Biomedical subjects

W W Brey

Publications and source records attributed to W W Brey.

7 recordsLinked to original sources

PubMed1999

A high-temperature superconducting Helmholtz probe for microscopy at 9.4 T.

The design and operation of a high-temperature superconducting (HTS) probe for magnetic resonance microscopy (MRM) at 400 MHz are presented. The design of the probe includes a Helmholtz coil configuration and a stable open-cycle cooling mechanism. Characterization of coil operating parameters is presented to demonstrate the suitability of cryo-cooled coils for MRM. Specifically, the performance of the probe is evaluated by comparison of signal-to-noise (SNR) performance with that of a copper Helmholtz pair, analysis of B1 field homogeneity, and quantification of thermal stability. Images are presented to demonstrate the SNR advantage of the probe for typical MRM applications.

Algorithms↗

PubMed1996

A field-gradient coil using concentric return paths.

An approach to transverse field-gradient coil design is presented which locates all current elements in planes perpendicular to the main magnetic field. The linear volume of the resulting coil structure can be made to extend nearly to both ends of the coil. This design is based on forming a concentric return path in the same plane as the field-producing arcs. The coil structure consists of stacked planar units which give a desired field-gradient configuration. The size of the linear-field region is optimized by varying the current in each plane, by varying the location of a plane relative to the others in the stack, or by varying both current and location. Coils with linear regions having a wide range of length-to-diameter ratios can be designed, as illustrated by two examples. The construction of a prototype coil is presented and its performance in imaging confirms the analysis. This type of design is suited to magnetic resonance of the human head without obstruction from the shoulders.

Equipment Design↗

PubMed1993

Fat tissue and fat suppression.

Fat tissues consist of fat cells, capillaries, and collagen fibers. In order to completely suppress the signals from fat tissues in clinical magnetic resonance imaging, the signal from capillaries and collagen fibers as well as from fat cells should all be suppressed. We have previously reported that fat signal can be uniformly suppressed by applying an optimized presaturation pulse. The inhomogeneously broadened fat peak of tissue spectrum is excited by the optimized pulse and dephased by a subsequent field gradient. The broadened water peak is not affected. In this paper we discuss a technique that suppresses signals from fat tissues completely as well as uniformly. This technique is based on the cancellation of fat and water signals in the same image voxel by combining the optimized selective excitation with the opposite phase imaging technique. Experimental and clinical images demonstrate that the new technique improves the delineation and depiction of anatomy in clinical fat suppression imaging.

Adipose Tissue↗

PubMed1987

In vivo proton spin-lattice relaxation times of normal and dystrophic muscles.

In vivo spin-lattice relaxation times (T1) of water and lipid protons were measured in normal and dystrophic chicken pectoralis muscles at different ages. Values were obtained with a surface coil used as both a receiver and a transmitter. A 2 theta-T1-theta-Acquisition sequence was used for these measurements. Accuracy was verified with an inversion-recovery method using a slotted tube resonator as the transmitter and a surface coil as the receiver. It was observed that the T1 values of water protons in normal muscles decrease with age, the T1 values of water protons do not change with age in dystrophic muscles, and the T1 values of lipid protons increase with age in normal and dystrophic muscles. These results indicate a failure of the normal maturation of dystrophic muscles.

Animals↗

PubMedDate not supplied

Compensation for surface coil sensitivity variation in magnetic resonance imaging.

A procedure which incorporates the aspects of both correction matrix and digital filtering to compensate for sensitivity fall-off of the surface coil has been applied to clinical imaging. In this method the surface coil profile is determined using the surface coil image and a crude body coil image. Our results indicate that the corrected surface coil image exhibits the homogeneity of the body coil image while essentially preserving the sensitivity of the surface coil image.

Humans↗

PubMedDate not supplied

Reduction of pulsed gradient settling time in the superconducting magnet of a magnetic resonance instrument.

The implementation of electronic compensation for eddy currents to reduce the gradient settling times on a superconducting magnet is described. Field plots inside the magnet indicate the importance of assessing the field changes at several positions in the magnet. The effect of an asymmetry between the gradient coil system and the cryostat is demonstrated. A modified compensation circuit is described to overcome this mechanical asymmetry.

Magnetic Resonance Imaging↗

PubMedDate not supplied

Correction for intensity falloff in surface coil magnetic resonance imaging.

A method has been developed to compensate for sensitivity variation in surface coil images. An algorithm to derive the surface coil profile by acquiring a crude body coil image of the region under study is presented and tested using a homogeneous phantom. Practical application is demonstrated on images of a tomato and rabbit acquired with a 2 T 33-cm bore magnetic resonance imager/spectrometer.

Animals↗