Abstract: A method is provided for 3-D MR imaging of structure such as a cardiac region of a subject, which is disposed to cyclical motion. The method comprises detecting commencement of each of a succession of motion cycles, and acquiring a set of MR views of the region during each motion cycle. Each view is at a known radial distance from the center of a two-dimensional k-space, and each set includes a view of lowest spatial frequency, which is located proximate to the k-space center. The order in which the views of respective sets are acquired is selected so that the lowest frequency views of respective sets are each acquired at the same specified time, following commencement of their respectively corresponding motion cycles. The views of each set collectively define a segment in the k-space, respective segments being placed in an interleaved spiral or elliptical arrangement with respect to one another.

Abstract: In an MR imaging system, a method is provided for operating an MR gradient coil to provide a pulse sequence which comprises first and second sub-sequences. During the first sub-sequence, the coil is operated to produce a pair of diffusion-weighted imaging pulses, each having a gradient amplitude and a slew-rate. During the second sub-sequence the coil is operated to produce a train of echo-planar imaging pulses, each having a gradient amplitude which is selectively less than the amplitude of the diffusion-weighted pulses, and a slew-rate which is selectively greater than the slew-rate of the diffusion-weighted pulses. Thus, the invention is directed to a gradient system which can provide optimal performance for both diffusion-weighted imaging and echo-planar imaging, while using only a single coil for a given gradient axis.

Abstract: A phase-sensitive method of inversion recovery MR imaging is provided, which is directed to a specified object. The method comprises the steps of applying an inversion-recovery MR sequence to the object to acquire a set of MR data for an initial image, wherein the initial image comprises a pixel matrix of specified size, each of the initial image pixels having an associated MR signal and a phase vector. The method further comprises generating a phase vector image from information provided by respective initial image pixels, the phase vector image having a matrix size which is substantially less than the matrix size of the initial image. A region-growing procedure is applied to the phase vector image to remove phase errors therefrom. Thereupon, the phase vector image is zoomed or expanded to a matrix of the same size as the initial image matrix. For multi-slice imaging where TI time is comparatively long, the method may employ a distributed interleave mode of data acquisition to reduce total imaging time.

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 method is provided for correcting for effects of translational motion or movement of an object in MR imaging. In accordance with the method, an MR point source is joined to the object for translational movement in unison therewith, the point source being maintained in selectively spaced-apart relationship with the object. The method further comprises acquiring a set of k-space data representing images of the object and point source collectively, and deriving a function representing the square of the magnitude of the k-space data set. An inverse Fourier transform operation is applied to the derived function to generate a correlation function with a number of correlation components, a specified one of the correlation components comprising the cross-correlation of the object and the point source.

Abstract: In a method for providing an MR image of a section taken through an object, wherein the section is acquired in the presence of in-plane translational motion of the object, an MR system is operated to acquire a set of imaging data points from the section, the set of imaging data points being contaminated by phase errors resulting from the motion. The MR system is further operated to acquire a plurality of correction data point sets, each correction data point in one of said sets being acquired along an alignment line or other trajectory and at a location coinciding with the location of one of the imaging data points. The imaging data points respectively coinciding with the correction data points comprise, collectively, a subset of the imaging data points. The phase difference between each correction data point set and its corresponding subset of imaging data points is determined, and then used to remove the phase errors from the set of imaging data points.

Abstract: A method is provided for acquiring MR image data, which comprises the steps of applying a succession of RF excitation pulses to a selected region of an imaging subject to produce a corresponding succession of MR data signals, generating a readout gradient in association with each of the MR data signals, and acquiring sets of data points from the MR data signals to provide views respectively corresponding thereto. The data points of a view are respectively identified by positions in k-space along a first k-space axis, each of the positions along the first k-space axis having a time offset with respect to a reference.

