Proton magnetic resonance spectroscopy in the brain: report of AAPM MR Task Group #9

CloudBrain-MRS: An intelligent cloud computing platform for in vivo magnetic resonance spectroscopy preprocessing, quantification, and analysis

Magnetic resonance spectroscopy (MRS) is an important clinical imaging method for diagnosis of diseases. MRS spectrum is used to observe the signal intensity of metabolites or further infer their concentrations. Although the magnetic resonance vendors commonly provide basic functions of spectrum plots and metabolite quantification, the spread of clinical research of MRS is still limited due to the lack of easy-to-use processing software or platform. To address this issue, we have developed CloudBrain-MRS, a cloud-based online platform that provides powerful hardware and advanced algorithms. The platform can be accessed simply through a web browser, without the need of any program installation on the user side. CloudBrain-MRS also integrates the classic LCModel and advanced artificial intelligence algorithms and supports batch preprocessing, quantification, and analysis of MRS data from different vendors. Additionally, the platform offers useful functions: (1) Automatically statistical analysis to find biomarkers for diseases; (2) Consistency verification between the classic and artificial intelligence quantification algorithms; (3) Colorful three-dimensional visualization for easy observation of individual metabolite spectrum. Last, data of both healthy subjects and patients with mild cognitive impairment are used to demonstrate the functions of the platform. To the best of our knowledge, this is the first cloud computing platform for in vivo MRS with artificial intelligence processing. We have shared our cloud platform at MRSHub, providing at least two years of free access and service. If you are interested, please visit https://mrshub.org/software_all/#CloudBrain-MRS or https://csrc.xmu.edu.cn/CloudBrain.html.

A Review on the Use of Imaging Biomarkers in Oncology Clinical Trials: Quality Assurance Strategies for Technical Validation

Imaging biomarkers (IBs) have been proposed in medical literature that exploit images in a quantitative way, going beyond the visual assessment by an imaging physician. These IBs can be used in the diagnosis, prognosis, and response assessment of several pathologies and are very often used for patient management pathways. In this respect, IBs to be used in clinical practice and clinical trials have a requirement to be precise, accurate, and reproducible. Due to limitations in imaging technology, an error can be associated with their value when considering the entire imaging chain, from data acquisition to data reconstruction and subsequent analysis. From this point of view, the use of IBs in clinical trials requires a broadening of the concept of quality assurance and this can be a challenge for the responsible medical physics experts (MPEs). Within this manuscript, we describe the concept of an IB, examine some examples of IBs currently employed in clinical practice/clinical trials and analyze the procedure that should be carried out to achieve better accuracy and reproducibility in their use. We anticipate that this narrative review, written by the components of the EFOMP working group on "the role of the MPEs in clinical trials"-imaging sub-group, can represent a valid reference material for MPEs approaching the subject.

Quantification of Extramyocellular Lipids and Intramuscular Fat from Muscle Echo Intensity in Lower Limb Muscles: A Comparison of Four Ultrasound Devices against Magnetic Resonance Spectroscopy

This study aimed to compare different ultrasound devices with magnetic resonance spectroscopy (MRS) to quantify muscle lipid content from echo intensity (EI). Four different ultrasound devices were used to measure muscle EI and subcutaneous fat thickness in four lower-limb muscles. Intramuscular fat (IMF), intramyocellular (IMCL) and extramyocellular lipids (EMCL) were measured using MRS. Linear regression was used to compare raw and subcutaneous fat thickness-corrected EI values to IMCL, EMCL and IMF. IMCL had a poor correlation with muscle EI (r = 0.17-0.32, NS), while EMCL (r = 0.41-0.84, p < 0.05-p < 0.001) and IMF (r = 0.49-0.84, p < 0.01-p < 0.001) had moderate to strong correlation with raw EI. All relationships were improved when considering the effect of subcutaneous fat thickness on muscle EI measurements. The slopes of the relationships were similar across devices, but there were some differences in the y-intercepts when raw EI values were used. These differences disappeared when subcutaneous fat thickness-corrected EI values were considered, allowing for the creation of generic prediction equations (r = 0.41-0.68, p < 0.001). These equations can be used to quantify IMF and EMCL within lower limb muscles from corrected-EI values in non-obese subjects, regardless of the ultrasound device used.

Baseline Correction of the Human 1H MRS(I) Spectrum Using T2* Selective Differential Operators in the Frequency Domain

The baseline distortion caused by water and fat signals is a crucial issue in the ¹H MRS(I) study of the human brain. This paper suggests an effective and reliable preprocessing technique to calibrate the baseline distortion caused by the water and fat signals exhibited in the MRS spectral signal. For the preprocessing, we designed a T₂* (or linewidth within the spectral signal) selective filter for the MRS(I) data based on differential filtering within the frequency domain. The number and types for the differential filtering were determined by comparing the T₂* selectivity profile of each differential operator with the T₂* profile of the metabolites to be suppressed within the MRS(I) data. In the performance evaluation of the proposed differential filtering, the simulation data for MRS spectral signals were used. Furthermore, the spectral signal of the human ¹H MRSI data obtained by 2D free induction decay chemical shift imaging with a typical water suppression technique was also used in the performance evaluation. The absolute values of the average of the filtered dataset were quantitatively analyzed using the LCModel software. With the suggested T₂* selective (not frequency selective) filtering technique, in the simulated MRS data, we removed the metabolites from the simulated MRS(I) spectral signal baseline distorted by the water and fat signal observed in the most frequency band. Moreover, in the obtained MRSI data, the quantitative analysis results for the metabolites of interest showed notable improvement in the uncertainty estimation accuracy, the CRLB (Cramer-Rao Lower Bound) levels.

Importance of skeletal muscle lipid levels for muscle function and physical function in older individuals

The skeletal muscle contains lipids inside (intramyocellular lipids, IMCL) or outside (extramyocellular lipids, EMCL) its cells. The muscle lipid content increases with age; however, the characteristics of IMCL and EMCL in older individuals are not well known. We aimed to examine the characteristics of skeletal muscle lipids by investigating their relationship with muscle function and physical functions. Seven elderly men and 16 elderly women participated. The skeletal muscle lipid content, including IMCL and EMCL, was measured in the vastus lateralis by proton magnetic resonance spectroscopy. Isometric knee extension with maximal voluntary contraction (MVC) and time-to-task failure for knee extension with 50% MVC were measured as muscle functions. The participants performed six physical function tests: preferred gait speed, maximal gait speed, Timed Up and Go, chair sit-to-stand, handgrip strength, and stand from the floor. The time to knee extension task failure had a significant relationship with the IMCL (r_s = -0.43, P < 0.05), but not with the EMCL content. Significant relationships were confirmed in the EMCL content with the sit-to-stand (r_s = -0.48, P < 0.05) and stand-from-the-floor (r_s = 0.53, P < 0.05) tests. These findings indicated that muscle lipids are associated with muscle and physical functional performances in older individuals. Novelty: No relationship was confirmed between IMCL and EMCL in older individuals. Muscle endurance performance had a relationship with IMCL, but not with EMCL. Relationships between EMCL and physical functional tests (e.g., sit-to-stand and stand from the floor) were confirmed.

