In vivo H-1 spectroscopy in humans at 1.5 T

Cardiac 1H MR spectroscopy: development of the past five decades and future perspectives

Continued advances in laboratory medicine are required to realize the potential of individualized medicine to impact common cardiovascular diseases. Magnetic resonance imaging (MRI) and spectroscopy (MRS) techniques have advanced over recent years and offer unique, powerful insights into cardiac anatomic and metabolic changes, respectively, occurring in both nascent and advanced heart disease. Although numerous MRI-based in vivo diagnostics are already used in routine clinical practice and more are anticipated, MRS has been less incorporated into routine clinical practice. Given the ability of ¹H MRS to identify and quantify specific molecules with high sensitivity and specificity, its potential utility should be successfully transition from "bench-to-bedside" is tantalizing. The present review will highlight the development of ¹H MRS techniques for cardiac applications, observations in seminal studies with ¹H MRS, and the prospects and challenges for widespread application in patients with cardiovascular disease.

Proton Spectroscopy of the Pediatric Brain

Initial results from proton spectroscopy performed on the brains of 80 pediatric patients indicate both a research and clinical investigative role for MRS in the future evaluation of pediatric patients. Proton spectroscopy in the evaluation of pediatric brain disease is only in its infancy. However, even though the number of cases that have been studied is not great, its value as a window into in vivo biochemistry is already obvious. The ability to correlate biochemical markers to imaging findings opens up a new era in magnetic resonance research.

Proton spectroscopy remains a research tool, but one that has proven to be of value by adding in vivo biochemical information regarding tissue abnormalities seen and not seen on MRI.

Basic Principles and Clinical Applications of Magnetic Resonance Spectroscopy in Neuroradiology

Magnetic resonance spectroscopy is a powerful tool to assist daily clinical diagnostics. This review is intended to give an overview on basic principles of the technology, discuss some of its technical aspects, and present typical applications in daily clinical routine in neuroradiology.

Reproducibility of brain metabolite concentration measurements in lesion free white matter at 1.5 T

Background

Post processing for brain spectra has a great influence on the fit quality of individual spectra, as well as on the reproducibility of results from comparable spectra. This investigation used pairs of spectra, identical in system parameters, position and time assumed to differ only in noise. The metabolite amplitudes of fitted time domain spectroscopic data were tested on reproducibility for the main brain metabolites.

Methods

Proton spectra of white matter brain tissue were acquired with a short spin echo time of 30 ms and a moderate repetition time of 1500 ms at 1.5 T. The pairs were investigated with one time domain post-processing algorithm using different parameters. The number of metabolites, the use of prior knowledge, base line parameters and common or individual damping were varied to evaluate the best reproducibility.

Results

The protocols with most reproducible amplitudes for N-acetylaspartate, creatine, choline, myo-inositol and the combined Glx line of glutamate and glutamine in lesion free white matter have the following common features: common damping of the main metabolites, a baseline using only the points of the first 10 ms, no additional lipid/macromolecule lines and Glx is taken as the sum of separately fitted glutamate and glutamine. This parameter set is different to the one delivering the best individual fit results.

Discussion

All spectra were acquired in “lesion free” (no lesion signs found in MR imaging) white matter. Spectra of brain lesions, for example tumors, can be drastically different. Thus the results are limited to lesion free brain tissue. Nevertheless the application to studies is broad, because small alterations in brain biochemistry of lesion free areas had been detected nearby tumors, in patients with multiple sclerosis, drug abuse or psychiatric disorders.

Conclusion

Main metabolite amplitudes inside healthy brain can be quantified with a normalized root mean square deviation around 5 % using CH₃ of creatine as reference. Only the reproducibility of myo-inositol is roughly twice as bad. The reproducibility should be similar using other references like internal or external water for an absolute concentration evaluation and are not influenced by relaxation corrections with literature values.

