Simultaneous Multislice Accelerated Diffusion Tensor Imaging of Thigh Muscles in Myositis

Diffusion Tensor Imaging of Rat Rotator Cuff Muscle With Histopathological Correlation: An Exploratory Study

The purpose of this exploratory study was to quantify the relationship between scalar-based measures of diffusion tensor imaging (DTI) and histologically derived microstructural measurements in precisely colocalized rat rotator cuff muscle tissue and to compare the results when imaged at 0.25- and 0.5-mm isotropic resolutions. Four Lewis rats subject to a unilateral chronic massive rotator cuff tear model were evaluated on a 3-T preclinical MRI scanner using spin echo DTI sequences at 0.25- and 0.5-mm isotropic resolutions, and histology was subsequently performed. Fractional anisotropy (FA), mean diffusivity (MD), and radial diffusivity (RD) were calculated. Whole muscle myofiber boundary segmentation was performed, and muscle fiber diameter and cross-sectional area were calculated on slides that passed rigorous histologic quality control. Scatter plots were generated on a pixel-by-pixel basis from meticulously colocalized DTI and histology data. Pearson's correlations were performed. Twenty-two distinct supraspinatus and infraspinatus muscle locations from two rats were included. Negligible correlations were found between DTI metrics, including FA, MD, and RD, and histological measurements, including muscle fiber diameters and cross-sectional areas. Using the most commonly employed spin echo DTI sequences with intermediate diffusion times, there may be negligible sensitivity to direct measures of muscle tissue microstructure. Our findings underscore the need for further research with optimized imaging parameters to enhance our knowledge regarding the capability of DTI to determine important features of muscle microstructure.

Diffusion tensor imaging of vastus lateralis in patients with inflammatory myopathies

OBJECTIVE

Inflammation in patients with myositis would increase diffusion of water molecules across sarcolemma that could be detected with the help of diffusion tensor imaging (DTI). We aimed to determine an association between DTI of vastus lateralis (VL) and histopathological findings in cases of myositis and to estimate diagnostic performance of different MRI variables in predicting histopathological outcomes.

METHODS

This prospective cross-sectional observational study included 43 patients with myositis. MRI of bilateral thighs with DWI/DTI protocol was performed in all the patients. Thirty-three patients further underwent biopsy of right VL muscle. Imaging analysis included grading of 'muscle oedema' based on signal intensity (SI) and extent and 'fatty infiltration' based on extent on conventional sequences and, acquiring DWI and DTI parameters. Gold standard method to determine inflammation in muscles was histopathological examination. Comparison of DTI/DWI variables with clinical and histopathological variables was done.

RESULTS

The average DWI apparent diffusion coefficient (ADC) and DTI ADC values in the patients were 1.77 ± 0.35 and 2.06 ± 0.35, respectively. The average functional anisotropy (FA) was 0.39 ± 0.17 and, the three eigenvalues in the patients were 2.96 ± 0.63, 2.05 ± 0.32 and 1.20 ± 0.39, respectively. VL oedema SI weighted score was the best parameter for predicting effaced fascicular architecture and marked lymphocytic inflammation in endomysium on histopathology. VL fatty infiltration weighted score was the best parameter in predicting perifascicular atrophy.

CONCLUSION

Addition of DWI or DTI did not add significantly in determining active inflammation in cases of myositis.

From Voxels to Physiology: A Review of Diffusion Magnetic Resonance Imaging Applications in Skeletal Muscle

Skeletal muscle has a classic structure function relationship; both skeletal muscle microstructure and architecture are directly related to force generating capacity. Biopsy, the gold standard for evaluating muscle microstructure, is highly invasive, destructive to muscle, and provides only a small amount of information about the entire volume of a muscle. Similarly, muscle fiber lengths and pennation angles, key features of muscle architecture predictive of muscle function, are traditionally studied via cadaveric dissection. Noninvasive techniques such as diffusion magnetic resonance imaging (dMRI) offer quantitative approaches to study skeletal muscle microstructure and architecture. Despite its prevalence in applications for musculoskeletal research, clinical adoption is hindered by a lack of understanding regarding its sensitivity to clinically important biomarkers such as muscle fiber cross-sectional area. This review aims to elucidate how dMRI has been utilized to study skeletal muscle, covering fundamentals of muscle physiology, dMRI acquisition techniques, dMRI modeling, and applications where dMRI has been leveraged to noninvasively study skeletal muscle changes in response to disease, aging, injury, and human performance. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

Assessment of Age-Related Microstructure Changes in Thigh Skeletal Muscle Based on Neurite Orientation Dispersion and Density Imaging

BACKGROUND

Neurite orientation dispersion and density imaging (NODDI) could offer information about the morphological properties of tissue. Diffusion microstructure imaging has been widely used, but the applicability of NODDI in skeletal muscle imaging remains to be explored.

