Mutsuo Yamazaki

Measurement of burn depths in rats using multiwavelength photoacoustic depth profiling.

We perform measurement of photoacoustic (PA) signals for burned skin in rats in the spectral range of 500 to 650 nm. The wavelength dependence of PA signal amplitude shows characteristics similar to those of the absorption spectrum of hemoglobin, suggesting that the PA signal originates from blood in the uninjured skin tissue under the injured tissue layer. High-contrast signals are obtained in the spectral range of 532 to 580 nm. At 550 nm, a PA detector is scanned on the wounds and PA tomograms are obtained. The tomograms clearly show the zones of stasis, demonstrating that a 2-D PA measurement is useful for burn depth assessment.

Accelerated binocular rivalry with anxious personality.

When dissimilar figures are presented to the two eyes individually, perception alternates spontaneously between each monocular view. This phenomenon, designated binocular rivalry, has been used by many scientists as a tool for investigating visual awareness. Some recent studies have suggested involvement of serotonergic neural systems in this phenomenon. We explored the relationship between binocular rivalry and anxiety, a state thought to be associated with serotonergic neural activity. Perceptual alternation rate in dominance of binocular rivalry were compared between normal volunteers with high and low general anxiety as measured using the harm avoidance (HA) scale of the Tridimensional Personality Questionnaire. Perceptual alternation rate and rhythmicity in the high-HA group was significantly greater than that in the low-HA group. The perceptual alternation rate in binocular rivalry was accelerated in anxious subjects, suggesting that binocular rivalry and anxiety may share some common serotonergic neural substrates.

Photoacoustic diagnosis of burns in rats: two-dimensional photo-acoustic imaging of burned tissue

We previously reported that for rat burn models, deep dermal burns and deep burns can be well differentiated by measuring the propagation time of the photoacoustic signals originated from the blood in the healthy skin tissue under the damaged tissue layer. However, the diagnosis was based on point measurement in the wound, and therefore site-dependent information on the injuries was not obtained; such information is very important for diagnosis of extended burns. In the present study, we scanned a photoacoustic detector on the wound and constructed two-dimensional (2-D) images of the blood-originated photoacoustic signals for superficial dermal burns (SDB), deep dermal burns (DDB), deep burns (DB), and healthy skins (control) in rats. For each burn model, site-dependent variation of the signal was observed; the variation probably reflects the distribution of blood vessels in the skin tissue. In spite of the variation, clear differentiation was obtained between SDB, DDB, and DB from the 2D images. The images were constructed as a function of post burn time. Temporal signal variation will be also presented.

Photoacoustic signal measurement for burned skins in the spectral range of 500-650 nm: experiment with rat burn models

This paper reports the burn diagnosis that is based on the measurement of photoacoustic waves from skin, where the acoustic waves originate from the absorption of light by blood. For this purpose, a transducer composed of a ring-shaped piezoelectric film and a quartz fiber was made. An optical parametric oscillator (500 - 650 nm) was used as a light source and its output pulses were coupled to the quartz fiber. To investigate the optimum light wavelength, we conducted experiments using rat burn models. We demonstrated that the superficial dermal burn (SDB), deep dermal burn (DDB), deep burn (DB), and control (healthy skin) could be clearly differentiated based on the photoacoustic signals induced by the light of 532 - 580nm.

Photoacoustic detection of neovascularities in skin graft

We previously proposed a new method for monitoring adhesion of skin graft by measuring photoacoustic (PA) signal originated from the neovascularities. In this study, immunohistochemical staining (IHC) with CD31 antibody was performed for grafted skin tissue to observe neovascularity, and the results were compared with PA signals. We also used a laser Doppler imaging (LDI) to observe blood flow in the grafted skin, and sensitivity of PA measurement and that of LDI were compared. In rat autograft models, PA signals were measured for the grafted skin at postgrafting times of 0-48 h. At 6 h postgrafting, PA signal was observed in the skin depth region of 500-600 mm, while the results of IHC showed that angiogenesis occurred at the depth of about 600 mm. Depths at which PA signal and angiogenesis were observed decreased with postgrafting time. These indicate that the PA signal observed at 6 h postgrafting originated from the neovascularities in the skin graft. Results of LDI showed no blood-originated signal before 48 h postgrafting. These findings suggest that PA measurement is effective in monitoring the adhesion of skin graft in early stage after transplantation.

In vivo scattering measurement of biological tissue by the use of a pyroelectric polymer transducer

We propose a new method, to our knowledge, for noninvasive scattering measurements of tissues by the use of a pyroelectric polymer transducer, poly(vinylidene fluoride trifluoroethylene) film. In this method, samples are irradiated with nanosecond, low-energy light pulses delivered from an optical fiber, and the pyroelectric signal induced by the diffuse reflectance is measured with a transducer. The signal is then converted into diffuse reflectance by use of a calibration factor. The validity of this method was confirmed by our measuring the scattering coefficient of a white acrylic resin within an accuracy of +/- 15%. We attempted to apply this method to the estimation of scattering coefficients of normal and burned skins in rats in vivo.

Adhesion monitoring of skin grafts by photoacoustic measurement: experiment using rat allograft models

Adhesion monitoring of grafted skins is very important in successful treatment of severe burns and traumas. However, current diagnosis of skin grafting is usually done by visual observation, which is not reliable and gives no quantitative information on the skin graft adhesion. When the grafted skin adheres well, neovascularities will be generated in the grafted skin tissue, and therefore adhesion may be monitored by detecting the neovascularities. In this study, we attempted to measure photoacoustic signals originate from the neovascularities by irradiating the grafted skins with 532-nm nanosecond light pulses in rat autograft and allograft models. The measurement showed that immediately after skin grafting, photoacoustic signal originate from the blood in the dermis was negligibly small, while 6 - 24 hours after skin grafting, signal was observed from the dermis in the graft. We did not observe a significant difference between the signals from the autograft and the allograft models. These results indicate that neovascularization would take place within 6 hours after skin grafting, and the rejection reaction would make little effect on adhesion within early hours after grafting.