Detection of cancer in cervical tissue biopsies using mobile lipid resonances measured with diffusion‐weighted 1H magnetic resonance spectroscopy

The purpose of this study was to implement a diffusion‐weighted sequence for visualisation of mobile lipid resonances (MLR) using high resolution magic angle spinning (HR‐MAS) ¹H MRS and to evaluate its use in establishing differences between tissues from patients with cervical carcinoma that contain cancer from those that do not. A stimulated echo sequence with bipolar gradients was modified to allow T₁ and T₂ measurements and optimised by recording signal loss in HR‐MAS spectra as a function of gradient strength in model lipids and tissues. Diffusion coefficients, T₁ and apparent T₂ relaxation times were measured in model lipid systems. MLR profiles were characterised in relation to T₁ and apparent T₂ relaxation in human cervical cancer tissue samples. Diffusion‐weighted (DW) spectra of cervical biopsies were quantified and peak areas analysed using linear discriminant analysis (LDA). The optimised sequence reduced spectral overlap by suppressing signals originating from low molecular weight metabolites and non‐lipid contributions. Significantly improved MLR visualisation allowed visualisation of peaks at 0.9, 1.3, 1.6, 2.0, 2.3, 2.8, 4.3 and 5.3 ppm. MLR analysis of DW spectra showed at least six peaks arising from saturated and unsaturated lipids and those arising from triglycerides. Significant differences in samples containing histologically confirmed cancer were seen for peaks at 0.9 (p < 0.006), 1.3 (p < 0.04), 2.0 (p < 0.03), 2.8 (p < 0.003) and 4.3 ppm (p < 0.0002). LDA analysis of MLR peaks from DW spectra almost completely separated two clusters of cervical biopsies (cancer, ‘no‐cancer’), reflecting underlying differences in MLR composition. Generated Receiver Operating Characteristic (ROC) curves and calculated area under the curve (0.962) validated high sensitivity and specificity of the technique. Diffusion‐weighting of HR‐MAS spectroscopic sequences is a useful method for characterising MLR in cancer tissues and displays an accumulation of lipids arising during tumourigenesis and an increase in the unsaturated lipid and triglyceride peaks with respect to saturated MLR. Copyright © 2009 John Wiley & Sons, Ltd.     

Brain GABA editing by localized in vivo (1)H magnetic resonance spectroscopy

Editing of GABA by (1)H MRS in a specific brain area is a unique tool for in vivo non-invasive investigation of neurotransmission disorders. Selective GABA detection is achieved using sequences based on double quantum coherence (DQC). Our pulse sequence makes accurate measurements without artefacts due to spatial localization. The sequence was tested on a phantom solution. The effect of vigabatrin, a specific inhibitor of GABA transaminase, was measured in rat brain and GABA detection was performed in vivo in monkey brain using this procedure. Rats were split into two groups. In the control group, the rats had access to water and, in the other group (vigabatrin, VGB, rats), animals were allowed free access to drinking water containing vigabatrin. After 3 weeks of treatment, rats were anesthetized for in vivo NMR spectroscopy investigation. At the end of the experiment, brains were quickly removed, freeze-clamped and extracted with 4% perchloric acid. One part of the acid extract was used for GABA concentrations assessment by ion exchange chromatography with ninhydrin detection. The second was used for high-resolution NMR analysis. By chromatography measurements, the GABA concentration was 1.23+/-0.06 micromol/g for controls, while for vigabatrin-treated rats the GABA concentration was 4.89+/-1.60 micromol/g. The NMR in vivo results were closely correlated with the NMR ex vivo (r=0.99, p<0.01) and chromatography results (r=0.98, p<0.01). The correlation between ex vivo results and chromatography results was also high (r=0.99, p<0.001). This pulse sequence performed GABA editing from a 376 microl voxel located on the right basal ganglia area in a non-human primate brain. This in vivo GABA editing scheme can thus be proposed for accurate measurement of brain GABA concentrations.     

