Clinical proton MR spectroscopy in central nervous system disorders

Quantitative in vivo neurochemical profiling in humans: where are we now?

Proton nuclear magnetic resonance spectroscopy of biofluids has become one of the key techniques for metabolic profiling and phenotyping. This technique has been widely used in a number of epidemiological studies and in a variety of health disorders. However, its utilization in brain disorders is limited due to the blood-brain barrier, which not only protects the brain from unwanted substances in the blood, but also substantially limits the potential of finding biomarkers for neurological disorders in serum. This review article focuses on the potential of localized in vivo proton magnetic resonance spectroscopy (¹H-MRS) for non-invasive neurochemical profiling in the human brain. First, methodological aspects of ¹H-MRS (data acquisition, processing and metabolite quantification) that are essential for reliable non-invasive neurochemical profiling are described. Second, the power of ¹H-MRS-based neurochemical profiling is demonstrated using some examples of its application in neuroscience and neurology. Finally, the authors present their vision and propose necessary steps to establish ¹H-MRS as a method suitable for large-scale neurochemical profiling in epidemiological research.

Neurochemical profile of the human cervical spinal cord determined by MRS

MRS enables insight into the chemical composition of central nervous system tissue. However, technical challenges degrade the data quality when applied to the human spinal cord. Therefore, to date detection of only the most prominent metabolite resonances has been reported in the healthy human spinal cord. The aim of this investigation is to provide an extended metabolic profile including neurotransmitters and antioxidants in addition to metabolites involved in the energy and membrane metabolism of the human cervical spinal cord in vivo. To achieve this, data quality was improved by using a custom-made, cervical detector array together with constructive averaging of a high number of echo signals, which is enabled by the metabolite cycling technique at 3T. In addition, the improved spinal cord spectra were extensively cross-validated, in vivo, post-mortem in situ and ex vivo. Reliable identification of up to nine metabolites was achieved in group analyses for the first time. Distinct features of the spinal cord neurochemical profile, in comparison with the brain neurotransmission system, include decreased concentrations of the sum of glutamate and glutamate and increased concentrations of aspartate, γ-amino-butyric acid, scyllo-inositol and the sum of myo-inositol and glycine.

Test-retest reproducibility of neurochemical profiles with short-echo, single-voxel MR spectroscopy at 3T and 7T

PURPOSE

To determine the test-retest reproducibility of neurochemical concentrations obtained with a highly optimized, short-echo, single-voxel proton MR spectroscopy (MRS) pulse sequence at 3T and 7T using state-of-the-art hardware.

METHODS

A semi-LASER sequence (echo time = 26-28 ms) was used to acquire spectra from the posterior cingulate and cerebellum at 3T and 7T from six healthy volunteers who were scanned four times weekly on both scanners. Spectra were quantified with LCModel.

RESULTS

More neurochemicals were quantified with mean Cramér-Rao lower bounds (CRLBs) ≤20% at 7T than at 3T despite comparable frequency-domain signal-to-noise ratio. Whereas CRLBs were lower at 7T (P < 0.05), between-session coefficients of variance (CVs) were comparable at the two fields with 64 transients. Five metabolites were quantified with between-session CVs ≤5% at both fields. Analysis of subspectra showed that a minimum achievable CV was reached with a lower number of transients at 7T for multiple metabolites and that between-session CVs were lower at 7T than at 3T with fewer than 64 transients.

CONCLUSION

State-of-the-art MRS methodology allows excellent reproducibility for many metabolites with 5-min data averaging on clinical 3T hardware. Sensitivity and resolution advantages at 7T are important for weakly represented metabolites, short acquisitions, and small volumes of interest. Magn Reson Med 76:1083-1091, 2016. © 2015 Wiley Periodicals, Inc.

Brain MR Contribution to the Differential Diagnosis of Parkinsonian Syndromes: An Update

Brain magnetic resonance (MR) represents a useful and feasible tool for the differential diagnosis of Parkinson's disease. Conventional MR may reveal secondary forms of parkinsonism and may show peculiar brain alterations of atypical parkinsonian syndromes. Furthermore, advanced MR techniques, such as morphometric-volumetric analyses, diffusion-weighted imaging, diffusion tensor imaging, tractography, proton MR spectroscopy, and iron-content sensitive imaging, have been used to obtain quantitative parameters useful to increase the diagnostic accuracy. Currently, many MR studies have provided both qualitative and quantitative findings, reflecting the underlying neuropathological pattern of the different degenerative parkinsonian syndromes. Although the variability in the methods and results across the studies limits the conclusion about which technique is the best, specific radiologic phenotypes may be identified. Qualitative/quantitative MR changes in the substantia nigra do not discriminate between different parkinsonisms. In the absence of extranigral abnormalities, the diagnosis of PD is more probable, whereas basal ganglia changes (mainly in the putamen) suggest the diagnosis of an atypical parkinsonian syndrome. In this context, changes in pons, middle cerebellar peduncles, and cerebellum suggest the diagnosis of MSA, in midbrain and superior cerebellar peduncles the diagnosis of PSP, and in whole cerebral hemispheres (mainly in frontoparietal cortex with asymmetric distribution) the diagnosis of Corticobasal Syndrome.

Response Assessment in Neuro-Oncology Criteria and Clinical Endpoints

The Response Assessment in Neuro-Oncology (RANO) Working Group is an international multidisciplinary group whose goal is to improve response criteria and define endpoints for neuro-oncology trials. The RANO criteria for high-grade gliomas attempt to address the issues of pseudoprogression, pseudoresponse, and nonenhancing tumor progression. Incorporation of advanced MR imaging may eventually help improve the ability of these criteria to define enhancing and nonenhancing disease better. The RANO group has also developed criteria for neurologic response and evaluation of patients receiving immunologic therapies. RANO criteria have been developed for brain metastases and are in progress for meningiomas, leptomeningeal disease, spinal tumors, and pediatric tumors.

Forecasting the quality of water-suppressed 1 H MR spectra based on a single-shot water scan

PURPOSE

To investigate whether an initial non-water-suppressed acquisition that provides information about the signal-to-noise ratio (SNR) and linewidth is enough to forecast the maximally achievable final spectral quality and thus inform the operator whether the foreseen number of averages and achieved field homogeneity is adequate.

METHODS

A large range of spectra with varying SNR and linewidth was simulated and fitted with popular fitting programs to determine the dependence of fitting errors on linewidth and SNR. A tool to forecast variance based on a single acquisition was developed and its performance evaluated on simulated and in vivo data obtained at 3 Tesla from various brain regions and acquisition settings.

RESULTS

A strong correlation to real uncertainties in estimated metabolite contents was found for the forecast values and the Cramer-Rao lower bounds obtained from the water-suppressed spectra.

CONCLUSION

It appears to be possible to forecast the best-case errors associated with specific metabolites to be found in model fits of water-suppressed spectra based on a single water scan. Thus, nonspecialist operators will be able to judge ahead of time whether the planned acquisition can possibly be of sufficient quality to answer the targeted clinical question or whether it needs more averages or improved shimming. Magn Reson Med 78:441-451, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Low plasma magnesium is associated with impaired brain metabolism in neonates with hypoxic-ischaemic encephalopathy

AIM

To determine the association between lowest plasma magnesium concentration and brain metabolism, and whether magnetic resonance imaging brain injury patterns moderated the association in hypoxic-ischemic encephalopathy.