PURPOSE

To evaluate microstructure parameters variations in skeletal muscle as indicators of age-related changes.

STUDY TYPE

Prospective, cross-sectional.

POPULATION

A total of 108 asymptomatic volunteers, divided into three age groups: 20-39 years (N = 34), 40-59 years (N = 40), and over 60 years (N = 34).

FIELD STRENGTH/SEQUENCE

3-T, three-dimensional (3D) gradient echo sequence.

ASSESSMENT

T1-weighted imaging, T2-weighted imaging with spectral adiabatic inversion recovery, and NODDI were used to image the thigh skeletal muscles. Four thigh skeletal muscle groups were analyzed, including bilateral thigh quadriceps femoris and hamstrings. The microstructure parameters included orientation dispersion index (ODI), intra-myofibrillar water volume fraction (V-intra), free-water fraction (V-csf), fractional anisotropy (FA), and mean diffusivity (MD). These parameters were quantified using NODDI images and compared among different age, body mass index (BMI), and skeletal muscle index (SMI) subgroups.

STATISTICAL TESTS

Segmentation measurement reliability was assessed using a two-way mixed intraclass correlation coefficient (ICC). Shapiro-Wilk tests were used to assess data distribution. Kruskal-Wallis and Mann-Whitney U tests were used to compare ODI, V-intra, V-csf, FA, and MD values among different age, BMI, and SMI subgroups. The Spearman correlation coefficient was utilized to assess the strength of the correlation between the age and microstructure parameters, as well as between age and SMI. Additionally, Bonferroni post hoc tests were conducted on microstructure parameters that exhibited significant differences across various age groups. A P-value <0.05 was considered statistically significant.

RESULTS

Significant differences in ODI, V-csf, FA, and MD values were observed among age, BMI, and SMI subgroups.

DATA CONCLUSION

NODDI may be used to reveal information about microstructure integrity and local physiological changes of thigh skeletal muscle fibers in relation to age.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 2.

Accelerated Musculoskeletal Magnetic Resonance Imaging

With a substantial growth in the use of musculoskeletal MRI, there has been a growing need to improve MRI workflow, and faster imaging has been suggested as one of the solutions for a more efficient examination process. Consequently, there have been considerable advances in accelerated MRI scanning methods. This article aims to review the basic principles and applications of accelerated musculoskeletal MRI techniques including widely used conventional acceleration methods, more advanced deep learning-based techniques, and new approaches to reduce scan time. Specifically, conventional accelerated MRI techniques, including parallel imaging, compressed sensing, and simultaneous multislice imaging, and deep learning-based accelerated MRI techniques, including undersampled MR image reconstruction, super-resolution imaging, artifact correction, and generation of unacquired contrast images, are discussed. Finally, new approaches to reduce scan time, including synthetic MRI, novel sequences, and new coil setups and designs, are also reviewed. We believe that a deep understanding of these fast MRI techniques and proper use of combined acceleration methods will synergistically improve scan time and MRI workflow in daily practice. EVIDENCE LEVEL: 3 TECHNICAL EFFICACY: Stage 1.

Magnetic Resonance Imaging Biomarkers of Muscle

This review is focused on the current status of quantitative MRI (qMRI) of skeletal muscle. The first section covers the techniques of qMRI in muscle with the focus on each quantitative parameter, the corresponding imaging sequence, discussion of the relation of the measured parameter to underlying physiology/pathophysiology, the image processing and analysis approaches, and studies on normal subjects. We cover the more established parametric mapping from T1-weighted imaging for morphometrics including image segmentation, proton density fat fraction, T2 mapping, and diffusion tensor imaging to emerging qMRI features such as magnetization transfer including ultralow TE imaging for macromolecular fraction, and strain mapping. The second section is a summary of current clinical applications of qMRI of muscle; the intent is to demonstrate the utility of qMRI in different disease states of the muscle rather than a complete comprehensive survey.

Clinical Applications and Recent Updates of Simultaneous Multi-slice Technique in Accelerated MRI

Simultaneous multi-slice (SMS) is a magnetic resonance imaging (MRI) acceleration technique that utilizes multi-band radio-frequency pulses to simultaneously excite and encode multiple slices. Currently, SMS has been widely studied and applied in the MRI examination to reduce acquisition time, which can significantly improve the examination efficiency and patient throughput. Moreover, SMS technique can improve spatial resolution, which is of great value in disease diagnosis, treatment response monitoring, and prognosis prediction. This review will briefly introduce the technical principles of SMS, and summarize its current clinical applications. More importantly, we will discuss the recent technical progress and future research direction of SMS, hoping to highlight the clinical value and scientific potential of this technique.

