Short TE phosphorus spectroscopy using a spin-echo pulse

Spin echoes in the regime of weak dephasing

PURPOSE

This article analyzes possibilities and limits of spin echoes beyond Hahn's theory. The regime of weak dephasing is explored with the purpose of combining the enhanced signal and reduced artifacts of spin echoes with the speed and flexibility of the fast low angle shot sequence.

METHODS

In the regime of weak dephasing, an upper boundary of the echo time is derived analytically. This limit is verified with optimal control pulses, which are also used to heuristically examine the transition to Hahn's regime of complete dephasing. The potential of the proposed pulses is demonstrated in proof-of-concept spin echo fast low angle shot images of a volunteer's lung and head.

RESULTS

It was found that the time between the end of the pulse and the spin echo can exceed the duration of the composite radio frequency-pulse, which stands in contrast to Hahn echoes where those measures are at most equal. The maximum echo time was found to mainly depend on the total amount of dephasing. In vivo spin echo fast low angle shot images show an increased pulmonary signal as well as reduced artifacts in areas affected by susceptibility differences.

CONCLUSION

The spin dynamics in the regime of weak dephasing was investigated and the feasibility of spin echo fast low angle shot imaging was demonstrated in vivo.

Muscle metabolic alterations assessed by 31-phosphorus magnetic resonance spectroscopy in mild Becker muscular dystrophy

Although the molecular defect causing Becker muscular dystrophy (BMD) has been identified, the biochemical mechanisms that lead to muscle necrosis remain unclear. Exercise-related muscle metabolism in 9 mildly affected BMD patients was assessed by muscle 31-phosphorus magnetic resonance spectroscopy ((31)P MRS) during an incremental workload. Compared with normal controls, BMD patients showed deregulation of resting pH and intramuscular membrane breakdown. We also observed increased reliance upon anaerobic metabolism during sustained submaximal contraction and maintenance of oxidative function during recovery.

Self-refocused spatial-spectral pulse for positive contrast imaging of cells labeled with SPIO nanoparticles

MRI has been used extensively to noninvasively track the location of cells labeled with superparamagnetic iron-oxide nanoparticles (SPIOs) in vivo. Typically, SPIOs are employed as a negative contrast agent which makes it difficult to differentiate labeled cells from extraneous sources of inhomogeneity and actual voids in the image. As a result, several novel approaches have been put forth to obtain positive contrast from SPIOs. One technique proposed by Cunningham et al. utilizes spectrally selective pulses to excite and refocus spins in the vicinity of the SPIOs. Although the frequency selectivity of this technique provides effective positive contrast, the lack of slice selectivity results in interfering signal from sources of off-resonance outside the slice of interest. We have developed a self-refocused spatial-spectral (SR-SPSP) pulse to achieve slice-selective spin-echo imaging of off-resonant spins. Using a self-refocused pulse affords flexibility in echo-time selection since the spin echo may be placed at any time after the end of the pulse. The spatial selectivity achieved by the SR-SPSP RF pulse eliminates background signal from out-of-slice regions and reduces the on-resonant water suppression requirements. Phantom and in vivo data demonstrate that positive contrast and slice-selectivity are achieved using this novel RF pulse.

Lithium-induced alterations in nucleoside triphosphate levels in human brain: a proton-decoupled 31P magnetic resonance spectroscopy study

We examined how lithium's demonstrated effects on various cellular processes in human brain would be reflected in the (31)P magnetic resonance spectra of living human beings with respect to brain high-energy phosphate metabolites. Eight healthy volunteers received a baseline (31)P magnetic resonance spectroscopy (MRS) scan, after which they received lithium carbonate, 900 mg/day, for 14 days. Follow-up MRS scans were obtained on day 7 and on day 14. We detected a lithium-induced decrease in alpha-, beta-, gamma- and total nucleoside triphosphate NTP levels with chronic administration of lithium. On day 7, significant decreases were noted in gamma-NTP (14%) and total NTP (11%) levels. There was a trend for a decrease in beta-NTP (11%) levels. On day 14, significant decreases were noted in alpha-NTP (7%) and total NTP (8%) levels. There was a trend for a decrease in beta-NTP (16%) levels. Lithium caused a 25% reduction in inorganic phosphate (P(i)) levels on day 14. The theoretical relevance of the lithium-induced alterations on brain high-energy phosphates to the lithium-induced modifications of neuroplasticity is discussed.

