Localized Magnetic Resonance Spectroscopy Research Articles

NMR Spectroscopy in Diagnosis and Monitoring of Methylmalonic and Propionic Acidemias.

Although both localized nuclear magnetic resonance spectroscopy (MRS) and non-localized nuclear magnetic resonance spectroscopy (NMR) generate the same information, i.e., spectra generated by various groups from the structure of metabolites, they are rarely employed in the same study or by the same research group. As our review reveals, these techniques have never been applied in the same study of methylmalonic acidemia (MMA), propionic acidemia (PA) or vitamin B12 deficiency patients. On the other hand, MRS and NMR provide complementary information which is very valuable in the assessment of the severity of disease and efficiency of its treatment. Thus, MRS provides intracellular metabolic information from localized regions of the brain, while NMR provides extracellular metabolic information from biological fluids like urine, blood or cerebrospinal fluid. This paper presents an up-to-date review of the NMR and MRS studies reported to date for methylmalonic and propionic acidemias. Vitamin B12 deficiency, although in most of its cases not inherited, shares similarities in its metabolic effects with MMA and it is also covered in this review.

In vivo 1 H MR spectroscopy with J-refocusing.

The goal of this study was to propose a novel localized proton MR spectroscopy (MRS) sequence that reduces signal loss due to J-modulation in the rat brain in vivo. Sprague-Dawley rats were studied at 9.4 T. A semi-LASER sequence with evenly distributed echo-time (TE ) was used, and a 90° J-refocusing pulse was inserted at TE /2. Proton spectra were acquired at two TE s (30 and 68 ms), with and without the J-refocused pulse. Data were processed in MATLAB and quantified with LCModel. The J-refocused spectrum acquired at TE = 30 ms did not show any signal losses due to J-modulation and had comparable spectral pattern to the one acquired with semi-LASER using the minimum achievable TE . Higher signal amplitudes for glutamine, γ-aminobutyric acid and glutathione led to more reliable quantification precision for these metabolites. The refocused signal intensities at TE = 68 ms were also unaffected by J-modulation but were smaller than the signals at TE = 30 ms mainly due to transverse T2 relaxation of metabolites. The proposed localized MRS sequence will be beneficial in both animal and human MRS studies when using ultra-short TE is not possible while also providing more reliable quantification precision for J-coupled metabolites.

Proton MR Spectroscopy Measurements of White and Brown Adipose Tissue in Healthy Humans: Relaxation Parameters and Unsaturated Fatty Acids.

Background Activation of brown adipose tissue (BAT) in rodents increases lipolysis in white adipose tissue (WAT) and improves glucose tolerance. Adult humans can have metabolically active BAT. Implications for diabetes and obesity in humans require a better characterization of BAT in humans. Purpose To study fat depots with localized proton MR spectroscopy relaxometry and to identify differences between WAT and fluorine 18 fluorodeoxyglucose (FDG) PET/CT proven cold-activated BAT in humans. Materials and Methods Participants were consecutively enrolled in this prospective study (ClinicalTrials.gov identifiers: NCT01568671 and NCT01399385) from August 2016 to May 2019. Supraclavicular potential BAT regions were localized with MRI. Proton densities, T1, and T2 were measured with localized MR spectroscopy in potential BAT and in subcutaneous WAT. FDG PET/CT after cold stimulation was used to retrospectively identify active supraclavicular BAT or supraclavicular quiescent adipose tissue (QAT) regions. MR spectroscopy results from BAT and WAT were compared with grouped and paired tests. Results Of 21 healthy participants (mean age, 36 years ± 16 [standard deviation]; 13 men) FDG PET/CT showed active BAT in 24 MR spectroscopy-targeted regions in 16 participants (eight men). Four men had QAT. The T2 for methylene protons was shorter in BAT (mean, 69 msec ± 6, 24 regions) than in WAT (mean, 83 msec ± 3, 18 regions, P < .01) and QAT (mean, 78 msec ± 2, five regions, P < .01). A T2 cut-off value of 76 msec enabled the differentiation of BAT from WAT or QAT with a sensitivity of 85% and a specificity of 95%. Densities of protons adjacent and between double bonds were 33% and 24% lower, respectively, in BAT compared with those in WAT (P = .01 and P = .03, respectively), indicating a lower content of unsaturated and polyunsaturated fatty acids, respectively, in BAT compared with WAT. Conclusion Proton MR spectroscopy showed shorter T2 and lower unsaturated fatty acids in brown adipose tissue (BAT) than that in white adipose tissue in healthy humans. It was feasible to identify BAT with MR spectroscopy without the use of PET/CT or cold stimulation. © RSNA, 2021 See also the editorial by Barker in this issue. Online supplemental material is available for this article.

