WET, a T1- and B1-insensitive water-suppression method for in vivo localized 1H NMR spectroscopy

J-refocused coherence transfer spectroscopic imaging at 7 T in human brain

Short echo spectroscopy is commonly used to minimize signal modulation due to J-evolution of the cerebral amino acids. However, short echo acquisitions suffer from high sensitivity to macromolecules which make accurate baseline determination difficult. In this report, we describe implementation at 7 T of a double echo J-refocused coherence transfer sequence at echo time (TE) of 34 msec to minimize J-modulation of amino acids while also decreasing interfering macromolecule signals. Simulation of the pulse sequence at 7 T shows excellent resolution of glutamate, glutamine, and N-acetyl aspartate. B(1) sufficiency at 7 T for the double echo acquisition is achieved using a transceiver array with radiofrequency (RF) shimming. Using an alternate RF distribution to minimize receiver phase cancellation in the transceiver, accurate phase determination for the coherence transfer is achieved with rapid single scan calibration. This method is demonstrated in spectroscopic imaging mode with n = 5 healthy volunteers resulting in metabolite values consistent with literature and in a patient with epilepsy.

Measurement of N-acetylaspartylglutamate in the human frontal brain by 1H-MRS at 7 T

N-Acetylaspartylglutamate in human brain has been measured with difference editing at 7 T. The CH(2) proton resonances (∼ 2.5 ppm) of the aspartyl groups of N-acetylaspartylglutamate and N-acetylaspartate were difference edited (MEGA) using 20-msec gaussian radiofrequency pulses for selective 180 ° rotations of the coupling partners at 4.61 and 4.38 ppm, respectively. The echo time of the editing sequence, 108 msec, was obtained in phantom tests. Single-voxel localized in vivo measurements were conducted in the medial prefrontal and right frontal cortices of five healthy volunteers. The gray and white matter fractions within the voxels were obtained from T(1)-weighted image segmentation. Using linear regression of the metabolite concentration vs. fractional white matter contents within the voxels, the N-acetylaspartylglutamate-to-N-acetylaspartate concentration ratios in gray and white matter were estimated to be 0.13 and 0.28 by difference editing (95% confidence intervals 0.07-0.19 and 0.22-0.34), respectively, assuming identical relaxation effects between the metabolites.

Dynamic 3-dimensional stress cardiac magnetic resonance perfusion imaging: detection of coronary artery disease and volumetry of myocardial hypoenhancement before and after coronary stenting

OBJECTIVES

The aim of this study was to establish a new, dynamic 3-dimensional cardiac magnetic resonance (3D-CMR) perfusion scan technique exploiting data correlation in k-space and time with sensitivity-encoding and to determine its value for the detection of coronary artery disease (CAD) and volumetry of myocardial hypoenhancement (VOLUME(hypo)) before and after percutaneous coronary stenting.

BACKGROUND

Dynamic 3D-CMR perfusion imaging might improve detection of myocardial perfusion deficits and could facilitate direct volumetry of myocardial hypoenhancement.

METHODS

In 146 patients with known or suspected CAD, a 3.0-T CMR examination was performed including cine imaging, 3D-CMR perfusion under adenosine stress and at rest followed by delayed enhancement imaging. Quantitative invasive coronary angiography defined significant CAD (≥ 50% luminal narrowing). Forty-eight patients underwent an identical repeat CMR examination after percutaneous stenting of at least 1 coronary lesion. The 3D-CMR perfusion scans were visually classified as pathologic if ≥ 1 segment showed an inducible perfusion deficit in the absence of delayed enhancement. The VOLUME(hypo) was measured by segmentation of the area of inducible hypoenhancement and normalized to left-ventricular myocardial volume (%VOLUME(hypo)).

RESULTS

The 3D-CMR perfusion resulted in a sensitivity, specificity, and diagnostic accuracy of 91.7%, 74.3%, and 82.9%, respectively. Before and after coronary stenting, %VOLUME(hypo) averaged to 14.2 ± 9.5% and 3.2 ± 5.2%, respectively, with a relative VOLUME(hypo) reduction of 79.4 ± 25.4%. Intrareader and inter-reader reproducibility of VOLUME(hypo) measurements was high (Lin's concordance correlation coefficient, 0.96 and 0.96, respectively).

CONCLUSIONS

The 3D-CMR stress perfusion provided high image quality and high diagnostic accuracy for the detection of significant CAD. The VOLUME(hypo) measurements were highly reproducible and allowed for the assessment of the treatment effect achievable by percutaneous coronary stenting.

Use of in vivo two-dimensional MR spectroscopy to compare the biochemistry of the human brain to that of glioblastoma

PURPOSE

To develop an in vivo two-dimensional localized correlation spectroscopy technique with which to monitor the biochemistry of the human brain and the pathologic characteristics of diseases in a clinically applicable time, including ascertainment of appropriate postprocessing parameters with which to allow diagnostic and prognostic molecules to be measured, and to investigate how much of the chemical information, known to be available from malignant cultured cells, could be recorded in vivo from human brain.

MATERIALS AND METHODS

The study was approved by the institutional review board and was compliant with HIPAA. With use of a 3.0-T clinical magnetic resonance (MR) unit and a 32-channel head coil, localized correlation spectroscopy was performed in six healthy control subjects and six patients with glioblastoma multiforme (GBM) with an acquisition time of 11 minutes. Two-dimensional spectra were processed and analyzed and peak volume ratios were tabulated. The data used were proved to be normally distributed by passing the Shapiro-Wilk normality test. The first row of the spectra was extracted to examine diagnostic features. The pathologic characteristics and grade of each GBM were determined after biopsy or surgery. Statistically significant differences were assessed by using a t test.

RESULTS

The localized correlation spectroscopy method assigned biochemical species from the healthy human brain. The correlation spectra of GBM were of sufficiently high quality that many of the cross peaks, recorded previously from malignant cell models in vitro, were observed, demonstrating a statistically significant difference (P < .05) between the cross peak volumes measured for healthy subjects and those with GBM (which include lipid, alanine, N-acetylaspartate, γ-aminobutyric acid, glutamine and glutamate, glutathione, aspartate, lysine, threonine, total choline, glycerophosphorylcholine, myo-inositol, imidazole, uridine diphosphate glucose, isocitrate, lactate, and fucose). The first row of the spectra was found to contain diagnostic features.

CONCLUSION

Localized correlation spectroscopy of the human brain at 3.0 T with use of a 32-channel head coil was performed in 11 minutes and provided information about neurotransmitters, metabolites, lipids, and macromolecules. The method was able to help differentiate healthy brain from the biochemical signature of GBM in vivo. This method may, in the future, reduce the need for biopsy and is now applicable for the study of selected neurologic diseases.