Metabolic profile of the hippocampus of Zucker Diabetic Fatty rats assessed by in vivo 1H magnetic resonance spectroscopy

Localized in vivo 1H magnetic resonance spectroscopy (MRS) was used to investigate metabolite levels in the brain of adult Zucker Diabetic Fatty (ZDF) rats, an animal model for type 2 diabetes mellitus. This study focussed on the hippocampus, assumed to be one of the main brain areas affected by this disease. Together with an almost 5-fold increase in blood glucose concentration measured by glucose oxidation, significant increases were found in the hippocampal concentrations of glucose (4.93 vs 1.66 mM p < 0.001), myo-inositol (6.52 vs 4.30 mM; p < 0.05), and total creatine (12.71 vs 10.50 mM; p < 0.05) in ZDF rats (n = 5) compared with littermates (n = 5). Although no obvious alterations were detected in the hippocampal levels of other metabolites, including NAA + NAAG and choline-containing compounds in the ZDF rats, the increase in Glc and Ins levels is in line with elevated brain tissue contents of these metabolites in patients with diabetes mellitus.     

The interaction between apparent diffusion coefficients and transverse relaxation rates of human brain metabolites and water studied by diffusion‐weighted spectroscopy at 7 T

The dependence of apparent diffusion coefficients (ADCs) of molecules in biological tissues on an acquisition‐specific timescale is a powerful mechanism for studying tissue microstructure. Unlike water, metabolites are confined mainly to intracellular compartments, thus providing higher specificity to tissue microstructure. Compartment‐specific structural and chemical properties may also affect molecule transverse relaxation times (T₂). Here, we investigated the correlation between diffusion and relaxation for N‐acetylaspartate, creatine and choline compounds in human brain white matter in vivo at 7 T, and compared them with those of water under the same experimental conditions. Data were acquired in a volume of interest in parietal white matter at two different diffusion times, Δ = 44 and 246 ms, using a matrix of three echo times (T_E) and five diffusion weighting values (up to 4575 s/mm²). Significant differences in the dependence of the ADCs on T_E were found between water and metabolites, as well as among the different metabolites. A significant decrease in water ADC as a function of T_E was observed only at the longest diffusion time (p < 0.001), supporting the hypothesis that at least part of the restricted water pool can be associated with longer T₂, as suggested by previous studies in vitro. Metabolite data showed an increase of creatine (p < 0.05) and N‐acetylaspartate (p < 0.05) ADCs with T_E at Δ = 44 ms, and a decrease of creatine (p < 0.05) and N‐acetylaspartate (p = 0.1) ADCs with T_E at Δ = 246 ms. No dependence of choline ADC on T_E was observed. The metabolite results suggest that diffusion and relaxation properties are dictated not only by metabolite distribution in different cell types, but also by other mechanisms, such as interactions with membranes, exchange between “free” and “bound” states or interactions with microsusceptibility gradients. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterisation of in vivo ovarian cancer models by quantitative 1H magnetic resonance spectroscopy and diffusion-weighted imaging