Detection of fatty acid composition of trabecular bone marrow by localized iDQC MRS at 3 T: A pilot study in healthy volunteers

BackgroundAlthough a growing body of research shows that the bone marrow adipose tissue (BMAT) may play an essential role in bone inflammation and energy metabolism, available noninvasive methods for distinguishing different fatty acids in BMAT are still limited, in spite of their potential to provide novel biomarkers for bone related diseases. PurposeTo assess the ability of a localized intermolecular double quantum coherence (iDQC) spectroscopy sequence to resolve more fatty acid peaks than conventional MR spectroscopy (MRS), like polyunsaturated fatty acids (PUFA), from the human BMAT in the presence of trabecular bone; To preliminarily investigate whether the fatty acids composition is different between different regions and groups. ResultsCompared with conventional MRS results, additional four fatty acids peaks were well resolved using the proposed method in human BMAT in the presence of trabecular bone. In addition, a different fat composition was found between distal femur and proximal tibia: fat was more unsaturated (vinyl, *p < 0.01; diallylic, *p < 0.01) in distal femur bone marrow than in proximal tibia, and this higher unsaturation level was caused by PUFA (r = 0.67, diallylic, *p < 0.01). No significant difference in fatty acid composition were found either between left and right legs, or between female and male in the healthy young subjects studied. ConclusionThis study demonstrated that the unsaturated fatty acids information of human BMAT in the presence of trabecular bone can be clearly identified with the localized iDQC at 3 T. The resolved peaks, especially PUFA, may serve as additional diagnostic biomarkers for BMAT related diseases in the future.

1099-P: Effects of Empagliflozin on Glucose Metabolism and Body Fat Composition in Patients with Prediabetes: A Randomized, Double-Blind, Placebo-Controlled Trial

Objective: In patients with diabetes, the beneficial effects of empagliflozin on glucose metabolism, body adiposity, and liver fat content are well established. As the mode of action of SGLT2 inhibitors partly depends on elevated blood glucose, we investigated if these effects also occur in prediabetes. Methods: Forty participants with prediabetes (mean ± SD: age: 60 ± 9 years; BMI: 31.5 ± 3.8 kg/m²; FG: 5.98 ± 0.57 mmol/l) were randomized to receive 25 mg empagliflozin qd or placebo for 8 weeks. Before and after treatment, all participants underwent a 75 g oral glucose tolerance test to evaluate glucose tolerance, peripheral insulin sensitivity and insulin secretion. Body fat was assessed by whole-body MRI and intrahepatic fat by localized MR-spectroscopy. Resting energy expenditure and respiratory quotient (RQ) were assessed by indirect calorimetry at fast. “Per protocol” analysis using ANCOVA was performed. Results: Fasting glucose, glucose tolerance, peripheral insulin sensitivity, and insulin secretion were not significantly changed by treatment. Though, after 8 weeks of treatment, total adipose tissue (mean difference between groups at the end of study ± SEM: 3.1 ± 2.3 liters; p=0.034) and intrahepatic fat (2.1 ± 2.3 %; p=0.029) were lower in patients who received empagliflozin, compared to placebo. Empagliflozin treatment resulted in a lower RQ compared to placebo (p=0.022) without differences in resting energy expenditure (p=0.2), indicating preferential lipid oxidation upon treatment. Conclusion: In prediabetes, treatment with empagliflozin for 8 weeks has no major effects on glucose metabolism. However, this SGLT2 inhibitor reduced body adiposity and liver fat content, presumably by shifting energy metabolism towards lipid oxidation. Therefore, empagliflozin might represent a treatment option for obesity and hepatic steatosis in prediabetes, independent of drug effects on blood glucose. Disclosure J. Hummel: None. C. Dannecker: None. L. Fritsche: None. A. Vosseler: None. K. Kantartzis: None. S. Kullmann: None. J. Machann: None. H. Preissl: None. H. Haering: None. A. Fritsche: None. R. Wagner: Advisory Panel; Self; Novo Nordisk A/S. Speaker’s Bureau; Self; Novo Nordisk A/S. Other Relationship; Self; Eli Lilly and Company. M. Heni: Research Support; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Sanofi. Speaker’s Bureau; Self; Novo Nordisk A/S. Funding Boehringer Ingelheim