METHODS

In 131 early (day-of-life 3) and 65 late (day-of-life 10) scans of term encephalopathic infants born between 2004 and 2012, we examined the association of lowest plasma magnesium (until day-of-life 3) on basal ganglia and white matter peak metabolite ratios on magnetic resonance spectroscopy independent of covariates, stratified by the predominant patterns of injury (normal, basal nuclei/total, watershed, multifocal) using multiple linear regression.

RESULTS

Lowest plasma magnesium was associated with lower white matter N-acetyl-aspartate/choline in the multifocal pattern on early scan (regression-coefficient, β: 0.13; 95% CI: 0.04, 0.22) and in the basal nuclei/total pattern on late scan (β: 0.08; 95% CI: 0.02, 0.15), and was negatively associated with basal ganglia lactate/N-acetyl-aspartate (β: -0.16; 95% CI: -0.05, -0.28) and lactate/choline (β: -0.1; 95% CI: -0.03, -0.17) ratio in the basal nuclei/total pattern on late scan independent of hypomagnesaemia correction, cooling and postmenstrual age at scan. Lowest plasma magnesium was not associated with metabolite ratios in other brain injury patterns.

CONCLUSION

In infants with hypoxic-ischaemic encephalopathy, predominant patterns of brain injury moderated the association between lowest plasma magnesium in the first three days of life and impaired brain metabolism.

(1) H MRS in the human spinal cord at 7 T using a dielectric waveguide transmitter, RF shimming and a high density receive array

Multimodal MRI is the state of the art method for clinical diagnostics and therapy monitoring of the spinal cord, with MRS being an emerging modality that has the potential to detect relevant changes of the spinal cord tissue at an earlier stage and to enhance specificity. Methodological challenges related to the small dimensions and deep location of the human spinal cord inside the human body, field fluctuations due to respiratory motion, susceptibility differences to adjacent tissue such as vertebras and pulsatile flow of the cerebrospinal fluid hinder the clinical application of (1) H MRS to the human spinal cord. Complementary to previous studies that partly addressed these problems, this work aims at enhancing the signal-to-noise ratio (SNR) of (1) H MRS in the human spinal cord. To this end a flexible tight fit high density receiver array and ultra-high field strength (7 T) were combined. A dielectric waveguide and dipole antenna transmission coil allowed for dual channel RF shimming, focusing the RF field in the spinal cord, and an inner-volume saturated semi-LASER sequence was used for robust localization in the presence of B1 (+) inhomogeneity. Herein we report the first 7 T spinal cord (1) H MR spectra, which were obtained in seven independent measurements of 128 averages each in three healthy volunteers. The spectra exhibit high quality (full width at half maximum 0.09 ppm, SNR 7.6) and absence of artifacts and allow for reliable quantification of N-acetyl aspartate (NAA) (NAA/Cr (creatine) 1.31 ± 0.20; Cramér-Rao lower bound (CRLB) 5), total choline containing compounds (Cho) (Cho/Cr 0.32 ± 0.07; CRLB 7), Cr (CRLB 5) and myo-inositol (mI) (mI/Cr 1.08 ± 0.22; CRLB 6) in 7.5 min in the human cervical spinal cord. Thus metabolic information from the spinal cord can be obtained in clinically feasible scan times at 7 T, and its benefit for clinical decision making in spinal cord disorders will be investigated in the future using the presented methodology. Copyright © 2016 John Wiley & Sons, Ltd.

Brain imaging and networks in restless legs syndrome

Several studies provide information useful to our understanding of restless legs syndrome (RLS), using various imaging techniques to investigate different aspects putatively involved in the pathophysiology of RLS, although there are discrepancies between these findings. The majority of magnetic resonance imaging (MRI) studies using iron-sensitive sequences supports the presence of a diffuse, but regionally variable low brain-iron content, mainly at the level of the substantia nigra, but there is increasing evidence of reduced iron levels in the thalamus. Positron emission tomography (PET) and single positron emission computed tomography (SPECT) findings mainly support dysfunction of dopaminergic pathways involving not only the nigrostriatal but also mesolimbic pathways. None or variable brain structural or microstructural abnormalities have been reported in RLS patients; reports are slightly more consistent concerning levels of white matter. Most of the reported changes were in regions belonging to sensorimotor and limbic/nociceptive networks. Functional MRI studies have demonstrated activation or connectivity changes in the same networks. The thalamus, which includes different sensorimotor and limbic/nociceptive networks, appears to have lower iron content, metabolic abnormalities, dopaminergic dysfunction, and changes in activation and functional connectivity. Summarizing these findings, the primary change could be the reduction of brain iron content, which leads to dysfunction of mesolimbic and nigrostriatal dopaminergic pathways, and in turn to a dysregulation of limbic and sensorimotor networks. Future studies in RLS should evaluate the actual causal relationship among these findings, better investigate the role of neurotransmitters other than dopamine, focus on brain networks by connectivity analysis, and test the reversibility of the different imaging findings following therapy.

MRS of pilocytic astrocytoma: The peak at 2 ppm may not be NAA

PURPOSE

To determine whether the chemical shift of residual N-acetylaspartate (NAA) signal in pilocytic astrocytomas (PA) is consistent with the position of the NAA peak in controls.

METHODS

MR spectra from 27 pediatric World Health Organization (WHO) grade I pilocytic astrocytoma patients, fifteen patients with WHO grade II and high-grade (III-IV) astrocytomas, and 36 controls were analyzed. All spectra were acquired with a short echo time (35 ms), single voxel point-resolved spectroscopy sequence on clinical 3 tesla scanners. Fully automated LCModel software was used for processing, which included the fitting of peak positions for NAA and creatine (Cr).

RESULTS

The chemical shift difference between the NAA and Cr peaks was significantly smaller (by 0.016 ± 0.005 parts per million, P < 1e-10) in PAs than in controls and was also smaller than what was observed in infiltrative astrocytomas.

CONCLUSION

The chemical shift position of the residual NAA peak in PAs is not consistent with NAA. The signal likely originates from an N-acetyl group of one or more other chemicals such as N-acetylated sugars. Magn Reson Med 78:452-456, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Advanced neuroimaging applied to veterans and service personnel with traumatic brain injury: state of the art and potential benefits

Traumatic brain injury (TBI) remains one of the most prevalent forms of morbidity among Veterans and Service Members, particularly for those engaged in the conflicts in Iraq and Afghanistan. Neuroimaging has been considered a potentially useful diagnostic and prognostic tool across the spectrum of TBI generally, but may have particular importance in military populations where the diagnosis of mild TBI is particularly challenging, given the frequent lack of documentation on the nature of the injuries and mixed etiologies, and highly comorbid with other disorders such as post-traumatic stress disorder, depression, and substance misuse. Imaging has also been employed in attempts to understand better the potential late effects of trauma and to evaluate the effects of promising therapeutic interventions. This review surveys the use of structural and functional neuroimaging techniques utilized in military studies published to date, including the utilization of quantitative fluid attenuated inversion recovery (FLAIR), susceptibility weighted imaging (SWI), volumetric analysis, diffusion tensor imaging (DTI), magnetization transfer imaging (MTI), positron emission tomography (PET), magnetoencephalography (MEG), task-based and resting state functional MRI (fMRI), arterial spin labeling (ASL), and magnetic resonance spectroscopy (MRS). The importance of quality assurance testing in current and future research is also highlighted. Current challenges and limitations of each technique are outlined, and future directions are discussed.