Magnetic resonance imaging (MRI) and spectroscopy (MRS) offer powerful approaches for detecting physiological and metabolic alterations in malignancies and help investigate underlying molecular mechanisms. Research on epithelial ovarian carcinoma (EOC), the gynaecological malignancy with the highest death rate characterised by frequent relapse and onset of drug resistance, could benefit from application of these molecular imaging approaches. In this study, MRI/MRS were used to characterise solid tumour models obtained by subcutaneous (s.c.) or intraperitoneal (i.p.) implantation of human SKOV3.ip cells in severe combined immunodeficiency (SCID) mice. In vivo MRI/MRS, ex vivo magic-angle-spinning (MAS), and in vitro (1)H-NMR measurements were carried out at 4.7 T, 9.4 T, and 9.4/16.5 T, respectively. MRI evaluation was performed by T1-, T2-, and diffusion-weighted (DW) multislice spin-echo imaging. The in vivo (1)H spectra of all tumour models showed a prominent resonance of total choline-containing metabolites (tCho). Quantitative in vivo MRS of both i.p. and s.c. SKOV3.ip xenografts showed that the mean tCho content was in the 2.9-4.5 mM range, with a mean PCho/tCho ratio of 0.99 ± 0.01 [23 examinations, 14-34 days post injection (dpi)], in good agreement with ex vivo and in vitro analyses. Myo-inositol ranged between 11.7 and 17.0 mM, with a trend towards higher values in i.p. xenografts at 14-16 dpi. The average apparent diffusion coefficient (ADC) values of SKOV3.ip xenografts [1.64 ± 0.11 (n = 9, i.p.) and 1.58 ± 0.03 x10(-3) mm(2)/s (n = 7, s.c.)] were in agreement with values reported for tumours from patients with EOC, while the mean vascular signal fraction (VSF) was lower (≤ 4%), probably due to the more rapid growth of preclinical models. Both s.c. and i.p. xenografts are valuable preclinical models for monitoring biochemical and physiopathological changes associated with in vivo EOC tumour growth and response to therapy, which may serve as the basis for further clinical development of noninvasive MR approaches.     

Non‐invasive diagnosis and metabolic consequences of congenital portosystemic shunts in C57BL/6 J mice

This study demonstrates the suitability of magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) for the imaging of congenital portosystemic shunts (PSS) in mice, a vascular abnormality in which mesenteric blood bypasses the liver and is instead drained directly to the systemic circulation. The non‐invasive diagnosis performed in tandem with other experimental assessments permits further characterization of liver, whole‐body and brain metabolic defects associated with PSS. Magnetic resonance measurements were performed in a 26‐cm, horizontal‐bore, 14.1‐T magnet. MRA was obtained with a three‐dimensional gradient echo sequence (GRE; in‐plane resolution, 234 × 250 × 234 μm³) using a birdcage coil. Two‐dimensional GRE MRI with high spatial resolution (in‐plane resolution, 100 × 130 μm²; slices, 30 × 0.3 mm) was performed using a surface coil. Brain‐ (dorsal hippocampus) and liver‐localized ¹H magnetic resonance spectroscopy (MRS) was also performed with the surface coil. Whole‐body metabolic status was evaluated with an oral glucose tolerance test (OGTT). Both MRA and anatomical MRI allowed the identification of hepatic vessels and the diagnosis of PSS in mice. The incidence of PSS was about 10%. Hepatic lipid content was higher in PSS than in control mice (5.1 ± 2.8% versus 1.8 ± 0.6%, p = 0.02). PSS mice had higher brain glutamine concentration than controls (7.3 ± 1.0 μmol/g versus 2.7 ± 0.6 μmol/g, p < 0.0001) and, conversely, lower myo‐inositol (4.2 ± 0.6 μmol/g versus 6.0 ± 0.4 μmol/g, p < 0.0001), taurine (9.7 ± 1.2 μmol/g versus 11.0 ± 0.4 μmol/g, p < 0.01) and total choline (0.9 ± 0.1 μmol/g versus 1.2 ± 0.1 μmol/g, p < 0.001) concentrations. Fasting blood glucose and plasma insulin were lower in PSS than in control mice (4.7 ± 0.5mM versus 8.8 ± 0.6mM, p < 0.0001; and 0.04 ± 0.03 μg/L versus 0.3 ± 0.2 μg/L, p = 0.02, respectively). Glucose clearance during OGTT was delayed and less efficient in PSS mice than in controls. Thus, given the non‐negligible incidence of PSS in inbred mice, the undiagnosed presence of PSS will, importantly, have an impact on experimental outcomes, notably in studies addressing brain, liver or whole‐body metabolism.     

