Reproducibility of 3.0 Tesla magnetic resonance spectroscopy for measuring hepatic fat content

Purpose

To investigate reproducibility of proton magnetic resonance spectroscopy (¹H‐MRS) to measure hepatic triglyceride content (HTGC).

Materials and Methods

In 24 subjects, HTGC was evaluated using ¹H‐MRS at 3.0 Tesla. We studied “between‐weeks” reproducibility and reproducibility of ¹H‐MRS in subjects with fatty liver. We also studied within liver variability and within day reproducibility. Reproducibility was assessed by coefficient of variation (CV), repeatability coefficient (RC), and intraclass correlation coefficient (ICC).

Results

The CV of between weeks reproducibility was 9.5%, with a RC of 1.3% HTGC (ICC 0.998). The CV in fatty livers was 4.1%, with a RC of 1.3% HTGC (ICC 0.997). Within day CV was 4.5%, with a RC of 0.4% HTGC (ICC 0.999). CV for within liver variability was 14.5%.

Conclusion

Reproducibility of ¹H‐MRS to measure HTGC for “between‐weeks” measurements and in fatty livers is high, which is important for follow‐up studies. Within liver variability displays a larger variation, meaning that liver fat is not equally distributed and during consecutive measurements the same voxel position should be used. J. Magn. Reson. Imaging 2009;30:444–448. © 2009 Wiley‐Liss, Inc.     

Reproducibility assessment of metabolic variables characterizing muscle energetics in Vivo: A 31P‐MRS study

The purpose of the present study was to assess the reliability of metabolic parameters measured using ³¹P magnetic resonance spectroscopy (³¹P MRS) during two standardized rest‐exercise‐recovery protocols. Twelve healthy subjects performed the standardized protocols at two different intensities; i.e., a moderate intensity (MOD) repeated over a two‐month period and heavy intensity (HEAVY) repeated over a year's time. Test‐retest reliability was analyzed using coefficient of variation (CV), limits of agreement (LOA), and intraclass correlation coefficients (ICC). During exercise and recovery periods, most of the metabolic parameters exhibited a good reliability. The CVs of individual concentration of phosphocreatine ([PCr]), concentration of adenosine diphosphate ([ADP]), and pH values recorded at end of the HEAVY exercise were lower than 15%. The CV calculated for the rate of PCr resynthesis and the maximal oxidative capacity were less than 13% during the HEAVY protocol. Inferred parameters such as oxidative and total adenosine triphosphate (ATP) production rates exhibited a good reliability (ICC ≈ 0.7; CV < 15% during the HEAVY protocol). Our results demonstrated that measurement error using ³¹P‐MRS during a standardized exercise was low and that biological variability accounted for the vast majority of the measurement variability. In addition, the corresponding metabolic measurements can reliably be used for longitudinal studies performed even over a long period of time. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Phosphorus‐31 magnetic resonance spectroscopy of skeletal muscle in maternally inherited diabetes and deafness A3243G mitochondrial mutation carriers

Purpose

To investigate high‐energy phosphate metabolism in striated skeletal muscle of patients with Maternally Inherited Diabetes and Deafness (MIDD) syndrome.

Materials and Methods

In 11 patients with the MIDD mutation (six with diabetes mellitus [DM] and five non‐DM) and eight healthy subjects, phosphocreatine (PCr) and inorganic phosphate (Pi) in the vastus medialis muscle was measured immediately after exercise using ³¹P‐magnetic resonance spectroscopy (MRS). The half‐time of recovery (t1/2) of monoexponentially fitted (PCr+Pi)/PCr was calculated from spectra obtained every 4 seconds after cessation of exercise. A multiple linear regression model was used for statistical analysis.

Results

Patients with the MIDD mutation showed a significantly prolonged t1/2 (PCr+Pi)/PCr after exercise as compared to controls (13.6±3.0 vs. 8.7±1.3 sec, P = 0.01). No association between the presence of DM and t1/2 (PCr + Pi)/PCr was found (P = 0.382).

