Optoacoustic tomography of breast cancer with arc-array transducer

The second generation of the laser optoacoustic imaging system for breast cancer detection, localization and characterization using a 32-element arc-shaped transducer array was developed and tested. Each acoustic transducer was made of 110-micrometers thick SOLEF PVDF film with dimensions of 1mm X 12.5mm. The frequency band of transducer array provided 0.4-mm axial in-depth resolution. Cylindrical shape of this 10-cm long transducer array provided an improved lateral resolution of 1.0 mm. Original and compact design of low noise preamplifiers and wide band amplifiers was employed. The system sensitivity was optimized by choosing limited bandwidth of ultrasonic detection 20-kHz to 2-MHz. Signal processing was significantly improved and optimized resulting in reduced data collection time of 13 sec. The computer code for digital signal processing employed auto- gain control, high-pass filtering and denoising. An automatic recognition of the opto-acoustic signal detected from the irradiated surface was implemented in order to visualize the breast surface and improve the accuracy of tumor locations. Radial back-projection algorithm was used for image reconstruction. Optimal filtering of image was employed to reduce low and high frequency noise. The advantages and limitations of various contrast-enhancing filters applied to the entire image matrix were studied and discussed. Time necessary for image reconstruction was reduced to 32 sec. The system performance was evaluated initially via acquisition of 2D opto-acoustic images of small absorbing spheres in breast-tissue-like phantoms. Clinical ex-vivo studies of mastectomy specimen were also performed and compared with x-ray radiography and ultrasound.