New insights into intrinsic foot muscle morphology and composition using ultra-high-field (7-Tesla) magnetic resonance imaging.

BACKGROUND: The intrinsic muscles of the foot are key contributors to foot function and are important to evaluate in lower limb disorders. Magnetic resonance imaging (MRI), provides a non-invasive option to measure muscle morphology and composition, which are primary determinants of muscle function. Ultra-high-field (7-T) magnetic resonance imaging provides sufficient signal to evaluate the morphology of the intrinsic foot muscles, and, when combined with chemical-shift sequences, measures of muscle composition can be obtained. Here we aim to provide a proof-of-concept method for measuring intrinsic foot muscle morphology and composition with high-field MRI. METHODS: One healthy female (age 39 years, mass 65 kg, height 1.73 m) underwent MRI. A T1-weighted VIBE - radio-frequency spoiled 3D steady state GRE - sequence of the whole foot was acquired on a Siemens 7T MAGNETOM scanner, as well as a 3T MAGNETOM Prisma scanner for comparison. A high-resolution fat/water separation image was also acquired using a 3D 2-point DIXON sequence at 7T. Coronal plane images from 3T and 7T scanners were compared. Using 3D Slicer software, regions of interest were manually contoured for each muscle on 7T images. Muscle volumes and percentage of muscle fat infiltration were calculated (muscle fat infiltration % = Fat/(Fat + Water) x100) for each muscle. RESULTS: Compared to the 3T images, the 7T images provided superior resolution, particularly at the forefoot, to facilitate segmentation of individual muscles. Muscle volumes ranged from 1.5 cm3 and 19.8 cm3, and percentage muscle fat infiltration ranged from 9.2-15.0%. CONCLUSIONS: This proof-of-concept study demonstrates a feasible method of quantifying muscle morphology and composition for individual intrinsic foot muscles using advanced high-field MRI techniques. This method can be used in future studies to better understand intrinsic foot muscle morphology and composition in healthy individuals, as well as those with lower disorders.

Impact of exercise selection on hamstring muscle activation.

OBJECTIVE: To determine which strength training exercises selectively activate the biceps femoris long head (BFLongHead) muscle. METHODS: We recruited 24 recreationally active men for this two-part observational study. Part 1: We explored the amplitudes and the ratios of lateral (BF) to medial hamstring (MH) normalised electromyography (nEMG) during the concentric and eccentric phases of 10 common strength training exercises. Part 2: We used functional MRI (fMRI) to determine the spatial patterns of hamstring activation during two exercises which (1) most selectively and (2) least selectively activated the BF in part 1. RESULTS: Eccentrically, the largest BF/MH nEMG ratio occurred in the 45° hip-extension exercise; the lowest was in the Nordic hamstring (Nordic) and bent-knee bridge exercises. Concentrically, the highest BF/MH nEMG ratio occurred during the lunge and 45° hip extension; the lowest was during the leg curl and bent-knee bridge. fMRI revealed a greater BF(LongHead) to semitendinosus activation ratio in the 45° hip extension than the Nordic (p<0.001). The T2 increase after hip extension for BFLongHead, semitendinosus and semimembranosus muscles was greater than that for BFShortHead (p<0.001). During the Nordic, the T2 increase was greater for the semitendinosus than for the other hamstring muscles (p≤0.002). SUMMARY: We highlight the heterogeneity of hamstring activation patterns in different tasks. Hip-extension exercise selectively activates the long hamstrings, and the Nordic exercise preferentially recruits the semitendinosus. These findings have implications for strategies to prevent hamstring injury as well as potentially for clinicians targeting specific hamstring components for treatment (mechanotherapy).

Impact of the Nordic hamstring and hip extension exercises on hamstring architecture and morphology: implications for injury prevention.

BACKGROUND: The architectural and morphological adaptations of the hamstrings in response to training with different exercises have not been explored. PURPOSE: To evaluate changes in biceps femoris long head (BFLH) fascicle length and hamstring muscle size following 10-weeks of Nordic hamstring exercise (NHE) or hip extension (HE) training. METHODS: 30 recreationally active male athletes (age, 22.0±3.6 years; height, 180.4±7 cm; weight, 80.8±11.1 kg) were allocated to 1 of 3 groups: (1) HE training (n=10), NHE training (n=10), or no training (control, CON) (n=10). BFLH fascicle length was assessed before, during (Week 5) and after the intervention with a two-dimensional ultrasound. Hamstring muscle size was determined before and after training via MRI. RESULTS: Compared with baseline, BFLH fascicles were lengthened in the NHE and HE groups at mid-training (d=1.12-1.39, p<0.001) and post-training (d=1.77-2.17, p<0.001) and these changes did not differ significantly between exercises (d=0.49-0.80, p=0.279-0.976). BFLH volume increased more for the HE than the NHE (d=1.03, p=0.037) and CON (d=2.24, p<0.001) groups. Compared with the CON group, both exercises induced significant increases in semitendinosus volume (d=2.16-2.50, ≤0.002) and these increases were not significantly different (d=0.69, p=0.239). CONCLUSION: NHE and HE training both stimulate significant increases in BFLH fascicle length; however, HE training may be more effective for promoting hypertrophy in the BFLH.

