Keywords: Muscle, Spectroscopy

Motivation: To explore quantification of skeletal muscle oxidative metabolism by ¹H MRS.

Goal(s): We used the increased accuracy of 7T MRS with a dedicated RF-coil, interleaved acquisition and localization of ³¹P information to compare Creatine-CH₂ and Phosphocreatine time courses during exercise and recovery.

Approach: Eight volunteers were measured on a 7T MR system with RF-coil and ergometer dedicated for exercise. ¹H and ³¹P MR spectra were acquired interleaved during exercise and recovery.

Results: Exercise led to disappearance of the Creatine-CH₂ resonance, while the CH₃ resonance remained stable during exercise. The recovery time constants were similar (τ_PCr=37±9s and τ_Cr=34±6s) and positively correlated.

Impact: The time course of the Creatine-CH₂ resonance in skeletal muscle can be accessed via dynamic ¹H MRS. If accurately reflecting oxidative metabolism, this technique has the potential to render non-invasive metabolic studies broadly accessible, without needing multi-nuclear MRI capabilities.

Keywords: Functional/Dynamic, Muscle, Genetic Diseases

Motivation: Changes to muscle twitch dynamics are overlooked in trials assessing resistance exercise in primary mitochondrial myopathies (PMM).

Goal(s): Motor unit MRI to measure twitch dynamics in PMM participants before and after a 12-week exercise programme.

Approach: Voxel-wise measurements of rise time (T_rise), contraction time (T_contract) and half-relaxation time (T_half-relax) in the tibialis anterior in 10 controls and 9 PMM participants. PMM participants scanned twice, before and after a 12-week exercise programme.

Results: T_contract of the tibialis anterior was significantly longer in PMM participants post exercise; T_rise, T_half-relax demonstrated no change. In participants who had the highest adherence to exercise T_contract increased the most.

Impact: Motor unit MRI (MUMRI) detected slower muscle contraction times in primary mitochondrial myopathies post resistance exercise programme. This may evidence increased numbers of type-I fibres post-exercise. MUMRI could be used to measure changes in muscle twitch dynamics in neuromuscular diseases.

Keywords: Muscle, Quantitative Imaging

Motivation: Parsonage-Turner syndrome (PTS) is a spontaneous peripheral neuropathy affecting upper extremity nerves and leading to severe muscle denervation. Quantitative MRI (qMRI) can objectively evaluate the degree of denervation and muscle recovery from PTS over time. 

Goal(s): To characterize PTS-related muscle denervation using qMRI biomarkers and to assess longitudinal changes.

Approach: In 21 PTS subjects at up to four timepoints, the associations of T2, apartment fiber diameter (AFD), fat fraction (FF), and muscle volume with electromyography and muscle function were analyzed.

Results: Associations between qMRI biomarkers reflect severity of muscle denervation in PTS. Recovery, involving reduced edema and increased atrophy, may follow non-linear patterns.

Impact: Quantitative MRI biomarkers including T2 mapping, apparent fiber diameter, fat fraction, and muscle volumetry correlate with electrodiagnostic and functional assessments of denervation and muscle function impairment in Parsonage-Turner syndrome (PTS), and they can longitudinally characterize PTS-related changes.

Keywords: Muscle, Fat, cerebral palsy

Motivation: Little is known about the fat content of the skeletal muscles of typically developing children or children with cerebral palsy.

Goal(s): To describe and compare muscle-specific intramuscular fat fractions in typically developing children and children with cerebral palsy.

Approach: Proton density fat fractions were calculated for 11 lower leg muscles using mDixon MRI scans of 280 children (5 to 15 years), including 79 with cerebral palsy.

Results: Age and sex did not affect mean fat fractions in typically developing children. Fat fractions varied across muscles. Fat fractions were larger, more variable, and increased with age in children with cerebral palsy.

Impact: The comprehensive dataset and automation measurement techniques for measurement of muscle-specific fat fractions in typically developing children and children with cerebral palsy may be used to monitor muscle-specific disease progression or measure the effect of interventions.

Keywords: Muscle, Muscle

Motivation: Combined ²³Na/³⁹K MRI at 7T can highlight ion disturbances related to patho-physiological processes within dystrophic muscle tissue. However, quantification of the apparent tissue potassium concentration (aTPC) using ³⁹K MRI is challenging due to low signal-to-noise and rapid signal decay.

Goal(s): Here, we investigated the feasibility of quantitative ³⁹K MRI in dystrophic muscle tissue.

Approach: The lower leg of 14 FSHD patients and 11 healthy controls was examined using ³⁹K/²³Na and ¹H MRI at 7T.

Results: We found a strongly reduced aTPC in fat infiltrated muscles. After correction for reduced potassium concentration in fat, aTPC values in dystrophic muscles were similar to healthy muscles.

