Biomedical subjects

S Amartur

Publications and source records attributed to S Amartur.

4 recordsLinked to original sources

PubMed1990

Optimizing blood vessel contrast in fast three-dimensional MRI.

Magnetic resonance angiography has matured to the point where clinically useful images can be acquired in half an hour or less. In this paper, the role of 3D imaging techniques is primarily considered. Specifically, the optimal imaging parameters, sequences, and reconstruction techniques are evaluated for moving spins. A variant of FISP known as ROAST with low flip angles, short repeat times, and a thick slab has been found to yield the best 3D survey scan of the cranial vessels with roughly 1 X 1 X 1-mm3 resolution in each of the processed images (slices). For the faster flowing carotids, a sagittal scout with as short a TE as possible is required to avoid spin dephasing. Localization is accomplished in both cases by acquiring thin slab 3D, thin partition, larger flip angle, longer repeat time FLASH sequences. Different choices of dephase/rephase sequences and directions are also reviewed. These choices are discussed from a practical and theoretical perspective. In particular, improvements in contrast and resolution are evaluated using half-Fourier, 512 acquisition, small fields of view and constrained reconstruction for both rephased gradient echo sequences and dephased thin slice long TR spin-echo sequences. A resolution of 0.5-0.75 mm is recommended to obtain sufficient image quality for consistent clinical interpretation of stenoses and vessel abnormalities.

Blood Flow Velocity↗

PubMedDate not supplied

Modified iterative model based on data extrapolation method to reduce Gibbs ringing.

An iterative algorithm that involves image filtering and data replacement (as suggested by Constable and Henkelman) is investigated for reducing the Gibbs artifact in magnetic resonance imaging. The image is processed with an edge-preserving filter to estimate the height and location of a set of model elements (delta functions or boxes) for generating the missing high-frequency information. Filtering was performed in the complex image domain to account for discontinuities in phase as well as magnitude. The process is repeated after each data replacement to handle varying degrees of contrast. The convergence and signal-to-noise characteristics of the algorithm are investigated by means of simulated and clinical examples. The results indicate that the algorithm performs reasonably well in reducing ringing artifacts due to nearby edge contrast seen in most of the homogeneous, isointense regions. Nevertheless, it may generate some spurious thickening of structures that do not match the assumed step-edge models.

Algorithms↗

PubMedDate not supplied

Phase-constrained data extrapolation method for reduction of truncation artifacts.

The authors present an improvement to a sigma-filter extrapolation method for the reconstruction of magnetic resonance (MR) images from symmetric discrete Fourier data. By making use of the phase information in the image data, the proposed method can overcome the data inconsistency problem of the original method for handling MR image data with large phase variations, such as those obtained in gradient-echo pulse sequences. Reconstruction results show that its performance is comparable with that of the modified complex sigma-filter method proposed previously to handle the inconsistency problem. However, the new approach has the advantage of reducing computation time by a factor of two with use of a sigma filter applied to real instead of complex images. It is expected that this method will be more practical for use in clinical MR imaging systems.

Algorithms↗

PubMedDate not supplied

3D MR myelography.

A three-dimensional (3D) fast imaging with steady state precession sequence structured to maintain constant phase at the radiofrequency pulse, in the presence of motion, was employed to produce high signal intensity of the CSF relative to the extradural and neural structures in 170 consecutive spine MR examinations. In addition to displaying the resulting partitions as two-dimensional (2D) images, the acquisition was subjected to a maximum intensity projection postprocessing algorithm for viewing at multiple angles. The projected images demonstrated a global view of the thecal sac and the dural root sleeves. The global depiction of the thecal sac and root sleeves was equivalent to contrast myelography in 15 patients where comparisons were available. These projection myelographic images, used in conjunction with 2D and reformatted 3D cross-sectional images, may provide clinical services with enough information (in a format with which they are comfortable) to eventually eliminate the need for contrast myelography in the evaluation of extradural disease.

Humans↗