Magnetic Resonance Microscopy at Cellular Resolution and Localised Spectroscopy of Medicago truncatula at 22.3 Tesla

Interactions between plants and the soil’s microbial & fungal flora are crucial for the health of soil ecosystems and food production. Microbe-plant interactions are difficult to investigate in situ due to their intertwined relationship involving morphology and metabolism. Here, we describe an approach to overcome this challenge by elucidating morphology and the metabolic profile of Medicago truncatula root nodules using Magnetic Resonance (MR) Microscopy, at the highest magnetic field strength (22.3 T) currently available for imaging. A home-built solenoid RF coil with an inner diameter of 1.5 mm was used to study individual root nodules. A 3D imaging sequence with an isotropic resolution of (7 μm)3 was able to resolve individual cells, and distinguish between cells infected with rhizobia and uninfected cells. Furthermore, we studied the metabolic profile of cells in different sections of the root nodule using localised MR spectroscopy and showed that several metabolites, including betaine, asparagine/aspartate and choline, have different concentrations across nodule zones. The metabolite spatial distribution was visualised using chemical shift imaging. Finally, we describe the technical challenges and outlook towards future in vivo MR microscopy of nodules and the plant root system.

Different energy transfer efficiencies and buffering capabilities in quadriceps and calves muscles with low-load isotonic exercise detected by dynamic localized phosphorus-31 magnetic resonance spectroscopy

Our aim was to investigate if there are differences in mitochondrial energy metabolism in working quadriceps and calves muscles by dynamic localized phosphorus-31 magnetic resonance spectroscopy. Phosphate metabolites of muscles were detected while subjects were in a state of rest, during exercise and recovery. The phosphocreatine (PCr), inorganic phosphate (Pi), adenosine triphosphate (ATP), PCr/Pi, PCr/ATP, pH, work/energy cost ratio (WE) and oxidative capacity were compared between muscles. The quadriceps had larger volume, heavier exercise load, greater WE, lower PCr and Pi concentration than calves muscles at rest. The PCr/Pi ratio of both muscles exhibited a sharp decline during exercise. PCr/ATP also had a downtrend in during exercise. Meanwhile, PCr/ATP of quadriceps during exercise was lower than that of calves muscles. The ATP concentration and pH value of quadriceps were decreased in end exercise compared to rest. And our results indicated that quadriceps had higher energy transfer efficiency and relatively poor energy buffering capability than calves muscles. The change in log(PCr) could adopt a linear fit model for both muscles at recovery. Quadriceps had higher energy transfer efficiency and relatively poor energy buffering capability than calves muscles in mitochondrial energy metabolism partially accounts for different fiber type compositions.

MRS Reveals Chronic Inflammation in T2w MRI-Negative Perilesional Cortex - A 6-Months Multimodal Imaging Follow-Up Study.

