Abstract: A method is for imaging in computer tomography, in which a periodically moved object to be examined is scanned with the aid of a beam of rays coming from a focus. A two-dimensionally designed detector array generates output data which are filtered in a suitable way and back-projected in order to obtain at least one sectional image which represents the absorption values of the section of the object to be examined in a particular movement state. In the method, on the one hand, a weighting function which weights the spatial distance of a ray in question from the voxel in question is used for the back-projection. Further, on the other hand, a weighting function which represents the time difference from the examination area movement state to be represented in each case is also used.

Abstract: A method is for determining correction coefficients or parameters, in particular channel correction coefficients and/or spacing coefficients, for detector channels for a computed tomograph. In the method, a scan is carried out in order to obtain a sinogram of a phantom which is formed with a smooth cross-sectional profile and is inserted into the computed tomograph in such a way that two or more different attenuation values are detected in a full scan of virtually all the detector channels. Attenuation profiles that are obtained from the sinogram are subjected to high-pass filtering for each projection of the scan, in order to obtain discrepancies of an ideal profile which is predetermined by the phantom. A model function is matched to the discrepancies that are obtained for each of the detector channels as a function of the detected attenuation values, from which the coefficients or parameters are obtained.

Abstract: In a spiral scan cone beam computed tomography method and apparatus, the output data are divided into sub-segments being shorter than the length required for the reconstruction of a CT image. Segment images having inclined image plane relative to the system axis are reconstructed for the sub-segments. A signal reproducing the time curve of the periodic motion is acquired during the scanning. A z-position on the system axis and a time position with respect to the periodic motion are allocated to the segment images. Segment images belonging to a desired range of z-positions and a desired range of time positions are selected such that the corresponding sub-segments have an overall length adequate for the reconstruction of a CT image. The selected segment images are at least indirectly combined into a resulting CT image with respect to a target image plane.

Abstract: In a method and apparatus for computed tomography, a subject is scanned with a conical ray beam emanating from a focus and the attenuated beam is detected with a matrix-like detector array. The focus is moved on a spiral path around a system axis relative to the subject, and the detector array supplies output data corresponding to the received radiation. The output data are supplied during the motion of the focus on a spiral segment and have a length adequate for the reconstruction of a CT image, and are divided into output datasets with respect to sub-segments. Segment images having an inclined image plane relative to the system axis are reconstructed for the sub-segments. The segment images respectively belonging to the sub-segments are combined into a partial image with respect to a target image plane, and the partial images are combined into a resulting CT image with respect to the target image plane.

Abstract: A method is used for checking the presentation quality of imaging systems for medical diagnostics with regard to ring artifacts. The method includes creating at least one test image and defining concentric circles in the test image around a rotational center that is fixed by the imaging system. The method further includes averaging the test image points, arranged along the respective circumferential lines of the circles in circumferential direction of the respective circle in order to create a ring profile in which ring artifacts are detected. Finally, the detected ring artifacts are compared to a pre-selected criterion for evaluating the visual detectability of the detected ring artifacts. The comparison of the detected ring artifacts to the pre-selected criterion is carried out by computing the visual signal noise for each ring artifact and comparing the computed signal noise to the pre-selected criterion.

Abstract: A method for computed tomography, includes, in order to scan an object to be examined with a conical beam originating from a focus and with a matrix-like detector array for detecting the beam, the focus is moved, relative to the object to be examined, on a focal path around a system axis. A detector array supplies an output data corresponding to received radiation. The output data is filtered, and the filtered output data is backprojected three-dimensionally in order to produce at least one slice of a layer of the, which has a layer thickness. The slice represents absorption values obtained from the output data of a voxel belonging to the layer for the radiation from the beam. Filtering is carried out at least also in the direction of the tangent to the focal path belonging to a respective focal position, and normalization is carried out for each voxel considered.

Abstract: In a computed tomography and a method for operating a computed tomography unit, in order to scan an object under investigation a radiation source emits a pyramid-shaped X-ray beam, which penetrates through the object under examination and strikes a radiation detector. The computer tomography unit has an optical recording device which, during the scanning, records optical images of a partial surface of the object, which faces the X-ray source and through which the pyramid-shaped X-ray beam has penetrated. An image of the surface of the object under examination is constructed from optical images obtained in this manner this image is assigned to a sectional image obtained by means of the scan, or to an overview image.

Abstract: In a computed tomography method and apparatus, having a subject with a conical ray beam emanating from a focus and with a matrix-like detector array for detecting the ray beam, while the focus is moved on a spiral path around a system axis relative to the subject, and the detector array supplies output data corresponding to the received radiation. The output data respectively supplied during the motion of the focus on a spiral segment and having a length adequate for the reconstruction of a CT image are divided into output data with respect to sub-segments, with the length of each sub-segments being shorter than the length required for the reconstruction of a CT image. Segment images having an inclined image plane relative to the system axis are reconstructed for the sub-segments. A signal reproducing the time curve of the periodic motion is acquired during the scanning. A z-position on the system axis and a time position with respect to the periodic motion are allocated to the segment images.

Abstract: In a method and filter and computer product for adaptive filtering of projection data acquired by a medical diagnostic apparatus, raw data-based filtering of the acquired projection data is undertaken using a filter with a filter kernel having a constant filter width, and the filtered projection data are mixed with the acquired projection data with a fixing of the respective quantitative relationships of filtered projection data to acquired projection data ensuing dependent on respective subsets of the acquired projection data.