Contribution of skeletal muscle and serum lipids to muscle contraction induced by neuromuscular electrical stimulation in older individuals

Intramyocellular lipids (IMCL) stored in droplets in muscle cells and free fatty acids (FFA) from fat cells in the blood are the main substrates of adenosine triphosphate during continuous muscle contractions of relatively lower intensity. Although it is known that the lipid oxidative capacity decreases with aging, the effect of IMCL and FFA on muscle contraction in older individuals remains unclear. The purpose of this study was to investigate the contribution of skeletal muscle lipids and blood lipids as energy sources for muscle contraction in older individuals. Eighteen older individuals (mean age: 70.4 ± 3.5 years) underwent muscle contraction intervention induced by intermittent neuromuscular electrical stimulation (NMES) to the vastus lateralis for 30 min. Fasting blood samples were obtained and proton magnetic resonance spectroscopy (¹H‐MRS) was performed before and after NMES, and the parameters (including IMCL and extramyocellular lipid [EMCL]) from ¹H‐MRS, along with FFA and adiponectin levels, were analyzed using the blood samples of all participants. Levels of IMCL and EMCL did not change (p > 0.05); however, FFA and adiponectin levels decreased from 1.1 ± 0.5 mEq/L to 0.8 ± 0.2 mEq/L and 12.0 ± 5.3 μg/ml to 11.4 ± 5.0 μg/ml, after NMES (p < 0.05), respectively. These findings indicate that serum lipids, but not skeletal muscle lipids, are the energy substrate utilized during involuntary muscle contraction in older individuals.

Comparison of two magnetic resonance imaging spectroscopy postprocessing methods

OBJECTIVE

The aim of this study was to compare the results obtained using SpectroView® (SV) and J-Magnetic Resonance User Interface (jMRUI) from the same magnetic resonance (MR) spectroscopy of hydrogen data.

METHODS

Data from 23 males with alcohol use disorder (AUD) and 23 healthy non-AUD males were acquired by a 1.5 Tesla MR using a PRESS sequence (TE=30 ms) in four voxels located in the right frontal and left frontal (RF and LF) lobes, and posterior cingulate (AC and PC). The ratio of the signals from both N-acetyl-aspartate (NAA) and choline (Cho) over creatine (Cr) was calculated automatically using SV and semiautomatically by an expert neuroradiologist using jMRUI. The software' agreement was calculated by the 95% limits of agreement (LoA) of the ratio of the obtained values.

RESULTS

The standard deviation was greater in jMRUI than in SV. Although there was a correlation between the results from both methods, it was not possible to predict their variance from one another. Additionally, the 95% LoA showed that jMRUI values were expected to vary from 38 to 190% of those obtained using SV for NAA/Cr in RF of AUD subjects and from 48 to 196% for NAA/Cr in CA of non-AUD individuals.

CONCLUSIONS

The difference between the methods may represent clinically significant magnitudes. We suggest the use of the same method when comparing spectroscopic data. We also suggest that in clinical practice, the automatic method should be preferred.

Imaging biomarkers for evaluating tumor response: RECIST and beyond

Response Evaluation Criteria in Solid Tumors (RECIST) is the gold standard for assessment of treatment response in solid tumors. Morphologic change of tumor size evaluated by RECIST is often correlated with survival length and has been considered as a surrogate endpoint of therapeutic efficacy. However, the detection of morphologic change alone may not be sufficient for assessing response to new anti-cancer medication in all solid tumors. During the past fifteen years, several molecular-targeted therapies and immunotherapies have emerged in cancer treatment which work by disrupting signaling pathways and inhibited cell growth. Tumor necrosis or lack of tumor progression is associated with a good therapeutic response even in the absence of tumor shrinkage. Therefore, the use of unmodified RECIST criteria to estimate morphological changes of tumor alone may not be sufficient to estimate tumor response for these new anti-cancer drugs. Several studies have reported the low reliability of RECIST in evaluating treatment response in different tumors such as hepatocellular carcinoma, lung cancer, prostate cancer, brain glioma, bone metastasis, and lymphoma. There is an increased need for new medical imaging biomarkers, considering the changes in tumor viability, metabolic activity, and attenuation, which are related to early tumor response. Promising imaging techniques, beyond RECIST, include dynamic contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI), diffusion-weight imaging (DWI), magnetic resonance spectroscopy (MRS), and ¹⁸ F-fluorodeoxyglucose (FDG) positron emission tomography (PET). This review outlines the current RECIST with their limitations and the new emerging concepts of imaging biomarkers in oncology.

Effect of electromyostimulation on intramyocellular lipids of the vastus lateralis in older adults: a randomized controlled trial

BACKGROUND

Excessive intramyocellular lipid (IMCL) accumulation is a primary cause of skeletal muscle insulin resistance, especially in older adults, and interventions that reduce IMCL contents are important to improve insulin sensitivity. Electromyostimulation (EMS)-induced changes in IMCL content in older adults remain unknown. The purpose of this study was to clarify the effects of a single bout of EMS on the IMCL content of the vastus lateralis muscle in older adults.

METHODS

Twenty-two physically active, non-obese older men and women were randomly assigned to an EMS intervention group (69.0 ± 5.2 years, n = 12) or a control group (68.4 ± 3.5 years, n = 10). EMS was applied to the vastus lateralis (7 s on and 7 s off) for 30 min; control participants sat quietly for 30 min. IMCL content within the vastus lateralis was quantified with ¹H-magnetic resonance spectroscopy (n = 7 per group). Fasting plasma glucose and insulin values were determined from blood samples collected before and after the EMS intervention.

RESULTS

EMS induced a significant reduction in plasma glucose (93.1 ± 9.6 to 89.5 ± 9.1 mg/dL, p < 0.01), but not IMCL content (15.7 ± 15.7 to 15.8 ± 13.1 mmol/kg wet weight, p = 0.49) or insulin (5.4 ± 2.4 to 4.7 ± 2.7 μIU/mL, p = 0.18). In the control group, no changes in IMCL content in the vastus lateralis was observed after prolonged quiet sitting.

CONCLUSION

EMS intervention for 30 min induces changes in plasma glucose, but no changes in IMCL content in older adults.

TRIAL REGISTRATION

University hospital Medical Information Network (UMIN) Center ID: UMIN000020126 . Retrospectively registered on December 222,015. https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000023242.

Magnetic resonance biomarkers in radiation oncology: The report of AAPM Task Group 294

A magnetic resonance (MR) biologic marker (biomarker) is a measurable quantitative characteristic that is an indicator of normal biological and pathogenetic processes or a response to therapeutic intervention derived from the MR imaging process. There is significant potential for MR biomarkers to facilitate personalized approaches to cancer care through more precise disease targeting by quantifying normal versus pathologic tissue function as well as toxicity to both radiation and chemotherapy. Both of which have the potential to increase the therapeutic ratio and provide earlier, more accurate monitoring of treatment response. The ongoing integration of MR into routine clinical radiation therapy (RT) planning and the development of MR guided radiation therapy systems is providing new opportunities for MR biomarkers to personalize and improve clinical outcomes. Their appropriate use, however, must be based on knowledge of the physical origin of the biomarker signal, the relationship to the underlying biological processes, and their strengths and limitations. The purpose of this report is to provide an educational resource describing MR biomarkers, the techniques used to quantify them, their strengths and weakness within the context of their application to radiation oncology so as to ensure their appropriate use and application within this field.

Motion correction in magnetic resonance spectroscopy

In vivo proton magnetic resonance spectroscopy and spectroscopic imaging (MRS/MRSI) are valuable tools to study normal and abnormal human brain physiology. However, they are sensitive to motion, due to strong crusher gradients, long acquisition times, reliance on high magnetic field homogeneity, and particular acquisition methods such as spectral editing. The effects of motion include incorrect spatial localization, phase fluctuations, incoherent averaging, line broadening, and ultimately quantitation errors. Several retrospective methods have been proposed to correct motion-related artifacts. Recent advances in hardware also allow prospective (real-time) correction of the effects of motion, including adjusting voxel location, center frequency, and magnetic field homogeneity. This article reviews prospective and retrospective methods available in the literature and their implications for clinical MRS/MRSI. In combination, these methods can attenuate or eliminate most motion-related artifacts and facilitate the acquisition of high-quality data in the clinical research setting.

