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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.

We demonstrate photoacoustic (PA) imaging using a compact gain-switched Ti:sapphire laser. Additionally, a simple laser configuration is provided. The Ti:sapphire laser is pumped using a frequency-doubled pulsed neodymium-doped yttrium aluminum garnet pulse laser operating at a repetition rate of 10 Hz, with a pump energy of 37 mJ. No water cooling is required for the Ti:sapphire crystal. The output pulse energy and pulse duration of the laser are 13.6 mJ and 11 ns, respectively. Thus, the power conversion efficiency is 36.7%. As the end mirror in a laser cavity is adjusted in a horizontal direction, the output wavelength can be tuned within a range of 725-880 nm with a spectral bandwidth of approximately 1 nm. The laser has a small footprint size of 50 cm×35 cm including even laser pumping. Because the near-infrared region has significant advantages in the context of absorption and scattering in biological tissues, our laser can be used for PA imaging. Apart from obtaining PA images of a tube filled with indocyanine green immersed in water and placed under chicken breast tissue, our laser system could also be used for the simultaneous PA and ultrasound (US) dual-modality imaging of blood vessels lying beneath the skin of a human middle finger. We used a commercially available US machine for the PA and US dual-modality imaging.

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