In-vivo muscle characterization by 3D Elastic and Backscatter Tensor Imaging using a low channel count system

Over the last decade, 3D ultrafast ultrasound imaging has been used in different applications including Elastic Tensor Imaging (ETI) based on 3D Shear Wave Elastography and Backscatter Tensor Imaging (BTI). BTI and ETI can provide important biomechanical and structural parameters of fibrous soft tissues such as the skeletal muscles or the myocardium. However, 3D ultrafast imaging requires 2D transducers arrays with a large number of elements, which mainly limits their use to laboratory research settings. This study aims to develop a clinically transposable ultrasound system combining 3D-ETI and BTI to characterize anisotropic tissues. A low channel count system with 128 channels based on a vantage system and a dedicated matrix transducer driven at 2.5MHz was developed. The performance of the approach was demonstrated on anisotropic and fibrous phantoms. In-vivo feasibility was performed on the brachii biceps of 4 healthy volunteers at controlled contractions levels using weights held in the hand. Using this approach, we could investigate the functional change of muscle stiffness during contraction (shear wave speed from 3.2±0.20m/s to 6.6±0.58m/s, and elastic fractional anisotropy from 0.26±0.04 to 0.49±0.07). Structural characterization was performed with BTI, fiber organization and coherence fractional anisotropy remained constant with contraction (0.27±0.05). This novel device enables non-invasive characterization of anisotropic tissues, discerning stress and structural anisotropy in promising applications in musculoskeletal and myocardial pathologies.