Magnetic Resonance Imaging to Detect Early Molecular and Cellular Changes in Alzheimer's Disease

Recent pharmaceutical trials have demonstrated that slowing or reversing pathology in Alzheimer's disease is likely to be possible only in the earliest stages of disease, perhaps even before significant symptoms develop. Pathology in Alzheimer's disease accumulates for well over a decade before symptoms are detected giving a large potential window of opportunity for intervention. It is therefore important that imaging techniques detect subtle changes in brain tissue before significant macroscopic brain atrophy. Current diagnostic techniques often do not permit early diagnosis or are too expensive for routine clinical use. Magnetic Resonance Imaging (MRI) is the most versatile, affordable, and powerful imaging modality currently available, being able to deliver detailed analyses of anatomy, tissue volumes, and tissue state. In this mini-review, we consider how MRI might detect patients at risk of future dementia in the early stages of pathological change when symptoms are mild. We consider the contributions made by the various modalities of MRI (structural, diffusion, perfusion, relaxometry) in identifying not just atrophy (a late-stage AD symptom) but more subtle changes reflective of early dementia pathology. The sensitivity of MRI not just to gross anatomy but to the underlying "health" at the cellular (and even molecular) scales, makes it very well suited to this task.

The effects of therapeutic hypothermia on cerebral metabolism in neonates with hypoxic-ischemic encephalopathy: An in vivo 1H-MR spectroscopy study

Therapeutic hypothermia has emerged as the first empirically supported therapy for neuroprotection in neonates with hypoxic-ischemic encephalopathy (HIE). We used magnetic resonance spectroscopy ((1)H-MRS) to characterize the effects of hypothermia on energy metabolites, neurotransmitters, and antioxidants. Thirty-one neonates with HIE were studied during hypothermia and after rewarming. Metabolite concentrations (mmol/kg) were determined from the thalamus, basal ganglia, cortical grey matter, and cerebral white matter. In the thalamus, phosphocreatine concentrations were increased by 20% during hypothermia when compared to after rewarming (3.49 ± 0.88 vs. 2.90 ± 0.65, p < 0.001) while free creatine concentrations were reduced to a similar degree (3.00 ± 0.50 vs. 3.74 ± 0.85, p < 0.001). Glutamate (5.33 ± 0.82 vs. 6.32 ± 1.12, p < 0.001), aspartate (3.39 ± 0.66 vs. 3.87 ± 1.19, p < 0.05), and GABA (0.92 ± 0.36 vs. 1.19 ± 0.41, p < 0.05) were also reduced, while taurine (1.39 ± 0.52 vs. 0.79 ± 0.61, p < 0.001) and glutathione (2.23 ± 0.41 vs. 2.09 ± 0.33, p < 0.05) were increased. Similar patterns were observed in other brain regions. These findings support that hypothermia improves energy homeostasis by decreasing the availability of excitatory neurotransmitters, and thereby, cellular energy demand.

In vivo imaging of neuroinflammation in schizophrenia

In recent years evidence has accumulated to suggest that neuroinflammation might be an early pathology of schizophrenia that later leads to neurodegeneration, yet the exact role in the etiology, as well as the source of neuroinflammation, are still not known. The hypothesis of neuroinflammation involvement in schizophrenia is quickly gaining popularity, and thus it is imperative that we have reliable and reproducible tools and measures that are both sensitive, and, most importantly, specific to neuroinflammation. The development and use of appropriate human in vivo imaging methods can help in our understanding of the location and extent of neuroinflammation in different stages of the disorder, its natural time-course, and its relation to neurodegeneration. Thus far, there is little in vivo evidence derived from neuroimaging methods. This is likely the case because the methods that are specific and sensitive to neuroinflammation are relatively new or only just being developed. This paper provides a methodological review of both existing and emerging positron emission tomography and magnetic resonance imaging techniques that identify and characterize neuroinflammation. We describe \how these methods have been used in schizophrenia research. We also outline the shortcomings of existing methods, and we highlight promising future techniques that will likely improve state-of-the-art neuroimaging as a more refined approach for investigating neuroinflammation in schizophrenia.

Hierarchical non-negative matrix factorization applied to three-dimensional 3 T MRSI data for automatic tissue characterization of the prostate

In this study non-negative matrix factorization (NMF) was hierarchically applied to simulated and in vivo three-dimensional 3 T MRSI data of the prostate to extract patterns for tumour and benign tissue and to visualize their spatial distribution. Our studies show that the hierarchical scheme provides more reliable tissue patterns than those obtained by performing only one NMF level. We compared the performance of three different NMF implementations in terms of pattern detection accuracy and efficiency when embedded into the same kind of hierarchical scheme. The simulation and in vivo results show that the three implementations perform similarly, although one of them is more robust and better pinpoints the most aggressive tumour voxel(s) in the dataset. Furthermore, they are able to detect tumour and benign tissue patterns even in spectra with lipid artefacts. Copyright © 2016 John Wiley & Sons, Ltd.

Metabolic Patterns in Chronic Multiple Sclerosis Lesions and Normal-appearing White Matter: Intraindividual Comparison by Using 2D MR Spectroscopic Imaging

Purpose To perform a direct metabolic comparison of chronic lesions and diffusely injured normal-appearing white matter (NAWM) in multiple sclerosis (MS). Materials and Methods In this institutional review board-approved study, with the written informed consent of all patients, two-dimensional magnetic resonance spectroscopic imaging data in 46 patients with relapsing-remitting MS (median disease duration, 0.8 year) were analyzed by using the spectral quantification tool LCModel. Metabolic patterns were evaluated for non-gadolinium-enhancing chronic lesions and the corresponding contralateral NAWM. The sensitivity of the method was assessed by reproducing the known metabolic differences between cortical gray matter (GM) and NAWM. In addition to individual spectra, averaged spectra were calculated by accumulating free induction decays over all subjects to yield an increased signal-to-noise ratio (SNR), and in turn, to allow improved curve fitting as demonstrated by lower error bounds for low-concentration metabolites. Metabolite concentrations were statistically tested for intraindividual differences (paired t tests) to avoid effects resulting from variations in disease severity or treatment. Results Differences between the metabolite concentrations in the NAWM and the cortical GM were highly significant (P < .001), demonstrating the reliability of the spectral analysis used here. The spectral patterns of the individual and averaged spectra of chronic lesions and NAWM were qualitatively very similar at visual inspection. Furthermore, in the quantitative comparison, the estimated metabolite concentrations showed only slight differences (P > .07). Owing to increased SNRs in the averaged spectra compared with individual spectra (eg, for chronic lesions, 63 vs 28.4 ± 4.1), it was possible to reliably (Cramér-Rao lower bound [CRLB], <20%) estimate scyllo-inositol levels with a CRLB of 14%. Conclusion These findings revealed that NAWM exhibits the same metabolic changes as chronic white matter lesions, even very early in the disease course, further supporting the view that such lesions may not be as relevant as widely assumed. ^© RSNA, 2016.

Basic Principles and Clinical Applications of Magnetic Resonance Spectroscopy in Neuroradiology

Magnetic resonance spectroscopy is a powerful tool to assist daily clinical diagnostics. This review is intended to give an overview on basic principles of the technology, discuss some of its technical aspects, and present typical applications in daily clinical routine in neuroradiology.

