Abstract: A new technique for maintaining the alignment of electric and magnetic fields in an x-ray tube so the tube can be operated in the presence of a static external magnetic field without being negatively affected thereby. Deflection of the electron beam of the x-ray tube by the high magnetic field is reduced or eliminated by modifying or canceling, at a location near the electron beam, the magnetic field components transverse to the beam. In a preferred embodiment, a set of electromagnet coils are positioned on or near the tube and oriented in a way that when current is applied internal magnetic fields are produced in a direction opposite to the transverse magnetic fields, thereby causing cancellation. In one implementation, one or more sensors are used to detect the transverse magnetic fields. The sensor is positioned near the electron beam, either inside or outside the x-ray tube.

Abstract: An imaging system and method combines a magnetic resonance imaging (MRI) system and an x-ray fluoroscopy system such that the two systems have coincident fields of view. X-rays are generated by a stationary anode x-ray tube in which an electron beam is accelerated from a cathode to an anode. In the presence of the static magnetic field of the MRI system, the electron beam is deflected unless it is parallel to the static magnetic field. The x-ray source of the invention contains elements used to steer the electron beam and increase its focusing on the anode. The beam can be steered electrostatically, electromagnetically, or by adding magnetic material to the x-ray source. In the resulting system, MR and x-ray images are acquired without moving the object, which is particularly useful for image-guided medical intervention procedures.

Abstract: A general mathematical framework is formulated to characterize the contribution of gradient non-uniformities to diffusion tensor imaging in MRI. Based on a model expansion, the actual gradient field is approximated and employed, after elimination of geometric distortions, for predicting and correcting the errors in diffusion encoding. Prior to corrections, experiments clearly reveal marked deviations of the calculated diffusivity for fields of view generally used in diffusion experiments. These deviations are most significant with greater distance from the magnet's isocenter. For a FOV of 25 cm the resultant errors in absolute diffusivity can range from approximately ?10 to +20 percent. Within the same field of view, the diffusion-encoding direction and the orientation of the calculated eigenvectors can be significantly altered if the perturbations by the gradient non-uniformities are not considered. With the proposed correction scheme most of the errors introduced by gradient non-uniformities can be removed.

Abstract: A generalized multi-point fat-water separation process is combined with steady-state free precession (SSFP) to obtain high quality images of articular cartilage with reduced imaging time.

Abstract: Perturbations in a static magnetic field of magnetic resonance imaging apparatus are compensated by creating magnetic fields near an object creating the perturbations with the magnetic fields adjusted to offset the perturbations in the static magnetic field. In an embodiment where the perturbations are caused by an x-ray detector in a combined modality imaging apparatus, the coils are positioned to surround the x-ray detector and create magnetic fields in the static magnetic field outside of the detector which compensate for the perturbations caused by the x-ray detector.

Abstract: An x-ray tube having sensors, magnets, and/or active compensation means operatively coupled thereto or integrated therein for aligning its electron beam with an external magnetic field. Permanent magnets positioned behind the anode and cathode respectively or electromagnets are used to produce a strong, properly aligned internal magnetic field. The x-ray tube is thus less sensitive to other magnetic fields that are not parallel to the anode-cathode axis. The x-ray tube can be mounted in a manner that it can pivot, allowing it to move and align itself. The x-ray tube can also be mounted such that a torque can be sensed. This sensed mechanical force is then used as an input to determine current applied to electromagnetic coils arranged to oppose a transverse magnetic field.

Abstract: A novel technique for velocity measurements (PC-SSFP) is disclosed that combines CINE Phase Contrast (PC) MRI and balanced Steady State Free Precession (SSFP) imaging. Flow encoding is performed without the introduction of additional velocity encoding gradients in order to permit data acquisition with short TR comparable to repetition times of typical SSFP imaging sequences. Sensitivity to through plane velocities is instead established by inverting (i.e. negating) all gradients along the slice select direction. Velocity sensitivity (venc) can be adjusted by altering the first moments of the slice select gradients. Disturbances of the SSFP steady state are avoided by acquiring different flow echoes in consecutively (i.e. sequentially) executed scans, each over several cardiac cycles, using separate steady state preparation periods. Comparison of phantom measurements with those from established 2D-CINE-PC MRI excellent correlation between both modalities.