Magnetic resonance spectroscopy and its application in colorectal cancer diagnosis and screening: A narrative review

There are several slightly invasive methods to detect colorectal carcinoma (CRC) including colonoscopy and sigmoidoscopy; but there is no noninvasive, accurate screening test. It is recommended to initiate screening at the age of 50 for non-familial CRC. Laboratory tests are routinely suggested if internal observation and imaging are recommended for further evaluation. Spectroscopic-based imaging, such as magnetic resonance spectroscopy (MRS) is an interesting and promising tool with the potential to be an alternative to some minimally invasive procedures, such as biopsy. Accordingly, MRS might be a suitable substitution for invasive methods, such as colonoscopy. This article aimed to review the studies that have evaluated the MRS technique as a screening tool in CRC.

B0 field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy

PURPOSE

The purpose is: (a) Relate magnetic resonance imaging (MRI) quality recommendations for radiation therapy (RT) to B₀ field homogeneity; (b) Evaluate manufacturer specifications of B₀ homogeneity for 34 commercial whole-body MRI systems based on the MRI quality recommendations and RT application; (c) Measure field homogeneity in five commercial MRI systems and one commercial MRI-Linac used in RT and compare the results with their B₀ homogeneity specifications.

METHODS

Magnetic resonance imaging quality recommendations for spatial integrity, image blurring, fat saturation, and null banding in RT were developed based on the literature. Guaranteed (maximum) and typical B₀ field homogeneity specifications for various diameter spherical volumes (DSVs) were provided by GE, Philips, Siemens, and Canon. For each system, the DSV that conforms to each MRI quality recommendation and anatomical RT application was estimated based on the manufacturer specifications. B₀ field homogeneity was measured on six MRI systems including Philips (1.5 T), Siemens (1.5 and 3 T), and ViewRay MRI (0.35 T) systems using 24 and 35 cm DSV spherical phantoms. Two measurement techniques were used: (a) MRI using phase contrast field mapping to measure peak-to-peak (pk-pk), volume root mean square (VRMS), and standard deviation (SD); and (b) Magnetic resonance (MR) spectroscopy by acquiring a volumetric free induction decay (FID) to measure full width at half maximum (FWHM). The measurements were used to assess: (a) conformance with the manufacturer specifications; and (b) the relationship between the various field homogeneity measurement units. Measurements were made with and without gradient shimming (gradshim) or second-order active shimming. Multiple comparisons, analysis of variance (ANOVA), and Pearson correlations were performed to assess the dependence of pk-pk, VRMS, SD, and FWHM measurements of field homogeneity on shim volume, level of shim, and MRI system.

RESULTS

For a 40 cm DSV, the B₀ homogeneity specifications ranged from 0.35 to 5 ppm (median = 0.75 ppm) VRMS for 1.5 T systems and 0.2 to 1.4 ppm (median = 0.5 ppm) VRMS for 3 T systems. The usable DSVs ranged from 16 to 49 cm (median = 35 cm) based on the image quality recommendations and the manufacturer specifications. There was general compliance between the six measured field homogeneities and manufacturer specifications although signal dephasing was observed in two systems at < 35 cm DSV. The relationships between pk-pk, VRMS, SD, and FWHM varied based on MRI system, shim volume, and quality of shim. However, VRMS and SD measurements were highly correlated.

CONCLUSIONS

The delineation of the diseased lesion from organs at risk is the main priority for RT. Therefore, field homogeneity performance for RT must minimize image blurring and image artifacts (null bands and signal dephasing) while optimizing spatial integrity and fat saturation. Based on the specifications and recommendations for field homogeneity, some MRI systems are not well suited to meet the strict demands of RT particularly for the large imaging volumes used in body MRI. VRMS and SD measurements of B₀ field homogeneity tend to be more stable and sensitive to field inhomogeneities in RT applications than pk-pk and FWHM.

A method for cranial target delineation in radiotherapy treatment planning aided by single-voxel magnetic resonance spectroscopy: evaluation using a custom-designed gel-based phantom and simulations

OBJECTIVE

Magnetic resonance spectroscopy (MRS) has been useful in radiotherapy treatment planning (RTP) especially in tumor delineation. Routinely, 2D/3D MRSI data are used for this application. However, not all centers have access to 2D/3D MRSI. The objective of this study was to introduce a method of using single-voxel spectroscopy (SVS) data in target delineation and assess its reliability.

METHODS

A gel-based phantom containing Creatine (Cr), N-acetyl-l-aspartic-acid (NAA), and Choline (Cho) was designed and built. The metabolite ratios simulate the normal and tumoral part of the brain. The jMRUI software (v. 6.0) was used to simulate a 1.5 T GE MRI scanner. The metabolite spectra provided by different time of echos (TE)s of the Point-RESolved Spectroscopy pulse-sequence (PRESS), different data-points, and post-processings were quantized by jMRUI. PseudoMRSI maps of Cho/Cr, NAA/Cr, and Cho + Cr/NAA were created. A conformity index (CI) was used to determine which metabolite-ratio isolines are more appropriate for tumor delineation.

RESULTS

The simulation accuracy was verified. There were no differences > 4% between the measured and simulated spectra in peak regions. The pseudoMRSI map of Cho + Cr/NAA smoothly followed the complicated geometry of the tumor inside the gel-based phantom. The results showed that the single-voxel spectra produced by the PRESS pulse sequence with the TE of 144 ms, 512 data-points, and minimum post-processings of water suppression, eddy current correction, and baseline correction can be used for target delineation.

CONCLUSION

This study suggests that SVS data can be used to aid target delineation by using a mathematical approach. This can enable a wider use of MR-derived information in radiotherapy.

ADVANCES IN KNOWLEDGE

To the best of our knowledge, until now, 2D or 3D MRSI data provided from 3T MRI scanners have been used for MRS-based radiotherapy treatment planning. However, there are a lot of centers that are equipped to 1.5 T MRI scanners and some of them just equipped to SVS. This study introduces a mathematical approach to help these centers to take the benefits of MRS-based treatment planning.

Methodological consensus on clinical proton MRS of the brain: Review and recommendations

Proton MRS (1 H MRS) provides noninvasive, quantitative metabolite profiles of tissue and has been shown to aid the clinical management of several brain diseases. Although most modern clinical MR scanners support MRS capabilities, routine use is largely restricted to specialized centers with good access to MR research support. Widespread adoption has been slow for several reasons, and technical challenges toward obtaining reliable good-quality results have been identified as a contributing factor. Considerable progress has been made by the research community to address many of these challenges, and in this paper a consensus is presented on deficiencies in widely available MRS methodology and validated improvements that are currently in routine use at several clinical research institutions. In particular, the localization error for the PRESS localization sequence was found to be unacceptably high at 3 T, and use of the semi-adiabatic localization by adiabatic selective refocusing sequence is a recommended solution. Incorporation of simulated metabolite basis sets into analysis routines is recommended for reliably capturing the full spectral detail available from short TE acquisitions. In addition, the importance of achieving a highly homogenous static magnetic field (B0 ) in the acquisition region is emphasized, and the limitations of current methods and hardware are discussed. Most recommendations require only software improvements, greatly enhancing the capabilities of clinical MRS on existing hardware. Implementation of these recommendations should strengthen current clinical applications and advance progress toward developing and validating new MRS biomarkers for clinical use.