The Use of Magnetic Resonance Spectroscopy in the Evaluation of Pediatric Patients With Seizures

BACKGROUND

The objective was to determine if it is useful to routinely add magnetic resonance spectroscopy (MRS) to magnetic resonance imaging (MRI) in the evaluation of seizure in the pediatric patient. Specifically, how often does MRS contribute information to conventional MRI?

METHODS

A retrospective search, over a period of 3 years, of patients <18 years of age who underwent both MRI and MRS as part of the evaluation of seizures yielded a total of 233 cases in 216 patients. The medical records were reviewed to determine how many patients carried a diagnosis relevant to seizures. The MRIs and MRSs were reviewed by two neuroradiologists and an MR physicist/spectroscopist who determined by consensus in how many cases MRS contributed information regarding management, diagnosis, or prognosis, in addition to the findings on MRI alone.

RESULTS

In 100 of 233 cases (43%), MRS contributed information additional to MRI. In 40 cases, MRS contributed information relevant to patient management by prompting an evaluation for an underlying inborn error of metabolism. MRS contributed information relevant to diagnosis in 24 of 100 cases (e.g., neoplasm versus dysplasia). MRS contributed information relevant to prognosis in 36 cases (e.g., hypoxic-ischemic injury). MRS added more information in cases where the patients had a diagnosis relevant to seizure before imaging. Interestingly, in 25 cases where the MRI was normal, MRS was found to be abnormal, which prompted evaluation for an inborn error of metabolism.

CONCLUSIONS

These results suggest that MRS is a useful evaluation tool in addition to MRI for children undergoing imaging for the evaluation of seizures.

A novel, integrated PET-guided MRS technique resulting in more accurate initial diagnosis of high-grade glioma

Glioblastoma multiforme (GBM) is the most common and lethal malignant glioma in adults. Currently, the modality of choice for diagnosing brain tumor is high-resolution magnetic resonance imaging (MRI) with contrast, which provides anatomic detail and localization. Studies have demonstrated, however, that MRI may have limited utility in delineating the full tumor extent precisely. Studies suggest that MR spectroscopy (MRS) can also be used to distinguish high-grade from low-grade gliomas. However, due to operator dependent variables and the heterogeneous nature of gliomas, the potential for error in diagnostic accuracy with MRS is a concern. Positron emission tomography (PET) imaging with (11)C-methionine (MET) and (18)F-fluorodeoxyglucose (FDG) has been shown to add additional information with respect to tumor grade, extent, and prognosis based on the premise of biochemical changes preceding anatomic changes. Combined PET/MRS is a technique that integrates information from PET in guiding the location for the most accurate metabolic characterization of a lesion via MRS. We describe a case of glioblastoma multiforme in which MRS was initially non-diagnostic for malignancy, but when MRS was repeated with PET guidance, demonstrated elevated choline/N-acetylaspartate (Cho/NAA) ratio in the right parietal mass consistent with a high-grade malignancy. Stereotactic biopsy, followed by PET image-guided resection, confirmed the diagnosis of grade IV GBM. To our knowledge, this is the first reported case of an integrated PET/MRS technique for the voxel placement of MRS. Our findings suggest that integrated PET/MRS may potentially improve diagnostic accuracy in high-grade gliomas.

Hitchhiker's Guide to Voxel Segmentation for Partial Volume Correction of In Vivo Magnetic Resonance Spectroscopy

Partial volume effects have the potential to cause inaccuracies when quantifying metabolites using proton magnetic resonance spectroscopy (MRS). In order to correct for cerebrospinal fluid content, a spectroscopic voxel needs to be segmented according to different tissue contents. This article aims to detail how automated partial volume segmentation can be undertaken and provides a software framework for researchers to develop their own tools. While many studies have detailed the impact of partial volume correction on proton magnetic resonance spectroscopy quantification, there is a paucity of literature explaining how voxel segmentation can be achieved using freely available neuroimaging packages.

Myo-inositol changes precede amyloid pathology and relate to APOE genotype in Alzheimer disease

OBJECTIVE

We aimed to test whether in vivo levels of magnetic resonance spectroscopy (MRS) metabolites myo-inositol (mI), N-acetylaspartate (NAA), and choline are abnormal already during preclinical Alzheimer disease (AD), relating these changes to amyloid or tau pathology, and functional connectivity.

METHODS

In this cross-sectional multicenter study (a subset of the prospective Swedish BioFINDER study), we included 4 groups, representing the different stages of predementia AD: (1) cognitively healthy elderly with normal CSF β-amyloid 42 (Aβ42), (2) cognitively healthy elderly with abnormal CSF Aβ42, (3) patients with subjective cognitive decline and abnormal CSF Aβ42, (4) patients with mild cognitive decline and abnormal CSF Aβ42 (Ntotal = 352). Spectroscopic markers measured in the posterior cingulate/precuneus were considered alongside known disease biomarkers: CSF Aβ42, phosphorylated tau, total tau, [(18)F]-flutemetamol PET, f-MRI, and the genetic risk factor APOE.

RESULTS

Amyloid-positive cognitively healthy participants showed a significant increase in mI/creatine and mI/NAA levels compared to amyloid-negative healthy elderly (p < 0.05). In amyloid-positive healthy elderly, mI/creatine and mI/NAA correlated with cortical retention of [(18)F] flutemetamol tracer ([Formula: see text] = 0.44, p = 0.02 and [Formula: see text] = 0.51, p = 0.01, respectively). Healthy elderly APOE ε4 carriers with normal CSF Aβ42 levels had significantly higher mI/creatine levels (p < 0.001) than ε4 noncarriers. Finally, elevated mI/creatine was associated with decreased functional connectivity within the default mode network (rpearson = -0.16, p = 0.02), independently of amyloid pathology.

CONCLUSIONS

mI levels are elevated already at asymptomatic stages of AD. Moreover, mI/creatine concentrations were increased in healthy APOE ε4 carriers with normal CSF Aβ42 levels, suggesting that mI levels may reveal regional brain consequences of APOE ε4 before detectable amyloid pathology.

Three-dimensional MR spectroscopic imaging using adiabatic spin echo and hypergeometric dual-band suppression for metabolic mapping over the entire brain

PURPOSE

Large lipid and water signals in MR spectroscopic imaging (MRSI) complicate brain metabolite quantification. In this study, we combined adiabatic hypergeometric dual-band (HGDB) lipid and water suppression with gradient offset independent adiabatic (GOIA) spin echo to improve three-dimensional (3D) MRSI of the entire brain.

METHODS

3D MRSI was acquired at 3T with a 32-channel coil. HGDB pulses were used before excitation and during echo time. A brain slab was selected with GOIA-W(16,4) pulses, weighted phase encoded stack of spirals, and real-time motion/shim correction. HGDB alone or in combination with OVS and MEGA (MEscher-GArwood) was compared with OVS only and no suppression.

RESULTS

The combined HGDB pulses suppressed lipids to 2%-3% of their full unsuppressed signal. The HGDB lipid suppression was on average 5 times better than OVS suppression. HGDB+MEGA provided 30% more suppression compared with a previously described HGDB+OVS scheme. The number of voxels with good metabolic fits was significantly larger in the HGDB data (91%-94%) compared with the OVS data (59%-80%).

