Investigation of broad resonances in 31P NMR spectra of the human brain in vivo

Use of 31 P magnetisation transfer magnetic resonance spectroscopy to measure ATP changes after 670 nm transcranial photobiomodulation in older adults

Mitochondrial function declines with age, and many pathological processes in neurodegenerative diseases stem from this dysfunction when mitochondria fail to produce the necessary energy required. Photobiomodulation (PBM), long-wavelength light therapy, has been shown to rescue mitochondrial function in animal models and improve human health, but clinical uptake is limited due to uncertainty around efficacy and the mechanisms responsible. Using 31 P magnetisation transfer magnetic resonance spectroscopy (MT-MRS) we quantify, for the first time, the effects of 670 nm PBM treatment on healthy ageing human brains. We find a significant increase in the rate of ATP synthase flux in the brain after PBM in a cohort of older adults. Our study provides initial evidence of PBM therapeutic efficacy for improving mitochondrial function and restoring ATP flux with age, but recognises that wider studies are now required to confirm any resultant cognitive benefits.

31 P-MRS of healthy human brain: Measurement of guanosine diphosphate mannose at 7 T

Guanosine diphosphate mannose (GDP-Man) is the donor substrate required for mannosylation in the synthesis of glycoproteins, glycolipids and the newly discovered glycoRNA. Normal GDP-Man biosynthesis plays a crucial role in support of a variety of cellular functions, including cell recognition, cell communication and immune responses against viruses. Here, we report the detection of GDP-Man in human brain for the first time, using ³¹ P MRS at 7 T. The presence of GDP-Man is evidenced by the detection of a weak ³¹ P doublet at -10.7 ppm that can be assigned to the phosphomannosyl group (Pβ) of the GDP-Man molecule. This weak but well-resolved signal lies 0.9 ppm upfield of UDP(G) Pβ-multiplet from a mixture of UDP-Glc, UDP-Gal, UDP-GlcNAc and UDP-GalNAc. In reference to ATP (2.8 mM), the concentration of GDP-Man in human brain was estimated to be 0.02 ± 0.01 mM, about 15-fold lower than the total concentration of UDP(G) (0.30 ± 0.04, N = 17) and consistent with previous reports of UDP-Man in cells and brain tissue extracts measured by high-performance liquid chromatography. The reproducibility of the measured GDP-Man between test and 2-week retest was 21% ± 15% compared with 5% ± 4% for UDP(G) (N = 7). The measured concentrations of GDP-Man and UDP(G) are linearly correlated ([UDP(G)] = 4.3 [GDP-Man] + 0.02, with R = 0.66 and p = 0.0043), likely reflecting the effect of shared sugar precursors, which may vary among individuals in response to variation in nutritional intake and consumption. Given that GDP-Man has another set of doublet (Pα) at -8.3 ppm that overlaps with NAD(H) and UDP(G)-Pα signals, the amount of GDP-Man could potentially interfere with the deconvolution of these mixed signals in composition analysis. Importantly, this new finding may be useful in advancing our understanding of glycosylation and its role in the development of cancer, as well as infectious and neurodegenerative diseases.

Unveiling a hidden 31 P signal coresonating with extracellular inorganic phosphate by outer-volume-suppression and localized 31 P MRS in the human brain at 7T

PURPOSE

The study was undertaken to demonstrate that there is more than 1 component in the extracellular Pi31 P signal ( Piex) acquired from human head using nonlocalized 31 P MRS.

METHODS

Outer-volume-suppression (OVS) saturation and 1D/2D 31 P CSI were utilized to reveal the presence of an additional component in the Piex signal.

RESULTS

67% of the head extracellular Pi signal was attenuated upon OVS saturation of the peripheral meningeal tissues, likely reflecting elimination of the Pi signal in the meningeal fluids (the blood and CSF). Localized 1D/2D CSI data provided further support for this assignment. Upon correction for the meningeal contribution, the extracellular Pi concentration was 0.51 ± 0.07 mM, whereas the intracellular Pi was 0.85 ± 0.10 mM. The extracellular pH was measured as 7.32 ± 0.04 when using OVS, as compared to 7.39 ± 0.03 when measured without OVS (N = 7 subjects).

CONCLUSION

The extracellular Pi signal acquired from the human head using nonlocalized 31 P MRS contains a significant component likely contributed by peripheral blood and CSF in meninges that must be removed in order to use this signal as an endogenous probe for measuring extracellular pH and other properties in the brain.