Proton MR spectroscopy in the breast: Technical innovations and clinical applications

Proton magnetic resonance spectroscopy (MRS) is a promising noninvasive diagnostic technique for investigation of breast cancer metabolism. Spectroscopic imaging data may be obtained following contrast-enhanced MRI by applying the point-resolved spectroscopy sequence (PRESS) or the stimulated echo acquisition mode (STEAM) sequence from the MR voxel encompassing the breast lesion. Total choline signal (tCho) measured in vivo using either a qualitative or quantitative approach has been used as a diagnostic test in the workup of malignant breast lesions. In addition to tCho metabolites, other relevant metabolites, including multiple lipids, can be detected and monitored. MRS has been heavily investigated as an adjunct to morphologic and dynamic MRI to improve diagnostic accuracy in breast cancer, obviating unnecessary benign biopsies. Besides its use in the staging of breast cancer, other promising applications have been recently investigated, including the assessment of treatment response and therapy monitoring. This review provides guidance on spectroscopic acquisition and quantification methods and highlights current and evolving clinical applications of proton MRS. Level of Evidence 5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2019.

Standardization of Small Animal Imaging-Current Status and Future Prospects

The benefit of small animal imaging is directly linked to the validity and reliability of the collected data. If the data (regardless of the modality used) are not reproducible and/or reliable, then the outcome of the data is rather questionable. Therefore, standardization of the use of small animal imaging equipment, as well as of animal handling in general, is of paramount importance. In a recent paper, guidance for efficient small animal imaging quality control was offered and discussed, among others, the use of phantoms in setting up a quality control program (Osborne et al. 2016). The same phantoms can be used to standardize image quality parameters for multi-center studies or multi-scanners within center studies. In animal experiments, the additional complexity due to animal handling needs to be addressed to ensure standardized imaging procedures. In this review, we will address the current status of standardization in preclinical imaging, as well as potential benefits from increased levels of standardization.

Relationship between physical activity and intramyocellular lipid content is different between young and older adults

PURPOSE

Intramyocellular lipid (IMCL) is influenced by physical exercise; however, whether the habitual level of physical activity affects resting IMCL content remains unclear. The purpose of this study was to determine the relationship between physical activity levels and resting IMCL content in young and older adults.

METHODS

In total, 15 nonobese young adults (21.0 ± 0.0 years) and 15 older adults (70.7 ± 3.8 years) were recruited. Time spent performing physical activities for 10 days was assessed using a three-dimensional ambulatory accelerometer, and intensity was categorized as light [< 3.0 metabolic equivalents (METs)], moderate (3.0-6.0 METs), or vigorous (> 6.0 METs). Physical activity level was calculated as the product of METs and time spent performing physical activities (MET h) at each intensity level. The IMCL content in the vastus lateralis was determined using ¹H-magnetic resonance spectroscopy after overnight fasting.

RESULTS

No significant differences in IMCL content were observed between young and older adults. Vigorous intensity physical activity (time and MET h) was significantly lower in older than young adults (p < 0.01); this difference was not observed for light and moderate intensity physical activity. Light intensity physical activity (time and MET h) was significantly and inversely correlated with IMCL content in young adults (r = - 0.59 and r = - 0.58; both p < 0.05), but not in older adults.

CONCLUSIONS

These results suggest that daily light intensity physical activity reduces resting IMCL content in young adults, whereas no significant relationship was seen between daily physical activity and resting IMCL content in older adults.

A straightforward multiparametric quality control protocol for proton magnetic resonance spectroscopy: Validation and comparison of various 1.5 T and 3 T clinical scanner systems

PURPOSE

The aim of this study was to propose and validate across various clinical scanner systems a straightforward multiparametric quality assurance procedure for proton magnetic resonance spectroscopy (MRS).

METHODS

Eighteen clinical 1.5 T and 3 T scanner systems for MRS, from 16 centres and 3 different manufacturers, were enrolled in the study. A standard spherical water phantom was employed by all centres. The acquisition protocol included 3 sets of single (isotropic) voxel (size 20 mm) PRESS acquisitions with unsuppressed water signal and acquisition voxel position at isocenter as well as off-center, repeated 4/5 times within approximately 2 months. Water peak linewidth (LW) and area under the water peak (AP) were estimated.

RESULTS

LW values [mean (standard deviation)] were 1.4 (1.0) Hz and 0.8 (0.3) Hz for 3 T and 1.5 T scanners, respectively. The mean (standard deviation) (across all scanners) coefficient of variation of LW and AP for different spatial positions of acquisition voxel were 43% (20%) and 11% (11%), respectively. The mean (standard deviation) phantom T₂values were 1145 (50) ms and 1010 (95) ms for 1.5 T and 3 T scanners, respectively. The mean (standard deviation) (across all scanners) coefficients of variation for repeated measurements of LW, AP and T₂ were 25% (20%), 10% (14%) and 5% (2%), respectively.

CONCLUSIONS

We proposed a straightforward multiparametric and not time consuming quality control protocol for MRS, which can be included in routine and periodic quality assurance procedures. The protocol has been validated and proven to be feasible in a multicentre comparison study of a fairly large number of clinical 1.5 T and 3 T scanner systems.

MRS Shimming: An Important Point Which Should not be Ignored

BACKGROUND

Proton magnetic resonance spectroscopy (MRS) is a well-known device for analyzing the biological fluids metabolically. Obtaining accurate and reliable information via MRS needs a homogeneous magnetic field in order to provide well-defined peaks and uniform water suppression. There are lots of reasons which can disturb the magnetic field homogeneity which can be corrected by a process known as shimming. This study is intended to recall the importance of shimming and also the significant role of quality control (QC) in achieving an accurate quantification.

MATERIAL AND METHOD

An acrylic cylindrical quality control phantom was designed as an analog of brain MRS test phantoms in order to control the accuracy of the obtained signal of a 1.5 T Siemens MRI system which belonged to one of Shiraz hospitals. The signal of NAA, Cho, Cr, the combination of these metabolites and also the distilled water, which was used in this study, was evaluated using separate phantoms. A QC test was performed using Siemens QC phantom and a standard test phantom.

RESULTS

The spectrum of our home- made phantom had a significant difference with the expected spectrum. The results of checking the spectrum of metabolites separately also confirmed that there was a systemic problem that affects all the signals originated from all metabolites and even the pure distilled water. The MRS system could not pass QC tests, and peak broadening was common in all spectra. The complex spectrum of standard test phantom was not produced successfully by the MRS system.

DISCUSSION

By a simple check of the water peak characteristics, lots of information can be obtained, one of which is the status of shimming that has a considerable effect on the accuracy of the spectrum. Thus, performing an automatic or manual shimming is not a criterion of the spectrum accuracy, and performing a periodic quality control using a test phantom by a specialist is necessary.

CONCLUSION

Briefly, the quality control of MRS and all the other clinical device must be taken seriously. Sometimes QC can be the boundary of a right or a wrong decision for the patient.

Cortical thickness and metabolite concentration in chronic stroke and the relationship with motor function

BACKGROUND

Hemiparesis is one of the most prevalent chronic disabilities after stroke. Biochemical and structural magnetic resonance imaging approaches may be employed to study the neural substrates underpinning upper-extremity (UE) recovery after chronic stroke.

