to motions of the patient, for example due to respiration or muscle contractions.
The multi-line detector which is known from EP 0 819 406 A1 concerns a two-dimensional array of detector elements, each of which is constructed on the basis of a ceramic scintillator which is succeeded by a photodiode. The detector signals are received by a multiplexer. The multiplexer applies the information to a computer and the images of the body are displayed on a monitor.
A computer tomograph provided with a two-dimensional array is also known from U.S. Pat. No. 5,291,402. As is customary in detectors of this kind, each detector element of the detector array is electrically independent. The signals of the decoupled detector elements are acquired by means of a data acquisition system. Those skilled in the art will know that such a data acquisition system requires a multitude of discrete amplifier elements which are associated with the individual detector elements.
It is a drawback that the relevant photodiodes are connected to the amplifier elements via individual supply leads. This leads to a very large number of connections, notably in the case of multi-line detectors. The high density of the connection leads may lead to crosstalk of the channels and irritations due to the coupling in of interference by capacitive and/or inductive coupling. This causes a high, undesirable electrical noise and a deterioration of the DQE (Detective Quantum Efficiency).
Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicant's invention of the invention subsequently claimed.
Therefore, it is an object of the invention to provide a computer tomograph detector which may comprise a plurality of detector rows, involves less electronic noise and at the same time offers a higher DQE and fast preparation of the desired image.
SUMMARY OF THE INVENTION
This object is achieved by means of a detector comprising: at least one detector row which further comprises a plurality of detector elements, each detector element including a scintillator for converting radiation of a first energy level into radiation of a second energy level, as well as a photosensor for converting the radiation into an electrical current, and an amplifier element which is associated with each photosensor, wherein a plurality of photosensors and the associated amplifier elements are arranged on the same substrate in an integrated semiconductor technique. Advantageous embodiments of the invention are disclosed in the dependent claims.
The photosensors and amplifier elements constructed in semiconductor technology, notably in standard CMOS technology, and arranged on the same substrate enable minimization of the configuration of leads for the high impedance signals between the photosensors and amplifier elements; such a configuration of leads can hardly be realized at acceptable costs in customary multi-line detectors. As a result of the minimization of the stretch of leads, the parasitic line capacitances can also be reduced to a minimum. This results in a reduction of the electrical noise and the susceptibility to interference, but the DQE remains high.
The faster preparation of the patient image makes it easier to work with such a computer tomograph and image artefacts are avoided due to the fast composition of the images.
Preferably, the detector chip is made using CMOS technology. However, other semiconductor technologies are also feasible, for example the bipolar technique or JFET technology (JFET=Junction Field Effect Transistor). The CMOS technique offers advantages in respect of cost, low current consumption, availability as well as the realization of logic circuit components. Process technologies such as bi-CMOS, (HV-CMOS), NMOS or PMOS are feasible.
Preferably, the detector consists of an array, i.e. a two-dimensional surface, of detector elements.
It is feasible to arrange the entire array of the detector elements on a single substrate., The array is customarily composed of a plurality of chips.
Each photosensor and the associated amplifier element in a first embodiment of the detector are arranged so as to be adjacent. In a second embodiment the amplifier elements are arranged at a distance from the photosensors, for example at the edge of a chip.
Each detector element includes a scintillator for converting the electromagnetic radiation, i.e. X-rays, into radiation of a different energy level. The scintillator is preferably constructed as a matrix of scintillator elements. The scintillator elements consist either of monocrystals or of a plurality of crystals. For example, a scintillator consists of cadmium tungstate (CdWO)
4
or of Gd
2
O
2
S:Pr, F, Ce).
In order to shield the sensitive amplifier elements from the electromagnetic radiation, there are provided shielding layers which reduce the radiation load on the electronic components, notably on the gate oxide.
In the first embodiment, i.e. the embodiment with the adjacently arr
Lauter Josef
Schneider Stefan
Wieczorek Herfried
Hobden Pamela R.
Kim Robert H.
U.S. Philips Corporation
Vodopia John F.
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