Evaluation of 31P metabolite differences in human cerebral gray and white matter

Translating pH-sensitive PROgressive saturation for QUantifying Exchange rates using Saturation Times (PRO-QUEST) MRI to a 3T clinical scanner

PURPOSE

To translate the recently developed PRO-QUEST (Progressive saturation for quantifying exchange rates using saturation times) sequence from preclinical 9.4T to 3T clinical magnetic field strength.

METHODS

Numerical simulations were performed to define the optimal saturation flip angles for PRO-QUEST saturation pulses at 3T and demonstrate the effect of a ∆T₂ error on the exchange rate (k_ex ) estimation at various field strengths. Exchange-dependent relaxation rate (R_ex ) was measured for glutamate solutions in various pH, healthy volunteers and patients with multiple sclerosis (MS). Additionally, concentration-independent ratiometric R_ex maps were produced to evaluate regional signal variations across the brain of human volunteers.

RESULTS

The calculated R_ex significantly correlates with pH in glutamate samples, however, k_ex values are underestimated as compared to those previously obtained at 9.4T. In the ratiometric R_ex map of healthy volunteers, no significant differences are found between grey matter, white matter, and basal ganglia. In patients with MS, white matter lesions are visible in single saturation power R_ex maps whereas only a periventricular lesion is apparent in the ratiometric R_ex map.

CONCLUSION

We demonstrate that quantification of pH sensitive indices using PRO-QUEST is feasible at 3T within clinically acceptable acquisition times. Our initial findings in patients with MS show that pH sensitive indices varied with the type of lesion examined whereas no significant difference was found in healthy volunteers between tissue types, suggesting that it would be worthwhile to apply PRO-QUEST in a larger cohort of patients to better understand its distinct imaging features relative to conventional techniques.

Phosphorus spectroscopy in acute TBI demonstrates metabolic changes that relate to outcome in the presence of normal structural MRI

Metabolic dysfunction is a key pathophysiological process in the acute phase of traumatic brain injury (TBI). Although changes in brain glucose metabolism and extracellular lactate/pyruvate ratio are well known, it was hitherto unknown whether these translate to downstream changes in ATP metabolism and intracellular pH. We have performed the first clinical voxel-based in vivo phosphorus magnetic resonance spectroscopy (³¹P MRS) in 13 acute-phase major TBI patients versus 10 healthy controls (HCs), at 3T, focusing on eight central 2.5 × 2.5 × 2.5 cm³ voxels per subject. PCr/γATP ratio (a measure of energy status) in TBI patients was significantly higher (median = 1.09) than that of HCs (median = 0.93) (p < 0.0001), due to changes in both PCr and ATP. There was no significant difference in PCr/γATP between TBI patients with favourable and unfavourable outcome. Cerebral intracellular pH of TBI patients was significantly higher (median = 7.04) than that of HCs (median = 7.00) (p = 0.04). Alkalosis was limited to patients with unfavourable outcome (median = 7.07) (p < 0.0001). These changes persisted after excluding voxels with > 5% radiologically visible injury. This is the first clinical demonstration of brain alkalosis and elevated PCr/γATP ratio acutely after major TBI. ³¹P MRS has potential for non-invasively assessing brain injury in the absence of structural injury, predicting outcome and monitoring therapy response.

Evaluation of the sensitivity of R1ρ MRI to pH and macromolecular density

The tumor microenvironment is characteristically acidic and this extracellular acidosis is known to play a role in carcinogenesis and metastasis and can affect tumor chemosensitivity and radiosensitivity. Intracellular pH has been used as a possible biomarker of salvageable tissue in ischemic stroke. A non-invasive MRI-based approach for the determination and imaging of cerebral pH would be a powerful tool in cancer diagnosis and monitoring, as well as stroke treatment planning. Several pH-based MRI imaging approaches have been proposed but for these to be useful, disentangling the effects of pH from other parameters which may affect the measured MRI signal is crucial to ensure accuracy and specificity. R1 relaxation in the rotating frame (R1ρ) is an example of a method that has been proposed to probe pH in vivo using MRI. In this study, we have investigated the relationship between R1ρ, pH, and macromolecular density in vitro using phantoms and in human volunteers. Here we show that the rate of R1ρ relaxation (=1/T1ρ) varies with pH but only in the presence of macromolecules. At constant pH, phantom macromolecular density inversely correlated with R1ρ. R1ρ imaging of the normal human brain demonstrated regional heterogeneity with significant differences between structurally distinct regions, which are likely to be independent of pH. For example, R1ρ was higher in the basal ganglia compared to grey matter and higher in grey matter compared to white matter. We conclude that R1ρ cannot be reliably used to image tissue pH without deconvolution from the effects of local tissue macromolecular composition.

JOURNAL CLUB: Evaluation of Diffusion Kurtosis Imaging of Stroke Lesion With Hemodynamic and Metabolic MRI in a Rodent Model of Acute Stroke

OBJECTIVE

Diffusion kurtosis imaging (DKI) has emerged as a new acute stroke imaging approach, augmenting routine DWI. Although it has been shown that a diffusion lesion without kurtosis abnormality is more likely to recover after reperfusion, whereas a kurtosis lesion shows poor response, little is known about the underlying pathophysiologic profile of the kurtosis lesion versus the kurtosis lesion-diffusion lesion mismatch.

MATERIALS AND METHODS

We performed multiparametric MRI, including arterial spin labeling, pH-sensitive amide proton transfer, and DKI, in a rodent model of acute stroke caused by embolic middle cerebral artery occlusion. Diffusion and kurtosis lesions were semiautomatically segmented, and multiparametric MRI indexes were compared among the kurtosis lesion, diffusion lesion, kurtosis lesion-diffusion lesion mismatch, and the contralateral normal tissue area.

