Real-time 3-D ultrafast ultrasound quasi-static elastography in vivo

Ultrasound elastography, a technique used to assess mechanical properties of soft tissue is of major interest in the detection of breast cancer as it is stiffer than the surroundings. Techniques such as ultrasound quasi-static elastography have been developed to assess the strain distribution in soft tissues in two dimensions using a quasi-static compression. However, tumors can exhibit very heterogeneous shape, a three dimensions approach would be then necessary to measure accurately the tumor volume and remove operator dependency. To ensure this issue, several 3-D quasi-static elastographic approaches have been proposed. However, all these approaches suffered from a long acquisition time to acquire 3-D volumes resulting in the impossibility to perform realtime and the creation of artifacts. The long acquisition time comes from both the use of focused ultrasound emissions and the fact that the volume was made from a stack of two dimensions images acquired by mechanically translating an ultrasonic array. Being able to acquire volume at high volume rates is thus crucial to perform real-time with a simple freehand compression and to avoid signal decorrelation coming from hand motions or natural motions such as the respiratory. In this study we developed for the first time, the 3-D ultrafast ultrasound quasi-static elastography method to estimate 3-D axial strain distribution in vivo in real-time. Acquisitions were performed with a 2-D matrix array probe of 256 elements (16-by-16 elements). 100 plane waves were emitted at a volume rate of 100 volumes/sec during a continuous motorized compression. 3-D B-mode volumes and 3-D B-mode cumulative axial strain volumes were estimated on a two-layers gelatin phantom with different stiffness, in a stiff inclusion embedded in a soft gelatin phantoms, in a soft inclusion embedded in a stiff gelatin phantom and in an ex vivo canine liver before and after a high focused ultrasound (HIFU) ablation. In each case, we were able to image in real-time and in entire volumes the axial strain distribution and were able to detect the differences between stiff and soft structures with a good sensitivity. In addition, we were able to detect the stiff lesion in the ex vivo canine liver after HIFU ablation. Finally, we demonstrated the in vivo feasibility of the method using freehand compression on the calf of a human volunteer and were able to retrieve 3-D axial strain volume in real-time depicting the differences in stiffness of the two muscles which compose the calf. The 3-D ultrafast ultrasound quasi-static elastography method could have a major clinical impact for the real-time detection in three dimensions of breast cancer in patients using a simple freehand scanning. Correspondence to: Dr. Elisa Konofagou, 1210 Amsterdam Ave., ET351, MC 8904, New York, NY, 10027, [email protected], Phone: 212-342-0863, Fax: 212-342-1648. HHS Public Access Author manuscript IEEE Trans Med Imaging. Author manuscript; available in PMC 2018 February 01. Published in final edited form as: IEEE Trans Med Imaging. 2017 February ; 36(2): 357–365. doi:10.1109/TMI.2016.2596706. A uhor M anscript