Sustained inflammation in the injured cortex is a promising therapeutic target for disease-modification after traumatic brain injury (TBI). However, its extent and dynamics of expansion are incompletely understood which challenges the timing and placement of therapeutics to lesioned area. Our aim was to characterize the evolution of chronic inflammation during lesion expansion in lateral fluid-percussion injury (FPI) rat model with focus on the MRI-negative perilesional cortex. T2-weighted MR imaging (T2w MRI) and localized magnetic resonance spectroscopy (MRS) were performed at 1, 3, and 6 months post-injury. End-point histology, including Nissl for neuronal death, GFAP for astrogliosis, and Prussian Blue for iron were used to assess perilesional histopathology. An additional animal cohort was imaged with a positron emission tomography (PET) using translocator protein 18 kDa (TSPO) radiotracer [18F]-FEPPA. T2w MRI assessed lesion growth and detected chronic inflammation along the lesion border while rest of the ipsilateral cortex was MRI-negative (MRI-). Instead, myo-inositol that is an inflammatory MRS marker for gliosis, glutathione for oxidative stress, and choline for membrane turnover were elevated throughout the 6-months follow-up in the MRI- perilesional cortex (all p < 0.05). MRS markers revealed chronically sustained inflammation across the ipsilateral cortex but did not indicate the upcoming lesion expansion. Instead, the rostral expansion of the cortical lesion was systematically preceded by a hyperintense band in T2w images months earlier. Histologic analysis of the hyperintensity indicated scattered astrocytes, incomplete glial scar, and intracellularly packed and free iron. Yet, the band was negative in [18F]-FEPPA-PET. [18F]-FEPPA also showed no cortical TSPO expression within the MRS voxel in MRI- perilesional cortex or anywhere along glial scar when assessed at 2 months post-injury. However, [18F]-FEPPA showed a robust signal increase, indicating reactive microgliosis in the ipsilateral thalamus at 2 months post-TBI. We present evidence that MRS reveals chronic posttraumatic inflammation in MRI-negative perilesional cortex. The mismatch in MRS, MRI, and PET measures may allow non-invasive endophenotyping of beneficial and detrimental inflammatory processes to aid targeting and timing of anti-inflammatory therapeutics.

OA018] Improved absolute metabolite quantification by localized magnetic resonance spectroscopy simulations

Purpose Magnetic resonance spectroscopy (MRS) provides a non-invasive method for assessment of the in vivo abundance of metabolites and serves as a useful diagnostic tool for several pathologies. The most common method for quantification of metabolite abundance includes fitting a linear combination of individual a priori acquired metabolite spectra. The set of individual metabolite spectra (basis set) can either be acquired through phantom measurements or simulations. While simulation has recently become more popular, it is not clear at what complexity level the simulations have to be run. The aim of this work was to study the impact of simulation complexity on absolute concentration estimates. Specifically, results based on non-localized and localized simulations were compared. Methods The Braino phantom (General Electric) containing the most common brain metabolites was used in this study. It included choline (Cho, 3.0 mM), creatine (Cr, 10.0 mM), lactate (Lac, 5.0 mM), myoinositole (mI, 7.5 mM), glutamic acid (Glu, 12.5 mM) and N-acetylactic acid (NAA, 12.5 mM). MR spectra were acquired on a Philips Achieva 3 T scanner with the PRESS pulse sequence. Parameters: echo time 35 ms, repetition time 5000 ms, number of acquisitions 128, volume of interest size 20 × 20 × 20 mm3. Basis sets were generated in MATLAB with the same sequence timing as on the scanner both with a non-localized simulation (using ideal RF pulses) and with a localized simulation (using the actual RF pulses, gradient waveforms and phase cycling scheme as on the scanner) using full density matrix calculations. The acquired spectra were analyzed with LCModel. Metabolite concentrations were separately estimated based on the two basis sets. Results The estimated concentrations based on localized simulations were closer to true ones for all metabolites: Cho 3.6/3.5 mM, Cr 10.8/10.5 mM, Lac 3.8/5.3 mM, mI 6.5/6.9 mM, Glu 12.7/12.6 mM, NAA 13.3/13.1 mM (ideal/localized). A substantial gain in accuracy was especially seen for lactate which was underestimated by 24% with the non-localized simulation, but overestimated by only 6% by the localized simulation. Conclusions Metabolite quantification was improved by inclusion of actual RF pulses, gradient waveforms and phase cycling scheme. This was especially seen for lactate.

