3-D ultrasound elastography of the breast: First steps towards ABVS implementation

Mammography is the gold standard for breast cancer screening but less suitable for women with dense breasts. Therefore, the ultrasound automated breast volume scanner (ABVS) was introduced as an alternative. Although clinical studies showed high sensitivity of ABVS to detect breast cancer, specificity and long acquisition times (>1 minute) remain an issue. Since specificity can be improved using elastography, the aim of this study was to develop 3-D strain imaging for ABVS scanning while also reducing acquisition times by plane wave imaging. To mimic the ABVS, an ATL L12-5 50mm transducer was attached to a motorized XZ-translational setup and connected to a Verasonics V1 ultrasound system. The aim was to obtain 150 equidistant (0.5 mm) 2-D strain images (60×25 mm
²
) of a breast phantom (model 059, CIRS) containing multiple inclusions. To obtain these images, beam-formed ultrasound radiofrequency (RF) data were acquired before and after deformation of the breast, followed by coarse-to-fine 2-D cross-correlation and 1-D least-squares strain estimation. The performance of strain estimation was compared for two transmission schemes at two frame rates of 2 Hz and 16 Hz (one breath hold) by calculating elastographic contrast-to-noise ratios (CNR
_e
) and signal-to-noise ratios (SNR
_e
). In transmission scheme 1 pre- and post-deformation RF data were acquired per position, whereas in scheme 2 (ABVS-like acquisition) RF data were acquired for all positions per state of deformation. All methods provided similar strain images upon visual inspection for most positions, although first and last 15 strain images (corresponding to rounder parts of the breast) resulted in reduced quality (SNR
_e
0±6 dB; CNR
_e
15±0 dB) in scheme 2 compared to scheme 1 (SNR
_e
16±1 dB; CNR
_e
28±4 dB). For the other 120 images, the two methods were similar (CNR
_e
33±1 dB; SNR
_e
15±1 dB). The frame rates did not seem to affect the CNR
_e
and SNR
_e
in both methods. In summary, scheme 1 performed similarly to the ABVS-like scheme 2 in the central part of the breast. Thus we might conclude that implementation of strain imaging in ABVS is feasible, although the reduced quality at the borders of the breast has to be improved. Moreover, plane wave imaging will enable high frame rates and lateral compounding and allow 3-D elastography within one breath hold.