Changes in phosphorus compounds and water content in skeletal muscle due to eccentric exercise

The interrelationship of the time courses of soreness and oedema, and of force and phosphorus metabolites after eccentric exercise was studied. Eight male subjects performed 120 maximal eccentric contractions with their left forearm flexors. Soreness, maximal force, flexion and extension elbow angle, and creatine kinase and myoglobin efflux were followed for 96 h after exercise. For equal periods T1 and T2 relaxation times and muscle cross-sectional area were calculated from magnetic resonance images as indications of oedema, and inorganic phosphate (P_i) and phosphocreatine (PCr) were measured with magnetic resonance spectroscopy. Soreness on extension increased at 1 h (P = 0.043), T1 and T2 (both P = 0.01) and soreness when the arm was pressed (P = 0.028) at 24 h, and muscle cross-sectional area increased at 48 h (P = 0.01) after exercise. Soreness on extension reached a maximum at 48 h, the other four parameters at 72 h. All parameters related to oedema, and soreness, showed an increasing pattern for the period after exercise as a whole, but the largest increase between two points of measurement occurred earlier for soreness than for oedema. Creatine kinase increased significantly from baseline from 24 h onwards (P = 0.017) and myoglobin from 1 h onwards (P = 0.012). The P_i: PCr ratio differed from baseline for the first time 24 h after exercise (P = 0.018), increased to 225%, and then remained on a plateau until 72 h. Maximal isotonic force decreased to 53% at 1 h (P = 0.012), and recovered from then on. It was concluded firstly that the largest increase in soreness precedes that of oedema, and secondly that the decrease in force after eccentric exercise is not related to an altered metabolic state. The combined imaging and spectroscopy results gave the impression that changes in phosphorus metabolites were homogeneously distributed over the flexor muscles whereas oedema was not.Parts of this study have already been presented during a conference as preliminary results (Rodenburg et al. 1992)     

Decreased water T2 in fatty infiltrated skeletal muscles of patients with neuromuscular diseases

Quantitative imaging techniques are emerging in the field of magnetic resonance imaging of neuromuscular diseases (NMD). T₂ of water (T_2w) is considered an important imaging marker to assess acute and chronic alterations of the muscle fibers, being generally interpreted as an indicator for “disease activity” in the muscle tissue. To validate the accuracy and robustness of quantitative imaging methods, ¹H magnetic resonance spectroscopy (MRS) can be used as a gold standard. The purpose of the present work was to investigate T_2w of remaining muscle tissue in regions of higher proton density fat fraction (PDFF) in 40 patients with defined NMD using multi‐TE single‐voxel ¹H MRS. Patients underwent MR measurements on a 3 T system to perform a multi‐TE single‐voxel stimulated echo acquisition method (STEAM) MRS (TE = 11/15/20/25(/35) ms) in regions of healthy, edematous and fatty thigh muscle tissue. Muscle regions for MRS were selected based on T₂‐weighted water and fat images of a two‐echo 2D Dixon TSE. MRS results were confined to regions with qualitatively defined remaining muscle tissue without edema and high fat content, based on visual grading of the imaging data. The results showed decreased T_2w values with increasing PDFF with R² = 0.45 (p < 10^?3) (linear fit) and with R² = 0.51 (exponential fit). The observed dependence of T_2w on PDFF should be considered when using T_2w as a marker in NMD imaging and when performing single‐voxel MRS for T_2w in regions enclosing edematous, nonedematous and fatty infiltrated muscle tissue.     

