Prior knowledge for time domain quantification of in vivo brain or liver 31P MR spectra

Bioenergetic impairment in Gulf War illness assessed via 31P-MRS

Time for post-exercise phosphocreatine-recovery (PCr-R), deemed a robust index of mitochondrial function in vivo, was previously reported to be elevated (signifying impaired ATP production) in veterans with Gulf War illness (GWI). Here we sought to replicate the finding and assess the impact of contravening previous eligibility requirements. The replication sample comprised white males. Cases reported ≥ moderate muscle-weakness to match the organ assessed to an organ affected; controls lacked recent headache or multiple symptoms. The expansion sample added cases without muscle-weakness, controls with recent headache, females, nonwhites. PCr-R, following pedal-depression-exercise, was compared in veterans with GWI versus controls (sample N = 38). In the replication sample, PCr-R results closely matched the prior report: PCr-R veterans with GWI mean(SD) = 47.7(16.5); control mean(SD) = 30.3(9.2), p = 0.017. (Prior-study PCr-R veterans with GWI mean(SD) = 46.1(17.9), control mean(SD) = 29.0(8.7), p = 0.023. Combined replication + prior samples: p = 0.001.) No case-control difference was observed in the expansion sample. In cases, PCr-R related to muscle-weakness: PCr-R = 29.9(7.1), 38.2(8.9), 47.8(15.2) for muscle-weakness rated none/low, intermediate, and high respectively (p for trend = 0.02), validating desirability of matching tissue assessed to tissue affected. In controls, headache/multiple symptoms, sex, and ethnicity each mattered (affecting PCr-R significantly). This study affirms mitochondrial/bioenergetic impairment in veterans with GWI. The importance of careful case/control selection is underscored.

Phosphorus MRS of healthy human spleen

Phosphorus (³¹ P-) MRS in vivo enables detection and quantification of important phosphorus-containing metabolites in biological tissues. ³¹ P-MRS of the normal spleen is challenging due to the relatively small volume and the larger distance between the spleen and surface coil. However, reference spectra of the healthy spleen are invaluable in studies of splenic malignancies and benign causes of splenomegaly, as well as in the study of its physiology. The purpose of this work was to investigate the feasibility of localized ³¹ P-MRS of healthy spleen in situ in a clinically acceptable measurement time using a clinical 3 T MR scanner. In this work, ³¹ P spectra of five healthy volunteers were measured using single-voxel image-selected in vivo spectroscopy (ISIS). The measurement sequence was augmented by broadband proton decoupling and nuclear Overhauser effect enhancement. It is demonstrated that localized ³¹ P-MRS of the spleen in situ using single-voxel ISIS is feasible on a clinical 3 T scanner in a clinically acceptable acquisition time. However, results have to be corrected for the transmitter excitation profile, and chemical shift displacement errors need to be taken into consideration during placement of the volume of interest. Results presented here could be used as a reference in future studies of splenomegaly caused by haematological malignancies.

Efficacy of in vivo31Phosphorus Magnetic Resonance Spectroscopy in Differentiation and Staging of Adult Human Brain Tumors

The aim of this study was to evaluate the efficacy of 31P magnetic resonance spectroscopy (31P-MRS) in the differentiation and staging of brain tumors. Fifteen volunteers and 44 patients with brain tumors (14 meningiomas, 13 low- and 17 high-grade gliomas) were prospectively evaluated by 31P-MRS. The pH (r=0.493, p<0.001), [Mg+2] (r=0.850, p<0.001) PME/α-ATP (r=0.776, p<0.001), PDE/α-ATP (r=-0.569, p<0.001) and (PCr+β-ATP)/Pi ratios were well correlated with tumor differentiation. High-grade gliomas had significantly higher pH (r=0.912, p<0.001) and [Mg+2] (r=0.855, p<0.001) and PME/α-ATP (r=0.894, p<0.001) ratio, and lower PCr/α-ATP (r= −0.959, p<0.001), Pi/α-ATP (r= −0.788, p<0.001) and PDE/α-ATP ratios (r=−0.968, p<0.001) than those of low-grade gliomas. Changes in 31P-MRS parameters by the degree of malignancy are good indicators of increased anaerobic metabolism and hypoxia of tumoral tissue to compensate intratumoral energy deficiency. 31P-MRS parameters are very useful for grading and differentiation of brain tumors.

