The optical properties of human brain tumor tissues, including glioblastoma, meningioma, oligodendroglioma, and metastasis, that were classified into “strong,” “vague,” and “unobservable” fluorescence by a neurosurgeon were measured and compared. The optical properties of the tissues were measured with a double integrating sphere and the inverse Monte Carlo technique from 350 to 1000 nm. Using reasons of ex-vivo measurement, the optical properties at around 420 nm were potentially affected by the hemoglobin content in tissues. Significant differences were not observed between the optical properties of the glioblastoma regions with “strong” and “unobservable” fluorescence. Sections of human brain tumor tissue with “strong” and “unobservable” fluorescence were stained with hematoxylin and eosin. The cell densities [mean ± standard deviation (S.D.)] in regions with “strong” and “unobservable” fluorescence were 31 ± 9 × 102 per mm2 and 12 ± 4 × 102 per mm2, respectively, which is a statistically significant difference. The higher fluorescence intensity is associated with higher cell density. The difference in cell density modified the scattering coefficient yet it does not lead to significant differences in the reduced scattering coefficient and thus does not affect the propagation of the diffuse fluorescent light. Hence, the false negatives, which mean a brain tumor only shows “unobservable” fluorescence and is hence classified incorrectly as nontumor, in using 5-ALA for detection of human glioblastoma do not result from the differences in optical properties of human brain glioblastoma tissues. Our results suggest that the primary cause of false negatives may be a lack of PpIX or a low accumulation of PpIX.
Spectroscopic setup for measuring anisotropy factor g spectrum of biological tissues was constructed. g of chicken liver tissue was lower than chicken breast tissue. High absorption of hemoglobin can have an influence on g spectrum.
Cholesteryl esters are main components of atherosclerotic plaques and have an absorption peak at the wavelength of 5.75 μm originated from C=O stretching vibration mode of ester bond. Our group achieved the selective ablation of atherosclerotic lesions using a quantum cascade laser (QCL) in the 5.7 μm wavelength range. QCLs are relatively new types of semiconductor lasers that can emit mid-infrared range. They are sufficiently compact and considered to be useful for clinical application. However, large thermal effects were observed because the QCL worked as quasicontinuous wave (CW) lasers due to its short pulse interval. Then we tried macro pulse irradiation (irradiation of pulses at intervals) of the QCL and achieved effective ablation with less-thermal effects than conventional quasi-CW irradiation. However, lesion selectivity might be changed by changing pulse structure. Therefore, in this study, irradiation effects of the macro pulse irradiation to rabbit atherosclerotic plaque and normal vessel were compared. The macro pulse width and the macro pulse interval were set to 0.5 and 12 ms, respectively, because the thermal relaxation time of rabbit normal and atherosclerotic aortas in the oscillation wavelength of the QCL was 0.5–12 ms. As a result, cutting difference was achieved between rabbit atherosclerotic and normal aortas by the macro pulse irradiation. Therefore, macro pulse irradiation of a QCL in the 5.7 μm wavelength range is effective for reducing thermal effects and selective ablation of the atherosclerotic plaque. QCLs have the potential of realizing less-invasive laser angioplasty.
Anisotropy factor g, one of the optical properties of biological tissues, is the most important parameter to accurately
determine scattering coefficient μs in the inverse Monte Carlo (iMC) simulation. It has been reported that g has
wavelength and absorption dependence, however, there are few attempts in order to calculate μs of biological tissue
considering the wavelength and absorption dependence of g. In this study, the scattering angular distributions of
biological tissue phantoms were measured in order to determine g by using goniometric measurements with three
polarization conditions at strongly and weakly absorbing wavelengths of hemoglobin. Then, optical properties,
especially, μs were measured by integrating sphere measurements and iMC simulation in order to confirm the influence
of measured g on optical properties in comparison of with general value of g (0.9) for soft biological tissue.
Consequently, it was found that μs was overestimated at strongly absorbing wavelength, however, μs was underestimated
at weakly absorbing wavelength if the g was not considered its wavelength and absorption dependence.
Atherosclerosis is a primary cause of critical ischemic diseases like heart infarction or stroke. A method that can provide detailed information about the stability of atherosclerotic plaques is required. We focused on spectroscopic techniques that could evaluate the chemical composition of lipid in plaques. A novel angioscope using multispectral imaging at wavelengths around 1200 nm for quantitative evaluation of atherosclerotic plaques was developed. The angioscope consists of a halogen lamp, an indium gallium arsenide (InGaAs) camera, 3 optical band pass filters transmitting wavelengths of 1150, 1200, and 1300 nm, an image fiber having 0.7 mm outer diameter, and an irradiation fiber which consists of 7 multimode fibers. Atherosclerotic plaque phantoms with 100, 60, 20 vol.% of lipid were prepared and measured by the multispectral angioscope. The acquired datasets were processed by spectral angle mapper (SAM) method. As a result, simulated plaque areas in atherosclerotic plaque phantoms that could not be detected by an angioscopic visible image could be clearly enhanced. In addition, quantitative evaluation of atherosclerotic plaque phantoms based on the lipid volume fractions was performed up to 20 vol.%. These results show the potential of a multispectral angioscope at wavelengths around 1200 nm for quantitative evaluation of the stability of atherosclerotic plaques.
Atherosclerotic plaques mainly consist of cholesteryl esters. Cholesteryl esters have an absorption peak at the wavelength of 5.75 μm originated from C=O stretching vibration mode of ester bond. Our group achieved making cutting difference between atherosclerotic lesions and normal vessels using a quantum cascade laser (QCL) in the 5.7 μm wavelength range. QCLs are relatively new types of semiconductor lasers that can emit mid-infrared range. They are sufficiently compact and have recently achieved their high-power emission. However, large thermal damage was observed because the QCL worked as a quasi-continuous wave laser due to its short pulse interval. To realize less invasive ablation by the QCL, reducing thermal effects to normal vessels is needed. In this study, we tried improving the thermal effects by changing the pulse structure. First, irradiation effects to rabbit atherosclerotic aortas by macro pulse irradiation (irradiation of pulses at intervals) and conventional continuous pulse irradiation were compared. The macro pulse width and the macro pulse interval were set to 0.54 and 12 ms, respectively, because the thermal relaxation time of rabbit normal and atherosclerotic aortas in the oscillation wavelength was 0.54-12 ms. As a result, ablation depth became longer and coagulation width became shorter by the macro pulse irradiation. In addition, cutting difference between rabbit normal and atherosclerotic aortas was observed by the macro pulse irradiation. Therefore, the macro pulse irradiation achieved the improvement of thermal effects by the QCL in the 5.7 μm wavelength range. The QCL has the potential of realizing less-invasive laser angioplasty.
