Search

We have developed a real-time (8~30 fps) photoacoustic (PA) imaging system with a linear-array transducer for burn diagnosis. In this system, PA signals originating from blood in the noninjured tissue layer located under the injured tissue layer are detected. The phantom study showed that thin light absorbers embedded in the tissue-mimicking scattering medium at depths of > 3 mm can be imaged with high contrast. The diagnostic experiments using rat burn models showed good agreements between the injury depths (zones of stasis) indicated by PA imaging and those by histological analysis. These results demonstrate the potential usefulness of the present system for clinical burn diagnosis.

Control of wound sepsis is an important challenge in traumatology. However, increase in the drug-resistant bacteria makes this challenge considerably difficult in recent years. In this study, we attempted to control burn wound sepsis in rats by photodynamic treatment, which has been reported to be effective against some drug-resistant bacteria. A 20% TBSA (total body surface area) full-thickness burn was made in rat dorsal skin, and five days after injury, a suspension of P. aeruginosa was applied to the wound surface. At 30 min after infection, a methylene blue (MB) solution was applied to the wound surface; 5 min afterwards, the wound was illuminated with a 665-nm light emitting diode (LED) array for 10 min. This treatment (application of MB and illumination) was repeated 3 times successively. The averaged light intensity on the wound surface was 3.3 mW/cm 2 , the corresponding total light dose being 5.9 J/cm 2 . One week after injury, the numbers of bacteria in the blood and liver were counted by colony forming assay. In the liver, the number of bacteria of the treated group was significantly lower than that of the sham control group without photodynamic treatment. In the blood, no bacteria were detected in the treated group, while a certain amount of bacteria was detected in the control group. These results demonstrate the efficacy of MB-mediated PDT with a red LED array to control burn wound sepsis.

Control of infection in wounds is critically important to avoid transition to sepsis; however, recent rise of drug-resistant bacteria makes it difficult. Thus, antimicrobial photodynamic therapy (APDT) has recently received considerable attention. In this study, we examined methylene blue (MB)-mediated photodynamic inactivation of Psuedomonas aeruginosa in rat burned skin. Two days after infection, the wound surface was contacted with a MB solution at different concentrations, and thereafter the wound was irradiated with cw 665-nm light at a constant power density of 250 mW/cm 2 for different time durations. We obtained a two orders of magnitude decrease in the number of bacteria by PDT with a 2-h contact of 0.5-mM MB solution and a illumination of 480 J/cm 2 , demonstrating the efficacy of PDT against infection with Ps. aeruginosa in burns.

In our previous study, we delivered plasmid DNA coding for human hepatocyto growth factor (hHGF) to rat skin grafts based on laser-induced stress wave (LISW), by which production of CD31-positive cells in the grafted skins was found to be enhanced, suggesting improved angiogenesis. In this study, we validated the efficacy of this method to accelerate adhesion of grafted skins; reperfusion and reepithelialization in the grafted skins were examined. As a graft, dorsal skin of a rat was exsected and its subcutaneous fat was removed. Plasmid DNA expression vector for hHGF was injected into the graft; on its back surface a laser target with a transparent sheet for plasma confinement was placed, and irradiated with three nanosecond laser pulses at a laser fluence of 1.2 J/cm2 (532 nm; spot diameter, 3 mm) to generate LISWs. After the application of LISWs, the graft was transplanted onto its donor site. We evaluated blood flow by laser Doppler imaging and analyzed reepithelialization based on immunohistochemistry as a function of postgrafting time. It was found that both reperfusion and reepithelialization were significantly enhanced for the grafts with gene transfection than for normal grafts; reepithelialization was completed within 7 days after transplantation with the transfected grafts. These findings demonstrate that adhesion of grafted skins can be accelerated by delivering HGF gene to the grafts based on LISWs.

We investigated the validity of photoacoustic (PA) measurement for monitoring granulation tissue formed in the grafted artificial dermis (AD) in rats. We found that the depths of granulation tissue or neovascularities in the grafted AD can be monitored by PA measurement. There was a significant correlation between the PA signal amplitude and the density of neovascularities in the granulation tissue. These results suggest the usefulness of PA measurement for monitoring the adhesion of grafted ADs.