Magnetic Resonance Spectroscopy: Principles and Techniques: Lessons for Clinicians

Magnetic resonance spectroscopy (MRS) provides a non-invasive 'window' on biochemical processes within the body. Its use is no longer restricted to the field of research, with applications in clinical practice increasingly common. MRS can be conducted at high magnetic field strengths (typically 11-14 T) on body fluids, cell extracts and tissue samples, with new developments in whole-body magnetic resonance imaging (MRI) allowing clinical MRS at the end of a standard MRI examination, obtaining functional information in addition to anatomical information. We discuss the background physics the busy clinician needs to know before considering using the technique as an investigative tool. Some potential applications of hepatic and cerebral MRS in chronic liver disease are also discussed.

Magnetic Resonance Imaging: Principles and Techniques: Lessons for Clinicians

The development of magnetic resonance imaging (MRI) for use in medical investigation has provided a huge forward leap in the field of diagnosis, particularly with avoidance of exposure to potentially dangerous ionizing radiation. With decreasing costs and better availability, the use of MRI is becoming ever more pervasive throughout clinical practice. Understanding the principles underlying this imaging modality and its multiple applications can be used to appreciate the benefits and limitations of its use, further informing clinical decision-making. In this article, the principles of MRI are reviewed, with further discussion of specific clinical applications such as parallel, diffusion-weighted, and magnetization transfer imaging. MR spectroscopy is also considered, with an overview of key metabolites and how they may be interpreted. Finally, a brief view on how the use of MRI will change over the coming years is presented.

Quantitative analysis of ³¹P NMR spectra of soil extracts--dealing with overlap of broad and sharp signals

Solution (31)P NMR analysis following extraction with a mixture of sodium hydroxide and ethylenediaminetetraacetic acid is the most widely used method for detailed characterization of soil organic P. However, quantitative analysis of the (31)P NMR spectra is complicated by severe spectral overlap in the monoester region. Various deconvolution procedures have been developed for the task, yet none of these are widely accepted or implemented. In this mini-review, we first describe and compare these varying approaches. We then review approaches to similar issues of spectral overlap in biomedical science applications including NMR-based metabolic profiling and analyzing (31)P magnetic resonance spectra of ex vivo and in vivo intact tissues. The greater maturity and resourcing of this biomedical research means that a wider variety of approaches has been developed. Of particular relevance are approaches to dealing with overlap of broad and sharp signals. Although the existence of this problem is still debated in the context of soil analyses, not only is it well-recognized in biomedical applications, but multiple approaches have been developed to deal with it, including T2 editing and time-domain fitting. Perhaps the most transferable concept is the incorporation of 'prior knowledge' in the fitting of spectra. This is well established in biomedical applications but barely touched in soil analyses. We argue that shortcuts to dealing with overlap in the monoester region (31)P NMR soil spectra are likely to be found in the biomedical literature, although some degree of adaptation will be necessary.

Quantification of in vivo ³¹P NMR brain spectra using LCModel

Quantification of (31)P NMR spectra is commonly performed using line-fitting techniques with prior knowledge. Currently available time- and frequency-domain analysis software includes AMARES (in jMRUI) and CFIT respectively. Another popular frequency-domain approach is LCModel, which has been successfully used to fit both (1)H and (13)C in vivo NMR spectra. To the best of our knowledge LCModel has not been used to fit (31)P spectra. This study demonstrates the feasibility of using LCModel to quantify in vivo (31)P MR spectra, provided that adequate prior knowledge and LCModel control parameters are used. Both single-voxel and MRSI data are presented, and similar results are obtained with LCModel and with AMARES. This provides a new method for automated, operator-independent analysis of (31)P NMR spectra.

Widespread pH abnormalities in patients with malformations of cortical development and epilepsy: a phosphorus-31 brain MR spectroscopy study

INTRODUCTION

Neuroimaging studies demonstrate that not only the lesions of malformations of cortical development (MCD) but also the normal-appearing parenchyma (NAP) present metabolic impairments, as revealed with (1)H-MRS. We have previously detected biochemical disturbances in MCD lesions with phosphorus-31 magnetic resonance spectroscopy (31P-MRS). Our hypothesis is that pH abnormalities extend beyond the visible lesions.