CONCLUSION

HGDB pulses provided efficient lipid and water suppression for full brain 3D MRSI. The HGDB suppression is superior to traditional OVS, and it can be combined with adiabatic spin echo to provide a sequence that is robust to B₁ inhomogeneity. Magn Reson Med 77:490-497, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Influence of macromolecule baseline on 1 H MR spectroscopic imaging reproducibility

Purpose

Poorly characterized macromolecular (MM) and baseline artefacts are known to reduce metabolite quantitation accuracy in ¹H MR spectroscopic imaging (MRSI). Increasing echo time (TE) and improvements in MM analysis schemes have both been proposed as strategies to improve metabolite measurement reliability. In this study, the influence of TE and two MM analysis schemes on MRSI reproducibility are investigated.

Methods

An experimentally acquired baseline was collected using an inversion recovery sequence (TI = 750 ms) and incorporated into the analysis method. Intrasubject reproducibility of MRSI scans, acquired at 3 Tesla, was assessed using metabolite coefficients of variance (COVs) for both experimentally acquired and simulated MM analysis schemes. In addition, the reproducibility of TE = 35 ms, 80 ms, and 144 ms was evaluated.

Results

TE = 80 ms was the most reproducible for singlet metabolites with COVs < 6% for total N‐acetyl‐aspartate, total creatine, and total choline; however, moderate multiplet dephasing was observed. Analysis incorporating the experimental baseline achieved higher Glu and Glx reproducibility at TE = 35 ms, and showed improvements over the simulated baseline, with higher efficacy for poorer data.

Conclusion

Overall, TE = 80 ms yielded the most reproducible singlet metabolite estimates. However, combined use of a short TE sequence and the experimental baseline may be preferred as a compromise between accuracy, multiplet dephasing, and T2 bias on metabolite estimates. Magn Reson Med 77:34–43, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Clinical magnetic resonance spectroscopy of the central nervous system

Proton magnetic resonance spectroscopy (1H MRS) is a noninvasive imaging technique that can easily be added to the conventional magnetic resonance (MR) imaging sequences. Using MRS one can directly compare spectra from pathologic or abnormal tissue and normal tissue. Metabolic changes arising from pathology that can be visualized by MRS may not be apparent from anatomy that can be visualized by conventional MR imaging. In addition, metabolic changes may precede anatomic changes. Thus, MRS is used for diagnostics, to observe disease progression, monitor therapeutic treatments, and to understand the pathogenesis of diseases. MRS may have an important impact on patient management. The purpose of this chapter is to provide practical guidance in the clinical application of MRS of the brain. This chapter provides an overview of MRS-detectable metabolites and their significance. In addition some specific current clinical applications of MRS will be discussed, including brain tumors, inborn errors of metabolism, leukodystrophies, ischemia, epilepsy, and neurodegenerative diseases. The chapter concludes with technical considerations and challenges of clinical MRS.

Noninvasive Quantification of 2-Hydroxyglutarate in Human Gliomas with IDH1 and IDH2 Mutations

Mutations in the isocitrate dehydrogenase genes (IDH1/2) occur often in diffuse gliomas, where they are associated with abnormal accumulation of the oncometabolite 2-hydroxyglutarate (2-HG). Monitoring 2-HG levels could provide prognostic information in this disease, but detection strategies that are noninvasive and sufficiently quantitative have yet to be developed. In this study, we address this need by presenting a proton magnetic resonance spectroscopy ((1)H-MRS) acquisition scheme that uses an ultrahigh magnetic field (≥ 7T) capable of noninvasively detecting 2-HG with quantitative measurements sufficient to differentiate mutant cytosolic IDH1 and mitochondrial IDH2 in human brain tumors. Untargeted metabolomics analysis of in vivo (1)H-MRS spectra discriminated between IDH-mutant tumors and healthy tissue, and separated IDH1 from IDH2 mutations. High-quality spectra enabled the quantification of neurochemical profiles consisting of at least eight metabolites, including 2-HG, glutamate, lactate, and glutathione in both tumor and healthy tissue voxels. Notably, IDH2 mutation produced more 2-HG than IDH1 mutation, consistent with previous findings in cell culture. By offering enhanced sensitivity and specificity, this scheme can quantitatively detect 2-HG and associated metabolites that may accumulate during tumor progression, with implications to better monitor patient responses to therapy.

Middle cerebellar peduncles: Magnetic resonance imaging and pathophysiologic correlate

We describe common and less common diseases that can cause magnetic resonance signal abnormalities of middle cerebellar peduncles (MCP), offering a systematic approach correlating imaging findings with clinical clues and pathologic mechanisms. Myelin abnormalities, different types of edema or neurodegenerative processes, can cause areas of abnormal T2 signal, variable enhancement, and patterns of diffusivity of MCP. Pathologies such as demyelinating disorders or certain neurodegenerative entities (e.g., multiple system atrophy or fragile X-associated tremor-ataxia syndrome) appear to have predilection for MCP. Careful evaluation of concomitant imaging findings in the brain or brainstem; and focused correlation with key clinical findings such as immunosuppression for progressive multifocal leukoencephalopahty; hypertension, post-transplant status or high dose chemotherapy for posterior reversible encephalopathy; electrolyte disorders for myelinolysis or suspected toxic-drug related encephalopathy; would yield an appropriate and accurate differential diagnosis in the majority of cases.

Classification of brain tumours from MR spectra: the INTERPRET collaboration and its outcomes

The INTERPRET project was a multicentre European collaboration, carried out from 2000 to 2002, which developed a decision-support system (DSS) for helping neuroradiologists with no experience of MRS to utilize spectroscopic data for the diagnosis and grading of human brain tumours. INTERPRET gathered a large collection of MR spectra of brain tumours and pseudo-tumoural lesions from seven centres. Consensus acquisition protocols, a standard processing pipeline and strict methods for quality control of the aquired data were put in place. Particular emphasis was placed on ensuring the diagnostic certainty of each case, for which all cases were evaluated by a clinical data validation committee. One outcome of the project is a database of 304 fully validated spectra from brain tumours, pseudotumoural lesions and normal brains, along with their associated images and clinical data, which remains available to the scientific and medical community. The second is the INTERPRET DSS, which has continued to be developed and clinically evaluated since the project ended. We also review here the results of the post-INTERPRET period. We evaluate the results of the studies with the INTERPRET database by other consortia or research groups. A summary of the clinical evaluations that have been performed on the post-INTERPRET DSS versions is also presented. Several have shown that diagnostic certainty can be improved for certain tumour types when the INTERPRET DSS is used in conjunction with conventional radiological image interpretation. About 30 papers concerned with the INTERPRET single-voxel dataset have so far been published. We discuss stengths and weaknesses of the DSS and the lessons learned. Finally we speculate on how the INTERPRET concept might be carried into the future.

Metabolic Alterations in Developing Brain After Injury: Knowns and Unknowns

Brain development is a highly orchestrated complex process. The developing brain utilizes many substrates including glucose, ketone bodies, lactate, fatty acids and amino acids for energy, cell division and the biosynthesis of nucleotides, proteins and lipids. Metabolism is crucial to provide energy for all cellular processes required for brain development and function including ATP formation, synaptogenesis, synthesis, release and uptake of neurotransmitters, maintaining ionic gradients and redox status, and myelination. The rapidly growing population of infants and children with neurodevelopmental and cognitive impairments and life-long disability resulting from developmental brain injury is a significant public health concern. Brain injury in infants and children can have devastating effects because the injury is superimposed on the high metabolic demands of the developing brain. Acute injury in the pediatric brain can derail, halt or lead to dysregulation of the complex and highly regulated normal developmental processes. This paper provides a brief review of metabolism in developing brain and alterations found clinically and in animal models of developmental brain injury. The metabolic changes observed in three major categories of injury that can result in life-long cognitive and neurological disabilities, including neonatal hypoxia-ischemia, pediatric traumatic brain injury, and brain injury secondary to prematurity are reviewed.