Neurochemical alterations in adolescent chronic marijuana smokers: a proton MRS study

Converging evidence from neuroimaging and neuropsychological studies indicates that heavy marijuana use is associated with cingulate dysfunction. However, there has been limited human data documenting in vivo biochemical brain changes after chronic marijuana exposure. Previous proton magnetic resonance spectroscopy studies have demonstrated reduced basal ganglia glutamate and dorsolateral prefrontal cortex N-acetyl aspartate levels in adult chronic marijuana users. Similar studies have not been reported in adolescent populations. The present study used proton magnetic resonance spectroscopy to determine whether reductions in glutamate, N-acetyl aspartate and/or other proton metabolite concentrations would be found in the anterior cingulate cortex (ACC) of adolescent marijuana users compared with non-using controls. Adolescent marijuana users (N=17; average age 17.8 years) and similarly aged healthy control subjects (N=17; average age 16.2 years) were scanned using a Siemens 3T Trio MRI system. Proton magnetic resonance spectroscopy data were acquired from a 22.5 mL voxel positioned bilaterally within the ACC. Spectra were fitted using commercial software and all metabolite integrals were normalized to the scaled unsuppressed water integral. Analysis of variance and analysis of covariance were performed to compare between-group metabolite levels. The marijuana-using cohort showed statistically significant reductions in anterior cingulate glutamate (-15%, p<0.01), N-acetyl aspartate (-13%, p=0.02), total creatine (-10%, p<0.01) and myo-inositol (-10%, p=0.03). Within-voxel tissue-type segmentation did not reveal any significant differences in gray/white matter or cerebrospinal fluid content between the two groups. The reduced glutamate and N-acetyl aspartate levels in the adolescent marijuana-using cohort are consistent with precedent human (1)H MRS data, and likely reflect an alteration of anterior cingulate glutamatergic neurotransmission and neuronal integrity within these individuals. The reduced total creatine and myo-inositol levels observed in these subjects might infer altered ACC energetic status and glial metabolism, respectively. These results expand on previous functional MRI data reporting altered cingulate function in individuals with marijuana-abuse.

Echo planar correlated spectroscopic imaging: implementation and pilot evaluation in human calf in vivo

Exploiting the speed benefits of echo-planar imaging (EPI), the echo-planar spectroscopic imaging (EPSI) sequence facilitates recording of one spectral and two to three spatial dimensions faster than the conventional magnetic resonance spectroscopic imaging (MRSI). A novel four dimensional (4D) echo-planar correlated spectroscopic imaging (EP-COSI) was implemented on a whole body 3 T MRI scanner combining two spectral with two spatial encodings. Similar to EPSI, the EP-COSI sequence used a bipolar spatial read-out train facilitating simultaneous spatial and spectral encoding, and the conventional phase and spectral encodings for the other spatial and indirect spectral dimensions, respectively. Multiple 2D correlated spectroscopy (COSY) spectra were recorded over the spatially resolved volume of interest (VOI) localized by a train of three slice-selective radiofrequency (RF) pulses (90°-180°-90°). After the initial optimization using phantom solutions, the EP-COSI data were recorded from the lower leg of eight healthy volunteers including one endurance trained volunteer. Pilot results showed acceptable spatial and spectral quality achievable using the EP-COSI sequence. There was a detectable separation of cross peaks arising from the skeletal muscle intramyocellular lipids (IMCLs) and extramyocellular lipids (EMCLs) saturated and unsaturated pools. Residual dipolar interaction between the N-methylene and N-methyl protons of creatine/phosphocreatine (Cr/PCr) was also observed in the tibialis anterior region.

Longitudinal and multi-echo transverse relaxation times of normal breast tissue at 3 Tesla

PURPOSE

To measure longitudinal (T(1)) and multi-echo transverse (T(2)) relaxation times of healthy breast tissue at 3 Tesla (T).

MATERIALS AND METHODS

High-resolution relaxation time measurements were made in six healthy female subjects. Inversion recovery images were acquired at 10 inversion times between 100 ms and 4000 ms, and multiple spin echo images were acquired at 16 echo times between 10 ms and 160 ms.

RESULTS

Longitudinal relaxation times T(1) were measured as 423 ± 12 ms for adipose tissue and 1680 ± 180 ms for fibroglandular tissue. Multi-echo transverse relaxation times T(2) were measured as 154 ± 9 ms for adipose tissue and 71 ± 6 ms for fibroglandular tissue. Histograms of the voxel-wise relaxation times and quantitative relaxation time maps are also presented.

CONCLUSION

T(1) and multi-echo T(2) relaxation times in normal human breast tissue are reported. These values are useful for pulse sequence design and optimization for 3T breast MRI. Compared with the literature, T(1) values are significantly longer at 3T, suggesting that longer repetition time and inversion time values should be used for similar image contrast.

Accuracy and stability of measuring GABA, glutamate, and glutamine by proton magnetic resonance spectroscopy: a phantom study at 4 Tesla

Proton magnetic resonance spectroscopy has the potential to provide valuable information about alterations in gamma-aminobutyric acid (GABA), glutamate (Glu), and glutamine (Gln) in psychiatric and neurological disorders. In order to use this technique effectively, it is important to establish the accuracy and reproducibility of the methodology. In this study, phantoms with known metabolite concentrations were used to compare the accuracy of 2D J-resolved MRS, single-echo 30 ms PRESS, and GABA-edited MEGA-PRESS for measuring all three aforementioned neurochemicals simultaneously. The phantoms included metabolite concentrations above and below the physiological range and scans were performed at baseline, 1 week, and 1 month time-points. For GABA measurement, MEGA-PRESS proved optimal with a measured-to-target correlation of R(2)=0.999, with J-resolved providing R(2)=0.973 for GABA. All three methods proved effective in measuring Glu with R(2)=0.987 (30 ms PRESS), R(2)=0.996 (J-resolved) and R(2)=0.910 (MEGA-PRESS). J-resolved and MEGA-PRESS yielded good results for Gln measures with respective R(2)=0.855 (J-resolved) and R(2)=0.815 (MEGA-PRESS). The 30 ms PRESS method proved ineffective in measuring GABA and Gln. When measurement stability at in vivo concentration was assessed as a function of varying spectral quality, J-resolved proved the most stable and immune to signal-to-noise and linewidth fluctuation compared to MEGA-PRESS and 30 ms PRESS.

In vivo magnetic resonance spectroscopy measurement of gray-matter and white-matter gamma-aminobutyric acid concentration in sensorimotor cortex using a motion-controlled MEGA point-resolved spectroscopy sequence

Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the brain. Understanding the GABA concentration, in vivo, is important to understand normal brain function. Using MEGA point-resolved spectroscopy sequence with interleaved water scans to detect subject motion, GABA level of sensorimotor cortex was measured using a voxel identified from a functional magnetic resonance imaging scan. The GABA level in a 20×20×20-mm(3) voxel consisting of 37%±7% gray matter, 52%±12% white matter and 11%±8% cerebrospinal fluid in the sensorimotor region was measured to be 1.43±0.48 mM. In addition, using linear regression analysis, GABA concentrations within gray and white matter were calculated to be 2.87±0.61 and 0.33±0.11 mM, respectively.

