RF coils for combined MR and hyperthermia studies: I. Hyperthermia applicator as an MR coil.

Combining hyperthermia, an experimental/adjuvant therapeutic modality for cancer, with the non-invasive metabolic studies using Magnetic Resonance (MR) is an interesting area of research. This two parts article discusses the development and testing of a conventional RF hyperthermia applicator for MR studies and vice versa. In this first part, an inductive type applicator known as 'Magnetrode' in RF hyperthermia has been used both as an MR volume resonator and a surface coil. Its concurrent performance as an hyperthermic applicator and an MR transmit/receive coil has been evaluated.

RF coils for combined MR and hyperthermia studies: II. MR coil as an hyperthermic applicator.

Single loop surface coil, often used in MR studies, was evaluated for its performance as an inductive hyperthermic applicator. The heat deposition pattern produced by the surface coil at 84 MHz and 34 MHz was mapped in muscle-mimicking agar phantoms. Temperatures were measured simultaneously at 64 points using multiple-junction thermocouples.

Simultaneous evaluation of the effects of RF hyperthermia on the intra- and extracellular tumor pH.

31P-magnetic resonance spectroscopy (MRS) and a fiberoptic pH meter were used simultaneously to follow the changes in intra- (pHi) and extracellular pH (pHe), respectively, of murine RIF-1 tumors with hyperthermia. Hyperthermia was induced at 34 MHz using the same coil used for MR. The study was carried out until 3.5 hr after hyperthermia. In untreated tumors (n = 29), pHi was always higher than pHe. pHi was reduced after hyperthermia (30 min) at both 42 degrees C and 45 degrees C. pHe registered an increase after 42 degrees C and a decrease after 45 degrees C. The reduction in pHi was larger than the initial differential between pHi and pHe, and the change in pHe was relatively small. Hyperthermia changed the acidity of the intra- and extracellular compartments, such that pHe became more alkaline than pHi by 0.15 +/- 0.13 units after 42 degrees C [pHe (7.20 +/- 0.12) and pHi (7.03 +/- 0.05)], and by 0.12 +/- 0.14 units after 45 degrees C [pHe (6.84 +/- 0.24) and pHi (6.72 +/- 0.19)]. Simultaneous measurements of pH from the intra- and extracellular compartments demonstrated reversal in the pH gradient after hyperthermic treatment.

A magnetic resonance-compatible experimental set-up for hyperthermia studies.

This study presents the development and testing of an experimental set-up for simultaneous measurements of pH (intracellular by MR and extracellular by fibre-optic pH meter), tumour bio-energetics (by MR), and core/tumour temperatures (by thermocouples) in tumour-bearing mice. Potential sources of measurement errors when using these techniques concurrently in an MR set-up are discussed. Emphasis is placed on simple practical solutions to these problems.

Visualisation of subchondral erosion in rat monoarticular arthritis by magnetic resonance imaging.

High-resolution magnetic resonance imaging (MRI) was used to investigate antigen-induced monoarticular arthritis (AIMA) in the rat. In sagittal, spin-echo images of the knee, characteristic parallel bands, in the order dark-light-dark, were consistently observed 5-8 days after arthritis induction; the bands ran concentric with, and just beneath, the femoral and tibial articular surfaces. Concurrent radiology, histology and MRI (chemical shift-selective imaging and contrast enhancement with magnetisation transfer and gadolinium) established that the phenomenon reflected subchondral erosion, not artefact. The outer hypointense band corresponded to calcified cartilage underlying the articular surface. The central hyperintense band reflected inflammatory matrix displacing normal haematopoietic tissue immediately subchondrally; here, trabecular bone had mostly disappeared, but adjacent articular cartilage, although under attack and lacking proteoglycan, appeared structurally normal. The inner hypointense band reflected deeper, truncated trabeculae within inflammatory matrix, layered with pallisading osteoblast-like cells. This study exemplifies the power of MRI for revealing localised joint pathology non-invasively, and shows that rat AIMA shares many pathological features with arthritis in human beings.

Comparison of pH measurements made using 31P NMR and a fibreoptic pH meter.

The objective of this study was to compare pH measurements made in biological samples using 31P NMR (pHNMR) with those made with a novel, dye-based fibreoptic pH measurement system (pHF), which is compatible with use in electromagnetic fields without field perturbation. Using protein-free model solutions, pHNMR was calibrated against pHF, giving a correlation coefficient of 0.969 and a mean difference (+/- SD) between pHNMR and pHF of 0.037 +/- 0.054 over the pH range 6.8-7.7. Further calibration of pHNMR with pHF was carried out for human red blood lysates and then pHNMR was compared with pHF for whole, packed red blood cells over the pH range 7.0-7.8. Values for pHNMR, the intracellular pH, were consistently lower than for pHF, the extracellular pH, by a mean (+/- SD) of 0.15 +/- 0.02 units. A close correlation of extracellular pHNMR with pHF was demonstrated for a blood sample exhibiting two P(i) peaks, over the pH range 7.03-7.71. We conclude that concurrent use of NMR and the fibreoptic pH meter provides a reliable method of simultaneous measurement of intracellular and extracellular pH in biological systems.

Relative metabolic efficiency of concentric and eccentric exercise determined by 31P magnetic resonance spectroscopy.

To determine the relative metabolic efficiency (metabolic energy used per unit of mechanical energy output) of negative to positive muscular power, we used 31P magnetic resonance spectroscopy to monitor the cellular energy metabolism of limb muscles in eight healthy subjects during a nonfatiguing, mixed concentric-eccentric activity and during its concentric and eccentric components. We also studied isometric contractions. We found that in terms of the flow of metabolic energy through the muscle cells, the cost of concentric exercise at this intensity was proportional to the mechanical power generated, but the cost of eccentric and isometric exercise did not increase significantly as the apparent intensity of the exercise increased over the range studied. Although the pattern was similar in all subjects, the quantitative relationship between metabolic cost and mechanical output was different in subjects with different muscular strength. The qualitative results can be explained in the context of the known biochemistry and biophysics of the cellular contractile apparatus (sliding filament theory, with independent force generators).