Effect of glycogen loading on skeletal muscle cross‐sectional area and T2 relaxation time

This study was performed to investigate if glycogen loading of skeletal muscles, by binding water, would effect the cross‐sectional area (CSA) and if an altered water content would alter the transverse relaxation time (T2) measured by magnetic resonance imaging (MRI). Five healthy volunteers participated in a programme with 4 days of extremely carbohydrate‐restricted meals followed by 4 days of extremely high carbohydrate intake. The CSA and T2 of thigh and calf muscles were related to the intramuscular glycogen content evaluated at days 4 and 8. An increase in glycogen content from 281 to 634 mmol kg^–1 dry wt increased the CSA of the vastus muscles by 3.5% from 78 ± 11 to 80 ± 12 cm² and the thigh circumference by 2.5% from 146 ± 20 to 150 ± 23 cm². Calf circumference increased non‐significantly by 4% from 78 ± 15 to 82 ± 19 cm². Mono‐exponential T2 decreased in m tibialis anterior from 27.8 ± 1.2 to 26.9 ± 1.7 ms, did not change in m. vastus lateralis 26.5 ± 1.9 ms/26.6 ± 1.3 ms or in m. gastrocnemius 29.5 ± 1.0 ms/29.8 ± 1.9 ms. Glycogen loading increased the signal intensity mainly at different echo times (TE) 15 and 30 ms. The study shows that increased glycogen filling in the muscles increases muscle CSA and that this can be detected by MRI. The signal intensity increased the most at shorter TEs suggesting a more tight intracellular binding of water in glycogen loaded muscles.     

Quantitative susceptibility mapping of the spine using in‐phase echoes to initialize inhomogeneous field and R2* for the nonconvex optimization problem of fat‐water separation

Quantitative susceptibility mapping (QSM) of human spinal vertebrae from a multi‐echo gradient‐echo (GRE) sequence is challenging, because comparable amounts of fat and water in the vertebrae make it difficult to solve the nonconvex optimization problem of fat‐water separation (R2*‐IDEAL) for estimating the magnetic field induced by tissue susceptibility. We present an in‐phase (IP) echo initialization of R2*‐IDEAL for QSM in the spinal vertebrae. Ten healthy human subjects were recruited for spine MRI. A 3D multi‐echo GRE sequence was implemented to acquire out‐phase and IP echoes. For the IP method, the R2* and field maps estimated by separately fitting the magnitude and phase of IP echoes were used to initialize gradient search R2*‐IDEAL to obtain final R2*, field, water, and fat maps, and the final field map was used to generate QSM. The IP method was compared with the existing Zero method (initializing the field to zero), VARPRO‐GC (variable projection using graphcuts but still initializing the field to zero), and SPURS (simultaneous phase unwrapping and removal of chemical shift using graphcuts for initialization) on both simulation and in vivo data. The single peak fat model was also compared with the multi‐peak fat model. There was no substantial difference on QSM between the single peak and multi‐peak fat models, but there were marked differences among different initialization methods. The simulations demonstrated that IP provided the lowest error in the field map. Compared to Zero, VARPRO‐GC and SPURS, the proposed IP method provided substantially improved spine QSM in all 10 subjects.     

The effect of noise and lipid signals on determination of Gaussian and non‐Gaussian diffusion parameters in skeletal muscle

This work characterizes the effect of lipid and noise signals on muscle diffusion parameter estimation in several conventional and non‐Gaussian models, the ultimate objectives being to characterize popular fat suppression approaches for human muscle diffusion studies, to provide simulations to inform experimental work and to report normative non‐Gaussian parameter values. The models investigated in this work were the Gaussian monoexponential and intravoxel incoherent motion (IVIM) models, and the non‐Gaussian kurtosis and stretched exponential models. These were evaluated via simulations, and in vitro and in vivo experiments. Simulations were performed using literature input values, modeling fat contamination as an additive baseline to data, whereas phantom studies used a phantom containing aliphatic and olefinic fats and muscle‐like gel. Human imaging was performed in the hamstring muscles of 10 volunteers. Diffusion‐weighted imaging was applied with spectral attenuated inversion recovery (SPAIR), slice‐select gradient reversal and water‐specific excitation fat suppression, alone and in combination. Measurement bias (accuracy) and dispersion (precision) were evaluated, together with intra‐ and inter‐scan repeatability. Simulations indicated that noise in magnitude images resulted in <6% bias in diffusion coefficients and non‐Gaussian parameters (α, K), whereas baseline fitting minimized fat bias for all models, except IVIM. In vivo, popular SPAIR fat suppression proved inadequate for accurate parameter estimation, producing non‐physiological parameter estimates without baseline fitting and large biases when it was used. Combining all three fat suppression techniques and fitting data with a baseline offset gave the best results of all the methods studied for both Gaussian diffusion and, overall, for non‐Gaussian diffusion. It produced consistent parameter estimates for all models, except IVIM, and highlighted non‐Gaussian behavior perpendicular to muscle fibers (α ~ 0.95, K ~ 3.1). These results show that effective fat suppression is crucial for accurate measurement of non‐Gaussian diffusion parameters, and will be an essential component of quantitative studies of human muscle quality.     