Spectroscopic techniques have been researched for intravascular diagnostic imaging of atherosclerotic plaque. Nearinfrared
(NIR) light efficiently penetrates of biological tissues, and the NIR region contains the characteristic absorption
range of lipid-rich plaques. The objective of this study is to observe atherosclerotic plaque using a NIR multispectral
angioscopic imaging. Atherosclerotic plaque phantoms were prepared using a biological tissue model and bovine fat. For
the study, we developed an NIR multispectral angioscopic imaging system with a halogen light, mercury-cadmiumtelluride
camera, band-pass filters and an image fiber. Apparent spectral absorbance was obtained at three wavelengths,
1150, 1200 and 1300 nm. Multispectral images of the phantom were constructed using the spectral angle mapper
algorithm. As a result, the lipid area, which was difficult to observe in a visible image, could be clearly observed in a
multispectral image. Our results show that image-enhanced observation and quantification of atherosclerotic plaque by
NIR multispectral imaging at wavelengths around 1200 nm is a promising angioscopic technique with the potential to
identify lipid-rich plaques.
Less invasive methods for treating dental caries are strongly desired. However, conventional dental lasers do not always selectively remove caries or ensure good bonding to the composite resin. According to our previous study, demineralized dentin might be removed by a nanosecond pulsed laser operating at wavelengths of around 5.8 μm. The present study investigated the irradiation effect of the light on carious human dentin classified into “remove,” “not remove,” and “unclear” categories. Under 5.85-μm laser pulses, at average power densities of 30 W/cm2 and irradiation time of 2 s, the ablation depth of “remove” and “not remove,” and also the ablation depth of “unclear” and “not remove,” were significantly different (p<0.01). The ablation depth was correlated with both Vickers hardness and Ca content. Thus, a nanosecond pulsed laser operating at 5.85 μm proved an effective less-invasive caries treatment.
Atherosclerosis is a primary cause of critical ischemic disease. The risk of critical event is involved the content of lipid
in unstable plaque. Near-infrared (NIR) range is effective for diagnosis of atherosclerotic plaque because of the
absorption peaks of lipid. NIR multispectral imaging (NIR-MSI) is suitable for the evaluation of plaque because it can
provide spectroscopic information and spatial image quickly with a simple measurement system. The purpose of this
study is to evaluate the lipid concentrations in plaque phantoms quantitatively with a NIR-MSI system. A NIR-MSI
system was constructed with a supercontinuum light, a grating spectrometer and a MCT camera. Plaque phantoms with
different concentrations of lipid were prepared by mixing bovine fat and a biological soft tissue model to mimic the
different stages of unstable plaque. We evaluated the phantoms by the NIR-MSI system with three wavelengths in the
band at 1200 nm. Multispectral images were processed by spectral angle mapper method. As a result, the lipid areas of
phantoms were effectively highlighted by using three wavelengths. In addition, the concentrations of lipid areas were
classified according to the similarity between measured spectra and a reference spectrum. These results suggested the
possibility of image enhancement and quantitative evaluation of lipid in unstable plaque with a NIR-MSI.
Less invasive treatment and preservation of teeth, referred to as minimal intervention, are strong requirements in dentistry.
In our previous study, the fundamental ablation properties of human dentin at wavelengths around 5.8 μm were investigated,
and the results indicated that the wavelength of 5.85 μm was optimal for selective removal of carious dentin with less
damage to normal dentin. The purpose of this study was to investigate the relationship between the ablation depth and
hardness of human dentin including carious lesion. A nanosecond pulsed laser produced by difference-frequency
generation was used for irradiations to human carious dentin. It was observed that correlation between ablation depth and
Vickers hardness after 2 s laser irradiation at the wavelength of 5.85 μm and the average power density of 30 W/cm2. On the other hand, ablations did not depend on Vickers hardness at the wavelength of 6.00 μm. A nanosecond pulsed laser
with the wavelength at 5.85 μm is useful for selective ablation of human carious dentin in accordance with the hardness.
Less-invasive treatment of caries has been needed in laser dentistry. Based on the absorption property of dentin substrates, 6 μm wavelength range shows specific absorptions and promising characteristics for the excavation. In our previous study, 5.8 μm wavelength range was found to be effective for selective excavation of carious dentin and restoration treatment using composite resin from the irradiation experiment with bovine sound and demineralized dentin. In this study, the availability of 5.8 μm wavelength range for selective excavation of human carious dentin was investigated for clinical application. A mid-infrared tunable nanosecond pulsed laser by difference-frequency generation was used for revealing the ablation property of human carious dentin. Irradiation experiments indicated that the wavelength of 5.85 μm and the average power density of 30 W/cm2 realized the selective excavation of human carious dentin, but ablation property was different with respect to each sample because of the different caries progression. In conclusion, the wavelength of 5.85 μm could realize the selective excavation of human carious dentin, but it was necessary to evaluate the stage of caries progression in order to control the ablation property.
We investigated the potential of a compact and high-power quantum cascade laser (QCL) in the 5.7 μm wavelength range for less-invasive laser angioplasty. Atherosclerotic plaques consist mainly of cholesteryl esters. Radiation at a wavelength of 5.75 μm is strongly absorbed in C=O stretching vibration mode of cholesteryl esters. Our previous study achieved to make cutting differences between a normal artery and an atherosclerotic lesions using nanosecond pulsed laser by difference-frequency generation (DFG laser) at the wavelength of 5.75 μm. For applying this technique to clinical treatment, a compact laser device is required. In this study, QCL irradiation effects to a porcine normal aorta were compared with DFG laser. Subsequently, QCL irradiation effects on an atherosclerotic aorta of myocardial infarction-prone Watanabe heritable hyperlipidemic rabbit (WHHLMI rabbit) and a normal rabbit aorta were observed. As a result, the QCL could make cutting differences between the rabbit atherosclerotic and normal aortas. On the other hand, the QCL induced more thermal damage to porcine normal aorta than the DFG laser at the irradiation condition of comparable ablation depths. In conclusion, the possibility of less-invasive and selective treatment of atherosclerotic plaques using the QCL in the 5.7 μm wavelength range was revealed, although improvement of QCL was required to prevent the thermal damage of a normal artery.