OBJECTIVE

The purposes of this study were to 1) quantify anatomical and metabolic differences in the precentral gyrus, and 2) test the relationships between anatomical and metabolic differences, and hemiparetic arm function in individuals in the chronic stage of stroke recovery. Our hypotheses were: 1) the Stroke group would exhibit reduced precentral gyrus cortical thickness and lower concentrations of total N-acetylaspartate (tNAA) and glutamate+glutamine (Glx) in the ipsilesional motor cortex; and 2) that each of these measures would be associated with UE motor function after stroke.

METHODS

Seventeen individuals with chronic (>6 months) subcortical ischemic stroke and eleven neurologically healthy controls were recruited. Single voxel proton magnetic resonance spectroscopy (H1MRS) was performed to measure metabolite concentrations of tNAA and Glx in the precentral gyrus in both ipsilesional and contralesional hemispheres. Surface-based cortical morphometry was used to quantify precentral gyral thickness. Upper-extremity motor function was assessed using the Wolf Motor Function Test (WMFT).

RESULTS

Results demonstrated significantly lower ipsilesional tNAA and Glx concentrations and precentral gyrus thickness in the Stroke group. Ipsilesional tNAA and Glx concentration and precentral gyrus thickness was significantly lower in the ipsilesional hemisphere in the Stroke group. Parametric correlation analyses revealed a significant positive relationship between precentral gyrus thickness and tNAA concentration bilaterally. Multivariate regression analyses revealed that ipsilesional concentrations of tNAA and Glx predicted the largest amount of variance in WMFT scores. Cortical thickness measures alone did not predict a significant amount of variance in WMFT scores.

CONCLUSION

While stroke impairs both structure and biochemistry in the ipsilesional hemisphere our data suggest that tNAA has the strongest relationship with motor function.

A Multi-Center Study on Human Brain Glutathione Conformation using Magnetic Resonance Spectroscopy

Molecular dynamics simulation and in vitro nuclear magnetic resonance (NMR) studies on glutathione (GSH) indicated existence of closed and extended conformations. The present work in a multi-center research setting reports in-depth analysis of GSH conformers in vivo using a common magnetic resonance spectroscopy (MRS) protocol and signal processing scheme. MEGA-PRESS pulse sequence was applied on healthy subjects using 3T Philips MRI scanner (India) and 3T GE MRI scanner (Norway) using the same experimental parameters (echo time, repetition time, and selective 180° refocusing ON-pulse at 4.40 ppm and 4.56 ppm). All MRS data were processed at one site National Brain Research Center (NBRC) using in-house MRS processing toolbox (KALPANA) for consistency. We have found that both the closed and extended GSH conformations are present in human brain and the relative proportion of individual conformer peak depends on the specific selection of refocusing ON-pulse position in MEGA-PRESS pulse sequence. It is important to emphasize that in vivo experiments with different refocusing and inversion pulse positions, echo time, and voxel size, clearly evidence the presence of both the GSH conformations. The GSH conformer peak positions for the closed GSH (Cys-Hβ) peak at ∼2.80 ppm and extended GSH (Cys-Hβ) peak at ∼2.95 ppm remain consistent irrespective of the selective refocusing OFF-pulse positions. This is the first in vivo study where both extended and closed GSH conformers are detected using the MEGA-PRESS sequence employing the parameters derived from the high resolution in vitro NMR studies on GSH.

Magnetic Resonance Spectroscopy and its Clinical Applications: A Review

In vivo NMR spectroscopy is known as magnetic resonance spectroscopy (MRS). MRS has been applied as both a research and a clinical tool in order to detect visible or nonvisible abnormalities. The adaptability of MRS allows a technique that can probe a wide variety of metabolic uses across different tissues. Although MRS is mostly applied for brain tissue, it can be used for detection, localization, staging, tumour aggressiveness evaluation, and tumour response assessment of breast, prostate, hepatic, and other cancers. In this article, the medical applications of MRS in the brain, including tumours, neural and psychiatric disorder studies, breast, prostate, hepatic, gastrointestinal, and genitourinary investigations have been reviewed.

Multi-voxel magnetic resonance spectroscopy of cerebral metabolites in healthy dogs at 1.5 Tesla

This study was conducted to measure the difference in levels of cerebral metabolites in the right and left hemispheres, gray (GM) and white matter (WM), imaging planes, and anatomical regions of healthy dogs to establish normal variations. Eight male Beagle dogs (1 to 4 years of age; mean age, 2 years) with no evidence of neurologic disease were studied. Using the multi-voxel technique on a 1.5 Tesla magnetic resonance imaging scanner, metabolite values (N-acetyl aspartate [NAA], choline [Cho], creatine [Cr]) were obtained from the frontoparietal WM, parietal GM, temporal GM, occipital GM, thalamus, cerebellum, mid-brain, and pons. There was no significant difference in levels of these metabolites between the right and left in any locations or between the GM and WM in the cerebral hemispheres. However, there were significant differences in metabolite ratios within imaging planes. The NAA/Cr was lower in the cerebellum than other regions and the thalamus had a higher Cho/Cr and lower NAA/Cho ratio than in other regions. The spectral and metabolic values will provide a useful internal reference for clinical practice and research involving multi-voxel magnetic resonance spectroscopy. Measurement of metabolite values in the transverse plane is recommended for comparing levels of regional metabolites.

Investigating lipids as a source of chemical exchange-induced MRI frequency shifts

While magnetic susceptibility is a major contributor to NMR resonance frequency variations in the human brain, a substantial contribution may come from the chemical exchange of protons between water and other molecules. Exchange-induced frequency shifts f_e have been measured in tissue and protein solutions, but relatively lipid-rich white matter (WM) has a larger f_e than gray matter, suggesting that lipids could contribute. Galactocerebrosides (GC) are a prime candidate as they are abundant in WM and susceptible to exchange. To investigate this, f_e was measured in a model of WM lipid membranes in the form of multilamellar vesicles (MLVs), consisting of a 1:2 molar ratio of GC and phospholipids (POPC), and in MLVs with POPC only. Chemical shift imaging with 15% volume fraction of dioxane, an internal reference whose protons are assumed not to undergo chemical exchange, was used to remove susceptibility-induced frequency shifts in an attempt to measure f_e in MLVs at several lipid concentrations. Initial analysis of these measurements indicated a necessity to correct for small unexpected variations in dioxane concentration due to its effect on the water frequency shift. To achieve this, the actual dioxane concentration was inferred from spectral analysis and its additional contribution to f_e was removed through separate experiments which showed that the water-dioxane frequency shift depended linearly on the dioxane concentration at low concentrations with a proportionality constant of -0.021 ± 0.002 ppb/mM in agreement with published experiments. Contrary to expectations and uncorrected results, for GC + POPC vesicles, the dependence of the corrected f_e on GC concentration was insignificant (0.023 ± 0.037 ppb/mM; r²  = 0.085, p > 0.57), whereas for the POPC-only vesicles a small but significant linear increase with POPC concentration was found: 0.044 ± 0.008 ppb/mM (r²  = 0.877, p < 0.01). These findings suggest that the exchange-induced contribution of lipids to frequency contrast in WM may be small. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Fast magnetic resonance spectroscopic imaging techniques in human brain- applications in multiple sclerosis

Multi voxel magnetic resonance spectroscopic imaging (MRSI) is an important imaging tool that combines imaging and spectroscopic techniques. MRSI of the human brain has been beneficially applied to different clinical applications in neurology, particularly in neurooncology but also in multiple sclerosis, stroke and epilepsy. However, a major challenge in conventional MRSI is the longer acquisition time required for adequate signal to be collected. Fast MRSI of the brain in vivo is an alternative approach to reduce scanning time and make MRSI more clinically suitable.Fast MRSI can be categorised into spiral, echo-planar, parallel and turbo imaging techniques, each with its own strengths. After a brief introduction on the basics of non-invasive examination (¹H-MRS) and localization techniques principles, different fast MRSI techniques will be discussed from their initial development to the recent innovations with particular emphasis on their capacity to record neurochemical changes in the brain in a variety of pathologies.The clinical applications of whole brain fast spectroscopic techniques, can assist in the assessment of neurochemical changes in the human brain and help in understanding the roles they play in disease. To give a good example of the utilities of these techniques in clinical context, MRSI application in multiple sclerosis was chosen. The available up to date and relevant literature is discussed and an outline of future research is presented.