Conclusion

MIDD patients showed impaired mitochondrial oxidative phosphorylation in skeletal muscle shortly after exercise, irrespective of the presence of DM. J. Magn. Reson. Imaging 2009;29:127–131. © 2008 Wiley‐Liss, Inc.     

ATP production and mechanical work in exercising skeletal muscle: A theoretical analysis applied to 31P magnetic resonance spectroscopic studies of dialyzed uremic patients

³¹P magnetic resonance spectroscopy (³¹P MRS) can yield much information about bioenergetics in skeletal muscle. During mixed aerobic/glycolytic exercise, changes in phos-phocreatine (PCr) concentration and pH may be abnormal because of reduced muscle mass or reduced efficiency (which the authors combine here as “effective muscle mass”) or because of reduced oxidative capacity. The authors show how these can be distinguished by calculating the nonoxidative and oxidative costs of mechanical work, and also of work per unit of effective muscle mass (measured using the initial rate of ATP turnover). These quantities are substantially time-independent during incremental exercise, and so can be used to compare exercise studies of differing duration. The authors illustrate this analysis by showing that in dialyzed patients with chronic renal failure, the substantial exercise abnormalities seen by ³¹P MRS are due mainly to a decrease in effective muscle mass, which outweighs the oxidative defect implied by the abnormal PCr recovery kinetics.     

Quantification of vertebral bone marrow fat content using 3 Tesla MR spectroscopy: reproducibility, vertebral variation, and applications in osteoporosis

Purpose:

To determine the reproducibility of proton MR spectroscopy (¹H‐MRS) for assessing vertebral bone marrow adiposity at 3 Tesla (T); to evaluate variation of marrow adiposity at different vertebral levels; and to demonstrate the feasibility of using ¹H‐MRS at 3T for evaluating marrow adiposity in subjects with low bone density.

Materials and Methods:

Single voxel MRS was acquired at vertebral body L1 to L4 at 3T in 51 postmenopausal females including healthy controls (n = 13) and patients with osteoporosis/osteopenia (n = 38). Marrow fat contents were compared between vertebral levels and between groups using analysis of variance (ANOVA). Six subjects were scanned twice to evaluate technique reproducibility.

Results:

The average coefficient of variation of vertebral marrow fat content quantification was 1.7%. Marrow fat content significantly increased from L1 to L4. The average fat content was significantly elevated in patients with osteoporosis/osteopenia compared with controls, adjusted for age and body mass index (P < 0.05).

Conclusion:

In vivo MRS at high field strength provides reliable measurement of marrow adiposity with excellent reproducibility and can be a valuable tool for providing complementary information on bone quality and potentially also fracture risk. J. Magn. Reson. Imaging 2011;33:974–979. © 2011 Wiley‐Liss, Inc.     

Quantitative characterization of bone marrow edema pattern in rheumatoid arthritis using 3 Tesla MRI

Purpose:

To develop imaging techniques that provide quantitative characterization of bone marrow edema pattern (BME) in wrist joints of patients with rheumatoid arthritis (RA), including volume, signal intensity changes, and perfusion properties.

Materials and Methods:

Fourteen RA patients and three controls were scanned using 3 Tesla MR. BME was semi‐automatically segmented in water images obtained from iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (IDEAL) sequences. BME perfusion parameters (enhancement and slope) were evaluated using three‐dimensional (3D) dynamic enhanced MRI (DCE‐MRI). Experimental reproducibility, inter‐ and intra‐observer reproducibility of BME quantification were evaluated using root mean square coefficients of variation (RMS‐CV) and intraclass correlation (ICC).

Results:

The RMS‐CV for BME volume quantification with repeated scans were 6.9%. The inter‐observer ICC was 0.993 and RMS CV was 5.2%. The intra‐observer ICC was 0.998 and RMS CV was 2.3%. Both maximum enhancement and slope during DCE‐MRI were significantly higher in BME than in normal bone marrow (P < 0.001). No significant correlation was found between BME quantification and clinical evaluations.