MRS: a noninvasive window into cardiac metabolism

A well-functioning heart requires a constant supply of a balanced mixture of nutrients to be used for the production of adequate amounts of adenosine triphosphate, which is the main energy source for most cellular functions. Defects in cardiac energy metabolism are linked to several myocardial disorders. MRS can be used to study in vivo changes in cardiac metabolism noninvasively. MR techniques allow repeated measurements, so that disease progression and the response to treatment or to a lifestyle intervention can be monitored. It has also been shown that MRS can predict clinical heart failure and death. This article focuses on in vivo MRS to assess cardiac metabolism in humans and experimental animals, as experimental animals are often used to investigate the mechanisms underlying the development of metabolic diseases. Various MR techniques, such as cardiac (31) P-MRS, (1) H-MRS, hyperpolarized (13) C-MRS and Dixon MRI, are described. A short overview of current and emerging applications is given. Cardiac MRS is a promising technique for the investigation of the relationship between cardiac metabolism and cardiac disease. However, further optimization of scan time and signal-to-noise ratio is required before broad clinical application. In this respect, the ongoing development of advanced shimming algorithms, radiofrequency pulses, pulse sequences, (multichannel) detection coils, the use of hyperpolarized nuclei and scanning at higher magnetic field strengths offer future perspective for clinical applications of MRS.

Integrating transcriptomics and metabonomics to unravel modes-of-action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in HepG2 cells

BACKGROUND

The integration of different 'omics' technologies has already been shown in several in vivo studies to offer a complementary insight into cellular responses to toxic challenges. Being interested in developing in vitro cellular models as alternative to animal-based toxicity assays, we hypothesize that combining transcriptomics and metabonomics data improves the understanding of molecular mechanisms underlying the effects caused by a toxic compound also in vitro in human cells. To test this hypothesis, and with the focus on non-genotoxic carcinogenesis as an endpoint of toxicity, in the present study, the human hepatocarcinoma cell line HepG2 was exposed to the well-known environmental carcinogen 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

RESULTS

Transcriptomics as well as metabonomics analyses demonstrated changes in TCDD-exposed HepG2 in common metabolic processes, e.g. amino acid metabolism, of which some of the changes only being confirmed if both 'omics' were integrated. In particular, this integrated analysis identified unique pathway maps involved in receptor-mediated mechanisms, such as the G-protein coupled receptor protein (GPCR) signaling pathway maps, in which the significantly up-regulated gene son of sevenless 1 (SOS1) seems to play an important role. SOS1 is an activator of several members of the RAS superfamily, a group of small GTPases known for their role in carcinogenesis.

CONCLUSIONS

The results presented here were not only comparable with other in vitro studies but also with in vivo studies. Moreover, new insights on the molecular responses caused by TCDD exposure were gained by the cross-omics analysis.

Influence of brain tumors on the MR spectra of healthy brain tissue

The neurochemical environment of nontumorous white matter tissue was investigated in 135 single voxel spectra of "healthy" white matter regions of 43 tumor patients and 129 spectra of 52 healthy subjects. Spectra were acquired with short TE and TR values. With the data of tumor patients, it was examined whether differences were caused by the tumor itself or aggressive tumor therapies as confounding factors. Comparing the spectra of both classes, an excellent differentiation was possible based on the metabolite peak of N-acetylaspartate (P ≈ 0) and myoinositol (P < 0.03). The area under curve of the receiver operating characteristic was calculated as 0.86 and 0.62, respectively. With linear discriminant analysis using combinations of integrals, a prediction was possible, whether a spectrum belonged to the patient or the healthy subject class with an overall accuracy above 80%. The confounding factors could be ruled out as source of the differences. The results show strong evidence for an influence of malignant growth on the biochemical environment of nontumorous white matter tissue. Because of the T(1) weighting, the measured differences between both classes were most likely concentration changes interfered by T(1) effects. The underlying processes will be subject of future studies.

Technology of in vivo two-dimension multi-voxel 1H magnetic resonance spectroscopy for rabbit liver VX2 tumor

AIM: To investigate the best techniques of in vivo two-dimension multi-voxel ¹H magnetic resonance spectroscopy (2D ¹H-MRS) for rabbit liver VX2 tumor.

METHODS: The liver of 8 New Zealand white rabbits was implanted directly and respectively with VX2 tumor lump after abdominal cavity was opened. 2D ¹H-MRS acquisition in vivo and unenhanced MRI was performed respectively from the 2^nd week to 4^th week after VX2 tumor was implanted. With knee coil, in vivo 2D ¹H-MRS acquisitions were performed respectively with different TR, different TE and different NEX at 1.5 T MR scanner when other parameters were the same. The distinction between groups was analyzed by SPSS11.0 with baseline and signal-noise ratio (SNR).