RESULTS

We confirmed a significant difference between diffusion lesion and kurtosis lesion volumes (mean [± SD] volume, 151 ± 65 vs 125 ± 47 mm³; p < 0.05). Although ischemic lesions have significantly reduced cerebral blood flow compared with contralateral normal tissue, we did not find a significant difference in cerebral blood flow between the kurtosis lesion and the kurtosis lesion-diffusion lesion mismatch (mean cerebral blood flow, 0.53 ± 0.10 vs 0.47 ± 0.14 mL/g of tissue per minute; p > 0.05). Of importance, the pH of the kurtosis lesion was significantly lower than that of the lesion mismatch (mean pH, 6.81 ± 0.08 vs 6.89 ± 0.09; p < 0.01).

CONCLUSION

The present study confirms that DKI provides an expedient approach for refining the heterogeneous DWI lesion that is associated with graded metabolic derangement, which is promising for improving the infarction core definition and ultimately helping to guide stroke treatment.

Assessing Metabolism and Injury in Acute Human Traumatic Brain Injury with Magnetic Resonance Spectroscopy: Current and Future Applications

Traumatic brain injury (TBI) triggers a series of complex pathophysiological processes. These include abnormalities in brain energy metabolism; consequent to reduced tissue pO₂ arising from ischemia or abnormal tissue oxygen diffusion, or due to a failure of mitochondrial function. In vivo magnetic resonance spectroscopy (MRS) allows non-invasive interrogation of brain tissue metabolism in patients with acute brain injury. Nuclei with “spin,” e.g., ¹H, ³¹P, and ¹³C, are detectable using MRS and are found in metabolites at various stages of energy metabolism, possessing unique signatures due to their chemical shift or spin–spin interactions (J-coupling). The most commonly used clinical MRS technique, ¹H MRS, uses the great abundance of hydrogen atoms within molecules in brain tissue. Spectra acquired with longer echo-times include N-acetylaspartate (NAA), creatine, and choline. NAA, a marker of neuronal mitochondrial activity related to adenosine triphosphate (ATP), is reported to be lower in patients with TBI than healthy controls, and the ratio of NAA/creatine at early time points may correlate with clinical outcome. ¹H MRS acquired with shorter echo times produces a more complex spectrum, allowing detection of a wider range of metabolites.³¹ P MRS detects high-energy phosphate species, which are the end products of cellular respiration: ATP and phosphocreatine (PCr). ATP is the principal form of chemical energy in living organisms, and PCr is regarded as a readily mobilized reserve for its replenishment during periods of high utilization. The ratios of high-energy phosphates are thought to represent a balance between energy generation, reserve and use in the brain. In addition, the chemical shift difference between inorganic phosphate and PCr enables calculation of intracellular pH.¹³ C MRS detects the ¹³C isotope of carbon in brain metabolites. As the natural abundance of ¹³C is low (1.1%), ¹³C MRS is typically performed following administration of ¹³C-enriched substrates, which permits tracking of the metabolic fate of the infused ¹³C in the brain over time, and calculation of metabolic rates in a range of biochemical pathways, including glycolysis, the tricarboxylic acid cycle, and glutamate–glutamine cycling. The advent of new hyperpolarization techniques to transiently boost signal in ¹³C-enriched MRS in vivo studies shows promise in this field, and further developments are expected.

Tissue Type-Specific Bioenergetic Abnormalities in Adults with Major Depression

Brain bioenergetic abnormalities have been observed frequently in adults with major depressive disorder (MDD); however, results have been inconsistent regarding whether decreased or increased metabolism was observed. Phosphorus-31 magnetic resonance spectroscopy (31P MRS) allows for the quantification of bioenergetic molecules, containing high-energy phosphates, over the whole brain as well as measuring the differences between gray matter and white matter. We recruited 50 subjects with a current diagnosis of MDD, not currently treated with psychotropic medication, between ages of 18 and 65 (mean±SD age: 43.4±13.6; 46% female) and 30 healthy volunteers, matched for age and gender (39.0±12.5 years of age; 36.6% female). All subjects received a T1 MP-FLASH scan for tissue segmentation followed by 31P MRS, chemical shift imaging scan with 84 voxels of data collected over the entire brain utilizing a dual-tuned, proton-phosphorus coil to minimize subject movement. Phosphocreatine and inorganic phosphate (Pi) varied in opposite directions across gray matter and white matter when MDD subjects were compared with controls. This finding suggests alterations in high-energy phosphate metabolism and regulation of oxidative phosphorylation in MDD patients. In addition, within the MDD group, gray matter Pi, a regulator of oxidative phosphorylation, correlated positively with severity of depression. These data support a model that includes changes in brain bioenergetic function in subjects with major depression.

High-performance radiofrequency coils for (23)Na MRI: brain and musculoskeletal applications

(23)Na RF coil design for brain and MSK applications presents a number of challenges, including poor coil loading for arrays of small coils and SNR penalties associated with providing (1)H capability with the same coil. The basics of RF coil design are described, as well as a review of historical approaches to dual tuning. There follows a review of published high performance coil designs for MSK and brain imaging. Several coil designs have been demonstrated at 7T and 3T which incorporate close-fitting receive arrays and in some cases design features which provide (1)H imaging with little penalty to (23)Na sensitivity. The "nested coplanar loop" approach is examined, in which small transmit-receive (1)H elements are placed within each (23)Na loop, presenting only a small perturbation to (23)Na performance and minimizing RF shielding issues. Other designs incorporating transmit-receive arrays for (23)Na and (1)H are discussed including a 9.4 T (23)Na/(1)H brain coil. Great gains in (23)Na SNR have been made with many of these designs, but simultaneously achieving high performance for 1H remains elusive.