31 P magnetization transfer magnetic resonance spectroscopy: Assessing the activation induced change in cerebral ATP metabolic rates at 3 T

Purpose

In vivo ³¹P magnetic resonance spectroscopy (MRS) magnetization transfer (MT) provides a direct measure of neuronal activity at the metabolic level. This work aims to use functional ³¹P MRS‐MT to investigate the change in cerebral adenosine triphosphate (ATP) metabolic rates in healthy adults upon repeated visual stimuli.

Methods

A magnetization saturation transfer sequence with narrowband selective saturation of γ‐ATP was developed for ³¹P MT experiments at 3 T.

Results

Using progressive saturation of γ‐ATP, the intrinsic T₁ relaxation times of phosphocreatine (PCr) and inorganic phosphate (Pi) at 3 T were measured to be 5.1 ± 0.8 s and 3.0 ± 1.4 s, respectively. Using steady‐state saturation of γ‐ATP, a significant 24% ± 14% and 11% ± 7% increase in the forward creatine kinase (CK) pseudo‐first‐order reaction rate constant, k₁, was observed upon visual stimulation in the first and second cycles, respectively, of a paradigm consisting of 10‐minute rest followed by 10‐minute stimulation, with the measured baseline k₁ being 0.35 ± 0.04 s⁻¹. No significant changes in forward ATP synthase reaction rate, PCr/γ‐ATP, Pi/γ‐ATP, and nicotinamide adenine dinucleotide/γ‐ATP ratios, or intracellular pH were detected upon stimulation.

Conclusion

This work demonstrates the potential of studying cerebral bioenergetics using functional ³¹P MRS‐MT to determine the change in the forward CK reaction rate at 3 T. Magn Reson Med 79:22–30, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Glycerophosphocholine and Glycerophosphoethanolamine Are Not the Main Sources of the In Vivo (31)P MRS Phosphodiester Signals from Healthy Fibroglandular Breast Tissue at 7 T

PURPOSE

The identification of the phosphodiester (PDE) (31)P MR signals in the healthy human breast at ultra-high field.

METHODS

In vivo (31)P MRS measurements at 7 T of the PDE signals in the breast were performed investigating the chemical shifts, the transverse- and the longitudinal relaxation times. Chemical shifts and transverse relaxation times were compared with non-ambiguous PDE signals from the liver.

RESULTS

The chemical shifts of the PDE signals are shifted -0.5 ppm with respect to glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE), and the transverse and longitudinal relaxation times for these signals are a factor 3 to 4 shorter than expected for aqueous GPC and GPE.

CONCLUSION

The available experimental evidence suggests that GPC and GPE are not the main source of the PDE signals measured in fibroglandular breast tissue at 7 T. These signals may predominantly originate from mobile phospholipids.

Bonded Cumomer Analysis of Human Melanoma Metabolism Monitored by 13C NMR Spectroscopy of Perfused Tumor Cells

A network model for the determination of tumor metabolic fluxes from (13)C NMR kinetic isotopomer data has been developed and validated with perfused human DB-1 melanoma cells carrying the BRAF V600E mutation, which promotes oxidative metabolism. The model generated in the bonded cumomer formalism describes key pathways of tumor intermediary metabolism and yields dynamic curves for positional isotopic enrichment and spin-spin multiplets. Cells attached to microcarrier beads were perfused with 26 mm [1,6-(13)C2]glucose under normoxic conditions at 37 °C and monitored by (13)C NMR spectroscopy. Excellent agreement between model-predicted and experimentally measured values of the rates of oxygen and glucose consumption, lactate production, and glutamate pool size validated the model. ATP production by glycolytic and oxidative metabolism were compared under hyperglycemic normoxic conditions; 51% of the energy came from oxidative phosphorylation and 49% came from glycolysis. Even though the rate of glutamine uptake was ∼ 50% of the tricarboxylic acid cycle flux, the rate of ATP production from glutamine was essentially zero (no glutaminolysis). De novo fatty acid production was ∼ 6% of the tricarboxylic acid cycle flux. The oxidative pentose phosphate pathway flux was 3.6% of glycolysis, and three non-oxidative pentose phosphate pathway exchange fluxes were calculated. Mass spectrometry was then used to compare fluxes through various pathways under hyperglycemic (26 mm) and euglycemic (5 mm) conditions. Under euglycemic conditions glutamine uptake doubled, but ATP production from glutamine did not significantly change. A new parameter measuring the Warburg effect (the ratio of lactate production flux to pyruvate influx through the mitochondrial pyruvate carrier) was calculated to be 21, close to upper limit of oxidative metabolism.