Quantitative MRI of skeletal muscle in a cross‐sectional cohort of patients with spinal muscular atrophy types 2 and 3

The aim of this study was to document upper leg involvement in spinal muscular atrophy (SMA) with quantitative MRI (qMRI) in a cross‐sectional cohort of patients of varying type, disease severity and age. Thirty‐one patients with SMA types 2 and 3 (aged 29.6 [7.6‐73.9] years) and 20 healthy controls (aged 37.9 [17.7‐71.6] years) were evaluated in a 3 T MRI with a protocol consisting of DIXON, T2 mapping and diffusion tensor imaging (DTI). qMRI measures were compared with clinical scores of motor function (Hammersmith Functional Motor Scale Expanded [HFMSE]) and muscle strength. Patients exhibited an increased fat fraction and fractional anisotropy (FA), and decreased mean diffusivity (MD) and T2 compared with controls (all P < .001). DTI parameters FA and MD manifest stronger effects than can be accounted for the effect of fatty replacement. Fat fraction, FA and MD show moderate correlation with muscle strength and motor function: FA is negatively associated with HFMSE and Medical Research Council sum score (τ = ?0.56 and ?0.59; both P < .001) whereas for fat fraction values are τ = ?0.50 and ?0.58, respectively (both P < .001). This study shows that DTI parameters correlate with muscle strength and motor function. DTI findings indirectly indicate cell atrophy and act as a measure independently of fat fraction. Combined these data suggest the potential of muscle DTI in monitoring disease progression and to study SMA pathogenesis in muscle.     

Evaluation of skeletal muscle DTI in patients with duchenne muscular dystrophy

Diffusion tensor imaging (DTI) is a popular method to assess differences in fiber organization in diseased and healthy muscle tissue. Previous work has shown that muscle DTI measurements depend on signal‐to‐noise ratio (SNR), %fat, and tissue T₂. The goal of this study was to evaluate the potential biasing effects of these factors on skeletal muscle DTI data in patients with Duchenne Muscular Dystrophy (DMD). MR images were obtained of the right lower leg of 21 DMD patients and 12 healthy controls on a Philips 3T system. DTI measurements were combined with quantitative in‐vivo measures of mean water T₂, %fat and SNR to evaluate their effect on DTI parameter estimation. All outcome measures were determined within ROIs drawn for six lower leg muscles. Between group analysis, using all ROIs, revealed a significantly elevated FA in the GCL, SOL and PER muscles (p<0.05) and an increased mean diffusivity (p<0.05) and λ₃ (p<0.05) in the TA muscle of DMD patients. In‐vivo evaluation of the individual confounders showed behaviour in line with predictions from previous simulation work. To account for these confounders, subsequent analysis used only ROIs with SNR greater than 20. With this criterion we found significantly greater MD in the TA muscle of DMD patient (p<0.009) and λ₃ in the TA and GCL muscles (p<0.001) of DMD patients, but no differences in FA. As both increased %fat and lower SNR are expected to reduce the apparent MD and λ₃, these between‐group differences are likely due to pathophysiology. However, the increased FA, observed when using all ROIs, likely reflects the effect of low SNR and %fat on the DTI parameter estimation. These findings suggest that measuring mean water T₂, %fat and SNR is essential to ascribe changes in DTI measures to intrinsic diffusion changes or to confounding influences. Copyright © 2015 John Wiley & Sons, Ltd.     

