Abstract: The present invention, in one form, is a system for producing incremental tomographic images of an object from projection data acquired in a helical scan. The system creates base image data arrays from the projection data. An interpolation algorithm is then applied to the base image data arrays to generate overlapped, or incremental, tomographic images.

Abstract: A present invention, in one form, is a method for removing artifacts from image data due to detector degradation. Particularly, data is obtained from a CT system including a detector and an x-ray source. The detector is formed from a plurality of detector cells. In accordance with one form of the invention, a detector degradation signature (S(i)) vector is generated prior to scanning a patient. Subsequent to scanning the patient, if the image data contains a ring error, a detector cell contributing to the error is identified using the detector degradation signature vector. The system then determines if the cell a degraded cell. If such cell is a degraded cell, ring error correction processing is then performed on the image data.

Abstract: A method and system for suppressing artifacts in a CT generated image are described. With respect to artifacts resulting from X-ray beam photon starvation conditions, and in accordance with one embodiment of the method, the steps of determining a minimum value X-ray beam flux for a projection data set and dynamically DC adjusting the projection data based on the determined minimum X-ray beam flux are performed.

Abstract: The present invention, in one form, is an apparatus for performing image reconstruction using data obtained by a helical scan. In reconstructing an image in accordance with the present invention, projection data arrays corresponding to data planes associated with the slice to be imaged are generated. Weighting factors are then applied to the data arrays to assign a weight to each particular data element thereby creating a weighted projection data array. The weighted projection data array is then filtered and back projected to create an image data array from which an image slice is generated. In accordance with the present invention, the weighting function used in creating the weighted projection data array is based upon a plane of reconstruction which is not necessarily perpendicular to the z-axis.

Abstract: The present invention, in one form, utilizes a region of reconstruction ROR in reconstructing an image from projection data. Particularly, once the region of reconstruction is established, a weighting function which is either a linear interpolation or a non-interpolation can be used. If 3.pi. of projection data is used, the weighting function can be divided into three parts. Each part corresponds to .pi. projection views. For a 50% overlapped reconstruction, the entire weighting functions advance .pi. degrees at a time, which synchronizes very well with the boundaries of the weighting functions. Section 1(S.sub.1) will contain projection views from 0 to .pi., section 2 (S.sub.2) contains views from .pi. to 2.pi., and section 3 (S.sub.3) contains views from 2.pi. to 3.pi.. In section S.sub.1, the weighting function is a ramp-up function, in section S.sub.2 the weighting function is a constant, and in section S.sub.3 the weighting function is ramped down.

Abstract: An x-ray CT scanner acquires projection profiles P during a scan which are corrected for errors caused by non-uniform response of the detectors along the z-axis. In addition to corrections using a calibration vector Q that offsets errors caused by variations in the detector response, additional corrections are made to offset object dependent errors caused by the same variations in detector response when imaging certain objects.

Abstract: An x-ray CT scanner is operated in a test mode to acquire attenuation projections using a phantom shaped to accentuate errors due to non-uniform detector response along the z-axis. Error values are calculated for detector elements and these error values are compared with preset limits to identify faulty or marginal detector elements.

Abstract: During acquisition of X-ray attenuation measurements of a patient being imaged, the measurements are processed to determine error factors for each detector in the system. In doing so, an average value is calculated for each detector from the X-ray attenuation measurements acquired during a scan of the patient. The set of average values should increase and decrease monotonically going toward and away from the value in the set for center detector. Deviation from such monotonic variation indicates a calibration error and is used to change a calibration factor in the signal processing circuit for the corresponding detector.

Abstract: Streaking artifacts in a computed tomography x-ray image are reduced by adaptively filtering each set of projection data. The adaptive filter produces an error vector (.theta.) by low-pass filtering the projection data (P) and subtracting the error vector (.theta.) from the projection data (P) prior to image reconstruction. A window function generator controls the low-pass filter as a function of x-ray detector readings.

Abstract: A CT apparatus employing a cone beam of x-rays reduces image artifacts by employing full as opposed to half scans of less than 360.degree.. The present invention recognizes that rays of a cone beam that cross the imaging plane are not redundant with opposing rays in the scan, as is the case with the rays within the imaging plane. In a second embodiment, half scans of less than 360.degree. are obtained using in-plane and cross-plane rays of the cone beam and the data from the in-plane rays is used to estimate the missing data from that collected with the cross-plane rays.