A method to identify vulnerable plaques that are likely to cause acute coronary events has been required. The object of
this study is identifying vulnerable plaques by hyperspectral imaging in near-infrared range (NIR-HSI) for an
angioscopic application. In this study, NIR-HSI of atherosclerotic tissue phantoms was demonstrated under simulated
angioscopic conditions. NIR-HSI system was constructed by a NIR super continuum light and a mercury-cadmium-telluride
camera. Spectral absorbance values were obtained in the wavelength range from 1150 to 2400 nm at 10 nm
intervals. The hyperspectral images were constructed with spectral angle mapper algorithm. As a result, detections of the
lipid area in the atherosclerotic tissue phantom under angioscopic observation conditions were achieved especially in the
wavelength around 1200 nm, which corresponds to the second overtone of CH stretching vibration mode.
Atherosclerosis is a primary cause of critical ischemic disease and disease attributed atherosclerosis is major mortality in
the world today. The risk of critical event is involved the content of lipid in plaque. Near-infrared multispectral imaging
(MSI) is suitable for the evaluation of plaque because it can provide spectroscopic information and spatial image quickly
with simple measurement system. In this paper, the optimal wavelengths to detect plaque were investigated in the near-infrared
wavelength range with atherosclerotic phantom. Supercontinuum light was illuminated on a grating
spectrometer for the selection of a specific wavelength, and the wavelength-limited light was irradiated to the phantom.
Two phantoms were observed by near-infrared camera in the wavelength range from 1150 to 1790 nm. Plaque phantom
can be detected with three wavelengths containing an absorption peak of lipid at 1210 nm or 1730 nm. Especially, the
absorption peak at 1730 nm had advantage over 1210 nm even considering the difference of penetration depth. The
multispectral images were blurred with decreasing the number of wavelengths. These result showed the possibility of
MSI using three wavelengths including 1210 nm and 1730 nm for enhancing diagnosis of atherosclerotic plaque.
Less-invasive treatment of caries has been needed in laser dentistry. Based on the absorption property of dentin substrates, 6 μm wavelength range shows specific absorptions and promising characteristics for the excavation. In our previous study, 5.8 μm wavelength range was found to be effective for selective excavation of carious dentin and restoration treatment using composite resin from the irradiation experiment with bovine sound and demineralized dentin. In this study, the availability of 5.8 μm wavelength range for selective excavation of human carious dentin was investigated for clinical application. A mid-infrared tunable nanosecond pulsed laser by difference-frequency generation was used for revealing the ablation property of human carious dentin. Irradiation experiments indicated that the wavelength of 5.85 μm and the average power density of 30 W/cm2 realized the selective excavation of human carious dentin, but ablation property was different with respect to each sample because of the different caries progression. In conclusion, 5.8 μm wavelength range was found to be effective for selective excavation of human carious dentin.
We evaluated the utility of a compact and high-power quantum cascade laser (QCL) in the 5.7 μm wavelength range for less-invasive laser angioplasty. Atherosclerotic plaques mainly consist of cholesteryl esters. The wavelength of 5.75 μm is well absorbed in C=O stretching vibration mode of cholesteryl esters. Our previous study achieved to make cutting differences between a normal tunica intima of an artery and an atherosclerotic lesions using a nanosecond pulsed laser by difference-frequency generation (DFG laser) at the wavelength of 5.75 μm. For realizing a clinical application of this technique, a compact laser device is required. In this study, QCL irradiation effects to a porcine normal aorta were compared with DFG laser. In addition QCL irradiation effects to an atherosclerotic aorta of myocardial infarction-prone Watanabe heritable hyperlipidemic rabbit (WHHLMI rabbit) and a normal aorta were observed. As a result, the QCL could make cutting difference between the rabbit atherosclerotic aorta and the normal aorta. On the other hand, the QCL induced more thermal damage to porcine normal aorta than the DFG laser at the irradiation condition of comparable ablation depth. In conclusion, the possibility of less-invasive and selective treatment of atherosclerotic plaques using the QCL in the 5.7 μm wavelength range was revealed, although improvement of QCL was required to prevent the thermal damage of a normal artery.
Hyperspectral imaging (HSI) of rabbit atherosclerotic plaque in near-infrared (NIR) range from 1150 to 2400 nm was demonstrated. A method to identify vulnerable plaques that are likely to cause acute coronary events has been required. The object of this study is identifying vulnerable plaques by NIR-HSI for an angioscopic application. In this study, we observed the hyperspectral images of the atherosclerotic plaque in WHHLMI rabbit (atherosclerotic rabbit) artery under simulated angioscopic conditions by NIR-HSI. NIR-HSI system was constructed by a NIR super continuum light and a mercury-cadmium-telluride camera. Spectral absorbance values (log (1/R) data) were obtained in the wavelength range from 1150 to 2400 nm at 10 nm intervals. The hyperspectral images were constructed with spectral angle mapper algorithm. As a result, the detections of atherosclerotic plaque under angioscopic observation conditions were achieved especially in the wavelength around 1200 nm, which corresponds to the second overtone of CH stretching vibration mode. The NIR-HSI was considered to serve as an angioscopic diagnosis technique to identify vulnerable plaques without clamping and saline injection.
Photodynamic therapy (PDT) is a photochemical modality approved for cancer treatment. PDT has demonstrated efficacy in early stage lung cancer and esophageal cancer. The accumulation of photosensitizers in cancer cells is necessary to enhance the therapeutic benefits of PDT; however, photosensitizers have low uptake efficiency. To overcome this limitation, a drug delivery system, such as the hemagglutinating virus of Japan envelope (HVJ-E) vector, is required. In this study, the combination of PDT and HVJ-E was investigated for enhancing the efficacy of PDT. The photosensitizers that were evaluated included 5-aminolaevulinic acid (5-ALA), protoporphyrin IX (PPIX), and HVJ-PPIX. The uptake of the photosensitizers as increased twenty-fold with the addition of HVJ-E. The cytotoxicity of conventional 5-ALA was enhanced by the addition of HVJ-E vector. In conclusion, HVJ-E vector improved the uptake of photosensitizers and the PDT effect.