RESULTS: From the qualified MRS spectrum, there were up to 6 peaks which could be identified: methyl lipids (Lip1), methylene lipids (Lip2), methylene lipids with double carbon bond (Lip3), glutamine and glutamate complex (Glx), Choline (Cho), and glycogen and glucose complex (Glyu). Baseline and SNR had no significant differences between TR = 1000 ms, 2000 ms and 3000 ms. Baseline had no significant difference between TE = 30 ms and 144 ms. Except that SNR of Glx with 30 ms in TE was higher than that with 144 ms in TE (1.95 ± 0.36 vs 1.24 ± 0.26, P < 0.05), SNR of other metabolites were similar. With NEX increasing, the distinctions of baseline between NEX = 4, 8 and 16 were significant (χ² = 10.000, P < 0.01). SNR of all metabolites increased when NEX was increased gradually. Both of baseline and SNR were the best when NEX was 16.

CONCLUSION: It's practical of in vivo two-dimension multi-voxel ¹H-MRS on the rabbit liver VX2 tumor by a 1.5 T MR scanner. Immobilization, pre-scan (reaching FWHM ≤ 10 Hz and WS ≥ 98%), knee coil, TR = 1000 ms, TE = 30 ms and NEX = 16 may be the best to acquire highly qualified spectra.

Differentiation of chronic focal pancreatitis from pancreatic carcinoma by in vivo proton magnetic resonance spectroscopy

OBJECTIVE

To determine the differences between the in vivo proton magnetic resonance spectroscopy (H-MRS) features of chronic focal pancreatitis and pancreatic carcinoma and to evaluate the possibility of discriminating chronic focal pancreatitis from pancreatic carcinoma by analysis of in vivo H-MR spectra.

METHODS

The H-MR spectra from 36 human pancreases were evaluated in vivo. This series included 15 cases of chronic focal pancreatitis and 21 cases of pancreatic carcinoma. All cases were confirmed histopathologically after surgical resection. The ratios of the peak area (P) of all peaks at 1.6-4.1 ppm to lipid (0.9-1.6 ppm) (P [1.6-4.1 ppm]/P [0.9-1.6 ppm]) in the chronic focal pancreatitis and pancreatic carcinoma groups were evaluated, and the results were compared. The sensitivity and specificity of the analysis were also evaluated by in vivo H-MR spectra for discriminating between chronic focal pancreatitis and pancreatic carcinoma.

RESULTS

In vivo H-MR spectra showed significantly less lipid in chronic focal pancreatitis than in pancreatic carcinoma. The ratio of P (1.6-4.1 ppm)/P (0.9-1.6 ppm) in chronic focal pancreatitis was significantly higher than that in pancreatic carcinoma (P < 0.05) because of a decreased peak area of lipids. The means +/- SDs of P (1.6-4.1 ppm)/P (0.9-1.6 ppm) in the chronic focal pancreatitis and pancreatic carcinoma groups were 2.78 +/- 1.67 and 0.51 +/- 0.49, respectively. Using a value of <2.5 as positive for pancreatic cancer, the sensitivity and the specificity for pancreatic cancer were 100% and 53.3%, respectively.

CONCLUSION

Chronic focal pancreatitis and pancreatic carcinoma can be distinguished from each other by analysis of in vivo H-MR spectra, and in vivo H-MRS can be a useful method for making a differential diagnosis between chronic focal pancreatitis and pancreatic carcinoma.

1H-Magnetresonanzspektroskopie (MRS) der Leber und von Lebermalignomen bei 3,0�Tesla

Use of whole-body MRI beyond 1.5 Tesla (T) has initiated a renaissance in spectroscopic procedures (MRS). The superior signal-to-noise ratio of clinical 3T tomographs allows reliable acquisition of MR spectra not only in fixed organs but also in targets moved by breathing such as the liver. The following contribution describes the principles of (1)H MRS and our own initial experiences with spectroscopy of the liver and hepatic malignant tumors with 3T whole-body MRI.

N-acetylcysteine decreases lactate signal intensities in liver tissue and improves liver function in septic shock patients, as shown by magnetic resonance spectroscopy: extended case report

Background

N-acetylcysteine (NAC) has been shown to improve splanchnic blood flow in experimental studies. This report evaluates the effects of NAC on liver perfusion and lactate signal intensities in the liver tissue of septic shock patients using proton magnetic resonance imaging and spectroscopy. Furthermore, the monoethylglycinexylidide (MEGX) test was used to investigate hepatic function.