Improved quantitative fatty acid values with correction of T2 relaxation time in terminal methyl group: In vivo proton magnetic resonance spectroscopy at ultra high field in hepatic steatosis

Proton magnetic resonance spectroscopy (MRS) with optimized relaxation time is an effective method to quantify hepatic fatty acid values and characterize steatosis. The aim of this study is to quantify the difference in hepatic lipid content with metabolic changes during the progression of steatosis by using localized MRS sequence with T2 relaxation time determination. Fatty liver disease was induced in C57BL/6N mice through a high-fat diet (HFD) of pellets containing 60% fat, 20% protein, and 20% carbohydrates. We used stimulated echo acquisition mode (repetition time: 3500 ms; mixing time: 10 ms; echo time: 20 ms) sequence. Using enhanced and mono exponential curve-fitting methods, the lipid relaxation time in mice was estimated at a fixed repetition time of 5000 ms and echo time ranging from 20 to 70 ms. The calculated lipid contents with incorrect and correct relaxation times were as follows: total saturated fatty acid (4.00 ± 2.90 vs 6.74 ± 2.25, p < 0.05 at week 0; 15.23 ± 9.94 vs 25.53 ± 10.49, p < 0.05 at week 4); total unsaturated fatty acid (0.40 ± 0.49 vs 0.56 ± 0.47, p < 0.05 at week 4; 0.33 ± 0.26 vs 0.60 ± 0.21, p < 0.01 at week 7); total unsaturated bond (0.48 ± 0.52 vs 1.05 ± 0.58, p < 0.05 at week 10). Furthermore, we determined that the correct relaxation times of triglycerides between 0 and 10 weeks were significantly altered in the resonances (∼2.03 ppm: 31.07 ± 1.00 vs 27.62 ± 1.20, p < 0.01; ∼2.25 ppm: 29.10 ± 1.52 vs 26.39 ± 1.08, p < 0.05; ∼2.78 ppm: 37.67 ± 2.92 vs 29.37 ± 2.64, p < 0.001). The work presented focused on the significance of the J-coupling effect. The selection of an appropriate relaxation time considering the J-coupling effect provides an effective method for quantifying lipid contents and characterizing hepatic steatosis.

Fully navigated 3 T proton magnetic resonance spectroscopy of liver metastases with inner-volume saturation.

To demonstrate that fully navigated magnetic resonance spectroscopy (MRS) with inner-volume saturation (IVS) at 3 T results in high-quality spectra that permit evaluating metabolic changes in hepatic metastases without the need for patient compliance. Nine patients with untreated, biopsy-proven large hepatic metastases (minimum diameter of 3cm) were included. In each patient, localized proton MRS was performed in the metastatic lesion and in uninvolved liver parenchyma. To improve quality and consistency of proton MRS, navigator gating was thereby performed not only during acquisition of the spectroscopic data but also during localization imaging and throughout the preparation phases. IVS was utilized to reduce chemical shift displacement between different metabolites and to diminish flow artifacts. Metabolite quantities were normalized relative to the unsuppressed water peak and choline-containing compounds (CCC) to lipid ratios were determined. Wilcoxon signed-rank tests were used to assess differences in the amounts of lipids and CCC as well as the CCC-to-lipid ratios between liver metastases and normal-appearing liver parenchyma. Fully navigated point-resolved spectroscopy with IVS resulted in high-quality spectra in all patients. Navigator gating during localization imaging and spectroscopic acquisition thereby ensured a precise localization of the spectroscopic voxel. Decreased quantities of lipid and CCC were observed in metastatic tissue compared with uninvolved liver parenchyma. However, the latter trend fell short of statistical significance. Moreover, elevated levels of the CCC-to-lipid ratios were detected in metastatic tissue relative to normal-appearing liver parenchyma. The present study demonstrates that fully navigated MRS of the liver with IVS at 3 T allows for a precise localization of the spectroscopic voxel and results in high-quality spectra that permit evaluating liver metabolism without the need for patient compliance.

