Enhanced photoacoustic detection of calcifications with molecular targeting: Feasibility study

Calcification is one of the important indicators for breast cancer diagnosis. Albiet the current gold standard for micro-calcification identification, X-ray mammography is inevitably with ionizing radiation and carcinogenic risk. Because of speckle noises, ultrasound (US) imaging owns low contrast between breast tissues and micro-calcifications and thus low detectability. In this study, we intend to verify the feasibility of enhanced photoacoustic (PA) detection of calcifications via molecular targeting and thus the potential in improvement of the imaging depth for visualization of micro-calcifications. An IR-Dye with bisphosphonate ligand offering specific binding to hydroxyapatite (HA), the major composition of breast calcification, was used as a molecular probe and a PA contrast agent as well. The HA particles were incubated with IR-Dye in 1X PBS solution. A fluorescent scan was made to confirm the binding after PBS flushing. Then the photoacoustic signals of IR-Dye incubated HA particles were measured from 680 to 830 nm using a custom-made 5-MHz photoacoustic imaging system. We demonstrated a boost of 160% in PA signals of IRDye binded HA particles relative to plain HA particles. The corresponding SNR of calcification in PA imaging was improved by about 7 dB.