Tissue-dependent cerebral energy metabolism in adolescents with bipolar disorder

OBJECTIVES

To investigate tissue-dependent cerebral energy metabolism by measuring high energy phosphate levels in unmedicated adolescents diagnosed with bipolar I disorder.

METHODS

Phosphorus-31 magnetic resonance spectroscopic imaging data were acquired over the entire brain of 24 adolescents with bipolar I disorder and 19 demographically matched healthy comparison adolescents. Estimates of phosphocreatine (PCr) and adenosine triphosphate (ATP, determined from the γ-resonance) in homogeneous gray and white matter in the right and left hemispheres of the cerebrum of each subject were obtained by extrapolation of linear regression analyses of metabolite concentrations vs. voxel gray matter fractions.

RESULTS

Multivariate analyses of variance showed a significant effect of group on high energy phosphate concentrations in the right cerebrum (p=0.0002) but not in the left (p=0.17). Post-hoc testing in the right cerebrum revealed significantly reduced concentrations of PCr in gray matter and ATP in white matter in both manic (p=0.002 and 0.0001, respectively) and euthymic (p=0.004 and 0.002, respectively) bipolar I disorder subjects relative to healthy comparisons.

LIMITATIONS

The small sample sizes yield relatively low statistical power between manic and euthymic groups; cross-sectional observations limit the ability to determine if these findings are truly independent of mood state.

CONCLUSIONS

Our results suggest bioenergetic impairment - consistent with downregulation of creatine kinase - is an early pathophysiological feature of bipolar I disorder.

Quantification of in vivo ³¹P NMR brain spectra using LCModel

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

Age-dependent decreases of high energy phosphates in cerebral gray matter of patients with bipolar I disorder: a preliminary phosphorus-31 magnetic resonance spectroscopic imaging study

OBJECTIVES

To identify abnormalities in high energy phosphate cerebral metabolism in euthymic bipolar disorder.

METHODS

Phosphorus-31 magnetic resonance spectroscopic imaging ((31)P MRSI) data were acquired from the entire brain of 9 euthymic adults with bipolar disorder and 13 healthy adults. Estimates of phosphocreatine (PCr) and adenosine triphosphate (ATP) in homogeneous gray and white matter were obtained by tissue regression analysis.

RESULTS

Analyses of covariance revealed the effect of age to be significantly different between bipolar and healthy groups for concentrations of PCr (p=0.0018) and ATP (p=0.013) in gray matter. These metabolites were negatively correlated with age in gray matter in bipolar subjects while PCr was positively correlated with age in gray matter of healthy subjects. Additionally, age-corrected concentrations of PCr in gray matter were significantly elevated in bipolar subjects (p=0.0048).

LIMITATIONS

Given that this cross-sectional study possessed a small sample and potentially confounding effects of medication status, we recommend a larger, longitudinal study to more robustly study relationships between bioenergetic impairment and duration of disease.

CONCLUSIONS

Our results suggest bioenergetic impairment related to mitochondrial function may be progressive in multi-episode bipolar subjects as they age.

Gray matter-specific changes in brain bioenergetics after acute sleep deprivation: a 31P magnetic resonance spectroscopy study at 4 Tesla

STUDY OBJECTIVES

A principal function of sleep may be restoration of brain energy metabolism caused by the energetic demands of wakefulness. Because energetic demands in the brain are greater in gray than white matter, this study used linear mixed-effects models to examine tissue-type specific changes in high-energy phosphates derived using 31P magnetic resonance spectroscopy (MRS) after sleep deprivation and recovery sleep.

DESIGN

Experimental laboratory study.

SETTING

Outpatient neuroimaging center at a private psychiatric hospital.

PARTICIPANTS

A total of 32 MRS scans performed in eight healthy individuals (mean age 35 y; range 23-51 y).

INTERVENTIONS

Phosphocreatine (PCr) and β-nucleoside triphosphate (NTP) were measured using 31P MRS three dimensional-chemical shift imaging at high field (4 Tesla) after a baseline night of sleep, acute sleep deprivation (SD), and 2 nights of recovery sleep. Novel linear mixed-effects models were constructed using spectral and tissue segmentation data to examine changes in bioenergetics in gray and white matter.

MEASUREMENTS AND RESULTS

PCr increased in gray matter after 2 nights of recovery sleep relative to SD with no significant changes in white matter. Exploratory analyses also demonstrated that increases in PCr were associated with increases in electroencephalographic slow wave activity during recovery sleep. No significant changes in β-NTP were observed.

CONCLUSIONS

These results demonstrate that sleep deprivation and subsequent recovery-induced changes in high-energy phosphates primarily occur in gray matter, and increases in PCr after recovery sleep may be related to sleep homeostasis.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Tissue-specific differences in brain phosphodiesters in late-life major depression

OBJECTIVE

Late-life depression has been hypothesized to have a neurodegenerative component that leads to impaired executive function and increases in subcortical white matter hyperintensities. Phosphorus magnetic resonance spectroscopy (MRS) can quantify several important phosphorus metabolites in the brain, particularly the anabolic precursors and catabolic metabolites of the constituents of cell membranes, which could be altered by neurodegenerative activity.

METHODS

Ten patients with late-life major depression who were medication free at time of study and 11 aged normal comparison subjects were studied using (31)P MRS three-dimensional chemical shift imaging at 4 Tesla. Phosphatidylcholine and phosphatidylethanolamine comprise 90% of cell membranes in brain but cannot be quantified precisely with (31)P MRS. We measured phosphocholine and phosphoethanolamine, which are anabolic precursors, as well as glycerophosphocholine and glycerophosphoethanolamine, which are catabolic metabolites of phosphatidylcholine and phosphatidylethanolamine.