From raw data to data-analysis for magnetic resonance spectroscopy--the missing link: jMRUI2XML

Background

Magnetic resonance spectroscopy provides metabolic information about living tissues in a non-invasive way. However, there are only few multi-centre clinical studies, mostly performed on a single scanner model or data format, as there is no flexible way of documenting and exchanging processed magnetic resonance spectroscopy data in digital format. This is because the DICOM standard for spectroscopy deals with unprocessed data.

This paper proposes a plugin tool developed for jMRUI, namely jMRUI2XML, to tackle the latter limitation. jMRUI is a software tool for magnetic resonance spectroscopy data processing that is widely used in the magnetic resonance spectroscopy community and has evolved into a plugin platform allowing for implementation of novel features.

Results

jMRUI2XML is a Java solution that facilitates common preprocessing of magnetic resonance spectroscopy data across multiple scanners. Its main characteristics are: 1) it automates magnetic resonance spectroscopy preprocessing, and 2) it can be a platform for outputting exchangeable magnetic resonance spectroscopy data. The plugin works with any kind of data that can be opened by jMRUI and outputs in extensible markup language format. Data processing templates can be generated and saved for later use.

The output format opens the way for easy data sharing- due to the documentation of the preprocessing parameters and the intrinsic anonymization - for example for performing pattern recognition analysis on multicentre/multi-manufacturer magnetic resonance spectroscopy data.

Conclusions

jMRUI2XML provides a self-contained and self-descriptive format accounting for the most relevant information needed for exchanging magnetic resonance spectroscopy data in digital form, as well as for automating its processing. This allows for tracking the procedures the data has undergone, which makes the proposed tool especially useful when performing pattern recognition analysis. Moreover, this work constitutes a first proposal for a minimum amount of information that should accompany any magnetic resonance processed spectrum, towards the goal of achieving better transferability of magnetic resonance spectroscopy studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-015-0796-5) contains supplementary material, which is available to authorized users.

Does superficial fat affect metabolite concentrations determined by MR spectroscopy with water referencing?

It has recently been reported in this journal that local fat depots produce a sizable frequency-dependent signal attenuation in magnetic resonance spectroscopy (MRS) of the brain. If of a general nature, this effect would question the use of internal reference signals for quantification of MRS and the quantitative use of MRS as a whole. Here, it was attempted to verify this effect and pinpoint the potential causes by acquiring data with various acquisition settings, including two field strengths, two MR scanners from different vendors, different water suppression sequences, RF coils, localization sequences, echo times, and lipid/metabolite phantoms. With all settings tested, the reported effect could not be reproduced, and it is concluded that water referencing and quantitative MRS per se remain valid tools under common acquisition conditions.

Whole-Brain N-Acetylaspartate Concentration Is Preserved during Mild Hypercapnia Challenge

BACKGROUND AND PURPOSE

Although NAA is often used as a marker of neuronal health and integrity in neurologic disorders, its normal response to physiologic challenge is not well-established and its changes are almost always attributed exclusively to brain pathology. The purpose of this study was to test the hypothesis that the neuronal cell marker NAA, often used to assess neuronal health and integrity in neurologic disorders, is not confounded by (possibly transient) physiologic changes. Therefore, its decline, when observed by using (1)H-MR spectroscopy, can almost always be attributed exclusively to brain pathology.

MATERIALS AND METHODS

Twelve healthy young male adults underwent a transient hypercapnia challenge (breathing 5% CO2 air mixture), a potent vasodilator known to cause a substantial increase in CBF and venous oxygenation. We evaluated their whole-brain NAA by using nonlocalizing proton MR spectroscopy, venous oxygenation with T2-relaxation under spin-tagging MR imaging, CBF with pseudocontinuous arterial spin-labeling, and the cerebral metabolic rate of oxygen, during normocapnia (breathing room air) and hypercapnia.

RESULTS

There was insignificant whole-brain NAA change (P = .88) from normocapnia to hypercapnia and back to normocapnia in this cohort, as opposed to highly significant increases: 28.0 ± 10.3% in venous oxygenation and 49.7 ± 16.6% in global CBF (P < 10(-4)); and a 6.4 ± 10.9% decrease in the global cerebral metabolic rate of oxygen (P = .04).

CONCLUSIONS

Stable whole-brain NAA during normocapnia and hypercapnia, despite significant global CBF and cerebral metabolic rate of oxygen changes, supports the hypothesis that global NAA changes are insensitive to transient physiology. Therefore, when observed, they most likely reflect underlying pathology resulting from neuronal cell integrity/viability changes, instead of a response to physiologic changes.

Metabolic mapping reveals sex-dependent involvement of default mode and salience network in alexithymia

Alexithymia, a personality construct marked by difficulties in processing one's emotions, has been linked to the altered activity in the anterior cingulate cortex (ACC). Although longitudinal studies reported sex differences in alexithymia, what mediates them is not known. To investigate sex-specific associations of alexithymia and neuronal markers, we mapped metabolites in four brain regions involved differentially in emotion processing using a point-resolved spectroscopy MRS sequence in 3 Tesla. Both sexes showed negative correlations between alexithymia and N-acetylaspartate (NAA) in pregenual ACC (pgACC). Women showed a robust negative correlation of the joint measure of glutamate and glutamine (Glx) to NAA in posterior cingulate cortex (PCC), whereas men showed a weak positive association of Glx to NAA in dorsal ACC (dACC). Our results suggest that lowered neuronal integrity in pgACC, a region of the default mode network (DMN), might primarily account for the general difficulties in emotional processing in alexithymia. Association of alexithymia in women extends to another region in the DMN-PCC, while in men a region in the salience network (SN) was involved. These observations could be representative of sex specific regulation strategies that include diminished internal evaluation of feelings in women and cognitive emotion suppression in men.

In vivo brain rosette spectroscopic imaging (RSI) with LASER excitation, constant gradient strength readout, and automated LCModel quantification for all voxels

PURPOSE

To optimize the Rosette trajectories for high-sensitivity in vivo brain spectroscopic imaging and reduced gradient demands.

METHODS

Using LASER localization, a rosette based sampling scheme for in vivo brain spectroscopic imaging data on a 3 Tesla (T) system is described. The two-dimensional (2D) and 3D rosette spectroscopic imaging (RSI) data were acquired using 20 × 20 in-plane resolution (8 × 8 mm(2) ), and 1 (2D) -18 mm (1.1 cc) or 12 (3D) -8 mm partitions (0.5 cc voxels). The performance of the RSI acquisition was compared with a conventional spectroscopic imaging (SI) sequence using LASER localization and 2D or 3D elliptical phase encoding (ePE). Quantification of the entire RSI data set was performed using an LCModel based pipeline.

RESULTS

The RSI acquisitions took 32 s for the 2D scan, and as short as 5 min for the 3D 20 × 20 × 12 scan, using a maximum gradient strength Gmax=5.8 mT/m and slew-rate Smax=45 mT/m/ms. The Bland-Altman agreement between RSI and ePE CSI, characterized by the 95% confidence interval for their difference (RSI-ePE), is within 13% of the mean (RSI+ePE)/2. Compared with the 3D ePE at the same nominal resolution, the effective RSI voxel size was three times smaller while the measured signal-to-noise ratio sensitivity, after normalization for differences in effective size, was 43% greater.