NMR and MS methods for metabonomics

Metabonomics, also often referred to as "metabolomics" or "metabolic profiling," is the systematic profiling of metabolites in bio-fluids or tissues of organisms and their temporal changes. In the last decade, metabonomics has become increasingly popular in drug development, molecular medicine, and other biotechnology fields, since it profiles directly the phenotype and changes thereof in contrast to other "-omics" technologies. The increasing popularity of metabonomics has been possible only due to the enormous development in the technology and bioinformatics fields. In particular, the analytical technologies supporting metabonomics, i.e., NMR, LC-MS, UPLC-MS, and GC-MS have evolved into sensitive and highly reproducible platforms allowing the determination of hundreds of metabolites in parallel. This chapter describes the best practices of metabonomics as seen today. All important steps of metabolic profiling in drug development and molecular medicine are described in great detail, starting from sample preparation, to determining the measurement details of all analytical platforms, and finally, to discussing the corresponding specific steps of data analysis.

A novel phase and frequency navigator for proton magnetic resonance spectroscopy using water-suppression cycling

Magnetic resonance spectroscopy is sensitive to movements, in part, because of motion-induced phase and frequency variations that lead to incoherent averaging. For in vivo proton magnetic resonance spectroscopy, the unsuppressed or under-suppressed water signal can be used to restore coherent averaging; however, this approach results in baseline distortions due to the large water peak. Therefore, a novel water-suppression cycling scheme was developed that alternates between positive and negative residual water signal. Using the residual water signal, the method allows for shot-to-shot phase and frequency correction of individual free induction decays and restoration of signal losses due to incoherent averaging, yet near-complete elimination of residual water. It is demonstrated that the residual water signal can be used to restore metabolite peaks in a brain spectrum from a subject who performed intentional head movements. The ability to correct phase and frequency fluctuations during subject motion is vital for use with adaptive motion correction approaches that ensure proper voxel positioning during head movements.

MR spectroscopy and spectroscopic imaging of the brain

Magnetic resonance spectroscopy (MRS) and the related technique of magnetic resonance spectroscopic imaging (MRSI) are widely used in both clinical and preclinical research for the non-invasive evaluation of brain metabolism. They are also used in medical practice, although their ultimate clinical value continues to be a source of discussion. This chapter reviews the general information content of brain spectra and commonly used protocols for both MRS and MRSI and also touches on data analysis methods and quantitation. The main focus is on proton MRS for application in humans, but many of the methods are also applicable to other nuclei and studies of animal models as well.

Magnetic resonance perfusion imaging without contrast media

PURPOSE

Principles of magnetic resonance imaging techniques providing perfusion-related contrast weighting without administration of contrast media are reported and analysed systematically. Especially common approaches to arterial spin labelling (ASL) perfusion imaging allowing quantitative assessment of specific perfusion rates are described in detail. The potential of ASL for perfusion imaging was tested in several types of tissue.

METHODS

After a systematic comparison of technical aspects of continuous and pulsed ASL techniques the standard kinetic model and tissue properties of influence to quantitative measurements of perfusion are reported. For the applications demonstrated in this paper a flow-sensitive alternating inversion recovery (FAIR) ASL perfusion preparation approach followed by true fast imaging with steady precession (true FISP) data recording was developed and implemented on whole-body scanners operating at 0.2, 1.5 and 3 T for quantitative perfusion measurement in various types of tissue.

RESULTS

ASL imaging provides a non-invasive tool for assessment of tissue perfusion rates in vivo. Images recorded from kidney, lung, brain, salivary gland and thyroid gland provide a spatial resolution of a few millimetres and sufficient signal to noise ratio in perfusion maps after 2-5 min of examination time.

CONCLUSIONS

Newly developed ASL techniques provide especially high image quality and quantitative perfusion maps in tissues with relatively high perfusion rates (as also present in many tumours). Averaging of acquisitions and image subtraction procedures are mandatory, leading to the necessity of synchronization of data recording to breathing in abdominal and thoracic organs.

Brain metabolite concentrations across cortical regions in healthy adults

Magnetic resonance spectroscopy (MRS) can provide in vivo information about metabolite levels across multiple brain regions. This study used MRS to examine concentrations of N-acetylaspartate (NAA), a marker of neuronal integrity and function, and choline (Cho), which is related to the amount of cell membrane per unit volume, in anterior cingulate cortex (ACC) and parieto-occipital cortex (POC) in healthy individuals. Data were drawn from two experiments which examined glutamatergic and GABAergic signaling in schizophrenia and bipolar disorder. After controlling for gray matter percentages, NAA/creatine (Cr) was 18% higher in POC than in ACC (p<0.001); Cho/Cr was 46% lower in POC than in ACC (p<0.001). There was an effect of study (p<0.001 for both metabolites), but no region by study interaction (NAA p=0.101, Cho p=0.850). Since NAA is localized to the intracellular space, these data suggest that ACC neuronal compartment is reduced as compared with POC, or that there is a lower concentration of NAA per cell in the ACC than POC, or both. Since elevated Cho suggests more cell membrane per unit volume, reduced NAA in ACC appears to be coupled with increases in overall cell membrane compartment. These findings are consistent with a number of previous studies using proton MRS which found increasing NAA and decreasing Cho moving caudally, and with postmortem anatomical studies which found neurons in more widely spaced bundles in ACC when compared to parietal and occipital cortices. MRS may be a useful tool for studying physical properties of the living human brain.

Low-power adiabatic sequences for in vivo localized two-dimensional chemical shift correlated MR spectroscopy

Novel low-power adiabatic sequences are demonstrated for in vivo localized two-dimensional correlated MR spectroscopy, such as correlated spectroscopy and total correlated spectroscopy. The design is based on three new elements for in vivo two-dimensional MRS: the use of gradient modulated constant adiabaticity GOIA-W(16,4) pulses for (i) localization (correlated spectroscopy and total correlated spectroscopy) and (ii) mixing (total correlated spectroscopy), and (iii) the use of longitudinal mixing (z-filter) for magnetization transfer during total correlated spectroscopy. GOIA-W(16,4) provides accurate signal localization, and more importantly, lowers the SAR for both total correlated spectroscopy mixing and localization. Longitudinal mixing improves considerably (fivefolds) the efficiency of total correlated spectroscopy transfer. These are markedly different from previous 1D editing total correlated spectroscopy sequences using spatially nonselective pulses and transverse mixing. Fully adiabatic (adiabatic mixing with adiabatic localization) and semiadiabatic (adiabatic mixing with nonadiabatic localization) methods for two-dimensional total correlated spectroscopy are compared. Results are presented for simulations, phantoms, and in vivo two-dimensional spectra from healthy volunteers and patients with brain tumors obtained on 3T clinical platforms equipped with standard hardware. To the best of our knowledge, this is the first demonstration of in vivo adiabatic two-dimensional total correlated spectroscopy and fully adiabatic two-dimensional correlated spectroscopy. It is expected that these methodological developments will advance the in vivo applicability of multi(spectrally)dimensional MRS to reliably identify metabolic biomarkers.