Pitfalls and advantages of different strategies for the absolute quantification of N‐acetyl aspartate,creatine and choline in white and grey matter by 1H‐MRS

This study extensively investigates different strategies for the absolute quantitation of N‐acetyl aspartate, creatine and choline in white and grey matter by ¹H‐MRS at 1.5 T. The main focus of this study was to reliably estimate metabolite concentrations while reducing the scan time, which remains as one of the main problems in clinical MRS. Absolute quantitation was based on the water‐unsuppressed concentration as the internal standard. We compared strategies based on various experimental protocols and post‐processing strategies. Data were obtained from 30 control subjects using a PRESS sequence at several TE to estimate the transverse relaxation time, T₂, of the metabolites. Quantitation was performed with the algorithm QUEST using two different metabolite signal basis sets: a whole‐metabolite basis set (WhoM) and a basis set in which the singlet signals were split from the coupled signals (MSM). The basis sets were simulated in vivo for each TE used. Metabolites' T₂s were then determined by fitting the estimated signal amplitudes of the metabolites obtained at different TEs. Then the absolute concentrations (mM) of the metabolites were assessed for each subject using the estimated signal amplitudes and either the mean estimated relaxation times of all subjects (mean protocol, MP) or the T₂ estimated from the spectra derived from the same subject (individual protocol, IP). Results showed that MP represents a less time‐consuming alternative to IP in the quantitation of brain metabolites by ¹H‐MRS in both grey and white matter, with a comparable accuracy when performed by MSM. It was also shown that the acquisition time might be further reduced by using a variant of MP, although with reduced accuracy. In this variant, only one water‐suppressed and one water‐unsuppressed spectra were acquired, drastically reducing the duration of the entire MRS examination. However, statistical analysis highlights the reduced accuracy of MP when performed using WhoM, particularly at longer echo times. Copyright © 2009 John Wiley & Sons, Ltd.     

Monitoring of gliomas in vivo by diffusion MRI and 1H MRS during gene therapy‐induced apoptosis: interrelationships between water diffusion and mobile lipids

The measurement of water diffusion by diffusion‐weighted MRI (DWI) in vivo offers a non‐invasive method for assessing tissue responses to anti‐cancer therapies. The pathway of cell death after anti‐cancer treatment is often apoptosis, which leads to accumulation of mobile lipids detectable by ¹H MRS in vivo. However, it is not known how these discrete MR markers of cell death relate to each other. In a rodent tumour model [i.e. ganciclovir‐treated herpes simplex thymidine kinase (HSV‐tk) gene‐transfected BT4C gliomas], we studied the interrelationships between water diffusion (Trace{D}) and mobile lipids during apoptosis. Water diffusion and water‐referenced concentrations of mobile lipids showed clearly increasing and interconnected trends during treatment. Of the accumulating ¹H MRS‐visible lipids, the fatty acid ? CH ?CH ? groups and cholesterol compounds showed the strongest associations with water diffusion (r² = 0.30; P < 0.05 and r² = 0.48; P < 0.01, respectively). These results indicate that the tumour histopathology and apoptotic processes during tumour shrinkage can be interrelated in vivo by DWI of tissue water and ¹H MRS of mobile lipids, respectively. However, there is considerable individual variation in the associations, particularly at the end of the treatment period, and in the relative compositions of the accumulating NMR‐visible lipids. The findings suggest that the assessment of individual treatment response in vivo may benefit from combining DWI and ¹H MRS. Absolute and relative changes in mobile lipids may indicate initiation of tumour shrinkage even when changes in tissue water diffusion are still small. Conversely, greatly increased water diffusion probably indicates that substantial cell decomposition has taken place in the tumour tissue when the ¹H MRS resonances of mobile lipids alone can no longer give a reliable estimate of tissue conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Proton magnetic resonance spectroscopy of brain metabolic shifts induced by acute administration of 2‐deoxy‐d‐glucose and lipopolysaccharides