METHODS

Three-dimensional 31P-MRS at 3.0 T was performed in 37 patients with epilepsy and MCD, and in 31 matched-control subjects. The patients were assigned into three main MCD subgroups: cortical dysplasia (n=10); heterotopia (n=14); schizencephaly/polymicrogyria (n=13). Voxels (12.5 cm3) were selected in five homologous regions containing NAP: right putamen; left putamen; frontoparietal parasagittal cortex; right centrum semiovale; and left centrum semiovale. Robust methods of quantification were applied, and the intracellular pH was calculated with the chemical shifts of inorganic phosphate (Pi) relative to phosphocreatine (PCr).

RESULTS

In comparison to controls and considering a Bonferroni adjusted p-value <0.01, MCD patients presented significant reduction in intracellular pH in the frontoparietal parasagittal cortex (6.985±0.022), right centrum semiovale (7.004±0.029), and left centrum semiovale (6.995±0.030), compared to controls (mean values±standard deviations of 7.087±0.048, 7.096±0.042, 7.088±0.045, respectively). Dunnet and Dunn tests demonstrated that the differences in pH values remained statistically significant in all MCD subgroups. No significant differences were found for the putamina.

CONCLUSION

The present study demonstrates widespread acidosis in the NAP, and reinforces the idea that MCD visible lesions are only the tip of the iceberg.

Measuring short-term liver metabolism non-invasively: postprandial and post-exercise ¹H and ³¹P MR spectroscopy

OBJECT

The objective of this study was to determine the effects of a standardized fat rich meal and subsequent exercise on liver fat content by ¹H MRS and on liver adenosine triphosphate (ATP) content by ³¹P MRS in healthy subjects.

MATERIALS AND METHODS

Hepatic ¹H and proton decoupled ³¹P MRS were performed on nine healthy subjects on a clinical 3.0 T MR imager three times during a day: after (1) an overnight fast, (2) a following standardized fat rich meal and (3) a subsequent exercise session. Blood parameters were followed during the day to serve as a reference to MRS.

RESULTS

Liver fat content increased gradually over the day (p = 0.0001) with an overall increase of 30 %. Also γ-NTP changed significantly over the day (p = 0.005). γ-NTP/tP decreased by 9 % (p = 0.019, post hoc) from the postprandial to the post-exercise state.

CONCLUSION

Our study shows that in vivo MRS can depict short lived physiological changes; entering of fat into liver cells and consumption of ATP during exercise can be measured non-invasively in healthy subjects. The physiological state may have an impact on fat and energy metabolite levels. Hepatic ¹H and ³¹P MRS studies should be performed under standardized conditions.

Non-alcoholic fatty liver disease: spectral patterns observed from an in vivo phosphorus magnetic resonance spectroscopy study

BACKGROUND & AIMS

Liver biopsy is the gold standard for diagnosing non-alcoholic fatty liver disease (NAFLD) but with practical constraints. Phosphorus magnetic resonance spectroscopy ((31)P-MRS) allows in vivo assessment of hepatocellular metabolism and has shown potential for biochemical differentiation in diffuse liver disease. Our aims were to describe spectroscopic signatures in biopsy-proven NAFLD and to determine diagnostic performance of (31)P-MRS for non-alcoholic steatohepatitis (NASH).

METHODS

(31)P-MRS was performed in 151 subjects, comprised of healthy controls (n=19) and NAFLD patients with non-NASH (n=37) and NASH (n=95). Signal intensity ratios for phosphomonoesters (PME) including phosphoethanolamine (PE), phosphodiesters (PDE) including glycerophosphocholine (GPC), total nucleotide triphosphate (NTP) including α-NTP, and inorganic phosphate (Pi), expressed relative to total phosphate (TP) or [PME+PDE] and converted to percentage, were obtained.