Cooperative pulses

We introduce the concept of cooperative (COOP) pulses which are designed to compensate each other's imperfections. In multi-scan experiments, COOP pulses can cancel undesired signal contributions, complementing and generalizing phase cycles. COOP pulses can be efficiently optimized using an extended version of the optimal-control-based gradient ascent pulse engineering (GRAPE) algorithm. The advantage of the COOP approach is experimentally demonstrated for broadband and band-selective pulses.

Two-dimensional MR spectroscopy of minimal hepatic encephalopathy and neuropsychological correlates in vivo

PURPOSE

To evaluate regional cerebral metabolic and structural changes in patients with minimal hepatic encephalopathy (MHE) using two-dimensional (2D) MR spectroscopy (MRS) and T( (1) )-weighted MRI, to correlate the observed MR changes with neuropsychological (NP) test scores, and to compare the diagnostic accuracy of MRI, 2D MRS, and NP tests in discriminating between patients and healthy subjects.

MATERIALS AND METHODS

Thirty-three MHE patients and 30 healthy controls were investigated. The 2D localized correlated spectroscopy (L-COSY) was performed in the frontal and occipital brain on a 1.5 Tesla (T) MR scanner. The NP test battery included 15 tests, grouped into 6 cognitive domains. Globus pallidus signal intensities were calculated from T(1)-weighted images.

RESULTS

The 2D MRS showed significant differences in ratios of the following metabolite(s) peaks with respect to creatine (Cr): decreased myo-inositol (mI), choline (Ch), mICh, and increased (glutamate plus glutamine) (Glx) in patients compared with healthy subjects in both occipital and frontal lobes. Frontal lobe taurine also showed a decline in patients. The NP test results revealed declines in cognitive speed, motor function, executive function, and global cognitive status. Significant correlations were found between the altered metabolites and NP tests. Alteration in the mICh/Cr ratio was noted as a powerful discriminant between healthy subjects and the patients.

CONCLUSION

The study demonstrates that relative metabolite levels determined by 2D MRS, in particular mICh/Cr, provide the best diagnostic prediction for MHE. The results suggest that depletions of myo-inositol, choline and taurine with respect to creatine correlate with measures of neuropsychological impairment.

The impact of pulse duration on composite WATERGATE pulse

As an effective method for solvent suppression, WATERGATE is widely used in high resolution NMR spectroscopy. It is usually composed of a number of pulses separated by constant intervals. However, theoretical and experimental analyses indicate that narrower bandwidth and lower intensities around the secondary suppression points occur in the excitation profile of the composite WATERGATE. The excitation profile distortion is caused by the chemical shift evolution during the RF pulses. The higher the ratio of pulse duration to the inter-pulse delay is, the severer the profile distorts. Therefore, in high magnetic fields, the effect will be serious when WATERGATE is applied to some biological samples whose resonances distribute over a wide range. As can be seen obviously by applying WATERGATE to detect a RNA-protein mixture sample in an 800 MHz spectrometer, the resonances of the imino protons were partially suppressed by showing decreased intensities, though the intended secondary suppression points were set far away from them. In this article, we proposed an optimized WATERGATE that could effectively compensate the chemical shift evolution during the RF pulses, and relieve the excitation profile distortion. The optimized experiment will be a good way to retain the imino signal intensities when WATERGATE is applied to detect the RNA samples in high magnetic field.

Dual-band water and lipid suppression for MR spectroscopic imaging at 3 Tesla

A dual-band water and lipid suppression sequence was developed for multislice sensitivity-encoded proton MR spectroscopic imaging of the human brain. The presaturation scheme consisted of five dual-band frequency-modulated radiofrequency pulses based on hypergeometric functions integrated with eight outer volume suppression (OVS) pulses. The flip angles of the dual-band pulses were optimized through computer simulations to maximize suppression factors over a range of transmitter amplitude of radiofrequency field and water and lipid T(1) values. The resulting hypergeometric dual band with OVS (HGDB + OVS) sequence was implemented at 3 T in a multislice sensitivity-encoded proton MR spectroscopic imaging experiment and compared to a conventional water suppression scheme (variable pulse power and optimized relaxation delays (VAPOR)) with OVS. The HGDB sequence was significantly shorter than the VAPOR sequence (230 versus 728 msec). Both HGDB + OVS and VAPOR + OVS produced good water suppression, while lipid suppression with the HGDB + OVS sequence was far superior. In sensitivity-encoded proton MR spectroscopic imaging data, artifacts from extracranial lipid signals were significantly lower with HGDB + OVS. The shorter duration of HGDB compared to VAPOR also allows reduced pulse repetition time values in the multislice acquisition.

Artificial neural networks for classification in metabolomic studies of whole cells using 1H nuclear magnetic resonance

We report the successful classification, by artificial neural networks (ANNs), of (1)H NMR spectroscopic data recorded on whole-cell culture samples of four different lung carcinoma cell lines, which display different drug resistance patterns. The robustness of the approach was demonstrated by its ability to classify the cell line correctly in 100% of cases, despite the demonstrated presence of operator-induced sources of variation, and irrespective of which spectra are used for training and for validation. The study demonstrates the potential of ANN for lung carcinoma classification in realistic situations.

A practical deuterium-free NMR method for the rapid determination of 1-octanol/water partition coefficients of pharmaceutical agents

A simple and rapid NMR method is described to determine the logP of pharmaceutical agents. This method is highly versatile and efficient, because it does not require the use of deuterated solvents or the addition of any internal/external standards to the sample. We demonstrate that logP can be accurately measured using NMR for pharmaceutical agents with known logP values. Our proposed method is made possible by the combination of state-of-the-art NMR techniques including the solvent concentration reference and robust solvent suppressions.

A phase I, pharmacokinetic, dosage escalation study of creatine monohydrate in subjects with amyotrophic lateral sclerosis

Creatine monohydrate (creatine) has potential neuroprotective properties and is a commonly used supplement in amyotrophic lateral sclerosis (ALS) and other neurodegenerative disorders. Minimum therapeutic and maximum tolerated dosages of creatine are not yet known, nor is it known what systemic plasma concentrations result from specific dosage regimens. The objectives of this study were to establish steady-state plasma pharmacokinetics of creatine at several dosages, and to evaluate the effects of creatine on brain metabolites using proton magnetic resonance spectroscopy ((1)H-MRS). Six participants with ALS received creatine at three weekly escalating oral dosages (5, 10, and 15 g b.i.d.). Plasma creatine levels and MR spectra were obtained at baseline and with each dosage increase. Mean pre-dose steady-state creatine plasma concentrations were 20.3, 39.3, and 61.5 ug/ml at 5, 10, and 15 g b.i.d., respectively. Creatine spectra increased by 8% (p = 0.06) and glutamate + glutamine signals decreased by 17% (p = 0.039) at higher dosages. There were no safety concerns at any of the dosages. In conclusion, creatine plasma concentrations increased in a dose-dependent manner. Creatine appears to cross the blood-brain barrier, and oral administration of 15 g b.i.d. is associated with increased in vivo brain creatine concentrations and decreased glutamate concentrations.