31P-magnetic resonance spectroscopy (31P-MRS) detects early changes in kidney high-energy phosphate metabolism during a 6-month Valsartan treatment in diabetic and non-diabetic kidney-transplanted patients

(31)P-magnetic resonance spectroscopy ((31)P-MRS) is a non-invasive tool to study high-energy phosphate (HEP) metabolism. We evaluate whether 31P-MRS can detect early changes in kidney HEP metabolism during a 6-month trial with Valsartan. Twenty consecutive stable and normotensive kidney-transplanted patients were enrolled. Nine of them received short-term low-dose Valsartan treatment (80 mg/day) for 6 months, while 11 controls received no medication. Kidney HEP metabolism was evaluated both at baseline and after treatment by (31)P-MRS with a 1.5 T system (Gyroscan Intera Master 1.5 MR System; Philips Medical Systems, Best, The Netherlands). Valsartan-treated patients (n = 9) showed a significant increase in β-ATP/Pi ratio, a marker of kidney HEP metabolism (baseline = 1.03 ± 0.08 vs. 6 months = 1.26 ± 0.07, p = 0.03). In contrast, the b-ATP/Pi ratio in the control group (n = 11) did not change (baseline = 0.85 ± 0.10 vs. 6 months = 0.89 ± 0.08, ns). The improvement in the β-ATP/Pi ratio was not associated with a reduction in arterial blood pressure or in urinary albumin excretion. Kidney-localized (31)P-MRS can detect early changes in kidney HEP metabolism during a short-term low-dose Valsartan treatment in stable normotensive kidney-transplanted patients.

Splitting of Pi and other ³¹P NMR anomalies of skeletal muscle metabolites in canine muscular dystrophy

Many anomalies exist in the resting (31) P muscle spectra of boys with Duchenne muscular dystrophy (DMD) but few have been reported in Golden Retriever muscular dystrophy (GRMD), the closest existing animal model for DMD. Because GRMD is recommended for preclinical evaluation of therapies and quantitative outcome measures are needed, we investigated anomalies of (31) P NMRS in tibial cranial and biceps femoris muscles from 14 GRMD compared to 9 control (CONT) dogs. Alterations observed in DMD children - low phosphocreatine and high phospho-monoesters and -diesters - were all found in GRMD but increased pH was not. More surprisingly, inorganic phosphate (Pi) appeared to present a prominent splitting with an enhanced Pi(b) resonance at 0.3 ppm downfield of Pi(a) . Assuming that both resonances are Pi, the pH for Pi(a) in GRMD corresponded to a physiological intracellular pH(a) (6.97 ± 0.05), while pH(b) approached the extracellular range (7.27 ± 0.10) and correlated with pH(a) in GRMD (R(2)  = 0.65). Both Pi(a) and Pi(b) were elevated compared to CONT and Pi(a) increased with age for GRMD (R(2)  = 0.48, p < 0.001). Magnetisation transfer experiments between γATP and Pi were conducted to better characterise Pi pools. Equal T1 relaxation times for Pi(b) and Pi(a) did not support a mitochondrial origin of Pi(b) . We suggest that Pi(b) could originate from degenerating hypercontracted cells that have a leaky membrane and inadequate cell homeostasis and pH regulation. Pi(b) showed minimal chemical exchange in all dogs, while the exchange rate of Pi(a) was reduced in GRMD and might extraneously reflect low glycolytic activity in DMD. Taken together, the ensemble of (31) P NMRS alterations identifies muscle dysfunction and could provide useful biomarkers of therapeutic efficacy. Furthermore, among these, two might relate more specifically to dystrophic processes and merit further investigation: one is the existence of the enhanced alkaline Pi(b) pool; the other, mechanisms by which membrane disruption might increase phosphodiesters in dystrophy.

pH as a biomarker of neurodegeneration in Huntington's disease: a translational rodent-human MRS study

