Quantitative spectroscopic imaging with in situ measurements of tissue water T1, T2, and density.

The use of tissue water as a concentration standard in proton magnetic resonance spectroscopy ((1)H-MRS) of the brain requires that the water proton signal be adjusted for relaxation and partial volume effects. While single voxel (1)H-MRS studies have often included measurements of water proton T(1), T(2), and density based on additional (1)H-MRS acquisitions (e.g., at multiple echo or repetition times), this approach is not practical for (1)H-MRS imaging ((1)H-MRSI). In this report we demonstrate a method for using in situ measurements of water T(1), T(2), and density to calculate metabolite concentrations from (1)H-MRSI data. The relaxation and density data are coregistered with the (1)H-MRSI data and provide detailed information on the water signal appropriate to the individual subject and tissue region. We present data from both healthy subjects and a subject with brain lesions, underscoring the importance of water parameter measurements on a subject-by-subject and voxel-by-voxel basis.

Multimodal Neuroimaging in Schizophrenia: Description and Dissemination.

In this paper we describe an open-access collection of multimodal neuroimaging data in schizophrenia for release to the community. Data were acquired from approximately 100 patients with schizophrenia and 100 age-matched controls during rest as well as several task activation paradigms targeting a hierarchy of cognitive constructs. Neuroimaging data include structural MRI, functional MRI, diffusion MRI, MR spectroscopic imaging, and magnetoencephalography. For three of the hypothesis-driven projects, task activation paradigms were acquired on subsets of ~200 volunteers which examined a range of sensory and cognitive processes (e.g., auditory sensory gating, auditory/visual multisensory integration, visual transverse patterning). Neuropsychological data were also acquired and genetic material via saliva samples were collected from most of the participants and have been typed for both genome-wide polymorphism data as well as genome-wide methylation data. Some results are also presented from the individual studies as well as from our data-driven multimodal analyses (e.g., multimodal examinations of network structure and network dynamics and multitask fMRI data analysis across projects). All data will be released through the Mind Research Network's collaborative informatics and neuroimaging suite (COINS).

Galactose neuropathy. Structural changes evaluated by nuclear magnetic resonance spectroscopy.

We examined the hypothesis that the polyol accumulation resulting from chronic galactose supplementation in the diet produces endoneurial edema that can be prevented by inhibition of aldose reductase. We explored the potential of nuclear magnetic resonance (NMR) spectroscopy to quantitate and characterize the water accumulation in the sciatic nerve in this "galactose neuropathy." The data demonstrate a 16% increase in gravimetrically determined total water content of nerve in the galactose-fed rat after 8 mo of this diet and a 50% increase in the T1 relaxation time for nerve water as determined by NMR spectroscopy. Prolongation of the T1 relaxation time reflects increased rotation of water in a magnetic field, consistent with an extracellular site of the additional water. Simultaneous feeding of sorbinil to inhibit aldose reductase resulted in normalization of both total nerve water and of the prolongation of T1 relaxation time. These data define the NMR-spectroscopic state of endoneurial edema in the galactose-fed rat and suggest specific application to the investigation of the role of aldose reductase in human diabetic neuropathy.

Decrease and recovery of N-acetylaspartate/creatine in rat brain remote from focal injury.

Magnetic resonance spectroscopy (MRS) studies on traumatic brain injury (TBI) have shown that the neuronal metabolite N-acetylaspartate (NAA) may be reduced in regions of brain remote from sites of focal injury. Such reductions have generally been attributed to diffuse axonal injury (DAI) or neuron death. The aim of the present study was to investigate the contribution of metabolic depression, in the absence of DAI or cell death, to remote NAA reduction after TBI. The right sensorimotor cortices of adult rats were injured by weight drop. Two and six days later, tissue slices from the ipsilateral occipital cortex, or from the same region in uninjured rats, were superfused and examined by 1H-MRS. The occipital cortex has been shown to have negligible DAI or cell death but marked transient metabolic depression in this model of TBI. Two days after injury, the ratio of the NAA peak height to the total creatine peak height (NAA/TCr) was 14% lower than in control samples. Six days after injury, NAA/TCr recovered to within 7% of the control value. The time course of NAA/TCr decrease and recovery was similar to the time courses of widespread depression and recovery of 2-deoxyglucose uptake and mitochondrial alpha-glycerophosphate dehydrogenase activity measured previously in this model of TBI. Together, these results suggest that at least one component of remote NAA depression after TBI may be associated with a widespread and reversible metabolic depression that is unrelated to either DAI or cell death.