RESULTS

In accordance with our hypotheses, glycerophosphoethanolamine was elevated in white matter of depressed subjects, suggesting enhanced breakdown of cell membranes in these subjects. Glycerophosphocholine did not show any significant difference between comparison and depressed subjects but both showed an enhancement in white matter compared with gray matter. Contrary to our hypotheses, neither phosphocholine nor phosphoethanolamine showed evidence for reduction in late-life depression.

CONCLUSION

These findings support the hypothesis that neurodegenerative processes occur in white matter in patients with late-life depression more than in the normal elderly population.

Energetic and cell membrane metabolic products in patients with primary insomnia: a 31-phosphorus magnetic resonance spectroscopy study at 4 tesla

STUDY OBJECTIVES

Primary insomnia (PI) is a sleep disorder characterized by difficulty with sleep initiation, maintenance, and/or the experience of nonrestorative sleep combined with a subsequent impairment of daytime functioning. The hyperarousal hypothesis has emerged as the leading candidate to explain insomnia symptoms in the absence of specific mental, physical, or substance-related causes. We hypothesized that the cellular energetic metabolites, including beta nucleoside triphosphate, which in magnetic resonance spectroscopy approximates adenosine triphosphate (ATP), and phosphocreatine (PCr), would show changes in PI reflecting increased energy demand.

DESIGN AND SETTING

Matched-groups, cross-sectional study performed at two university-based hospitals.

PATIENTS

Sixteen medication-free individuals (eight males, eight females; mean ± standard deviation (SD) age = 37.2 ± 8.4 y) with PI and 16 good sleepers (nine males, seven females; mean ± SD age = 37.6 ± 4.7 y).

MEASUREMENTS

Diagnosis was established for all individuals by unstructured clinical interview, Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (SCID), sleep diary, and actigraphy. Polysomnography was collected in individuals with PI. Phosphorous magnetic resonance spectroscopy (31P MRS) data were collected on all individuals at 4 Tesla. We assessed cell membrane (anabolic precursors and catabolic metabolites) and bioenergetic (ATP, phosphocreatine) metabolites in gray matter and white matter to determine their relationship to the presence and severity of PI.

RESULTS

Individuals with PI showed lower phosphocreatine in gray matter and an unexpected decrease of phosphocholine, a precursor of the cell membrane compound phosphatidylcholine, in white matter. In addition, there was a trend toward a negative association between polysomnographically determined wake after sleep onset and gray matter beta-nucleoside triphosphate and white matter phosphocholine in the primary insomnia group.

CONCLUSIONS

These results support the hyperarousal hypothesis in PI based on lower phosphocreatine in gray matter in the PI group.

PCr/ATP ratio mapping of the human head by simultaneously imaging of multiple spectral peaks with interleaved excitations and flexible twisted projection imaging readout trajectories at 9.4 T

Quantitative (31)P magnetic resonance imaging of the whole human brain is often time-consuming even at low spatial resolution due to the low concentrations, long T(1) relaxation times, and low detection sensitivity of phosphorus metabolites. We report herein the results of combining the increased detection sensitivity of an ultra-high field 9.4 T scanner designed for human imaging with a new pulse sequence termed simultaneously imaging of multiple spectral peaks with interleaved excitations and flexible twisted projection imaging readout trajectories to rapidly sample multiple resonances in the (31)P spectrum. The phosphocreatine and γ-adenosine triphosphate images, obtained simultaneously from the entire human head, are demonstrated at 1.5 cm isotropic nominal resolution in a total acquisition time of 33 min. The phosphocreatine/γ-adenosine triphosphate ratio calculated for brain parenchyma (1-2) and the superficial temporalis muscle (3-5) are in agreement with literature values.

Creatine kinase and ATP synthase reaction rates in human frontal lobe measured by ³¹P magnetization transfer spectroscopy at 4T

The human frontal lobe is critical for cognitive function in the healthy brain. Many psychiatric disorders including schizophrenia and bipolar disorder are associated with apparent mitochondrial dysfunction and bioenergetic abnormalities in the frontal lobe. Therefore, measuring cerebral bioenergetics associated with creatine kinase and adenosine triphosphate (ATP) synthase reactions could provide crucial information regarding the underlying molecular mechanisms associated with psychiatric disorders. In this study, the unidirectional forward chemical exchange metabolic fluxes of creatine kinase and ATP synthase reactions as well as reverse chemical exchange metabolic flux associated with ATP hydrolysis were determined at 4T by (31)P magnetization transfer. The current experiments indicate that the kinetic network of PCr↔ATP↔Pi can be measured reliably in the human frontal lobe at 4T, which will enable detailed in vivo characterization of bioenergetic abnormalities in a variety of neuropsychiatric disorders.

Prevalence and progression of basal ganglia calcification and its pathogenic mechanism in patients with idiopathic hypoparathyroidism

BACKGROUND

The pathogenesis of basal ganglia calcification (BGC) in hypoparathyroidism is not clear. Its occurrence in hypocalcaemic milieu of hypoparathyroidism is believed to be due to high serum calcium-phosphorus product and poor calcium control.

OBJECTIVE

To report details of BGC in patients with idiopathic hypoparathyroidism (IH) and factors determining its progression during follow-up.

METHOD

Clinical, biochemical characteristics and a meningioma-expressed antigen-6 (MGEA6) gene polymorphism were analysed in 145 patients with IH, recruited since 1998, to determine the factors associated with BGC. The progression of BGC and its relationship with metabolic control of serum calcium, phosphorus, serum 25(OH)D and 1,25(OH)(2) D were assessed after a mean of 6·9 ± 3·5 years in 49 of them.