In vivo proton magnetic resonance spectroscopy (¹H MRS) of outbred stock ICR male mice (originating from the Institute of Cancer Research) was used to study the brain (hippocampus) metabolic response to the pro‐inflammatory stimulus and to the acute deficiency of the available energy, which was confirmed by measuring the maximum oxygen consumption. Inhibition of glycolysis by means of an injection with 2‐deoxy‐d ‐glucose (2DG) reduced the levels of gamma‐aminobutyric acid (GABA, p < 0.05, in comparison with control, least significant difference (LSD) test), N‐acetylaspartate (NAA, p < 0.05, LSD test) and choline compounds, and at the same time increased the levels of glutamate and glutamine. An opposite effect was found after injection with bacterial lipopolysaccharide (LPS) – a very common pro‐inflammatory inducer. An increase in the amounts of GABA, NAA and choline compounds in the brain occurred in mice treated with LPS. Different metabolic responses to the energy deficiency and the pro‐inflammatory stimuli can explain the contradictory results of the brain ¹H MRS studies under neurodegenerative pathology, which is accompanied by both mitochondrial dysfunction and inflammation. The prevalence of the excitatory metabolites such as glutamate and glutamine in 2DG treated mice is in good agreement with excitation observed during temporary reduction of the available energy under acute hypoxia or starvation. In turn, LPS, as an inducer of the sickness behavior, which was manifested as depression, sleepiness, loss of appetite etc., shifts the brain metabolic pattern toward the prevalence of the inhibitory neurotransmitter GABA. Copyright © 2014 John Wiley & Sons, Ltd.     

A comparative study of feature extraction and blind source separation of independent component analysis (ICA) on childhood brain tumour 1H magnetic resonance spectra

Independent component analysis (ICA) has the potential of determining automatically the metabolite signals which make up MR spectra. However, the realiability with which this is accomplished and the optimal approach for investigating in vivo MRS have not been determined. Furthermore, the properties of ICA in brain tumour MRS with respect to dataset size and data quality have not been systematically explored. The two common techniques for applying ICA, blind source separation (BSS) and feature extraction (FE) were examined in this study using simulated data and the findings confirmed on patient data. Short echo time (TE 30 ms), low and high field (1.5 and 3 T) in vivo brain tumour MR spectra of childhood astrocytoma, ependymoma and medulloblastoma were generated by using a quantum mechanical simulator with ten metabolite and lipid components. Patient data (TE 30 ms, 1.5 T) were acquired from children with brain tumours. ICA of simulated data shows that individual metabolite components can be extracted from a set of MRS data. The BSS method generates independent components with a closer correlation to the original metabolite and lipid components than the FE method when the number of spectra in the dataset is small. The experiments also show that stable results are achieved with 300 MRS at an SNR equal to 10. The FE method is relatively insensitive to different ranges of full width at half maximum (FWHM) (from 0 to 3 Hz), whereas the BSS method degrades on increasing the range of FWHM. The peak frequency variations do not affect the results within the range of ±0.08 ppm for the FE method, and ±0.05 ppm for the BSS method. When the methods were applied to the patient dataset, results consistent with the synthesized experiments were obtained. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of metabolites in infiltrating gliomas using ex vivo 1H high‐resolution magic angle spinning spectroscopy

Gliomas are routinely graded according to histopathological criteria established by the World Health Organization. Although this classification can be used to understand some of the variance in the clinical outcome of patients, there is still substantial heterogeneity within and between lesions of the same grade. This study evaluated image‐guided tissue samples acquired from a large cohort of patients presenting with either new or recurrent gliomas of grades II–IV using ex vivo proton high‐resolution magic angle spinning spectroscopy. The quantification of metabolite levels revealed several discrete profiles associated with primary glioma subtypes, as well as secondary subtypes that had undergone transformation to a higher grade at the time of recurrence. Statistical modeling further demonstrated that these metabolomic profiles could be differentially classified with respect to pathological grading and inter‐grade conversions. Importantly, the myo‐inositol to total choline index allowed for a separation of recurrent low‐grade gliomas on different pathological trajectories, the heightened ratio of phosphocholine to glycerophosphocholine uniformly characterized several forms of glioblastoma multiforme, and the onco‐metabolite D‐2‐hydroxyglutarate was shown to help distinguish secondary from primary grade IV glioma, as well as grade II and III from grade IV glioma. These data provide evidence that metabolite levels are of interest in the assessment of both intra‐grade and intra‐lesional malignancy. Such information could be used to enhance the diagnostic specificity of in vivo spectroscopy and to aid in the selection of the most appropriate therapy for individual patients. © 2014 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd.     