Application of LC-NMR to the identification of bulk drug impurities in NK1 antagonist GW597599 (vestipitant)

Liquid chromatography-NMR (LC-NMR) spectroscopy was used to obtain detailed information regarding the structure of the major bulk drug impurities present in GW597599 (vestipitant). The one-dimensional (1)H LC-NMR experiments were performed in both continuous and stop-flow modes on a sample of GW597599 (vestipitant) enriched with mother liquor impurities. The information derived from both LC-NMR and LC-MS data provided the structural information of all major impurities. The full characterisation of the impurities by high-resolution NMR spectroscopy was ultimately performed on appropriately synthesised compounds.

Detection of Amide and Aromatic Proton Resonances of Human Brain Metabolites Using Localized Correlated Spectroscopy Combined with Two Different Water Suppression Schemes

The purpose of the study was to demonstrate the J-coupling connectivity network between the amide, aliphatic, and aromatic proton resonances of metabolites in human brain using two-dimensional (2D) localized correlated spectroscopy (L-COSY). Two different global water suppression techniques were combined with L-COSY, one before and another after localizing the volume of interest (VOI). Phantom solutions containing several cerebral metabolites at physiological concentrations were evaluated initially for sequence optimization. Nine healthy volunteers were scanned using a 3T whole body MRI scanner. The VOI for 2D L-COSY was placed in the right occipital white/gray matter region. The 2D cross and diagonal peak volumes were measured for several metabolites such as N-acetyl aspartate (NAA), creatine (Cr), free choline (Ch), glutamate/glutamine (Glx), aspartate (Asp), myo-inositol (mI), GABA, glutathione (GSH), phosphocholine (PCh), phosphoethanolamine (PE), tyrosine (Tyr), lactate (Lac), macromolecules (MM) and homocarnosine (Car). Using the pre-water suppression technique with L-COSY, the above mentioned metabolites were clearly identifiable and the relative ratios of metabolites were calculated. In addition to detecting multitude of aliphatic resonances in the high field region, we have demonstrated that the amide and aromatic resonances can also be detected using 2D L-COSY by pre water suppression more reliably than the post-water suppression.

Proton magnetic resonance spectroscopy reveals neuroprotection by oral minocycline in a nonhuman primate model of accelerated NeuroAIDS

BACKGROUND

Despite the advent of highly active anti-retroviral therapy (HAART), HIV-associated neurocognitive disorders continue to be a significant problem. In efforts to understand and alleviate neurocognitive deficits associated with HIV, we used an accelerated simian immunodeficiency virus (SIV) macaque model of NeuroAIDS to test whether minocycline is neuroprotective against lentiviral-induced neuronal injury.

METHODOLOGY/PRINCIPAL FINDINGS

Eleven rhesus macaques were infected with SIV, depleted of CD8+ lymphocytes, and studied until eight weeks post inoculation (wpi). Seven animals received daily minocycline orally beginning at 4 wpi. Neuronal integrity was monitored in vivo by proton magnetic resonance spectroscopy and post-mortem by immunohistochemistry for synaptophysin (SYN), microtubule-associated protein 2 (MAP2), and neuronal counts. Astrogliosis and microglial activation were quantified by measuring glial fibrillary acidic protein (GFAP) and ionized calcium binding adaptor molecule 1 (IBA-1), respectively. SIV infection followed by CD8+ cell depletion induced a progressive decline in neuronal integrity evidenced by declining N-acetylaspartate/creatine (NAA/Cr), which was arrested with minocycline treatment. The recovery of this ratio was due to increases in NAA, indicating neuronal recovery, and decreases in Cr, likely reflecting downregulation of glial cell activation. SYN, MAP2, and neuronal counts were found to be higher in minocycline-treated animals compared to untreated animals while GFAP and IBA-1 expression were decreased compared to controls. CSF and plasma viral loads were lower in MN-treated animals.

CONCLUSIONS/SIGNIFICANCE

In conclusion, oral minocycline alleviates neuronal damage induced by the AIDS virus.

In vivo 1D and 2D correlation MR spectroscopy of the soleus muscle at 7T

AIM

This study aims to (1) undertake and analyse 1D and 2D MR correlation spectroscopy from human soleus muscle in vivo at 7T, and (2) determine T1 and T2 relaxation time constants at 7T field strength due to their importance in sequence design and spectral quantitation.

METHOD

Six healthy, male volunteers were consented and scanned on a 7T whole-body scanner (Siemens AG, Erlangen, Germany). Experiments were undertaken using a 28cm diameter detunable birdcage coil for signal excitation and an 8.5cm diameter surface coil for signal reception. The relaxation time constants, T1 and T2 were recorded using a STEAM sequence, using the 'progressive saturation' method for the T1 and multiple echo times for T2. The 2D L-Correlated SpectroscopY (L-COSY) method was employed with 64 increments (0.4ms increment size) and eight averages per scan, with a total time of 17min.

RESULTS

T1 and T2 values for the metabolites of interest were determined. The L-COSY spectra obtained from the soleus muscle provided information on lipid content and chemical structure not available, in vivo, at lower field strengths. All molecular fragments within multiple lipid compartments were chemically shifted by 0.20-0.26ppm at this field strength. 1D and 2D L-COSY spectra were assigned and proton connectivities were confirmed with the 2D method.

CONCLUSION

In vivo 1D and 2D spectroscopic examination of muscle can be successfully recorded at 7T and is now available to assess lipid alterations as well as other metabolites present with disease. T1 and T2 values were also determined in soleus muscle of male healthy volunteers.

Correlation of endorectal 2D JPRESS findings with pathological Gleason scores in prostate cancer patients

To determine the metabolite ratios of (Cho + Cr)/Cit and (Cho + Cr)/Spm in patients with two ranges of pathological Gleason scores, namely (3 + 4) and (4 + 3). By using the localized two-dimensional (2D) J-resolved spectroscopy (JPRESS) technique, the metabolites ratios can be calculated and correlated with prostate cancer aggressiveness. A total of 24 patients who underwent endorectal 2D JPRESS between April 2006 and July 2007 were included in this study. The 2D JPRESS voxel was localized predominantly in the peripheral zone suspected for malignancy based on pathology. Using the metabolites such as total choline (Cho), creatine (Cr), spermine (Spm) and citrate (Cit), the ratios (Cho + Cr)/Cit and (Cho + Cr)/Spm were calculated. In 14 prostate cancer patients who had a final pathologic Gleason scores of i) (3 + 4 = 7, n = 7) and ii) (4 + 3 = 7, n = 7), the metabolite ratios (mean +/- SD) of (Cho + Cr)/Cit and (Cho + Cr)/Spm were calculated using the 2D JPRESS spectra as follows: i) (1.48 +/- 0.83) and (1.59 +/- 0.73); ii) (2.90 +/- 0.94) and (2.71 +/- 1.47), respectively. Higher percentage of aggressive disease correlates with higher metabolites ratio. Our pilot study suggests that 2D JPRESS can be reliably evaluated in a clinical setting using an endorectal coil. In addition to the citrate ratio, the spermine ratio also correlates with pathology based Gleason score.

