Abstract: Methods and apparatus for scanning an object in a computed tomography system during an interventional procedure are described. The computed tomography system includes an x-ray source, a detector, and a display. The detector detects x-rays projected from the x-ray source and attenuated by an object. A processor is coupled to the detector and coupled to the display for generating images of the object on the display. A helical scan is executed to generate an image slice of the object corresponding to each gantry rotation. At least one image slice and one three-dimensional image are simultaneously displayed on the display.

Abstract: A method for reconstructing an image in a computed tomography system performing a cone beam helical scan is described. In accordance with one embodiment, a point is selected for which image data is to be generated and a ray pair is identified wherein each ray passes through the selected point. Further, each ray in the ray pair is related according to view angle and detector angle associated with each ray. Projection data of each ray is then weighted to generate image data for the selected point.

Abstract: Apparatus and methods for determining cradle support elevation in an imaging system are described. In one form, the apparatus includes a support rail secured to and between table support legs of a table arrangement. The support rail is maintained substantially parallel with the cradle support. An encoder, coupled to the support rail, generates signals indicative of the cradle support elevation. The encoder signals can be used to determine, using a linear function, cradle support elevation. More specifically, although the cradle support movements are non-linear, the cradle support elevation apparatus provide linear feedback which may be used to determine cradle support elevation.

Abstract: An attenuator and detector cell arrangement for generating a signal ratio representative of focal spot position is described. The ratio is highly sensitive to focal spot position and facilitates generating, or reconstructing, a high quality image from the projection data. Further, and importantly, even if one detector cell is fully flooded, the signal intensity from such cell will vary depending upon the alignment between the focal spot and attenuator slot. Therefore, the focal spot movement detector is effective for detecting fan beam movement even if the detector cell is fully flooded. In one embodiment, the x-ray beam attenuator is configured to be positioned over the detecting surface of z-position detection cells. Slots or openings extend through the attenuator so that at least a portion of each detector cell is in free communication with an x-ray beam from the x-ray source.

Abstract: A series resonant circuit (SRC) which includes, in one embodiment, an inverter having four (4) IGBTs is described. The SRC also includes a series coupled inductor and capacitor, a transformer, and a diode bridge. The SRC further includes a controller which utilizes, simultaneously, phase and frequency modulation in conjunction with a logarithmic amplifier to control the inverter.

Abstract: The present invention, in one form, is a pre-patient collimator for reducing patient x-ray dose during a scan with a computed tomography system. The collimator has a contoured aperture for emitting a generally rectangular shaped x-ray fan beam. The fan beam approximates the rectangular shape of x-ray detectors which gather data for producing an image.

Abstract: The present invention, in one form, is an x-ray CT system that modulates x-ray tube current as a function of gantry angle and reconstruction algorithm weighting coefficients. View indexes are stored in a table, and during scanning, values are periodically read from this table to determine weighting coefficients. An algorithm is applied to the weighting coefficients to generate an x-ray tube modulating factor. This modulating factor is then applied to the x-ray tube current to generate modulated x-ray tube current.

Abstract: A method for forward projecting data from an image volume to a projection plane is described. In one embodiment, the method includes the steps of rotating the image data by a transaxial angle .phi. to align the image data with the projection plane. Then, for every axial angle .crclbar., and for each y'.sub.0 and for each value v in the projection plane:(a) determining z'.sub.0 =(v-y'.sub.0 sin .crclbar.)/ cos.crclbar. and interpolating in the z' direction for each x', to form the line I(x', y'.sub.0, z'.sub.0); and(b) interpolating I(x', y'.sub.0, z'.sub.0) for each value of u.

Abstract: Cathode cup assemblies for an x-ray tube are described. In one embodiment, the cathode cup assembly includes a cathode cup and a focus tab. The cathode cup includes filament receiving channels, and each channel is sized to receive a filament. The focus tab is a plate having a filament aligning aperture. The focus tab cooperates with the cathode cup so that a periphery of the filament aligning aperture limits the positioning of the filaments within the filament receiving channels.