Conclusion:

A highly reproducible semi‐automatic method for quantifying BME lesion burden in RA was developed, which may enhance our capability of predicting disease progression and monitoring treatment response. J. Magn. Reson. Imaging 2012;35:211‐217. © 2011 Wiley Periodicals, Inc.     

Exercise over-stress and maximal muscle oxidative metabolism: a 31P magnetic resonance spectroscopy case report

Objective: ³¹P magnetic resonance spectroscopy (MRS) was used to document long lasting losses in muscle oxidative capacity after bouts of intense endurance exercise.

Methods: The subject was a 34 year old highly fit female cyclist (VO₂MAX = 53.3 ml/kg/min). Over a five month period, she participated in three separate intense bouts of acute unaccustomed exercise. ³¹P MRS measurements were performed seven weeks after the first bout and every two weeks for 14 more weeks. In all cases, ³¹P MRS measurements followed three days after each bout.

Results: The subject showed a decreased ability to generate ATP from oxidative phosphorylation and an increased reliance on anaerobic ATP production during the 70% and 100% maximal voluntary contractions after the exercise bouts. Increased rates of fatigue and increased indicators of exercise difficulty also accompanied these reductions in muscle oxidative capacity. Increased oxidative and anaerobic ATP production were needed to maintain the work level during a submaximal 45% maximal voluntary contraction exercise.

Conclusions: Acute increases in intensity accompanied by a change in exercise mode can influence the ability of muscle to generate ATP. The muscles were less economical and required more ATP to generate force during the submaximal exercises. During the maximal exercises, the muscle's mitochondria showed a reduced oxidative capacity. However, these reductions in oxidative capacity at the muscle level were not associated with changes in whole body maximal oxygen uptake. Finally, these reductions in muscular oxidative capacity were accompanied by increased rates of anaerobic ATP production, fatigue, and indicators of exercise difficulty.

     

P magnetic resonance spectroscopy to measure in vivo cardiac energetics in normal myocardium and hypertrophic cardiomyopathy: Experiences at 3 T

Background

³¹P magnetic resonance spectroscopy (MRS) allows measurement of in vivo high-energy phosphate kinetics in the myocardium. While traditionally ³¹P cardiac spectroscopy is performed at 1.5 T, cardiac MRS at higher field strength can theoretically increase signal to noise ratio (SNR) and spectral resolution therefore improving sensitivity and specificity of the cardiac spectra. The reproducibility and feasibility of performing cardiac spectroscopy at 3 T is presented here in this study in healthy volunteers and patients with hypertrophic cardiomyopathy.

Methods

Cardiac spectroscopy was performed using a Phillips 3T Achieva scanner in 37 healthy volunteers and 26 patients with hypertrophic cardiomyopathy (HCM) to test the feasibility of the protocol. To test the reproducibility a single volunteer was scanned eight times on separate occasions. A single voxel ³¹P MRS was performed using Image Selected In vivo Spectroscopy (ISIS) volume localization.

Results

The mean phosphocreatine/adenosine triphosphate (PCr/ATP) ratio of the eight measurements performed on one individual was 2.11 ± 0.25. Bland Altman plots showed a variance of 12% in the measurement of PCr/ATP ratios. The PCr/ATP ratio was significantly reduced in HCM patients compared to controls, 1.42 ± 0.51 and 2.11 ± 0.57, respectively, P < 0.0001. (All results are expressed as mean ± standard deviation).

Conclusions

Here we demonstrate that cardiac ³¹P MRS at 3 T is a reliable method of measuring in vivo high-energy phosphate kinetics in the myocardium for clinical studies and diagnostics. Based on our data an impairment of cardiac energetic state in patients with hypertrophic cardiomyopathy is indisputable.     

