Diffusion tensor imaging and T2 mapping in early denervated skeletal muscle in rats

Diffusion MRI fiber diameter for muscle denervation assessment

BACKGROUND

To develop and evaluate a diffusion MRI-based apparent muscle fiber diameter (AFD) method in patients with muscle denervation. It was hypothesized that AFD differences between denervated, non-denervated and control muscles would be greater than those from standard diffusion metrics.

METHODS

A spin-echo diffusion acquisition with multi-b-valued diffusion sampling was used. An orientation-invariant dictionary approach utilized a cylinder-based forward model and multi-compartment model for obtaining restricted and free fractions. Simulations were performed to determine precision, bias, and optimize dictionary parameters. In all, 18 exams of patients with muscle denervation and 8 exams of healthy subjects were performed at 3T. Six regions of interests (ROIs) within separate shoulder muscles were selected, yielding three groups consisting 47 control (healthy), 36 non-denervated (patients), and 68 denervated (patients) muscle ROIs. Two-sample t-tests (α=0.05) between groups were performed with Holm-Bonferroni correction. T2- and fat fraction (FF)-mapping were acquired for comparison.

RESULTS

Mean AFD was 89.7±13.6 µm in control, 71.6±15.3 µm in non-denervated, and 60.7±15.9 µm in denervated muscles and were significantly different (P<0.001) in paired comparisons and in 10/12 individual muscle region comparisons. Correlation between AFD and FF (-0.331, P<0.001) was low, but correlation between FA and FF was negligible (0.197, P=0.016). Correlation was low between AFD and T2 (-0.395, P<0.001) and between FA and T2 (0.359, P<0.001).

CONCLUSIONS

Diffusion MRI-based AFD complements T2- and FF-mapping techniques to non-invasively assess muscle denervation.

MR Neurography of Peripheral Nerve Injury in the Presence of Orthopedic Hardware: Technical Considerations

As the frequency of orthopedic procedures performed each year in the United States continues to increase, evaluation of peripheral nerve injury (PNI) in the presence of pre-existing metallic hardware is in higher demand. Advances in metal artifact reduction techniques have substantially improved the capability to reduce the susceptibility effect at MRI, but few reports have documented the use of MR neurography in the evaluation of peripheral nerves in the presence of orthopedic hardware. This report delineates the challenges of MR neurography around metal given the high spatial resolution often required to adequately depict small peripheral nerves. It offers practical tips, including strategies for prescan assessment and protocol optimization, including use of more conventional two-dimensional proton density and T2-weighted fat-suppressed sequences and specialized three-dimensional techniques, such as reversed free-induction steady-state precession and multispectral imaging, which enable vascular suppression and metal artifact reduction, respectively. Finally, this article emphasizes the importance of real-time monitoring by radiologists to optimize the diagnostic yield of MR neurography in the presence of orthopedic hardware. © RSNA, 2021.

Combined T2 Mapping and Diffusion Tensor Imaging: A Sensitive Tool to Assess Myofascial Trigger Points in a Rat Model

Background

Myofascial trigger points (MTrPs) are defined as very small and hypersensitive points in skeletal muscle that are palpable, and produce localized pain on compression. The aim of this study was to explore the feasibility of combining T2 mapping with diffusion tensor imaging (DTI) for assessing MTrPs in a rat model and to investigate properties of the pathophysiological mechanisms.

Methods

Twenty-four Sprague-Dawley rats (model group, n = 14; control group, n = 10) underwent a magnetic resonance imaging (MRI) examination on a 3 T-MRI-scanner with a protocol consisting of T2 mapping and DTI. The MTrPs were established by blunt strike in combination with eccentric exercise. Enzyme-linked immunosorbent assays (ELISAs) were used to detect the levels of interleukin-1ß (IL-1ß) and interleukin-2 (IL-2) and their results were correlated with T2 values. Parameters from MRI including T2 values, fractional anisotropy (FA), axial diffusivity (AD), mean diffusivity (MD), and radial diffusivity (RD) were compared between the two groups. Histological analysis was applied to provide an additional supply for MRI findings.

Results

The MTrPs of rats displayed significantly increased T2 values and FA (= 0.000) compared with normal controls, whereas MD and RD values were significantly lower (P= 0.031, = 0.000, respectively). There was no statistically significant difference in AD between the two groups (P= 0.400). These differences were accompanied by elevated levels of IL-1ß and interleukin-2 IL-2 in the MTrP group compared with controls. T2 values were positively correlated with elevated IL-1ß levels (r = 0.543, P < 0.05) but were not correlated with IL-2 levels (P > 0.05).