Dynamic MR Spectroscopy of brain metabolism using a non-conventional spectral averaging scheme

PURPOSE

MRS acquisition based on the blood oxygenation level dependent (BOLD) contrast mechanism was implemented at 3T to investigate the impact of a non-conventional spectral averaging scheme (determined by the number of RF excitations, NEX) on the dynamics of cerebral metabolism during neuroactivation. Using NEX=2, water and metabolite BOLD responses were compared to previous results from standard experiments.

METHODS

Spectra were recorded from the visual cortex of five healthy volunteers during single and block visual stimulations. The height, width and area of the spectral peaks were calculated (using SAGE v7) in order to estimate their percentage changes from baseline (representing the BOLD change) following visual stimulation. BOLD changes were statistically significant at a significance level of p<0.05 by paired t-test.

RESULTS

Significantly greater BOLD changes in all spectra were observed in the single than block stimulation (p<0.05). The water resonance showed significant (p<0.01) BOLD changes in all peak parameters in both paradigms. All metabolites showed significant increase in spectral height (p<0.01) in the single paradigm, but none of them (except the height of Cho) showed significant BOLD response in the block paradigm. BOLD changes observed in the block paradigm were generally lower than reported changes.

CONCLUSIONS

The time interval of 6s offered by NEX=2 during which each line of spectral data is recorded by the scanner is rather long, leading to some BOLD data loss particularly in a block experimental design.

An MRspec database query and visualization engine with applications as a clinical diagnostic and research tool

PURPOSE

Proton magnetic resonance spectroscopy (MRspec), one of the very few techniques for in vivo assessment of neuro-metabolic profiles, is often complicated by lack of standard population norms and paucity of computational tools.

METHODS

7035 scans and clinical information from 4430 pediatric patients were collected from 2008 to 2014. Scans were conducted using a 1.5T (n=3664) or 3T scanner (n=3371), and with either a long (144ms, n=5559) or short echo time (35ms, n=1476). 3055 of these scans were localized in the basal ganglia (BG), 1211 in parieto-occipital white matter (WM). 34 metabolites were quantified using LCModel. A web application using MySQL, Python and Flask was developed to facilitate the exploration of the data set.

RESULTS

Already piloting the application revealed numerous insights. (1), N-acetylaspartate (NAA) increased throughout all ages. During early infancy, total choline was highly varied and myo-inositol demonstrated a downward trend. (2), Total creatine (tCr) and creatine increased throughout childhood and adolescence, though phosphocreatine (PCr) remained constant beyond 200days. (3), tCr was higher in BG than WM. (4), No obvious gender-related differences were observed. (5), Field strength affects quantification using LCModel for some metabolites, most prominently for tCr and total NAA. (6), Outlier analysis identified patients treated with vigabatrin through elevated γ-aminobutyrate, and patients with Klippel-Feil syndrome, Leigh disease and L2-hydroxyglutaric aciduria through low choline in BG.

CONCLUSIONS

We have established the largest MRSpec database and developed a robust and flexible computational tool for facilitating the exploration of vast metabolite datasets that proved its value for discovering neurochemical trends for clinical diagnosis, treatment monitoring, and research. Open access will lead to its widespread use, improving the diagnostic yield and contributing to better understanding of metabolic processes and conditions in the brain.

Uncovering a third dissolved-phase 129 Xe resonance in the human lung: Quantifying spectroscopic features in healthy subjects and patients with idiopathic pulmonary fibrosis

PURPOSE

The purpose of this work was to accurately characterize the spectral properties of hyperpolarized ¹²⁹ Xe in patients with idiopathic pulmonary fibrosis (IPF) compared to healthy volunteers.

METHODS

Subjects underwent hyperpolarized ¹²⁹ Xe breath-hold spectroscopy, during which 38 dissolved-phase free induction decays (FIDs) were acquired after reaching steady state (echo time/repetition time = 0.875/50 ms; bandwidth = 8.06 kHz; flip angle≈22 °). FIDs were averaged and then decomposed into multiple spectral components using time-domain curve fitting. The resulting amplitudes, frequencies, line widths, and starting phases of each component were compared among groups using a Mann-Whitney-Wilcoxon U test.

RESULTS

Three dissolved-phase resonances, consisting of red blood cells (RBCs) and two barrier compartments, were consistently identified in all subjects. In subjects with IPF relative to healthy volunteers, the RBC frequency was 0.70 parts per million (ppm) more negative (P = 0.05), the chemical shift of barrier 2 was 0.6 ppm more negative (P = 0.009), the line widths of both barrier peaks were ∼2 ppm narrower (P < 0.001), and the starting phase of barrier 1 was 20.3 ° higher (P =  0.01). Moreover, the ratio RBC:barriers was reduced by 52.9% in IPF (P < 0.001).

CONCLUSIONS

The accurate decomposition of ¹²⁹ Xe spectra not only has merit for developing a global metric of pulmonary function, but also provides necessary insights to optimize phase-sensitive methods for imaging ¹²⁹ Xe gas transfer. Magn Reson Med 78:1306-1315, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Fast frequency-sweep spectroscopic imaging with an ultra-low flip angle

Magnetic resonance (MR) spectroscopic imaging has become an important tool in clinical settings for noninvasively obtaining spatial and metabolic information on a molecular scale. Conventional spectroscopic imaging is acquired in the time domain, and its clinical application is limited by the long acquisition time, restricted spatial coverage, and complex suppression and reconstruction procedures. We introduce a fast MR spectroscopic imaging technique in the frequency domain, termed phase-cycled spectroscopic imaging (PCSI). PCSI uses a balanced steady-state free precession (bSSFP) sequence with an ultra-low flip angle to achieve very high acquisition efficiency with a short repetition time. This approach enables faster frequency sweeping by changing the cycled RF phase and using flexible non-uniform sampling, and it greatly reduces the RF energy deposition in tissue. With its intrinsic water and fat suppression, PCSI more closely resembles routine clinical scans because it eliminates the suppression steps. We demonstrate that it is feasible to acquire PCSI spectra in a phantom and in humans and that PCSI provides an efficient spectroscopic imaging method, even for J-coupled metabolites. PCSI may enable spectroscopic imaging to play a larger role in the clinical assessment of the spatial tissue distribution of metabolites.

Optimization of Single Voxel MR Spectroscopy Sequence Parameters and Data Analysis Methods for Thermometry in Deep Hyperthermia Treatments

OBJECTIVE

The difference in the resonance frequency of water and methylene moieties of lipids quantifies in magnetic resonance spectroscopy the absolute temperature using a predefined calibration curve. The purpose of this study was the investigation of peak evaluation methods and the magnetic resonance spectroscopy sequence (point-resolved spectroscopy) parameter optimization that enables thermometry during deep hyperthermia treatments.