Fast and accurate initialization of the free‐water imaging model parameters from multi‐shell diffusion MRI

Cerebrospinal fluid partial volume effect is a known bias in the estimation of Diffusion Tensor Imaging (DTI) parameters from diffusion MRI data. The Free‐Water Imaging model for diffusion MRI data adds a second compartment to the DTI model, which explicitly accounts for the signal contribution of extracellular free‐water, such as cerebrospinal fluid. As a result the DTI parameters obtained through the free‐water model are corrected for partial volume effects, and thus better represent tissue microstructure. In addition, the model estimates the fractional volume of free‐water, and can be used to monitor changes in the extracellular space. Under certain assumptions, the model can be estimated from single‐shell diffusion MRI data. However, by using data from multi‐shell diffusion acquisitions, these assumptions can be relaxed, and the fit becomes more robust. Nevertheless, fitting the model to multi‐shell data requires high computational cost, with a non‐linear iterative minimization, which has to be initialized close enough to the global minimum to avoid local minima and to robustly estimate the model parameters. Here we investigate the properties of the main initialization approaches that are currently being used, and suggest new fast approaches to improve the initial estimates of the model parameters. We show that our proposed approaches provide a fast and accurate initial approximation of the model parameters, which is very close to the final solution. We demonstrate that the proposed initializations improve the final outcome of non‐linear model fitting.     

The use of magnetic resonance images to investigate the influence of recruitment on the relationship between torque and cross-sectional area in human muscle

The purpose of the present study was to investigate the effect of recruitment on the relationship between peak torque and physiological cross-sectional area (PCSA) in human muscle. A group of 11 healthy men participated in this study. Isokinetic knee extension torques at seven (0, 30, 60, 120, 180, 240, and 300° · s⁻¹) velocities were determined. Magnetic resonance imaging (MRI) was performed to calculate PCSA of right quadriceps femoris (QF) muscle. Exercise-induced contrast shifts in spin-spin relaxation time (T2)-weighted MRI were taken at rest and immediately after repetitive knee-extension exercise and T2 of QF were calculated. The MRI pixels with T2 values more than 1 SD greater than the means at rest were considered to represent QF muscle that had contracted. The area of activated PCSA within the total in QF was expressed as percentage activated PCSA and used as an index of muscle recruitment. The PCSA correlated with peak torque at 0° · s⁻¹ (r=0.615, P < 0.05); in contrast, activated PCSA correlated with peak torque at 120° · s⁻¹ (r=0.603, P < 0.05) and 180° · s⁻¹ (r=0.606, P < 0.05). Additionally, there was a significant difference in correlation coefficients between the activated PCSA-peak torque relationship and the PCSA-torque relationship (P < 0.05). These results suggested that muscle recruitment affects the PCSA-torque relationship. Accepted: 11 August 2000     

DTI of human skeletal muscle: the effects of diffusion encoding parameters,signal‐to‐noise ratio and T2 on tensor indices and fiber tracts

In this study, we have performed simulations to address the effects of diffusion encoding parameters, signal‐to‐noise ratio (SNR) and T₂ on skeletal muscle diffusion tensor indices and fiber tracts. Where appropriate, simulations were corroborated and validated by in vivo diffusion tensor imaging (DTI) of human skeletal muscle. Specifically, we have addressed: (i) the accuracy and precision of the diffusion parameters and eigenvectors at different SNR levels; (ii) the effects of the diffusion gradient direction encoding scheme; (iii) the optimal b value for diffusion tensor estimation; (iv) the effects of changes in skeletal muscle T₂; and, finally, the influence of SNR on fiber tractography and derived (v) fiber lengths, (vi) pennation angles and (vii) fiber curvatures. We conclude that accurate DTI of skeletal muscle requires an SNR of at least 25, a b value of between 400 and 500 s/mm², and data acquired with at least 12 diffusion gradient directions homogeneously distributed on half a sphere. Furthermore, for DTI studies focusing on skeletal muscle injury or pathology, apparent changes in the diffusion parameters need to be interpreted with great care in view of the confounding effects of T₂, particularly for moderate to low SNR values. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of beta‐hydroxy‐beta‐methylbutyrate supplementation on skeletal muscle in healthy and cirrhotic rats