RESULTS

Basal ganglia calcification was present in 73·8% (95% CI: 66·6%-81·0%) of subjects affecting the globus pallidus (68·8%) putamen (55·9%) and caudate nucleus (54·8%). The other sites calcified were grey-white junction (39·8%), cerebellar parenchyma (31·2%), thalamus (29·0%) and dentate nuclei (24·7%). Parkinsonism and dystonic symptoms were present in three cases. The presence of BGC at presentation was associated with calcification of the choroid plexus, cataract and an increased risk of seizures but not tetany. The progression of BGC during follow-up was related to calcium/phosphorus ratio. For every 1% increase in this ratio, the odds of progression decreased by 5% (OR: 0·95, 95% CI: 0·93-0·99, P < 0·001). A MGEA6 polymorphism, serum 25(OH)D and 1,25(OH)(2)D did not affect progression of BGC.

CONCLUSION

Basal ganglia calcification occurs in 73·8% of patients with IH and correlates with the duration of hypocalcaemia, choroid plexus calcification, seizures and cataract. The progression of BGC is related to the calcium/phosphorus ratio during follow-up. This brings forth the importance of adequate phosphorus control in the management of hypoparathyroidism.

Phosphorus magnetic resonance spectroscopy in malformations of cortical development

PURPOSE

The aim of this study was to evaluate phospholipid metabolism in patients with malformations of cortical development (MCDs).

METHODS

Thirty-seven patients with MCDs and 31 control subjects were studied using three-dimensional phosphorus magnetic resonance spectroscopy ((31)P-MRS) at 3.0 T. The voxels in the lesions and in the frontoparietal cortex of the control subjects were compared (the effective volumes were 12.5 cm(3)). Robust quantification methods were applied to fit the time-domain data to the following resonances: phosphoethanolamine (PE); phosphocholine (PC); inorganic phosphate (Pi); glycerophosphoethanolamine (GPE); glycerophosphocholine (GPC); phosphocreatine (PCr); and α-, β-, and γ-adenosine triphosphate (ATP). We also estimated the total ATP (ATP(t) = α-+β-+γ-ATP), phosphodiesters (PDE = GPC+GPE), phosphomonoesters (PME = PE+PC), and the PME/PDE, PCr/ATP(t) and PCr/Pi ratios. The magnesium (Mg(2+)) levels and pH values were calculated based on PCr, Pi, and β-ATP chemical shifts.

KEY FINDINGS

Compared to controls and assuming that a p-value < 0.05 indicates statistical significance, the patients with MCDs exhibited significantly lower pH values and higher Mg(2+) levels. In addition, the patients with MCDs had lower GPC and PDE and an increased PME/PDE ratio.

SIGNIFICANCE

Mg(2+) and pH are important in the regulation of bioenergetics and are involved in many electrical activity pathways in the brain. Our data support the idea that neurometabolic impairments occur during seizure onset and propagation. The GPC, PDE, and PME/PDE abnormalities also demonstrate that there are membrane turnover disturbances in patients with MCDs.

Age-related changes in brain energetics and phospholipid metabolism

Evidence suggests that mitochondria undergo functional and morphological changes with age. This study aimed to investigate the relationship of brain energy metabolism to healthy aging by assessing tissue specific differences in metabolites observable by phosphorus ((31)P) MRS. (31)P MRSI at 4 Tesla (T) was performed on 34 volunteers, aged 21-84, screened to exclude serious medical and psychiatric diagnoses. Linear mixed effects models were used to analyze the effects of age on phosphorus metabolite concentrations, intracellular magnesium and pH estimates in brain tissue. A significant age associated decrease in brain pH (-0.53% per decade), increase in PCr (1.1% per decade) and decrease in PME (1.7% per decade) were found in total tissue, with PCr effects localized to the gray matter. An increase in beta NTP as a function of age (1% per decade) approached significance (p = 0.052). There were no effects demonstrated with increasing age for intracellular magnesium, PDE or inorganic phosphate. This study reports the effects of healthy aging on brain chemistry in the gray matter versus white matter using (31)P MRS measures of high energy phosphates, pH and membrane metabolism. Increased PCr, increased beta NTP (reflecting ATP) and reduced pH may reflect altered energy production with healthy aging. Unlike some previous studies of aging and brain chemistry, this study examined healthy, non-demented and psychiatrically stable older adults and specifically analyzed gray-white matter differences in brain metabolism.

31Phosphorus magnetic resonance spectroscopy study of tissue specific changes in high energy phosphates before and after sertraline treatment of geriatric depression

INTRODUCTION

We investigated tissue specific differences in markers of energy metabolism, including high energy phosphate compounds (beta and total NTP, PCr) and pH, in older adults with depression compared with healthy controls, before and after a 12-week treatment trial of sertraline.

METHODS

Thirteen older adults, age > or =55, with Major Depressive Disorder (HAMD(17) score of > or =18) were recruited along with ten age-matched controls. The depression subjects had a pre- and post-treatment 4T (31)P-MRS scan using a three-dimensional chemical shift imaging sequence. The extracted brain images were segmented into white matter (WM), gray matter (GM) and CSF. A linear mixed effects model analyzed the effects of pre-treatment and post-treatment depression on phosphorus metabolite concentration estimates (including calculated pH and Mg(++)).

RESULTS

Total tissue beta-NTP (-8%, t(18.66) = 3.50; p = 0.0024) and total tissue total NTP (-6%, t(17.41) = 2.68; p = 0.0156) were lower in subjects with geriatric depression compared with healthy controls. Total tissue levels of total-NTP changed significantly with treatment (-2%, t(14.84) = -2.47; p = 0.0259). Total NTP was reduced in the WM, but not the GM, in the pre-treatment depression group (t(51.65) = 4.02; p = 0.0002). Intracellular pH was higher in the GM of subjects with pre-treatment depression (t(1133.84) = -2.10; p = 0.0353) and decreased to approximate control levels after treatment (t(648.86) = -2.53; p = 0.0115).