Evidence for a “metabolically inactive” inorganic phosphate pool in adenosine triphosphate synthase reaction using localized 31P saturation transfer magnetic resonance spectroscopy in the rat brain at 11.7 T

With the increased spectral resolution made possible at high fields, a second, smaller inorganic phosphate resonance can be resolved on 31P magnetic resonance spectra in the rat brain. Saturation transfer was used to estimate de novo adenosine triphosphate synthesis reaction rate. While the main inorganic phosphate pool is used by adenosine triphosphate synthase, the second pool is inactive for this reaction. Accounting for this new pool may not only help us understand 31P magnetic resonance spectroscopy metabolic profiles better but also better quantify adenosine triphosphate synthesis.

Erratum to: Interleukin-1beta-induced reduction of tissue water diffusion in the juvenile rat brain on ADC MRI is not associated with 31P MRS-detectable energy failure

[This corrects the article DOI: 10.1186/s12950-016-0118-3.].

Developmental patterning and segregation of alkaloids in areca nut (seed of Areca catechu) revealed by magnetic resonance and mass spectrometry imaging

Areca nut (seed of Areca catechu) is consumed by people from different parts of Asia, including India. The four major alkaloids present in areca nut are arecoline, arecaidine, guvacoline and guvacine. Upon cutting, the nut reveals two kinds of regions; white and brown. In our present study, we have monitored the formation of these two regions within the nut during maturation, using the non-invasive techniques of magnetic resonance imaging (MRI) and volume localized magnetic resonance spectroscopy (MRS). Electrospray ionization mass spectrometry (ESI MS) and desorption electrospray ionization mass spectrometry (DESI MS) imaging have been used to study the associated change in the alkaloid contents of these two regions during the growth of the nut. Our study reveals that white and brown regions start forming within the nut when the liquid within starts solidifying. At the final stage of maturity, arecoline, arecaidine and guvacoline get segregated in the brown region whereas guvacine gets to the white region of the nut. The transport of molecules with maturity and corresponding pattern formation are expected to be associated with a multitude of physiochemical changes.

Parallel reconstruction in accelerated multivoxel MR spectroscopy.

To develop the simultaneous acquisition of multiple voxels in localized MR spectroscopy (MRS) using sensitivity encoding, allowing reduced total scan time compared to conventional sequential single voxel (SV) acquisition methods. Dual volume localization was used to simultaneously excite voxels in both hemispheres. Receiver coil sensitivity profiles were used to unfold the data. To demonstrate the method, MRS voxels in the left and right hippocampus were measured at 3 tesla (T) and the left and right motor cortices at 7T. Spectra were compared to conventional SV acquisitions. Spectra were also recorded from the lesion and contralateral hemisphere of a patient with a low-grade oligodendroglioma at 7T. It was possible to generate signal in two voxels simultaneously and separate the signal originating from the different locations, with spectral results almost identical to those observed using conventional single voxel methods. The method results in an increased chemical shift displacement artifact, which might be improved by advanced pulse designs, and a noise increase due to the unfolding g-factor, which was larger at 3T than 7T. The simultaneous acquisition of voxels for MRS is possible by using modulated slice-selective pulses and receive coil sensitivity profiles to unfold the resulting signals.

Abstracts of the Hunter Cancer Research Alliance Annual Symposium 2014, November 21, 2014, New Lambton Heights, New South Wales, Australia.

Despite no evidence of any changes to breast tissue from current imaging modalities, in vivo two-dimensional localized correlated MR spectroscopy can be used to identify biochemical abnormalities that may represent preinvasive changes in the breast tissue of women carrying BRCA1 or BRCA2 gene mutations.

Neurochemical Changes Observed by In Vivo Proton Magnetic Resonance Spectroscopy in the Mouse Brain Postadministration of Scopolamine

This study is aimed at investigating neurochemical changes in scopolamine (SCP)-induced memory impairment using spatially localized invivo magnetic resonance spectroscopy (MRS) of the hippocampus. Four groups of mice (eight mice per group) were scanned after the injection of different SCP doses: 0, 1, 3, and 5 mg/kg (intraperitoneally). All the animals received (1)H MRS of their hippocampus at two time intervals: 30minutes and 72hours after SCP injection. This work demonstrated that the doses of 3 mg/kg SCP or higher reduce the concentration of total choline-containing compounds, and these levels returned to baseline after 72hours. These results are consistent with observations made by others using more invasive brain dialysis approaches. The levels of glutamate and glutamic compounds (glutamate+glutamine) were slightly changed at 3 and 5mg/kg SCP dose, but the differences were not statistically significant (P>.05). These findings suggest that SCP produces transient, invivo measurable alterations in the cholinergic system in the hippocampus. On this basis, we conclude that invivo MRS is a feasible noninvasive method to probe aspects of the alterations induced by SCP in the cholinergic neurotransmission pathways in both animal models and human studies of memory impairment.