Conclusion

Combining T2 and DTI sequences creates a sensitive tool to assess MTrPs in a rat model. These data clarify a hypothesis that a trigger point is a chronic and mild muscle injury with inflammation.

Quantitative T2 -mapping magnetic resonance imaging for assessment of muscle motor unit recruitment patterns

INTRODUCTION

In this study, we aimed to determine whether muscle transverse relaxation time (T₂ ) magnetic resonance (MR) mapping results correlate with motor unit loss, as defined by motor unit recruitment patterns on electromyography (EMG).

METHODS

EMG and 3-Tesla MRI exams were acquired no more than 31 days apart in subjects referred for peripheral nerve MRI. Two musculoskeletal radiologists qualitatively graded T₂ -weighted, fat-suppressed sequences for severity of muscle edema-like patterns and manually placed regions of interest within muscles to obtain T₂ values from T₂ -mapping sequences. Concordance was calculated between qualitative and quantitative MR grades and EMG recruitment categories (none, discrete, decreased) as well as interobserver agreement for both MR grades.

RESULTS

Thirty-four muscles (21 abnormal, 13 control) were assessed in 13 subjects (5 females and 8 males; mean age, 46 years) with 14 EMG-MRI pairs. T₂ -relaxation times were significantly (P < .001) increased in all EMG recruitment categories compared with control muscles. T₂ differences were not significant between EMG grades of motor unit recruitment (P = .151-.702). T₂ and EMG score concordance was acceptable (Harrell's concordance index [c index]: rater A, 0.71; 95% confidence interval [CI], 0.51-0.87; rater B, 0.77; 95% CI, 0.57-0.91). Qualitative MRI and EMG score concordance was poor to acceptable (c index: rater A, 0.60; 95% CI, 0.50-0.79; rater B, 0.72; 95% CI, 0.55-0.89). T₂ values had moderate-to-substantial ability to distinguish between absent vs incomplete (ie, decreased or discrete) motor unit recruitment (c index: rater A, 0.78; 95% CI, 0.50-1.00; rater B, 0.86; 95% CI, 0.57-1.00).

DISCUSSION

Quantitative T₂ MR muscle mapping is a promising tool for noninvasive evaluation of the degree of motor unit recruitment loss.

Simultaneous R2, R2' and R2* measurement of skeletal muscle in a rabbit model of unilateral artery embolization

PURPOSE

To demonstrate the feasibility of using a susceptibility-based MRI technique with multi-echo gradient and spin echo (MEGSE) sequence to achieve simultaneous R2, R2' and R2* measurement and assess skeletal muscle oxygenation alternations in a rabbit model of unilateral artery embolization.

MATERIALS AND METHODS

Approved by the local institutional review board for experimental animal studies, nine New Zealand White rabbits were included in this study. The MEGSE sequence consists of embedding a set of gradient echoes around the echo of a single spin-echo sequence using several gradient echoes to collect the magnetization intensity during the formation and attenuation of spin-echo simultaneously after 180° radio frequency pulse. Within-session and between-day tests were conducted to evaluate the reproducibility of this skeletal muscle oxygenation alternations measurement. Furthermore, all the MEGSE scans of skeletal muscle were conducted using a 3-T clinical MRI scanner during resting state (before unilateral artery embolization operation, pre), 1 h after unilateral artery embolization operation (post1) and 2 h after unilateral artery embolization operation (post2) model to verify the feasibility and sensitivity of this method.

RESULTS

The within-session coefficient of variations (CVs) of R2, R2' and R2* measurements were 1.57%, 3.33% and 2.57%, while the between-day CVs of were 1.42%, 5.85% and 2.85%. In all rabbits, the mean R2 decreased significantly from 36.46 ± 1.03 s^-1 (pre) to 30.58 ± 2.11 s^-1 (post1,**P < 0.01, relative to pre) and 28.62 ± 1.53 s^-1 (post2, **P < 0.01, relative to post1), and the mean R2' went up markedly from 9.88 ± 2.14 s^-1 (pre) to 16.10 ± 2.74 s^-1 (post1, **P < 0.01) and 17.33 ± 2.25 s^-1 (post2, **P < 0.05). The mean R2* increased from 43.27 ± 3.75 s^-1 (pre) to 47.90 ± 5.08 s^-1 (post1, *P < 0.05) and to 48.04 ± 4.42 s^-1 (post2, NS, P > 0.05).

