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.

Sodium transport and phosphorus metabolism in sodium-loaded yeast: simultaneous observation with sodium-23 and phosphorus-31 NMR spectroscopy in vivo.

Simultaneous 23Na and 31P NMR spectra were obtained from a number of yeast suspensions. Prior to NMR spectroscopy, the yeast cells were Na-loaded: this replaced some of the intracellular K+ with Na+. These cells were also somewhat P-deficient in that they had no polyphosphate species visible in the 31P NMR spectrum. In the NMR experiments, the Na-loaded cells were suspended in media which contained inorganic phosphate, very low Na+, and a shift reagent for the Na+ NMR signal. The media differed as to whether dioxygen, glucose, or K+ was present individually or in combinations and as to whether the medium was buffered or not. The NMR spectra revealed that the cells always lost Na+ and gained phosphorus. However, the nature of the Na+ efflux time course and the P metabolism differed depending on the medium. The Na+ efflux usually proceeded linearly until the amount of Na+ extruded roughly equalled the amount of NH4+ and orthophosphate initially present in the medium (external phosphate was added as NH4H2PO4). Thus, we presume this first phase reflects a Na+ for NH4+ exchange. The Na+ efflux then entered a transition phase, either slowing, ceasing, or transiently reversing, before resuming at about the same value as that of the first phase. We presume that this last phase involves the simultaneous extrusion of intracellular anions as reported in the literature. The phosphorus metabolism was much more varied. In the absence of exogenous glucose, the P taken up accumulated first as intracellular inorganic phosphate; otherwise, it accumulated first in the "sugar phosphate" pool. In most cases, at least some of the P left the sugar phosphate pool and entered the polyphosphate reservoir in the vacuole. However, this never happened until the phase probably representing Na+ for NH4+ exchange was completed, and the P in the polyphosphate pool never remained there permanently but always eventually reverted back to the sugar phosphate pool. These changes are interpreted in terms of hierarchical energy demands on the cells under the different conditions. In particular, the energy for the Na+ for NH4+ exchange takes precedence over that required to produce and store polyphosphate. This conclusion is supported by the fact that when the cells are "forced" to exchange K+, as well as NH4+, for Na+ (by the addition of 5 times as much K+ to the NH4+-containing medium), polyphosphates are never significantly formed, and the initial linear Na+ efflux phase persists possibly 6 times as long.(ABSTRACT TRUNCATED AT 400 WORDS)

Pulse sequence design for volume selective excitation in magnetic resonance.

The design of a pulse sequence for volume localization in magnetic resonance spectroscopy is described in detail. The sequence is based on the volume selective excitation technique (VSE) proposed by Aue et al. [J. Magn. Reson. 56, 350 (1984)] and overcomes the high rf power requirements of VSE. The implications of various design stages are demonstrated experimentally and by computer simulations.

In vivo 31P NMR studies of avian dystrophic muscles.

In vivo 31P NMR studies of normal and dystrophic pectoralis muscles of chicks were carried out in the age group of 2 to 8 weeks. It was observed that the ratios [PCr]/[Pi] and [PCr]/[ATP] were essentially the same in both normal and dystrophic muscles. The cellular pH for normal muscles however, was found to be higher (7.24 +/- 0.08) compared to the dystrophic muscles (7.0 +/- 0.07).

Nuclear magnetic resonance for the differentiation of benign and malignant breast tissues and axillary lymph nodes.

We have utilized proton T1 (spin-lattice relaxation time) values of Nuclear Magnetic Resonance to study 110 tissue samples obtained from 11 mastectomy specimens. Samples of 1 cm3 from primary tumor sites, nipples, and other breast quadrants, as well as intact lymph nodes were studied and then histologically scored for the presence or absence of carcinoma and, if present, whether it was an isolated microscopic focus (micro). Of 54 samples of breast tissue, 12 contained carcinoma, 5 micro: of 45 lymph nodes, 15 contained metastatic carcinoma, 2 micro; of the 11 nipples, 2 had carcinoma, both micro. For the malignant samples (excluding micro) mean T1 value was 0.47 +/- 0.07 sec, (range 0.39-0.79 sec). For the 72 benign samples (excluding nipple) mean T1 value was 0.26 +/- 0.03 sec (range 0.14-0.36 sec). The 13 tumor-bearing nodes had a mean T1 value of 0.47 +/- 0.03 sec (range 0.40-0.63 sec); mean for the benign nodes was 0.26 +/- 0.007 sec (range 0.19-0.35 sec). The differences were highly significant in each case (p less than 0.001). For micro examples, T1 values were at malignancy threshold levels or just below, except for nipple tissues, where discrimination was poor. For the 20 other malignant samples, there was no correlation between T1 value and the per cent of sample containing malignancy.

Gated sodium-23 nuclear magnetic resonance images of an isolated perfused working rat heart.

Sodium-23 nuclear magnetic resonance images of phantoms and gated images of isolated perfused working rat hearts were obtained. By synchronizing the nuclear magnetic resonance process to the heartbeat, images were obtained at systole and at diastole.