Photoacoustic array imaging of calcifications: phantom study

Breast calcification is one of the most important indicators for early breast cancer detection. In this study, based on a medical ultrasound array imaging platform, we attempt to develop a real-time and high penetration photoacoustic (PA) array imaging system for visualization of breast calcifications. Phantom studies were used to verify the imaging capability and penetration depth of the developed PA array system for calcification imaging. Intralipid gelatin phantoms with different-sized hydroxyapatite (HA) particles - major chemical composition of the breast calcification associated with malignant breast cancers - embedded were imaged. Laser at 750 nm was used for photoacoustic excitation and a custom-made 5-MHz photoacoustic array transducer with linear light guides was applied for photoacoustic signal detection. Experimental results demonstrated that this system is capable of calcification imaging of 0.3-0.5 mm HA particles. For the 0.5-mm HA particles, the imaging contrast was about 34 dB and the achievable penetration was 20 mm where the axial, lateral, and elevational resolution of this PA array imaging system is 0.39 mm, 0.38 mm, and 1.25 mm, respectively. The highest frame rate was 10 frames/sec limited by the laser pulse rate. Overall, our results demonstrate that it is promising for PA imaging as a real-time diagnosis and biopsy guidance tool of breast micro-calcifications outside mass lesion. Future work will focus on optimization of the photoacoustic transducer to further improve the penetration depth and development of photoacoustic and ultrasound dual-modal imaging to enhance the calcification imaging capability.