Magnetic resonance elastography of the supraspinatus muscle: A preliminary study on test-retest repeatability and wave quality with different frequencies and image filtering

Evaluation of the Reproducibility of MR Elastography Measurements of the Lumbar Back Muscles

BACKGROUND

MR elastography (MRE) may provide quantitative imaging biomarkers of lumbar back muscles (LBMs), complementing MRI in spinal diseases by assessing muscle mechanical properties. However, reproducibility analyses for MRE of LBM are lacking.

PURPOSE

To assess technical failure, within-day and inter-day reproducibility, robustness with the excitation source positioning, and inter-observer agreement of MRE of muscles.

STUDY TYPE

Prospective.

SUBJECTS

Seventeen healthy subjects (mean age 28 ± 4 years; 11 females).

FIELD STRENGTH/SEQUENCE

1.5 T, gradient-echo MRE, T1-weighted turbo spin echo.

ASSESSMENT

The pneumatic driver was centered at L3 level. Four MRE were performed during two visits, 2-4 weeks apart, each consisting of two MRE with less than 10 minutes inter-scan interval. At Visit 1, after the first MRE, the coil and driver were removed, then reinstalled. The MRE was repeated. At Visit 2, following the first MRE, only the driver was moved down 5 cm. The MRE was repeated. Two radiologists segmented the multifidus and erector spinae muscles.

STATISTICAL TESTS

Paired t-test, analysis of variance, intraclass correlation coefficients (ICCs). P-values <0.05 were considered statistically significant.

RESULTS

Mean stiffness of LBM ranged from 1.44 to 1.60 kPa. Mean technical failure rate was 2.5%. Inter-observer agreement was excellent (ICC ranging from 0.82 [0.64-0.96] to 0.99 [0.98-0.99] in the multifidus, and from 0.85 [0.69-0.92] to 0.99 [0.97-0.99] in the erector spinae muscles). Within-day reproducibility was fair in the multifidus (ICC: 0.53 [0.47-0.77]) and good in the erector spinae muscles (ICC: 0.74 [0.48-0.88]). Reproducibility after moving the driver was excellent in both multifidus (ICC: 0.85 [0.69-0.93]) and erector spinae muscles (ICC: 0.84 [0.67-0.92]). Inter-day reproducibility was excellent in the multifidus (ICC: 0.76 [0.48-0.89]) and poor in the erector spinae muscles (ICC: 0.23 [-0.61 to 0.63]).

DATA CONCLUSION

MRE of LBM provides measurements of stiffness with fair to excellent reproducibility and excellent inter-observer agreement. However, inter-day reproducibility in the multifidus muscles indicated that the herein used MRE protocol may not be optimal for this muscle.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 1.

High-frequency Quantitative Ultrasound Imaging of Human Rotator Cuff Muscles: Assessment of Repeatability and Reproducibility

This study evaluated the repeatability and reproducibility of using high-frequency quantitative ultrasound (QUS) measurement of backscatter coefficient (BSC), grayscale analysis, and gray-level co-occurrence matrix (GLCM) textural analysis, to characterize human rotator cuff muscles. The effects of varying scanner settings across two different operators and two US systems were investigated in a healthy volunteer with normal rotator cuff muscles and a patient with chronic massive rotator cuff injury and substantial muscle degeneration. The results suggest that BSC is a promising method for assessing rotator cuff muscles in both control and pathological subjects, even when operators were free to adjust system settings (depth, level of focus, and time-gain compensation). Measurements were repeatable and reproducible across the different operators and ultrasound imaging platforms. In contrast, grayscale and GLCM analyses were found to be less reliable in this setting, with significant measurement variability. Overall, the repeatability and reproducibility measurements of BSC indicate its potential as a diagnostic tool for rotator cuff muscle evaluation.

Objective Methods of Muscle Tone Diagnosis and Their Application-A Critical Review

"Muscle tone" is a clinically important and widely used term and palpation is a crucial skill for its diagnosis. However, the term is defined rather vaguely, and palpation is not measurable objectively. Therefore, several methods have been developed to measure muscle tone objectively, in terms of biomechanical properties of the muscle. This article aims to summarize these approaches. Through database searches, we identified those studies related to objective muscle tone measurement in vivo, in situ. Based on them, we described existing methods and devices and compared their reliability. Furthermore, we presented an extensive list of the use of these methods in different fields of research. Although it is believed by some authors that palpation cannot be replaced by a mechanical device, several methods have already proved their utility in muscle biomechanical property diagnosis. There appear to be two issues preventing wider usage of these objective methods in clinical practice. Firstly, a high variability of their reliability, and secondly, a lack of valid mathematical models that would provide the observed mechanical characteristics with a clear physical significance and allow the results to be compared with each other.