RESULTS

Compared to controls, both NAFLD groups had increased PDE/TP (p<0.001) and decreased Pi/TP (p=0.011). Non-NASH patients showed decreased PE/[PME+PDE] (p=0.048), increased GPC/[PME+PDE] (p<0.001), and normal NTP/TP and α-NTP/TP. Whereas, NASH patients had normal PE/[PME+PDE] and GPC/[PME+PDE], but decreased NTP/TP (p=0.004) and α-NTP/TP (p<0.001). The latter was significantly different between non-NASH and NASH (p=0.047) and selected as discriminating parameter, with area under the receiver-operating characteristics curve of 0.71 (95% confidence interval, 0.62-0.79). An α-NTP/TP cutoff of 16.36% gave 91% sensitivity and cutoff of 10.57% gave 91% specificity for NASH.

CONCLUSIONS

(31)P-MRS shows distinct biochemical changes in different NAFLD states, and has fair diagnostic accuracy for NASH.

Mitochondrial dysfunction in Gulf War illness revealed by 31Phosphorus Magnetic Resonance Spectroscopy: a case-control study

BACKGROUND

Approximately 1/3 of 1990-1 Gulf War veterans developed chronic multisymptom health problems. Implicated exposures bear mechanisms that adversely affect mitochondria. Symptoms emphasize fatigue, cognition and muscle (brain and muscle are aerobically demanding); with protean additional domains affected, compatible with mitochondrial impairment. Recent evidence supports treatments targeting cell bioenergetics (coenzyme10) to benefit Gulf War illness symptoms. However, no evidence has directly documented mitochondrial or bioenergetic impairment in Gulf War illness.

OBJECTIVE

We sought to objectively assess for mitochondrial dysfunction, examining post-exercise phosphocreatine-recovery time constant (PCr-R) using (31)Phosphorus Magnetic Resonance Spectroscopy ((31)P-MRS), in Gulf War veterans with Gulf War illness compared to matched healthy controls. PCr-R has been described as a "robust and practical" index of mitochondrial status.

DESIGN AND PARTICIPANTS

Case-control study from 2012-2013. Fourteen community-dwelling Gulf War veterans and matched controls from the San Diego area comprised 7 men meeting CDC and Kansas criteria for Gulf War illness, and 7 non-deployed healthy controls matched 1:1 to cases on age, sex, and ethnicity.

OUTCOME MEASURE

Calf muscle phosphocreatine was evaluated by (31)P-MRS at rest, through 5 minutes of foot pedal depression exercise, and in recovery, to assess PCr-R. Paired t-tests compared cases to matched controls.

RESULTS

PCr-R was significantly prolonged in Gulf War illness cases vs their matched controls: control values, mean ± SD, 29.0 ± 8.7 seconds; case values 46.1 ± 18.0 seconds; difference 17.1 ± 14.9 seconds; p = 0.023. PCr-R was longer for cases relative to their matched controls for all but one pair; moreover while values clustered under 31 seconds for all but one control, they exceeded 35 seconds (with a spread up to 70 seconds) for all but one case.

DISCUSSION

These data provide the first direct evidence supporting mitochondrial dysfunction in Gulf War illness. Findings merit replication in a larger study and/or corroboration with additional mitochondrial assessment tools.

Assessing bioenergetic compromise in autism spectrum disorder with 31P magnetic resonance spectroscopy: preliminary report

We sought to examine, via Phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) in a case-control design, whether bioenergetic deficits in autism spectrum disorders extend to the brain and muscle. Six cases with autism spectrum disorder with suspected mitochondrial dysfunction (age 6-18 years) and 6 age/sex-matched controls underwent (31)P magnetic resonance spectroscopy. The outcomes of focus were muscle resting phosphocreatine and intracellular pH as well as postexercise phosphocreatine recovery time constant and frontal brain phosphocreatine. Intracellular muscle pH was lower in each autism spectrum disorder case than their matched control (6/6, P = .03; P = .0048, paired t test). Muscle phosphocreatine (5/6), brain phosphocreatine (3/4), and muscle phosphocreatine recovery time constant (3/3) trends were in the predicted direction (not all participants completed each). This study introduces (31)P magnetic resonance spectroscopy as a noninvasive tool for assessment of mitochondrial function in autism spectrum disorder enabling bioenergetic assessment in brain and provides preliminary evidence suggesting that bioenergetic defects in cases with autism spectrum disorder are present in muscle and may extend to brain.