Abstract: Generalized series-based image reconstruction as used in dynamic imaging for high-speed imaging with limited k-space coverage for each time frame. Further, in acquiring low resolution data for a plurality of image frames, a full k-space data set is generated for each time frame with the measured low-resolution data and high spatial frequency data generated by the GS model constructed based on the high-resolution image(s). The algorithms of the invention have computational complexity of O(N log N) and arc capable of producing high-resolution dynamic images with a small number of Fourier transform samples.

Abstract: Errors in qualitative phase contrast measurements due to gradient field heterogeneities are reduced by using either a generalized reconstruction algorithm or an approximate reconstruction algorithm. True velocities are calculated using measured velocity information and phase differences, first moments of gradients, and gyromagnetic ratio.

Abstract: A novel technique for velocity measurements (PC-SSFP) is disclosed that combines CINE Phase Contrast (PC) MRI and balanced Steady State Free Precession (SSFP) imaging. Flow encoding is performed without the introduction of additional velocity encoding gradients in order to permit data acquisition with short TR comparable to repetition times of typical SSFP imaging sequences. Sensitivity to through plane velocities is instead established by inverting (i.e. negating) all gradients along the slice select direction. Velocity sensitivity (venc) can be adjusted by altering the first moments of the slice select gradients. Disturbances of the SSFP steady state are avoided by acquiring different flow echoes in consecutively (i.e. sequentially) executed scans, each over several cardiac cycles, using separate steady state preparation periods. Comparison of phantom measurements with those from established 2D-CINE-PC MRI excellent correlation between both modalities.

Abstract: A general mathematical framework is formulated to characterize the contribution of gradient non-uniformities to diffusion tensor imaging in MRI. Based on a model expansion, the actual gradient field is approximated and employed, after elimination of geometric distortions, for predicting and correcting the errors in diffusion encoding. Prior to corrections, experiments clearly reveal marked deviations of the calculated diffusivity for fields of view generally used in diffusion experiments. These deviations are most significant with greater distance from the magnet's isocenter. For a FOV of 25 cm the resultant errors in absolute diffusivity can range from approximately −10 to +20 percent. Within the same field of view, the difflision-encoding direction and the orientation of the calculated eigenvectors can be significantly altered if the perturbations by the gradient non-uniformities are not considered.

Abstract: Generalized series-based image reconstruction as used in dynamic imaging for high-speed imaging with limited k-space coverage for each time frame. Further, in acquiring low resolution data for a plurality of image frames, a full k-space data set is generated for each time frame with the measured low-resolution data and high spatial frequency data generated by the GS model constructed based on the high-resolution image(s). The algorithms of the invention have computational complexity of O(N log N) and are capable of producing high-resolution dynamic images with a small number of Fourier transform samples.

Abstract: Perturbations in a static magnetic field of magnetic resonance imaging apparatus are compensated by creating magnetic fields near an object creating the perturbations with the magnetic fields adjusted to offset the perturbations in the static magnetic field. In an embodiment where the perturbations are caused by an x-ray detector in a combined modality imaging apparatus, the coils are positioned to surround the x-ray detector and create magnetic fields in the static magnetic field outside of the detector which compensate for the perturbations caused by the x-ray detector.

Abstract: An x-ray tube having sensors, magnets, and/or active compensation means operatively coupled thereto or integrated therein for aligning its electron beam with external magnetic field. Permanent magnets positioned behind the anode and cathode respectively or electromagnets are used to produce a strong, properly aligned internal magnetic field. The x-ray tube is thus less sensitive to other magnetic fields that are not parallel to the anode-cathode axis. The x-ray tube can be mounted in a manner that it can pivot, allowing it to move and align itself. The x-ray tube can also be mounted such that a torque can be sensed. This sensed mechanical force is then used as an input to determine current applied to electromagnetic coils arranged to oppose transverse magnetic field.

