X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2001-11-23
2004-07-13
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C382S275000, C382S128000
Reexamination Certificate
active
06763084
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for operating an image system of an imaging medical examination device, the image system having a reception unit for receiving a plurality of signals arising at different locations, and a display unit for the imaging representation of pixels, the pixels each being assigned at least one signal. The invention additionally relates to an imaging medical examination device having an image system, the image system having a reception unit for receiving a plurality of signals arising at different locations, and a display unit for the imaging representation of pixels, the pixels each being assigned at least one signal.
In medical X-ray technology use is made of digital imaging systems having a reception unit with a digital image converter—instead of an analog image converter. Such a digital image converter acquires an image comprising a plurality of pixels. An individual pixel can be generated e.g. by the signal of an individual element of a photodiode array, of a CCD image converter or an amorphous silicon detector (a:Si detector). The individual elements receive light signals arising at different locations and image them on a display unit in an imaging fashion.
Image converters of this type can be affected by pixel failures caused e.g. by the failure of an individual converter element. There may also be pixel failures in groups (so-called clusters), which lead to the failure of entire lines or columns and are caused for example by interruptions in the address lines.
The failure of one or more pixels or measurement channels can lead to image artifacts of greater or lesser severity, which become visible for example as black rings in a computer tomograph image. If every image converter affected by such an artifact were discarded from the series during the production of a digital image system, this would lead to a high reject rate. On the other hand, however, given the multiplicity of pixels present, it is not necessary for the signal of every individual measurement channel to reach the imaging stage. In order to decrease the rejection of detectors, it is known, therefore, for example from DE 195 27 179 C1 or from DE 195 27 148 C1, to correct a defective pixel. For this purpose, the procedure is performed in two steps: firstly a defect determination takes place, which yields information about which pixels are defective and which are good. When this information is present, the defective pixels can be corrected in a second step. The correction can be achieved for example by replacing the defective pixels by linear interpolation of adjacent pixels. For the correction of column or line defects, DE 195 27 179 C1 discloses proceeding separately according to line defects in a first correction step and according to column defects in a second correction step.
A correction circuit—based on an interpolation method—for correcting defective pixels in an image system or a CCD apparatus is also disclosed in EP 0 687 106 A1.
SUMMARY OF THE INVENTION
Proceeding from an image system with a potentially defective pixel, the invention is based on the object of specifying a method for operating such an image system in an imaging medical examination device which improves the reliability of the operation of the image system. An imaging medical examination device having an image system is also intended to be specified for the same purpose.
The first-mentioned object is achieved, relative to a method of the type mentioned in the introduction, by virtue of the fact that an event of the undisturbed operation of the medical examination device automatically triggers a defect determination for determining a defective pixel possibly present in the image.
The defect determination can be performed as it were on line during use and not just once after the production of the digital image sensor or during the calibration thereof. This makes it possible firstly for imminent defects already to be identified at a point in time at which the image is not yet severely disturbed. Secondly, it is thus possible to effect continuous correction of newly occurring defects, so that even over a long period of operation, the quality of the images recorded by the image sensor having an increasing number of defects is not impaired or is virtually unimpaired.
In particular, an event that occurs anyway during operation is used or a triggering event is generated during the undisturbed operation.
In this case, the invention is based on the insight that in image systems of future medical examination devices, defective pixels will have to be reckoned with to an increasing extent, since the number of detector channels will rise. It will increasingly happen that such image or channel failures will not occur until during clinical operation and interrupt the latter or at least cause massive disruption thereto. Although occasionally the defects may arise as early as during the production of the digital image converter, there is nonetheless the risk that further defects or indeed the first manifestation of defects will occur during the use and operation of the digital image converter, that is to say e.g. during clinical use, and interrupt the latter or at least cause massive disruption thereto. In the case of the method according to the invention, such defects and, consequently, an operational disruption are counteracted since the defect determination is triggered automatically. This means that it is possible, in particular, for an imminent defect already to be detected at a point in time at which the image is not yet severely disturbed, in order to initiate suitable countermeasures before the occurrence of a later severe disturbance. The method additionally has the advantage that separate intervention by an operator is not necessary to trigger the defect determination. Rather, the defect determination can take place without the action and even without the knowledge of an operator.
According to a preferred embodiment, the triggering event is derived from an operating process which does not serve for the defect determination, in particular from an operator's control process which does not serve for the defect determination.
Preferably, the triggering event is derived from a switch-on process performed on the medical examination device. By way of example, a defect determination sequence or a defect determination algorithm is automatically triggered when the medical examination device is switched on.
It is likewise preferred for the triggering event to be derived from a calibration process performed on the medical examination device. Such a calibration process is carried out e.g. when the examination device is switched on or during the operation of said examination device by an operator, e.g. by a doctor. During this calibration process, the image channels or pixels are calibrated individually and immediately examined with regard to a defect during this opportunity.
Preferably, the triggering event is generated at a defined point in time before, during or after an image acquisition procedure, in particular before, during or after a patient examination or a scan.
The triggering event can also be generated by a counting process. In particular, the counting process counts a process which is repeated during operation of the medical examination device, in particular a switch-on process, a calibration process and/or examination process. A trigger signal as the triggering event is triggered for example whenever the counting process has continued counting by a constant interval. This affords the advantage that a defect determination is automatically triggered whenever the image system has been exposed to a high load and, accordingly, it is with increased probability that the occurrence of defects is to be reckoned with.
It is likewise preferred for the triggering event to be generated by a time measuring process. For this purpose, a corresponding trigger signal can be derived for example from a clock generator or a timer of a computer which controls the examination device. By way of example, a tr
Boehm Stefan
Spahn Martin
Bruce David V.
Ikiknadze Irakli
Siemens Aktiengesellschaft
Young & Thompson
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