MATERIALS AND METHODS

Different Lorentz peak-fitting methods and a peak finding method using singular value decomposition of a Hankel matrix were compared. Phantom measurements on organic substances (mayonnaise and pork) were performed inside the hyperthermia 1.5-T magnetic resonance imaging system for the parameter optimization study. Parameter settings such as voxel size, echo time, and flip angle were varied and investigated.

RESULTS

Usually all peak analyzing methods were applicable. Lorentz peak-fitting method in MATLAB proved to be the most stable regardless of the number of fitted peaks, yet the slowest method. The examinations yielded an optimal parameter combination of 8 cm³ voxel volume, 55 millisecond echo time, and a 90° excitation pulse flip angle.

CONCLUSION

The Lorentz peak-fitting method in MATLAB was the most reliable peak analyzing method. Measurements in homogeneous and heterogeneous phantoms resulted in optimized parameters for the magnetic resonance spectroscopy sequence for thermometry.

Simultaneous PET/MRI with (13)C magnetic resonance spectroscopic imaging (hyperPET): phantom-based evaluation of PET quantification

Background

Integrated PET/MRI with hyperpolarized ¹³C magnetic resonance spectroscopic imaging (¹³C-MRSI) offers simultaneous, dual-modality metabolic imaging. A prerequisite for the use of simultaneous imaging is the absence of interference between the two modalities. This has been documented for a clinical whole-body system using simultaneous ¹H-MRI and PET but never for ¹³C-MRSI and PET. Here, the feasibility of simultaneous PET and ¹³C-MRSI as well as hyperpolarized ¹³C-MRSI in an integrated whole-body PET/MRI hybrid scanner is evaluated using phantom experiments.

Methods

Combined PET and ¹³C-MRSI phantoms including a NEMA [¹⁸F]-FDG phantom, ¹³C-acetate and ¹³C-urea sources, and hyperpolarized ¹³C-pyruvate were imaged repeatedly with PET and/or ¹³C-MRSI. Measurements evaluated for interference effects included PET activity values in the largest sphere and a background region; total number of PET trues; and ¹³C-MRSI signal-to-noise ratio (SNR) for urea and acetate phantoms. Differences between measurement conditions were evaluated using t tests.

Results

PET and ¹³C-MRSI data acquisition could be performed simultaneously without any discernible artifacts. The average difference in PET activity between acquisitions with and without simultaneous ¹³C-MRSI was 0.83 (largest sphere) and −0.76 % (background). The average difference in net trues was −0.01 %. The average difference in ¹³C-MRSI SNR between acquisitions with and without simultaneous PET ranged from −2.28 to 1.21 % for all phantoms and measurement conditions. No differences were significant. The system was capable of ¹³C-MRSI of hyperpolarized ¹³C-pyruvate.

Conclusions

Simultaneous PET and ¹³C-MRSI in an integrated whole-body PET/MRI hybrid scanner is feasible. Phantom experiments showed that possible interference effects introduced by acquiring data from the two modalities simultaneously are small and non-significant. Further experiments can now investigate the benefits of simultaneous PET and hyperpolarized ¹³C-MRI in vivo studies.

Intramuscular adipose tissue determined by T1-weighted MRI at 3T primarily reflects extramyocellular lipids

PURPOSE

The purpose of this study was to assess relationships between intramuscular adipose tissue (IntraMAT) content determined by MRI and intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL) determined by (1)H magnetic resonance spectroscopy ((1)H MRS) or echo intensity determined by B-mode ultrasonography of human skeletal muscles.

METHODS

Thirty young and elderly men and women were included. T1-weighted MRI was taken from the right mid-thigh to measure IntraMAT content of the vastus lateralis (VL) and biceps femoris (BF) using a histogram shape-based thresholding technique. IMCL and EMCL were measured from the VL and BF at the right mid-thigh using (1)H MRS. Ultrasonographic images were taken from the VL and BF of the right mid-thigh to measure echo intensity based on gray-scale level for quantitative analysis.

RESULTS

There was a significant correlation between IntraMAT content by MRI and EMCL of the VL and BF (VL, r=0.506, P<0.01; BF, r=0.591, P<0.001) and between echo intensity and EMCL of the VL and BF (VL, r=0.485, P<0.05; BF, r=0.648, P<0.01). IntraMAT content was also significantly correlated with echo intensity of the VL and BF (VL, r=0.404, P<0.05; BF, r=0.493, P<0.01).

CONCLUSION

Our study suggests that IntraMAT content determined by T1-weighted MRI at 3T primarily reflects extramyocellular lipids, not intramyocellular lipids, in human skeletal muscles.

Improving spectral quality in fetal brain magnetic resonance spectroscopy using constructive averaging

PURPOSE

A common source of loss in signal-to-noise ratio (SNR) in fetal brain magnetic resonance spectroscopy (MRS) is from fetal movement and temporal magnetic field drift. We investigated the feasibility of using constructive averaging strategies for improving the spectral quality and recovering the SNR loss from these effects.

MATERIALS AND METHODS

Eight fetuses, between 20 3/7 and 38 2/7 weeks' gestation, were scanned with MRS at 1.5 T. Single-voxel point-resolved spectroscopy of the fetal brain with TE = 144 ms (in one case additional TE = 288 ms) was performed in a dynamic mode, and individual spectra of 128 acquisitions were saved. With constructive averaging strategy individual acquisitions were corrected for phase variations and frequency drift before averaging. Constructively averaged spectra were compared to those using conventional averaging to evaluate differences in spectral quality and SNR.

RESULTS

The definition of key metabolite peaks was qualitatively improved using constructive averaging, including the doublet structure of lactate in one case. Constructive averaging was associated with SNR increases, ranging from 11% to 40%, and the SNR further improved in one case when outliers from severe motion were rejected before averaging.

CONCLUSION

Our results demonstrate the feasibility of using constructive averaging for improving SNR in fetal MRS, which is likely to improve the characterization of fetal brain metabolites.

Application of ICA to realistically simulated (1)H-MRS data

INTRODUCTION

(1)H-MRS signals from brain tissues capture information on in vivo brain metabolism and neuronal biomarkers. This study aims to advance the use of independent component analysis (ICA) for spectroscopy data by objectively comparing the performance of ICA and LCModel in analyzing realistic data that mimics many of the known properties of in vivo data.

METHODS

This work identifies key features of in vivo (1)H-MRS signals and presents methods to simulate realistic data, using a basis set of 12 metabolites typically found in the human brain. The realistic simulations provide a much needed ground truth to evaluate performances of various MRS analysis methods. ICA is applied to collectively analyze multiple realistic spectra and independent components identified with our generative model to obtain ICA estimates. These same data are also analyzed using LCModel and the comparisons between the ground-truth and the analysis estimates are presented. The study also investigates the potential impact of modeling inaccuracies by incorporating two sets of model resonances in simulations.

RESULTS

The simulated fid signals incorporating line broadening, noise, and residual water signal closely resemble the in vivo signals. Simulation analyses show that the resolution performances of both LCModel and ICA are not consistent across metabolites and that while ICA resolution can be improved for certain resonances, ICA is as effective as, or better than, LCModel in resolving most model resonances.

CONCLUSION

The results show that ICA can be an effective tool in comparing multiple spectra and complements existing approaches for providing quantified estimates.

