Abstract: An x-ray CT system acquires a series of views during a scan and reconstructs a slice image by backprojecting the filtered projection data from each acquired view. Backprojection is facilitated by employing a Cordic processor that produces the angle (.gamma.) and distance (L) of each pixel location from the x-ray source. The angle (.gamma.) selects the proper value from the filtered projection data, and this value is divided by the square of the distance (L) to arrive at a value used to update the slice image pixel value.

Abstract: A high speed communication apparatus for a Computerized Axial Tomography (CAT) scanner utilizes large diameter slip rings to permit continuous rotation of a rotatable gantry. A communication signal is applied at a first point on one slip ring, and is terminated by a resistive termination point 180.degree. opposite the driving point. The communication signal may then be received at any point on the slip ring by a receive connection and a matching receive connection which are 180.degree. opposite one another. The drive and termination connections to the slip ring may be made by brushes, with the receive and matching receive connections being made by a physical connection to the slip ring. Alternately, the drive and terminate connections may be made by physical contact, with the receive and matching receive connections being made by brushes.

Abstract: A high speed communication apparatus for a computerized axial tomography (CAT) scanner utilizes large diameter slip rings to permit continuous rotation of a rotatable gantry. A communication signal is applied at a first point on one slip ring, and is terminated by a resistive termination at a point 180.degree. opposite the driving point. The communication signal may then be received at any point on the slip ring. The drive and termination connections to the slip ring may be made by brushes, with the receive connection being made by a physical connection to the slip ring. Alternately, the drive and terminate connection may be made by physical contact, with the receive connection being made by a brush.

Abstract: Dual control of image level and window of a display is accomplished by rotation of a single trackball. Rotation of the trackball within a first band including the X axis controls one parameter, and rotation of the trackball in a second band including the Y axis controls a second parameter. No changes are made in the parameters in response to rotation of the trackball in a third deadband laying between the first band and second band. The operator of a tomography system can readily change display parameters by rotation of the trackball while viewing the display.

Abstract: The values of pixels in a new image matrix are obtained by mapping pixels of the new matrix in the old matrix and then using polynomial interpolation of a plurality of values of pixels in the old matrix to obtain values of interim pixels in the new matrix and then using polynomial interpolation of a plurality of interim values to obtain final values of pixels in the new matrix. A precalculated table of weighting coefficients based on offset of a new pixel from an adjacent old pixel is used to expedite the polynomial interpolation.

Abstract: A system for writing cursors on a raster scanned television screen that uses the microprocessor in a display controller to produce blocks of data defining the parameters of vectors that compose the cursor. The blocks are put in a first-in first-out memory during a vertical blanking inerval or during active picture time. Each block specifies where writing of a cursor segment is to start and stop on a horizontal scan line and it also specifies a repeat count that indicates the number of lines on which the segment is to be written. Each block contains a delta value to indicate how much, if any each segment is to be displaced left or right from line to line so vertical and angulated vertical vectors can be produced. The blocks are read out of the memory consecutively by a circuit that converts the segment start and stop data to pixel counts. Pixel counters determine the writing start and stop points.

Abstract: Apparatus for applying a gamma correction to digital CT numbers at a selected level and within a window. A memory is loaded sequentially with the gamma correction lookup table. At the start a counter generates a sequence of addresses, in response to clock pulses. These are addresses to another memory. Simultaneously, a variable address generator addresses the gamma lookup table memory to effect transfer of the gamma correction data to the other memory (window-gamma lookup table) at locations that are represented by the ratio of the locations in the gamma lookup table to the address in the window-gamma table. To read out and produce an image, the window black value is subtracted from the stored CT numbers in sequence. The resulting differences constitute addresses to the window-gamma lookup table whose output is then the gamma corrected values for CT numbers in the window. This digitized data is converted to analog video signals for driving a television monitor that displays the image.