Body fat and circulating leptin levels in the captive short-beaked echidna (Tachyglossus aculeatus).

It is possible that the reproductive strategy of the short-beaked echidna is related to seasonal changes in fat deposition and energy availability, regulated by seasonal changes in endocrine function. We predicted that circulating leptin levels would be directly proportional to adiposity during most of the year, but that a change in this relationship would occur during the pre-breeding season to allow increased fat deposition. To test this hypothesis, we made use of a captive colony of echidnas to describe and quantify changes in fat distribution and the adipostatic hormone leptin. First we assessed seasonal changes in circulating leptin levels, body mass and adiposity for three male and three female adult echidnas maintained on a standard diet. Second, we explored the relationship between circulating leptin levels and increased caloric intake for an additional five adult female echidnas that were provided with supplemented nutrition. Third we visualised fat distribution in male and female adult echidnas using magnetic resonance imaging (MRI) before and after the breeding season, to determine where fat is deposited in this species. For echidnas maintained on the standard diet, there were no seasonal changes in body mass, body fat or plasma leptin levels. However, female echidnas provided with supplemented nutrition had significantly elevated plasma leptin levels during the breeding season, compared to the pre-and post- breeding periods. MRI showed substantial subcutaneous fat depots extending dorso-laterally from the base of the skull to the base of the tail, in both sexes. Pre-breeding season, both sexes had considerable fat deposition in the pelvic/rump region, whilst the female echidna accumulated most fat in the abdominal region. This study shows that male and female echidnas accumulate body fat in the pelvic/rump and the abdominal regions, respectively and that circulating leptin may promote fattening in female echidnas during the breeding season by means of leptin resistance. However, further research is required to evaluate the precise relationship between seasonal changes in leptin and adiposity.

Comparison between 2D and 3D MEDIC for human cervical spinal cord MRI at 3T.

INTRODUCTION: High-resolution magnetic resonance imaging (MRI) of the cervical spinal cord is important to provide accurate diagnosis and pathological assessment of injuries. MEDIC (Multiple Echo Data Image Combination) sequences have been used in clinical MRI; however, a comparison of the performance of 2D and 3D MEDIC for cervical spinal cord imaging has not been reported. The aim of this study is to compare axial 2D and 3D MEDIC for the visualisation of the grey matter (GM) and white matter (WM) of the human cervical spinal cord. METHODS: Eight healthy participants were scanned using Siemens Prismafit 3T MRI. T2*-weighted gradient spoiled 2D and 3D MEDIC sequences were acquired at 0.4 × 0.4 × 3.0 and 0.3 × 0.3 × 3.0 mm resolutions, with the acquisition times of 6 and 7 min, respectively. Quantitative analyses of the images were made based on the image signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and non-uniformity (NU). Two independent radiologists (CS and FN), each provided Likert scoring assessments of anatomical visibility of the GM and WM structures and image clarity for all samples. RESULTS: Quantitative evaluation showed that 3D MEDIC provided higher SNR, higher CNR and lower NU than 2D MEDIC. However, 2D MEDIC provided better anatomical visibility for the GM, WM and CSF, and higher image clarity (lower artefacts) compared to 3D MEDIC. CONCLUSIONS: 2D MEDIC provides better information for depicting the internal structures of the cervical spinal cord compared to 3D MEDIC.

7-Tesla Functional Cardiovascular MR Using Vectorcardiographic Triggering-Overcoming the Magnetohydrodynamic Effect.