DISCUSSION

These findings demonstrate bioenergetic changes including tissue specific differences in (31)P-MRS metabolites in geriatric depression. Decreased white matter total NTP may reflect alterations in white matter function.

Citicoline enhances frontal lobe bioenergetics as measured by phosphorus magnetic resonance spectroscopy

Citicoline supplementation has been used to ameliorate memory disturbances in older people and those with Alzheimer's disease. This study used MRS to characterize the effects of citicoline on high-energy phosphate metabolites and constituents of membrane synthesis in the frontal lobe. Phosphorus ((31)P) metabolite data were acquired using a three-dimensional chemical-shift imaging protocol at 4 T from 16 healthy men and women (mean +/- SD age 47.3 +/- 5.4 years) who orally self-administered 500 mg or 2000 mg Cognizin Citicoline (Kyowa Hakko Kogyo Co., Ltd, Ibaraki, Japan) for 6 weeks. Individual (31)P metabolites were quantified in the frontal lobe (anterior cingulate cortex) and a comparison region (parieto-occipital cortex). Significant increases in phosphocreatine (+7%), beta-nucleoside triphosphates (largely ATP in brain, +14%) and the ratio of phosphocreatine to inorganic phosphate (+32%), as well as significant changes in membrane phospholipids, were observed in the anterior cingulate cortex after 6 weeks of citicoline treatment. These treatment-related alterations in phosphorus metabolites were not only regionally specific, but tended to be of greater magnitude in subjects who received the lower dose. These data show that citicoline improves frontal lobe bioenergetics and alters phospholipid membrane turnover. Citicoline supplementation may therefore help to mitigate cognitive declines associated with aging by increasing energy reserves and utilization, as well as increasing the amount of essential phospholipid membrane components needed to synthesize and maintain cell membranes.

Grey and white matter differences in brain energy metabolism in first episode schizophrenia: 31P-MRS chemical shift imaging at 4 Tesla

Altered high energy and membrane metabolism, measured with phosphorus magnetic resonance spectroscopy (31P-MRS), has been inconsistently reported in schizophrenic patients in several anatomical brain regions implicated in the pathophysiology of this illness, with little attention to the effects of brain tissue type on the results. Tissue regression analysis correlates brain tissue type to measured metabolite levels, allowing for the extraction of "pure" estimated grey and white matter compartment metabolite levels. We use this tissue analysis technique on a clinical dataset of first episode schizophrenic patients and matched controls to investigate the effect of brain tissue specificity on altered energy and membrane metabolism. In vivo brain spectra from two regions, (a) the fronto-temporal-striatal region and (b) the frontal-lobes, were analyzed from 12 first episode schizophrenic patients and 11 matched controls from a (31)P chemical shift imaging (CSI) study at 4 Tesla (T) field strength. Tissue regression analyses using voxels from each region were performed relating metabolite levels to tissue content, examining phosphorus metabolite levels in grey and white matter compartments. Compared with controls, the first episode schizophrenic patient group showed significantly increased adenosine triphosphate levels (B-ATP) in white matter and decreased B-ATP levels in grey matter in the fronto-temporal-striatal region. No significant metabolite level differences were found in grey or white matter compartments in the frontal cortex. Tissue regression analysis reveals grey and white matter specific aberrations in high-energy phosphates in first episode schizophrenia. Although past studies report inconsistent regional differences in high-energy phosphate levels in schizophrenia, the present analysis suggests more widespread differences that seem to be strongly related to tissue type. Our data suggest that differences in grey and white matter tissue content between past studies may account for some of the variance in the literature.

Graded image segmentation of brain tissue in the presence of inhomogeneous radio frequency fields

Image segmentation is used increasingly to interpret MR spectroscopic data of the brain, using image contrast to identify gray matter (GM), white matter (WM), and cerebral spinal fluid (CSF). T(1)- or T(2)-weighted images are typically used, but poor shimming, susceptibility effects, and small variations in B(1) and receptivity cause difficulties in tissue identification. Quantitative imaging of T(1) can reduce many of these difficulties but is still subject to complications when B(1) has large variations like those observed with the surface coils often used for spectroscopy. In this study, B(1) imaging was implemented to support quantitative imaging of T(1) with either a surface coil or a volume coil. The T(1) observed by this method is a continuous function across mixtures of WM/GM and GM/CSF, and this function was measured and used to convert the images of T(1) to maps of percent GM, WM, and CSF.

Adenosine in relation to calcium homeostasis: comparison between gray and white matter ischemia

In vitro studies suggest that adenosine may attenuate anoxic white matter damage as an intrinsic protective substance. The authors investigated ischemic alterations of purines in relation to tissue depolarization and extracellular calcium and amino acid concentrations in vivo using microdialysis and ion-selective electrodes in cortical gray and subcortical white matter of 10 cats during 120 minutes of global brain ischemia. Immediately on induction of ischemia, regional cerebral blood flow ceased in all cats in both gray and white matter. The direct current potential rapidly decreased, the decline being slower and shallower in white matter. Extracellular calcium levels decreased in gray matter. In contrast, they first increased in white matter and started to decrease below control levels only after approximately 30 minutes. Adenosine levels transiently increased in both tissue compartments; the peak was delayed by 30 minutes in white matter. Thereafter, levels declined faster in gray than in white matter and remained elevated in the latter tissue compartment. Inosine and hypoxanthine elevations were progressive in both regions but smaller in white matter. Levels of gamma-aminobutyric acid, another putatively protective agent, steadily increased, starting immediately in gray matter and delayed by almost 1 hour in white matter. The delayed and prolonged accumulation of adenosine correlates with a slower adenosine triphosphate breakdown in white matter ischemia and may result in protection of white matter by suspending cellular calcium influx.

