In vivo temperature measurements in brain tumors using proton MR spectroscopy

The chemical shift difference between the water resonance and the methyl resonance of N-acetylaspartate was used to determine the in vivo temperature in 43 patients with histologically proven brain tumors. Temperatures were also estimated from the contralateral side in 15 of these patients. There was a significant difference (p < 0.05) ] in temperature between meningiomas and the other tumors viz. low grade astrocytomas, grade IV astrocytomas and oligoastrocytomas. Temperature was also significantly different between the contralateral side and the meningiomas (p < 0.05).

Human brain: biochemical lateralization in normal subjects

Chemical asymmetries in normal human brain were studied using the non-invasive technique of volume localized proton magnetic resonance spectroscopy (MRS). The technique of STEAM was used to acquire water-suppressed proton spectra from 8 ml voxels placed in bilaterally symmetrical positions in the two hemispheres of the brain. One hundred and sixty eight right-handed male volunteers were studied for six different regions in the brain (n=28, for each region). Parietal, occipital, temporal, frontal, thalamus and cerebellum regions were studied. The focus was on metabolites such as N-acetyl aspartate (NAA), creatine/phosphocreatine (Cr/PCr) and choline (Cho) containing compounds. Ratios of the peak areas were calculated for them. Quantitation of the metabolites were carried for data on 18 volunteers. Significant interhemispheric differences in the distribution of metabolites were observed for all the regions studied. There were statistically significant differences on right and left side for the metabolite ratios in all the regions studied. The study has shown the existence of significant lateralization in the distribution of proton MR visible metabolites for all the regions studied.

Sequential proton MRS study of brain metabolite changes monitored during a complete pathological cycle of demyelination and remyelination in a lysophosphatidyl choline (LPC)-induced experimental demyelinating lesion model

Metabolite changes in rat brain internal capsule (ic) area were monitored using volume localized in vivo proton MR spectroscopy (MRS) in a lysophosphatidyl choline (LPC)-induced experimental demyelinating lesion model of multiple sclerosis (MS), during the early phase (pre-acute) as well as during the complete pathological cycle of de- and re-myelination processes. The N-acetyl aspartate (NAA) peak showed reduction during the early phase of the lesion progression (demyelination) until day 10 and increased thereafter during remyelination. However, choline (Cho) and lipid resonances showed increased signal intensity during the early phase and decreased during remyelination. A progressive reduction of the NAA/Cr metabolite ratio in lesioned rats was observed during demyelination (up to day 10) compared with before lesion (control), and the value increased thereafter during remyelination (from day 15). During this period, however, the Cho/Cr ratio was a higher until day 10 and subsequently declined and was close to that calculated before lesion creation. The changes in NAA/Cr and Cho/Cr metabolite ratios correspond to changes in the individual metabolite peaks such as NAA and Cho. The increase in the intensity of the choline resonance during the early phase is indicative of the onset of an inflammatory demyelination process, and its rapid decrease thereafter is due to reduction in the inflammatory process associated with remyelination. Similarly, the increase in the intensity of lipids during the pre-acute stage of the lesion is attributed to active demyelination, which significantly decreased during remyelination. These MR results correlate well with the histology data obtained.

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.

Inflammatory granulomas: evaluation with proton MRS

Intracranial inflammatory lesions consisting mainly of tuberculomas (n = 28), neurocysticercosis (NCC) (n = 10), and non-specific inflammatory granulomas (IG) (n = 22) were evaluated with proton MRS. Water-suppressed proton spectra were acquired from 60 patients using the STEAM sequence with an echo time of 135 ms and metabolite ratios determined from the spectra. Student's paired t-test and chi2-test were used to analyse the data. Statistically significant differences were observed for the following ratios between the three patient categories: NAA/ Cr (p < 0.0001), NAA/Cho (p = 0.001) and Cr/Cho (p = 0.02) for the non-specific IG and NCC, NAA/Cho (p = 0.03) for non-specific IG and tuberculoma, and NAA/Cr (p < 0.0001) for NCC and tuberculoma. While lipids were seen in 86% of the tuberculomas, they were observed in only 20% of the NCCs (chi2 = 6.81, p = 0.009), and 21% of the non-specific IGs (chi2 = 10.75, p = 0.0001). While the presence of lipid can be used for differentiating tuberculomas from both non-specific IG and NCC, the extremely low levels of metabolites together with a poor signal/noise ratio could itself act as a marker for NCC.

Evaluation of the pituitary gland in idiopathic hypogonadotropic hypogonadism

PURPOSE

Evaluation of the pituitary gland has been carried out in idiopathic hypogonadotropic hypogonadism (IHH) to test the potential of MR imaging in differentiating IHH patients from normals.

MATERIAL AND METHODS

Thirty-seven patients (aged 18-30 years), and 20 volunteers (aged 20-30 years) were studied by T1-weighted MR imaging. Length (LA and LP), height (H), width (W), area (AA and AP), and volume (V1A, V1B V2A, V2P) of the pituitary gland were determined. (Subscripts P and A refer to measurements made with and without the posterior lobe, respectively.) V1 and V2 were estimated using two different methods.