Beta‐hydroxy‐beta‐methylbutyrate (HMB) is a leucine metabolite with protein anabolic effects. We examined the effects of an HMB‐enriched diet in healthy rats and rats with liver cirrhosis induced by multiple doses of carbon tetrachloride (CCl4). HMB increased branched‐chain amino acids (BCAAs; valine, leucine and isoleucine) in blood and BCAA and ATP in muscles of healthy animals. The effect on muscle mass and protein content was insignificant. In CCl4‐treated animals alterations characteristic of liver cirrhosis were found with decreased ratio of the BCAA to aromatic amino acids in blood and lower muscle mass and ATP content when compared with controls. In CCl4‐treated animals consuming HMB, we observed higher mortality, lower body weight, higher BCAA levels in blood plasma, higher ATP content in muscles, and lower ATP content and higher cathepsin B and L activities in the liver when compared with CCl4‐treated animals without HMB. We conclude that (1) HMB supplementation has a positive effect on muscle mitochondrial function and enhances BCAA concentrations in healthy animals and (2) the effects of HMB on the course of liver cirrhosis in CCl4‐treated rats are detrimental. Further studies examining the effects of HMB in other models of hepatic injury are needed to determine pros and cons of HMB in the treatment of subjects with liver cirrhosis.     

Prediction and validation of total and regional skeletal muscle mass by ultrasound in Japanese adults

The present study was performed to develop regression-based prediction equations for skeletal muscle (SM) mass by ultrasound and to investigate the validity of these equations in Japanese adults. Seventy-two Japanese men (n=38) and women (n=34) aged 18–61 years participated in this study and were randomly separated into two groups: the model development group (n=48) and the validation group (n=24). The total and regional SM mass were measured using magnetic resonance imaging (MRI) 1.5 T-scanners with spin-echo sequence. Contiguous transverse images (about 150 slices) with a slice thickness of 1 cm were obtained from the first cervical vertebra to the ankle joints. The volume of SM was calculated from the summation of digitized cross-sectional area. The SM volume was converted into mass units (kg) by an assumed SM density of 1.04 kg l⁻¹. The muscle thickness (MTH) was measured by B-mode ultrasound (5 MHz scanning head) at nine sites on the anatomical SM belly. Strong correlations were observed between the site-matched SM mass (total, arm, trunk body, thigh, and lower leg) by MRI measurement and the MTH × height (in m) in the model development group (r=0.83–0.96 in men, r=0.53–0.91 in women, P<0.05). When the SM mass prediction equations were applied to the validation group, significant correlations were also observed between the MRI-measured and predicted SM mass (P<0.05). The predicted total SM mass for the validation group was 19.6 (6.5) kg and was not significantly different from the MRI-measured SM mass of 20.2 (6.5) kg. Bland–Altman analysis did not indicate a bias in prediction of the total SM mass for the validation group (r=0.00, NS). These results suggested that ultrasound-derived prediction equations are a valid method to predict SM mass and an alternative to MRI measurement in healthy Japanese adults.     

Interaction of exercise and diet on GLUT‐4 protein and gene expression in Type I and Type II rat skeletal muscle

We determined the interaction of exercise and diet on glucose transporter (GLUT‐4) protein and mRNA expression in type I (soleus) and type II [extensor digitorum longus (EDL)] skeletal muscle. Forty‐eight Sprague Dawley rats were randomly assigned to one of two dietary conditions: high‐fat (FAT, n=24) or high‐carbohydrate (CHO, n=24). Animals in each dietary condition were allocated to one of two groups: control (NT, n=8) or a group that performed 8 weeks of treadmill running (4 sessions week^–1 of 1000 m @ 28 m min^–1, RUN, n=16). Eight trained rats were killed after their final exercise bout for determination of GLUT‐4 protein and mRNA expression: the remainder were killed 48 h after their last session for measurement of muscle glycogen and triacylglycerol concentration. GLUT‐4 protein expression in NT rats was similar in both muscles after 8 weeks of either diet. However, there was a main effect of training such that GLUT‐4 protein was increased in the soleus of rats fed with either diet (P < 0.05) and in the EDL in animals fed with CHO (P < 0.05). There was a significant diet–training interaction on GLUT‐4 mRNA, such that expression was increased in both the soleus (100% ↑P < 0.05) and EDL (142% ↑P < 0.01) in CHO‐fed animals. Trained rats fed with FAT decreased mRNA expression in the EDL (↓ 45%, P < 0.05) but not the soleus (↓ 14%, NS). We conclude that exercise training in CHO‐fed rats increased both GLUT‐4 protein and mRNA expression in type I and type II skeletal muscle. Despite lower GLUT‐4 mRNA in muscles from fat‐fed animals, exercise‐induced increases in GLUT‐4 protein were largely preserved, suggesting that control of GLUT‐4 protein and gene expression are modified independently by exercise and diet.     

