We propose a compact and easy to use photoacoustic imaging (PAI) probe structure using a single strand of optical fiber and a beam combiner doubly reflecting acoustic waves for convenient detection of lymph nodes and cancers. Conventional PAI probes have difficulty detecting lymph nodes just beneath the skin or simultaneously investigating lymph nodes located in shallow as well as deep regions from skin without any supplementary material because the light and acoustic beams are intersecting obliquely in the probe. To overcome the limitations and improve their convenience, we propose a probe structure in which the illuminated light beam axis coincides with the axis of the ultrasound. The developed PAI probe was able to simultaneously achieve a wide range of images positioned from shallow to deep regions without the use of any supplementary material. Moreover, the proposed probe had low transmission losses for the light and acoustic beams. Therefore, the proposed PAI probe will be useful to easily detect lymph nodes and cancers in real clinical fields.
An Nd:YAG laser is generally used as the optical source for photoacoustic imaging (PAI) systems, which support a high-power pulsed laser. However, PAI systems based on Nd:YAG lasers have several disadvantages, such as instability against impact and vibration, poor mobility, and large size. To overcome the limitations, we demonstrate a PAI system using a master oscillator power amplifier (MOPA) fiber laser and an arrayed ultrasound transducer. The fabricated MOPA fiber laser has a variable repetition rate in the range of 1–50 kHz, a pulse width of 10–70 ns, and an output power of 160 μJ. Furthermore, it is stable to impact and vibration, mobile, and compact with a size of 427×250×170 mm<sup>3</sup>. We achieved PAI 150 times faster using MOPA fiber laser than using Nd:YAG laser with the arrayed ultrasound transducer composed of 128 elements. Therefore, we believe that the PAI system based on the MOPA fiber laser has significant potential for use as a clinical ultrasound imaging system.