Abstract: The present invention provides a volumetric computed tomography (VCT) system capable of producing data for reconstructing an entire three-dimensional (3D) image of a subject during a single rotation without suffering from cone beam artifacts. The VCT system comprises an array of source positions distributed along a line parallel to an axis of rotation, a plurality of collimators, and an array of x-ray detectors. In a preferred embodiment, a reversed imaging geometry is used. A 2D array of source positions provides x-rays emanating from each focal spot toward an array of detectors. The x-rays are restricted by a collimator array and measured by a detector array separately per each source position. The axial extent of the source array and the detector array are comparable to or larger than the axial extent of the portion of the object being imaged.

Abstract: In some dynamic applications of MRI, only a part of the field-of-view (FOV) actually undergoes dynamic changes. A class of methods, called reduced-FOV (rFOV) methods, convert the knowledge that some part of the FOV is static or not very dynamic into an increase in temporal resolution for the dynamic part, or into a reduction in the scan time. Although cardiac imaging is an important example of an imaging situation where changes are concentrated into a fraction of the FOV, the rFOV methods developed up to now are not compatible with one of the most common cardiac sequences, the so-called retrospective cine method. The present work is a rFOV method designed to be compatible with cine imaging. An increase by a factor n in temporal resolution or a decrease by n in scan time is obtained in the case where only one nth of the FOV is dynamic (the rest being considered static). Results are presented for both Cartesian and spiral imaging.

Abstract: Disclosed is a method for nonrigid cyclic motion analysis using a series of images covering the cycle, acquired, for example, from phase contrast magnetic resonance imaging. The method is based on fitting a global spatiotemporal finite element mesh model to motion data samples of an extended region at all time frames. A spatiotemporal model is composed of time-varying finite elements, with the nonrigid motion of each characterized by a set of Fourier harmonics. The model is suitable for accurately modeling the kinematics of a cyclically moving and deforming object with complex geometry, such as that of the myocardium. The model has controllable built-in smoothing in space and time for achieving satisfactory reproducibility in the presence of noise. Motion data measured, with PC MRI for example, can be used to quantify motion and deformation by fitting the model to data.

Abstract: Disclosed is an apparatus and a method for three dimensional magnetic resonance data acquisitions using a fast 3D sequence to acquire volumetric data in a cine mode. The entire heart can be imaged in the same amount of time that a conventional cine scan requires for a single section. The true temporal resolution is similar to that of the segmented k-space acquisition. The sequence uses very short repetition times (TR), and hence the inherent contrast is poor. This problem is overcome with the use of a T1 shortening agent. Since contrast between blood and the myocardium is no longer flow dependent, it is more stable throughout the heart cycle.

Abstract: MRI is used to monitor the time behavior or an organ of interest. Images of such organ may change in time due to physiological motion, and/or due to contrast-agent accumulation. Dynamic applications generally involve acquiring data in a k-t space, which contains both temporal and spatial information. In some dynamic applications, the t axis of the k-t space is not densely filled with information. A method is introduced which can transfer information from the k axes to the t axis, allowing a denser, smaller k-t space to be acquired, and leading to significant reductions in the acquisition time of the temporal frames. Results are presented for cardiac imaging and functional MRI (fMRI). In the case of cardiac imaging, the present method is shown to reduce the data requirement by nearly a factor two. In the case of fMRI, reductions by as much as a factor six can be obtained. The behavior of the method is assessed by comparing the results to data obtained in a conventional way.

Abstract: Disclosed is a method for characterizing the gradient subsystem of a Magnetic Resonance (MR) system. The method uses a Fourier-transform analysis to directly measure the k-space trajectory produced by an arbitrary gradient waveform. In addition, the method can be easily extended to multiple dimensions, and can be adapted to measuring residual gradient effects such as eddy currents. Several examples of gradient waveform and eddy-current measurements are presented. Also, it is demonstrated how the eddy-current measurements are presented. Also, it is demonstrated how the eddy-current measurements can be parameterized with an impulse-response formalism for later use in system tuning. When compared to a peak-fitting analysis, this technique provides a more direct extraction of the k-space measurements, which reduces the possibility of analysis error.