3-D Handheld Harmonic Motion Imaging System for Breast Tumor Assessment: A Clinical Feasibility Study

Harmonic motion imaging (HMI) is a displacement-based ultrasound elastography that simultaneously induces and tracks oscillatory on-axis motion using focused ultrasound and imaging transducers. Single transducer (ST)-HMI was recently developed to perform harmonic excitation and tracking using 1-D imaging arrays and electronic steering to exclude redundant raster-scanning. However, ST-HMI is limited to 2D imaging. This study develops 3-D-HMI with a handheld system.

Harmonic radiation force (200 or 400 Hz) was generated using row or column elements of a row-column array (RCA), with resulting displacements estimated using the same elements for focused transmission and the remaining orthogonal elements in receive, interleaved between excitation pulses.

The proposed method was first validated in phantoms with stiff (Young's moduli: 22, 31, 44 and 56 kPa in 5.3-kPa background) or soft (5.1 kPa in 18.6-kPa background) inclusions (n = 12, diameters: 2.2-13.2 mm) mimicking malignant and benign tumors. The 3-D estimated normalized displacement detected all inclusions, including the smallest at 2 mm, and was found to be inversely proportional to the Young's modulus ratio of inclusions to background. 3-D HMI displacement maps of human breast tumors (n = 5) were reconstructed, including fibroadenoma (FA, n = 1) and invasive ductal carcinoma (IDC, n = 4), among which two were residual diseases after up to 12 wk of neoadjuvant chemotherapy.

3-D-HMI was hereby described and found to be feasible, accurate and time-efficient volumetric mapping of relative stiffness. The proposed method increases the clinical potential of HMI to assess the mechanical properties of entire tumor volumes in a typical handheld manner, as in conventional breast sonography.