Evaluation of the RF field uniformity of a double-tuned31P/1H birdcage RF coil for spin-echo MRI/MRS of the diabetic foot

PURPOSE

To evaluate the B1 field uniformity of a double-tuned birdcage coil designed for (31)P/(1)H MRI/MRS spin-echo (SE) imaging of the metatarsal head region of the foot in neuropathic diabetic patients.

MATERIALS AND METHODS

A low-pass double-tuned (31)P/(1)H RF birdcage coil was constructed to fit over the adult forefoot. Flip angle (FA) maps were created from B1 data acquired at the 3T (31)P (four normal subjects) and (1)H (five normal subjects) frequencies. T2-weighted (T2-W) (1)H images, (31)P rapid acquisition with relaxation enhancement (RARE) images, and composite SE pulse CSI data were acquired to demonstrate the uniformity of the resulting images and data.

RESULTS

The means and standard deviations (SDs) of the range of FAs across the feet of the volunteer subjects indicated good uniformity (the maximum coefficients of variation (CVs) for all of the (31)P and (1)H FA maps were 7.6% and 7.3%, respectively). The FA values across the metatarsal head region indicated a maximum signal intensity variation of +/-3% in a RARE image acquired using an echo train length of 32.

CONCLUSION

A (31)P/(1)H birdcage coil constructed for MRI/MRS studies of the human forefoot provided sufficient signal uniformity of SE data to facilitate accurate (31)P concentration measurements in muscle.

Control of respiration and bioenergetics during muscle contraction

(1)H-NMR experiments have determined intracellular O(2) consumption (Vo(2)) with oxymyoglobin (MbO(2)) desaturation kinetics in human calf muscle during plantar flexion exercise at 0.75, 0.92, and 1.17 Hz with a constant load. At the onset of muscle contraction, myoglobin (Mb) desaturates rapidly. The desaturation rate constant of approximately 30 s reflects the intracellular Vo(2). Although Mb desaturates quickly with a similar time constant at all workload levels, its final steady-state level differs. As work increases, the final steady-state cellular Po(2) decreases progressively. After Mb desaturation has reached a steady state, however, Vo(2) continues to rise. On the basis of current respiratory control models, the analysis in the present report reveals two distinct Vo(2) phases: an ADP-independent phase at the onset of contraction and an ADP-dependent phase after Mb has reached a steady state. In contrast to the accepted view, the initial intracellular Vo(2) shows that oxidative phosphorylation can support up to 36% of the energy cost, a significantly higher fraction than expected. Partitioning of the energy flux shows that a 31% nonoxidative component exists and responds to the dynamic energy utilization-restoration cycle (which lasts for only milliseconds) as postulated in the glycogen shunt theory. The present study offers perspectives on the regulation of respiration, bioenergetics, and Mb function during muscle contraction.

Cerebral phosphorus metabolite and transverse relaxation time abnormalities in heroin-dependent subjects at onset of methadone maintenance treatment

Cerebral bioenergetic and phospholipid abnormalities have been reported in heroin-dependent subjects. The goal of the present study was to characterize the neurochemical profile of subjects voluntarily enrolled in a methadone maintenance (MM) treatment program to overcome their heroin addiction. Participants included 43 heroin-dependent subjects during their first month of MM and 15 age-matched healthy individuals. Phosphorus magnetic resonance spectroscopy ((31)P MRS) and transverse relaxation times (T2-RT), which can reflect steady state cerebral perfusion and metabolism, were acquired at 1.5 T from an axial slice prescribed through the orbitofrontal and occipital cortices, including basal ganglia and frontal cortex. MM subjects exhibited reduced phosphocreatine (PCr) levels (-15.3%), elevated phosphodiesters (+ 12.9%, PDE) and significantly longer T2-RT ((+) 2.1%) compared with healthy comparison subjects. When MM subjects were stratified into subgroups based on treatment duration, we found a treatment duration effect on metabolite values but not T2-RT; reduced PCr was observed only after 8+ days of MM, and phosphomonoesters (PME) were elevated in the 15-28 day MM group. Taken together, these cross-sectional data suggest that the first month of MM treatment may be associated with altered cerebral bioenergetics and phospholipid metabolite levels.