Conventional dental lasers have not realized a selective excavation of carious dentin. Objective of this study is to
determine the optimal irradiation condition for the selective excavation by using a wavelength around 5.8 μm. A
nanosecond pulsed laser with a wavelength of 5.8 μm was obtained by difference-frequency generation technique. The
laser delivers 5 ns pulse width at a repetition rate of 10 Hz. 5.8 μm wavelength range, a short wavelength required high
excavation energy and a long wavelength required low excavation energy to induce the selective excavation with a low
thermal side effect. 5.8 μm wavelength provides a selective excavation technique for minimal intervention.
Laser ablation therapy combined with photodynamic therapy (PDT) is studied for treatment of advanced cancers. The
clinical outcome of PDT may be improved by the accurate knowledge about the light distribution within tissue. Optical
properties [absorption coefficient (μa), scattering coefficient (μs), anisotropy factor (g), refractive index, etc.] of tissues
help us realizing a light propagation through the tissue. It is important to understand of the effect of laser coagulation
formed by laser ablation to PDT. The aim of this study is to estimate of influence of coagulated region to PDT for
effective PDT combined laser ablation therapy. We evaluated the optical property of mouse tumor tissue in native and
coagulated state using a double integrating sphere system and an inverse Monte Carlo method in the wavelength range
from 350 to 1000 nm. After laser ablation, the μa and reduced scattering coefficient spectra of coagulated tissues were
increased in the wavelength range from 350 to 1000 nm. The optical penetration depth of coagulated tissues is 1.2-2.9
times lower than the native state in the wavelength range from 350 to 1000 nm. The intensity of the light energy inside
the coagulated tissue falls to about 60% of its original value at the end of coagulated layer. The evaluation of light energy
distribution by the determination of the tissues optical properties could be useful for optimization of the treatment
procedure in combined laser ablation with PDT.
In laser medicine, the accurate knowledge about the optical properties (absorption coefficient; μa, scattering coefficient;
μs, anisotropy factor; g) of laser irradiated tissues is important for the prediction of light propagation in tissues, since the
efficacy of laser treatment depends on the photon propagation within the irradiated tissues. Thus, it is likely that the
optical properties of tissues at near-ultraviolet, visible and near-infrared wavelengths will be more important due to more
biomedical applications of lasers will be developed. For improvement of the laser induced thermotherapy, the optical
property change during laser treatment should be considered in the wide wavelength range. For estimation of the optical
properties of the biological tissues, the optical properties measurement system with a double integrating sphere setup and
an inverse Monte Carlo technique was developed. The optical properties of chicken muscle tissue were measured in the
native state and after laser coagulation using the optical properties measurement system in the wavelength range from
350 to 2100 nm. A CO2 laser was used for laser coagulation. After laser coagulation, the reduced scattering coefficient of
the tissue increased. And, the optical penetration depth decreased. For improvement of the treatment depth during laser
coagulation, a quantitative procedure using the treated tissue optical properties for determination of the irradiation power
density following light penetration decrease might be important in clinic.
Conventional lasers, Er:YAG laser and Er,Cr:YSGG laser, lack the ability for selective excavation to discriminate
carious tissue only because they use the laser tissue interaction derived from a strong absorption of water. Based on the
absorption property of carious dentin, characteristic absorption bands around 6 μm are candidate for selective excavation.
Our group has already observed the difference of ablation depth between demineralized and normal dentin in the
wavelength range from 5.75 to 6.60 μm. Also this study has showed the effectiveness of 5.8 μm. Objective of this study
is to determine optimal irradiation parameters of selective excavation by using 5.8 μm. Bovine dentin plates
demineralized by soaking in lactic acid solution were used as a carious dentin model. A nanosecond pulsed laser at 5.8
μm wavelength was obtained by difference-frequency generation technique. The laser delivers 5 ns pulse width at a
repetition rate of 10 Hz. After irradiation, morphological change and measurement of ablation depth was observed with a
scanning electron microscope and a confocal laser microscope, respectively. In 5.8 μm wavelength, high ablation
efficiency with a low thermal side effect was observed. 5.8 μm wavelength provides a selective excavation technique for
minimal intervention.
Selective caries treatment has been anticipated as an essential application of dentistry. In clinic, some lasers have already
realized the optical drilling of dental hard tissue. However, conventional lasers lack the selectivity, and still depend on
the dentist's ability. Based on the absorption property of carious dentin, 6 μm wavelength range shows specific
absorptions and promising characteristics for excavation. The objective of this study is to develop a selective excavation
of carious dentin by using the laser ablation with 6 μm wavelength range. A mid-infrared tunable pulsed laser was
obtained by difference-frequency generation technique. The wavelength was tuned around the absorption bands called
amide 1 and amide 2. In the wavelength range from 5.75 to 6.60 μm, the difference of ablation depth between
demineralized and normal dentin was observed. The wavelength at 6.02 μm and the average power density of 15 W/cm2,
demineralized dentin was removed selectively with less-invasive effect on normal dentin. The wavelength at 6.42 μm
required the increase of average power density, but also showed the possibility of selective ablation. This study provided
a valuable insight into a wavelength choice for a novel dental laser device under development for minimal intervention
dentistry.
Endovenous laser ablation (EVLA) is a common treatment method for varicose vein. However, the precise irradiation
dose for EVLA is not understood quantitatively. The objective of this study is to evaluate EVLA quantitatively based on
optical properties of the varicose vein tissue, and compare the efficacy and the safety at wavelengths of 980 nm and 1470
nm. A human varicose vein tissue was used as a sample. The samples were irradiated by using the 980 nm and 1470 nm
laser diodes in various irradiation parameters. The power density was varied from 260 to 1710 W/cm2 and the irradiation
time was varied from 3 to 10 s. The optical properties of samples were determined by using a double integrating sphere
and an inverse Monte Carlo method. The optical penetration depth of samples was estimated from the optical properties.
In the 980 nm laser irradiation, the initial shrinkage of the tissue was observed during laser irradiation conducted at the
average energy density of 3630 J/cm2 (1210 W/cm2, 3 s). In the 1470 nm laser irradiation, the initial shrinkage of the
tissue was observed during laser irradiation conducted at the average energy density of 2600 J/cm2 (260 W/cm2, 10 s).
Penetration depth of the vein wall at the wavelength of 980 nm and 1470 nm were 1.3 mm and 0.22 mm, respectively.
