Photoacoustic and Thermoacoustic Imaging with a Multi-channel Breast Scanner

Photoacoustic and thermoacoustic phantom images obtained with a multi-channel breast scanner designed for breast cancer screening are presented here. A tunable laser system (OPOTEK Vibrant 355 I, Calsbad, CA) with a pulse duration of 5 ns was used for photoacoustic irradiation, and a 3.0 GHz microwave source with a pulse width of 0.3-1 mu s was used for thermoacoustic tomography. Multiple (>=16) 2.25 MHz single-element unfocused ultrasonic transducers at different depths were scanned simultaneously for a full 360 degrees to obtain a full data set for three-dimensional (3D) tomography. Negative acoustic lenses were attached to these unfocused transducers to increase their acceptance angles. An ultrasound receiving system with 64 parallel receiving channels (Verasonics Inc. Redmond, WA) was used for data acquisition. A filtered backprojection algorithm was used to reconstruct two-dimensional (2D) and 3D images. Different phantoms were imaged to evaluate the performance of the scanner. A lateral resolution of less than 1 mm and an elevational resolution of less than 5 mm were achieved. The phantom studies demonstrate that this scanner can potentially provide high-resolution, dual-modality, three-dimensional images and can potentially be used for human breast cancer screening.