Abstract: At least one imaging parameter (e.g., the repetition interval TR or the initial nutation angle .theta.) is varied during the course of a single MR image sequence. This variation in at least one imaging parameter is preferably controlled so as to increase the contrast and signal-to-noise ratio of lower spatial frequency image components. For example, by using longer TR intervals (or smaller initial nutation angle .theta.) during lower spatial frequency phase encoding sub-sequences, relatively more signal is gathered from NMR nuclei having long T1 parameters thus providing a resultant image with many characteristics of a much longer overall sequence (e.g., one using uniform relatively long TR intervals for all spatial frequency phase encoding sub-sequences).

Abstract: At least one imaging parameter (e.g., the repetition interval TR or the initial nutation angle .theta.) is varied during the course of a single MR image sequence. This variation in at least one imaging parameter is preferably controlled so as to increase the contrast and signal-to-noise ratio of lower spatial frequency image components. For example, by using longer TR intervals (or smaller initial nutation angle .theta.) during lower spatial frequency phase encoding sub-sequences, relatively more signal is gathered from NMR nuclei having long T1 parameters thus providing a resultant image with many characteristics of a much longer overall sequence (e.g., one using uniform relatively long TR intervals for all spatial frequency phase encoding sub-sequences).

Abstract: Continuously updated real-time magnetic resonance imaging processes are used to display an MR image volume to an operator and/or patient co-located with the MRI magnet, viewing console and other elements of an MRI system within the same shielded gantry room. A CRT display may be used for lower field MRI systems while liquid crystal displays may be necessary for higher field MRI systems since the viewing console is to be co-located within the shielded gantry room near the MRI magnet assembly. Suitable RF shielding is provided to RF-isolate the viewing console and its related power and video signal cables from the MRI RF coils being used to monitor relatively weak NMR signals emanating from the image volume within the magnet assembly.

Abstract: A measure of magnetic field inhomogeneity along a phase-encoded (e.g. y-axis) dimension is derived in k-space from previously acquired MRI phase-encoded projection data. From this, a measure of MRI data skewing caused by such inhomogeneity is obtained and used to compensate therefor. Since the MRI data is to be multi-dimensionally Fourier Transformed in most instances anyway, a transform in the relevant phase encoded dimension (e.g., y-axis) is taken followed with phase shifting each digitized data point by an amount proportional to the measured magnitude of inhomogeneity and to the datum coordinate in the read-out dimension (e.g., x-axis) and to the datum coordinate in each phase-encode dimension (e.g., y-axis) before the data is further Fourier Transformed with respect to the read-out dimension (e.g., x-axis). If two-dimensional phase encoding is employed (e.g., as in 3DFT), then a second level of similar inhomogeneity compensation can be had in the third dimension (e.g., z-axis) as well.

Abstract: Positioning of interventional devices within the patient image volume of an MRI system is performed while viewing real-time fluoroscopic MR images of such devices superimposed upon a saved prior image ("ghost") of patient anatomy that was earlier located within the same image volume. After such interventional medical procedure is thoroughly planned using the earlier acquired three-dimensional ghost image, the patient anatomy is relocated within the image volume and the final selected trajectory for the interventional device or medical procedure is then performed (preferably while real time MRI fluoroscopy is used to monitor the actual interventional procedure within the real patient anatomy).

Abstract: Techniques for rapidly and accurately calibrating RF transmitter parameters in a Nuclear Magnetic Resonance (NMR) magnetic resonance imaging (MRI) system obtain an estimate of flip (nutation) angle by determining a ratio of plural echo responses to a plural (e.g., three) RF pulse sequence. The ratio may be selected to be independent of relaxation times T.sub.1 and T.sub.2 so no relaxation waiting time between successive iterations is required. Accurate RF transmitter level calibration can be performed within on the order of three to five seconds. The techniques are robust and can discriminate flip angles over a wide range.

Abstract: Static B.sub.o field strength is measured during each TR interval of an MRI sequence providing field calibration data used to compensate for rapid variations in B.sub.o during the MRI sequence.

Abstract: Variable voxel shifts required for shifting a 3D structure into a common oblique or contoured slice volume based on an existing 3D image are achieved by effecting variable f(x,y) phase shifts in corresponding frequency domain data parallel to a selected axis dimension and then reconstructing a new three-dimensional image having the 3D structure all located within a common oblique or otherwise contoured slice volume such that it may viewed in a single planar image display without loss of volume resolution. Equivalent convolution processes withing the spatial domain may also be empolyed. Oblique or curved reconstructions can thus be made using either originally acquired frequency domain data (used to construct the original image) or frequency domain data obtained by inverse Fourier transforming the available spatial domain data of the images themselves.

Abstract: An optical system for individually testing each one of a plurality of fibers for continuity. Each fiber having a proximal end and a distal end with a dichroic reflector at each distal end reflective of wavelengths respective to a source of testing light and transmissive to other wavelengths. The selection of which fiber is to be tested is only a matter of manipulating a rotator element which has the capacity to rotate the angle of polarization by 90 degrees. The polarization of the light determines the respective fiber to be tested.

Abstract: A technique for producing multiple spin echo signals following an initial excitation pulse is provided. A first inverting pulse is applied a given time interval following the initial excitation pulse, resulting in the formation of the usual first spin echo signal after passage of the given time interval. At a later point in time, a second inverting pulse is applied. The time interval between the initial excitation pulse and this second inverting pulse is not required to be harmonically related to the first given time interval. This results in the production of at least a second, later occurring spin echo signal which does not contain harmonically-related artifact components of the earlier pulses and spin echo signals.

Abstract: In a magnetic resonance imaging system, the same reference signal is used for both radio frequency transmission and phase sensitive detection. The use of the same reference signal for both transmission and reception prevents phase unlock between the two events. However, this technique results in variation in the demodulated, frequency encoded information, which is corrected by digitally filtering the received signal information as a function of the demodulation frequency used.

Abstract: In a magnetic resonance imaging system, a multiplexing technique is used to image volumetric regions by performing a number of scans within the recovery time of the spin systems. The multiple scans acquire signal information from sub-regional volumes by phase-encoding in the direction of the excitation gradient.

Abstract: The null point in the gradient field of an NMR imaging system is offset from its nominal position in the static magnetic field by application of a bias field to the gradient field. The bias field produces a substantially uniform offset in the field intensity at every point in the gradient field. Alternatively, null point offset may be achieved by controllably superimposing two gradient fields of separately located null points.

Abstract: In an NMR imaging system, two-pulse excitation sequences are used to acquire lines of NMR signal information. Artifact signal components may also be present during the times of NMR signal acquisition. In order to remove these artifacts from the center of the image, the artifact signals are alternately phase-encoded from line to line by alternating the phase of one of said excitation pulses from line to line. Fourier transformation is performed on the lines of information in at least the direction of alternate phasing of the artifact components, which relocates the artifacts to the edge of the resulting image.