Quantitation of localized (31)P magnetic resonance spectra based on the reciprocity principle

There is a need for absolute quantitation methods in (31)P magnetic resonance spectroscopy, because none of the phosphorous-containing metabolites is necessarily constant in pathology. Here, a method for absolute quantitation of in vivo (31)P MR spectra that provides reproducible metabolite contents in institutional or standard units is described. It relies on the reciprocity principle, i.e., the proportionality between the B(1) field map and the map of reception strength for a coil with identical relative current distributions in receive and transmit mode. Cerebral tissue contents of (31)P metabolites were determined in a predominantly white matter-containing location in healthy subjects. The results are in good agreement with the literature and the interexamination coefficient of variance is better than that in most previous studies. A gender difference found for some of the (31)P metabolites may be explained by different voxel composition.

Quantitative (31)P spectroscopic imaging of human brain at 4 Tesla: assessment of gray and white matter differences of phosphocreatine and ATP

This report describes the implementation and application of a multicompartment analysis of (31)P spectroscopic imaging data to determine the tissue-specific heterogeneities in metabolite content in the human brain and surrounding tissue. Using this information and a multicompartment regression analysis the phosphocreatine and ATP content of "pure" cerebral gray and white matter, the cerebellum, and skeletal muscle was determined in a group of 10 healthy volunteers. The data were converted to mM units using previously reported values for the T(1)s of phosphocreatine and ATP at 4 T, the water content of human brain, and an external reference for absolute quantification. The phosphocreatine concentration in cerebral gray and white matter, the cerebellum, and skeletal muscle was 3.53 +/- 0.33, 3.33 +/- 0.37, 3.75 +/- 0.66, and 25.8 +/- 2.3 mM, respectively. The ATP concentration in cerebral gray and white matter, the cerebellum, and skeletal muscle was 2.19 +/- 0.33, 3.41 +/- 0.33, 1.75 +/- 0.58, and 8.5 +/- 1.9 mM, respectively. Magn Reson Med 45:46-52, 2001.

Quantitative analysis of short echo time (1)H-MRSI of cerebral gray and white matter

Quantitative analysis of (1)H-magnetic resonance spectroscopic imaging (MRSI) data was developed using the user-independent spectral analysis routine LCModel. Tissue segmentation was performed using statistical parametric mapping software (SPM 96), and the results were used to correct for cerebrospinal fluid contamination. A correction was developed for the imperfections in the spectroscopic excitation profile in order to improve the uniformity of metabolite images. After validation in phantoms, these techniques were applied to study differences in metabolite concentrations between gray and white matter in normal volunteers (n = 13). A positive correlation was found between concentration and gray matter content for most metabolites studied. The estimated ratios of metabolite concentration in gray vs. white matter were: N-acetyl aspartate + N-acetyl aspartyl glutamate (NAc) = 1.16+/- 0.11; creatine = 1.7+/-0.3; glutamate + glutamine = 2.4+/-0.5; myo-inositol = 1.6+/-0.3; choline = 0.9+/-0.2. The ratio of NAc/Cr was negatively correlated with gray matter content: gray/white = 0.69 +/-0.08. These methods will be useful in the evaluation of metabolite concentrations in MRSI voxels with mixed tissue composition in patient groups.

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.

Optimal voxel size for measuring global gray and white matter proton metabolite concentrations using chemical shift imaging

Quantification of gray and white matter levels of spectroscopically visible metabolites can provide important insights into brain development and pathological conditions. Chemical shift imaging offers a gain in efficiency for estimation of global gray and white matter metabolite concentrations compared to single voxel methods. In the present study, the optimal voxel size is calculated from segmented human brain data and accompanying field maps. The optimal voxel size is found to be approximately 8 cc, but a wide range of values, 4-64 cc, can be chosen with little increase in estimated concentration error (<15%). Magn Reson Med 44:10-18, 2000.

Administration and (1)H MRS detection of histidine in human brain: application to in vivo pH measurement

Measurement of histidine in vivo offers the potential for tissue pH measurement using routinely performed (1)H MR spectroscopy. In the brain, however, histidine concentrations are generally too low for reliable measurement. By using oral loading of histidine, this study demonstrates that brain concentrations can be significantly increased, enabling detection of histidine by localized (1)H MR measurements and making in vivo pH measurement possible. In studies carried out on healthy human subjects at 1.5 T, a consistent spectral quality downfield from water was achieved using a PRESS sequence at short echo times. Measurements at different TE values helped to characterize the downfield spectral region. Histidine loading of 400 mg/kg of body weight increased brain histidine levels by approximately 0.8 mM, with maximum histidine concentration reached 4 to 7 hr after consumption. The pH calculated from histidine resonances was 6.96, and a hyperventilation study demonstrated the potential for measuring altered pH.

In vivo development of brain phosphocreatine in normal and creatine-treated rabbit pups

To study the effects of creatine (Cr) on brain energy metabolism and on hypoxia-induced seizures, 5- to 30-day-old rabbit pups were given subcutaneous Cr (3 g/kg) for 3 days before exposure to 4% O2 for 8 min. In saline-treated controls, hypoxic seizures were most frequent at 15 days (80% of pups) and 20 days (60%) of age. Seizures were prevented at 15 days and reduced 60% at 20 days in Cr-treated pups. In surface coil-localized brain 31P nuclear magnetic resonance spectra, with signal from both cerebral gray (GM) and white (WM) matter, the phosphocreatine (PCr)/nucleoside triphosphate (NTP) ratio doubled between 5 and 30 days of age in controls. In all Cr-injected pups, brain PCr/NTP increased to values seen in 30-day-old controls. When spectra were acquired in predominantly GM and WM slices in vivo, the PCr/NTP ratio was very low in GM at 5 days but reached adult levels by 15 days in controls. In WM, the ratio increased steadily from 5 to 30 days of age. In Cr-injected pups, PCr/NTP increased to mature levels in WM and in GM at all ages. In conclusion, hypoxic seizures occur midway in the time course of brain PCr/NTP increase in rabbit pups as previously described in rat pups. In both altricial pups, systemic Cr increases brain PCr/NTP ratio and prevents hypoxic seizures. These results suggest that mature levels of PCr and/or Cr in brain limit EEG activation either directly or indirectly by preventing hypoxic metabolic changes.

