Abstract: To acquire tomographs, two detectors (1, 2) are secured together in a support structure (3) in such a manner that their detection fields are inclined relative to each other. The angle of inclination between them is preferably 90°. This pair of detectors is then placed in such a manner that the plane (9) bisecting the two detection fields includes the axis of rotation (4) around which the pair of detectors is to rotate to perform tomography on a subject. For fat subjects, the pair is moved away (13) from the axis, and for thin subjects it is moved towards it. It is shown that to avoid detector displacement interfering with tomography computation, it suffices merely to change computation parameters in the reconstruction algorithm.

Abstract: A serial digital bit signal having signal bits occurring in a bit interval and at a signal bit speed, and each signal bit representing, alternatively, a first logic state and a second logic state, is transferred across a rotating interface by encoding each first logic state bit with a digital radio frequency (RF) carrier signal and coupling the encoded signal across the interface with an RF slipring.

Abstract: A method for shimming a magnetic resonance imaging magnet requiring higher magnetic field homogneity on a small imaging volume and by magnetic field measurements on a larger volume providing small measurement error and practical field strength measurements and utilizing the spherical harmonic coefficients of the measurements.

Abstract: An MRI system acquires NMR signals at a fixed sample rate. The acquired NMR signals are decimated to produce an output NMR signal at a prescribed sample rate. The acquired NMR signal is fast Fourier transformed to the frequency domain, and additional signal samples are produced by phase shifting in the frequency domain. The frequency domain signal samples needed to produce the prescribed sample rate are then fast Fourier transformed back to the time domain to produce the output NMR signal.

Abstract: A method of calibrating Doppler time-velocity waveforms obtained using a duplex ultrasound scanner. A spectral broadening error margin for the maximum velocity waveform is determined based on a unified theory of intrinsic spectral broadening for pulsed Doppler signals. The error margin is colorized or highlighted in the Doppler waveform display.

Abstract: A method and an apparatus for color mapping of flow power data in which the flow states containing information of most interest to the user are enhanced, while flow states not containing information of interest are suppressed. This is accomplished using a color mapping having three segments which are connected at upper and lower knee points, the latter being settable either automatically or via operator inputs. In the automatic mode, the host computer determines the positions of the knee points based on analysis of a single or a mean image frame of power Doppler data or based on system parameters (e.g., dynamic range) set by the operator. The host computer then constructs a color mapping having the determined knee points and loads that color mapping into the video processor.

Abstract: A method is used for interfacing materials of dissimilar thermal expansion in an X-ray tube. Initially, a first joint is identified, which has a first component to be received into a second component. Typically, the first component has a higher coefficient of expansion than the second component, so the purpose of the invention is to reduce the physical expansion of that component in the joint. A plurality of slots is introduced along the approximate axial length of a coupling member at the joint, to achieve the aforementioned purpose. The coupling member is provided between the two components, and has a thermal expansion rate greater than one component and less than the other component.

Abstract: A method for acquiring spatially and spectrally selective MR images by means of an MR imaging system includes the step of selecting an SPSP pulse sequence, comprising a succession of RF sub-pulses and an oscillatory gradient magnetic field, which is disposed to select a slice through a subject. The method further includes measuring specified parameters of a perturbation magnetic field associated with the imaging system, and deriving an expression for the perturbation field from respective measured parameters and from the oscillatory gradient magnetic field. A specified ideal frequency modulation function, associated with the SPSP sequence, is disposed to offset the slice to a particular spatially localized region of the subject. The SPSP pulse sequence is modified by adjusting the frequency modulation function in specified corresponding relationship with the expression.

Abstract: A discrete pixel image is enhanced to bring out particular features of interest such as edges. The enhancement includes decomposition of the original processed image data, enhancement by application of gain images to the decomposed images, and reconstruction of the enhanced image. The decomposition proceeds through a series of low-pass filters to arrive at decomposed images of progressively lower spatial frequencies. These decomposed images are then multiplied by gain images during the enhancement phase. Gain images for at least the higher spatial frequency level images are derived from lower spatial frequency level images. These spatial frequency-based gain images may be based upon operator inputs, including a spatial sensitivity function and an edge enhancement value. Lower spatial frequency level images may be processed by application of predetermined gain values.

Abstract: The present invention, in one form, is a method for improving image reconstruction in computed tomography systems by using a reconstruction algorithm and a detector cell algorithm. In accordance with one embodiment of the present invention, the reconstruction algorithm generates fan-parallel data directly from projection data which is processed to generate image data. In particular and in one embodiment, after view to view rebinning of the projection data, the data is pre- and post-convolution weighted, filtered and backprojected to generate image data. In another embodiment, the detector cell algorithm is utilized to determine the shape of the detector to include an arc sin dependency to eliminate axial interpolation of the projection data.