The sample irradiated with the 1470 nm laser diode showed vein shrinkage in lower energy density than the 980 nm laser
irradiation. The penetration depth at the wavelength of 1470 nm was smaller than the sample thickness about 0.8 mm.
These data indicate that EVLA with the 1470 nm laser diode may be more effective and safer than EVLA with the 980
nm laser diode.
Photodynamic therapy (PDT) efficacy depends on the amount of light distribution within the tissue. However, conventional PDT does not consider the laser irradiation dose during PDT. The optical properties of biological tissues (absorption coefficient μa, reduced scattering coefficient μ′s, anisotropy factor g, refractive index, etc.) help us to recognize light propagation through the tissue. The goal of this paper is to acquire the knowledge of the light propagation within tissue during and after PDT with the optical property of PDT-performed mouse tumor tissue. The optical properties of mouse tumor tissues were evaluated using a double integrating sphere setup and the algorithm based on the inverse Monte Carlo method in the wavelength range from 350 to 1000 nm. During PDT, the μa and μ′s were not changed after 1 and 5 min of irradiation. After PDT, the μ′s in the wavelength range from 600 to 1000 nm increased with the passage of time. For seven days after PDT, the μ′s increased by 1.7 to 2.0 times, which results in the optical penetration depth decreased by 1.4 to 1.8 times. To ensure an effective procedure, the adjustment of laser parameters for the decreasing penetration depth is recommended for the re-irradiation of PDT.
To estimate the error of scattering coefficient spectrum determined by using double-integrating sphere system and
inverse Monte Carlo method, optical properties of tissue phantom were measured. The tissue phantom was composed of
hemoglobin, intralipid and gelatin. The thickness of samples
(0.1-1.0 mm) and hemoglobin concentration (0.5-4.0
mg/ml) were changed and the effects of optical properties spectra were investigated. As the results, when the value of μa
was large, μ's spectrum was not consistent with scattering theory. The higher hemoglobin concentration of samples was
the lager the errors of μ's spectra were. The thinner the sample was, the smaller the errors were. However μa spectrum
was not accurate when the sample was thin. It was predicted that when the sample thickness was 0.1 mm μ's spectrum
was accurate. And when the sample thickness was 1.0 mm, μa spectrum was accurate.
Hyperspectral imaging (HSI) is a chemical imaging modality with spectroscopic information. This technique was often
used in agricultural or pharmaceutical industries. But there have been a few reports for clinical medical applications. In
near-infrared (NIR) wavelength region, the significant absorption peaks are often observed by the overtone of midinfrared
molecular vibration. In addition, NIR light has a high penetration because of low scattering and less absorption
by water or protein. In this study, we constructed the NIR-HSI system and the high-contrast subcutaneous adipose tissue
imaging was conducted in-vitro. In the absorption spectra which are obtained by our NIR-HSI system, the characteristic
absorption bands were observed around 1200 nm and 1700 nm. In the processed images using these wavelength bands,
subcutaneous adipose tissue was observed through a skin. In a hyperspectral image by another processing using all
wavelengths, a high-contrast image of subcutaneous adipose tissue is also obtained. NIR-HSI system is a powerful
diagnostic technique for adipose tissues distribution and their morphological change on/inside a tissue.
Optical technologies have good potential for caries detection, prevention, excavation, and the realization of minimal
intervention dentistry. This study aimed to develop a selective excavation technique of carious tissue using the specific
absorption in 6 μm wavelength range. Bovine dentin demineralized with lactic acid solution was used as a carious dentin
model. A mid-infrared tunable pulsed laser was obtained by difference-frequency generation technique. The wavelength
was tuned to 6.02 and 6.42 μm which correspond to absorption bands called amide I and amide II, respectively. The laser
delivers 5 ns pulse width at a repetition rate of 10 Hz. The morphological change after irradiation was observed with a
scanning electron microscope, and the measurement of ablation depth was performed with a confocal laser microscope.
At λ = 6.02 μm and the average power density of 15 W/cm2, demineralized dentin was removed selectively with less-invasive
effect on sound dentin. The wavelength of 6.42 μm also showed the possibility of selective removal. High
ablation efficiency and low thermal side effect were observed using the nanosecond pulsed laser with λ = 6.02 μm. In the
near future, development of compact laser device will open the minimal invasive laser treatment to the dental clinic.
Conventional laser light sources for the treatment of a hard tissue in dental are good for removal of caries. However
these lasers cannot achieve to give a selective treatment effect for caries without a side effect for normal tissue. The
objective of this study is to develop the minimal invasive treatment technique of carious dentin by selective absorption
effect using the laser with a wavelength of 6.02 μm which corresponds to an absorption peak of organic matters called
amide 1 band. Mid-infrared nanosecond pulsed laser by difference-frequency generation was used for the experiment of
selective treatment. A tunable wavelength range, pulse width and repetition rate is from 5.5 to 10 μm, 5 ns and 10 Hz,
respectively. The laser with a wavelength of 6.02 μm and predetermined energy parameters was irradiated to a carious
dentin model. After laser irradiation, the surface and cross-sectional surface of samples were observed. Average power
density about 15 W/cm2 realized to excavate a demineralized region selectively. In the same energy condition, serious
side effect was not observed on the surface of normal dentin. A wavelength of 6.02 μm realizes a selective excavation of
carious dentin. Using 6.02 μm is a novel and promising technique toward to next-generation dental treatment procedure
for realizing minimal intervention.
Conventional laser light sources for the treatment of a hard tissue in dental (Er:YAG laser, Er,Cr:YSGG laser and CO2
laser etc.) are good for removal of caries. However these lasers cannot achieve to give a selective treatment effect for
caries without a side effect for normal tissue. The objective of this study is to develop the less-invasive treatment
technique of carious dentin by selective absorption effect using the laser with a wavelength of 6.02 μm which
corresponds to an absorption peak of organic matters called amide 1 band. Mid-infrared nanosecond pulsed laser by
difference-frequency generation was used for the experiment of selective treatment. A tunable wavelength range, pulse
width and repetition rate is from 5.5 to 10 μm, 5 ns and Hz, respectively. The laser with a wavelength of 6.02 μm and
predetermined energy parameters was irradiated to the plate of carious dentin model which is made by soaking in lactic
acid solution. After laser irradiation, the surface and
cross-sectional surface of samples were observed by a scanning
electron microscope (SEM). Average power density about 15 W/cm2 realized to excavate a demineralized region
(carious dentin model) selectively in a SEM observation. In the same energy condition, serious side effect was not
observed on the surface of normal dentin. A wavelength of 6.02 μm realizes a selective excavation of carious dentin.