Brain imaging and hepatic encephalopathy

Novel imaging techniques allow the investigation of structural and functional neuropathology of hepatic encephalopathy in greater detail, but limited techniques are applicable to the clinic. Computed tomography and magnetic resonance imaging (MRI) can rule out other diagnoses and, in MRI, give diagnostic features in widely available sequences. An internationally accepted diagnostic framework that includes an objective imaging test to replace or augment psychometry remains elusive. Quantitative MRI is likely to be the best candidate to become this test. The utility of MR and nuclear medical techniques to the clinic and results from recent research are described in this article.

Phosphorus liver MRSI at 3 T using a novel dual-tuned eight-channel ³¹P/¹H H coil

Although phosphorus-31 (³¹P) magnetic resonance spectroscopy holds potential as noninvasive tool to monitor treatment response of liver malignancies, the lack of appropriate coils has so far restricted its use to liver lesions close to the surface. A novel eight-channel phased-array dual-tuned ³¹P/¹H coil that can assess ³¹P metabolism in deeper liver tissue as well is presented in this article. Analysis of its performance demonstrates that this coil can provide good sensitivity across a width of 20 cm, thereby enabling magnetic resonance spectroscopic imaging (MRSI) scans that can fully cover axial views of the abdomen in lean subjects. In vivo results and reproducibility of ³¹P MRSI at 3 T of axial slices covering the full depth of the liver are shown in healthy volunteers. To minimize intrasubject and intersubject data variability, spectra are corrected for coil sensitivities. Methods to maximize the reproducibility of coil placement and spectroscopic planning are discussed. The phosphomonoesters/phosphodiesters ratio calculated in healthy volunteers has an average intrasubject variation of 23% averaged over voxels selected from the entire liver. Finally, the feasibility of using the coil in the clinic is shown by preliminary ³¹P liver MRSI data obtained from a patient with hepatocellular carcinoma.

A comparison of single-voxel clinical in vivo hepatic 31P MR spectra acquired at 1.5 and 3.0 Tesla in health and diseased states

With the increasing availability of human MR scanners at various field strengths, the optimal field strength for in vivo clinical MR studies of the liver has become a focus of attention. Comparison between results at 3.0 and 1.5 T is of particular clinical interest, especially for multicentre studies. For MRS studies, higher field strengths should be advantageous, because improved sensitivity and chemical shift dispersion are expected. We report a comparison between single-voxel hepatic proton-decoupled (31)P MRS performed at 1.5 and 3.0 T in the same subjects using similar methodologies. Twelve healthy volunteers and 15 patients with chronic liver disease were studied. Improved spectral resolution was achieved using proton decoupling, and there was an improvement (21%) in the signal-to-noise ratio (SNR) of the phosphomonoester (PME) resonance at 3.0 T relative to 1.5 T. There was no significant change in nuclear Overhauser effects for PME or phosphodiesters (PDEs) between the two field strengths. The T(1) value of PDE was significantly longer at 3 T, although there was no significant change in the T(1) value of PME. There was no significant difference in the mean PME/PDE ratios for either the control or patient groups at both 1.5 and 3.0 T, but there was a small positive mean difference in PME/PDE at 3.0 T on pairwise testing between field strengths (+ 0.05, p < 0.01). There were significant correlations between PME/PDE values at the two magnetic field strengths (r = 0.806, p < 0.001). The underlying broad resonance was reduced at 3.0 T relative to 1.5 T, related to line broadening of the phospholipid bilayer signal. In conclusion, there was an improvement in hepatic (31)P MR signal quality at 3.0 T relative to 1.5 T. Broadly similar hepatic (31)P MR parameters were obtained at 1.5 and 3.0 T. The modest difference noted in the PME/PDE ratio between field strengths for patients with chronic liver disease should inform multicentre study design involving these field strengths.

Hepatic lipid profiling in chronic hepatitis C: an in vitro and in vivo proton magnetic resonance spectroscopy study

BACKGROUND & AIMS

Hepatic steatosis is an important factor in pathogenesis, progression and response to treatment in hepatitis C. We aimed to investigate differences in hepatic lipid composition in liver biopsies from patients with chronic hepatitis C using proton magnetic resonance spectroscopy ((1)H MRS) and to translate these findings to the in vivo clinical setting.