CONCLUSION

3D LASER-RSI is a fast, high-sensitivity spectroscopic imaging sequence, which can acquire medium-to-high resolution SI data in clinically acceptable scan times (5-10 min), with reduced stress on the gradient system. Magn Reson Med 76:380-390, 2016. © 2015 Wiley Periodicals, Inc.

β-Hydroxybutyrate attenuates NMDA-induced spasms in rats with evidence of neuronal stabilization on MR spectroscopy

BACKGROUND

Infantile spasms (IS) is a devastating epileptic encephalopathy. The ketogenic diet (KD) has been successfully used as a treatment for IS. This study was designed to test whether beta-hydroxybutyrate (BHB), a major metabolite of the KD, is effective in an animal model of IS.

METHODS

Pregnant rats received betamethasone on gestational day 15. The offspring received either single [30min prior to NMDA-triggered spasms on postnatal day (P) 15] or prolonged (three per day from P12 to P15) i.p. BHB. An additional experiment used repeated bouts of spasms on P12, P13, and P15 with randomized prolonged BHB treatment initiated after the first spasms. We determined the latency to onset of spasms and the number of spasms after the NMDA injection on P15. The rats that received randomized BHB treatment were also monitored with open field, sociability, and fear-conditioning tests and underwent in vivo (1)H MR imaging on a 9.4T MR system after NMDA-induced spasms. The acquired (1)H MR spectra were quantified using LC model.

RESULTS

Single-dose BHB pretreatment had no effect on spasms. In contrast, prolonged pretreatment with BHB significantly delayed the onset and decreased the frequency of spasms. In addition, randomized prolonged BHB treatment resulted in a significant reduction in number of spasms at P15. BHB treatment had no significant effect on motor activities, but significantly decreased the interactions with strangers and increased the contextual memory. On MR spectroscopic analysis of randomized prolonged BHB-treated rats at 24h after the cluster of spasms, the elevation of GABA, glutamine, glutamate, total creatine, macromolecule-plus lipids, and N-acetylaspartate levels after spasms were significantly attenuated by randomized BHB treatment (p<0.05).

SIGNIFICANCE

Prolonged administration of BHB directly suppresses development of spasms in a rat model of IS with acute stabilization of brain metabolites. Additionally, BHB appears to decrease the interests to other rats and improve memory responses.

Improved Diagnostic Accuracy in Characterization of Adnexal Masses by Detection of Choline Peak Using 1H MR Spectroscopy in Comparison to Internal Reference at 3 Tesla

BACKGROUND

The aim of this study was to assess the role of the presence of a choline peak in 3 Tesla 1H magnetic resonance spectroscopy (MRS) for differentiating benign from malignant adnexal masses.

MATERIALS AND METHODS

A total of 46 adnexal masses (23 malignant and 23 benign) underwent 1H MRS study prior to surgery to assess the presence of choline peak.

RESULTS

A choline peak was detected in 16 malignant masses (69.5%) and was absent in the other 7 (30.5%). A choline peak was only detected in 6 (26%) of the benign adnexal masses. The presence of an MRS choline peak had a sensitivity of 69.5%, a specificity of 74%, a positive predictive value (PPV) of 72.7%, and a negative predictive value (NPV) of 71% for diagnosing malignant adnexal masses. A significant difference between the frequency of mean choline peaks in benign and malignant adnexal masses was observed (P value<0.01).

CONCLUSIONS

A 1H MRS choline peak is seen in malignant adnexal masses more frequently than the benign masses, and may be helpful for diagnosing malignant adnexal masses.

Metabolic Alterations in Developing Brain After Injury: Knowns and Unknowns

Brain development is a highly orchestrated complex process. The developing brain utilizes many substrates including glucose, ketone bodies, lactate, fatty acids and amino acids for energy, cell division and the biosynthesis of nucleotides, proteins and lipids. Metabolism is crucial to provide energy for all cellular processes required for brain development and function including ATP formation, synaptogenesis, synthesis, release and uptake of neurotransmitters, maintaining ionic gradients and redox status, and myelination. The rapidly growing population of infants and children with neurodevelopmental and cognitive impairments and life-long disability resulting from developmental brain injury is a significant public health concern. Brain injury in infants and children can have devastating effects because the injury is superimposed on the high metabolic demands of the developing brain. Acute injury in the pediatric brain can derail, halt or lead to dysregulation of the complex and highly regulated normal developmental processes. This paper provides a brief review of metabolism in developing brain and alterations found clinically and in animal models of developmental brain injury. The metabolic changes observed in three major categories of injury that can result in life-long cognitive and neurological disabilities, including neonatal hypoxia-ischemia, pediatric traumatic brain injury, and brain injury secondary to prematurity are reviewed.

Combined MRI and MRS improves pre-therapeutic diagnoses of pediatric brain tumors over MRI alone

INTRODUCTION

The specific goal of this study was to determine whether the inclusion of MRS had a measureable and positive impact on the accuracy of pre-surgical MR examinations of untreated pediatric brain tumors over that of MRI alone in clinical practice.

METHODS

Final imaging reports of 120 pediatric patients with newly detected brain tumors who underwent combined MRI/MRS examinations were retrospectively reviewed. Final pathology was available in all cases. Group A comprised 60 subjects studied between June 2001 and January 2005, when MRS was considered exploratory and radiologists utilized only conventional MRI to arrive at a diagnosis. For group B, comprising 60 subjects studied between January 2005 and March 2008, the radiologists utilized information from both MRI and MRS. Furthermore, radiologists revisited group A (blind review, time lapse >4 years) to determine whether the additional information from MRS would have altered their interpretation.

RESULTS

Sixty-three percent of patients in group A were diagnosed correctly, whereas in 10% the report was partially correct with the final tumor type mentioned (but not mentioned as most likely tumor), while in 27% of cases the reports were wrong. For group B, the diagnoses were correct in 87%, partially correct in 5%, and incorrect in 8% of the cases, which is a significant improvement (p < 0.005). Re-review of combined MRI and MRS of group A resulted 87% correct, 7% partially correct, and 7% incorrect diagnoses, which is a significant improvement over the original diagnoses (p < 0.05).

CONCLUSION

Adding MRS to conventional MRI significantly improved diagnostic accuracy in preoperative pediatric patients with untreated brain tumors.

Hyperpolarized (13)C Magnetic Resonance and Its Use in Metabolic Assessment of Cultured Cells and Perfused Organs

Diseased tissue is often characterized by abnormalities in intermediary metabolism. Observing these alterations in situ may lead to an improved understanding of pathological processes and novel ways to monitor these processes noninvasively in human patients. Although (13)C is a stable isotope safe for use in animal models of disease as well as human subjects, its utility as a metabolic tracer has largely been limited to ex vivo analyses employing analytical techniques like mass spectrometry or nuclear magnetic resonance spectroscopy. Neither of these techniques is suitable for noninvasive metabolic monitoring, and the low abundance and poor gyromagnetic ratio of conventional (13)C make it a poor nucleus for imaging. However, the recent advent of hyperpolarization methods, particularly dynamic nuclear polarization (DNP), makes it possible to enhance the spin polarization state of (13)C by many orders of magnitude, resulting in a temporary amplification of the signal sufficient for monitoring kinetics of enzyme-catalyzed reactions in living tissue through magnetic resonance spectroscopy or magnetic resonance imaging. Here, we review DNP techniques to monitor metabolism in cultured cells, perfused hearts, and perfused livers, focusing on our experiences with hyperpolarized [1-(13)C]pyruvate. We present detailed approaches to optimize the DNP procedure, streamline biological sample preparation, and maximize detection of specific metabolic activities. We also discuss practical aspects in the choice of metabolic substrates for hyperpolarization studies and outline some of the current technical and conceptual challenges in the field, including efforts to use hyperpolarization to quantify metabolic rates in vivo.

