Skin aging is characterized by color and wrinkle caused by degeneration of collagen and elastin in the dermis. Recently, the volume, diameter and branching of the micro vessels in the skin are proved to affect these biomechanical changes. Thus, high resolution imaging for both micro structure and micro vessels of the skin is desired. In the present study, dual-wavelength photoacoustic microscope (PAM) combined with high frequency ultrasound (HFUS) is developed to visualize both the morphology and microcirculation of the skin. Two Nd:YAG laser light sources with the wavelength of 532/556 nm, pulse width of 1.2/3.6 ns, pulse energy of 16 μJ/pulse and repetition rate of 1 kHz were equipped in the HFUS-PAM system. The optical fiber for laser delivery was inserted through the center hole of the concave ultrasound transducer with the central frequency of 75 MHz. Both HFUS and PA signals were acquired at the sampling rate of 500 MHz and the resolution of 12 bits. The transducer was scanned by voice coil actuators to obtain 3D dataset of HFUS and PA signals. Oxygen saturation of the micro circulation was calculated by the PA signals alternately obtained at 532 nm and 556 nm. 3D image of the layered structure and the micro vessels representing oxygen saturation in the 6 mm x 6 mm x 3 mm volume of the skin was successfully obtained with the system. HFUS-PAM will provide important information of skin morphology and microcirculation for assessment of skin aging.
We will report newly developed polymer-based phantom for photoacoustic (PA) imaging systems. Phantoms are important for performance evaluation and calibration of new modalities; however, there is no established method for making phantoms with no long-term change. We have developed skin mimicking phantoms simulating both optical and acoustic properties (i.e. optical scattering and absorption coefficients, and sound velocity). Furthermore, the phantoms are able to give accurate simulation of blood vessels by Inkjet-printing. Newly developed phantoms are consisted of castor oil included acrylic block copolymer and we can fabricate 0.8mm or less thick sheets and pile them using their self-adhesiveness.
Hemodynamic responses of the brain to hypoxia or ischemia are one of the major interests in neurosurgery and
neuroscience. In this study, we performed real-time transcutaneous PA imaging of the rat brain that was exposed to a
hypoxic stress and investigated depth-resolved responses of the brain, including the hippocampus. A linear-array 8ch
10-MHz ultrasonic sensor (measurement length, 10 mm) was placed on the shaved scalp. Nanosecond, 570-nm and 595-
nm light pulses were used to excite PA signals indicating cerebral blood volume (CBV) and blood deoxygenation,
respectively. Under spontaneous respiration, inhalation gas was switched from air to nitrogen, and then reswitched to
oxygen, during which real-time PA imaging was performed continuously. High-contrast PA signals were observed from
the depth regions corresponding to the scalp, skull, cortex and hippocampus. After starting hypoxia, PA signals at 595
nm increased immediately in both the cortex and hippocampus for about 1.5 min, showing hemoglobin deoxygenation.
On the other hand, PA signals at 570 nm coming from these regions did not increase in the early phase but started to
increase at about 1.5 min after starting hypoxia, indicating reactive hyperemia to hypoxia. During hypoxia, PA signals
coming from the scalp decreased transiently, which is presumably due to compensatory response in the peripheral tissue
to preserve blood perfusion in the brain. The reoxygenation caused a gradual recovery of these PA signals. These
findings demonstrate the usefulness of PA imaging for real-time, depth-resolved observation of cerebral hemodynamics.
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