Magnetic resonance lipid signals in rat brain after experimental stroke correlate with neutral lipid accumulation.

Proton magnetic resonance spectroscopy (MRS) signals from lipids in brain have been observed to increase after ischemic brain injury. However, neither the chemical identity nor the cellular location of these lipids has been established. The aim of the present study was to identify the origin of MRS lipid signals in rat brain after temporary (90 min) middle cerebral artery occlusion (MCAO). Fatty acyl proton signals were detected by short-echo one and two dimensional (1)H MRS in superfused brain slices from the infarcted hemisphere 1-5 days after MCAO. The intensities of these signals were strongly correlated with the amount of triacylglyceride and cholesterol ester in lipid extracts from the samples (r(2)=0.96, P<0.05) and were not correlated with the amount of free fatty acids in the tissue. Histological staining of tissue revealed the presence of neutral lipid droplets in infarcted regions. Dual labeling by immunohistochemistry demonstrated that these droplets were localized to microglia/macrophage (OX-42-labeled cells). These results strongly suggest that (1)H MRS lipid signals from brain after stroke arise from microglia/macrophage phagocytosis of cellular membranes.

Metabolism in single rat brain slices measured by magnetic resonance spectroscopy.

Nuclear magnetic resonance spectroscopy (MRS) has been used to study brain biochemistry in superfused brain slice preparations for over a decade. However, unlike techniques that monitor electrical activity, ion fluxes, or the release of radio-labeled compounds in single brain slices, MRS studies have required samples composed of several slices and inherently poor anatomical specificity in order to achieve adequate signal-to-noise levels, spectral resolution, or, in the case of 1H MRS, a high degree of artifact-free water signal suppression. We report that gradient-enhanced 1H MRS techniques combined with a simple slice positioning and perfusion technique yield high-quality spectra from single 400 microns rat forebrain or neocortical-hippocampal slices within 15 min of data acquisition time. Spectra of comparable quality were obtained from samples with three neocortical or three hippocampal slices within the same time frame. The assessment of anaerobic energy metabolism in single slices by 1H MRS is also demonstrated. In addition to greater anatomical resolution in studies on brain slice biochemistry, single slice MRS also presents the possibility of correlating, within the same slice, 1H MRS-detectable metabolite levels with other physiological measurements commonly performed on single brain slices.

The line shapes of the water proton resonances of red blood cells containing carbonyl hemoglobin, deoxyhemoglobin, and methemoglobin: implications for the interpretation of proton MRI at fields of 1.5 T and below.

The 300 MHz (7 T) water proton resonances of suspensions of red blood cells containing paramagnetic deoxyhemoglobin or methemoglobin can be resolved into two broad lines assignable to intra- and extracellular water which undergoes rapid T2 relaxation by diffusion in magnetic field gradients induced by the intracellular paramagnets. The width of the resolved lines allowed an estimate of the maximum contribution that diffusion makes to T2 relaxation at 7 T. The dependence of the diffusion contribution on the square of the strength of the static magnetic field suggest that diffusion makes a small contribution to water proton T2 relaxation at 1.5 T compared to 7 T, and a negligible one at 0.5 T in early and intermediate hematomas containing deoxyhemoglobin or methemoglobin in intact red blood cells. At the lower field strengths, water proton T2 relaxation is apparently dominated by the rapid chemical exchange (mean lifetime tau = 10 msec) between the intra- and extracellular environments.

A prospective diffusion tensor imaging study in mild traumatic brain injury.