Magnetic resonance imaging measurement reproducibility for calf muscle and adipose tissue volume

Purpose:

To describe a new semiautomated method for segmenting and measuring the volume of the muscle, bone, and adipose (subcutaneous and intermuscular) tissue in calf muscle compartments using magnetic resonance (MR) images and determine the intrarater and interrater reproducibility of the measures.

Materials and Methods:

Proton‐density weighted MR images were acquired from the right calf of 21 subjects. Three raters segmented and measured the volumes of bones, adipose tissue, and five individual muscle compartments. Two raters repeated the segmentations. The intra‐ and interrater reproducibility of the measures (intraclass correlation coefficients; ICC) were determined using generalizability theory.

Results:

All ICC values were greater than 0.96. The average standard error of the mean (SEM) of all measures was 1.21 cm³ and none were greater than 2.3 cm³. Essentially all variation (≥97% for all measures) was due to subject differences, indicating low error in the measurements.

Conclusion:

The volumetric measurements for the bones, adipose tissue, and muscle in each of the compartments using MRI were highly reproducible. MRI can provide quantitative, reproducible volumetric measures of bone, adipose tissue, and individual muscle compartments in the calf. We believe these methods can be used to quantify specific muscle or adipose volumetric measures for other clinical or research purposes. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Human in-vivo 31P MR Spectroscopy of Benign and Malignant Breast Tumors

Objective

To assess the potential clinical utility of in-vivo 31P magnetic resonance spectroscopy (MRS) in patients with various malignant and benign breast lesions.

Materials and Methods

Seventeen patients with untreated primary malignant breast lesions (group I), eight patients with untreated benign breast lesions (group II) and seven normal breasts (group III) were included in this study. In-vivo 31P MRS was performed using a 1.5 Tesla MR scanner. Because of the characteristics of the coil, the volume of the tumor had to exceed 12 cc (3×2×2 cm), with a superoinferior diameter at least 3 cm. Mean and standard deviations of each metabolite were calculated and metabolite ratios, such as PME/PCr, PDE/PCr, T-ATP/PCr and PCr/T-ATP were calculated and statistically analyzed.

Results

Significant differences in PME were noted between groups I and III (p=0.0213), and between groups II and III (p=0.0213). The metabolite ratios which showed significant differences were PME/PCr (between groups II and III) (p=0.0201), PDE/PCr (between groups I and III, and between groups II and III) (p=0.0172), T-ATP/PCr (between groups II and III) (p=0.0287), and PCr/T-ATP (between groups II and III) (p=0.0287). There were no significant parameters between groups I and II.

Conclusion

In-vivo 31P MRS is not helpful for establishing a differential diagnosis between benign and malignant breast lesions, at least with relatively large lesions greater than 3 cm in one or more dimensions.     

Test‐retest reliability and reproducibility of short‐echo‐time spectroscopic imaging of human brain at 3T

A ¹H magnetic resonance spectroscopic imaging study at 3T and short echo time was conducted to evaluate both the reproducibility, as measured by the interscan coefficient of variation (CV), and test‐retest reliability, as measured by the intraclass correlation coefficient (ICC), of measurements of glutamate (Glu), combined glutamate and glutamine (Glx), myo‐inositol (mI), N‐acetylaspartate, creatine, and choline in 21 healthy subjects. The effect of partial volume correction on these measures and the relationship of reproducibility and reliability to data quality were also examined. A ¹H magnetic resonance spectroscopic imaging slice was prescribed above the lateral ventricles and single repeat scans were performed within 30 min to minimize physiologic variability. Interscan CVs based on all the voxels varied from 0.05 to 0.07 for N‐acetylaspartate, creatine, and choline to 0.10–0.13 for mI, Glu, and Glx. Findings on the reproducibility of gray and white matter estimates of N‐acetylaspartate, creatine, and choline are consistent with previous studies using longer echo times, with CVs in the range of 0.02–0.04 and ICC in the range of 0.65–0.90. CVs for Glu, Glx, and mI are much lower than reported in previous studies at 1.5T, while white matter mI (CV = 0.04, ICC = 0.93) and gray matter Glx (CV = 0.04, ICC = 0.68) demonstrated both high reproducibility and test‐retest reliability. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

In vivo detection of GABA and glutamate with MEGA-PRESS: reproducibility and gender effects

Purpose:

To evaluate the reproducibility of γ‐amino‐butyric acid (GABA) and glutamate concentrations derived using three different spectral fitting methods, and to investigate gender‐related differences in neurotransmitter levels.

