Characterization of tumour-like inclusions in breast-mimicking phantoms using ultrasound optical tomography

Ultrasound Optical Tomography (UOT) combines the high-resolution imaging capability of ultrasound with measurements of light absorption and scattering properties of human tissue. In this work, UOT working at 794.2 nm wavelength and equipped with a spectral hole burning filter was used to image through 5 cm thick tissue phantoms with embedded cubic 12 × 12 × 12 mm³ inclusions at a 2.5 cm depth. In contrast to earlier UOT works at tissue-relevant wavelengths, these inclusions have orders of magnitude lower absorption and actually mimic the optical properties of human breast tissue with various lesions. Phantoms with inclusions of increasing reduced scattering (inclusions 9.37-14.1 cm^-1, background 7.83 and 8.5 cm^-1) and absorption (inclusions 0.061-0.086 cm^-1, background 0.044 and 0.045 cm^-1) coefficients were investigated. In the UOT images, the contrast-to-noise ratios varied between 3.87 ± 1.71 and 6.25 ± 2.96, and the inclusions could be easily identified by eye. This indicates that the UOT technique has the potential for spatially resolved imaging and optical data acquisition through at least 5 cm of soft tissue. Our findings suggest that UOT equipped with a spectral hole burning filter is a promising technique for breast tumour imaging as well as qualitative and quantitative characterization of their optical properties.