Purpose: To measure the elastic properties of the vastus lateralis (VL), vastus medialis (VM), and sartorius (Sr) muscles using magnetic resonance elastography (MRE). Materials and Methods:To obtain a normative database of the aforementioned muscles, oblique scan directions were prescribed passing through each muscle. Shear waves were induced into the muscles using pneumatic and mechanical drivers at 90 and 120 Hz, respectively. These drivers were attached to the distal end of the right thigh with the knee flexed at 30°. The foot was placed in a footplate containing MR-compatible load cells to record the force during a contraction (10% and 20% of the maximum voluntary contraction). Results:The shear moduli measured at rest in the VL (N ϭ 12), VM (N ϭ 14), and Sr (N ϭ 13) were 3.73 Ϯ 0.85 kPa, 3.91 Ϯ 1.15 kPa, and 7.53 Ϯ 1.63 kPa, respectively. The stiffness of both vasti increased with the level of contraction, while the stiffness of the Sr remained the same. Conclusion:The MRE technique was able to approximate the stiffness of different thigh muscles. Furthermore, the wave length was sensitive to the morphology (unipennate or longitudinal) and fiber composition (type I or II) in each muscle.

Magnetic resonance elastography (MRE) is capable of noninvasively quantifying the mechanical properties of skeletal muscles in vivo. This information can be clinically useful to understand the effects of pathologies on the mechanical properties of muscle and to quantify the effects of treatment. Advances in inversion algorithms quantify muscle anisotropy in two-dimensional (2D) and three-dimensional (3D) imaging. Databases of the shear stiffness of skeletal muscle have been presented in the relaxed and contracted states in the upper extremity (biceps brachii, flexor digitorum profundus, and upper trapezius), distal leg muscles (tibialis anterior, medial gastrocnemius, lateral gastrocnemius, and trapezius), and proximal leg muscles (vastus lateralis, vastus medialis, and sartorius). MRE measurements have successfully validated a mathematical model of skeletal muscle behavior in the biceps brachii, correlated to electromyographic data in the distal leg muscles and quantified the effects of pathologies on the distal and proximal leg muscles. Future research efforts should be directed toward improving one-dimensional (1D) and 3D MRE data acquisition and image processing, tracking the effects of treatment on pathologic muscle and correlating the shear stiffness with clinical measurements.

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Purpose:To measure the stiffness of the vastus medialis (VM) in hyperthyroid patients before and after treatment. Materials and Methods:A total of five healthy euthyroid patients and five hyperthyroid patients were tested using magnetic resonance elastography (MRE), which involves the induction of shear waves in the thigh muscles using a pneumatic driver at 90 Hz.Results: Among the pretreatment hyperthyroid cohort a lower stiffness was found when the muscle was relaxed (2.11 Ϯ 0.61 kPa) compared the stiffness following treatment of hyperthyroidism (5.52 Ϯ 1.52 kPa), which was accompanied by an improvement in the contractile function of the VM. Pretreatment muscle stiffness was also less than that of age matched healthy volunteers (4.56 Ϯ 0.40 kPa). The behavior of the waves was sensitive to the stage of this myopathy and to the amount of free thyroxine (FT4). Conclusion:The MRE technique provides a new tool to gain new insights into pathophysiology of thyroid associated and other muscle diseases and their response to treatment.

Purpose:To cross-validate the magnetic resonance elastography (MRE) technique with a clinical device, based on an ultrasound elastometry system called Fibroscan. Materials and Methods:Ten healthy subjects underwent an MRE and a Fibroscan test. The MRE technique used a round pneumatic driver at 60 Hz to generate shear waves inside the liver. An elastogram representing a map of the liver stiffness was generated allowing for the measurement of the average liver stiffness inside a region of interest. The Fibroscan technique used an ultrasound probe (3.5 MHz) composed of a vibrator that sent low-frequency (50 Hz) shear waves inside the right liver lobe. The probe acts as an emitter-receptor that measures the velocity of the waves propagated inside the liver tissue. Results:The mean shear stiffness measured with the MRE and Fibroscan techniques were 1.95 Ϯ 0.06 kPa and 1.79 Ϯ 0.30 kPa, respectively. A higher standard deviation was found for the same subject with Fibroscan. Conclusion:This study shows why MRE should be investigated beyond the Fibroscan. The MRE technique provided elasticity of the entire liver, meanwhile the Fibroscan provided values of elasticity locally.

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