Objective: Ultra-high-field B0 ≥ 7 tesla (7T) cardiovascular magnetic resonance (CMR) offers increased resolution. However, electrocardiogram (ECG) gating is impacted by the magneto-hydrodynamic effect distorting the ECG trace. We explored the technical feasibility of a 7T magnetic resonance scanner using an ECG trigger learning algorithm to quantitatively assess cardiac volumes and vascular flow. Methods: 7T scans were performed on 10 healthy volunteers on a whole-body research MRI MR scanner (Siemens Healthineers, Erlangen, Germany) with 8 channel Tx/32 channels Rx cardiac coils (MRI Tools GmbH, Berlin, Germany). Vectorcardiogram ECG was performed using a learning phase outside of the magnetic field, with a trigger algorithm overcoming severe ECG signal distortions. Vectorcardiograms were quantitatively analyzed for false negative and false positive events. Cine CMR was performed after 3rd-order B0 shimming using a high-resolution breath-held ECG-retro-gated segmented spoiled gradient echo, and 2D phase contrast flow imaging. Artefacts were assessed using a semi-quantitative scale. Results: 7T CMR scans were acquired in all patients (100%) using the vectorcardiogram learning method. 3,142 R-waves were quantitatively analyzed, yielding sensitivity of 97.6% and specificity of 98.7%. Mean image quality score was 0.9, sufficient to quantitate both cardiac volumes, ejection fraction, and aortic and pulmonary blood flow. Mean left ventricular ejection fraction was 56.4%, right ventricular ejection fraction was 51.4%. Conclusion: Reliable cardiac ECG triggering is feasible in healthy volunteers at 7T utilizing a state-of-the-art three-lead trigger device despite signal distortion from the magnetohydrodynamic effect. This provides sufficient image quality for quantitative analysis. Other ultra-high-field imaging applications such as human brain functional MRI with physiologic noise correction may benefit from this method of ECG triggering.

Cardiac Magnetic Resonance Imaging at 7 Tesla.

CMR at an ultra-high field (magnetic field strength B0 ≥ 7 Tesla) benefits from the signal-to-noise ratio (SNR) advantage inherent at higher magnetic field strengths and potentially provides improved signal contrast and spatial resolution. While promising results have been achieved, ultra-high field CMR is challenging due to energy deposition constraints and physical phenomena such as transmission field non-uniformities and magnetic field inhomogeneities. In addition, the magneto-hydrodynamic effect renders the synchronization of the data acquisition with the cardiac motion difficult. The challenges are currently addressed by explorations into novel magnetic resonance technology. If all impediments can be overcome, ultra-high field CMR may generate new opportunities for functional CMR, myocardial tissue characterization, microstructure imaging or metabolic imaging. Recognizing this potential, we show that multi-channel radio frequency (RF) coil technology tailored for CMR at 7 Tesla together with higher order B0 shimming and a backup signal for cardiac triggering facilitates high fidelity functional CMR. With the proposed setup, cardiac chamber quantification can be accomplished in examination times similar to those achieved at lower field strengths. To share this experience and to support the dissemination of this expertise, this work describes our setup and protocol tailored for functional CMR at 7 Tesla.

Hamstring Muscle Use in Women During Hip Extension and the Nordic Hamstring Exercise: A Functional Magnetic Resonance Imaging Study.

Background Understanding hamstring muscle activation patterns in resistance training exercises may have implications for the design of strength training and injury prevention programs. Unfortunately, surface electromyography studies have reported conflicting results regarding hamstring muscle activation patterns in women. Objectives To determine the spatial patterns of hamstring muscle activity during the 45° hip extension and Nordic hamstring exercises in women using functional magnetic resonance imaging (fMRI). Methods This was a cross-sectional study in which 6 recreationally active women with no history of lower-limb injury underwent fMRI on both thighs before and immediately after 5 sets of 6 bilateral eccentric contractions of the 45° hip extension exercise or the Nordic exercise. Using fMRI, the transverse (T2) relaxation times were measured from pre-exercise and postexercise scans, and the percentage increase in T2 was used as an index of muscle activation. Results The fMRI revealed a significantly higher biceps femoris long head-to-semitendinosus ratio during the 45° hip extension exercise than in the Nordic exercise (P = .028). The T2 increase after the 45° hip extension exercise was greater for the biceps femoris long head (P<.001), semitendinosus, and semimembranosus (P≤.001) than that for the biceps femoris short head. During the Nordic exercise, the T2 increase of the semitendinosus was greater than that of the biceps femoris short head (P<.001) and biceps femoris long head (P = .001). Conclusion While both exercises involve high levels of semitendinosus activation in women, the Nordic exercise preferentially recruits that muscle, while the hip extension exercise more evenly activates all the biarticular hamstrings. J Orthop Sports Phys Ther 2018;48(8):607-612. Epub 23 Apr 2018. doi:10.2519/jospt.2018.7748.

The pearls and pitfalls of magnetic resonance imaging for the spine.

Musculoskeletal imaging of the spine can be an invaluable tool to inform clinical decision making in patients with spinal pain. An understanding of the technology involved in producing and interpreting high-resolution images produced from magnetic resonance imaging (MRI) of the human spine is necessary to better appreciate which sequences can be used for, or tailored to, individual patients and their conditions. However, there is substantial variability in the clinical meaningfulness of some MRI findings of spinal tissues. For example, normal variants can often mimic significant musculoskeletal pathology, which could increase the risk of misinformed clinical decisions and, even worse, poor or adverse outcomes. This clinical commentary will highlight some of the pearls and pitfalls of MRI for the cervical, thoracic, and lumbar regions, and include cases to illustrate some of the common imaging artifacts and normal variants for MRI of the spine.