In vivo assessment of neurotransmitters and modulators with magnetic resonance spectroscopy: application to schizophrenia

In vivo measurement of neurotransmitters and modulators is now feasible with advanced proton magnetic resonance spectroscopy ((1)H MRS) techniques. This review provides a basic tutorial of MRS, describes the methods available to measure brain glutamate, glutamine, γ-aminobutyric acid, glutathione, N-acetylaspartylglutamate, glycine, and serine at magnetic field strengths of 3T or higher, and summarizes the neurochemical findings in schizophrenia. Overall, (1)H MRS holds great promise for producing biomarkers that can serve as treatment targets, prediction of disease onset, or illness exacerbation in schizophrenia and other brain diseases.

A cross-validation of near-infrared spectroscopy measurements of skeletal muscle oxidative capacity with phosphorus magnetic resonance spectroscopy

The purpose of this study was to cross-validate measurements of skeletal muscle oxidative capacity made with near-infrared spectroscopy (NIRS) measurements to those made with phosphorus magnetic resonance spectroscopy ((31)P-MRS). Sixteen young (age = 22.5 ± 3.0 yr), healthy individuals were tested with both (31)P-MRS and NIRS during a single testing session. The recovery rate of phosphocreatine was measured inside the bore of a 3-Tesla MRI scanner, after short-duration (∼10 s) plantar flexion exercise as an index of skeletal muscle oxidative capacity. Using NIRS, the recovery rate of muscle oxygen consumption was also measured using repeated, transient arterial occlusions outside the MRI scanner, after short-duration (∼10 s) plantar flexion exercise as another index of skeletal muscle oxidative capacity. The average recovery time constant was 31.5 ± 8.5 s for phosphocreatine and 31.5 ± 8.9 s for muscle oxygen consumption for all participants (P = 0.709). (31)P-MRS time constants correlated well with NIRS time constants for both channel 1 (Pearson's r = 0.88, P < 0.0001) and channel 2 (Pearson's r = 0.95, P < 0.0001). Furthermore, both (31)P-MRS and NIRS exhibit good repeatability between trials (coefficient of variation = 8.1, 6.9, and 7.9% for NIRS channel 1, NIRS channel 2, and (31)P-MRS, respectively). The good agreement between NIRS and (31)P-MRS indexes of skeletal muscle oxidative capacity suggest that NIRS is a valid method for assessing mitochondrial function, and that direct comparisons between NIRS and (31)P-MRS measurements may be possible.

Optimizing a protocol for (1) H-magnetic resonance spectroscopy of the canine brain at 3T

Intracranial diseases are common in dogs and improved noninvasive diagnostic tests are needed. Magnetic resonance (MR) spectroscopy is a technique used in conjunction with conventional MR imaging to characterize focal and diffuse pathology, especially in the brain. As with conventional MR imaging, there are numerous technical factors that must be considered to optimize image quality. This study was performed to develop an MR spectroscopy protocol for routine use in dogs undergoing MR imaging of the brain. Fifteen canine cadavers were used for protocol development. Technical factors evaluated included use of single-voxel or multivoxel acquisitions, manual placement of saturation bands, echo time (TE), phase- and frequency-encoding matrix size, radiofrequency coil, and placement of the volume of interest relative to the calvaria. Spectrum quality was found to be best when utilizing a multivoxel acquisition with the volume of interest placed entirely within the brain parenchyma without use of manually placed saturation bands, TE = 144 ms, and a quadrature extremity radiofrequency coil. An 18 × 18 phase- and frequency-encoding matrix size also proved optimal for image quality, specificity of voxel placement, and imaging time.

Assessment of brain metabolites change during visual sexual stimulation in healthy women using functional MR spectroscopy

INTRODUCTION

Numerous functional magnetic resonance imaging (fMRI) studies demonstrated the key brain areas associated with visual sexual arousal. However, the changes in brain metabolites involved in sexual stimuli have not been reported.

AIM

This study utilized functional MR spectroscopy (fMRS) to evaluate the changes in brain metabolites associated with sexual arousal induced by stimulation with erotic video clips in healthy women.

METHODS

Twenty-three healthy, right-handed women (38.4 ± 10.0 years) participated in (1) H-fMRS and fMRI studies. T1 and T2 MR images were used for voxel localization of the anterior cingulate gyrus, which is one of the most important key centers associated with sexual arousal.

MAIN OUTCOME MEASURES

The changes of brain metabolites were measured using (1) H-fMRS during time-course activation: "before," "during," and "after" visual sexual stimulation. The time-course variation of the brain metabolites was analyzed by the repeated-measures analysis of variance.

RESULTS

The CVmean of all the metabolites had <30% (range, 9-29%). The ICCs of α-glutamine-glutamate (Glx), choline (Cho), β·γ-Glx, N-acetylaspartate (NAA) and lactate (Lac) all exceeded 0.6. However, myo-inositol (mI) and lipid (Lip) were <0.6. The concentration of brain metabolites including α-Glx, β·γ-Glx, Cho, and Lac comparatively increased significantly during visual sexual stimulation.

CONCLUSIONS

(1) H-fMRS, for the first time, was applied to assess the brain metabolic changes during visually-evoked sexual arousal. The fMRS outcomes in relation to functional MRI data will be useful to understand the neural mechanism associated with sexual arousal.

Proton magnetic resonance spectroscopy: technique for the neuroradiologist

Magnetic resonance spectroscopy (MRS) provides information on neuronal and axonal viability, energetics of cellular structures, and status of cellular membranes. Proton MRS appeals to clinicians and scientists because its application in the clinical setting can increase the specificity of MR imaging. The objective of this article is to provide descriptive concepts of the technique and its application in vivo for a variety of patient populations. When appropriately incorporating MRS into the neuroradiologic evaluation, this technique produces relevant information to radiologists and clinicians for their understanding of adult and pediatric neurologically based disease processes.

Metabolic response of glioma to dichloroacetate measured in vivo by hyperpolarized (13)C magnetic resonance spectroscopic imaging

BACKGROUND

The metabolic phenotype that derives disproportionate energy via glycolysis in solid tumors, including glioma, leads to elevated lactate labeling in metabolic imaging using hyperpolarized [1-(13)C]pyruvate. Although the pyruvate dehydrogenase (PDH)-mediated flux from pyruvate to acetyl coenzyme A can be indirectly measured through the detection of carbon-13 ((13)C)-labeled bicarbonate, it has proven difficult to visualize (13)C-bicarbonate at high enough levels from injected [1-(13)C]pyruvate for quantitative analysis in brain. The aim of this study is to improve the detection of (13)C-labeled metabolites, in particular bicarbonate, in glioma and normal brain in vivo and to measure the metabolic response to dichloroacetate, which upregulates PDH activity.

METHODS

An optimized protocol for chemical shift imaging and high concentration of hyperpolarized [1-(13)C]pyruvate were used to improve measurements of lactate and bicarbonate in C6 glioma-transplanted rat brains. Hyperpolarized [1-(13)C]pyruvate was injected before and 45 min after dichloroacetate infusion. Metabolite ratios of lactate to bicarbonate were calculated to provide improved metrics for characterizing tumor metabolism.

RESULTS

Glioma and normal brain were well differentiated by lactate-to-bicarbonate ratio (P = .002, n = 5) as well as bicarbonate (P = .0002) and lactate (P = .001), and a stronger response to dichloroacetate was observed in glioma than in normal brain.

CONCLUSION

Our results clearly demonstrate for the first time the feasibility of quantitatively detecting (13)C-bicarbonate in tumor-bearing rat brain in vivo, permitting the measurement of dichloroacetate-modulated changes in PDH flux. The simultaneous detection of lactate and bicarbonate provides a tool for a more comprehensive analysis of glioma metabolism and the assessment of metabolic agents as anti-brain cancer drugs.