Early diagnosis and follow-up of neurodegenerative diseases are often hampered by the lack of reliable biomarkers. Neuroimaging techniques like magnetic resonance spectroscopy (MRS) offer promising tools to detect biochemical alterations at early stages of degeneration. Intracellular pH, which can be measured noninvasively by (31)P-MRS, has shown variations in several brain diseases. Our purpose has been to evaluate the potential of MRS-measured pH as a relevant biomarker of early degeneration in Huntington's disease (HD). We used a translational approach starting with a preclinical validation of our hypothesis before adapting the method to HD patients. (31)P-MRS-derived cerebral pH was first measured in rodents during chronic intoxication with 3-nitropropionic acid (3NP). A significant pH increase was observed early into the intoxication protocol (pH=7.17±0.02 after 3 days) as compared with preintoxication (pH=7.08±0.03). Furthermore, pH changes correlated with the 3NP-induced inhibition of succinate dehydrogenase and preceded striatum lesions. Using a similar MRS approach implemented on a clinical MRI, we then showed that cerebral pH was significantly higher in HD patients (n=7) than in healthy controls (n=6) (7.05±0.03 versus 7.02±0.01, respectively, P=0.026). Altogether, both preclinical and human data strongly argue in favor of MRS-measured pH being a promising biomarker for diagnosis and follow-up of HD.

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.

Implementation and evaluation of CSI-localizedJ cross-polarization for detection of31P magnetic resonance spectra in vivo

Double resonance techniques such as INEPT (insensitive nuclei enhanced by polarization transfer) and JCP (J cross-polarization) have previously been applied in vitro to enhance the SNR of low-sensitivity nuclei and detect altered metabolism, for example, with 13C magnetic resonance spectroscopy (MRS), where the 1H-13C scalar couplings are of the order of 130 Hz. The aim of the present study was to investigate the potential advantage of using JCP for the detection of phosphomonoesters (PME) and phosphodiesters (PDE) with 31P MRS in vivo. These metabolites are involved in membrane metabolism and their concentration is altered in tumors and other pathologies. JCP has been implemented and compared with INEPT and pulse-and-acquire in vivo both in unlocalized and in localized spectra in order to select the optimum method for in vivo applications for PME and PDE detection. The results suggest that JCP can give up to 20% more signal in the PME region and up to 70% more signal in the PDE region, with 20 to 70% lower power deposition than INEPT. Such enhancement could be used to reduce the measurement times for equivalent signal-to-noise ratios. The JCP sequence is, however, slightly more sensitive than INEPT to RF field inhomogeneities, as predicted from theory.

In vivo31P NMR spectroscopy shows an increase in glycerophosphorylcholine concentration without alterations in mitochondrial function in the prefrontal cortex of medicated schizophrenic patients at rest

The (31)P NMR localised method was used to study the metabolism of phospholipid and high energy phosphate in the prefrontal cortex. The spectra were taken from patients with schizophrenia (11 males) receiving neuroleptic medication, and were compared to normal controls (15 males). Their spectral intensities were analysed using a non-linear least-squares method with a prior knowledge of the fixed chemical shifts and linewidths, leading to further resolution into resonances of glycerophosphorylethanolamine (GPE), glycerophosphorylcholine (GPC), phosphorylethanolamine (PE) and phosphorylcholine (PC). The metabolite concentrations were calculated referring to the spectral intensities of phosphate phantoms with known concentrations. T1 values of phantom and cerebrum were estimated from a series of localised inversion recovery spectra to correct for the signal saturation effects. The schizophrenic patients showed an increased concentration of GPC but not GPE, PE or PC. Furthermore, no difference was observed regarding the concentration of high-energy phosphates such as phosphocreatine, inorganic phosphate and ATP. The patients did not show any differences in mitochondrial function such as phosphorylation potential and the ratio of the rate of ATP synthesis. Thus, an increase in GPC concentration in the prefrontal cortex could be characteristic of the pathophysiology of schizophrenia with mild negative symptoms.

Comparison of polarization transfer sequences for enhancement of signals in clinical 31P MRS studies

Several (31)P MRS studies in tumors in vivo have shown that levels of phosphocholine (PC) and other phosphomonoesters (PME) and phosphodiesters (PDE) are useful prognostic or early-response indicators. To improve sensitivity for such measurements, four polarization transfer (PT) sequences (insensitive nuclei enhanced by PT (INEPT), distortionless enhancement by PT (DEPT), reverse-INEPT, and heteronuclear single-quantum coherence (HSQC)) were assessed theoretically and experimentally. The presence of homonuclear ((1)H-(1)H) and heteronuclear ((31)P-(1)H) couplings of similar magnitude makes theoretical analysis very sensitive to precise model parameters, especially for the (1)H-detected sequences. The (1)H-(1)H coupling causes the splitting of (1)H peaks, and hence reduces the proton spectral resolution. This effect and a 50% signal loss from gradient-enhanced water suppression negate the usual advantages of (1)H-detection. Among the PT methods, INEPT gave the higher signal enhancement. However, T(2) losses during the long echo times (TEs) required by the weak coupling limited the resulting signals from PC.