OBJECTIVES: Only a handful of studies have investigated the nature, functional significance, and course of white matter abnormalities associated with mild traumatic brain injury (mTBI) during the semi-acute stage of injury. The present study used diffusion tensor imaging (DTI) to investigate white matter integrity and compared the accuracy of traditional anatomic scans, neuropsychological testing, and DTI for objectively classifying mTBI patients from controls. METHODS: Twenty-two patients with semi-acute mTBI (mean = 12 days postinjury), 21 matched healthy controls, and a larger sample (n = 32) of healthy controls were studied with an extensive imaging and clinical battery. A subset of participants was examined longitudinally 3-5 months after their initial visit. RESULTS: mTBI patients did not differ from controls on clinical imaging scans or neuropsychological performance, although effect sizes were consistent with literature values. In contrast, mTBI patients demonstrated significantly greater fractional anisotropy as a result of reduced radial diffusivity in the corpus callosum and several left hemisphere tracts. DTI measures were more accurate than traditional clinical measures in classifying patients from controls. Longitudinal data provided preliminary evidence of partial normalization of DTI values in several white matter tracts. CONCLUSIONS: Current findings of white matter abnormalities suggest that cytotoxic edema may be present during the semi-acute phase of mild traumatic brain injury (mTBI). Initial mechanical damage to axons disrupts ionic homeostasis and the ratio of intracellular and extracellular water, primarily affecting diffusion perpendicular to axons. Diffusion tensor imaging measurement may have utility for objectively classifying mTBI, and may serve as a potential biomarker of recovery.

Mitochondrial function in physically active elders with sarcopenia.

Physical activity is reported to protect against sarcopenia and preserve mitochondrial function. Healthy normal lean (NL: n=15) and sarcopenic (SS: n=9) participants were recruited based on body composition (DXA, Lunar DPX), age, and physical activity. Gastrocnemius mitochondrial function was assessed by (31)P MRS using steady-state exercise in a 4T Bruker Biospin. Total work (429.3+/-160.2J vs. 851.0+/-211.7J, p<0.001) and muscle volume (p=0.006) were lower in SS, although these variables were not correlated (NL r=-0.31, p=0.33, SS r=(0.03, p=0.93). In the SS resting ATP/ADP was lower (p=0.03) and ATP hydrolysis higher (p=0.02) at rest. Free energy ATP hydrolysis was greater at the end of exercise (p=0.02) and [ADP] relative to total work output was higher in SS (ANCOVA, p=0.005). [PCr] recovery kinetics were not different between the groups. Adjusting these parameters for differences in total work output and muscle volume did not explain these findings. These data suggest that aerobic metabolism in physically active older adults with sarcopenia is mildly impaired at rest and during modest levels of exercise where acidosis was avoided. Muscle energetics is coordinated at multiple cellular levels and further studies are needed to determine the loci/locus of energy instability in sarcopenia.

Modelling the magnetic signature of neuronal tissue.

Neuronal communication in the brain involves electrochemical currents, which produce magnetic fields. Stimulus-evoked brain responses lead to changes in these fields and can be studied using magneto- and electro-encephalography (MEG/EEG). In this paper we model the spatiotemporal distribution of the magnetic field of a physiologically idealized but anatomically realistic neuron to assess the possibility of using magnetic resonance imaging (MRI) for directly mapping the neuronal currents in the human brain. Our results show that the magnetic field several centimeters from the centre of the neuron is well approximated by a dipole source, but the field close to the neuron is not, a finding particularly important for understanding the possible contrast mechanism underlying the use of MRI to detect and locate these currents. We discuss the importance of the spatiotemporal characteristics of the magnetic field in cortical tissue for evaluating and optimizing an experiment based on this mechanism and establish an upper bound for the expected MRI signal change due to stimulus-induced cortical response. Our simulations show that the expected change of the signal magnitude is 1.6% and its phase shift is 1 degrees . An unexpected finding of this work is that the cortical orientation with respect to the external magnetic field has little effect on the predicted MRI contrast. This encouraging result shows that magnetic resonance contrast directly based on the neuronal currents present in the cortex is theoretically a feasible imaging technique. MRI contrast generation based on neuronal currents depends on the dendritic architecture and we obtained high-resolution optical images of cortical tissue to discuss the spatial structure of the magnetic field in grey matter.

Accumulation of acetyl groups following cycling: a 1H-MR spectroscopy study.