S-adenosyl-L-methionine: effects on brain bioenergetic status and transverse relaxation time in healthy subjects

BACKGROUND

S-adenosyl-L-methionine is an effective treatment for clinical depression, although the mechanism underlying this effect is unclear. Presently, in vivo phosphorus magnetic resonance spectroscopy (31P MRS) and brain transverse relaxometry were employed to test if S-adenosyl-L-methionine supplementation alters brain bioenergetics and/or transverse relaxation time (T2RT) in a nondepressed cohort. If these magnetic resonance techniques are sensitive to S-adenosyl-L-methionine induced alterations in neurochemical processes, these methods may be used in cases of clinical depression to elucidate the mechanism underlying the antidepressant effect of S-adenosyl-L-methionine.

METHODS

Twelve subjects self-administered 1600 mg of oral S-adenosyl-L-methionine daily. Phosphorus spectra and transverse relaxation time were acquired at baseline and after treatment using a 1.5 Tesla scanner.

RESULTS

Phosphocreatine levels were significantly higher after treatment, whereas beta nucleoside triphosphate levels, predominantly adenosine triphosphate in brain, were significantly lower after treatment. A surprising gender difference in T2RT emerged after supplementation, with women exhibiting significantly lower T2RT than men.

CONCLUSIONS

Alterations in phosphocreatine and beta nucleoside triphosphate are consistent with the report that S-adenosyl-L-methionine is involved in the production of creatine, which in turn is phosphorylated to phosphocreatine using adenosine triphosphate. These findings suggest that S-adenosyl-L-methionine alters parameters associated with cerebral bioenergetic status and that some effects of S-adenosyl-L-methionine (T2RT) occur in a gender-specific manner.

Multinuclear magnetic resonance spectroscopy of high-energy phosphate metabolites in human brain following oral supplementation of creatine-monohydrate

Alterations in brain high-energy phosphate metabolism, determined by in vivo magnetic resonance spectroscopy (MRS), have been reported in subjects with a number of brain disorders including major depression, schizophrenia, and substance abuse. It is not clear to what extent these changes can be modified by pharmacological or nutritional means. To address this possibility, we evaluated changes in brain chemistry that were associated with oral creatine (Cr) administration. We hypothesized that oral Cr supplementation, by increasing brain creatine and high-energy phosphate stored in phosphocreatine, would result in an increase in the creatine resonance, as measured using proton 1H-MRS, and a decrease in the beta-nucleoside triphosphate (NTP) peak and an increase in the phosphocreatine (PCr) peak, as measured by phosphorus 31P-MRS, in brain of healthy human subjects. Fifteen healthy male subjects (age=22.9+/-2.2; body mass index=22.9+/-1.7), who were without any axis I disorders or physical or neurological illness, were recruited. Ten subjects took creatine-monohydrate, 0.3 g/kg/day for the first 7 days and 0.03 g/kg/day for the next 7 days (creatine group). Five comparison subjects took equivalent amounts of sucrose as placebo (placebo group). Both 1H- and 31P-MRS scans were acquired at baseline, as well as at day 7 and day 14 of oral supplementation. 1H-MRS: Water suppressed localized spectra were acquired using a single-voxel (1.5 cm x 2 cm x 2 cm) proton MRS PRESS sequence in the left frontal lobe. 31P-MRS: Phosphorus spectral data were recorded from a 5-cm-thick axial brain slice using a short-TE slice selective spin-echo pulse sequence. The creatine group had significantly increased brain creatine levels (8.1% and 9.3%, in creatine/N-acetyl aspartate and creatine/choline ratios, respectively) compared to the placebo group over the 2-week period. The creatine group had significantly decreased beta-NTP levels (7.8%) and marginally increased PCr (3.4%) over the same period. In addition, the brain inorganic phosphate level increased over the same period in the creatine group (9.8%). The current study is the first multinuclear (1H and 31P) MRS study to evaluate changes in brain high-energy phosphate metabolism following oral creatine supplementation in healthy human subjects. These findings suggest the possibility of using oral creatine supplementation to modify brain high-energy phosphate metabolism in subjects with various brain disorders, including major depression, schizophrenia, cocaine and opiate abuse, where alterations in brain high-energy phosphate metabolism have been reported.

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.

