In Vivo Demonstration of Single Transducer Harmonic Motion Imaging (ST-HMI) in a Breast Cancer Mouse Model and Breast Cancer Patients

Harmonic motion imaging (HMI) interrogates the mechanical properties of tissues by simultaneously generating and tracking amplitude-modulated (AM) force-induced motion using focused ultrasound and imaging transducers, respectively. The main advantages of HMI are that motion at oscillation frequency can be easily filtered from different motion artifacts. However, the current configuration of two separate transducers renders the HMI system highly complex. The objective of this study is to develop a single transducer HMI (ST-HMI) and test its feasibility of generating and mapping of harmonic motion using a linear array transducer to facilitate data acquisition. The feasibility of ST-HMI was performed by imaging commercially available two elastic phantoms with two inclusions (N=4),
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monitoring of changes in the tumor stiffness of 4T1, orthotropic breast cancer mouse model, and patient with invasive ductal carcinoma (IDC) breast cancer. ST-HMI-derived peak-to-peak displacements (P2PD) successfully contrasted all 4 inclusions with nominal Young's modulus of 8, 10, 40, and 60 kPa and the P2PD ratio of background to inclusion was highly correlated with Young's modulus ratio of inclusion to background with R2 of 0.93. In the mouse study, the median P2PD ratio of the tumor to non-cancerous tissue was 2.0, 3.6, 7.0, and 6.6 at 1, 2, 3, and 4 weeks, respectively, post-injection of the tumor cell. In the clinical study, ST-HMI detected IDC cancer with the P2PD ratio of 1.78. These results indicate that ST-HMI can assess the mechanical properties of tissues via generation and tracking of harmonic motion using a single transducer.