Abstract: Apparatus and methods for generating z-axis profiles for a CT system detector are described. In one form, the method includes the steps of directing x-ray beams having different z-axis centroids and slice thicknesses at the detector and collecting detector signals for each beam. The detector signal for a first beam is then subtracted from the detector signal for a second beam to obtain a differential, or composite, detector signal which corresponds to a third beam having yet another z-axis centroid and slice thickness. The full z-axis profile of the detector is generated from measured detector signals and composite detector signals.

Abstract: Methods and apparatus for performing a computed tomography scan are described. In one embodiment of the apparatus, a twin beam computed tomography scanner includes a beam splitter, an x-ray source for generating an x-ray to be projected generally towards, and at least partially through, an object, and a detector array comprising a plurality of detector cells arranged to form at least two cell rows. The beam splitter is positioned so that the x-ray projected from the x-ray source is substantially split to form at least two beams prior to being projected at least partially through the object.

Abstract: The present invention, in one form, is a method for performing image reconstruction from projection data acquired in a multislice helical scan. More specifically, a helical weighting factors is generated and then a modified weighting factor Wm(.beta.,.gamma.), which is a shifted and weighted average version of the helical weighting factor, is generated. The modified weighting factor is then applied to projection data.

Abstract: The present invention, in one form, is a method for enhancing image sharpness in images generated from CT scan data by using enhancement masks. The enhancement masks are generated, in one embodiment, by generating difference image data from the original age data and low pass filtered image data. The original image data CT numbers are assigned to image regions, e.g., bone, air, and soft tissue, and based on such CT number classifications, certain data in the difference image is fully or partially suppressed. Subsequent to suppressing some difference image data, the difference image data set, which is sometimes referred to as an enhancement mask, is then combined With the original image data to increase image sharpness.

Abstract: The present invention, in one form, is a method for determining and applying a ZCAL correction vector to the channel outputs from the detector array in a multi-slice CT system. More specifically, and in accordance with one embodiment of the present invention, the signal gain for each detector cell, or channel, at multiple z-axis locations is measured. For each channel, a correction polynomial Q.sub.n is fitted to the signal variation curve as a function of z-axis position so that the correction polynomial value multiplied by its channel signal produces a constant value over the operational range of z-axis positions. Beam positions (Z.sub.r) are measured as a function of each position reference signal (D.sub.r) and the Z position of the beam at the sensor channel and the location of the focal spot are determined. The z-axis location for each channel and the ZCAL correction vector are then determined. The ZCAL correction vector is then multiplied by the channel signal to calibrate the channel signal.

Abstract: The present invention, in one form, is a method for improving image quality in CT helical scan systems by using a post reconstruction filtering algorithm. In accordance with one embodiment of the algorithm, image data is segmented into sharp structure data and background data. The background data is then filtered to remove reconstruction and data artifacts. The filtered background data is then combined with the sharp structure data. The combined data can then be used to generate an artifact reduced image.

Abstract: The present invention, in one form, is an apparatus for performing image reconstruction using data obtained by a four beam helical scan. In reconstructing an image, projection data arrays are generated. Such projection data is then weighted by weighting factors to generate a weighted projection data array. The weighted projection data array is filtered and back projected to generate an image data array. The image data arrays for the beams are then summed to generate a slice image data array.

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: An algorithm for creating a normalization data array to use in generating a three-dimensional image is described. In one embodiment, the algorithm includes performing the steps of acquiring geometric factors from a two-dimensional normalization scan, determining the three-dimensional crystal sensitivities from a three-dimensional phantom acquisition scan, and using such geometric factors and crystal sensitivities, creating a three-dimensional normalization data array.

Abstract: The present invention, in one form, is an apparatus for performing image reconstruction using data obtained by a four beam helical scan. In reconstructing an image, projection data arrays are generated. Such projection data is then weighted by weighting factors to generate a weighted projection data array. The weighted projection data array is filtered and back projected to generate an image data array. The image data arrays for the beams are then summed to generate a slice image data array.

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.