Methods

Five septic shock patients received 150 mg/kg body weight NAC as an intravenous bolus injection over 15 min. Lidocaine was injected both prior to and following NAC administration in order to determine MEGX formation. Measurements (hemodynamics, oxygen transport-related variables, blood samples for lactate, liver-related markers) were performed 1 hour before and 1 hour after NAC injection. In addition to the proton magnetic resonance imaging patients received two proton magnetic resonance spectra, one prior to and one 30 min subsequent to the onset of the NAC infusion at a 1.5 Tesla clinical scanner, for measurement of liver perfusion and liver lactate signal intensity.

Main findings

Following NAC infusion, the lactate signal intensity in the liver tissue showed a median decrease of 89% (11–99%), there was a median increase in liver perfusion of 41% (-14 to 559%), and the MEGX serum concentration increased three times (1.52–5.91).

Conclusions

A decrease in the lactate signal intensity in the liver tissue and an increase in the MEGX serum concentration and in liver perfusion might indicate improved liver function as a result of NAC administration. Patients with compromised hepatosplanchnic function, such as patients with septic shock due to peritonitis, may therefore benefit from NAC therapy.

Chronic hepatitis: in vivo proton MR spectroscopic evaluation of the liver and correlation with histopathologic findings

PURPOSE

To correlate the in vivo hydrogen 1 ((1)H) magnetic resonance (MR) spectroscopic features of the chronic hepatitis-involved liver with the histopathologic stages of fibrosis.

MATERIALS AND METHODS

Seventy-five patients with chronic hepatitis were examined with (1)H MR spectroscopy, which was performed in the right hepatic lobe. The peak areas of glutamine and glutamate complex (Glx), phosphomonoesters (PME), glycogen and glucose complex (Glyu), and lipid were measured on the liver spectra. The histopathologic features were correlated with the in vivo (1)H MR spectroscopic findings at each stage of chronic hepatitis. Fifteen healthy volunteers also were included as a control group.

RESULTS

(1)H MR spectroscopy depicted Glx, PME, Glyu, and lipid in all livers. In the normal livers, the calculated mean (+/- SD) relative metabolite-to-lipid ratios of Glx, PME, and Glyu were 0.14 +/- 0.04, 0.03 +/- 0.01, and 0.21 +/- 0.04, respectively. The mean value of each metabolite-to-lipid ratio was significantly different between all stages of chronic hepatitis, and with the exception of the mean ratio at the interval between stages 0 and 1 (P > .05), the mean value increased significantly with increasing stage (P < .05). A pronounced peak was demonstrated at 3.9-4.1 ppm at (1)H MR spectroscopy of all stages of chronic hepatitis except stage 0.

CONCLUSION

The increased Glx, PME, and Glyu levels relative to the lipid content with chronic hepatitis indicated the severity of fibrosis and thus were concordant with the histopathologic stages. In vivo (1)H MR spectroscopy might be a substitute for liver biopsy in the diagnosis and staging of chronic hepatitis.

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.

High-resolution 1H-magnetic resonance spectroscopy of pediatric posterior fossa tumors in vitro

High-resolution proton magnetic resonance (MR) spectroscopy was performed on perchlorate extracts of tumors (24 cases) or peritumoral vermis (five cases) obtained at surgery. Fifteen tumors were typical cerebellar astrocytomas and nine were posterior fossa primitive neuroectodermal tumors/medulloblastomas. Spectra obtained from the five samples of peritumoral vermis revealed a pattern of metabolites similar to that reported for cerebellar tissue, but concentrations of most metabolites were low, perhaps due to dilution from peritumoral edema. The astrocytomas were characterized by high levels of valine, alanine, and choline, an increase in the choline:N-acetylaspartate (NAA) ratio, and a shift from glutamate to glutamine. Elevations in lactate, pyruvate, and glucose were the result of ischemia during sampling. The primitive neuroectodermal tumors/medulloblastomas were distinguished from astrocytomas by a greater increase in the choline:NAA ratio, a smaller decrease in the glutamate:glutamine ratio, and a relative increase in glycine, taurine, and inositol levels. These metabolic patterns may be of value diagnostically as in vivo MR spectroscopy achieves higher resolution.