Abstract: In an X-ray tube provided with a frame, a rotary bearing, and a target and anode supported by the rotary bearing for rotation with respect to the frame, an improved arrangement is provided for preloading the rotary bearing. The arrangement comprises a housing fixably joined to the frame, the housing provided with a cylindrical inner wall and disposed to receive the rotary bearing, and a spring or the like for applying an axial force to the bearing race, to selectively preload the bearing balls or other rotary elements of the bearing. The arrangement further comprises a linear bearing positioned between the bearing race and the cylindrical inner wall, to enable the bearing race to move axially with respect to the housing in response to the applied axial force.

Abstract: In an arrangement for cooling an X-ray tube mounted on the gantry of a CT system, a path of flow is established by means of conduits or the like for circulating a cooling fluid between the tube and a heat exchanger. As fluid passes through the heat exchanger, a stream of air is applied to the path of flow, by means of a radial fan, to carry heat away from the fluid. The axis of the fan is maintained in parallel relationship with the axis of the gantry, to prevent gyroscopic loading of the fan as the fan rotates about the gantry axis with the gantry. The fan comprises a device for exhausting air heated by the exchange process radially, with respect to the fan axis, to minimize fan-generated acoustic noise while maintaining good thermal performance. Fan support structure lying in the path of the exhausted air is selectively shaped to reduce air flow turbulence, and to thereby further reduce fan noise.

Abstract: A method is provided for correcting an imaging function g acquired by and MR surface coil having associated spatial inhomogeneity, the function g defining an image comprising a matrix array having a specified number of pixels, and being directed to specified structure within an imaging subject. A shrinking operation is applied to the function g to generate the function g.sub.shrunk comprising an array having a number of pixels equal to the specified number, as reduced by a shrink parameter with respect to each edge of the g function array. Pixels of the function g.sub.shrunk are compared with a threshold value to produce a thresholded function THRESH?g!.sub.shrunk and a low pass filtering operation is applied to both g.sub.shrunk and THRESH?g!.sub.shrunk to generate filtered shrunk and filtered thresholded functions, respectively. A first function representing the filtered shrunk function is divided by a second function representing the filtered thresholded function to produce a distortion function h.sub.

Abstract: A method is provided for use in constructing an MR image associated with the flow of blood or other fluid through an imaging volume, wherein material flowing through a selected voxel of the imaging volume is distinguished from static material. The method includes the step of applying a first MR pulse sequence to the imaging volume to produce a first MR data signal, having a magnitude which encodes first and second flow parameters for respective voxels comprising the volume, and having a phase which encodes a third flow parameter. The method further includes the step of applying a second MR pulse sequence to the volume, to produce a second MR data signal which indicates the content of respective voxels without flow encoding. The first and second MR data signals are compared to one another, such as by computing the difference therebetween, to determine the presence or absence of flowing material in respective voxels of the imaging volume.

Abstract: A spiral scan MR imaging method is provided for acquiring an image of a specified section taken through an object, wherein the section has a generally elongated shape. Thus, first and second dimensions of the section, measured along first and second mutually orthogonal section reference axes, respectively, have a relationship such that the first dimension is substantially greater than the second dimension. The method includes the step of applying spatially selective RF excitation to an imaging volume containing the object, in order to select a slice which includes the specified section. The method further includes the step of generating a read-out gradient defining a selected anisotropic spiral trajectory in an associated k-space domain having first and second mutually orthogonal k-space reference axes, which respectively correspond to the first and second section reference axes.

Abstract: In an X-ray tube having a housing, an outer frame for providing a vacuum, a cathode mounted in the outer frame to project a stream of electrons, and an anode disposed to receive the electron stream at a focal spot position to produce X-rays, apparatus is provided for selectively mounting the anode within the housing. More particularly, the apparatus is disposed to respond to the heat generated by the X-ray production process to provide compensation for undesirable effects resulting from thermal expansion of the anode.

Abstract: Control apparatus is provided for a medical diagnostic imaging system, such as a mobile X-ray unit. The imaging system includes a battery or like power storage device of limited capacity, and a number of components disposed to perform respective corresponding functions. The control apparatus includes a user interface for enabling an operator to generate commands which selectively direct the components to perform their respective corresponding functions. The control apparatus further includes a system control means, comprising a controller and set of control circuits, for initially placing the imaging system in a powered-up mode, wherein each component is coupled to receive power from the battery. A sleep mode activation device is included in the system control for decoupling a first set of components from the battery, while allowing a second set of components to remain coupled thereto, following a first time period during which no command is generated by the user interface.