Measurement of the tricarboxylic acid cycle rate in human grey and white matter in vivo by 1H-[13C] magnetic resonance spectroscopy at 4.1T

13C isotopic labeling data were obtained by 1H-observed/13C-edited magnetic resonance spectroscopy in the human brain in vivo and analyzed using a mathematical model to determine metabolic rates in human grey matter and white matter. 22.5-cc and 56-cc voxels were examined for grey matter and white matter, respectively. When partial volume effects were ignored, the measured tricarboxylic acid cycle rate was 0.72+/-0.22 (mean +/- SD) and 0.29+/-0.09 micromol min(-1) g(-1) (mean +/- SD) in voxels of approximately 70% grey and approximately 70% white matter, respectively. After correction for partial volume effects using a model with two tissue compartments, the tricarboxylic acid cycle rate in pure grey matter was higher (0.80+/-0.10 mol min(-1) g(-1); mean +/- SD) and in white matter was significantly lower (0.17+/-0.01 micromol min(-1) g(-1); mean +/- SD). In 1H-observed/13C-edited magnetic resonance spectroscopy labeling studies, the larger concentrations of labeled metabolites and faster metabolic rates in grey matter biased the measurements heavily toward grey matter, with labeling time courses in 70% grey matter appearing nearly identical to labeling in pure grey matter.

Ketosis and epilepsy: 31P spectroscopic imaging at 4.1 T

PURPOSE

To determine whether changes in the high-energy phosphates occur with use of the ketogenic diet in patients with intractable epilepsy.

METHODS

31P magnetic resonance spectroscopic imaging studies were performed at 4.1 T in seven patients with intractable epilepsy (four Lennox-Gastaut syndrome, one absence, one primary generalized tonic-clonic, and one partial complex) before and after institution of the ketogenic diet. Coronal 1H anatomic imaging also was performed to provide correlation to the 31P data.

RESULTS

Taking the patients as a group, the ratio of phosphocreatine (PC)/gamma-adenosine triphosphate (ATP) measured at baseline (regular diet) compared with that measured after the ketogenic diet showed a small but significant increase from 0.61+/-0.08 to 0.69+/-0.08 (p < 0.05). Comparing the ratio of PCr inorganic phosphorus (Pi) measured at baseline with the postketogenic diet, there was a significant increase from 2.45+/-0.27 to 2.99+/-0.44 (p < 0.05).

CONCLUSIONS

As a group, improvement of energy metabolism occurs with use of the ketogenic diet. This is in agreement with the chronic ketosis studies performed earlier in rodents.

GABA changes with vigabatrin in the developing human brain

PURPOSE

Changes in gamma-aminobutyric acid (GABA) physiology are important in determining seizure susceptibility in the developing nervous system. Noninvasive measurements of brain GABA in adults with epilepsy have demonstrated important relations among seizure control, brain GABA levels, and changes in brain GABA with drugs designed to alter GABA metabolism. The purpose of this study was to demonstrate the changes in GABA in the occipital lobes of children with epilepsy after treatment with vigabatrin (VGB).

METHODS

Ten proton nuclear magnetic resonance spectroscopic (NMRS) studies were obtained on four subjects with epilepsy. The subjects were between ages 1 and 5 years. Occipital lobe GABA levels were measured before and after treatment with VGB.

RESULTS

Brain GABA levels increased significantly in these subjects after VGB treatment (p < 0.05, paired Student's t test). In one subject, brain GABA was decreased in the region of the epileptic focus compared with the homologous region of the opposite hemisphere. A nearly fivefold increase in GABA occurred in the epileptic region after VGB treatment in this subject.

CONCLUSIONS

VGB increases brain GABA levels in children with epilepsy. NMRS can be used to monitor the response of brain GABA levels to drugs known to alter GABA physiology and serve as an important tool to understand the role of GABA-mediated inhibition in pediatric epilepsies.

Magnesium and pH imaging of the human brain at 3.0 Tesla

Multislice, two-dimensional phosphorus 31 spectroscopic imaging (SI) of human brain was performed in 15 normal volunteers on a 3-Tesla magnetic resonance system. Images of free magnesium concentrations and pH as well as phosphoesters, inorganic phosphate, phosphocreatine, and adenosine triphosphate (ATP), were calculated from the SI data. By using the equations of Golding and Golding (Magn. Reson. Med. 1995;33: 467-474), average [Mg2+] for all brain regions studied was 0.42+/-0.05 mM, whereas average brain pH was found to be 7.07+/-0.03, with no significant regional variations. Phosphorus metabolite concentrations (relative to ATP, assumed to be 3.0 mM/kg wet weight)were 5.39+/-1.88, 1.30+/-0.39, 5.97+/-3.17, and 4.33+/-1.45 mM/kg wet weight for phosphomonoesters, inorganic phosphate, phosphodiesters, and phosphocreatine (PCr), respectively. These values are in good general agreement with those reported previously. Typical signal-to-noise ratios of 15:1 were obtained for PCr in spectra from nominal 31.5 cc voxel sizes with a 34-min scan time. Limits on spatial resolution and the likely error of the magnesium and pH values are discussed.