Mapping of cerebral metabolites in rats by 1H magnetic resonance spectroscopic imaging. Distribution of metabolites in normal brain and postmortem changes

The goal of this study was to examine metabolic differences between cortex and basal ganglia in normal rat brain and to determine postmortem changes using in vivo 1H magnetic resonance spectroscopic imaging at 300 MHz. The resonances observed were: choline, creatine + phosphocreatine, N-acetyl aspartate (NAA), lactate (Lac), and three small resonances in the amino acid region which included resonances from aspartate + NAA (Asp), glutamine + NAA (Gln), and glutamate + GABA (Glu). A previously unassigned resonance was observed at 1.13 ppm in brain of rats anesthetized with pentobarbital. Spectroscopic images in normal brain demonstrated increased NAA and Gln and decreased Glu in cortex compared to basal ganglia. The major postmortem changes were an increase of Lac, Glu and Cho and a decrease of NAA and Asp. The rise in Lac was significantly higher in cortex than in basal ganglia.

Comparison of localized proton NMR signals of skeletal muscle and fat tissue in vivo: two lipid compartments in muscle tissue

In vivo 1H NMR spectra of small volumes-of-interest (VOI) were localized in human soleus muscle (8 ml) and compared with volume selective spectra of subcutaneous fat tissue and femoral yellow bone marrow (2 ml). All examinations were performed by the double spin echo (PRESS) localization technique. To provide comparability, spectra of different tissues were recorded using identical sequence timing. Clearly improved resolution of the lipid signals of muscle tissue was obtained using long echo times TE > 200 ms. The spectra of muscle tissue exhibit lipid signals that stem from two compartments with a difference of their resonance frequencies of about 0.2 ppm (Larmor frequency difference 12-13 Hz at 1.5 T). The existence of two fatty acid compartments is supported by measurements of the relaxation times and line shape analysis. Both compartments contain fatty acids or triglycerides with similar composition. Probably one compartment corresponds to fat cells within muscle tissue, the other compartment with lower Larmor frequency is located within muscle cells.

Decreased brain N-acetylaspartate in Huntington's disease

The concentration of N-acetylaspartic acid (NAA) was measured in perchloric acid extracts of postmortem brain tissue obtained from patients with Huntington's disease and from control subjects. The material in the desalted extracts was resolved on an ion exclusion column and the content of NAA was determined by subsequent fluorometric quantitation of aspartate in hydrolyzates of the resolved NAA. The concentration of NAA in the putamen from patients with Huntington's disease was less than half that of controls (2.74 vs. 6.06 mumol/g wet weight). A smaller but significant reduction was also evident in samples of cerebral cortex from Brodmann area 10 (3.99 vs. 5.29 mumol/g), while the difference in concentrations in the cerebellum was not statistically significant. Though NAA could play a direct role in Huntington's disease, it seems more likely that the changes observed reflect illness or death of neurons, and that it may be feasible to monitor the course of Huntington's disease from NAA determinations. The same tissue extracts were also examined for the presence of D-isomers of amino acids. Only traces were found in NAA, aspartate, or glutamate.

High-resolution 1H NMR spectroscopy studies of extracts of human cerebral neoplasms

High-resolution 1H NMR spectroscopy has been used to measure the concentrations of metabolites (alanine, N-acetylaspartate, gamma-aminobutyric acid, glutamate, glutamine, aspartate, taurine, glycine, succinate, creatine, cholines, inositol, and glucose) in perchloric acid extracts of human epileptic cortex and brain tumors. All tissue was obtained by surgical biopsy, excised before thermal coagulation, and immediately frozen in liquid nitrogen. Lower levels of N-acetylaspartate and gamma-aminobutyric acid and a shift in the glutamate/glutamine ratio toward glutamine in the tumors reflect neuronal loss. Abnormal glucose metabolism (aerobic glycolysis) in the tumors gives decreased levels of succinate, glutamate, aspartate, glutamine, and creatine and generally increased concentrations of glycine and alanine. Differences in metabolite concentrations that may be of use in differential tumor diagnosis include lower creatine and inositol in meningiomas than in astrocytomas. Lower taurine differentiates benign from malignant astrocytomas. Malignant astrocytomas and metastatic tumors are more regionally heterogeneous than meningiomas or benign astrocytomas. Mannitol, administered perioperatively to all patients from whom tissue was obtained, was observed only in the spectra of extracts of tissue from tumors which enhanced on computerized tomographic imaging.