Materials and Methods:

Single voxel MEGA‐edited PRESS MR spectra were acquired from a 30‐mL voxel in the dorso‐lateral prefrontal cortex in 14 adult volunteers (7 female) at 3 Tesla (3T). For each participant, four consecutive resting spectra were acquired within the same scanning session. Metabolite concentrations were derived using LCModel, jMRUI, and locally written peak fitting software. The within‐session reproducibility for each analysis method was calculated as the average coefficient of variation (CV) of the GABA and Glx (glutamate+glutamine) concentrations. Gender differences in GABA and Glx were evaluated using a two‐tailed unpaired t‐test.

Results:

LCModel provided the best reproducibility for both GABA (CV 7%) and Glx (CV 6%). GABA, Glx, and glutamate concentrations were significantly higher in the male participants, (P = 0.02, P = 0.001, and P < 0.001, respectively).

Conclusion:

GABA and glutamate can be quantified in vivo with high reproducibility (CV 6–7%) using frequency‐domain spectral fitting methods like LCModel. However, the GABA and glutamate concentrations vary significantly between men and women, emphasizing the importance of gender‐matching for studies investigating differences in neurotransmitter concentrations between mixed‐cohort groups. J. Magn. Reson. Imaging 2011;33:1262–1267. © 2011 Wiley‐Liss, Inc.     

Reproducibility of MRI‐determined proton density fat fraction across two different MR scanner platforms

Purpose:

To evaluate magnetic resonance imaging (MRI)‐determined proton density fat fraction (PDFF) reproducibility across two MR scanner platforms and, using MR spectroscopy (MRS)‐determined PDFF as reference standard, to confirm MRI‐determined PDFF estimation accuracy.

Materials and Methods:

This prospective, cross‐sectional, crossover, observational pilot study was approved by an Institutional Review Board. Twenty‐one subjects gave written informed consent and underwent liver MRI and MRS at both 1.5T (Siemens Symphony scanner) and 3T (GE Signa Excite HD scanner). MRI‐determined PDFF was estimated using an axial 2D spoiled gradient‐recalled echo sequence with low flip‐angle to minimize T1 bias and six echo‐times to permit correction of T2* and fat‐water signal interference effects. MRS‐determined PDFF was estimated using a stimulated‐echo acquisition mode sequence with long repetition time to minimize T1 bias and five echo times to permit T2 correction. Interscanner reproducibility of MRI determined PDFF was assessed by correlation analysis; accuracy was assessed separately at each field strength by linear regression analysis using MRS‐determined PDFF as reference standard.

Results:

1.5T and 3T MRI‐determined PDFF estimates were highly correlated (r = 0.992). MRI‐determined PDFF estimates were accurate at both 1.5T (regression slope/intercept = 0.958/‐0.48) and 3T (slope/intercept = 1.020/0.925) against the MRS‐determined PDFF reference.

Conclusion:

MRI‐determined PDFF estimation is reproducible and, using MRS‐determined PDFF as reference standard, accurate across two MR scanner platforms at 1.5T and 3T. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Structural and mechanical parameters of trabecular bone estimated from in vivo high‐resolution magnetic resonance images at 3 tesla field strength

Purpose:

To evaluate the performance of a new 3 Tesla (T) high‐resolution trabecular bone (TB) imaging technique at two resolution regimens in terms of serial reproducibility and sensitivity.