Correlations between peripheral polyunsaturated fatty acid content and in vivo membrane phospholipid metabolites

BACKGROUND

There is evidence for membrane abnormalities in schizophrenia. It is unclear whether the observed membrane deficits in peripheral cells parallel central membrane phospholipid metabolism. To address this question we examined the relations between red blood cell polyunsaturated fatty acids and brain phospholipid metabolites from different regions of interest in schizophrenia and healthy subjects.

METHODS

Red blood cell membrane fatty acids were measured by capillary gas chromatography and in vivo brain phospholipid metabolite levels were measured using a multi-voxel (31)P Magnetic Resonance Spectroscopy technique on 11 first-episode, neuroleptic-naïve schizophrenic subjects and 11 normal control subjects.

RESULTS

Both the total polyunsaturated fatty acids and the individual 20:4(n-6) contents were significantly correlated with the freely-mobile phosphomonoester [PME(s-tau(c))] levels (r =.5643, p =.0062 and r =.6729, p =.0006, respectively). The 18:2(n-6) polyunsaturated fatty acids content correlated positively with freely-mobile phosphodiester [PDE(s-tau(c))] levels (r =.5573, p =.0071). The above correlations were present in the combined right and left prefrontal region of the brain, while other regions including the basal ganglia, occipital, inferior parietal, superior temporal and centrum semiovale yielded no significant correlations.

CONCLUSIONS

Our preliminary data support the association between the decreased red blood cell membrane phospholipid polyunsaturated fatty acids content and the decreased building blocks [PME(s-tau(c))] and breakdown products [PDE(s-tau(c))] of membrane phospholipids in the prefrontal region of first-episode, neuroleptic-naïve schizophrenic subjects.

Psychosis in Alzheimer disease: postmortem magnetic resonance spectroscopy evidence of excess neuronal and membrane phospholipid pathology

BACKGROUND

The presence of psychotic symptoms in Alzheimer Disease subjects (AD+psychosis, AD+P) is a marker for a phenotype characterized by more severe cognitive impairment and a more rapidly deteriorating course. Although AD+P has been inconsistently associated with more severe neuropathology, no prior studies have examined measures of neuronal and synaptic integrity.

OBJECTIVE

To determine whether AD+P is associated with evidence of disrupted neuronal and synaptic integrity, as indicated by magnetic resonance spectroscopy (MRS) measurement of N-acetyl-L-aspartate and the membrane breakdown products, glycerophosphocholine and glycerophosphoethanolamine.

METHODS

31P and 1H MRS studies of perchloric acid extract from postmortem brain of AD subjects with and without a history of psychotic symptoms. All subjects were characterized for the presence of comorbid cortical Lewy body pathology and for history of neuroleptic use. Brain tissue from dorsolateral prefrontal, superior temporal, inferior parietal, and occipital cortex, amygdala, and cerebellum were examined in all subjects. Statistical analysis accounted for correlated observations across brain regions within-subjects.

RESULTS

AD+P subjects demonstrated significant elevations of glycerophosphoethanolamine and significant reductions of N-acetyl-L-aspartate. Between group differences were greatest in neocortical brain regions.

CONCLUSION

Excess impairment of neocortical neuronal and synaptic integrity may provide the structural substrate underlying AD+P. Confirmation of these findings using in vivo MRS measures is indicated.

In vivo magnetic resonance spectroscopy and its application to neuropsychiatric disorders

In vivo magnetic resonance spectroscopy (MRS) is the only noninvasive imaging technique that can directly assess the living biochemistry in localized brain regions. In the past decade, spectroscopy studies have shown biochemical alterations in various neuropsychiatric disorders. These first-generation studies have, in most cases, been exploratory but have provided insightful biochemical information that has furthered our understanding of different brain disorders. This review provides a brief description of spectroscopy, followed by a literature review of key spectroscopy findings in schizophrenia, affective disorders, and autism. In schizophrenia, phosphorus spectroscopy studies have shown altered metabolism of membrane phospholipids (MPL) during the early course of the illness, which is consistent with a neurodevelopmental abnormality around the critical period of adolescence when the illness typically begins. Children and adolescents who are at increased genetic risk for schizophrenia show similar MPL alterations, suggesting that schizophrenia subjects with a genetic predisposition may have a premorbid neurodevelopmental abnormality. Independent of medication status, bipolar subjects in the depressive state tended to have higher MPL precursor levels and a deficit of high-energy phosphate metabolites, which also is consistent with major depression, though these results varied. Further bipolar studies are needed to investigate alterations at the early stage. Lastly, associations between prefrontal metabolism of high-energy phosphate and MPL and neuropsychological performance and reduced N-acetylaspartate in the temporal and cerebellum regions have been reported in individuals with autism. These findings are consistent with developmental alterations in the temporal lobe and in the cerebellum of persons with autism. This paper discusses recent findings of new functions of N-acetylaspartate.