CONCLUSION

This study demonstrates the feasibility of simultaneous R2, R2' and R2* measurement method for the evaluation of skeletal muscle ischemia. Besides, this study indicates the sensitivity of the R2 and R2' compared with R2* and especially the necessity of R2 and R2' measurement for the further evaluation of skeletal muscle ischemia which always causes both edema and hypoxia in a rabbit model of unilateral artery embolization.

Dynamic contrast-enhanced magnetic resonance imaging in denervated skeletal muscle: Experimental study in rabbits

Purpose

To investigate the value of dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) for evaluating denervated skeletal muscle in rabbits.

Materials and methods

24 male rabbits were randomly divided into an irreversible neurotmesis group and a control group. In the experimental group, the sciatic nerves of rabbits were transected for irreversible neurotmesis model. A sham operation was performed in the control group. MRI of rabbit lower legs was performed before nerve surgery and 1 day, 3 days, 5 days, 1 week, 2 weeks, 3 weeks, 4 weeks, 6 weeks, 8 weeks, 10 weeks, and 12 weeks after surgery.

Results

Signal intensity changes were seen in the left gastrocnemius muscle on the T2-weighted images. DCE-MRI derived parameters (K^trans, K_ep, and V_p) were measured in vivo. In the irreversible neurotmesis group, T2-weighted images showed increased signal intensity in the left gastrocnemius muscle. K^trans, V_p values changes occur as early as 1 day after denervation, and increased gradually until 4 weeks after surgery. There are significant increases in both K^trans and V_p values compared with those in the control group after surgery (P < 0.05). K_ep values show no significant difference between the irreversible neurotmesis group and the control group.

Conclusion

DCE-MRI hold the promise of an early and sensitive diagnosis of denervated skeletal muscle.

Skeletal Muscle Quantitative Nuclear Magnetic Resonance Imaging and Spectroscopy as an Outcome Measure for Clinical Trials

Recent years have seen tremendous progress towards therapy of many previously incurable neuromuscular diseases. This new context has acted as a driving force for the development of novel non-invasive outcome measures. These can be organized in three main categories: functional tools, fluid biomarkers and imagery. In the latest category, nuclear magnetic resonance imaging (NMRI) offers a considerable range of possibilities for the characterization of skeletal muscle composition, function and metabolism. Nowadays, three NMR outcome measures are frequently integrated in clinical research protocols. They are: 1/ the muscle cross sectional area or volume, 2/ the percentage of intramuscular fat and 3/ the muscle water T2, which quantity muscle trophicity, chronic fatty degenerative changes and oedema (or more broadly, “disease activity”), respectively. A fourth biomarker, the contractile tissue volume is easily derived from the first two ones. The fat fraction maps most often acquired with Dixon sequences have proven their capability to detect small changes in muscle composition and have repeatedly shown superior sensitivity over standard functional evaluation. This outcome measure will more than likely be the first of the series to be validated as an endpoint by regulatory agencies. The versatility of contrast generated by NMR has opened many additional possibilities for characterization of the skeletal muscle and will result in the proposal of more NMR biomarkers. Ultra-short TE (UTE) sequences, late gadolinium enhancement and NMR elastography are being investigated as candidates to evaluate skeletal muscle interstitial fibrosis. Many options exist to measure muscle perfusion and oxygenation by NMR. Diffusion NMR as well as texture analysis algorithms could generate complementary information on muscle organization at microscopic and mesoscopic scales, respectively. ³¹P NMR spectroscopy is the reference technique to assess muscle energetics non-invasively during and after exercise. In dystrophic muscle, ³¹P NMR spectrum at rest is profoundly perturbed, and several resonances inform on cell membrane integrity. Considerable efforts are being directed towards acceleration of image acquisitions using a variety of approaches, from the extraction of fat content and water T2 maps from one single acquisition to partial matrices acquisition schemes. Spectacular decreases in examination time are expected in the near future. They will reinforce the attractiveness of NMR outcome measures and will further facilitate their integration in clinical research trials.