Materials and Methods:

The left distal tibial metaphysis of seven healthy volunteers was imaged at three time‐points using a FLASE (fast large‐angle spin‐echo) pulse sequence at 137 × 137 × 410 μm³ and (160 μm)³ voxel sizes. Image artifacts, motion degradation, and serial image volume misalignments were controlled to maximize reproducibility of image‐derived measures of scale, topology, orientation in terms of structural anisotropy, and finite‐element derived Young's and shear moduli. Coefficients of variation (CV) and intraclass correlation coefficients (ICC) for structural and mechanical parameters were evaluated as measures of reproducibility and reliability. The ability of structural and mechanical parameters to distinguish between subjects was tested by analysis of variance.

Results:

Reproducibility was generally higher in the anisotropic data (CVs 1–5% versus 1–9% for isotropic images). Anisotropic voxel size yielded greater measurement reliability (ICCs 0.75–0.99, mean = 0.92 versus 0.62–0.99, mean = 0.86) and better discrimination of the seven subjects (75% versus 50% of the possible comparisons were significantly different [P < 0.05]) except for measures of structural anisotropy and topology. Isotropic resolution improved detection of structural orientation and permitted visualization of small perforations in longitudinal trabecular plates not detected at anisotropic resolution.

Conclusion:

Improved image acquisition and processing techniques enhance reproducibility of structural and mechanical parameters derived from high‐resolution MRI of metaphyseal bone in the distal tibia. J. Magn. Reson. Imaging 2010;31:1157–1168. © 2010 Wiley‐Liss, Inc.     

Blood‐oxygen level dependent MRI measures of cerebrovascular reactivity using a controlled respiratory challenge: Reproducibility and gender differences

Purpose:

To evaluate the reproducibility and gender differences in cerebrovascular reactivity (CVR) measurements obtained using the blood‐oxygen level dependent (BOLD) response to controlled changes in end‐tidal partial pressure of carbon dioxide (PET CO₂).

Materials and Methods:

We obtained ethical approval to image 19 healthy volunteers (10 men, 9 women) on a 1.5 Tesla (T) MRI scanner twice on two separate days using identical procedures. CVR images were generated by collecting BOLD MRI data during controlled changes in PET CO₂ induced by a sequential gas delivery system.

Results:

Using the intraclass correlation coefficient (ICC), we demonstrated excellent within‐day CVR measures in gray matter (GM) (ICC = 0.92) and white matter (WM) (ICC = 0.88) regions, excellent between‐day reproducibility in GM (ICC = 0.81), and good between‐day reproducibility in the WM (ICC = 0.66). CVR values between men and women were significantly different in the GM and WM. Men exhibited a 22 ± 2% greater CVR in GM and a 17 ± 2% greater CVR in WM compared with females.

Conclusion:

Our results demonstrate the reliability of BOLD MRI CVR measurements obtained using a controlled cerebrovascular challenge. Using this technique, we also revealed significantly increased BOLD response to CO₂ in males compared with females. J. Magn. Reson. Imaging 2010; 31: 298–304. © 2010 Wiley‐Liss, Inc.     

Scan‐rescan reproducibility of carotid atherosclerotic plaque morphology and tissue composition measurements using multicontrast MRI at 3T

Purpose:

To evaluate interscan reproducibility of both vessel morphology and tissue composition measurements of carotid atherosclerosis using a fast, optimized, 3T multicontrast protocol.

Materials and Methods:

A total of 20 patients with carotid stenosis >15% identified by duplex ultrasound were recruited for two independent 3T MRI (Philips) scans within one month. A multicontrast protocol including five MR sequences was applied: TOF, T1‐/T2‐/PD‐weighted and magnetization‐prepared rapid acquisition gradient‐echo (MP‐RAGE). Carotid artery morphology (wall volume, lumen volume, total vessel volume, normalized wall index, and mean/maximum wall thickness) and plaque component size (lipid rich/necrotic core, calcification, and hemorrhage) were measured over two time points.