In vitro proton spectroscopy of normal and abnormal prostate

Previous biochemical and 13C NMR spectroscopic data have suggested that the metabolism of citrate, a secretory product of normal prostate, may be interrupted in prostate cancer. In the present study in vitro 1H NMR spectroscopy was used to see if cell strains derived from prostate cancers could be reliably distinguished from those of normal prostate epithelium. High-resolution one-dimensional and two-dimensional J-resolved 1H NMR spectra as well as gas chromatography coupled with mass spectroscopy were used to study extracts of highly defined cell strains from normal peripheral zone, normal central zone, adenocarcinoma, and benign prostatic hyperplasia. Resonances assigned to citric acid and related metabolites were identified. Cell strains derived from prostate cancers tended to have smaller amounts of citrate than those from normal prostate epithelium. However, the differences were small and not statistically significant. The lack of statistically significant differences may reflect the variability present in both normal and abnormal cell strains and thus underscore the well-known difficulty in differentiating normal and cancerous tissues.

Localized proton NMR spectroscopy using stimulated echoes: applications to human skeletal muscle in vivo

Localized proton NMR spectroscopy using stimulated echoes (STEAM) has been used to study metabolites in different proximal skeletal muscles of normal volunteers at rest. Single scan water-suppressed proton NMR spectra obtained at 1.5 and 2.0 T (Siemens Magnetom) from a 64-ml volume-of-interest (VOI) yield resonances due to triglycerides, phosphocreatine plus a minor contribution from creatine, and betaines comprising carnitine and choline-containing compounds. The observation of the pH-dependent resonances of carnosine required multiple acquisitions and echo times as short as 20 ms. T1 and T2 relaxation times of muscle metabolites were obtained by varying the repetition time and echo time of the STEAM sequence, respectively. Although rather long T2 values such as 180 ms for (phospho-) creatine correspond to natural resonance linewidths of only 2 Hz, the observed linewidths of typically 10-12 Hz are entirely determined by the short T2 relaxation times (25-30 ms) of the water protons used for shimming. The spectroscopic results from 24 muscle studies on 17 young male volunteers show remarkable intra- and interindividual differences in the absolute signal intensities of mobile lipids. Further metabolic variations were observed for the relative concentrations of betaines (by a factor of 2) and carnosine (by a factor of 3) when total creatine is assumed to be constant.

Effects of nicardipine, a calcium antagonist, on myocardial salvage and high energy phosphate stores in reperfused myocardial injury

The current study determined the effectiveness of nicardipine, a 1,4-dihydropyridine calcium antagonist, in preserving reperfused myocardium in a cat model of temporary coronary occlusion and ascertained if replenishment of myocardial phosphate stores during reperfusion as defined by phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy was indicative of salvage. Twenty open chest, anesthetized cats were studied with use of a snare ligature around the proximal left anterior descending coronary artery, with a coil sutured to the epicardial surface overlying the distribution of the artery. Peak areas of phosphocreatine, inorganic phosphate and adenosine triphosphate (ATP) NMR signals were measured during 1 h of occlusion followed by 1.5 h of reperfusion. Infarct size and jeopardy area were determined in vitro by simultaneous infusion of phthalocyanine blue dye and triphenyltetrazolium chloride into the aorta and the left anterior descending coronary artery, respectively, after 5 h of myocardial reperfusion. Nicardipine-treated and control groups had similar jeopardy area values (41.2 +/- 1.6% versus 47.4 +/- 3.1% of the left ventricle), but infarct area was significantly reduced in the nicardipine-treated group (3.2 +/- 1.1% versus 24.9 +/- 7.5% of jeopardy area, p less than 0.01). High energy phosphate compounds remained markedly altered during reperfusion in both groups. No significant improvement in phosphocreatine or inorganic phosphate recovery was observed in animals pretreated with nicardipine despite an 87% reduction in infarct size. Myocardial ATP was greater during reperfusion in the nicardipine-treated compared with the control group (average over initial 90 min of reperfusion 58 +/- 6% versus 46 +/- 3% of baseline values, p less than 0.05), suggesting improved recovery of ATP. However, the measured levels of high energy phosphate compounds during reperfusion and their ratios did not correlate with infarct size and thus were not predictive of myocardial salvage.