Using in vivo proton magnetic resonance spectroscopy (1H-MRS), a new peak resonating at 2.13 ppm post-exercise has been attributed in the literature to the acetyl groups of acetylcarnitine. Since this peak is inconsistently generated by various submaximal exercise regimens, this study aimed at (a) verification of the previous chemical assignment, (b) determination of exercise conditions necessary for its induction, and (c) documentation of the recovery kinetics through 60 minutes following exercise. Ten healthy males (31 +/- 4 yr) cycled continuously for 45 minutes with intensity alternating between 50% (3 min) and 110% (2 min) of ventilatory threshold (VT). 1H-MR spectra were acquired from the vastus lateralis before and for 60 minutes following exercise. The peak at 2.13 ppm was not quantifiable at rest in any subject. However, it was present in all subjects following intense exercise (p < 0.0001), and expressed the chemical characteristics of an acetyl-containing compound. The estimated concentration, accumulation with high-intensity exercise, the presence as a single peak at 2.13 ppm, and the chemical shift were all consistent with the chemical and biophysical characteristics of acetyl groups associated with acetylcarnitine. This study provides further evidence that acetyl groups are robustly generated by intense exercise, and that the accumulation of acetyl groups in healthy subjects is dependent on the degree of exercise intensity. 1H-MRS may be used for the noninvasive study of muscle metabolism during exercise and recovery and may have special applications for studying the generation and transport of acetyl compounds, including acetylcarnitine.

Mobile lipids in rat brain slices observed by gradient-enhanced NMR.

Short-echo gradient-enhanced nuclear magnetic resonance (NMR) spectroscopy was utilized to identify mobile lipids in perfused neonate and juvenile rat brain slices. Lipid signals were present at low levels within 1 hr of tissue preparation and increased with time under standard perfusion conditions and in the presence of high phosphocreatine and low lactate levels. Both one- and two-dimensional NMR spectra demonstrate peaks consistent with the generation of free fatty acids or neutral lipids following tissue trauma. The present work demonstrates that injury-induced mobile lipids may make appreciable contributions to regions of brain tissue spectra that have recently been assigned to lactate or polypeptides alone.

Ca2+- and Mg2+-modulated lipolysis in neonatal rat brain slices observed by one- and two-dimensional NMR.

Superfused cortical brain slices from neonatal rats demonstrated large increases in levels of NMR-detectable lipids after sample preparation and perfusion with standard artificial CSF. These increases were reduced by an average of 58% by perfusion with buffer with low (no added) Ca2+ or by perfusion in Ca2+-free buffer. Perfusion with buffer with elevated MgSO4 (10 mmol/L) reduced the lipid changes by 47%. A reduction of 88% was observed in samples perfused in buffer with both low Ca2+ and high Mg2+, suggesting a role for Mg2+ in reducing lipolysis distinct from its known ability to block Ca2+ influx.

A simple approach to the design of a shielded gradient probe for high-resolution in vivo spectroscopy.

A simple approach to the design of a shielded gradient coil set for a high-resolution NMR probe is described in detail. An Appendix is provided that shows the step-by-step Mathematica routine used to carry out the necessary calculations. The probe provided excellent water suppression and gradient-accelerated acquisition of one- and two-dimensional spectra from perfused bovine retina.

The magnetic properties and water dynamics of the red blood cell: a study by proton-NMR lineshape analysis.

The magnetic properties and water dynamics of human red blood cells were examined by analysis of the water proton spectra of suspensions of oxygenated, deoxygenated, carbon monoxide-treated, and methemoglobin-containing cells at a magnetic field strength of 7.05 T. Total lineshape analysis of spectra from deoxygenated red blood cell suspensions was performed to determine the transmembrane water exchange rate, the contribution of diffusion in local magnetic field gradients to the transverse relaxation rate, and the difference between the intra- and extracellular chemical shifts of water protons. Mathematical models are proposed to account for the dependence of the chemical shifts and linewidths of these spectra on the magnetic susceptibility or density of the cells.

On the origin of paramagnetic inhomogeneity effects in whole blood.

Asymmetric 7 T proton NMR signals of water in RBC suspensions containing intracellular deoxyhemoglobin are composites of chemically shifted extracellular and intracellular resonances broadened by gradient diffusion and modulated by transmembrane water exchange. This allows assessment of field dependences of acute hematoma intensities in proton MRIs at lower field strengths (less than or equal to 1.5 T).