Post-COVID exercise intolerance is associated with capillary alterations and immune dysregulations in skeletal muscles

The SARS-CoV-2 pandemic not only resulted in millions of acute infections worldwide, but also in many cases of post-infectious syndromes, colloquially referred to as "long COVID". Due to the heterogeneous nature of symptoms and scarcity of available tissue samples, little is known about the underlying mechanisms. We present an in-depth analysis of skeletal muscle biopsies obtained from eleven patients suffering from enduring fatigue and post-exertional malaise after an infection with SARS-CoV-2. Compared to two independent historical control cohorts, patients with post-COVID exertion intolerance had fewer capillaries, thicker capillary basement membranes and increased numbers of CD169+ macrophages. SARS-CoV-2 RNA could not be detected in the muscle tissues. In addition, complement system related proteins were more abundant in the serum of patients with PCS, matching observations on the transcriptomic level in the muscle tissue. We hypothesize that the initial viral infection may have caused immune-mediated structural changes of the microvasculature, potentially explaining the exercise-dependent fatigue and muscle pain.

Consistency of muscle fibers directionality in human thigh derived from diffusion-weighted MRI

Objective.Diffusion-weighted MR imaging (DW-MRI) is known to quantify muscle fiber directionality and thus may be useful for radiotherapy target definition in sarcomas. Here, we investigate the variability of tissue anisotropy derived from diffusion tensor (DT) in the human thigh to establish the baseline parameters and protocols for DW-MRI acquisition for future studies in sarcoma patients.Approach.We recruited ten healthy volunteers to acquire diffusion-weighted MR images of the left and right thigh. DW-MRI data were used to reconstruct DT eigenvectors within each individual thigh muscle. Deviations of the principal eigenvector from its mean were calculated for different experimental conditions.Main results.Within the majority of muscles in most subjects, the mode of the histogram of the angular deviation of the principal eigenvector of the water DT from its muscle-averaged value did not exceed 20°. On average for all subjects, the mode ranged from 15° to 24°. Deviations much larger than 20° were observed in muscles far from the RF coil, including cases with significant amounts of subcutaneous fat and muscle deformation under its own weight.Significance.Our study is a robust characterization of angular deviations of muscle fiber directionality in the thigh as determined by DW-MRI. We show that an appropriate choice of experimental conditions reduces the variability of the observed directionality. Precise determination of tissue directionality will enable reproducible models of microscopic tumor spread, with future application in defining the clinical target volume for soft tissue sarcoma.

Clinical applications of skeletal muscle diffusion tensor imaging

Diffusion tensor imaging (DTI) may allow the determination of new threshold values, based on water anisotropy, to differentiate between healthy muscle and various pathological processes. Additionally, it may quantify treatment monitoring or training effects. Most current studies have evaluated the potential of DTI of skeletal muscle to assess sports-related injuries or therapy, and training monitoring. Another critical area of application of this technique is the characterization and monitoring of primary and secondary myopathies. In this manuscript, we review the application of DTI in the evaluation of skeletal muscle in these and other novel clinical scenarios, with emphasis on the use of quantitative imaging-derived biomarkers. Finally, the main limitations of the introduction of DTI in the clinical setting and potential areas of future use are discussed.

Imaging biomarkers in the idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are a group of acquired muscle diseases with muscle inflammation, weakness, and other extra-muscular manifestations. IIMs can significantly impact the quality of life, and management of IIMs often requires a multi-disciplinary approach. Imaging biomarkers have become an integral part of the management of IIMs. Magnetic resonance imaging (MRI), muscle ultrasound, electrical impedance myography (EIM), and positron emission tomography (PET) are the most widely used imaging technologies in IIMs. They can help make the diagnosis and assess the burden of muscle damage and treatment response. MRI is the most widely used imaging biomarker of IIMs and can assess a large volume of muscle tissue but is limited by availability and cost. Muscle ultrasound and EIM are easy to administer and can even be performed in the clinical setting, but they need further validation. These technologies may complement muscle strength testing and laboratory studies and provide an objective assessment of muscle health in IIMs. Furthermore, this is a rapidly progressing field, and new advances are going to equip care providers with a better objective assessment of IIMS and eventually improve patient management. This review discusses the current state and future direction of imaging biomarkers in IIMs.