Abstract: An eddy current correction method is provided for use in an MR system disposed to generate difflusion-weighted echo planar images by employing a bipolar diffusion-weighting gradient as well as the nominal components in an echo planar imaging pulse sequence. The correction method comprises the steps of deriving eddy current parameters (i.e., amplitude and time constant) associated with each eddy-current-induced magnetic field component caused by the diffusion-weighting gradient, and generating a set of correction terms, each of the correction terms being a function of the parameters. The method includes the further steps of modifyg a set of ideal echo planar imaging gradients and the receiver phase and frequency to respectively offset the eddy current induced magnetic field gradient and the spatially independent B.sub.0 -magnetic field. The modification occurs in two stages.

Abstract: Apparatus for routing a resilient cable of specified length, such as an electric power transmission cable, across a rotary joint between first and second members, wherein the first member is supported for rotation with respect to the second member. The apparatus includes a first guide element disposed to rotate with the first member, for guiding a first component or portion of a cable along a first arcuate path of specified radius, the length of the first cable component disposed to vary as the first member rotates. The apparatus further includes a second guide element, in fixed relationship to the second member, for guiding a second component of the cable along a second arcuate path, the length of the second cable component disposed to vary in inverse relation to the length of the first cable component.

Abstract: In a CT imaging system which includes a gantry having a rotatable ring member and a DAS comprising circuit boards grouped in a selected number of sets, a DAS housing is provided which is disposed to dissipate heat away from the DAS circuit boards. The housing includes a frame for mounting each of the circuit boards on the gantry ring so that the boards of a set are in spaced-apart relationship with each other, and further includes a cover for each frame, to form an enclosure for the circuit boards supported thereby. Each cover is provided with a panel member, a section of each panel being provided with a specified pattern of perforations. Each panel is positioned with respect to its set of circuit boards to provide an unobstructed space of selected dimension between its pattern of perforations and its corresponding circuit board set.

Abstract: A CT cone beam imaging system is provided wherein a source of cone beam radiation and a detector array are mounted for movement with respect to an object, to provide a reconstructed image of the object. Relative movement is established between the cone beam source and the object along a scan path comprising a circular component and a linear component. The source is operated to irradiate the object during such movement to project cone beam data onto the detector, the projected data comprising linear and circular data sets which respectively correspond to the linear and circular components of the scan path. To significantly minimize processing requirements, a subset of data elements is selected from the linear data set, wherein each of the selected data elements is associated with a set of spatial parameters which define spatial regions contained within a hypothetical sphere in the Radon space, but which are not intersected by a Radon shell defined by dimensions of the circular path and the cone beam.

Abstract: A phase unwrapping method is provided comprising a post-processing MR operation for an array of phase-related MR data elements. The method includes the steps of defining a Region of Interest, of comparing each data element with the first and second data elements which are adjacent thereto in the array, in order to generate respectively corresponding first and second gradient values. A subset of the data elements is constructed, wherein a data element is assigned to the subset only if its corresponding first and second gradient values are less than a selected threshold value VENC/2. The data element subset is employed to generate a fitted phase function having a value at the position of each data element in the array, and the value of the fitted function thereof, for a given data element, is subtracted from the measured value thereof.

Abstract: A method and apparatus is provided for generating an MR image of a structural portion of a subject, the portion lying within a hypothetical imaging volume. A specified level of hyperpolarized magnetization is provided within the imaging volume, and a series of MR pulse sequences are applied to the imaging volume to generate respective corresponding MR data signals, each pulse sequence comprising a number of magnetic field gradient pulses and an excitation pulse, and having an associated flip angle determined by the excitation pulse. The associated flip angles of successive pulse sequences are progressively increased to maintain the signal strength of the corresponding MR data signals at a substantially constant level. Acquired MR data signals are cumulatively processed to provide an image of the structural portion.