Detection of optoacoustic transients with a rectangular transducer of finite dimension

Laser optoacoustic tomography system (LOIS) for breast cancer detection and diagnostics utilizes optical generation of acoustic pressure profiles in tumors and piezoelectric detection of these pressure transients within an ultra-wideband of ultrasonic frequencies. Temporal profile of optoacoustic pulses provides information on tumor dimensions and its location inside the breast. A finite spatial dimension of receiving transducers results in distortions of the optoacoustic profile and corresponding reduction of the resolution in LOIS. The impulse response approach for calculation of the pulse profiles originated from a uniformly absorbing sphere and detected with a rectangular transducer was employed. The pressure profiles were expressed as convolution integrals of velocity-potential distribution over the transducer surface with the corresponding impulse response function. The impulse response function was evaluated for different locations of optoacoustic sources with respect to the receiving transducer. Numerical simulations were performed for acoustic transducers with dimensions of 1x10 mm and located on the cylindrical surface with radius of 60-mm. Results demonstrated that detected N-shaped pressure profiles become smoother and their duration increases with increased linear dimensions of the transducer. This effect depends on relative position of the spherical acoustic source and the detector.