Results:

After exclusion of images with poor image quality, 257 matched locations from 18 subjects were available for analysis. For the quantitative carotid morphology measurements, coefficient of variation (CV) ranged from 2% to 15% and intraclass correlation coefficient (ICC) ranged from 0.87 to 0.99. Except for maximum wall thickness (ICC = 0.87), all ICC were larger than 0.90. For the quantitative plaque composition measurements, the ICC of the volume and relative content of lipid rich/necrotic core and calcification were larger than 0.90 with CV ranging from 22% to 32%.

Conclusion:

The results from the multicontrast high‐resolution 3T MR study show high reliability for carotid morphology and plaque component measurements. 3T MRI is a reliable tool for longitudinal clinical trials, with shorter scan time compared to 1.5T. J. Magn. Reson. Imaging 2010;31:168–176. © 2009 Wiley‐Liss, Inc.     

Rapid 3D‐imaging of phosphocreatine recovery kinetics in the human lower leg muscles with compressed sensing

The rate of phosphocreatine (PCr) resynthesis following physical exercise is an accepted index of mitochondrial oxidative metabolism and has been studied extensively with unlocalized ³¹P‐MRS methods and small surface coils. Imaging experiments using volume coils that measure several muscles simultaneously can provide new insights into the variability of muscle function in healthy and diseased states. However, they are limited by long acquisition times relative to the dynamics of PCr recovery. This work focuses on the implementation of a compressed sensing technique to accelerate imaging of PCr resynthesis following physical exercise, using a modified three‐dimensional turbo‐spin‐echo sequence and principal component analysis as sparsifying transform. The compressed sensing technique was initially validated using 2‐fold retrospective undersampling of fully sampled data from four volunteers acquired on a 7T MRI system (voxel size: 1.6 mL, temporal resolution: 24 s), which led to an accurate estimation of the mono‐exponential PCr resynthesis rate constant (mean error <6.4%). Acquisitions with prospective 2‐fold acceleration (temporal resolution: 12 s) demonstrated that three‐dimensional mapping of PCr resynthesis is possible at a temporal resolution that is sufficiently high for characterizing the recovery curve of several muscles in a single measurement. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

Two‐dimensional J‐resolved proton MR spectroscopy and prior knowledge fitting (ProFit) in the frontal and parietal lobes of healthy volunteers: Assessment of metabolite discrimination and general reproducibility

Purpose:

To investigate human brain metabolite discriminability and general measurement reproducibility of two‐dimensional (2D) J‐resolved ¹H MRS and Prior Knowledge Fitting (ProFit).

Materials and Methods:

2D J‐resolved ¹H MRS spectra were acquired from the anterior cingulate cortex (ACC) and the parietal‐occipital cortex (POC) of 10 healthy subjects at a magnetic field strength of 2.9 Tesla. Amplitude correlation matrices were constructed for each subject and brain region to assess metabolite discriminability. ProFit‐estimated metabolite peak areas were normalized to a water reference signal, and intra‐ and inter‐subject reproducibility was evaluated.

Results:

Favorable between‐metabolite correlation coefficients (<20%) were observed for a range of metabolites. Lower correlation coefficients between a given pair of metabolite estimates were consistently observed for POC metabolites. The group mean correlation coefficient existing between glutamate and glutamine was calculated as ?18% and ?13% for ACC and POC, respectively. Most ACC and POC metabolites showed intra‐ and inter‐subject CV values of <15% and <20%, respectively.

Conclusion:

The observed Glu and Gln signal discrimination makes these techniques suitable for investigating a variety of psychiatric disorders. Intra‐ and inter‐subject metabolite level reproducibility was comparable to the existing literature findings. These data serve as a valuable benchmark for assessing future modifications to 2D ¹H MRS data acquisition and ProFit analysis. J. Magn. Reson. Imaging 2013;37:642–651. © 2012 Wiley Periodicals, Inc.