The contribution of cerebellar proton magnetic resonance spectroscopy in the differential diagnosis among parkinsonian syndromes

INTRODUCTION

The in vivo differential diagnosis between idiopathic Parkinson's disease (PD) and atypical parkinsonian syndromes (PS), such as multiple system atrophy [MSA with a cerebellar (C) and parkinsonian (P) subtype] and progressive supranuclear palsy - Richardson's Syndrome (PSP-RS) is often challenging. Previous brain MR proton spectroscopy ((1)H-MRS) studies showed biochemical alterations in PS, despite results are conflicting. Cerebellum plays a central role in motor control and its alterations has been already demonstrated in atypical PS. The main aim of this study was to evaluate diagnostic accuracy of cerebellar (1)H-MRS in the differential diagnosis between PD and atypical PS.

METHODS

We obtained (1)H-MRS spectra from the left cerebellar hemisphere of 57 PS (21 PD, and 36 atypical PS) and 14 unaffected controls by using a 1.5 T GE scanner. N-acetyl-aspartate (NAA)/Creatine (Cr), choline-containing compounds (Cho)/Cr, myoinositol (mI)/Cr, and NAA/mI ratios were calculated.

RESULTS

NAA/Cr and NAA/mI ratios were significantly lower (p < 0.01) in atypical PS compared to PD and controls, and in MSA-C compared to PD, MSA-P, PSP-RS and controls. PSP-RS group showed reduced NAA/Cr ratios compared to PD (p < 0.05) and controls (p < 0.05), and reduced NAA/mI compared to controls (p < 0.01). NAA/Cr ratio values higher than 1.016 showed 100% sensitivity and negative predictive value, 62% positive predictive value and 64% specificity in discriminating PD.

CONCLUSION

Cerebellar biochemical alterations detected by using (1)H-MRS could represent an adjunctive diagnostic tool to improve the differential diagnosis of PS.

Feasibility and reproducibility of neurochemical profile quantification in the human hippocampus at 3 T

Hippocampal dysfunction is known to be associated with several neurological and neuropsychiatric disorders such as Alzheimer's disease, epilepsy, schizophrenia and depression; therefore, there has been significant clinical interest in studying hippocampal neurochemistry. However, the hippocampus is a challenging region to study using (1) H MRS, hence the use of MRS for clinical research in this region has been limited. Our goal was therefore to investigate the feasibility of obtaining high-quality hippocampal spectra that allow reliable quantification of a neurochemical profile and to establish inter-session reproducibility of hippocampal MRS, including reproducibility of voxel placement, spectral quality and neurochemical concentrations. Ten healthy volunteers were scanned in two consecutive sessions using a standard clinical 3 T MR scanner. Neurochemical profiles were obtained with a short-echo (T(E) = 28 ms) semi-LASER localization sequence from a relatively small (~4 mL) voxel that covered about 62% of the hippocampal volume as calculated from segmentation of T1 -weighted images. Voxel composition was highly reproducible between sessions, with test-retest coefficients of variation (CVs) of 3.5% and 7.5% for gray and white matter volume fraction, respectively. Excellent signal-to-noise ratio (~54 based on the N-acetylaspartate (NAA) methyl peak in non-apodized spectra) and linewidths (~9 Hz for water) were achieved reproducibly in all subjects. The spectral quality allowed quantification of NAA, total choline, total creatine, myo-inositol and glutamate with high scan-rescan reproducibility (CV ≤ 6%) and quantification precision (Cramér-Rao lower bound, CRLB < 9%). Four other metabolites, including glutathione and glucose, were quantified with scan-rescan CV below 20%. Therefore, the highly optimized, short-echo semi-LASER sequence together with FASTMAP shimming substantially improved the reproducibility and number of quantifiable metabolites relative to prior reports. In addition, the between-session variation in metabolite concentrations, as well as CRLB, was lower than the between-subject variation of the concentrations for most metabolites, indicating that the method has the sensitivity to detect inter-individual differences in the healthy brain.

Proton MRS and MRSI of the brain without water suppression

Water suppression (WS) techniques have played a vital role in the commencement and development of in vivo proton magnetic resonance spectroscopy (MRS, including spectroscopic imaging - MRSI). WS not only made in vivo proton MRS functionally available but also made its applications conveniently accessible, and it has become an indispensable tool in most of the routine applications of in vivo proton MR spectroscopy. On the other hand, WS brought forth some challenges. Therefore, various techniques of proton MRS without WS have been developed since the pioneering work in the late 1990s. After more than one and a half decades of advances in both hardware and software, non-water-suppressed proton MRS is coming to the stage of maturity and seeing increasing application in biomedical research and clinical diagnosis. In this article, we will review progress in the technical development and applications of proton MRS without WS.

Detection of lactate in the striatum without contamination of macromolecules by J-difference editing MRS at 7T

Lactate levels are measurable by MRS and are related to neural activity. Therefore, it is of interest to accurately measure lactate levels in the basal ganglia networks. If sufficiently stable, lactate measurements may be used to investigate alterations in dopaminergic signalling in the striatum, facilitating the detection and diagnosis of metabolic deficits. The aim of this study is to provide a J-difference editing MRS technique for the selective editing of lactate only, thus allowing the detection of lactate without contamination of overlapping macromolecules. As a validation procedure, macromolecule nulling was combined with J-difference editing, and this was compared with J-difference editing with a new highly selective editing pulse. The use of a high-field (7T) MR scanner enables the application of editing pulses with very narrow bandwidth, which are selective for lactate. We show that, despite the sensitivity to B0 offsets, the use of a highly selective editing pulse is more efficient for the detection of lactate than the combination of a broad-band editing pulse with macromolecule nulling. Although the signal-to-noise ratio of uncontaminated lactate detection in healthy subjects is relatively low, this article describes the test-retest performance of lactate detection in the striatum when using highly selective J-difference editing MRS at 7 T. The coefficient of variation, σw and intraclass correlation coefficients for within- and between-subject differences of lactate were determined. Lactate levels in the left and right striatum were determined twice in 10 healthy volunteers. Despite the fact that the test-retest performance of lactate detection is moderate with a coefficient of variation of about 20% for lactate, these values can be used for the design of new studies comparing, for example, patient populations with healthy controls.

Proceedings of the workshop on Cerebellum, Basal Ganglia and Cortical Connections Unmasked in Health and Disorder held in Brno, Czech Republic, October 17th, 2013

The proceedings of the workshop synthesize the experimental, preclinical, and clinical data suggesting that the cerebellum, basal ganglia (BG), and their connections play an important role in pathophysiology of various movement disorders (like Parkinson's disease and atypical parkinsonian syndromes) or neurodevelopmental disorders (like autism). The contributions from individual distinguished speakers cover the neuroanatomical research of complex networks, neuroimaging data showing that the cerebellum and BG are connected to a wide range of other central nervous system structures involved in movement control. Especially, the cerebellum plays a more complex role in how the brain functions than previously thought.