Impact: Potassium concentration in fatty tissue is strongly reduced compared to healthy skeletal muscle tissue. This has to be considered when investigating and interpreting aTPC values measured with ³⁹K MRI in fat-replaced skeletal muscle tissue.

Keywords: Muscle, Spectroscopy, Muscle Inflammation, Integrative Physiology

Motivation: Exercise Induced Muscle Damage (EIMD) presents as a viable model to study the muscle inflammation  and fatigue which may present across various age-related pathologies.

Goal(s): Our model presents as a useful tool to test therapies aimed at improved patient rehabilitation.

Approach: Here we use  multi-parametric ³¹P, ²³Na and ¹H based MRI to show EMID is charactered by reduced muscle oxygenation with an increase in phosphate metabolism, sodium perturbation and overall perception of effort. Interestingly the cardiovascular response to exercise remained unchanged.

Results: Our results suggest a discrepancy between cardiovascular and muscle metabolic demand leads to altered oxygen delivery during exercise and  increased fatigability. 

Impact: This study highlights the importance of an integrative multi-parametric MRI approach to study the physiological consequences underlying muscle inflammation. This is crucial for advance our understanding on the abnormal responses present in age-related/health conditions characterised by muscle weakness and fatigue. 

Keywords: Muscle, Diffusion/other diffusion imaging techniques, diffusion-relaxation

Motivation: Quantifying muscle tissue properties is crucial for understanding physio-pathological changes occurring in skeletal muscle (SM). However, current methods measure T2 and diffusion separately, and hence conflate them.

Goal(s): Demonstrate a combined diffusion-relaxation MRI approach for disentangling T2 and diffusivity properties in SM.

Approach: We devise and implement a combined T2-diffusion sequence in the leg muscles in five healthy volunteers after exercise. DTI and an advanced diffusion model were implemented and compared.

Results: We calculated disentangled T2 and diffusion-related parameter maps. Our maps capture muscle tissue differences in specific muscle groups highlighting differences related to muscle involvement during exercise.

Impact: Combined diffusion-relaxation MRI can provide detailed non-invasive estimation of muscle tissue properties by mitigating T2 effects on diffusion parameters. These approaches could reduce the need for invasive biopsies for evaluating muscle changes related to neuromuscular diseases, exercise, and rehabilitation.

Keywords: Muscle, Diabetes

Motivation: Quantitative MRI is used for muscle parameter mapping, but single-parameter techniques and manual muscle segmentations take long.

Goal(s): Develop an automatic processing pipeline to generate parameter maps from 3D MRF and fat fraction images to extract quantitative biomarkers.

Approach: 3D MRF and fat fraction images were acquired on patients with diabetic peripheral neuropathy, deep-learning methods and post-processing were used to generate muscle masks and parameter maps before and after exercise intervention.

Results: Automatic muscle segmentation and 3D MRF are able to generate quantitative fat fraction, T₁, T₂, T_1ρ volumetric maps within muscle ROIs for tracking changes in patients before and after exercise intervention.

Impact: Both the 3D MRF sequence and automatic muscle extraction help reduce acquisition and post-processing time, allowing faster assessment of treatment response in diabetic patients.

Keywords: Muscle, MSK

Motivation: Fat fraction and water T2 have been identified as biomarkers of muscle tissue alterations in neuromuscular diseases. Tongue muscles are involved in several muscular disorder, but due to swallowing motion, quantitative MRI is almost never applied at this level.

Goal(s): Assess the feasibility of a water T2 mapping in the tongue.

Approach: In this feasibility study, we proposed an RF phase-modulated gradient-echo acquisition with 3D radial encoding to obtain FF and water T2 maps of the tongue.

Results: The proposed method enables 3D mapping. The values found in the tongue are consistent with those found with the same methods in the leg muscles.

Impact: Performing quantitative imaging in the tongue is challenging due to swallowing motion. Applying a 3D radial sequence appears the appropriate strategy for water T2 imaging.

Keywords: Data Processing, Segmentation

Motivation: The incidence of abdominal hernia recurrence is reaching up to 45%; so the integration of biomechanical concepts into management could be helpful.

Goal(s): Few tools are currently available to assess the behaviour of the abdominal wall in vivo under physiological conditions.

Approach: Dynamic MRI was employed to obtain motion of the abdominal wall of patients before and after hernia surgery during a range of exercises. The areas of interest were segmented.

Results: Quantification of displacements and deformations in the abdominal muscles, hernia sac area, and inter-muscular distance demonstrate anatomical and functional changes in the abdominal wall post-hernia surgery.

Impact: A better understanding of the biomechanical behaviour of pathologic abdominal wall could be helpful to understand the mechanisms involved in the appearance and recurrence of hernias, thereby opening the way to more effective interventions for hernia patients.