In vivo 1H MRS of human gallbladder bile at 3 T in one and two dimensions: detection and quantification of major biliary lipids

In vitro ¹H MRS of human bile has shown potential in the diagnosis of various hepatopancreatobiliary (HPB) diseases. Previously, in vivo ¹H MRS of human bile in gallbladder using a 1.5 T scanner demonstrated the possibility of quantification of choline‐containing phospholipids (chol‐PLs). However, other lipid components such as bile acids play an important role in the pathophysiology of the HPB system. We have employed a higher magnetic field strength (3 T), and a custom‐built receive array coil, to improve the quality of in vivo ¹H MRS of human bile in the gallbladder. We obtained significant improvement in the quality of 1D spectra (17 healthy volunteers) using a respiratory‐gated PRESS sequence with well distinguished signals for total bile acids (TBAs) plus cholesterol resonating at 0.66 ppm, taurine‐conjugated bile acids (TCBAs) at 3.08 ppm, chol‐PLs at 3.22 ppm, glycine‐conjugated bile acids (GCBAs) at 3.74 ppm, and the amide proton (?NH) arising from GCBAs and TCBAs in the region 7.76–8.05 ppm. The peak areas of these signals were measured by deconvolution, and subsequently the molar concentrations of metabolites were estimated with good accuracy, except for that of TBAs plus cholesterol. The concentration of TBAs plus cholesterol was overestimated in some cases, which could be due to lipid contamination. In addition, we report the first 2D L‐COSY spectra of human gallbladder bile in vivo (obtained in 15 healthy volunteers). 2D L‐COSY spectra will be helpful in differentiating various biliary chol‐PLs in pathological conditions of the HPB system. Copyright © 2014 John Wiley & Sons, Ltd.     

Rat strain-dependent variations in brain metabolites detected by in vivo (1) H NMR spectroscopy at 16.4T

Localized in vivo (1) H NMR spectroscopy is playing an increasing role in preclinical studies, because of its ability to quantify the concentrations of up to 20 metabolites in rat brain. To assess the differences between often-used rat strains, the neurochemical profiles of Sprague-Dawley, Wistar and Fischer rats were determined at ultrashort TE at 16.4 T. To ascertain high-qualitative quantification, a first experiment examined the dependence of the measuring time on the quantification results and precision by precisely the number of averages between 16 and 320. It was shown that most metabolites can be quantified accurately within a short scan time, yielding Cramér-Rao lower bounds below 20% and stable concentrations for 16 metabolites with as few as 32 or 64 averages in the thalamus and hippocampus, respectively. Interstrain differences in metabolite concentrations were shown to be moderate, with taurine varying significantly between Sprague-Dawley and Wistar rats, and slightly more distinct differences from Fischer rats, including variations in glutamate and myo-inositol. The high spectral quality and quantification precision of all data again demonstrated the potential of in vivo (1)H NMR spectroscopy at ultrahigh field.     

A comparative study of short‐ and long‐TE 1H MRS at 3 T for in vivo detection of 2‐hydroxyglutarate in brain tumors

2‐Hydroxyglutarate (2HG) is produced in gliomas with mutations of isocitrate dehydrogenase (IDH) 1 and 2. The ¹H resonances of the J‐coupled spins of 2HG are extensively overlapped with signals from other metabolites. Here, we report a comparative study at 3 T of the utility of the point‐resolved spectroscopy sequence with a standard short TE (35 ms) and a long TE (97 ms), which had been theoretically designed for the detection of the 2HG 2.25‐ppm resonance. The performance of the methods is evaluated using data from phantoms, seven healthy volunteers and 22 subjects with IDH‐mutated gliomas. The results indicate that TE = 97 ms provides higher detectability of 2HG than TE = 35 ms, and that this improved capability is gained when data are analyzed with basis spectra that include the effects of the volume localizing radiofrequency and gradient pulses. Copyright © 2013 John Wiley & Sons, Ltd.     