Abstract: The present invention comprises a system and method for correcting for z-slope variations in detector cell outputs represented by data obtained by a scan in a CT system. According to one aspect of the invention, a final error factor, based upon a combination of a correction factor and an initial error factor, is applied to the data. The correction factor having a computational complexity independent of the order of correction desired. The present invention transfers all of the computational complexity of z-slope correction to a calibration process, thereby improving the computational speed and efficiency of producing an accurate image based on the scan data. In another aspect, the present invention improves image quality by providing a correction factor comprising a plurality of channel correction factors, where each of the plurality of channels is the center channel for a corresponding moving segment used to respectively determine each of the channel correction factors.

Abstract: A multislice detector module producing an alterable quantity of slices and slice resolutions. In one embodiment, the detector module includes a plurality of photodiodes arranged in an array of rows and columns, a switch apparatus electrically coupled to photodiode output signals, and a decoder. The decoder is configured to enable or prevent each photodiode from being transmitted through the switch apparatus. The configuration of the decoder determines how many slices of data are transmitted and the resolution of each slice.

Abstract: Methods and apparatus for dose reduction in a computed tomography (CT) system are described. In one embodiment, the CT system includes a pre-patient collimator and a configurable multislice detector array. The pre-patient collimator includes a plurality of eccentric cams and a filtration device for altering the x-ray beam radiated from a x-ray source. The eccentric cams are positioned to collimate the x-ray beam and may be independently positioned to provide z-axis correction of the x-ray beam. The filtration device includes a plurality of filters for altering the x-ray beam. In operation, an operator selects the type of test and the quantity and thickness of the slices. After altering the detector and collimator configuration, slice data for each slice is gathered.

Abstract: Structures are identified in pixel data representative of a discrete pixel image and are differentiated from non-structures. The structures are identified by comparing gradient magnitudes with a selected gradient value and by comparing gradient directions of adjacent pixels. Pixels having desired relationships are counted and a focus parameter is applied to the resulting count. A final gradient threshold value is identified based upon the count and the focus parameter. The threshold value identifies structural pixels. Isolated adjacent regions may be eliminated from the structures. Edges defined by the structures are binary rank order filtered to arrive at the final structural definition. The structural and non-structural pixels may be further processed to enhance the image for subsequent display.

Abstract: A vibration cancellation system for a magnetic resonance imager superconducting C-shaped magnet includes a vibration sensor at a remote end of the separated pole pieces to provide a vibration signal which is phase inverted and converted to an opposing force by a magnetoresistive actuator connected across the support member between the opposite ends of the pole pieces to cancel vibrations which would otherwise adversely affect the homogeneity of the magnetic field in the imaging region of the magnet.

Abstract: In an X-ray tube target, a shaft is welded to the anode target, the shaft typically being TZM or a molybdenum alloy. This defines a first weld location and creates an integral shaft-target assembly. The shaft-target assembly is then machined. A heat sink material, such as graphite, is brazed to the integral shaft-target assembly. A hub is then welded to the shaft, at an end opposite the target, defining a second weld location and creating a hub-target assembly. The hub can be columbium or columbium alloy. Subsequently, the hub-target assembly can be machined. Having a dual weld procedure, and eliminating the subsequent brazing step to join the hub to the shaft, enables the alloys to maintain their high strength without annealing, thereby allowing the shaft materials to keep their high strength and reducing plastic deformation at the lower (hub) portion of the shaft.

Abstract: An apparatus for properly centering and/or collimating an X-ray beam with respect to a target to be radiographically imaged. A field definer is situated between an X-ray source and an X-ray detector at the location where the target is to be situated. The field definer includes a pair of stops between which the target may be located, and the stops may be horizontally relocated relative to each other to be placed in abutment with the target. A sensor in communication with the stops produces a signal dependent on the distance between the stops, and a controller utilizes this signal to adjust the X-ray source to emit radiation in a desired area with respect to the field between the stops. As an example, a target may be situated between the stops, the stops may be adjusted in abutment with the target, and the X-ray source will then be collimated to emit a radiation beam which is incident only on the target between the stops.

Abstract: A magnet cartridge for an open architecture superconducting magnet including an iron ring sandwiched between two coil forms, and including radial and axial positioning and securing apparatus to position, secure and maintain the relative positions of the coils on the coil forms and the iron ring in the presence of the strong superconducting magnet field generated by superconducting operation of said magnet.

Abstract: Disclosed herein is a radiographic imaging system which performs system performance monitoring by (1) using automatic exposure control (AEC) components to predict the average image gray level; (2) obtaining measured average image gray levels from the portions of the X-ray detector situated in the X-ray shadow of the AEC components; and then (3) comparing the predicted and measured values. The predicted values are determined by use of a prediction model which is modified by a learning system over successive exposures to provide more accurate predictions. After the learning system has sufficiently developed the prediction model, the error between the predicted and measured gray level values may be monitored in later exposures and an error routine can be activated if the error exceeds a predetermined threshold. In this case, the error may indicate that system components in the imaging chain (e.g., the detector or AEC components) require maintenance.

Abstract: A non-uniform multi-layer thermally insulating blanket assembly for use in a superconducting magnet in the tapered space between the thermal radiation shield and a conical support assembly includes three steps at different thicknesses provided by multiple blankets with layer staking and blanket positioning.