A new photoacoustic breast cancer tomography system that images the patient in standing pose

We have developed a photoacoustics-based imaging system that combines optical contrasts with acoustic detection, to obtain a snapshot of the angiographic features in human breast. The system uses near-infrared (NIR) light at 1064 nm wavelength for excitation and hemoglobin in blood as endogenous contrast agent. The light source is a 10 ns Nd:YAG laser with 10-Hz pulse repetition rate. Tumor-angiogenesis, the increase in neovasculature in rapidly growing tumors, is a known biomarker for malignancy. By mapping total hemoglobin levels, we are able to pinpoint the tumor location based on vessel density. For acoustic detection, two 128-element linear-array transducers with 2.25 MHz central frequency are employed. Photoacoustic data is acquired by scanning the breast mildly compressed in the craniocaudal plane, similar to a mammogram, with a scan time of less than 1 minute. The system simultaneously acquires ultrasound (US) data, which can be correlated easily with the photoacoustic data obtained as well as clinical ultrasound images. The photoacoustic images can also be correlated with maximum intensity projection (MIP) subtraction images of contrast MRI (magnetic resonance imaging) 6 minutes post-injection of Gadolinium, and the same vessels could be identified. With our dual transducer geometry, we are able to visualize through 7 cm of breast tissue, a first in this field. The resolution was measured to be 0.97 mm in lateral and 1.05 mm in elevational directions. Our system offers high spatial resolution, fast imaging capability, and convenient correlation with all existing imaging modalities, along with better sensitivity towards dense breast tissue.