Using 6.02 μm is a novel and promising technique toward to
next-generation dental treatment procedure for realizing MI.
Endoscopic submucosal dissection (ESD) is accepted as a minimally invasive treatment technique for small early gastric
cancers. Procedures are carried out using some specialized electrosurgical knifes with a submucosal injection solution.
However it is not widely used because its procedure is difficult. The objective of this study is to develop a novel ESD
method which is safe in principle and widely used by using laser techniques. In this study, we used CO2 lasers with a
wavelength of 10.6 μm for mucosal ablation. Two types of pulse, continuous wave and pulsed wave with a pulse width
of 110 ns, were studied to compare their values. Porcine stomach tissues were used as a sample. Aqueous solution of
sodium hyaluronate (MucoUpR) with 50 mg/ml sodium dihydrogenphosphate is injected to a submucosal layer. As a
result, ablation effect by CO2 laser irradiation was stopped because submucosal injection solution completely absorbed
CO2 laser energy in the invasive energy condition which perforates a muscle layer without submucosal injection
solution. Mucosal ablation by the combination of CO2 Laser and a submucosal injection solution is a feasible technique
for treating early gastric cancers safely because it provides a selective mucosal resection and less-invasive interaction to
muscle layer.
The clinical outcome of photodynamic therapy (PDT) may be improved by the accurate knowledge about the light
distribution within the tissue. Optical properties [absorption coefficient (μa), scattering coefficient (μs), anisotropy factor
(g), refractive index, etc.] of tissues help us realizing a light propagation through the tissue. The aim of this study is
acquisition of the knowledge of light propagation within tissue with the optical property of mouse tumor tissue
performed PDT. We evaluated the optical property of mouse tumor tissue before and after PDT using the double
integrating sphere setup and algorithms based on the inverse Monte Carlo method in the wavelength range from 350 to
1000 nm. During PDT, the reduced scattering coefficient spectra were decreased entirely after 5 and 10 min irradiation.
1, 2, 7 days after PDT, the absorption coefficient was increased in the wavelength range from 400 to 660 nm. And, the
reduced scattering coefficient at the wavelength of 664 nm was increased with the passage of time. These results are used
for medical diagnostic applications for the quantitative assessment of the PDT effect. 7 days after PDT, the reduced
scattering coefficient at the wavelength of 664 nm was increased significantly from 0.64 mm-1 to 1.24 mm-1, which
results in the optical penetration depth decreased from 1.49 mm to 0.84 mm, respectively. To ensure the effective
procedure, an adjustment of the laser parameter for the decreasing penetration depth is recommended for a second PDT.
XeCl excimer laser coronary angioplasty (ELCA), has gained more attention for the treatment of serious stenosis blocked by plaque. Low degrees of thermal damage after ablation of atherosclerotic plaques have been achieved by ELCA. However, the large number of risks associated with the procedure, for example, dissections or perforations of the coronary arteries limits its application. The laser treatment technique with high ablation efficiency but low arterial wall injury is desirable. Mid-infrared laser with a wavelength of 5.75 μm is selectively well absorbed in C=O stretching vibration mode of ester bonds in cholesteryl ester. We studied the effectiveness of nanosecond pulsed laser at 5.75 μm
for novel less-invasive laser angioplasty. In this study, we used a mid-infrared tunable solid-state laser which is operated by difference-frequency generation, at 5.75 μm, a pulse width of 5 ns and a pulse repetition rate of 10 Hz as a treatment
light source, and a thoracic aorta of WHHLMI rabbit as an atherosclerosis model. As a result, less-invasive treatment
parameters for removing atherosclerotic plaques in a wet condition were confirmed. This study shows that the nanosecond pulsed laser irradiation at 5.75 μm is a powerful tool for selective and less-invasive treatment of atherosclerotic plaques.
Laser angioplasty, for example XeCl excimer laser coronary angioplasty (ELCA), has gained more attention for the treatment of serious stenosis blocked by plaque. Low degrees of thermal damage after ablation of atherosclerotic plaques have been achieved by ELCA. However, the large number of risks associated with the procedure, for example, dissections or perforations of the coronary arteries limits its application. A laser treatment technique with high ablation efficiency but low arterial wall injury is desirable. Mid-infrared laser with a wavelength of 5.75 µm is selectively well absorbed in C=O stretching vibration mode of ester bonds in cholesteryl ester. The purpose of this study is to determine the effectiveness of nanosecond pulsed laser at 5.75 µm irradiation for atherosclerotic plaques. We made a study on the irradiation effect to atherosclerotic plaques in tunica intima in a wet condition. In this study, we used a mid-infrared tunable solid-state laser which is operated by difference-frequency generation, with a wavelength of 5.75 µm, a pulse width of 5 ns and a pulse duration of 10 Hz as a treatment light source, and a thoracic aorta of WHHLMI rabbit as an atherosclerosis model. As a result, less-invasive interaction parameters for removing atherosclerotic plaques were confirmed. This study shows that the nanosecond pulsed laser irradiation at 5.75 µm is a powerful tool for selective and less-invasive treatment of atherosclerotic plaques.
It is widely recognized for the realization of the pre-estimated treatment effects that the knowledge about the optical
properties of the target tissues used to understanding the prediction of propagation and distribution of light within tissues
would suffer from the technical problem such as the kinetic changes of the optical properties in laser irradiation. In this
study, the optical properties of normal and laser coagulated chicken breast tissues and porcine intervertebral disks,
normal and laser ablation have been determined in vitro in the spectral range between 350 and 1000 nm. In addition, the
optical properties of the normal and photodynamic therapy (PDT) treated tumor, Lewis lung carcinoma, tissues have
been determined. Diffuse reflectance and total transmittance of the samples are measured using an integrating-sphere
technique. From these experimental data, the absorption coefficients and the reduced scattering coefficients of the
samples are determined employing an inverse adding-doubling method. Laser coagulations and ablations have clearly
increased the reduced scattering coefficient and slightly reduced the absorption coefficient. PDT treatment has increased
absorption and reduced scattering coefficient. It is our expectation that these data will provide fundamental
understandings on laser irradiation interactions behavior with tissues. The changes of the optical properties should be
accounted for while planning the therapeutic procedure for the realization of safe laser treatments.