Clinical nuclear magnetic resonance spectroscopy: insight into metabolism

Nuclear magnetic resonance (NMR) spectroscopy can nondestructively evaluate changes in metabolites with different disease states, as well as with therapeutic interventions. Animal studies have provided the basis for understanding changes in high-energy phosphates with myocardial ischemia. Studies of graded ischemia due to partial coronary stenosis have shown the sensitivity of the ratio of phosphocreatinine to inorganic phosphate to small reductions in myocardial blood flow and its relation to myocardial function. The application of NMR spectroscopy to humans requires precise localization techniques to avoid acquiring contaminating information from structures around the heart, such as the chest wall and diaphragm. With these localization techniques, metabolic evidence of ischemia has been demonstrated in patients with myocardial infarction and patients with known coronary disease, although the sensitivity of this technique for the diagnosis of inducible ischemia is unknown. At rest, patients with dilated and hypertrophic cardiomyopathies often have an elevated phosphodiester resonance, possibly signifying abnormal breakdown of membrane phospholipids. Increasing oxygen demand in these patients does not usually alter high-energy phosphates, suggesting that oxidative energy metabolism is preserved under these conditions. NMR spectroscopy is a powerful tool to increase understanding of metabolic changes in a variety of pathologic conditions.

Determination of metabolite and nucleotide concentrations in proliferating lymphocytes by 1H-NMR of acid extracts

Nuclear magnetic resonance (NMR) studies of extracts have proven to be a powerful window onto the intracellular machinery of cells and tissues. The major advantages of in vitro 1H-NMR, namely chemical preservation, simultaneous detection, identification, and quantitation of compounds, and sensitivity to a large variety of classes of compounds, are employed in this study to characterize the metabolic course of mitogen-stimulated proliferation of human peripheral lymphocytes. A reliable method to quantitate amino acids, metabolic intermediates, soluble membrane lipid precursors, and purine, pyridine and pyrimidine nucleotides is presented, using samples as small as 30 mg wet weight. A total of 53 substances were detected in lymphocytes and other blood cells. During the course of lymphocyte culture, changes in intracellular concentrations of lactate, taurine, inositol and nucleotides, including NAD, IMP and high-energy phosphates, were especially marked. 1H-NMR compares favorably to 31P-NMR and to HPLC, and is especially attractive in light of expectations for future in vivo application.

Image-guided 31P magnetic resonance spectroscopy of normal and transplanted human kidneys

Image-guided 31-phosphorus magnetic resonance spectroscopy (MRS) was used to obtain spatially localized 31P spectra of good quality from healthy normal human kidneys and from well-functioning renal allografts. A surface coil of 14 cm diameter was used for acquiring phosphorus signals solely from a volume-of-interest located within the kidney. To determine the effects of kidney transplantation on renal metabolism, patients with well functioning allografts were studied. Little or no phosphocreatine in all spectra verifies the absence of muscle contamination, and is consistent with proper volume localization. The intensity ratio of phosphomonoesters (PME) to adenosine triphosphate (ATP) resonances in transplanted kidneys (PME/ATP = 1.1 +/- 0.4) was slightly elevated (P = 0.2) compared to that of healthy normal kidneys (PME/ATP = 0.8 +/- 0.3). The inorganic phosphate (Pi) to ATP ratio was similar in the two groups (Pi/ATP = 1.1 +/- 0.1 in transplanted kidneys vs. 1.2 +/- 0.6 in normal kidneys). Acid/base status, as evidenced from the chemical shift of Pi, was the same in both normal controls and transplanted kidneys. Despite the practical problems produced by organ depth, respiratory movement, and tissue heterogeneity, these results demonstrate that image-guided 31P MR spectra can reliably be obtained from human kidneys.

In vivo proton spectroscopy in presence of eddy currents

Spatially localized methods in spectroscopy often operate with magnetic field gradients for volume selection. The eddy currents induced by these gradients produce time-dependent shifts of the resonance frequency in the selected volume, which results in a distortion of the spectrum after Fourier transformation. In whole-body systems the complete compensation of eddy currents is a difficult procedure. To avoid this, a correction method is proposed for proton spectroscopy, which uses the signal of prominent water protons as a reference for the water-suppressed signal. The correction is performed in the time domain, dividing the water-suppressed signal by the phase factor of the water signal for each data point. The corrected spectra have a good resolution as shown by phantom measurements and brain and muscle spectra of volunteers.