METHODS

Two cohorts of patients with histologically defined chronic hepatitis C were studied. High-resolution MR spectra were obtained from 47 liver biopsy samples. These data were used to derive biologically relevant prior knowledge for the assignment and interpretation of lower-resolution in vivo hepatic MRS data acquired at 1.5T from a second cohort of 59 patients. MRS data were obtained both in vitro and in vivo from a subset of 11 patients.

RESULTS

Multivariate factor analysis demonstrated characteristic MR spectral differences by fibrosis stage and genotype. Total lipid increased with fibrosis stage (r=0.43, p=0.003) and was higher in genotype 3 compared to genotype 1 (p=0.03), while lipid polyunsaturation decreased with increasing fibrosis stage (r=-0.55, p<0.0005) and, independently, with increasing steatosis. Non-invasive assessment using in vivo hepatic (1)H MRS corroborated in vitro findings, but the signal-to-noise ratio was insufficient for reliable assessment of lipid polyunsaturation in vivo.

CONCLUSIONS

Hepatic lipid composition was analysed using MRS in patients with chronic hepatitis C in vitro and in vivo, demonstrating significant differences in indices by disease severity. High-resolution data informed the analysis and interpretation of in vivo spectra, but further improvements in spectral quality in vivo are required.

Multimodal neuroimaging provides a highly consistent picture of energy metabolism, validating 31P MRS for measuring brain ATP synthesis

Neuroimaging methods have considerably developed over the last decades and offer various noninvasive approaches for measuring cerebral metabolic fluxes connected to energy metabolism, including PET and magnetic resonance spectroscopy (MRS). Among these methods, (31)P MRS has the particularity and advantage to directly measure cerebral ATP synthesis without injection of labeled precursor. However, this approach is methodologically challenging, and further validation studies are required to establish (31)P MRS as a robust method to measure brain energy synthesis. In the present study, we performed a multimodal imaging study based on the combination of 3 neuroimaging techniques, which allowed us to obtain an integrated picture of brain energy metabolism and, at the same time, to validate the saturation transfer (31)P MRS method as a quantitative measurement of brain ATP synthesis. A total of 29 imaging sessions were conducted to measure glucose consumption (CMRglc), TCA cycle flux (V(TCA)), and the rate of ATP synthesis (V(ATP)) in primate monkeys by using (18)F-FDG PET scan, indirect (13)C MRS, and saturation transfer (31)P MRS, respectively. These 3 complementary measurements were performed within the exact same area of the brain under identical physiological conditions, leading to: CMRglc = 0.27 +/- 0.07 micromol x g(-1) x min(-1), V(TCA) = 0.63 +/- 0.12 micromol x g(-1) x min(-1), and V(ATP) = 7.8 +/- 2.3 micromol x g(-1) x min(-1). The consistency of these 3 fluxes with literature and, more interestingly, one with each other, demonstrates the robustness of saturation transfer (31)P MRS for directly evaluating ATP synthesis in the living brain.

Brain cell membrane motion-restricted phospholipids: a cerebral 31-phosphorus magnetic resonance spectroscopy study of patients with schizophrenia

This study directly assessed, for the first time, whether there was a change in brain cell motion-restricted membrane phospholipids in vivo in patients with schizophrenia with mild to moderate negative symptoms, by quantification of the underlying broad resonance signal of cerebral 31-phosphorus magnetic resonance scans. Cerebral 31-phosphorus magnetic resonance spectroscopy was carried out in 16 schizophrenia patients and 16 age- and gender-matched normal controls. Spectra were obtained from 70x70x70 mm3 voxels using an image-selected in vivo spectroscopy pulse sequence. There was no significant difference in the broad resonances between the two groups, with the mean (S.E.) percentage signal being 59.4 (5.6) for the patients and 53.5 (5.9) for the controls. The phosphomonoesters and phosphodiesters narrow signals also did not differ significantly, their ratio being 0.26 (0.01) in the patients and 0.25 (0.01) in the controls. These results appear to be at variance with the changes expected under the membrane phospholipid hypothesis of schizophrenia.

Cerebral immune activation in chronic hepatitis C infection: a magnetic resonance spectroscopy study

BACKGROUND/AIMS

Abnormal cerebral metabolism and cognitive impairments have been reported in patients with chronic hepatitis C (HCV) but studies have failed to demonstrate a relationship between these findings.