31P-MRS study of acetyl-L-carnitine treatment in geriatric depression: preliminary results

OBJECTIVE

This 12-week study of two elderly, depressed subjects investigated the effect of acetyl-L-carnitine (ALCAR) treatment on the Hamilton Depression Rating Scale (HDRS) and on measures of high-energy phosphate and membrane phospholipid metabolism.

METHODS

Two mildly depressed (HDRS 15-20), non-demented male subjects 70 and 80 years old were compared with six non-demented controls (all males, mean age of 73.6 +/- 3.6 years). High-energy and membrane phospholipid metabolites were measured by phosphorus magnetic resonance spectroscopic imaging (31P MRSI) analysis. HDRS and 31P MRSI measurements were taken at entry, 6 and 12 weeks for the depressed subjects.

RESULTS

31P MRSI analysis revealed elevated levels of phosphomonesters [PME(s - tau(c))] in the prefrontal region of these mildly depressed subjects, which decreased with ALCAR treatment and showed a trend for correlation of the PME(s - tau(c)) levels with HDRS. ALCAR treatment also resulted in increasing levels of the prefrontal phosphocreatine (PCr), which correlated with HDRS.

CONCLUSIONS

In the prefrontal region, the mildly depressed subjects compared with controls had elevated PME(s - tau(c)) levels which normalized after 12 weeks of ALCAR and increased PCr levels after ALCAR treatment. These preliminary findings suggest further studies are warranted.

Effect of lithium on phosphoinositide metabolism in human brain: a proton decoupled (31)P magnetic resonance spectroscopy study

BACKGROUND

The objective of our study was to evaluate whether lithium increases brain phosphomonoester (PME) levels in human subjects.

METHODS

Proton decoupled (31)P magnetic resonance spectra were obtained from eight healthy volunteers before and after the administration of lithium carbonate, 450 mg b.i.d., for 7 and 14 days.

RESULTS

Pairwise comparisons of the mole percent PME revealed a significant increase from baseline at day 7 and day 14 of lithium administration.

CONCLUSIONS

An increase in PME concentration with 7 and 14 days of lithium administration in the human brain in vivo was observed. Because the inositol-1-monophosphate contributes to the PME peak, this result suggests that some of the initial actions of lithium may occur through a reduction of myo-inositol, which in turn may initiate a cascade of secondary changes at different levels of signal transduction process and gene expression in brain, effects that are ultimately responsible for the therapeutic benefits of lithium.

Delayed-focus pulses optimized using simulated annealing

Unlike prefocused pulses and shaped pulses based on the linear response theory, delayed-focus pulses (X.-L. Wu et al., 1991, Magn. Reson. Med. 20, 165--170) produce a selective spin echo after a predefined short delay without using a pi refocusing pulse. In this paper, a series of delayed-focus pulses of different flip angles are proposed based on optimization using Fourier series representation and simulated annealing. The resistance of these delayed-focus pulses to T(2) relaxation is also demonstrated using numerical simulation of Bloch equations.

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.

Molecular insights into neurodevelopmental and neurodegenerative diseases

Magnetic resonance spectroscopy (MRS) is a non-invasive physical technique that is routinely used to determine the quantity and structure of organic molecules in solution. Technical advances that have expanded the usefulness of this technique include: (1) high resolution MRS to identify and quantify individual molecules present in complex mixtures of tissue extracts; (2) in vivo MRS techniques to non-invasively monitor metabolites in humans; (3) structure determination of proteins of moderate size; and (4) improved structure characterization of solids and liquid crystals, such as the detection of phase changes in membranes. The focus of this review is on the first two technical advances mentioned above. The strengths of MRS as a research tool to investigate molecular alterations in disease states include ease of sample preparation, minimum sample manipulation, avoidance of the preparation of derivatives, and the ability to analyze an unfractionated sample. The strengths of MRS in the clinic are its ability to measure neuronal metabolite levels non-invasively in humans and its potential for disease diagnosis, monitoring disease progression, and assessing the efficacy of experimental therapies.