     

Application of localized 31P MRS saturation transfer at 7 T for measurement of ATP metabolism in the liver: reproducibility and initial clinical application in patients with non-alcoholic fatty liver disease

Objectives

Saturation transfer (ST) phosphorus MR spectroscopy (³¹P MRS) enables in vivo insight into energy metabolism and thus could identify liver conditions currently diagnosed only by biopsy. This study assesses the reproducibility of the localized ³¹P MRS ST in liver at 7 T and tests its potential for noninvasive differentiation of non-alcoholic fatty liver (NAFL) and steatohepatitis (NASH).

Methods

After the ethics committee approval, reproducibility of the localized ³¹P MRS ST at 7 T and the biological variation of acquired hepato-metabolic parameters were assessed in healthy volunteers. Subsequently, 16 suspected NAFL/NASH patients underwent MRS measurements and diagnostic liver biopsy. The Pi-to-ATP exchange parameters were compared between the groups by a Mann–Whitney U test and related to the liver fat content estimated by a single-voxel proton (¹H) MRS, measured at 3 T.

Results

The mean exchange rate constant (k) in healthy volunteers was 0.31?±?0.03 s^?1 with a coefficient of variation of 9.0 %. Significantly lower exchange rates (p?<?0.01) were found in NASH patients (k?=?0.17?±?0.04 s^?1) when compared to healthy volunteers, and NAFL patients (k?=?0.30?±?0.05 s^?1). Significant correlation was found between the k value and the liver fat content (r?=?0.824, p?<?0.01).

Conclusions

Our data suggest that the ³¹P MRS ST technique provides a tool for gaining insight into hepatic ATP metabolism and could contribute to the differentiation of NAFL and NASH.

Key Points

? 1D localized ³¹ P MRS saturation transfer in the liver is reproducible at 7 T ? NASH patients have decreased hepatic Pi-to-ATP exchange rate ? In this study, hepatic metabolic activity correlates with liver fat content     

Reproducibility of measurement of apparent diffusion coefficients of malignant hepatic tumors: Effect of DWI techniques and calculation methods

Purpose:

To evaluate the effect of diffusion‐weighted imaging (DWI) methods, apparent diffusion coefficient (ADC) calculation methods, and selection of b‐values on the ADCs and the measurement reproducibility of malignant hepatic tumors.

Materials and Methods:

Nineteen patients with pathologically confirmed malignant hepatic tumors underwent breath‐hold DWI (b‐values = 0, 50, 500 s/mm²) and respiratory‐triggered DWI (0, 50, 300, 500, 1000 s/mm²) twice on a 1.5 T magnetic resonance imaging (MRI) scanner. ADCs were calculated using a two b‐value and/or a multiple b‐value method. The reproducibility of the ADC measurements was evaluated from the intraclass correlation coefficients (ICCs) and the 95% Bland–Altman limit‐of‐agreement (LOA).

Results:

The ADCs were different according to the DWI methods (P = 0.040–0.282), ADC calculation methods (P = 0.003–0.825), and the choice of b‐values (P < 0.001). The ADC tended to be more reproducible with use of breath‐hold DWI (ICC: 0.898–0.933; LOA, 18.8%–24.0%) than respiratory‐triggered DWI (ICC: 0.684–0.928; LOA, 15.0%–31.9%) (P = 0.008–0.122). For respiratory‐triggered DWI, the multiple b‐value method using five b‐values had better reproducibility than the two b‐value method for measurement of ADC (P = 0.009–0.221).

Conclusion:

The DWI method, ADC calculation method, and selection of b‐values potentially influence the ADCs and the reproducibility of malignant hepatic tumors. ADCs calculated from breath‐hold DWI are more reproducible than from respiratory‐triggered DWI. A multiple b‐value method may improve the reproducibility of respiratory‐triggered DWI. J. Magn. Reson. Imaging 2012;36:1131–1138. © 2012 Wiley Periodicals, Inc.