Prefrontal membrane phospholipid metabolism of child and adolescent offspring at risk for schizophrenia or schizoaffective disorder: an in vivo 31P MRS study

In vivo (31)P magnetic resonance spectroscopy ((31)P MRS) studies have shown abnormal membrane phospholipid metabolism in the prefrontal cortex (PF) in the early course of schizophrenia. It is unclear, however, whether these alterations also represent premorbid risk indicators in schizophrenia. In this paper, we report in vivo (31)P MRS data on children and adolescents at high risk (HR) for schizophrenia. In vivo (31)P MRS studies of the PF were conducted on 16 nonpsychotic HR offspring of parents with schizophrenia or schizoaffective disorder, and 37 age-matched healthy comparison (HC) subjects. While 11 of the HR subjects had evidence of Axis I psychopathology (HR-P), five HR subjects had none (HR-NP). We quantified the freely mobile phosphomonoester (PME) and phosphodiester (PDE) levels reflecting membrane phospholipid precursors and breakdown products, respectively, and the relatively broad signal underlying PDE and PME peaks, comprised of less mobile molecules with PDE and PME moieties (eg, synaptic vesicles and phosphorylated proteins). Compared to HC subjects, HR subjects had reductions in freely mobile PME; the differences were accounted for mainly by the HR-P subjects. Additionally, HR-P subjects showed increases in the broad signal underlying the PME and PDE peaks in the PF. To conclude, these data demonstrate new evidence for decreased synthesis of membrane phospholipids and possibly altered content or the molecular environment of synaptic vesicles and/or phosphoproteins in the PF of young offspring at risk for schizophrenia. Follow-up studies are needed to examine the predictive value of these measures for future emergence of schizophrenia in at-risk individuals.

In vivo brain (31)P-MRS: measuring the phospholipid resonances at 4 Tesla from small voxels

An optimized phosphorous ((31)P) three-dimensional chemical-shift imaging (3D-CSI) protocol was developed at 4 T to study the phospholipid metabolism from discrete regions in the human brain without the need for (1)H-decoupling or nuclear Overhauser enhancement (NOE). In this study, a spherically bound, weighted average, random point omission 3D-CSI technique was developed and tested, based on methods proposed in the literature. The technique yields a significant (p < 0.001, two-tailed, 5% confidence level) increase in signal-to-noise (SNR) efficiency over conventional 3D-CSI (phantom 32%), without an increase in voxel bleedthrough. An automated time-domain fitting procedure utilizing prior spectral knowledge quantified the individual brain phospholipid metabolites from 15 cm(3) effective (8.0 cm(3) nominal) volumes from the left/right-parieto-occipital cortex and left/right thalamus in 10 normal volunteers. Individual constituents from the phosphomonoester (PME) region; phosphoethanolamine (PEth), phosphocholine (PCh) and the phosphodiester (PDE) region; glycerophosphoethanolamine (GPEth), glycerophosphocholine (GPCh) and membrane phospholipids (MP) were separately quantified to assess the precision of our method at 4 T against previous (1)H-decoupled (31)P-MRS brain studies at lower fields and much larger voxels. Derived concentrations (mM/l tissue) for PEth, PCh, GPEth, GPCh and MP in the left-parieto-occipital cortex were 0.81 +/- 0.21, 0.46 +/- 0.14, 0.74 +/- 0.30, 1.15 +/- 0.43 and 1.54 +/- 0.95 mM, respectively, and 0.94 +/- 0.16, 0.46 +/- 0.17, 0.83 +/- 0.22, 1.14 +/- 0.40 and 1.26 +/- 0.78 mM for the right parieto-occipital cortex. Derived concentrations (mM/l tissue) for PEth, PCh, GPEth, GPCh and MP in the left-thalamus were 0.69 +/- 0.18, 0.42 +/- 0.16, 0.63 +/- 0.20, 1.05 +/- 0.42 and 0.93 +/- 0.56 mM, respectively, and 0.68 +/- 0.24, 0.34 +/- 0.18, 0.60 +/- 0.23, 1.09 +/- 0.36 and 0.74 +/- 0.48 mM for the right-thalamus. This is the first study to our knowledge that has been able to quantify each of these individual phospholipid metabolites from such small voxels in the brain within a clinically reasonable scan time and without (1)H-decoupling or NOE.

