Abstract: An MRI system acquires NMR tracking data from a tracking coil imbedded in a medical device which is guided by a physician using real time anatomic images produced from image data acquired by the MRI system. A Hadamard magnetic resonance tracking sequence is used to update the tracking coil location which is indicated on the anatomic image. The Hadamard sequence uses four different acquisition, but tracking coil location is updated after each acquisition, using the new acquisition and three previously acquired acquisitions.

Abstract: A micrometer system includes a motorized drive for repeatedly advancing and retracting the micrometer barrel, and a touch sensor for sensing when the barrel tip has just touched the target surface. The drive is preferably mounted on the micrometer body. By performing a measurement repeatedly, a series of readings can be obtained which cumulatively increases measurement accuracy, especially when contact must be made to a compliant surface.

Abstract: An MRI system is employed to acquire image data using a pulse sequence in which k-space is sampled in a Fibonacci spiral trajectory. A single pulse sequence may be used to sample all of k-space with a single spiral arm, or k-space can be sampled with a plurality of interleaved Fibonacci spiral arms by performing a corresponding series of pulse sequences.

Abstract: A scan control device located in the bore of an MRI system magnet includes tracking coils and a display. Location and alignment of the scan control device is tracked by the MRI system using signals acquired from the tracking coils. These signals are also used to update the scan parameters such that the scan plane of the image acquired by the MRI system is controlled by the scan control device location and orientation. The image is produced on the display to provide an attending physician with interactive control of the image from the magnet bore.

Abstract: An imaging system enables cardiac functioning within a particular cardiac chamber to be imaged. The system acquires imaging data that includes intensity values for four-dimensional voxels within a region of interest (ROI). A seed voxel is identified, and neighbor voxels to the seed voxel are also identified. The intensity values for each neighbor voxel are compared to a threshold to determine whether the voxel corresponds to blood or muscle tissue. For each neighbor voxel corresponding to blood, its neighbor voxels are identified and compared to the threshold, and this process is repeated until a pre-established spatial boundary is encountered or the number of new neighbor voxels indicates that processing is migrating into an adjacent cardiac chamber. At that point, the set of identified blood voxels represents a blood volume for the desired cardiac chamber. Voxels adjacent to the interior and exterior surface boundaries of the blood volume are added to the set.

Abstract: A method for modeling an object with a polygonal mesh includes obtaining a closed-surface polygonal mesh and positioning the closed-surface polygonal mesh relative to the object. A ray is projected through a point-of-interest on said closed-surface polygonal mesh. The existence of an intersection point between said ray and a surface of the object is determined and the location of the point-of-interest is adjusted in response to the existence and location of the intersection point. The projecting is repeated for a plurality of points in the closed-surface polygonal mesh in order to approximate the object.

Abstract: An MRI system acquires NMR tracking data from a tracking coil imbedded in an ablation device which is guided by a physician using real time anatomic images produced from image data acquired by the MRI system. The same tracking coil is energized by an RF power source to deliver energy which ablates tissue after the device is guided into proper position.

Abstract: Anisotropic data having data spacing significantly larger between layers of data compared with spacing between adjacent data values, is supplemented with additional data to approximate isometric data. The ratio of spacing in one dimension to another is referred to as an aspect ratio A. Preferably, spacing is halved until spacing a modified aspect ratio A′ is near unity. Intermediate values are interpolated between existing values of the anisotropic data to create approximate isotropic data having a modified aspect ratio A′. Surface voxels are determined from the approximate isotropic data. The values of the adjacent voxels are then used to determine a vector normal to the surface at the central voxel. This is repeated for a number of central voxels to determine a surface. The viewing elevation angle is converted to an effective elevation angle. The surface is then rendered into a 2D screen image as if it were created from isotropic data.

Abstract: The present invention is capable of more accurately tracking an invasive device in a subject's body in the presence of eddy current inducing structures. Current patterns applied to the tracking system's transmit coils are modified to compensate for the effect of the eddy currents. The current supplied to the coils is a linear combination of the current needed to create the desired electromagnetic field in the region of interest; and one or more error terms. These terms are determined experimentally during system calibration and are mathematically modeled as a series of exponential functions having a given amplitude and time constant. The error terms in the current applied to the transmit coils cancel the magnetic fields created by eddy currents within the tracking region and result in an actual electromagnetic field which is close to the desired ideal electromagnetic field.

Abstract: An MRI system receives scan parameters from an operator which define the prescribed pulse sequence to be used in acquiring image data. The amplitude and slew rate of gradient pulses in the pulse sequence are calculated based on their prescribed areas to have optimal duration without exceeding physiologic gradient slew rate limits and to produce the pulse area required by the scan parameters.

Abstract: A sweep generator 230 applies a range of frequencies to an rf coil 140 to detect the resonant frequency of a field generated by a magnet 125a,b. A frequency to current converter 220 applies an auxiliary magnetic field to tune an MRI apparatus to the resonant frequency of the rf coil. A flexible coil of one turn (300) or two or more turns (500) has a plurality of segments (301-307; 501-513). One of the belt has a contact k0, (k0′), which is electrically connectable to one or more contacts k1, (k1′), k2, (k2′), etc. located between the ends of the segments. For each connection to successive contacts, the length of the coil and its inductance increases by the added impedance DLij between contacts ki and kj. That increase of inductance is nullified by capacitors DCsij located between segments.

