X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2001-01-13
2002-12-31
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S016000
Reexamination Certificate
active
06501820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for scanning an examination subject using a CT device with a radiation source with a focus which can be displaced around about a system axis with a radiation beam emanating from the focus and striking a detector system which produces scanning data, and wherein the effective radiation is a first volumetric region, in which a body part of an examiner is located during the scanning, is reduced with respect to the effective radiation in a comparable second volumetric region of the same size and at the same distance from the system axis in which no body part of the examiner is located.
2. Description of the Prior Art
CT devices and known which have a radiation source, for example an X-ray tube, which directs a collimated, pyramidal radiation beam through the examination subject, for example a patient, onto a detector system assembled from a number of detector elements. The radiation source and, depending on the design of the CT device, the detector system as well, are fitted on a gantry which rotates around the examination subject. A support device for the examination subject can be displaced or moved along the system axis relative to the gantry. The starting position from which the radiation beam penetrates the examination subject, and the angle at which the radiation beam penetrates the examination subject, are continuously varied as a consequence of the rotation of the gantry. Each detector element of the detector system, when struck by the radiation, produces a signal which constitutes a measure of the total transparency of the examination subject for the radiation emanating from the radiation source on its path to the detector system. The set of output signals of the detector elements of the detector system, which set is obtained for a specific position of the radiation source, is known as a projection. A scan comprises a set of projections which have been obtained at different positions of the gantry and/or different positions of the support device. The CT device picks up a multiplicity of projections during a scan, in order to be able to build up a two-dimensional tomographic image of a section of the examination subject. A number of sections can be picked up simultaneously with using a detector system formed as an array of a number of rows and columns of detector elements.
Relatively large volumes of the examination subject are usually picked up by means of sequential scanning or spiral scanning. In the case of sequential scanning, the data are picked up during the rotary movement of the gantry, while the examination subject is located in a fixed position, and thus planar sections are scanned. The examination subject is moved between the scanning of successive sections into a new position in which the next section can be scanned. This process continues until all sections designated before the examination are scanned. In the case of spiral scanning, the gantry rotates continuously with the radiation source around the examination subject, while the support table and the gantry are continuously displaced relative to one another along a system axis. Relative to the examination subject, the radiation source therefore describes a spiral path until the volume designated before the examination has been scanned. Images of individual sections are then calculated from the spiral data.
Furthermore, CT devices are known in the case of which the X-ray power can be modulated during the rotation of the radiation source around the examination subject with a non-circular cross section in order to scan the examination subject. If, for example, a patient lying on his or her back is being scanned, as a rule the path of the X-ray radiation through the body of the patient is longer in the horizontal direction than in the vertical direction. If a modulation of the X-ray power is not possible, the power must be set such that the signal quality supplied by the detector system is still sufficient to calculate correct images even for the projections with the longest path of the radiation through the body. The X-ray power therefore is unnecessarily high for all other projections. In order not to stress the object under examination with an excessive radiation dose, an attempt is made to set the X-ray power in accordance with the attenuation profile as a function of the angular position of the radiation source. Such a method is described, for example, in German OS 19 806 063.
CT devices are used principally in the field of medicine. In addition to examinations for purely diagnostic purposes, interventions (for example biopsies, centeses) are increasingly being carried out with the aid of CT monitoring. During the intervention, the position of medical instruments required to carry out the intervention, for example a needle, can thus be monitored continuously. When a radiation source is switched on and manual guidance of such a medical instrument is employed by an examiner, body parts of the examiner, for example a hand, which are located in the region penetrated by the radiation beam between the focus and detector system can be struck by unattenuated radiation.
U.S. Pat. No. 5,873,826 discloses an X-ray CT device wherein the radiant power of the X-ray source can be temporarily reduced during scanning in order to reduce the radiation dose to an examiner. The volumetric region for which this reduction is effective is designated before scanning, and is identified during scanning by marking with a light source.
U.S. Pat. No. 5,841,830 discloses a CT device wherein diagnostic image information is obtained with x-rays at a first intensity, and image information relating to the movement of an invasive surgical instrument is obtained with x-rays at a second intensity, reduced by comparison with the first intensity. The diagnostic image information and the image information relating to the movement of the surgical instrument are superimposed to form a resulting image.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for operating a CT device such that the radiation dose to an examiner is reduced and, at the same time, a good quality of the calculated images is achieved. It is also an object of the invention to provide a CT device for carrying out the method.
The above object is achieved in accordance with the principles of the present invention an x-ray CT apparatus of the type described above, and a method for operating such a CT apparatus, wherein movement of a body part of an examiner into an examination region covered by the x-ray beam is automatically detected, and the effective radiation is automatically reduced for a first volumetric region which includes the body part of the examiner, with respect to a comparable second volumetric region in which no body part of the examiner is located. The radiation dose to the examiner is thereby reduced. The size of the first volumetric region is automatically adjusted dependent on a detected size and/or position and/or movement direction of the body part. The adjustment of the effective radiation in the volumetric region in which the body part is located can be achieved by varying the tube current of the x-ray tube, by adjusting a beam diaphragm through which the radiation beam passes, or by inserting a radiation absorber into the beam path.
An important advantage of the inventive method and apparatus is that the radiation dose to the examiner is reduced without the examiner needing to define, before starting the scanning, a volumetric region inside the examination space into which the examiner will bring one or more body parts during the examination. The invention thus advantageously simplifies the operation of the CT device, and incorrect inputs are prevented. The invention provides a further advantage by allowing the size of the volumetric region for which the effective radiation is reduced to be limited to a minimum. This is because, for the personal safety of the examiner, the examiner need not establish, before the examination, a rela
Kiknadze Irakli
Kim Robert H.
Siemens Aktiengesellschaft
LandOfFree
X-ray CT apparatus and method for operating same for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with X-ray CT apparatus and method for operating same for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and X-ray CT apparatus and method for operating same for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2938004