Neurochemical investigation of the schizophrenic brain by in vivo phosphorus magnetic resonance spectroscopy

Abnormal phospholipid metabolisms may play important roles in the pathophysiology of schizophrenia. Phosphorus magnetic resonance spectroscopy (31P-MRS) offers a new method for studying phosphorus-related metabolism in vivo. A decrease in the level of phosphomonoesters (PME) and an increase in the level of phosphodiesters (PDE) has been demonstrated in the prefrontal lobe of neuroleptic-naive schizophrenic patients. Most of the studies in medicated schizophrenic patients have shown decreased PME and/or increased PDE. The decreased PME in the frontal lobe appears to be associated with negative symptoms and poor working memory performance. 1H-decoupled 31P-MRS revealed a reduction in the phosphocholine element of PME and an elevation in the mobile phospholipids of PDE in the prefrontal region of medicated schizophrenic patients. PDE were elevated in the temporal lobes of neuroleptic-naive schizophrenic patients, and this increase was partially normalized by haloperidol administration. Data about the temporal lobes of medicated schizophrenic patients have not been consistent. Except for the reduction in the adenosine triphosphate (ATP) in the basal ganglia and the correlation between the increase in the frontal lobe phosphocreatine (PCr) and negative symptomatology, data related to changes in high-energy phosphates are contradictory. No consensus on the effect of neuroleptics on phosphorus metabolites has been achieved. Methodological problems inherent in 31P-MRS may have contributed to the confusion in understanding available data. Future directions of MRS studies are suggested in the last section of the paper.

Postprocessing method to segregate and quantify the broad components underlying the phosphodiester spectral region of in vivo (31)P brain spectra

In a typical, in vivo (31)P brain spectrum, the phosphomonoester (PME) and phosphodiester (PDE) spectral region not only contains signals from freely mobile PMEs and PDEs (which are anabolic and catabolic products of membrane phospholipids) but also signals of broader underlying lineshapes from less-mobile molecules. In general, either the PME and PDE resonances are quantified as a combined value of freely mobile metabolites plus less-mobile molecules or the broader underlying signal is reduced/eliminated prior to or post data collection. In this study, a postprocessing method that segregates and quantifies the individual contributions of the freely mobile metabolites and the less-mobile molecules is introduced. To demonstrate the precision and accuracy of the method, simulated data and in vivo (31)P brain spectroscopy data of healthy individuals were quantified. The ability to segregate and quantify these various PME and PDE contributions provides additional spectral information and improves the accuracy of the interpretation of (31)P spectroscopy results. Magn Reson Med 45:390-396, 2001.

Magnetic resonance spectroscopy in schizophrenia: methodological issues and findings--part I

Our knowledge of the biological basis of schizophrenia has significantly increased with the contribution of in vivo proton and phosphorus magnetic resonance spectroscopy (MRS), a noninvasive tool that can assess the biochemistry from a localized region in the human body. Studies thus far suggest altered membrane phospholipid metabolism at the early stage of illness and reduced N-acetylaspartate, a measure of neuronal volume/viability in chronic schizophrenia. Inconsistencies remain in the literature, in part due to the complexities in the MRS methodology. These complexities of in vivo spectroscopy make it important to understand the issues surrounding the design of spectroscopy protocols to best address hypotheses of interest. This review addresses these issues, including 1) understanding biochemistry and the physiologic significance of metabolites; 2) the influence of acquisition parameters combined with spin-spin and spin-lattice relaxation effects on the MRS signal; 3) the composition of spectral peaks and the degree of overlapping peaks, including the broader underlying peaks; 4) factors affecting the signal-to-noise ratio; 5) the various types of localization schemes; and 6) the objectives to produce accurate and reproducible quantification results. The ability to fully exploit the potentials of in vivo spectroscopy should lead to a protocol best optimized to address the hypotheses of interest.

Changes in levels of phosphorus metabolites in temporal lobes of drug-naive schizophrenic patients

OBJECTIVE

The authors examined phospholipids and high-energy phosphorus metabolism in the temporal lobes of drug-naive schizophrenic patients.

