Photoacoustic imaging of breast microcalcifications: A validation study with 3-dimensional ex vivo data

Breast microcalcification has been served as an important early-indicator of breast cancer. In the conventional screening procedure for the breast cancer, X-ray mammography is first conducted and the malignancy of the suspicious patient is confirmed by conducting needle biopsy with real-time imaging-assisted guidance, i.e., stereotactic and US imaging. However, these biopsy guidance methods suffer from large amount of radiative exposure and limited sensitivity on microcalcifications without a mass, respectively. In this paper, we verify the capability of photoacoustic imaging (PAI) for detection of the breast microcalcifications by comparing their locations in a 3-D PA image with those in the corresponding X-ray mammography. For this, cross-sectional PA/US images of breast ex vivo specimens were sequentially acquired with 7.2-MHz linear array transducer and the procedure was repeated by moving the transducer along the elevation direction at an increment of 0.3 mm. A Surelite Nd:YAG OPO system (Continuum Inc., USA) was used for the laser excitation at the rate of 10 Hz with a bifurcated optical fiber bundle for laser delivery. PA signals generated in the specimen were captured with SonixTouch research package (Ultrasonix Corp., Canada). With a volume-rendered PA/US image, it is shown that the locations of the microcalcifications in the X-ray mammography meshed well with those in PA images. From the experimental results, therefore, it is demonstrates that PAI can be an effective alternative for noninvasive, real-time biopsy guidance for breast cancer screening.