Duration of sleep at 3 years of age is associated with fat and fat‐free mass at 4 years of age: the Southampton Women's Survey

Many studies have shown that shorter sleep duration in childhood is associated with higher body mass index (BMI), and have proposed that it is due to an effect of sleep on adiposity. There is little evidence about the association of sleep with fat‐free mass. This study examined the association between child's sleep duration at age 3 years and fat and fat‐free mass at 4 years of age in a prospective cohort study of 302 boys and 285 girls. Study participants were taking part in the Southampton Women's Survey, a longitudinal study of mothers and children from preconception onwards. Total sleep duration at age 3 years was derived from parental report of night sleep and nap duration. Body composition was assessed by Dual‐energy X‐ray Absorptiometry (DXA) at 4 years. Mean total sleep duration was 11.5 hours. In linear regression analyses, adjusted for potentially confounding factors (maternal educational attainment, prepregnancy BMI, smoking during pregnancy, child's gestational age at birth, age at DXA, sex, age last breastfed, dietary quality at 3 years, TV watching and hours actively on the move and parental social class), shorter sleep in hours was associated with higher BMI (kg/m²) [β: ?0.2340, 95% confidence interval (CI): ?0.373 to ?0.096], a greater fat mass index (kg) (β: ?0.1182, 95% CI: ?0.218 to ?0.018) and a greater fat‐free mass index (kg) (β: ?0.100, 95% CI: ?0.185 to ?0.015). Previous research suggested that the association between shorter sleep and higher body mass index is due to an effect on adiposity. Our findings are novel, suggesting that the relationship between sleep and BMI is also determined by an effect on muscle.     

Association between cervical lordotic curvature and cervical muscle cross‐sectional area in patients with loss of cervical lordosis

Disruption of the cervical lordotic curve can cause undesirable symptoms such as neck pain, and cord compression. The purpose of this study was to investigate the biomechanics of loss of cervical lordosis by measuring the cross‐sectional area (CSA) of the cervical muscles using magnetic resonance imaging (MRI), and to determine the relationship between cervical lordosis angle and cervical muscle status. The cervical lordosis angle was measured on standing lateral plain radiography using the posterior tangent technique in patients who complained of neck pain. The CSAs of the cervical flexor muscles including the longus cervicis and longus capitis, the cervical extensor muscles including the splenius capitis and semispinalis capitis, and the sternocleidomastoid muscle, were measured at the maximum levels by axial T1‐weighted MRI. We compared neck muscle CSAs between the two groups, the correlation with cervical lordosis angle, and muscle status including CSA and imbalance. The CSA of the semispinalis capitis was significantly lower in the loss of cervical lordosis group, and the ratio of cervical flexor to extensor was significantly different between the two groups (P < 0.05). Partial correlation analysis revealed that the cervical lordotic angle was significantly positively correlated with the ratio of flexor to extensor muscle CSAs (P < 0.05). There is a significant relationship between cervical muscle imbalance, including extensor muscle weakness, and loss of cervical lordosis. An exercise program focusing on cervical extensor muscle strengthening and restoring the balance of flexor and extensor muscles is recommended for patients with loss of cervical lordosis. Clin. Anat. 31:710–715, 2018. © 2018 Wiley Periodicals, Inc.     