METHOD

In vivo 31P magnetic resonance spectroscopy was performed on 17 first-episode, drug-naive schizophrenic patients and 17 age- and gender-matched healthy subjects.

RESULTS

Patients showed higher levels of phosphodiesters and lower levels of phosphomonoesters than the comparison group. Phosphocreatine levels were increased in the left temporal lobes of patients.

CONCLUSIONS

The results suggest disturbed membrane phospholipid metabolism in both temporal lobes and decreased energy demands in the left temporal lobes of drug-naive schizophrenic patients.

A dual-tuned resonator for proton-decoupled phosphorus-31 chemical shift imaging of the brain

A fully quadrature dome-shaped resonator is presented that has been dual-tuned for proton and phosphorus operation at 1.5 T. The resonator is 16.5 cm in length and 23 cm in diameter. Phantom studies were performed to demonstrate the utility of the resonator for proton imaging, shimming, and proton-decoupled phosphorus spectroscopy. In human subjects, proton-decoupled phosphorus chemical shift imaging spectra of the brain were acquired at 27 cm3 resolution in 34 min. Volunteer studies demonstrated improved resolution of phosphomonoesters, phosphodiesters, and nucleoside triphosphates due to proton decoupling. Sensitive coverage of the brain extended from the most superior cerebral cortex to the cerebellum. Acquisition of good quality 31P spectra over this volume is due to the dome structure as well as quadrature operation at both proton and phosphorus frequencies.

A 1H-decoupled 31P chemical shift imaging study of medicated schizophrenic patients and healthy controls

BACKGROUND

Current 31P spectroscopy research in schizophrenia has examined phospholipid metabolism by measuring the sum of phosphomonoesters and the sum of phosphodiester-containing molecules. Proton decoupling was implemented to measure the individual phosphomonoester and phosphodiester components. This is the first study employing this technique to examine schizophrenic patients.

METHODS

Multivoxel two-dimensional chemical shift in vivo phosphorous-31 magnetic resonance spectroscopy with proton decoupling was used to examine a 50-cm3 volume in prefrontal, motor, and parieto-occipital regions in the brain. Eleven chronic medicated schizophrenic patients were compared to 11 healthy controls of comparable gender, education, parental education, and handedness.

RESULTS

A significant increase in the mobile phospholipid peak area and its full width at half maximum was observed in the medicated schizophrenic patients compared to the healthy controls in the prefrontal region. Inorganic orthophosphate and phosphocholine were lower in the schizophrenic group in the prefrontal region.

CONCLUSIONS

The increased sum of phosphodiester [mobile phospholipid + glycerol-3-phosphoethanolamine (GPEth) + glycerol-3-phosphocholine (GPCh)] in schizophrenic patients, measured in earlier studies, arises from the phospholipid peak (MP) and not the more mobile phosphodiesters (GPEth, GPCh) as was originally suspected. A decrease in the phosphocholine component of the phosphomonoesters was also observed in the schizophrenic patients. These findings are consistent with an abnormality in membrane metabolism in the prefrontal region in schizophrenics.

31Phosphorus magnetic resonance spectroscopy of the dorsolateral prefrontal region in schizophrenics--a study including 50 patients and 36 controls

BACKGROUND

In a preliminary study we found decreased phosphodiester (PDE)% values and an increased phosphomonoester (PME)/phosphodiester ratio in the dorsolateral prefrontal region (DLPFR) of 13 chronic schizophrenics vs. 14 controls using 31phosphorus magnetic resonance spectroscopy (31P-MRS). Since these results are in contrast to the findings of other groups, we increased our study group to a total of 50 chronic schizophrenics on stable neuroleptic medication and 36 controls to minimize the possibility of a chance result due to small sample size.

METHODS

An image-selected in vivo 31P-MRS method on a Philips Gyroscan ACS II scanner working at 1.5 T was used.

RESULTS

We could confirm our earlier findings of decreased PDE% levels in schizophrenics. Additionally, we found phosphocreatine (PCr)% and PCr/adenosine triphosphate (ATP) to be increased in the schizophrenics. While no association between PME% and PDE% with neuroleptic medication was found, ATP% correlated positively and PCr/ATP negatively with the chlorpromazine equivalent dose.

CONCLUSIONS

The decreased PDE% levels might be characteristic only for chronic, neuroleptic-treated patients. The finding of altered high-energy phosphate levels can be interpreted as an indication of decreased energy-demanding processes in the DLPFR of the investigated patients compared to controls.