Cardiovascular applications of nuclear magnetic resonance spectroscopy

Nuclear magnetic resonance spectroscopy has great potential for defining noninvasively the metabolic status of the heart and skeletal muscle. This technique uses the spin properties of certain nuclei (such as phosphorus-31, hydrogen-1 and carbon-13) to measure high energy phosphates, intracellular pH, lactate and glycogen. Animal studies have formed the basis for human investigations and have demonstrated well-defined changes in high energy phosphates during myocardial ischemia and reperfusion, as well as in cardiomyopathies. Human studies have been limited by issues of sensitivity and localization, although techniques such as rotating frame, depth-resolved surface coil spectroscopy, image-selected in vivo spectroscopy and spectroscopic imaging have been used to acquire phosphorus-31 spectra from the human heart. The few human studies of patients with disease have demonstrated elevated inorganic phosphate peaks after myocardial infarction and abnormal phosphodiester peaks in patients with hypertrophic cardiomyopathy. Studies of patients with heart failure have shown that these patients acidify their peripheral muscles with exercise more easily than do control subjects. Clinical application of nuclear magnetic resonance spectroscopy will depend on technical advances and the demonstration of sensitivity of metabolic changes with disease.

Magnetic resonance imaging versus computed tomography of leukocoric eyes and use of in vitro proton magnetic resonance spectroscopy of retinoblastoma

To evaluate the usefulness of magnetic resonance imaging (MRI) in the evaluation of leukocoric eyes, the authors studied 28 patients with either leukocoria or intraocular mass with a 1.5-tesla (T) MRI imager. Retinoblastomas were reliably distinguished from Coats' disease, toxocariasis, and persistent hyperplastic primary vitreous on the basis of MRI findings. Calcification cannot be reliably detected on MRI scans. Lesions elevated less than 4 mm may not be detected reliably by MRI at this time. Computed tomography (CT) can detect calcification with a high degree of accuracy. Retinoblastomas appeared as moderately hyperintense masses on T1- and proton-weighted MRIs. They became hypointense in T2-weighted MRIs. This MRI characteristic is similar to that of uveal melanoma. Intraocular calcification in children especially younger than 3 years of age is highly suggestive of retinoblastoma. In the diagnosis of retinoblastoma, MRI is not as specific as CT because of its lack of sensitivity in detecting calcification. However, MRI, because of its superior contrast resolution, offers more information in the differentiation of pathologic intraocular conditions responsible for leukocoria. The authors also describe their preliminary work of in vitro proton magnetic resonance spectroscopy of eyes with retinoblastoma and an eye with uveal melanoma in an 18-year-old black woman.

Quantitative and qualitative fat analysis in human leg muscle of neuromuscular diseases by 1H MR spectroscopy in vivo

1H MR spectra were recorded from human gastrocnemius muscle at 63.86 MHz using the body coil of the Signa scanner as transmitter and a 3-in. surface coil as receiver. The fat content of the muscle was quantified relative to that of water in a selected volume or slice. The fat/water ratio was 0.05-0.07 for normal muscle but increased to 0.5-6.0 in primary and secondary muscular disorders such as Duchenne and myotonic dystrophy, Charcot-Marie-Tooth and polio muscular atrophy, cerebral palsy, and spina bifida. In Werdnig-Hoffmann spinal atrophy the ratio was above 10. Water-suppressed and slice-selective 1H spectroscopy was used for qualitative analysis of fat. The 1H profile of gastrocnemius muscles between healthy individuals and patients with neuromuscular diseases showed two major differences. In the normal muscle spectra, the resonance from the -(CH2)n- protons at 1.6 ppm was the most pronounced, whereas in the diseased muscle spectra resonances also appeared between 1.1 and 1.4 ppm. Some diseased muscle spectra showed multiple resonances from -CH = CH- in polyunsaturated fatty acids between 5.5 and 7.0 ppm. The corresponding resonances from = CH-CH2-, 1.9-2.0 ppm, and = CH-CH2-CH =, 2.7-2.9 ppm, were also seen. These peaks are usually not detected in normal muscle.

MR imaging of cerebral tumors: state of the art and work in progress

MR imaging of the brain has made tremendous progress during the last years. This technique is generally superior to computed tomography (CT) in brain tumors, due to its capability for direct imagining in various planes and its high tissue contrast. Moreover, the detectability and differentiation of extraaxial tumors, previously the domain of CT, has been improved with paramagnetic contrast agents (PCA). Although, the sensitivity of MRI for intracranial tumors is unchallenged, the specificity for such tumors is not remarcably greater than that of CT. Differentiation between high grade glioma, abscess and metastasis still requires biopsy for definitive diagnosis. Methods for improvement of specificity--tissue characterization--are currently being evaluated in a clinical setting. Further development in this field is necessary before such methods can be applied on a routine basis.