METHODS

Twenty-five HCV-positive patients with histologically-mild liver disease were studied with cerebral proton magnetic resonance spectroscopy (MRS), using acquisition parameters to quantify myo-inositol (mI) and other metabolites in frontal white matter (FWM). Patients underwent automated attention and working memory tests (Cognitive Drug Research test system).

RESULTS

The mean mI/ creatine ratio in the HCV+ve patients (0.64, SD 0.21) was significantly higher (p=0.02) than in healthy controls (0.52, SD 0.10). On cognitive testing, the HCV+ve patients showed impairments in 2/4 composite scores, reflecting working memory and attention, compared to normative data from healthy volunteers (p<0.005) and HCV-ve controls (p=0.03). There was a significant association between elevated FWM mI/creatine and prolonged working memory reaction times (R=0.72, p=0.002).

CONCLUSIONS

Elevated FWM mI/ creatine is a feature of HIV-related minor cognitive-motor disorder. It is associated with infection and immune activation of microglial cells. The similar findings in this study suggest that cerebral immune activation may also occur in HCV infection. This may underlie the mild neurocognitive impairment and neuropsychological symptoms observed in a proportion of patients.

Evidence from in vivo 31-phosphorus magnetic resonance spectroscopy phosphodiesters that exhaled ethane is a biomarker of cerebral n-3 polyunsaturated fatty acid peroxidation in humans

BACKGROUND

This study tested the hypothesis that exhaled ethane is a biomarker of cerebral n-3 polyunsaturated fatty acid peroxidation in humans. Ethane is released specifically following peroxidation of n-3 polyunsaturated fatty acids. We reasoned that the cerebral source of ethane would be the docosahexaenoic acid component of membrane phospholipids. Breakdown of the latter also releases phosphorylated polar head groups, giving rise to glycerophosphorylcholine and glycerophosphorylethanolamine, which can be measured from the 31-phosphorus neurospectroscopy phosphodiester peak. Schizophrenia patients were chosen because of evidence of increased free radical-mediated damage and cerebral lipid peroxidation in this disorder.

METHODS

Samples of alveolar air were obtained from eight patients and ethane was analyzed and quantified by gas chromatography and mass spectrometry (m/z = 30). Cerebral 31-phosphorus spectra were obtained from the same patients at a magnetic field strength of 1.5 T using an image-selected in vivo spectroscopy sequence (TR = 10 s; 64 signal averages localized on a 70 x 70 x 70 mm3 voxel). The quantification of the 31-phosphorus signals using prior knowledge was carried out in the temporal domain after truncating the first 1.92 ms of the signal to remove the broad component present in the 31-phosphorus spectra.

RESULTS

The ethane and phosphodiester levels, expressed as a percentage of the total 31-phosphorus signal, were positively and significantly correlated (rs = 0.714, p < 0.05).

CONCLUSION

Our results support the hypothesis that the measurement of exhaled ethane levels indexes cerebral n-3 lipid peroxidation. From a practical viewpoint, if human cerebral n-3 polyunsaturated fatty acid catabolism can be measured by ethane in expired breath, this would be more convenient than determining the area of the 31-phosphorus neurospectroscopy phosphodiester peak.

Brain cell membrane motion-restricted phospholipids in patients with schizophrenia who have seriously and dangerously violently offended

This study directly assessed, for the first time, whether there was a change in brain cell motion-restricted membrane phospholipids in vivo in male forensic patients with schizophrenia who had seriously and violently offended (homicide, attempted murder, or wounding with intent to cause grievous bodily harm) while psychotic, by quantification of the broadband resonance signal from 31-phosphorus neurospectroscopy scans. Cerebral 31-phosphorus magnetic resonance spectroscopy was carried out in 15 such patients, who suffered from positive symptoms of schizophrenia, and in 12 age- and sex-matched normal control subjects. Spectra were obtained from 70 x 70 x 70 mm(3) voxels using an image-selected in vivo spectroscopy pulse sequence. There was no significant difference in the broad resonances between the two groups, with the mean (standard error) percentage broadband signal for the patients being 57.8 (5.6) and that for the control subjects 57.7 (6.0). The phosphomonoesters and phosphodiesters narrow signals also did not differ between the groups. These results suggest that patients with schizophrenia who have predominantly positive symptoms may not show neuroimaging-based signs compatible with the membrane phospholipid hypothesis of schizophrenia.