In laser medicine, the accurate knowledge about the optical properties of target tissue is important for the understanding
prediction of propagation and distribution of light in tissues. Light propagations, absorption and scattering, changes by
the kinetic changes of optical properties in laser irradiations. This problem is clinically very important for the realization
of safe laser treatments because the understandings of optical properties by several laser parameters can realize the pre-estimated
treatment effects. The objective of this study is determination of the optical properties of treated tissues for the
safe laser treatments. In this paper, we examined to determine the optical properties changes of a coagulated tissue after
the Er:YAG laser irradiations by using double integrating sphere system and inverse adding-doubling method in the
wavelength range of 350 - 1000 nm. After laser irradiations with a variety of irradiation parameters, the absorption
coefficient of a treated tissue decreased and the reduced scattering coefficient of a treated tissue increase. In
carbonization, observed in 30 sec-300 mJ irradiation, the absorption coefficient of a treated tissue re-increased and the
reduced scattering coefficient of a treated tissue re-decrease. The changes of optical properties should be accounted for
while planning the therapeutic procedure for the realization of safe laser treatments.
We conducted fundamental research on a novel lithotripsy technique using mid-infrared pulsed lasers. We irradiated
gallstones extracted from the common bile duct using two mid-infrared lasers, namely, a difference-frequency generation
(DFG) laser tunable within a wavelength range of 5.5-10 μm and an Er:YAG laser with a 2.94 μm wavelength, and then
examined the depth and dimension of the crater formed. Some of the gallstones were continuously wet with distilled
water during laser irradiation. The absorption spectrum of the gallstones was measured using a Fourier transform
infrared spectrometer. The gallstones showed a strong peak around the wavelengths of 2.94 and 6.83 μm. In the case of
DFG laser irradiation, the wavelength used was 6.83 μm and the average power density range of the laser was about
2-52 W/cm2. After irradiation, a relatively small hole with a depth range of 0.1-0.2 mm and a dimension within 0.01-0.04
mm2 was created. On the other hand, in the case of Er:YAG laser irradiation, the average power density range was about
0.20-0.78 kW/cm2. As the result, a large hole was made and the mass of 0.4-1.6 mg was removed. In conclusion, wet
gallstones were more decomposed than dry gallstones in both cases of laser irradiation, and these techniques proved to
be effective for gallstone lithotripsy.
Laser angioplasty, for example XeCl excimer laser angioplasty, has gained more attention in addition to conventional
methods of surgical and interventional treatment of atherosclerotic diseases such as bypass operation and balloon
dilatation. Low degrees of thermal damage after ablation of atherosclerotic lesions have been achieved by XeCl excimer
laser at 308 nm. However, in most cases, laser ablation is not selective and normal arterial wall is also damaged. To
avoid complications such as severe dissections or perforation of the arterial wall in an angioplasty, a laser light source
with high ablation efficiency but low arterial wall injury is desirable. At atherosclerotic lesions, cholesterol accumulates
on the tunica intima by establishing an ester bond with fatty acids such as oleic acid, and thus cholesterol ester is the
main component of atherosclerotic plaques. Mid-infrared pulsed laser at 5.75 μm is selectively well absorbed in C=O
stretching vibration mode of ester bonds. The purpose of this study is to determine the effectiveness of nanosecond
pulsed laser at 5.75 μm irradiation of cholesterol ester in atherosclerotic plaques. In this study, we used a mid-infrared
tunable solid-state laser which is operated by difference frequency generation method, with a wavelength of 5.75 μm, a
pulse width of 5 nsec and a pulse duration of 10 Hz. It was confirmed that non-invasive interaction to normal thoracic
aortas could be induce by the parameters, the wavelength of 5.75 μm, the average power densities of 35 W/cm2 and the
irradiation time under 10 sec. This study shows that nanosecond pulsed laser irradiations at 5.75 μm provide an
alternative laser light source as an effectively cutting, less traumatic tool for removal of atherosclerotic plaque.
Tissue specific progenitor cells and its differentiations have got a lot of attentions in regenerative medicine. The process of
differentiations, the formation of tissues, has become better understood by the study using a lot of cell types progressively.
These studies of cells and tissue dynamics at molecular levels are carried out through various approaches like histochemical
methods, application of molecular biology and immunology. However, in case of using regenerative sources (cells, tissues
and biomaterials etc.) clinically, they are measured and quality-controlled by non-contact and non-destructive methods
from the view point of safety. Or the analysis with small quantities of materials could be possible if the quantities of
materials are acceptable. A non-contact and non-destructive quality control method has been required. Recently, the use of
Fourier Transform Infrared spectroscopy (FT-IR) has been used to monitor biochemical changes in cells, and has gained
considerable importance. The changes in the cells and tissues, which are subtle and often not obvious in the
histpathological studies, are shown to be well resolved using FT-IR. Moreover, although most techniques designed to
detect one or a few changes, FT-IR is possible to identify the changes in the levels of various cellular biochemicals
simultaneously under in vivo and in vitro conditions. The objective of this study is to establish the infrared spectroscopy of
tissue specific progenitor cell differentiations as a quality control of cell sources for regenerative medicine. In the present
study, as a basic study, we examine the adipose differentiation kinetics of preadipose cells (3T3-L1) and the osteoblast
differentiation kinetics of mesenchymal stem cells (Kusa-A1) to analyze the infrared absorption spectra.
Tendon and ligament are the transition tissues from a hard tissue to a soft tissue. The regenerative medicine of tendons needs reasonable biomaterials to regenerate precisely from the view point of composition and adhesion properties. In regenerative medicine of hard tissues, it has been reported that calcifications are influenced by phosphorylated proteins (phosphate groups) and the biomaterial possessing phosphate groups promote or inhibit the formation of HAP. We have studied to develop and evaluate the phosphorylated soft biomaterials, which is possible to control a calcification by the introduction ratio of phosphate groups, as biomaterials for tendon regeneration. In addition, we have studied measurement technologies. In the present study, we studied a FT-IR analysis of gelatins with different introduction ratio of phosphate groups, an evaluation of calcifications by the difference of introduction ratio of phosphate groups, and a fundamental survey on OCT imaging for calcifications of a gelatin and a phosphorylated gelatin. We use phosphorylated gelatins with different introduction ratios of phosphate group linked by ester bonds. The introduction ratios are measured by the FT-IR calibrated by a molybdenum blue method. Phosphorylated gelatin sheets were calcified using 1.5SBF soaking process and alternative soaking process. These gelatin sheets with different calcification conditions were measured using SD-OCT systems with 843nm centered wavelength SLD. As a result, we demonstrated that it was possible to measure the calcification on/in the gelatin sheets and sponges and phosphorylated using OCT. The main mechanism is the strong back scattering and the high scattering of deposited calcium particles.