Spectroscopic imaging with improved gradient modulated constant adiabaticity pulses on high-field clinical scanners

The purpose of this work was to design and implement constant adiabaticity gradient modulated pulses that have improved slice profiles and reduced artifacts for spectroscopic imaging on 3T clinical scanners equipped with standard hardware. The newly proposed pulses were designed using the gradient offset independent adiabaticity (GOIA, Tannus and Garwood[13]) method using WURST modulation for RF and gradient waveforms. The GOIA-WURST pulses were compared with GOIA-HSn (GOIA based on nth-order hyperbolic secant) and FOCI (frequency offset corrected inversion) pulses of the same bandwidth and duration. Numerical simulations and experimental measurements in phantoms and healthy volunteers are presented. GOIA-WURST pulses provide improved slice profile that have less slice smearing for off-resonance frequencies compared to GOIA-HSn pulses. The peak RF amplitude of GOIA-WURST is much lower (40% less) than FOCI but slightly higher (14.9% more) to GOIA-HSn. The quality of spectra as shown by the analysis of lineshapes, eddy currents artifacts, subcutaneous lipid contamination and SNR is improved for GOIA-WURST. GOIA-WURST pulse tested in this work shows that reliable spectroscopic imaging could be obtained in routine clinical setup and might facilitate the use of clinical spectroscopy.

T2 relaxation time abnormalities in bipolar disorder and schizophrenia

There are substantial abnormalities in the number, density, and size of cortical neurons and glial cells in bipolar disorder and schizophrenia. Because molecule-microenvironment interactions modulate metabolite signals characteristics, these cellular abnormalities may impact transverse (T2) relaxation times. We measured T2 relaxation times for three intracellular metabolites (N-acetylaspartate+N-acetylaspartylglutamate, creatine+phosphocreatine, and choline-containing compounds) in the anterior cingulate cortex and parieto-occipital cortex from 20 healthy subjects, 15 patients with bipolar disorder, and 15 patients with schizophrenia at 4 T. Spectra used in T2 quantification were collected from 8-cc voxels with varying echo times (30 to 500 ms, in 10-ms steps). Both bipolar disorder and schizophrenia groups had numerically shorter T2 relaxation times than the healthy subjects group in both regions; these differences reached statistical significance for creatine+phosphocreatine and choline-containing compounds in bipolar disorder and for choline-containing compounds in schizophrenia. Metabolite T2 relaxation time shortening is consistent with reduced cell volumes and altered macromolecule structures, and with prolonged water T2 relaxation times reported in bipolar disorder and schizophrenia. These findings suggest that metabolite concentrations reported in magnetic resonance spectroscopy studies of psychiatric conditions may be confounded by T2 relaxation and highlight the importance of measuring and correcting for this variable.

Short echo time 1H MRSI of the human brain at 3T with adiabatic slice-selective refocusing pulses; reproducibility and variance in a dual center setting

PURPOSE

To assess the reproducibility of (1)H-MR spectroscopic imaging (MRSI) of the human brain at 3T with volume selection by a double spin echo sequence for localization with adiabatic refocusing pulses (semi-LASER).

MATERIALS AND METHODS

Twenty volunteers in two different institutions were measured twice with the same pulse sequence at an echo time of 30 msec. Magnetic resonance (MR) spectra were analyzed with LCModel with a simulated basis set including an experimentally acquired macromolecular signal profile. For specific regions in the brain mean metabolite levels, within and between subject variance, and the coefficient of variation (CoV) were calculated (for taurine, glutamate, total N-acetylaspartate, total creatine, total choline, myo-inositol + glycine, and glutamate + glutamine).

RESULTS

Repeated measurements showed no significant differences with a paired t-test and a high reproducibility (CoV ranging from 3%-30% throughout the selected volume). Mean metabolite levels and CoV obtained in similar regions in the brain did not differ significantly between two contributing institutions. The major source of differences between different measurements was identified to be the between-subject variations in the volunteers.

CONCLUSION

We conclude that semi-LASER (1)H-MRSI at 3T is an adequate method to obtain quantitative and reproducible measures of metabolite levels over large parts of the brain, applicable across multiple centers.

Detection of lactate with a hadamard slice selected, selective multiple quantum coherence, chemical shift imaging sequence (HDMD-SelMQC-CSI) on a clinical MRI scanner: Application to tumors and muscle ischemia

Lactate is an important metabolite in normal and malignant tissues detectable by NMR spectroscopy; however, it has been difficult to clinically detect the lactate methyl resonance because it is obscured by lipid resonances. The selective homonuclear multiple quantum coherence transfer technique offers a method for distinguishing lipid and lactate resonances. We implemented a three-dimensional selective homonuclear multiple quantum coherence transfer version with Hadamard slice selection and two-dimensional phase encoding (Hadamard encoded-selective homonuclear multiple quantum coherence transfer-chemical shift imaging) on a conventional clinical MR scanner. Hadamard slice selection is explained and demonstrated in vivo. This is followed by 1-cm(3) resolution lactate imaging with detection to 5-mM concentration in 20 min on a 3-T clinical scanner. An analysis of QSel gradient duration and amplitude effects on lactate and lipid signal is presented. To demonstrate clinical feasibility, a 5-min lactate scan of a patient with a non-Hodgkin's lymphoma in the superficial thigh is reported. The elevated lactate signal coincides with the T(2)-weighted image of this tumor. As a test of selective homonuclear multiple quantum coherence transfer sensitivity, a thigh tourniquet was applied to a normal volunteer and an increase in lactate was detected immediately after tourniquet flow constriction. In conclusion, the Hadamard encoded-selective homonuclear multiple quantum coherence transfer-chemical shift imaging sequence is demonstrated on a phantom and in two lipid-rich, clinically relevant, in vivo conditions.

Hybrid adiabatic-rectangular pulse train for effective saturation of magnetization within the whole heart at 3 T

Uniform T(1)-weighting is a major challenge for first-pass cardiac perfusion MRI at 3 T. Previously proposed adiabatic amplitude of radiofrequency field (B(1))-insensitive rotation (BIR-4) pulse and standard and tailored pulse trains of three nonselective pulses have been important developments but each pulse has limitations at 3 T. As an extension of the tailored pulse train, we developed a hybrid pulse train by synergistically combining two nonselective rectangular radiofrequency pulses and an adiabatic half-passage pulse, in order to achieve effective saturation of magnetization within the heart, while remaining within clinically acceptable specific absorption rate limits. The standard pulse train, tailored pulse train, hybrid pulse train, and BIR-4 pulse train were evaluated through numerical, phantom, and in vivo experiments. Among the four saturation pulses, only the hybrid pulse train yielded residual magnetization <2% of equilibrium magnetization in the heart while remaining within clinically acceptable specific absorption rate limits for multislice first-pass cardiac perfusion MRI at 3 T.