Dynamic 2D and 3D mapping of hyperpolarized pyruvate to lactate conversion in vivo with efficient multi‐echo balanced steady‐state free precession at 3 T

The aim of this study was to acquire the transient MRI signal of hyperpolarized tracers and their metabolites efficiently, for which specialized imaging sequences are required. In this work, a multi‐echo balanced steady‐state free precession (me‐bSSFP) sequence with Iterative Decomposition with Echo Asymmetry and Least squares estimation (IDEAL) reconstruction was implemented on a clinical 3 T positron‐emission tomography/MRI system for fast 2D and 3D metabolic imaging. Simulations were conducted to obtain signal‐efficient sequence protocols for the metabolic imaging of hyperpolarized biomolecules. The sequence was applied in vitro and in vivo for probing the enzymatic exchange of hyperpolarized [1–¹³C]pyruvate and [1–¹³C]lactate. Chemical shift resolution was achieved using a least‐square, iterative chemical species separation algorithm in the reconstruction. In vitro, metabolic conversion rate measurements from me‐bSSFP were compared with NMR spectroscopy and free induction decay‐chemical shift imaging (FID‐CSI). In vivo, a rat MAT‐B‐III tumor model was imaged with me‐bSSFP and FID‐CSI. 2D metabolite maps of [1–¹³C]pyruvate and [1–¹³C]lactate acquired with me‐bSSFP showed the same spatial distributions as FID‐CSI. The pyruvate‐lactate conversion kinetics measured with me‐bSSFP and NMR corresponded well. Dynamic 2D metabolite mapping with me‐bSSFP enabled the acquisition of up to 420 time frames (scan time: 180‐350 ms/frame) before the hyperpolarized [1–¹³C]pyruvate was relaxed below noise level. 3D metabolite mapping with a large field of view (180 × 180 × 48 mm³) and high spatial resolution (5.6 × 5.6 × 2 mm³) was conducted with me‐bSSFP in a scan time of 8.2 seconds. It was concluded that Me‐bSSFP improves the spatial and temporal resolution for metabolic imaging of hyperpolarized [1–¹³C]pyruvate and [1–¹³C]lactate compared with either of the FID‐CSI or EPSI methods reported at 3 T, providing new possibilities for clinical and preclinical applications.     

Mapping tissue water T1 in the liver using the MOLLI T1 method in the presence of fat,iron and B0 inhomogeneity

Modified Look‐Locker inversion recovery (MOLLI) T₁ mapping sequences can be useful in cardiac and liver tissue characterization, but determining underlying water T₁ is confounded by iron, fat and frequency offsets. This article proposes an algorithm that provides an independent water MOLLI T₁ (referred to as on‐resonance water T₁) that would have been measured if a subject had no fat and normal iron, and imaging had been done on resonance. Fifteen NiCl₂‐doped agar phantoms with different peanut oil concentrations and 30 adults with various liver diseases, nineteen (63.3%) with liver steatosis, were scanned at 3 T using the shortened MOLLI (shMOLLI) T₁ mapping, multiple‐echo spoiled gradient‐recalled echo and ¹H MR spectroscopy sequences. An algorithm based on Bloch equations was built in MATLAB, and water shMOLLI T₁ values of both phantoms and human participants were determined. The quality of the algorithm's result was assessed by Pearson's correlation coefficient between shMOLLI T₁ values and spectroscopically determined T₁ values of the water, and by linear regression analysis. Correlation between shMOLLI and spectroscopy‐based T₁ values increased, from r = 0.910 (P < 0.001) to r = 0.998 (P < 0.001) in phantoms and from r = 0.493 (for iron‐only correction; P = 0.005) to r = 0.771 (for iron, fat and off‐resonance correction; P < 0.001) in patients. Linear regression analysis revealed that the determined water shMOLLI T₁ values in patients were independent of fat and iron. It can be concluded that determination of on‐resonance water (sh)MOLLI T₁ independent of fat, iron and macroscopic field inhomogeneities was possible in phantoms and human subjects.