Significance of Diffusion Tensor Imaging of Vastus Medialis Oblique in Recurrent Patellar Dislocation

Background:

Numerous studies have investigated the influence of osseous factors on patellofemoral joint instability, but research on the influence of dynamic muscle factors in vivo is still in the exploratory stage. This study aimed to use magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) to evaluate vastus medialis oblique (VMO) fiber bundles in patients with recurrent patellar dislocation to explore the changes in muscle morphology and function.

Methods:

This prospective study involved 30 patients (7 males and 23 females; average age, 21.4 ± 3.8 years) clinically diagnosed with recurrent patellar dislocation in Peking University Third Hospital and 30 healthy volunteers matched for age, sex, and body mass index in our medical school between January 2014 and October 2014. None of the patients had a recent history of traumatic patellar dislocation or transient patellar dislocation. All patients underwent conventional MRI and DTI of the knee. The cross-sectional area of the VMO on MRI and the fractional anisotropy (FA), apparent diffusion coefficient (ADC), and primary (λ1), secondary (λ2), and three-level characteristic (λ3) values on DTI were measured. The independent-samples t-test was used to compare these parameters between the two groups.

Results:

Compared with the control group, the patient group showed significantly higher FA values (0.39 ± 0.05 vs. 0.33 ± 0.03) and significantly lower ADC (1.51 ± 0.13 vs. 1.58 ± 0.07), λ2 (4.96 ± 0.13 vs. 5.04 ± 0.07), and λ3 values (4.44 ± 0.14 vs. 4.58 ± 0.07; t = 5.99, t = –2.58, t = –3.02, and t = –4.88, respectively; all P < 0.05). Cross-sectional VMO area and λ1 values did not differ between the two groups (t = –1.82 and t = 0.22, respectively; both P > 0.05).

Conclusions:

The functional status of the VMO is closely associated with recurrent patellar dislocation. MRI, especially DTI (FA, ADC, λ2, and λ3), can detect early changes in VMO function and might facilitate the noninvasive monitoring of the functional status of the VMO in patients with recurrent patellar dislocation.

Bilateral Changes in Deep Tissue Environment After Manual Lymphatic Drainage in Patients with Breast Cancer Treatment-Related Lymphedema

BACKGROUND

Breast cancer treatment-related lymphedema (BCRL) arises from a mechanical insufficiency following cancer therapies. Early BCRL detection and personalized intervention require an improved understanding of the physiological processes that initiate lymphatic impairment. Here, internal magnetic resonance imaging (MRI) measures of the tissue microenvironment were paired with clinical measures of tissue structure to test fundamental hypotheses regarding structural tissue and muscle changes after the commonly used therapeutic intervention of manual lymphatic drainage (MLD).

METHODS AND RESULTS

Measurements to identify lymphatic dysfunction in healthy volunteers (n = 29) and patients with BCRL (n = 16) consisted of (1) limb volume, tissue dielectric constant, and bioelectrical impedance (i.e., non-MRI measures); (2) qualitative 3 Tesla diffusion-weighted, T₁-weighted and T₂-weighted MRI; and (3) quantitative multi-echo T₂ MRI of the axilla. Measurements were repeated in patients immediately following MLD. Normative control and BCRL T₂ values were quantified and a signed Wilcoxon Rank-Sum test was applied (significance: two-sided p < 0.05). Non-MRI measures yielded significant capacity for discriminating between arms with versus without clinical signs of BCRL, yet yielded no change in response to MLD. Alternatively, a significant increase in deep tissue T₂ on the involved (pre T₂ = 0.0371 ± 0.003 seconds; post T₂ = 0.0389 ± 0.003; p = 0.029) and contralateral (pre T₂ = 0.0365 ± 0.002; post T₂ = 0.0395 ± 0.002; p < 0.01) arms was observed. Trends for larger T₂ increases on the involved side after MLD in patients with stage 2 BCRL relative to earlier stages 0 and 1 BCRL were observed, consistent with tissue composition changes in later stages of BCRL manifesting as breakdown of fibrotic tissue after MLD in the involved arm. Contrast consistent with relocation of fluid to the contralateral quadrant was observed in all stages.

CONCLUSION

Quantitative deep tissue T₂ MRI values yielded significant changes following MLD treatment, whereas non-MRI measurements did not vary. These findings highlight that internal imaging measures of tissue composition may be useful for evaluating how current and emerging therapies impact tissue function.