Magnetic resonance spectroscopy in traumatic brain injury.

Magnetic resonance spectroscopy (MRS) offers a unique non-invasive approach for assessing the metabolic status of the brain in vivo and is particularly suited to studying traumatic brain injury (TBI). In particular, MRS provides a noninvasive means for quantifying such neurochemicals as N-acetylaspartate (NAA), creatine, phosphocreatine, choline, lactate, myo-inositol, glutamine, glutamate, adenosine triphosphate (ATP), and inorganic phosphate in humans following TBI and in animal models. Many of these chemicals have been shown to be perturbed following TBI. NAA, a marker of neuronal integrity, has been shown to be reduced following TBI, reflecting diffuse axonal injury or metabolic depression, and concentrations of NAA predict cognitive outcome. Elevation of choline-containing compounds indicates membrane breakdown or inflammation or both. MRS can also detect alterations in high energy phosphates reflecting the energetic abnormalities seen after TBI. Accordingly, MRS may be useful to monitor cellular response to therapeutic interventions in TBI.

31P and 23Na NMR studies of the structure and lability of the sodium shift reagent, bis(tripolyphosphate)dysprosium(III) ([Dy(P3O10)]7-) ion, and its decomposition in the presence of rat muscle.

The 31P NMR of aqueous [Dy(P3O10)2]7- demonstrates that it is in slow exchange with P3O5-10 on the NMR time scale. In the presence of tissue, [Dy(P3O10)2]7- decomposes to PO4 with an accompanying slow change of the tissue 23Na NMR of extracellular Na+ ion in several NMR distinguishable extracellular sites.

A study of imidazole-based nuclear magnetic resonance probes of cellular pH.

A number of imidazole-based compounds were tested for their utility as (1)H NMR molecular probes of intracellular pH. Imidazole, previously found useful as a probe of erythrocyte pH, reported a pH in perfused canine glioma cells that was more than 1 pH unit lower than that reported by inorganic phosphate, consistent with the known lysosomal compartmentation of the molecule. Imidazole acetate, also proposed as an NMR probe of cellular pH, was found not to enter the cells of this study. Histidine was found to be readily taken up by cells and reported a pH consistent with that reported by inorganic phosphate. Using the chemical shift of the histidine H2 proton in cells incubated with 10 mM histidine, cellular pH measurements could be obtained in less than 1 s. This compares quite favorably with the measurement time, typically several minutes, needed to assess in vivo pH by (31)P NMR. The use of histidine as a probe of pH is demonstrated in perfused canine and rat glioma cells subjected to ischemia or to low extracellular pH.

Effect of hypoxia on cerebral metabolites measured by proton nuclear magnetic resonance spectroscopy in rats.

Proton nuclear magnetic resonance spectroscopy is a unique method to monitor noninvasively the concentrations of cerebral metabolites. N-Acetyl-L-aspartate, the concentration of which is assumed to be stable during hypoxia, has been used to form ratios with lactate. To determine the stability of the signal from N-acetyl-L-aspartate, we used a model of graded hypoxia in rats to monitor the percentage changes from baseline of the peak heights for lactate, lipids, and N-acetyl-L-aspartate. Anesthetized adult rats were exposed sequentially to 15% and 10% O2 while proton nuclear magnetic resonance spectra were collected with a surface coil in a 7-T 89-mm-bore spectrometer. Brain lactate concentration was either increased by feeding or infusion of glucose (n = 9) or lowered by fasting (n = 7). After death the brains were removed and frozen, and the water- and lipid-soluble compounds were extracted to identify the origin of the signals. We analyzed the data both as the percentage change from baseline for heights of the lactate (1.33 ppm), lipids (1.5 ppm), and N-acetyl-L-aspartate (2.02 ppm) peaks and as the ratios of heights of the 1.33 and 2.02 and the 1.5 and 2.02 ppm peaks. Both hypoxic episodes caused a 45% decrease from baseline in the 2.02 ppm peak. During the second hypoxic episode, the 1.33:2.02 ppm peak height ratio increased significantly in hyperglycemic rats (p less than 0.05) but was unchanged in hypoglycemic rats.(ABSTRACT TRUNCATED AT 250 WORDS)