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R A Lerski

Publications and source records attributed to R A Lerski.

11 recordsLinked to original sources
PubMed1989

A test material for tissue characterisation and system calibration in MRI.

A tissue-equivalent test material for MRI has been produced from a polysaccharide gel, agarose, containing gadolinium chloride chelated to EDTA. By varying the amounts of each constituent, the T1 and T2 of the material can be varied independently. As a result, the entire range of in vivo tissue relaxation times can be covered. Through the mathematical modelling of the 1H relaxation theories for both the gel and chelated paramagnetic ion, it has been possible to create a material with relaxation properties and behaviour predictable as functions of both the Larmor frequency and temperature. The similarity of the material to in vivo tissues, in terms of its biological and physical NMR characteristics, makes it an excellent tissue-equivalent substance, in addition to being an accurate calibration standard for routine MRI.

Edetic Acid↗
PubMed1988

Quantitative magnetic resonance imaging in assessment of the blood-retinal barrier.

Application of magnetic resonance imaging (MRI) in two-dimensional quantitative assessment of blood-retinal barrier dysfunction was investigated in rabbits using a 0.1 T (4.25 MHz) resistive system. Reliable and consistent measurements of vitreous T1 were obtained repeatedly, in slices of width 5 mm and X-Y resolution of 1.2 mm. Calibration of reduction of T1 in eyes after injection of gadolinium-DTPA (Gd-DTPA) was performed, resulting in a dose-related response of relaxation rate (1/T1) to the dose of Gd-DTPA injected. Follow-up scans of injected eyes demonstrated a gradual spread of the T1 "hot-spot" as the contrast agent diffused through the vitreous. T1 rose gradually to basal levels by 72 hr. No local effect of Gd-DTPA was found by ophthalmoscopy. Xenon arc photocoagulation of rabbit retina reduced T1 from 1638 +/- 54 (n = 6, mean +/- SD) ms to 1408 +/- 118 (n = 4) msec (P less than 0.01) throughout the vitreous 5-7 hr after treatment. In treated rabbits receiving 1.0 mmol/l Gd-DTPA intravenously, T1 adjacent to lesions 90-120 min after injection was further reduced in a 63 microliter voxel to 670 +/- 50 ms (mean +/- SD, n = 5) with a minimum pixel value of 285 +/- 52 ms. It was estimated that this represented leakage into vitreous of 8.3 nmol Gd-DTPA. Plasma Gd-DTPA concentrations declined rapidly, with half-life of 20-40 min. The findings indicate that MRI is a technique with the potential for repeated quantitative three-dimensional assessment of blood-retinal barrier dysfunction.

Animals↗
PubMed1986

Practical aspects of ghosting in resistive nuclear magnetic resonance imaging systems.

The concept of 'ghosting' in NMR images is discussed and it is demonstrated that, among other things, any external modulation of the NMR signal can produce such effects. A simple theoretical model, based on elementary Fourier modulation theory is presented for saturation recovery imaging sequences. Both amplitude (AM) and frequency (FM) modulations are considered. The predictions of the theory with regard to the positions and amplitudes of the ghosts produced by such modulations are outlined. Appropriate AM and FM conditions are generated experimentally on a 0.1 T resistive NMR system and measurements on the concomitant ghost images verify the theoretical predictions. Some practical implications of the phenomenon, with particular relevance to resistive magnet systems, are highlighted.

Humans↗
PubMedDate not supplied

Multi-center trial with protocols and prototype test objects for the assessment of MRI equipment. EEC Concerted Research Project.

A trial was carried out in which the protocols and prototype test objects developed under a European Economic Community concerted research project for the assessment of MR imaging equipment were tested in a series of commercial imaging systems situated throughout Europe. In general, many imperfections were discovered in the imaging performance of the scanners and, in particular, the accuracy and precision with which the relaxation times T1 and T2 could be measured from the images were found to be rather disappointing.

European Union↗
PubMedDate not supplied

Preparation of agarose gels as reference substances for NMR relaxation time measurement. EEC Concerted Action Program.

A standard method has been developed for the production of reference materials for NMR relaxation time measurement. These are based on agarose gels doped with gadolinium. The reproducibility and temporal stability of the gels have been found to be excellent. Electron microscope studies have shown good homogeneity. The relaxation behavior of such gels has been mathematically modeled with good agreement with experiment.

European Union↗
PubMedDate not supplied

Principles of nuclear magnetic resonance (NMR)--current state of the art.

Nuclear magnetic resonance (NMR) imaging has progressed rapidly from laboratory curiosity to commercial exploitation and clinical application in the space of only three years. The physical principles underlying the technique are described and the equipment requirements outlined. The question of optimal magnetic field strength is discussed.

Humans↗