On the use of Cramér–Rao minimum variance bounds for the design of magnetic resonance spectroscopy experiments

Localized Magnetic Resonance Spectroscopy (MRS) is in widespread use for clinical brain research. Standard acquisition sequences to obtain one-dimensional spectra suffer from substantial overlap of spectral contributions from many metabolites. Therefore, specially tuned editing sequences or two-dimensional acquisition schemes are applied to extend the information content. Tuning specific acquisition parameters allows to make the sequences more efficient or more specific for certain target metabolites. Cramér–Rao bounds have been used in other fields for optimization of experiments and are now shown to be very useful as design criteria for localized MRS sequence optimization. The principle is illustrated for one- and two-dimensional MRS, in particular the 2D separation experiment, where the usual restriction to equidistant echo time spacings and equal acquisition times per echo time can be abolished. Particular emphasis is placed on optimizing experiments for quantification of GABA and glutamate. The basic principles are verified by Monte Carlo simulations and in vivo for repeated acquisitions of generalized two-dimensional separation brain spectra obtained from healthy subjects and expanded by bootstrapping for better definition of the quantification uncertainties.

Ultrafast acquisition of localized two-dimensional magnetic resonance correlated spectra of inhomogeneous biological tissues with resolution improvements

Long acquisition time and strict requests of homogeneous magnetic fields restrain wide applications of localized 2D magnetic resonance spectroscopy. Here, a pulse sequence utilizing the spatial encoding technique and spin echo is proposed to obtain localized 2D correlated spectra with resolution improvements under inhomogeneous fields within greatly reduced times. The localized correlated spectrum of pig marrow obtained with the proposed scheme retained more information compared to the conventional spectrum. The method proposed herein offers important perspectives for fast in vivo analyses of metabolites in living inhomogeneous organisms and in situ characterization of intermediates of inhomogeneous chemical reaction systems.

In vivo intracellular oxygen dynamics in murine brain glioma and immunotherapeutic response of cytotoxic T cells observed by fluorine-19 magnetic resonance imaging.

Noninvasive biomarkers of anti-tumoral efficacy are of great importance to the development of therapeutic agents. Tumor oxygenation has been shown to be an important indicator of therapeutic response. We report the use of intracellular labeling of tumor cells with perfluorocarbon (PFC) molecules, combined with quantitative 19F spin-lattice relaxation rate (R1) measurements, to assay tumor cell oxygen dynamics in situ. In a murine central nervous system (CNS) GL261 glioma model, we visualized the impact of Pmel-1 cytotoxic T cell immunotherapy, delivered intravenously, on intracellular tumor oxygen levels. GL261 glioma cells were labeled ex vivo with PFC and inoculated into the mouse striatum. The R1 of 19F labeled cells was measured using localized single-voxel magnetic resonance spectroscopy, and the absolute intracellular partial pressure of oxygen (pO2) was ascertained. Three days after tumor implantation, mice were treated with 2×107 cytotoxic T cells intravenously. At day five, a transient spike in pO2 was observed indicating an influx of T cells into the CNS and putative tumor cell apoptosis. Immunohistochemistry and quantitative flow cytometry analysis confirmed that the pO2 was causally related to the T cells infiltration. Surprisingly, the pO2 spike was detected even though few (∼4×104) T cells actually ingress into the CNS and with minimal tumor shrinkage. These results indicate the high sensitivity of this approach and its utility as a non-invasive surrogate biomarker of anti-cancer immunotherapeutic response in preclinical models.