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.

Brain biochemistry using magnetic resonance spectroscopy: relevance to psychiatric illness in the elderly

Magnetic resonance spectroscopy (MRS) allows for the noninvasive study of cerebral biochemistry. It has been used to investigate cerebral metabolic changes associated with mental illness in vivo and in vitro. In this review, we will discuss the application of MRS to psychiatric illness in the elderly. Following a brief description of the basic principles of MRS, the use of phosphorus (31P) and proton (1H) MRS to enable a better understanding of normal brain aging, dementia (Alzheimer's disease, multiple subcortical infarct dementia, Down syndrome, frontotemporal dementia, vascular dementia, age-associated memory impairment, and other dementias), major depression, and electroconvulsive therapy is detailed.

Myoglobin desaturation with exercise intensity in human gastrocnemius muscle

The present study evaluated whether intracellular partial pressure of O(2) (PO(2)) modulates the muscle O(2) uptake (VO(2)) as exercise intensity increased. Indirect calorimetry followed VO(2), whereas nuclear magnetic resonance (NMR) monitored the high-energy phosphate levels, intracellular pH, and intracellular PO(2) in the gastrocnemius muscle of four untrained subjects at rest, during plantar flexion exercise with a constant load at a repetition rate of 0.75, 0.92, and 1.17 Hz, and during postexercise recovery. VO(2) increased linearly with exercise intensity and peaked at 1.17 Hz (15. 1 +/- 0.37 watts), when the subjects could maintain the exercise for only 3 min. VO(2) reached a peak value of 13.0 +/- 1.59 ml O(2). min(-1). 100 ml leg volume(-1). The (31)P spectra indicated that phosphocreatine decreased to 32% of its resting value, whereas intracellular pH decreased linearly with power output, reaching 6.86. Muscle ATP concentration, however, remained constant throughout the exercise protocol. The (1)H NMR deoxymyoglobin signal, reflecting the cellular PO(2), decreased in proportion to increments in power output and VO(2). At the highest exercise intensity and peak VO(2), myoglobin was approximately 50% desaturated. These findings, taken together, suggest that the O(2) gradient from hemoglobin to the mitochondria can modulate the O(2) flux to meet the increased VO(2) in exercising muscle, but declining cellular PO(2) during enhanced mitochondrial respiration suggests that O(2) availability is not limiting VO(2) during exercise.

Comparative analysis of NMR and NIRS measurements of intracellular PO2 in human skeletal muscle

1H NMR has detected both the deoxygenated proximal histidyl NdeltaH signals of myoglobin (deoxyMb) and deoxygenated Hb (deoxyHb) from human gastrocnemius muscle. Exercising the muscle or pressure cuffing the leg to reduce blood flow elicits the appearance of the deoxyMb signal, which increases in intensity as cellular PO2 decreases. The deoxyMb signal is detected with a 45-s time resolution and reaches a steady-state level within 5 min of pressure cuffing. Its desaturation kinetics match those observed in the near-infrared spectroscopy (NIRS) experiments, implying that the NIRS signals are actually monitoring Mb desaturation. That interpretation is consistent with the signal intensity and desaturation of the deoxyHb proximal histidyl NdeltaH signal from the beta-subunit at 73 parts per million. The experimental results establish the feasibility and methodology to observe the deoxyMb and Hb signals in skeletal muscle, help clarify the origin of the NIRS signal, and set a stage for continuing study of O2 regulation in skeletal muscle.

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.

