Theoretical basis and experimental validation of harmonic coherence-based ultrasound imaging for breast mass diagnosis

Abstract

Coherence-based ultrasound imaging has demonstrated potential to improve breast mass diagnosis by distinguishing solid from fluid-filled masses. Harmonic imaging, which is known to reduce acoustic clutter, has the potential to offer additional improvements. However, the lack of a theoretical basis to describe these improvements precludes clinical recommendations based on physics and engineering principles. This work is the first to develop a theoretical model of coherence-based ultrasound imaging to describe both solid vs. fluid mass distinction and the effects of harmonic short-lag spatial coherence (SLSC) imaging. The scattering function and the transmit ultrasound beam of the van Cittert-Zernike theorem applied to ultrasound imaging were redefined to generate the theoretical model for solid vs. fluid mass distinction and for harmonic imaging, respectively. The derived theory was used to compare fundamental and harmonic SLSC images for hypoechoic solid, hypoechoic fluid, hyperechoic, and point targets. Theoretical simulations showed improved resolution, mitigated dark-region artifacts around hyperechoic targets, and increased spatial coherence of fluid masses in harmonic SLSC images when compared to fundamental SLSC images. Experimental data from tissue-mimicking phantoms and in vivo breast ultrasound images agreed with theoretical results. In particular, when compared to fundamental SLSC imaging, harmonic SLSC imaging improved resolution by 0.19 ± 0.25 mm, mitigated dark region artifacts by 0.55 ± 0.54 mm, and increased the spatial coherence of fluid-filled masses, resulting in a 6.50 ± 4.28 dB decrease in contrast. Results will enable future clinical recommendations supporting the use of fundamental or harmonic SLSC imaging for analyses of fluid or solid masses, respectively. These contributions establish a theoretical foundation to combine fundamental and harmonic coherence-based imaging with harmonic B-mode imaging to improve the accuracy of breast mass diagnoses.

Spatial Coherence Approaches to Distinguish Suspicious Mass Contents in Fundamental and Harmonic Breast Ultrasound Images

“…In fundamental and harmonic SLSC images, dark regions are visible at the boundary of the mass (and in other areas of the tissue). These dark regions, representing areas of low spatial coherence and previously identified as artifacts [32], are more prominent in the fundamental coherence images when compared to matched harmonic coherence images. These darkregion artifacts are not unique to breast images, and they typically appear in coherence images when bright, coherent regions exist laterally to a less coherent region [18].…”

“…In addition, Wiacek et al [30] demonstrated that including R-SLSC images alongside B-mode images would have decreased the percentage of unnecessary biopsies from 43.3% to 13.3%, due to the improved diagnostic certainty of breast ultrasound images when assessed by five board-certified radiologists in a randomized reader study. Sharma et al [31] and Kokumo et al [32] combined harmonic imaging with R-SLSC imaging and SLSC imaging, respectively, to assess additional potential benefits of these combinations. Despite these advances, variations among radiologists were observed when diagnosing breast masses during the reader study noted above, highlighting the importance of reader-independent metrics to distinguish solid from fluid masses [23], [30], [33].…”

“…Although multiple imaging modes and metrics have the potential to differentiate solid from fluid breast masses, these various demonstrations were performed with independent sets of breast data, which limit direct comparisons across studies [22], [23], [30]- [32]. A systematic, comparative investigation applied to a single dataset is required to determine the relative benefits and limitations.…”