Abstract: An invasive probe for mapping the walls of a lumen employs a real-time tracking means and a wall distance measurement means. As the probe is advanced within the lumen, the real-time tracking means provides three-dimensional coordinates of the probe's position and orientation. Concurrent with probe localization, the distance between the probe and the lumen walls is measured. Both the probe position and the wall distance measurement are sent to a data acquisition system which in turn provides a graphic or numeric display to the operator. Probe tracking can be performed with radio-frequency, magnetic resonance, ultrasonic techniques or the like. If desired, lumen wall distance measurements can be performed with magnetic resonance or ultrasound methods. Lumen wall distance measurements can also be performed with mechanical devices such as balloons and/or expanding structures.

Abstract: Pole faces for an open magnetic resonance (MR) imaging system are constructed from a number of blocks having laminate sheets. The laminate sheets of the blocks are aligned, such that they are parallel to the flux of an applied time-changing magnetic field. Each laminate sheet is constructed of an amorphous material such that there is no predominant magnetic field alignment. This construction reduces eddy currents induced in the pole faces, and reduces residual magnetization, thereby reducing artifacts in an acquired image.

Abstract: A local RF antenna assembly for a magnetic resonance imaging (MRI) system includes a conducting RF antenna structure. First and second capacitors are connected in series with the inductance of the RF antenna structure to form a circuit that resonates at a Larmor frequency. An inductor has a first terminal connected to a node between the first and second capacitors and has a second terminal. A photosensitive first semiconductor switch is connected between the second terminal of the inductor and one terminal of the RF antenna inductance. A receive coil control selectively provides illumination that places the photosensitive first semiconductor switch in a conductive state. When the photosensitive first semiconductor switch is conductive, the inductor disables resonance of the RF antenna circuit at the Larmor frequency. This action inhibits the RF receive antenna from interacting with other antennae in the MRI system.

Abstract: A digital transmitter/receiver communications system transmits audio voice signals over a channel with increased quality for a specified bit rate. The method of encoding takes advantage of spherical symmetry of error vectors associated with encoding Line Spectral Frequency (LSF) coefficients, to reduce the information transmitted. Errors in encoding the LSF coefficient sets, vectors J, are modeled by a number of vectors J.sub.p having all positive components, and a sign vector s indicating the polarity of each component of the vector. Each LSF vector J intended to be transmitted is approximated by a positive vector J.sub.p and a sign vector s. An index I.sub.p of the positive vector J.sub.p and the sign vector corresponding to vector J are transmitted, along with other audio information to a receiver/decoder where the signal is decoded into an audio signal closely representing the original signal intended to be transmitted.

Abstract: An invasive probe for determining the morphological characteristics of walls of a lumen employs a real-time tracking means and an optical spectral measurement means. As the probe is advanced within the lumen, the real-time tracking means provides three-dimensional coordinates of the probe's position and orientation. Concurrent with probe localization, measurement of the spectral properties of the lumen wall are made by detecting the reflectance and/or absorption of light at the lumen wall. Both the probe position and the spectral measurement are sent to a data acquisition system which in turn provides an graphic or numeric display to the operator. Probe tracking can be performed with radio-frequency, magnetic resonance, ultrasonic techniques or the like. If desired, spectral measurements can be made in the visible, ultra-violet or infra-red spectral bands to provide optimized detection of chemical species of interest.

Abstract: A reference image R is selected and a region of interest (ROI) is interactively selected encompassing a desired structure from a sequence of images of a moving structure. This ROI is cross-correlated with other real-time images by multiplication in the Fourier frequency domain, to determine if the desired structure is present in the image. If the structure is present, this image may be averaged with other images in which the structure is present to produce higher resolution adaptively averaged images. This invention is particularly useful in imaging coronary vessels. In an alternative embodiment, the offset of the desired structure may be calculated in a series of images. The images may then be sorted by this offset, and played back in that order to provide a "movie-like" display of the desired structure moving with the periodic motion.

Abstract: A volumetric data set having a high intensity, dominant structure, near smaller, less intense structures is smoothed and segmented to separate the dominant structure. The dominant structure is masked out to result in the smaller, less intense structures which are displayed. For example, dominant structures such as the blood pool in atria, ventricles, and the aorta of a 3D angiography data set is segmented and removed from the data set using mathematical morphology operations to result in an enhanced data set. The enhanced data set is displayed by conventional means such as a maximum intensity projection (MIP) at different views to yield images of coronary arteries.

Abstract: A sweep generator 230 applies a range of frequencies to an rf coil 140 to detect the resonant frequency of a field generated by a magnet 125a,b. A frequency to current converter 220 applies an auxiliary magnetic field to tune an MRI apparatus to the resonant frequency of the rf coil. A flexible coil of one turn (300) or two or more turns (500) has a plurality of segments (301-307; 501-513). One of the belt has a contact k0, (k0'), which is electrically connectable to one or more contacts k1, (k1'), k2, (k2'), etc. located between the ends of the segments. For each connection to successive contacts, the length of the coil and its inductance increases by the added impedance .DELTA.L.sub.ij between contacts k.sub.i and k.sub.j. That increase of inductance is nullified by capacitors .DELTA.C.sub.sij located between segments.

Abstract: This present invention makes use of a method for automatically finds collision-free part removal paths. The system sparsely samples the high-dimensional state space and maps the rest of the space using proximity assumptions (assumptions about states near the samples). The present invention is less complex and faster than previously known methods.