Stem cells and its differentiations have got a lot of attentions in regenerative medicine. The process of differentiations, the formation of tissues, has become better understood by the study using a lot of cell types progressively. These studies of cells and tissue dynamics at molecular levels are carried out through various approaches like histochemical methods, application of molecular biology and immunology. However, in case of using regenerative sources (cells, tissues and biomaterials etc.) clinically, they are measured and quality-controlled by non-invasive methods from the view point of safety. Recently, the use of Fourier Transform Infrared spectroscopy (FT-IR) has been used to monitor biochemical changes in cells, and has gained considerable importance. The objective of this study is to establish the infrared spectroscopy of cell differentiation as a quality control of cell sources for regenerative medicine. In the present study, as a basic study, we examined the adipose differentiation kinetics of preadipocyte (3T3-L1) and the osteoblast differentiation kinetics of bone marrow mesenchymal stem cells (Kusa-A1) to analyze the infrared absorption spectra. As a result, we achieved to analyze the adipose differentiation kinetics using the infrared absorption peak at 1739 cm-1 derived from ester bonds of triglyceride and osteoblast differentiation kinetics using the infrared absorption peak at 1030 cm-1 derived from phosphate groups of calcium phosphate.
Phosphorylation and dephosphorylation are considered to be important reactions that control the active and inactive factors of proteins. In regenerative medicine of the osteoconnective tissue (a tendon, a ligament), it has been reported that the biomaterial possessing phosphate groups promote formation of HAP, the main component of hard tissues. The noncontact measurement of phosphate groups and low-destructive controlling of phosphate groups allow for the accurate regeneration of the osteoconnective tissue, and the validation. Our objective is to propose the nondestructive controlling and measuring method of phosphorylation for regenerative medicine. In this study, as the indirect quantitative analysis of phosphate groups, we examine the correlation between the mid-infrared absorbance ratio and the ratio of phosphate groups introduction theoretically calculated from a colorimetric determination method. And the noncontact controlling method of the quantities of phosphate groups, we examine the selective and low-destructive bond cutting of phosphate groups in the phosphogelatin using a mid-infrared laser.
A new type of cell-cultivation system based on laser processing has been developed for the on-chip cultivation of living cells. We introduce a "laser cell-chip", on which migration of cells, such as stem cells, tumor cells or immunocompetent cells, can be observed. A sheet prepared from epoxy resin was processed by KrF excimer laser (248 nm, 1.6 J/cm2) for preparation of microgrooved surfaces with various groove width, spacing, and depth. A laser cell-chip can make kinetic studies of cell migration depending on the concentration gradient of a chemoattractant. In this study, megakaryocytes were used for the migration on a groove of laser cell-chip by the concentration gradient of the stromal cell derived factor 1 (SDF-1/CXCL12). SDF-1/CXCL12 plays an important and unique role in the regulation of stem/progenitor cell trafficking. A megakaryocyte was migrated on a groove of laser cell-chip depending on the optical concentration gradient of SDF-1/CXCL12. Since SDF-1/CXCL12-induced migration of mature megakaryocyte was known to increase the platelet production in the bone marrow extravascular space, the diagnosis of cell migration on laser cell-chip could
provide a new strategy to potentially reconstitute hematopoiesis and avoid life-threatening hemorrhage after myelosuppression or bone marrow failure.
A cholesterol ester is selective dissociated by MIR-FEL irradiation with wavelength of 5.75 μm correspond to C=O stretching vibration of ester bond. To evaluate the optimum irradiation condition for cholesterol ester decomposition without normal endothelium cell damage, we perform a 5.75 μm-FEL irradiation to a two-layer vessel model which is cholesterol oleate as a model of atherosclerotic lesions and gelatin as a model of endothelial cells. The ester decomposition and gelatin damege depends on total power density of 5.75 μm-FEL provided the two-layer model. Exposure of the FEL with power density exceed 17.8 W/cm2 decomposed cholesterol ester thorough gelain layer of 15 μm thickness. If FEL with power density of 25.0 W/cm2 is exposed during 10 seconds, the gelatin is evaporized. Therefore, the optimum condition for ester decomposition without gelatin evaporation is between 75 J/cm2 from 20 J/cm2 in the case of 15 μm gelatin layer thickness. The maximum ester decomposition rate without gelatin vaporization is 71% on FEL of power density of 17.8 W/cm2 for 10 seconds.
Phosphorylation and dephosphorylation, which are the most remarkable posttranslational modifications, are considered to be important chemical reactions that control the activation of proteins. In regenerative medicine, it has been reported that phosphorylated proteins are instrumental in the calcification of osteoconnective tissue. We examine the phosphorylation analysis method by measuring the infrared absorption peak of phosphate group that observed at about 1070 cm-1 (9.4 mm) with Fourier Transform Infrared Spectrometer (FT-IR). This result indicates that it is possible to identify a phosphorylation by measuring the infrared absorption peak of phosphate group observed at about 1070 cm-1 with FT-IR method. And we examine laser-dephosphorylation using Free Electron Laser (FEL) as a novel dephosphorylation method. After irradiation of 9.4mm-FEL, infrared absorption peak of phosphate group is reduced. It is suspected that this lowering of the peak of phosphate group is the effect like dephosphorylation. These novel methods can be applied to quality control technology in regenerative medicine.
Phosphorylation and dephosphorylation, which are the most remarkable posttranslational modifications, are considered to be important chemical reactions that control the activation of proteins. We examine the phosphorylation analysis method by measuring the infrared absorption peak of phosphate group that observed at about 1070cm-1 (9.4μm) with Fourier Transform Infrared Spectrometer (FT-IR). This study indicates that it is possible to identify a phosphorylation by measuring the infrared absorption peak of phosphate group observed at about 1070 cm-1 with FT-IR method. As long as target peptides have the same amino acid sequence, it is possible to identify the phosphorylated sites (threonine, serine and tyrosine).
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