31P MR Spectroscopy in Assessment of Response to Antiviral Therapy for Hepatitis C Virus–Related Liver Disease

OBJECTIVE

An increase in the ratio of phosphomonoester (PME) to phosphodiester (PDE) during 31P MR spectroscopy of the liver has been observed with increasing severity of hepatitis C-related liver disease. The purpose of this study was to investigate the utility of 31P MR spectroscopy as a biomarker of response to interferon and ribavirin treatment.

SUBJECTS AND METHODS

Forty-seven patients with biopsy-proven hepatitis C undergoing viral eradication treatment with interferon and ribavirin underwent hepatic 31P MR spectroscopy at 1.5 T (voxel size, 70 x 70 x 70 mm; TR, 10,000; number of signals averaged, 48). All underwent baseline imaging before treatment and repeated imaging at 6-month intervals after the start of treatment.

RESULTS

All patients underwent follow-up imaging 6 months after the start of treatment; 25 patients, 12 months; and 10 patients, 18 months after the start of treatment. According to the Ishak histologic scoring system, nine patients had mild hepatitis; 30 patients, moderate to severe hepatitis; and eight patients, cirrhosis. Thirty-two patients responded to antiviral treatment. Among these patients, 25 had a decrease in PME/PDE ratio on follow-up imaging. Among responders the mean baseline PME/PDE ratio decreased from 0.27 +/- 0.02 (standard error) to 0.16 +/- 0.01 after treatment (paired Student's t test, p < 0.001). Among the 15 virologic nonresponders, the ratios were similar in six patients; six other patients had an increase on follow-up imaging. In the latter nonresponder group, the mean baseline PME/PDE ratio was 0.21 +/- 0.03 compared with 0.31 +/- 0.08 after treatment (paired Student's t test, p =0.24).

CONCLUSION

The in vivo hepatic PME/PDE ratio decreased in patients with hepatitis C who responded to antiviral treatment and remained similar or increased in patients without a virologic response. These results suggest that PME and PDE can be used as biomarkers in a noninvasive test of response to treatment.

Variations due to analysis technique in intracellular pH measurements in simulated and in vivo31P MR spectra of the human brain

PURPOSE

To investigate variation in pH generated by different analysis techniques and to find the most robust method, 31P MR brain spectra were acquired in vivo. Three different methods were used to measure the chemical shift of inorganic phosphate (Pi) relative to phosphocreatine (PCr).

MATERIALS AND METHODS

Eight healthy volunteers were scanned four times, and manual measurement of the chemical shift in a frequency domain spectrum using the manufacturer's software was compared with values produced by a frequency-domain analysis method (NMR1) and a prior-knowledge-based time-domain technique (MRUI). To explain the in vivo data, simulations of brain spectra, modified in ways typical of real variations in vivo, were produced and the pH was measured using manual measurement and MRUI.

RESULTS

Different measurement techniques produced systematically different pH values, with manual measurement producing the lowest variability (manual measurement: pH = 6.999, CoV = 0.297; NMR1: pH = 7.042, CoV = 0.501; MRUI: pH = 7.036, CoV = 0.606). While MRUI more accurately measured the pH of unaltered simulations, it was systematically affected by altering the simulated spectra. Manual measurement was unaffected.

CONCLUSION

Manual measurement produces the most consistent pH value, and there is no benefit in using more complex automated spectral fitting methods to measure the pH.

Hepatic 31P magnetic resonance spectroscopy: a hepatologist's user guide

Hepatic phosphorus magnetic resonance spectroscopy (31P MRS) offers the exciting potential of studying metabolic processes in the human liver in vivo. Many investigators have utilized 31P MRS to research a broad range of metabolic questions, and there is outstanding potential for this imaging modality in the future. However, at times it is difficult to appreciate this potential because most published series have been small, and comparisons between studies are difficult. Indeed, the published literature contains significant variation in data acquisition and data analysis techniques and, perhaps most importantly, the interpretation of the data itself. As MR technology continues to evolve and more studies are being performed, perhaps a greater consensus of study techniques and endpoints will emerge. This review summarizes the present literature on human hepatic 31P MRS.