Abstract: Methods and systems for calibrating a digital gamma camera using a hole phantom are described. In one embodiment, the method includes the steps of performing offset adjustments and gain adjustments, and then using a source to flood the hole phantom, image data of the phantom is collected by the camera to be calibrated. The image data collected from such flood is used to generate a light distribution function for the camera. In addition, residual distortions are measured, and a spatial corrections map and an energy deficit map are created. A quality control image also can be generated to verify that the camera is calibrated.

Abstract: In a magnetic resonance imaging (MRI) system, a method is provided for reducing oblique Nyquist ghost artifact in an image produced by an oblique EPI scan. Prior to commencing the EPI scan, referencing pre-scans are conducted to generate pre-scan echo trains respectively corresponding to the physical gradient axes. Distortion compensating parameters are derived from the pre-scan echo trains for reducing Nyquist ghost by alternatively modifying the data acquisitions stage of the oblique EPI scan, or the post-data acquisition image processing stage thereof. In one mode of operation, the pre-scan echo trains are generated while a subject is in the MRI system. In another mode of operation, pre-scan echo trains are generated while no subject is present in the MR system, so that the distortion compensating parameters represent characteristics of the MR system only, and thus may be used for EPI scans of different protocols.

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: An improved actively shielded superconducting magnet in which the main and bucking coils are directly wound onto respective coil support structures made of glass fiber-reinforced epoxy. The main and bucking coil cartridges are held in a fixed concentric relationship via a pair of flanges located at opposite ends of a helium vessel. During manufacture of the main and bucking coil cartridges, the outer diameters of the respective coil support structures are machined with high precision. Also, the diameters of two concentric grooves are precisely machined on the inner surface of each helium vessel end flange to match the outer diameters of the main and bucking coil support structures, so that at room temperature the main and bucking coil cartridges can slide smoothly into these grooves. The helium vessel is made of aluminum alloy and has a coefficient of thermal expansion which is greater than that of the fiber-reinforced epoxy coil support structures.

Abstract: An amplification device is provided for driving a gradient coil in an MR system, wherein the gradient coil is required to generate a rapidly changing gradient magnetic field during a first time period, and a substantially constant field during an immediately following second time period. The device includes a adjustable bus, for providing first and second voltage levels, and a switching or PWM amplifier. A switch is coupled between the bus and the switching amplifier for applying the first voltage to the amplifier during the first time period, and the second voltage to the amplifier during the second time period. The switching amplifier comprises an inverter for generating a PWM voltage in response to its input, and an LC filter for converting the PWM wave into a DC voltage. The switching amplifier generates a substantially higher coil driving voltage during the first period, in response to the first voltage level, than during the second period in response to the second voltage level.

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: A sleeve assembly for reducing the thermal conduction heat load from the bellows penetration tube to the heliumvessel of a superconducting magnet assembly. The sleeve assembly is designed to force helium boil-off gas to flow in intimate contact with the bellows convolutions. The helium boil-off gas thereby intercepts or removes a portion of the heat that would normally be conducted from the bellows convolutions to the helium vessel. The sleeve assembly consists of a circular cylindrical rolled tube made of laminated thermosetting material. The outer diameter of the tube is wrapped with tape in a helical pattern. The diameter of the sleeve and the thickness of the tape wrapping are selected so that the outer circumferential surface of the helically wrapped tape abuts the inner diameter of the bellows. The sleeve is fabricated with a relatively small thickness to minimize thermal con-duction load.

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 method for identifying and correcting bad pixels in an x-ray image produced by a large area solid state x-ray detector is disclosed. Initially, each bad pixel is identified. An appropriate correction scheme is then selected from a predetermined list. A correction code is then assigned to each bad pixel, the correction code corresponding to the selected correction scheme. The correction code is stored in a pixel-correction memory, and the correction code for each pixel is read during imaging. Finally, each bad pixel value found during the correction code reading is replaced using the selected correction scheme, and can be immediately displayed.

Abstract: An apparatus for generating the required beamforming delays for an ultrasound imaging system with minimal hardware and software. The apparatus performs an algorithm which allows the required computations to be separated into three groups. The first group includes transducer array geometry computations which are beam independent. The second group includes a small number of beam-dependent computations which are channel independent. The final group includes the channel- and beam-dependent calculations which combine the results of the first two groups to generate the required beamforming delays. This last computation is distributed to logic and simple real-time state machines per channel. This approach reduces the required computations and takes advantage of simple parallel processing to reduce the required hardware and computational time relative to conventional beamformer designs.

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: A method is used to bond dissimilar metals, such as for an x-ray tube. Copper and steel tubular components are provided. An interlayer material situated between the metal layers is used to bond the copper and steel tubular components by solid state diffusion process. The interlayer material may be pure nickel, pure copper, or a layered combination of nickel and copper or copper alloy. The use of the low cost interlayer material and the solid state diffusion process yields a strong bond between the dissimilar metals.

Abstract: A method for correcting MR data elements acquired in the presence of an imperfectly linear gradient field, each element comprising nominal first and second quadrature components. The quadrature components are multiplied by an artifact correction factor to provide respective first and second quantities. A Gradwarp geometric correction operation is applied to respective quantities to provide a corrected first and second quadrature component, corresponding to each data element. For a given data element, the arctangent function is applied to the result obtained by dividing the first corrected component by the second corrected component to provide a corrected phase component for use in forming an image.

Abstract: A method is provided for fabricating a gradient coil for an MR imaging system having an open magnet. The method includes forming a structure from thin conductive material such as copper, the structure generally comprising a section of a cylinder and a section of an annulus joined to an edge of the cylinder section as a flange. During a first cutting operation, a plurality of first groove segments are cut through the material, each of the first groove segments lying in one of a plurality of cutting zones selectively positioned around the structure, a strip of material positioned between two adjacent groove segments comprising a coil turn segment. The coil turn segments of a cutting zone are rigidly joined to one another and to a support frame comprising the outer edge of the structure by suitable means. Thereafter, a second cutting operation is performed, whereby a plurality of second groove segments are cut through the material to completely form the gradient coil.

Abstract: X-ray tube electron beam focusing utilizing a cathode having a large cavity therein in which an electron cloud is generated and which is shielded from the primary electric field between the cathode and the anode. The electron cloud flows from the cavity through a small narrow passage and into the primary electric field. An opposed spaced apart pair of electrical grids each comprising an array of individual electrode segments have selected opposed segments electronegatively biased to change the cross-section of the passing electron stream therebetween. The altered cross-section of the electron stream determines the size of the focal spot of the electron beam impacting the target anode.

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.