The standard-of-care for evaluating lymph node status in breast cancers and melanoma metastasis is sentinel lymph node (SLN) assessment performed with a handheld gamma probe and radioisotopes. However, this method inevitably exposes patients and physicians to radiation, and the special facilities required limit its accessibility. Here, we demonstrate a non-ionizing, cost-effective, handheld photoacoustic finder (PAF) fully integrated with a solid-state dye laser and transparent ultrasound transducer (TUT). The solid-state dye laser handpiece is coaxially aligned with the spherically focused TUT. The integrated finder readily detected photoacoustic signals from a tube filled with methylene blue (MB) beneath a 22 mm thick layer of chicken tissue. In live animals, we also photoacoustically detected both SLNs injected with MB and subcutaneously injected melanomas. We believe that our radiation-free and inexpensive PAF can play a vital role in SLN assessment.

Current miniaturized ultrasound transducers suffer from insufficient attenuation from the backing layer due to their limited thickness. The thickness of the backing layer is one of the critical factors determining the device size and transducer performance for miniaturized transducers inserted and operated in a limited space. Glass bubbles, polyamide resin, and tungsten powder are combined to form a new highly attenuative backing material. It has high attenuation (>160 dB/cm at 5 MHz), which is five times greater than silver-based conductive epoxy commonly used for high-frequency ultrasound transducers, appropriate acoustic impedance (4.6 MRayl), and acceptable damping capability. An intravascular ultrasound (IVUS) transducer constructed with the 170 $\mu \text{m}$ of the proposed backing layer demonstrated that the amplitude of the signal returned from the backing layer was 1.8 times smaller, with ring-down attenuated by 6 dB. Wire-phantom imaging revealed that the axial resolution was 30% better with the suggested backing than silver-based conductive epoxy backing. Because of its excellent attenuation capability even at a limited thickness, simple manufacturing process, and easy customization capability, the suggested highly attenuative backing layer may be used for miniaturized ultrasound transducers.

Photoacoustic imaging (PAI) is being actively investigated as a non-invasive and non-radioactive imaging technique for sentinel lymph node (SLN) biopsy. By taking advantage of optical and ultrasound imaging, PAI probes SLNs non-invasively with methylene blue (MB) in both live animals and breast cancer patients. However, these PAI systems have limitations for widespread use in clinics and commercial marketplaces because the lasers used by the PAI systems, e.g., tunable liquid dye laser systems and optical parametric oscillator (OPO) lasers, are bulky in size, not economical, and use risky flammable and toxic liquid dyes. To overcome these limitations, we are proposing a novel dual-modal photoacoustic and ultrasound imaging system based on a solid-state dye laser (SD-PAUSI), which is compact, convenient, and carries far less risk of flammability and toxicity. Using a solid-state dye handpiece that generates 650-nm wavelength, we successfully imaged the MB tube positioned deeply (~3.9 cm) in chicken breast tissue. The SLNs were also photoacoustically detected in the in vivo rats beneath a 2.2-cm-thick layer of chicken breast, which is deeper than the typical depth of SLNs in humans (1.2 ± 0.5 cm). Furthermore, we showed the multispectral capability of the PAI by switching the dye handpiece, in which the MB-dyed SLN was selectively highlighted from the surrounding vasculature. These results demonstrated the great potential of the SD-PAUSI as an easy but effective modality for SLN detection.

The sentinel lymph node (SLNb) is generally performed using radioisotopes, blue dyes, or both to improve false negative rate. However, ionizing radiation is involved in a gamma probe with radioisotopes and the blue dye detection relies on native visual inspection by an operator. To overcome these limitations, we developed the photoacoustic finder (PAF), a highly sensitive, non-radioactive detector that uses only blue dye and a photoacoustic signal to detect SLNs. A total of 121 patients with breast cancer were enrolled, and 375 lymph nodes were excised using conventional SLNb. The PAF was used to measure the signal from the excised lymph nodes. We compared the SLN detection rates of each method (gamma probe, visual inspection, and PAF) and conducted a non-inferiority test. The PAF detected 87 % of SLNs, comparable to the gamma probe (85 %) and superior to visual inspection (73 %). Non-inferiority tests confirmed PAF's performance was not inferior to visual inspection (p < 0.001) or the gamma probe (p < 0.015). Using the dual-modal method (gamma probe + visual inspection) as the gold standard, PAF showed a sensitivity of 0.81 and specificity of 0.63. This study demonstrates that PAF, using only blue dye, offers a non-inferior alternative to the standard dual-modal SLN detection method with radioactive materials, opening new avenues for radiation-free SLNb in the future.

We developed a single-camera-based near-infrared (NIR) fluorescence imaging device using indocyanine green (ICG) NIR fluorescence contrast agents for image-induced surgery. In general, a fluorescent imaging system that simultaneously provides color and NIR images uses two cameras, which is disadvantageous because it increases the imaging head of the system. Recently, a single-camera-based NIR optical imaging device with quantum efficiency partially extended to the NIR region was developed to overcome this drawback. The system used RGB_NIR filters for camera sensors to provide color and NIR images simultaneously; however, the sensitivity and resolution of the infrared images are reduced by 1/4, and the exposure time and gain cannot be set individually when acquiring color and NIR images. Thus, to overcome these shortcomings, this study developed a compact fluorescent imaging system that uses a single camera with two complementary metal–oxide semiconductor (CMOS) image sensors. Sensitivity and signal-to-background ratio were measured according to the concentrations of ICG solution, exposure time, and camera gain to evaluate the performance of the imaging system. Consequently, the clinical applicability of the system was confirmed through the toxicity analysis of the light source and in vivo testing.

Introduction: Obesity is a global problem because it causes various complications. Methods for reducing fat for healthy life are being studied. In this study, we developed a minimally invasive and non-invasive lipolysis laser system for effective fat reduction. Methods: The laser had the wavelengths of 1980 nm and 2300 nm which have very good absorption of fat and water. We developed a minimally invasive laser system that breaks down fat by direct irradiation of fat tissue. This minimally invasive laser system uses a 808 nm diode laser and Nd:YVO4 to generate the 1064 nm wavelength, which is the pumping source of the nonlinear crystals. It is a mid-infrared lipolysis laser system having two wavelengths of 1980 nm and 2300 nm by controlling the temperature of nonlinear crystals. We also developed a non-invasive laser system that reduces fat with hyperthermia treatment by raising the temperature of adipocytes with a 1060 nm penetrating depth into the skin. In this non-invasive laser system, the In gallium arsenide (GaAs) diode laser is irradiated on the skin with an area of 4 × 8 cm2 through the hand-piece. The cooling system in the hand-piece protects the skin from burns. We studied the effectiveness and safety of each system through animal experiment. We studied the effects of lipolysis when these two systems were combined. Results: This research uses new wavelengths (1980 nm, 2300 nm) to increase the fat reduction effect with low energy (1.3 W). After using the 1060 nm (1.1 W/cm2 ) wavelength laser, when the 1980 nm and 2300 nm (1.3 W) laser were used, a lipolysis effect of about 35 % was obtained. Conclusion: We have developed a 1.3 W mid-infrared (1980 nm, 2300 nm) laser with good lipolysis effect with low power.