A handbook for beginners in skeletal muscle diffusion tensor imaging: physical basis and technical adjustments

Magnetic resonance imaging (MRI) of skeletal muscle is routinely performed using morphological sequences to acquire anatomical information. Recently, there is an increasing interest in applying advanced MRI techniques that provide pathophysiologic information for skeletal muscle evaluation to complement standard morphologic information. Among these advanced techniques, diffusion tensor imaging (DTI) has emerged as a potential tool to explore muscle microstructure. DTI can noninvasively assess the movement of water molecules in well-organized tissues with anisotropic diffusion, such as skeletal muscle. The acquisition of DTI studies for skeletal muscle assessment requires specific technical adjustments. Besides, knowledge of DTI physical basis and skeletal muscle physiopathology facilitates the evaluation of this advanced sequence and both image and parameter interpretation. Parameters derived from DTI provide a quantitative assessment of muscle microstructure with potential to become imaging biomarkers of normal and pathological skeletal muscle. KEY POINTS: • Diffusion tensor imaging (DTI) allows to evaluate the three-dimensional movement of water molecules inside biological tissues. • The skeletal muscle structure makes it suitable for being evaluated with DTI. • Several technical adjustments have to be considered for obtaining robust and reproducible DTI studies for skeletal muscle assessment, minimizing potential artifacts.

The diagnostic value of T2 map, diffusion tensor imaging, and diffusion kurtosis imaging in differentiating dermatomyositis from muscular dystrophy

BACKGROUND

Dermatomyositis (DM) and muscular dystrophy are clinically difficult to differentiate.

PURPOSE

To confirm the feasibility and assess the accuracy of conventional magnetic resonance imaging (MRI), T2 map, diffusion tensor imaging (DTI), and diffusion kurtosis imaging (DKI) in the differentiation of DM from muscular dystrophy.

MATERIAL AND METHODS

Forty-two patients with DM proven by diagnostic criteria were enrolled in the study along with 23 patients with muscular dystrophy. Conventional MR, T2 map, DTI, and DKI images were obtained in the thigh musculature for all patients. Intramuscular T2 value, apparent diffusion coefficient (ADC), fractional anisotropy (FA), mean diffusivity (MD), and mean kurtosis (MK) values were compared between the patients with DM and muscular dystrophy. Student's t-tests and receiver operating characteristic (ROC) curve analyses were performed for all parameters. P values < 0.05 were considered statistically significant.

RESULTS

The intramuscular T2, ADC, FA, MD, and MK values within muscles were statistically significantly different between the DM and muscular dystrophy groups (P<0.01). The MK value was statistically significantly different between the groups in comparison with T2 and FA value. As a supplement to conventional MRI, the parameters of MD and MK differentiated DM and muscular dystrophy may be valuable. The optimal cut-off value of ADC and MD values (with respective AUC, sensitivity, and specificity) between DM and muscular dystrophy were 1.698 ×10^-3mm²/s (0.723, 54.1%, and 78.1%) and 1.80 ×10^-3mm²/s (61.9% and 70.2%), respectively.

CONCLUSION

Thigh muscle ADC and MD parameters may be useful in differentiating patients with DM from those with muscular dystrophy.

Decreased Muscular Perfusion in Dermatomyositis: Initial Results Detected by Inflow-Based Vascular-Space-Occupancy MRI

OBJECTIVE. This study aimed to determine whether inflow-based vascular-space-occupancy (iVASO) MRI could reproducibly quantify skeletal muscle perfusion and differentiate patients with dermatomyositis (DM) from healthy subjects. MATERIALS AND METHODS. A total of 25 patients with DM and 22 healthy volunteers underwent iVASO MRI in a 3-T MRI scanner. Maximum and mean arteriolar muscle blood volume (MBV) values of four subgroups of muscles (normal muscles, morphologically normal-appearing muscles, edematous muscles, and atrophic or fat-infiltrated muscles) were obtained. Maximum and mean arteriolar MBV values were compared among the different subgroups, and repeat testing was performed in 20 subjects to assess reproducibility. RESULTS. Compared with normal muscles in healthy subjects, morphologically normal-appearing muscles, edematous muscles, and atrophic or fat-infiltrated muscles in patients with DM showed a significant decrease of both maximum and mean arteriolar MBV (p < .001). Both parameters were significantly lower in atrophic or fat-infiltrated muscles than in morphologically normal-appearing and edematous muscles (p < .001). ROC AUCs for discriminating patients with DM from healthy volunteers were 0.842 and 0.812 for maximum and mean arteriolar MBV values, respectively. As a measure of test-retest studies, the intraclass correlation coefficients (ICCs) were 0.990 (95% CI, 0.986-0.993) and 0.990 (95% CI, 0.987-0.993) for maximum and mean arteriolar MBV, respectively. For interobserver reproducibility, the ICCs were 0.989 (95% CI, 0.986-0.991) and 0.980 (95% CI, 0.975-0.983), respectively. CONCLUSION. iVASO MRI can reproducibly quantify arteriolar MBV in the thigh and discriminate between healthy volunteers and patients with DM.