Abstract: A computed tomography imaging system has a source of radiation and a radiation detector that has an exponential impulse response characterized by a plurality of N components with different time constants. The source and the detector are revolved about an object to be imaged and the output of the detector is sampled periodically to acquire a set of radiation attenuation values, with the values for each revolution being designated as a scan. A recursive filter function is applied sequentially to the radiation attenuation values from a given scan to generate approximated values for variables of the filter function that define residual detector response from the previous scan. A set of filtered attenuation values then is produced by applying the filter function again to the radiation attenuation values from the given scan. The approximated values for variables are used when the filter function is applied to the first radiation attenuation value of the scan.

Abstract: An x-ray CT scanner is operated in a calibration procedure to produce error signature vectors that indicate detector elements that have a non-uniform response along the z-axis and which may generate ring or band artifacts when certain anatomies are scanned. A correction process employs these error signatures during the scan to determine when correction is necessary and to make those corrections to the projection data as it is acquired.

Abstract: A medical imaging system has a source of X-rays and a detector which produces an electrical signal in response to X-rays. A signal generated by the detector, during an acquisition interval, is used to construct an image of a medical patient, which may contain artifacts due to motion of patient. A signal is produced indicative of the motion, which has a quiescent period of minimum movement. A first portion of the signal is selected such that if image acquisition commenced at the end of the first portion, the acquisition interval would occur during a quiescent period. This first portion is initially used as a reference signal portion. Then subsequent portions of the signal are compared to the reference signal portion to produce a descriptor of the degree of similarity. An image acquisition is commenced when the descriptor indicates a given degree of similarity that is above a defined threshold.

Abstract: A computed tomography apparatus includes a gantry rotatable about an object being imaged, an X-ray source mounted on said gantry in opposing relationship to an array of X-ray detectors. An X-ray controller causing emission of X-rays from the X-ray source to shift between the two focal spots to produce first and second sets of projection data. X-rays are emitted from a first focal spot of the source while one projection of the object is acquired. Then the operation of the source is altered to emit X-rays from a second focal spot and the gantry is rotated by one-half the pitch of the detectors. Another projection is acquired at the new gantry position. Additional projections are acquired by alternately emitting the X-ray beam from the two focal spots and advancing the gantry by equivalent amounts between each acquisition.

Abstract: A medical imaging system includes a source of X-rays and a radiation detector that produces an output signal in response to radiation from the source. The detector has an exponential impulse response that is characterized by a plurality of components with different time constants. The output signal from the detector is sampled periodically to acquire a set of radiation attenuation values. A recursive filter applies a filter function to the set of attenuation values that removes effects due to the non-ideal impulse response of the detector. The filter function includes a term for each of the time constant components. An image is reconstructed from the filtered data.

Abstract: An apparatus for reducing image artifacts caused by over-ranging or clipping of the data collected in a tomographic scan using a patient support, models the density profile of the patient support with a polynomial. Coefficients of the polynomial are stored in a look-up table according to gantry angle and used to estimate the over-range data. The estimated data is blended with the in-range data by convolving an over-range mask indicating which data is in-range and which data is over-range with a box car convolution kernel which produces a trapezoidal weighting mask. This weighting mask is multiplied by the estimated data and then summed to the in-range data to correct for the over-range portions of the data collected.

Abstract: An apparatus for reducing image artifacts caused by over-ranging or clipping of the data collected in a tomographic scan fits a geometric model to the in-range data of each projection. The geometric model is sized to the in-range data by summing all of the data of the projection to obtain a value of the total slice volume. This geometric model is used to compute the slope of the over-range data from the last point of in-range data and this extrapolated data is substituted for the over-range data. The correction process is implemented in pipeline form by convolving an over-range mask indicating which data is in-range and which data is over-range with a box car convolution kernel which produces a trapezoidal correction mask. This correction mask, multiplied by the uncorrected projection data provides the appropriate slope to its clipped portions.

Abstract: A collimator is designed for use in rotational camera transaxial SPECT in which the camera head is inclined with respect to the axis of rotation. The principal ray of the collimator is offset so that the transaxial plane bisects the angle bounded by the radially outermost collimated rays (cone-beam case) or by the radially outermost fan strips (astigmatic and anamorphic cases.

Abstract: A fan-beam collimator has a plurality of focal lengths. The shortest focal length is located at the center of the collimator. The longest focal length is located at the periphery of the collimator. The focal length increases between the minimum focal length and the maximum focal length.

Abstract: A collimator has a plurality of focal points in the transaxial direction and at least one focal point in the axial direction. The shortest focal lengths are located at the center of the collimator. The longest focal length is located at the periphery of the collimator. The focal length increases between the minimum focal length and the maximum focal length.