Phosphorus-31 magnetic resonance brain spectroscopy of children at risk for a substance use disorder: preliminary results

The purpose of this exploratory investigation was to evaluate the heuristic potential of 31P magnetic resonance spectroscopy (MRS) in elucidating a neurobiologic component of the liability for a substance use disorder (SUD). We investigated 31P MRS spectra employing chemical shift imaging (CSI) derived from four distinct anatomic brain locations (i.e. frontal, occipital, right parietal, left parietal) in three groups of peripubertal children who are hypothesized to be at increasing levels of familial SUD risk. Specifically, we studied children with a positive paternal family history of SUD and a disruptive behavior disorder (DBD) diagnosis (SUD+/DBD+; n = 10), in contrast, to those with a positive paternal SUD history in the absence of other psychopathology (SUD+/DBD-; n = 13) and matched control children from normal families (SUD-/DBD-; n = 13). In addition, we examined neurocognitive tests of our subjects to determine any associations between cognitive capacities with regional 31P MRS spectra. The highest-risk sample (SUD+/DBD+) demonstrated a diminished proportion of phosphodiesters confined to the right parietal voxel. This right parietal phosphodiester proportion correlated only with the Information Scale score on a standard intelligence test for children. This suggested a relationship between general learning ability and motivation for academic achievement and right parietal physiology in the highest-risk sample. Variations in synaptic pruning could account for this observation.

Fast 3D large-angle spin-echo imaging (3D FLASE)

A rapid steady-state 3D spin-echo imaging pulse sequence, based on the principle of nutating the spins by an angle greater than 90 degrees, has been designed and implemented on a clinical 1.5-T whole-body MR scanner. The pulse sequence, denoted fast large-angle spin-echo (FLASE), has been optimized for high-resolution imaging of tissues with short T2 and T2*. Features of FLASE include a minimum-phase Shinnar-Le Roux excitation pulse and distribution of phase- and slice-encoding gradients before and after the 180 degrees refocusing pulse to minimize the critical time delay between inversion and restoration of the residual longitudinal magnetization and for minimizing echo time. A Bloch equation analysis, corroborated by experimental data, shows FLASE signal-to-noise to be superior to its closest analog, 3D rapid spin-echo excitation (RASEE) (Jara et al., Magn Reson Medicine 29, 528 (1993)), and 3D gradient-recalled acquisition in steady state (GRASS). It is demonstrated that with judicious RF phase-cycling and steady state operation, FLASE can produce high-quality microimages free of intravoxel phase dispersion from susceptibility-induced background gradients. The performance of the method is exemplified with ultra high-resolution images of trabecular bone in vitro and in vivo in the human calcaneus and wrist at voxel sizes as low as 98 x 98 x 200 microns3. Finally, the contrast behavior of refocused FLASE can be altered by disrupting the steady state analogous to gradient echo imaging.

Quantitation of phosphorus metabolites in newborn human brain using internal water as reference standard

A new method for noninvasive, in vivo quantitation of cerebral phosphorus (31P) metabolites is described. The technique employs point-resolved spectroscopy (PRESS) to obtain both 31P-metabolite and proton (1H) water spectra: brain water is used as an internal concentration reference. Spin-spin relaxation times (T2s) of cerebral 31P metabolites are much longer than the minimum echo time (TE) usable on a spectrometer equipped with actively shielded gradient coils. With short-TE (approximately 10 ms) 31P PRESS, T2 relaxation is minimal and phase modulation of the nucleotide triphosphate (NTP) multiplets can be accounted for 1H water spectra were acquired using several TEs so that extra- and intracellular water signals could be separated from that due to cerebrospinal fluid. Prior calibration of the 31P and 1H spectrometer channels and an assumed brain-water concentration enabled estimations of metabolite concentrations. Using this method, mean 31P metabolite concentrations in the brains of eight normal infants of gestational plus postnatal age 34 to 39 wk were: phosphomonoester (PME) 5.6 (SD 0.9); inorganic phosphate 1.4 (0.4); mobile phosphodiester 2.3 (0.6); phosphocreatine 2.9 (0.3); nucleotide triphosphate 2.8 (0.6); and total mobile phosphate 21.4 (2.8) mmol/kg wet.

Quantitative combined phosphorus and proton PRESS of the brains of newborn human infants

Techniques for quantitative, combined phosphorus and proton, point-resolved spectroscopy (PRESS) studies of newborn-infant brain have been developed. Phosphorus PRESS advantages include: voxel-shimming; rapid transmitter-pulse setting; novel use of brain-water as a localized quantitation reference; and reduced broad components. Proton spectra from 1-ml voxels and phosphorus spectra can both be acquired quantitatively within acceptable time. Cerebral lactate was consistently detected by proton PRESS and the normal concentration (approximately 3 mmol/kg wet weight) may be higher than in adult brain. Phosphorus PRESS provided metabolite peak-area ratios and concentrations comparable with those obtained using ISIS.