Metabolic correlatives of brain activity in a FOS epilepsy patient

The correlation and the interactions between neuronal activity and underlying metabolic dynamics are still a matter of debate, especially in pathological conditions. This study reports findings obtained on a subject suffering from fixation-off sensitivity (FOS) epilepsy, exploited as a model system of triggerable anomalous electrical activity. Functional Magnetic Resonance Spectroscopy was used to investigate the metabolic response to visual spike-inducing stimuli in a single voxel placed in the temporo-occipital lobe of a FOS epilepsy patient. MRS measurements were additionally performed on a control group of five healthy volunteers. The FOS patient also underwent an EEG session with the same stimulus paradigm. Uniquely in the FOS patient, glutamate and glutamine concentration increased during the first 10 min of stimulation and then returned to baseline. On the other hand, FOS-induced epileptic activity (spiking) endured throughout all the stimulation epoch. The observed metabolic dynamics may be likely linked to a complex interplay between alterations of the metabolic pathways of glutamate and modulation of the neuronal activity.

Magnetic resonance T2-relaxometry and 2D L-correlated spectroscopy in patients with minimal hepatic encephalopathy

PURPOSE

To evaluate T(2)-relaxation changes in patients with minimal hepatic encephalopathy (MHE) using T(2) relaxometry and to correlate T(2) values with brain metabolites evaluated using 2D magnetic resonance spectroscopy (MRS).

MATERIALS AND METHODS

Eight MHE patients and 13 healthy subjects were evaluated using T(2) relaxometry, and eight patients and nine healthy subjects underwent 2D MRS in right frontal and left occipital regions. Whole-brain T(2)-relaxation maps were compared between MHE and control subjects using analysis-of-covariance, with age and gender included as covariates. T(2) values derived from the right frontal and left occipital lobes were correlated with the metabolite ratios.

RESULTS

Multiple brain regions including anterior and mid cingulate cortices, right anterior and left posterior insular cortices, right prefrontal, medial frontal, and right superior temporal cortices showed significantly increased T(2) values in MHE patients compared to control subjects. MRS showed significantly increased ratios of glutamine/glutamate (Glx) and decreased ratios of myo-inositol, taurine, choline, and myo-inositol/choline (mICh) with respect to creatine (Cr_d) in patients compared to controls. Frontal Glx/Cr_d showed significantly positive correlation with T(2) values.

CONCLUSION

MHE patients showed significantly increased T(2) values in multiple brain regions reflecting increased free water content and T(2) values in frontal lobe correlated with the increased Glx/Cr_d ratio.

Quantitative multivoxel proton chemical shift imaging of the breast

The study of focal pathology by single-voxel magnetic resonance spectroscopy (MRS) is hampered by the impossibility to study tissue heterogeneity or compare the metabolite signals in breast lesion directly to those in unaffected tissue. Multivoxel MRS studies, while potentially allowing for truly quantitative tissue characterization, have up to now also been far from quantitative with, for example, the signal-to-noise ratio of the choline (Cho) signal serving as measure of tumor activity. Shown in this study is that in a standard clinical setting with a regular 1.5-T magnetic resonance scanner, it is possible to perform quantitative multivoxel MRS. With the use of literature values for the T1 and T2 relaxation times of Cho and water in fibroglandular breast tissue and tumors, one can determine the concentrations of Cho in different tumor compartments and surrounding tissues in two brief multivoxel MRS measurements. This opens excellent perspectives to quantitative diagnostic and follow-up studies of focal pathology such as lesions suspected of breast cancer.

High dynamic-range magnetic resonance spectroscopy (MRS) time-domain signal analysis

In the absence of water signal suppression, the proton magnetic resonance spectroscopy ((1)H MRS) in vivo water resonance signal-to-noise ratio (SNR) is orders of magnitude larger than the SNR of all the other resonances. In this case, because the high-SNR water resonance dominates the data, it is difficult to obtain reliable parameter estimates for the low SNR resonances. Herein, a new model is described that offers a solution to this problem. In this model, the time-domain signal for the low SNR resonances is represented as the conventional sum of exponentially decaying complex sinusoids. However, the time-domain signal for the high SNR water resonance is assumed to be a complex sinusoid whose amplitude is slowly varying from pure exponential decay and whose phase is slowly varying from a constant frequency. Thus, the water resonance has only an instantaneous amplitude and frequency. The water signal is neither filtered nor subtracted from the data. Instead, Bayesian probability theory is used to simultaneously estimate the frequencies, decay-rate constants, and amplitudes for all the low SNR resonances, along with the water resonance's time-dependent amplitude and phase. While computationally intensive, this approach models all of the resonances, including the water and the metabolites of interest, to within the noise level.

In vivo detection of serine in the human brain by proton magnetic resonance spectroscopy (1H-MRS) at 7 Tesla

A single-voxel proton magnetic resonance spectroscopy ((1)H-MRS) filtering strategy for in vivo detection of serine (Ser) in human brain at 7T is proposed. Spectral difference of coupled resonances arising from different subecho times of triple refocusing at a constant total echo time (TE) was utilized to detect the Ser multiplet and cancel the overlapping creatine (Cr) 3.92-ppm singlet via difference editing. Dependence of the Ser signal on subecho times was investigated using density-matrix simulation incorporating the slice-selective radio frequency (RF) pulses. The simulation indicated that the difference-edited Ser CH(2) multiplet at approximately 3.96 ppm is maximized with (TE(1), TE(2), TE(3)) = (54, 78, 78) and (36, 152, 22) ms. The edited Ser peak amplitude was estimated, with both numerical and phantom analyses of the performance, as 83% with respect to 90 degrees acquisition for a localized volume, ignoring relaxation effects. From the area ratio of the edited Ser and unedited Cr 3.03-ppm peaks, assuming identical T(1) and T(2) between Ser and Cr, the Ser-to-Cr concentration ratio for the frontal cortex of healthy adults was estimated to be 0.8 +/- 0.2 (mean +/- SD; N = 6).

Difference spectroscopy using PRESS asymmetry: application to glutamate, glutamine, and myo-inositol

A simple, clinically viable technique utilizing PRESS and strong coupling properties is presented for discrimination of coupled brain metabolites. The method relies on signal variation due to alteration of inter-echo timings (PRESS asymmetry) while maintaining a constant total echo time. Spin response of singlets and weakly coupled spins is unchanged due to PRESS asymmetry, allowing difference spectroscopy to detect unobstructed strongly coupled resonances. No changes to the standard PRESS sequence are required except variation of inter-echo timings. The procedure is illustrated for the separate detection of glutamate from glutamine and the detection of myo-inositol in simulation, phantom, and in vivo experiments at 4.7 T. The subtraction yields calculated from the simulation were 53% for glutamate and 75% for myo-inositol, and a resultant contribution of 96% glutamate to the total glutamate/glutamine multiplet in the 2.04-2.14 ppm range. To extend the treatment to other field strengths and metabolites, an analytical approximation based on a strongly coupled AB system was used to model individual spin groups. Subtraction spectroscopy yields for different combinations of coupling parameters were calculated for the detection of various strongly coupled metabolites at common clinical field strengths. The approximation also predicts adequate glutamate/glutamine discrimination at 3.0 T using the difference spectroscopy method.