Measurement of regional variation of GABA in the human brain by optimized point‐resolved spectroscopy at 7 T in vivo

The ¹H resonances of γ‐aminobutyric acid (GABA) in the human brain in vivo are extensively overlapped with the neighboring abundant resonances of other metabolites and remain indiscernible in short‐TE MRS at 7 T. Here we report that the GABA resonance at 2.28 ppm can be fully resolved by means of echo time optimization of a point‐resolved spectroscopy (PRESS) scheme. Following numerical simulations and phantom validation, the subecho times of PRESS were optimized at (TE, TE₂) = (31, 61) ms for detection of GABA, glutamate (Glu), glutamine (Gln), and glutathione (GSH). The in vivo feasibility of the method was tested in several brain regions in nine healthy subjects. Spectra were acquired from the medial prefrontal, left frontal, medial occipital, and left occipital brain and analyzed with LCModel. Following the gray and white matter (GM and WM) segmentation of T₁‐weighted images, linear regression of metabolite estimates was performed against the fractional GM contents. The GABA concentration was estimated to be about seven times higher in GM than in WM. GABA was overall higher in frontal than in occipital brain. Glu was about twice as high in GM as in WM in both frontal and occipital brain. Gln was significantly different between frontal GM and WM while being similar between occipital GM and WM. GSH did not show significant dependence on tissue content. The signals from N‐acetylaspartylglutamate were clearly resolved, giving the concentration more than 10 times higher in WM than in GM. Our data indicate that the PRESS TE = 92 ms method provides an effective means for measuring GABA and several challenging J‐coupled spin metabolites in human brain at 7 T. Copyright © 2014 John Wiley & Sons, Ltd.     

A quantitative comparison of metabolite signals as detected by in vivo MRS with ex vivo 1H HR‐MAS for childhood brain tumours

¹H MRS provides a powerful method for investigating tumour metabolism by allowing the measurement of metabolites in vivo. Recently, the technique of ¹H high‐resolution magic angle spinning (HR‐MAS) has been shown to produce high‐quality data, allowing the accurate measurement of many metabolites present in unprocessed biopsy tissue. The purpose of this study was to evaluate the agreement between the techniques of in vivo MRS and ex vivo HR‐MAS for investigating childhood brain tumours. Short‐TE (30 ms), single‐voxel, in vivo MRS was performed on 16 paediatric patients with brain tumours at 1.5 T. A frozen biopsy sample was available for each patient. HR‐MAS was performed on the biopsy samples, and metabolite quantities were determined from the MRS and HR‐MAS data using the LCModel? and TARQUIN algorithms, respectively. Linear regression was performed on the metabolite quantities to asses the agreement between MRS and HR‐MAS. Eight of the 12 metabolite quantities were found to correlate significantly (P < 0.05). The four worst correlating metabolites were aspartate, scyllo‐inositol, glycerophosphocholine and N‐acetylaspartate, and, except for glycerophosphocholine, this error was reflected in their higher Cramer–Rao lower bounds (CRLBs), suggesting that low signal‐to‐noise was the greatest source of error for these metabolites. Glycerophosphocholine had a lower CRLB implying that interference with phosphocholine and choline was the most significant source of error. The generally good agreement observed between the two techniques suggests that both MRS and HR‐MAS can be used to reliably estimate metabolite quantities in brain tumour tissue and that tumour heterogeneity and metabolite degradation do not have an important effect on the HR‐MAS metabolite profile for the tumours investigated. HR‐MAS can be used to improve the analysis and understanding of MRS data. Copyright © 2009 John Wiley & Sons, Ltd.