To obtain efficient antibacterial photodynamic effect in traumatic injuries such as burns, depth-resolved dosimetry of photosensitizer is required. In this study, we performed dual-wavelength photoacoustic (PA) measurement for rat burned skins injected with a photosensitizer. As a photosensitizer, methylene blue (MB) or porfimer sodium was injected into the subcutaneous tissue in rats with deep dermal burn. The wound was irradiated with red (665 nm or 630 nm) pulsed light to excite photosensitizers and green (532 nm) pulsed light to excite blood in the tissue; the latter signal was used to eliminate blood-associated component involved in the former signal. Acoustic attenuation was also compensated from the photosensitizer-associated PA signals. These signal processing was effective to obtain high-contrast image of a photosensitizer in the tissue. Behaviors of MB and porfimer sodium in the tissue were compared.

We attempted to monitor the healing process of burn injuries by multiwavelength photoacoustic (PA) measurement. Deep dermal burn with 20% total body surface area was made in the dorsal skins of rats. The wavelengths of 532 nm, 556 nm, 576 nm and 600 nm were used: 532 nm is isosbestic point for oxyhemoglobin (HbO2) and deoxyhemoglobin (HHb); 576 nm is HbO2 absorption dominant; and 556 nm and 600 nm are HHb absorption dominant. At 532 nm, 556 nm and 576 nm, the depths of PA signal peak were shifted to the shallower region of the wound with the elapse of time, which was found to reflect angiogenesis due to wound healing by histological analysis. The amplitudes of PA signals increased at all the wavelengths until 24 h postburn time. At 48 h postburn time, the signal amplitude continued to increase at 532 nm and 576 nm, while it decreased at 556 nm and 600 nm. This is attributable to the change from a shock phase to the phase of hyperdynamic state, which is accompanied by increases in cardiac output and oxygen consumption. These results suggest that multiwavelength photoacoustic measurement is useful for monitoring healing process of burn injuries.

We delivered a therapeutic gene, hepatocyte growth factor (HGF), to skin grafts of rats using laser-induced stress waves (LISWs) with the objective of enhancing their adhesion. The density and uniformity of neovascularities were enhanced significantly in the grafted skins that were transfected using LISWs, suggesting the efficacy of this method to improve the outcome of skin transplantation.

We successfully delivered a therapeutic vector construct, which carries hepatocyte growth factor (HGF) gene, to rat skin in vivo . After HGF expression vector had been intradermally injected to rat skin, LISWs were generated by irradiating the laser target put on the rat skin with nanosecond pulses from the second harmonics (532 nm) of a Q-switched Nd:YAG laser. Concentration of HGF protein increased by a factor of four by the application of LISWs when compared with that of control samples without LISW application. We also investigated the effects of LISWs on the integrity of plasmid DNA.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We successfully delivered therapeutic gene, Hepatocyte Growth Factor (HGF), to rat skin in vivo. The level of hHGF protein increased by the application of LISWs when compared with that of control samples without LISW application.

We assumed that edema causes a decrease in the scattering coefficient of brain tissue and hence a decrease in the intensity of diffuse reflectance from the brain. On the basis of this assumption, we attempted to transcranially detect a formation of brain edema by measuring diffuse light reflectance. In rats, edema was induced by making a cold injury in the brain. The skull was irradiated with 633-nm and 532-nm laser light delivered through an optical fiber, and the diffuse light reflectance from the brain was collected with another optical fiber. We observed that reflectance intensities were significantly decreased around the cold injury both at 633 nm and 532 nm, suggesting that scattering coefficient of brain tissue was reduced due to a formation of edema in this area. In the injury, reflectance intensity was increased at 532 nm, indicating that cerebral blood volume was decreased in this region.

Brain edema causes an increase in brain tissue volume which results from an accumulation of transudate due to the increased permeability of the brain capillaries. Assuming the transudate to be the material with a low scattering coefficient, brain edema would decrease scattering coefficient of the brain tissue, and diffuse reflectance from the brain may, therefore, be decreased. We examined whether brain edema can be detected or not by measuring the diffuse light reflected from the brain. We induced brain edema by cold injury in rats. The rat skull was irradiated with 633-nm HeNe laser through an optical fiber, and the diffuse light reflected from the brain was collected through another optical fiber. Intensity of the diffuse light reflectance was measured with a polychromator as functions of the time and position on the skull. We found that intensity of the detected diffuse light reflectance decreased at 24 h after injury in the surround area of the injury, suggesting that brain edema can be detected by measuring the diffuse light reflected from the brain.