RESULTS

In the control group, LB W and V2A exhibited significant differences between female and male volunteers. While W was the only parameter that did not show significant difference between normals and patients (in both men and women), all other parameters except LB H and AP showed statistically significant differences between normals and IHH patients in both males and females. While LP was significantly different between normals and patients (men), H and AP were significantly different between normals and patients only in the female group.

CONCLUSION

Correlation analysis between various parameters has shown that LA can be used for evaluating the pituitary in both the male and female IHH patients.

The effects of anesthesia and physical restraint on intra- and extracellular tumor pH, tumor temperature and bioenergetics in murine RIF-1 tumors

The effects of pentobarbital anesthetic and physical restraint have been evaluated in murine RIF-1 tumors in terms of their suitability in providing minimal temporal variations in core and tumor temperatures, intracellular (pHMR) and extracellular (pHF) tumor pH, and tumor bioenergetics. pHF was measured using a fibreoptic pH probe. The implications of the changes in these parameters on the combined studies of in vivo MRS and hyperthermia have been discussed. The temporal variations of core and tumor temperatures, pHF and pHMR between the anesthetised and restrained mice were statistically significant (p < 0.0001, p < 0.005, and p < 0.0001, respectively). Differences in the temperatures between the two groups varied with time, and were maximum at about 2 h after pentobarbital. In the anesthetised mice, while there was a net increase of 0.28 pH units in pHF, there was a drop by 0.32 pH units in pHMR (p < 0.001). Temporal variations of both pHF and pHMR in the restrained mice were relatively constant. In light of these findings, wherever possible, physical restraint in a suitably designed holder is suggested for immobilizing animals for magnetic resonance spectroscopy studies.

Evidence for left-right asymmetries in the proton MRS of brain in normal volunteers

Although there is ample evidence in the literature for structural, functional and physiological asymmetries in the two hemispheres of human brain, direct evidence of a similar asymmetry in the in vivo distribution of brain metabolites has been lacking. In this study, the existence of chemical asymmetries in six different regions in normal human brain has been probed with single voxel proton spectroscopy using the STEAM technique in 100 normal right-handed male volunteers. Significant interhemispheric differences in the spectra were observed for all the regions studied in all the volunteers, although statistically significant asymmetries existed only for temporal, occipital and parietal regions. In addition to proven structural and functional asymmetries in the human brain, in vivo evidence of chemical asymmetry has been provided using Magnetic Resonance Spectroscopy.

Proton resonance imaging and relaxation in raw and cooked hen eggs

In-vivo proton magnetic resonance imaging and relaxation time measurements were carried out on raw and cooked eggs. The relaxation time measurements revealed several interesting results. While there was very little change in the T1 values between the raw and cooked egg white, the T2 values followed the decreasing trend expected of water becoming bound. However, both the CH2 and CH3 moieties of the yolk lipids registered a statistically significant increase in their relaxation times. The T2 of the CH2 group, in particular, increased by 113% in the cooked egg. No striking changes, however, were observed between the proton images of the raw and cooked eggs.

Cervical intramedullary lipoma with unusual MRI features: case report

Intramedullary (subpial) lipomas not associated with spinal dysraphism are very unusual [1]. A confident preoperative diagnosis is usually possible with MRI. We present a case of an isolated cervical intramedullary lipoma with unusual imaging morphology and imaging characteristics (distinctly low-signal on T2-weighted images) on MRI. An explanation for these features is proposed.

Proton MRS in Pott's spine--a case report

Proton Magnetic Resonance Spectroscopy was carried out at 1.5 T on a patient with histologically proven Pott's spine affecting D11 vertebral body. In addition to the significantly reduced signals from the lipids in the region between 1 and 2 ppm, a prominent resonance at 5.1 ppm is seen. The spectrum is very different from that recorded on the one hand for a normal spine and, on the other, for a tumor arising from the vertebral body of a patient.

Proton MRS similarity between central nervous system non-Hodgkin lymphoma and intracranial tuberculoma

Proton magnetic resonance spectroscopy (MRS) was carried out on a patient with histologically proven non-Hodgkin lymphoma (NHL) of the central nervous system (CNS). The observation of the presence of a huge resonance in the region between 0.5-1.5 ppm and the absence of any other signals is not in agreement with those published for NHL in the literature but has a striking similarity to that reported for an intracranial tuberculoma.

Spectral editing techniques for 31P NMR spectroscopy of blood

Although the measurement of the pH of biological systems using the 31P NMR response of inorganic phosphate is well known, sometimes in blood absolute determination of the intensity and position of the Pi resonance is precluded by overlap from the doublet resonance of 2,3-diphosphoglycerate. Three techniques which overcome this problem by eliminating the doublet are described and their sensitivity to the experimental parameters is assessed.