Evaluation of the masseter muscle elasticity with the use of acoustic coupling agents as references in strain sonoelastography

Abstract

Objectives: To verify the use of a single coupling agent as a reference to obtain the elasticity index (EI) ratios and to investigate the EI ratios of the masseter muscles of healthy volunteers. Methods: Muscle phantoms with known elasticity (20, 40 and 60 kPa in the Young's modulus) were examined by strain-type sonoelastography using a coupling agent as the reference. Eight examiners tested soft (with 7 kPa) and hard (with 40 kpa) reference coupling agents separately. The correlation coefficients were determined between the EI ratio and Young's modulus of muscle phantoms. The interclass correlation coefficients were calculated for inter-and intraexaminer agreement. Results: Strong correlations were found between the EI ratios and Young's modulus for both soft and hard references. The variations of the EI ratios were larger with soft coupling agents than those with hard coupling agents, and they increased in phantoms with 60 kPa elasticity. There were no differences in the EI ratios of the masseter muscle at rest between males and females or between the right and left sides. The ratio increased during clenching. Conclusions: The hard reference coupling agent was suitable for obtaining EI ratio of the masseter muscle. No differences were found in the EI ratios of the masseter muscle either between sexes or between the right and left sides at rest, and the ratios increased with the widening of their variations during clenching.

Shear-wave sonoelastography for assessing masseter muscle hardness in comparison with strain sonoelastography: study with phantoms and healthy volunteers

“…elasticity of 20-60 kPa also showed lower ICCs for the interoperator (0.80 to 0.89) and intraoperator (0.74-0.86) agreements in strain sonoelastography. 16 This study was subject to the tissue-mimicking phantom with a wider range of elasticity (20-140 kPa), and scanned by experienced examiners, and, therefore, high interoperator ICC (0.98) and intraoperator ICC (0.99) of strain sonoelastography could be obtained.…”

“…This discrepancy may be caused by the reasons that strain sonoelastography displayed relative values of the phantom against the coupling agent and that the EI was determined for the softer tissue as 0-1 and the harder tissue as 1-6; that is, it would be due to the degree of difference in the hardness of the subject and reference. 13,16 The results of the phantom experiment would be helpful for developing coupling agents used in vivo.…”

“…7,16 The materials were made from agar, talc, ticking agent and lowmolecular-weight gel. The size of the phantoms was set at a length of 110 mm, width of 60 mm and thickness of 40 mm.…”

“…[12][13][14] Our previous study experimentally verified the utility of elasticity index (EI) ratio obtained by a strain-type sonoelastography for evaluating muscle hardness with simultaneous use of a coupling agent as a reference. 16 However, the hardness expected based on the EI ratio at clenching in the human masseter muscle was over the range of muscle phantom hardness that ensured measurement accuracy. Moreover, strain-type sonoelastography has some disadvantages, including operator dependency, a low reproducibility and a relative evaluation of stiffness, 7,[17][18][19][20][21] because it displays images based on the distortion of the tissue caused by manual compression.…”

Strain sonoelastography of inflammatory myopathies: comparison with clinical examination, magnetic resonance imaging and pathologic findings

“…Tissue strain can be calculated semi-quantitatively using strain ratios. Strain ratios have been used for the diagnosis of focal lesions in the breast, 10,11 thyroid glands 8 and muscles. 12 Currently used SWSE depends on the acoustic radiation force generated by the ultrasound beam or the measurement of shear-wave induction.…”