Photoacoustic microscopy (PAM) allows for the visualization of microscale structures and functionalities by detecting various chromophores in biological tissues based on their absorption spectra at specific laser wavelengths. PAM differentiates oxy and deoxy blood, water, collagen, and lipid with unique absorption spectra in NIR. To enhance the functionality of PAM, integrating multi-wavelength laser sources, particularly Ti:Sapphire lasers, is gaining significant attention. Ti:Sapphire lasers are considered an advanced solution due to their high energy efficiency and wavelength tunability. This presentation introduces a single-shot, wavelength-tunable Ti:Sapphire-based multispectral PAM system capable of rapidly performing functional imaging of blood concentrations and ICG-lymphography.
In this study, we introduce a measurement system based on DS-PAM (dichroism-sensitive photoacoustic microscopy) for assessing quench cracks. We evaluated a quench crack sample with dimensions of 300 μm in width and 150 μm in depth. Our observations revealed the presence of dichroism specifically at the edges of the crack.
Photoacoustic imaging technology using multi-wavelength can achieve functional image that provide information about a singularity in an image target. We developed a wavelength tunable light source pumped by few tens kHz pulsed laser with 532 nm wavelength for single scan functional photoacoustic imaging. The laser has individual output pulses with about 200 nsec time delay between the original 532 nm pump pulse and the wavelength tunable pulse. By using the ping-pong pulse output, we have make enable to obtain a functional photoacoustic image in a single laser scanning and demonstrated functional photoacoustic microscopy imaging to show a mouse activity.
Significance: Collagen is a basic component of many tissues such as tendons, muscles, and skin, and its imaging helps diagnose and monitor treatments in a variety of fields, including orthopedics. However, due to the overlapping peaks of the absorption spectrum with water in the short-wave infrared region (SWIR), it is difficult to select an optimal wavelength and obtain the photoacoustic (PA) image for collagen-based tissues. Therefore, an additional approach to selecting the proper wavelength is needed.
Aim: The aim of this study is to derive an effective PA absorption spectrum of collagen to select the optimal wavelength for high-sensitive PA imaging (PAI).
Approach: We measure the absorption spectrum by acquiring the PA signal from various collagen-based samples. To derive an effective PA absorption spectrum in the SWIR band, the following two parameters should be considered: (1) the laser excitation for generating the PA signal and (2) the absorption spectrum for water in the SWIR band. This molecular intrinsic property suggests the optimal wavelength for high-sensitive PAI of collagen-based samples.
Results: PA absorption spectral peaks of collagen were found at wavelengths of 1200, 1550, and 1700 nm. Thereby, the PA signal increased by up to five times compared with the wavelength commonly used in collagen PAI. We applied a pulsed fiber laser with a center wavelength of 1560 nm, and the three-dimensional PA image of a collagen patch was obtained.
Conclusions: The effective PA absorption spectrum contributes to the improvement of the PA image sensitivity by presenting the optimal wavelength of the target samples.
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 mm3. 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.
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