A highly sensitive laser-EMAT imaging system for biomedical applications

This paper describes a novel technique using an elctromagnetic acoustic transducer (EMAT) for biomedical photoacoustic measurements. The physical principle underlying and EMAT sensor is based on the detection of electromagnetic signals, which are responses from the interaction of ultrasonic waves and magnetic fields within the electrically conductive sample surface. A recent prototype EMAT sensor has miniaturized the receiver size (1.0 cm diameter). It is incorporated with a specially designed low noise preamplifier. Calibration procedures with a Michelson interferometer revealed that the EMAT sensor detected small displacement amplitudes as low as 1.0±0.2 pm in ultrasonic frequency range using an aluminium sample. For the first time, we present the use of an EMAT sensor to detect photoacoustic pressure signals in tissue phantoms and real tissues (chicken breast) in vitro. Corresponding B-scan images were constructed by the compilation of a series of received photoacoustic signals. A B-scan image of human hairs in a chicken breast sample revealed that the lateral resolution about 1.57 mm (FWHM) was achieved.