N-acetyl resonances in in vivo and in vitro NMR spectroscopy of cystic ovarian tumors

An unassigned and prominent resonance in the region from delta 2.0-2.1 ppm has frequently been found in the in vivo MR spectra of cancer patients. We demonstrated the presence of this resonance with in vivo MRS in the cyst fluid of a patient with an ovarian tumor. (1)H-NMRS on the aspirated cyst fluid of this patient confirmed the observation. A complex of resonances was observed between 2.0 and 2.1 ppm. It was also present in 11 additional ovarian cyst fluid samples randomly chosen from our biobank. The resonance complex was significantly more prominent in samples from mucinous tumors than in samples from other histological subtypes. A macromolecule (>10 kDa) was found responsible for this complex of resonances. A correlation spectroscopy (COSY) experiment revealed cross peaks of two different types of bound sialic acid suggesting that N-glycans from glycoproteins and/or glycolipids cause this resonance complex. In the literature, plasma alpha-1 acid glycoprotein (AGP), known for its high content of N-linked glycans, has been suggested to contribute to the delta 2.0-2.1 spectral region. The AGP cyst fluid concentration did not correlate significantly with the peak height of the delta 2.0-2.1 resonance complex in our study. AGP may be partly responsible for the resonance complex but other N-acetylated glycoproteins and/or glycolipids also contribute. After deproteinization of the cyst fluid, N-acetyl-L-aspartic acid (NAA) was found to contribute significantly to the signal in this spectral region in three of the 12 samples. GC-MS independently confirmed the presence of NAA in high concentration in the three samples, which all derived from benign serous tumors. We conclude that both NAA and N-acetyl groups from glycoproteins and/or glycolipids may contribute to the delta 2.0-2.1 ppm resonance complex in ovarian cyst fluid. This spectral region seems to contain resonances from biomarkers that provide relevant clinical information on the type of ovarian tumor.

Application of WET sequence for the detection of the ligand signals resonating close to water

An efficient pulse sequence for observing the ligand signals resonating close to the water signal has been developed by incorporating the WET technique into the saturation transfer difference pulse sequence. Although several pulse sequences have been developed for observing a ligand binding with a protein receptor, the ligand signals resonating close to the water were undetectable owing to the interference of the huge water signal in the samples containing 95% (1)H(2)O. On the point of sample preparation, it is preferable to avoid the solvent exchange in the protein samples. In the proposed pulse sequence, a WET sequence is incorporated for the selective suppression of the water resonance. The efficient water suppression and the clear observation of the bound ligand signals close to the water have been demonstrated using the lysozyme-glucose complex.

Simultaneous convection compensation and solvent suppression in biomolecular NMR diffusion experiments

Thermal convection and high intensity solvent resonances can significantly hamper diffusion estimates in pulsed gradient spin-echo nuclear magnetic resonance diffusion experiments on biomolecule samples. To overcome these two problems, a new double functional NMR diffusion sequence, double echo PGSTE-WATERGATE, is presented. The new sequence provides excellent convection compensation and solvent suppression (with a suppression factor in excess of at least 10(5) in a single scan) in biomolecular NMR diffusion experiments. Due to its stimulated echo nature, the new sequence is much less susceptible to spin-spin relaxation than Hahn spin-echo based sequences. Furthermore, the new sequence is not susceptible to spin diffusion due to the application of bipolar pulsed gradients. The new sequence is also much easier to set up compared to previously developed stimulated echo based convection compensation and solvent suppression sequence. The utility of the new sequence is demonstrated on an aqueous lysozyme sample.

Spectral editing of weakly coupled spins using variable flip angles in PRESS constant echo time difference spectroscopy: application to GABA

A general in vivo magnetic resonance spectroscopy editing technique is presented to detect weakly coupled spin systems through subtraction, while preserving singlets through addition, and is applied to the specific brain metabolite gamma-aminobutyric acid (GABA) at 4.7 T. The new method uses double spin echo localization (PRESS) and is based on a constant echo time difference spectroscopy approach employing subtraction of two asymmetric echo timings, which is normally only applicable to strongly coupled spin systems. By utilizing flip angle reduction of one of the two refocusing pulses in the PRESS sequence, we demonstrate that this difference method may be extended to weakly coupled systems, thereby providing a very simple yet effective editing process. The difference method is first illustrated analytically using a simple two spin weakly coupled spin system. The technique was then demonstrated for the 3.01 ppm resonance of GABA, which is obscured by the strong singlet peak of creatine in vivo. Full numerical simulations, as well as phantom and in vivo experiments were performed. The difference method used two asymmetric PRESS timings with a constant total echo time of 131 ms and a reduced 120 degrees final pulse, providing 25% GABA yield upon subtraction compared to two short echo standard PRESS experiments. Phantom and in vivo results from human brain demonstrate efficacy of this method in agreement with numerical simulations.

Oral glycine administration increases brain glycine/creatine ratios in men: a proton magnetic resonance spectroscopy study

Oral high-dose glycine administration has been used as an adjuvant treatment for schizophrenia to enhance glutamate neurotransmission and mitigate glutamate system hypofunction thought to contribute to the disorder. Prior studies in schizophrenia subjects documented clinical improvements after 2 weeks of oral glycine administration, suggesting that brain glycine levels are sufficiently elevated to evoke a clinical response within that time frame. However, no human study has reported on brain glycine changes induced by its administration. We utilized a noninvasive proton magnetic resonance spectroscopy ((1)H-MRS) technique termed echo time-averaged (TEAV) (1)H-MRS, which permits noninvasive quantification of brain glycine in vivo, to determine whether 2 weeks of oral glycine administration (peak dose of 0.8 g/kg/day) increased brain glycine/creatine (Gly/Cr) ratios in 11 healthy adult men. In scans obtained 17 h after the last glycine dose, brain (Gly/Cr) ratios were significantly increased. The data indicate that it is possible to measure brain glycine changes with proton spectroscopy. Developing a more comprehensive understanding of human brain glycine dynamics may lead to optimized use of glycine site agonists and glycine transporter inhibitors to treat schizophrenia, and possibly to treat other disorders associated with glutamate system dysfunction.

In vivo magnetic resonance spectroscopy: basic methodology and clinical applications

The clinical use of in vivo magnetic resonance spectroscopy (MRS) has been limited for a long time, mainly due to its low sensitivity. However, with the advent of clinical MR systems with higher magnetic field strengths such as 3 Tesla, the development of better coils, and the design of optimized radio-frequency pulses, sensitivity has been considerably improved. Therefore, in vivo MRS has become a technique that is routinely used more and more in the clinic. In this review, the basic methodology of in vivo MRS is described-mainly focused on (1)H MRS of the brain-with attention to hardware requirements, patient safety, acquisition methods, data post-processing, and quantification. Furthermore, examples of clinical applications of in vivo brain MRS in two interesting fields are described. First, together with a description of the major resonances present in brain MR spectra, several examples are presented of deviations from the normal spectral pattern associated with inborn errors of metabolism. Second, through examples of MR spectra of brain tumors, it is shown that MRS can play an important role in oncology.