Abstract: In a method and apparatus for computed tomography, a subject is scanned with a conical ray beam emanating from a focus and the attenuated beam is detected with a matrix-like detector array. The focus is moved on a spiral path around a system axis relative to the subject, and the detector array supplies output data corresponding to the received radiation. The output data are supplied during the motion of the focus on a spiral segment and have a length adequate for the reconstruction of a CT image, and are divided into output datasets with respect to sub-segments. Segment images having an inclined image plane relative to the system axis are reconstructed for the sub-segments. The segment images respectively belonging to the sub-segments are combined into a partial image with respect to a target image plane, and the partial images are combined into a resulting CT image with respect to the target image plane.

Abstract: A method is used for checking the presentation quality of imaging systems for medical diagnostics with regard to ring artifacts. The method includes creating at least one test image and defining concentric circles in the at least one test image. The definition of the concentric circles in the at least one test image occurs around a rotational center that is fixed in the test image by the imaging system for medical diagnostics. The method further includes averaging the test image points, arranged along the respective circumferential lines of the circles in circumferential direction of the respective circle in order to create a ring profile. Thereafter, ring artifacts in the generated ring profile are detected. Finally, the detected ring artifacts are compared to a pre-selected criterion for evaluating the visual detectability of the detected ring artifacts.

Abstract: In a method for computed tomography and a computed tomography apparatus for scanning a subject with a conical ray beam emanating from a focus that detects a matrix-like detector array, the focus is moved relative to the subject on a spiral path around a system axis, and the detector array supplies output data corresponding to the incident radiation, and images having an inclined image plane are reconstructed from output data respectively supplied during the movement of the focus on a spiral segment, the image planes of these images are inclined by an inclination angle &ggr; around a first axis intersecting the system axis at a right angle and also are inclined by a tilt angle &dgr; with respect to the system axis around a second axis that intersects the first axis as well as the system axis at a right angle.

Abstract: In an X-ray computed tomography apparatus having a radiation filter, a patient attenuation value representative of the linear beam attenuation by a patient under examination is determined in an equation containing a correction function. The correction function is determined by first determining a set of reference overall attenuation values that, for a given different thicknesses of a reference material and different thicknesses of the radiation filter arrangement, represent the actual overall attenuation by the two materials. Then, an appertaining attenuation error value is determined for each reference overall attenuation value. Subsequently, a variable is defined changes in a direction transverse to straight lines of constant attenuation error values in a characteristic field of the attenuation error.

Abstract: In an X-ray computed tomography apparatus with retrospective beam hardening correction, an overall image of a body slice under examination is determined from overall attenuation values that are obtained from the body slice. At least one partial image that shows essentially only one body substance, such as bone substance, is extracted from this overall image. Attenuation partial values are employed for determining a correction value. The attenuation values are determined for each overall attenuation value from the at least one partial image by re-projection. A correction value is derived from the beam hardening error that is determined for a material combination of two different reference materials.

Abstract: In a method and apparatus for reducing line artifacts in a CT image D1, which is acquired during a scan by a CT device with a detector system having a number of proper detector channels and at least one defective detector channel, the image M1 is obtained first by a median filtering the image D1, which contains a circle artifact on a circle K1. A difference value image F1=D1−M1 is then produced. Filtering then is carried out in each picture element of the image F1 in the direction of the tangents t11 and t21 to the circle K1 extending through the respective picture element in order to produce two resulting images G11 and G21. A correction image D2 is subsequently produced by subtracting the resulting images G11 and G21 from D1.

Abstract: In a computed tomography and a method for operating a computed tomography unit, in order to scan an object under investigation a radiation source emits a pyramid-shaped X-ray beam, which penetrates through the object under examination and strikes a radiation detector. The computer tomography unit has an optical recording device which, during the scanning, records optical images of a partial surface of the object, which faces the X-ray source and through which the pyramid-shaped X-ray beam has penetrated. An image of the surface of the object under examination is constructed from optical images obtained in this manner this image is assigned to a sectional image obtained by means of the scan, or to an overview image.

Abstract: In an X-ray computed tomography apparatus having a radiation filter, a patient attenuation value representative of the linear beam attenuation by a patient under examination is determined in an equation containing a correction function The correction function is determined by first determining a set of reference overall attenuation values that, for a given different thicknesses of a reference material and different thicknesses of the radiation filter arrangement, represent the actual overall attenuation by the two materials. Then, an appertaining attenuation error value is determined for each reference overall attenuation value. Subsequently, a variable is defined changes in a direction transverse to straight lines of constant attenuation error values in a characteristic field of the attenuation error.

Abstract: In an X-ray computed tomography apparatus with retrospective beam hardening correction, an overall image of a body slice under examination is determined from overall attenuation values that are obtained from the body slice. At least one partial image that shows essentially only one body substance, such as bone substance, is extracted from this overall image. Attenuation partial values are employed for determining a correction value. The attenuation values are determined for each overall attenuation value from the at least one partial image by re-projection. A correction value is derived from the beam hardening error that is determined for a material combination of two different reference materials.

Abstract: In a method and apparatus for reducing line artifacts in a CT image D1, which is acquired during a scan by a CT device with a detector system having a number of proper detector channels and at least one defective detector channel, the image M1 is obtained first by a median filtering. the image D1, which contains a circle artifact on a circle K1. A difference value image F1=D1−M1 is then produced. Filtering then is carried out in each picture element of the image F1 in the direction of the tangents t11 and t21 to the circle K1 extending through the respective picture element in order to produce two resulting images G11 and G21. A correction image D2 is subsequently produced by subtracting the resulting images G11 and G21 from D1.

Abstract: An X-ray computed tomography apparatus has a radiation detector composed of X-ray converters so that the scattering of light in a scintillator or the inductive disturbance in a directly converting semiconductor is minimized or eliminated. Each X-ray converter, e.g. a scintillator is in fixed contact with a number of signal converters, e.g. photodiodes. From the output signals of the signal converters, the unsharpness can be calculated and then compensated.