Chemical and physiologic brain imaging in schizophrenia

Technologic advances in functional brain imaging have provided exciting and informative insights into the functional neuroanatomy and neurochemistry of schizophrenia. Using MR spectroscopy, it has been possible to examine in vivo brain metabolism and to relate observed changes to physiological processes occurring at a cellular level. Positron emission tomography and single photon emission computed tomography have revealed disturbances of cerebral blood flow and glucose metabolism in patients with schizophrenia. More recently, these tools have also proved most useful in studying the relative receptor occupancy of typical and atypical antipsychotic medications.

In vivo phosphorus polarization transfer and decoupling from protons in three-dimensional localized nuclear magnetic resonance spectroscopy of human brain

Refocused insensitive nucleus enhancement by polarization transfer (RINEPT) from protons (1H) to a J-coupled phosphorus (31P) has been incorporated into three-dimensional (3D) chemical-shift-imaging (CSI) sequence on a clinical imager. The technique is demonstrated on a phantom and in in vivo human brain. The polarization-transfer efficiency (approximately 1.2) is lower than the theoretical maximum of gamma1H/gamma31P approximately 2.4 resulting from 1H-1H homonuclear J couplings of similar magnitude competing with the 1H --> 31P transfer. Nevertheless, compared with direct 31P Ernst-angle excitation, signal gains of up to x1.8 were obtained mainly as a result of T1 differences between 31P and the 1H. Spectral interpretation is simplified by editing out all non-proton-coupled 31P signals. The duration, approximately 50 min, and power deposition, approximately 1 W x kg(-1), make the application suitable for human studies.

Molar quantitation of hepatic metabolites in vivo in proton-decoupled, nuclear Overhauser effect enhanced 31P NMR spectra localized by three-dimensional chemical shift imaging

Proton decoupling and nuclear Overhauser effect (NOE) enhancement significantly improve the signal-to-noise ratio and enhance resolution of metabolites in in vivo 31P MRS. We obtained proton-decoupled, NOE-enhanced, phospholipid-saturated 31P spectra localized to defined regions within the normal liver using three-dimensional chemical shift imaging. Proton-decoupling resulted in the resolution of two major peaks in the phosphomonoester (PME) region, three peaks in the phosphodiester (PDE) region and a diphosphodiester peak. In order to obtain molar quantitation, we measured the NOE of all hepatic phosphorus resonances, and we corrected for saturation effects by measuring hepatic metabolite T1 using the variable nutation angle method with phase-cycled, B1-independent rotation, adiabatic pulses. After corrections for saturation effects, NOE enhancement, B1 variations and point spread effects, the following mean concentrations (mmol/l of liver) (+/-SD) were obtained: [PME1] = 1.2 +/- 0.4, [PME2 + 2,3-DPG] = 1.1 +/- 0.1, [Pi + 2,3-DPG] = 2.8 +/- 0.5, [GPEth] = 2.8 +/- 0.7, [GPChol] = 3.5 +/- 0.6 and [beta-NTP] = 3.8 +/- 0.3. T1 and NOE enhancement were strongly correlated (r = 90), and indicated that the fractional contribution of 1H-31P dipolar relaxation to total 31P relaxation is minimal for NTPs, moderate for PMEs and high for PDEs in liver. Proton-decoupling and NOE enhancement permit one to obtain more information about in vivo metabolism of liver than previously available and should enhance the utility of 31P MRS for the study of hepatic disorders.

Heteronuclear multivoxel spectroscopy of in vivo human brain: two-dimensional proton interleaved with three-dimensional 1H-decoupled phosphorus chemical shift imaging

Multivoxel, heteronuclear interleaved two-dimensional proton and three-dimensional 1H-decoupled 31P CSI of human brain is demonstrated. This method offers efficient use of limited examination time as patient preparation, coil tuning, shimming and imaging are done only once and the CSI data sets from both nuclei are obtained concurrently. Effective interleaving of 31P and 1H is possible due to the shorter T1s of proton brain metabolites, allowing a 1H acquisition cycle to be inserted into each 31P TR. This way, the entire MRS time is available to both nuclei, increasing their SNR per-unit-time by approximately 12% for 31P and approximately 80% for 1H, compared with sequential detection of equal (45-50 min) length. The spectral resolution and SNR of 31P are further increased through bi-level 1H-decoupling and NOE.