Localization of spherical lesions in tumor-mimicking phantoms by 3D sparse array photoacoustic imaging

Methods: The authors constructed an array of phantoms that include spherical lesions of sizes 1.5-9 mm, buried in highly scattering tissue phantoms at depths of 3-30 mm. The authors investigated both homogeneous lesions made of blood at varying concentrations and heterogeneous lesions containing vessel-like structures. Volumetric images of the deeply buried lesions were taken at increasingly shallower depths and image-based localization was compared to measured depth. Results: The authors were able to detect and accurately localize homogeneous lesions having a realistic absorption coefficient of 0.2 cm(-1) down to depths of 9-20 mm, and heterogeneous lesions containing 0.5 mm diameter vessel-like structures down to depths of 13-20 mm. Image acquisition required 2.5 s for each volumetric lesion image. Conclusions: These results suggest that 3D SPAI can detect highly vascularized lesions well below 1 cm in diameter and can overcome optical scatter of tissue to depths of 1-2 cm. With further improvement in the sensitivity and noise characteristics of the imaging system, similar imaging depths should be within reach in real breast tissue. The method, due to its optical contrast, 3D imaging, and fast acquisition, may prove useful in the clinic as an adjunct to existing breast screening tools.