Emerging Quantitative Imaging Techniques in Sports Medicine

This article describes recent advances in quantitative imaging of musculoskeletal extremity sports injuries, citing the existing literature evidence and what additional evidence is needed to make such techniques applicable to clinical practice. Compositional and functional MRI techniques including T2 mapping, diffusion tensor imaging, and sodium imaging as well as contrast-enhanced US have been applied to quantify pathophysiologic processes and biochemical compositions of muscles, tendons, ligaments, and cartilage. Dual-energy and/or spectral CT has shown potential, particularly for the evaluation of osseous and ligamentous injury (eg, creation of quantitative bone marrow edema maps), which is not possible with standard single-energy CT. Recent advances in US technology such as shear-wave elastography or US tissue characterization as well as MR elastography enable the quantification of mechanical, elastic, and physical properties of tissues in muscle and tendon injuries. The future role of novel imaging techniques such as photon-counting CT remains to be established. Eventual prediction of return to play (ie, the time needed for the injury to heal sufficiently so that the athlete can get back to playing their sport) and estimation of risk of repeat injury is desirable to help guide sports physicians in the treatment of their patients. Additional values of quantitative analyses, as opposed to routine qualitative analyses, still must be established using prospective longitudinal studies with larger sample sizes.

Reliability of Gradient-Echo Magnetic Resonance Elastography of Lumbar Muscles: Phantom and Clinical Studies

Magnetic resonance elastography (MRE) has been used to successfully characterize the mechanical behavior of healthy and diseased muscles, but no study has been performed to investigate the reliability of MRE on lumbar muscles. The objective of this work was to determine the reliability of MRE techniques on lumbar muscles in both ex vivo phantom and in vivo human studies. In this study, fresh porcine leg muscles were used in the phantom study, and 80 healthy adults (38.6 ± 11.2 years, 40 women) were recruited in the human study. Five repeated stiffness maps were obtained from both the phantom and human muscles by using a gradient-echo MRE sequence with a pneumatic vibration on a 1.5 T MR scanner. The technical failure rate, coefficient of variation (CV), and quality score were assessed to evaluate the reliability of MRE, respectively. Analysis of variance was performed to compare the stiffness between different lumbar muscles, and the difference was significant if p < 0.05 after Bonferroni correction. The results showed that the MRE achieved a zero technical failure rate and a low CV of stiffness (6.24 ± 1.41%) in the phantom muscles. However, in the human study, the MRE exhibited high CVs of stiffness (21.57%−25.24%) in the lumbar muscles, and the technical failure rate was higher in psoas muscles (60.0−66.3% in) than in paraspinal muscles (0.0−2.5%). Further, higher quality scores were noticed in paraspinal muscles (7.31−7.71) than those in psoas muscles (1.83−2.06). In conclusion, the MRE was a reliable technique to investigate the mechanical property of lumbar muscles, but it was less reliable to assess stiffness in psoas muscles than paraspinal muscles.

A novel technique for automating stiffness measurement and emphasizing the main wave: Coherent-wave auto-selection (CHASE)

This study aims to develop and assess a new automated processing technique in MR elastography (MRE), namely coherent-wave auto-selection (CHASE). CHASE enables automatic selection of the region of interest (ROI) for stiffness measurement by extraction of the coherent wave region (CHASE ROI), and it improves the reconstruction of stiffness by a directional filter oriented along the main wave in each pixel (CHASE filtering). In this study, MRE of a phantom and of the liver of four healthy volunteers was performed. To investigate the potential of CHASE, this study assessed the CHASE according to three indices through the phantom study: 1) agreement on the ROI settings between CHASE and expert observers, 2) noise dependency, and 3) effect of the CHASE on stiffness variability within the CHASE ROI. The agreements on the ROI settings were analyzed by Cohen's kappa coefficient (κ). The noise dependency was analyzed by the mean absolute percentage errors (MAPEs) within the ROI between low (20%-80% amplitudes) and high vibration amplitudes (100% amplitude). The stiffness variability was assessed by standard deviation (SD) within the ROI. In the volunteer study, agreements on the ROI settings (or stiffness value) and stiffness variability within the CHASE ROI were assessed using κ-value (or intraclass correlation coefficient: ICC) and coefficient of variation, respectively. The results showed close agreement on the ROI settings and stiffness (κ-value: greater than 0.61 in both the phantom and volunteer studies, ICC: 0.97 in the volunteer study). The MAPEs within the CHASE ROI were much smaller than those in the whole region of the phantom (CHASE ROI vs. the whole region at 20% amplitude: 10.3% vs. 50.8%). Moreover, in both the phantom and volunteer studies, the stiffness variation within the CHASE ROI was smaller in the elastogram processed with CHASE filtering than in the unprocessed one. Our results demonstrated that the CHASE has high robustness against noise and the potential to provide ROI settings for stiffness measurement comparable to expert observers, as well as improve the reconstruction of stiffness.