signs of hemoglobin in low power cw- laser induced human ... · signs of hemoglobin in low power...
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Signs of hemoglobin in low power cw-laser induced human skin detected by diffuse reflectance spectroscopy and
multi-spectral imaging
Janis Lesins, Inesa Ferulova, Dainis Jakovels,
Alexey Lihachev, Janis Spigulis
Institute of Atomic Physics and Spectroscopy
University of Latvia, Riga, Latvia
This work has been supported by the European Social Fund
within the projects
«Support for Doctoral Studies at University of Latvia» and
No. 2009.0211/1DP/1.1.1.1.2.0/09/APIA/VIAA/077
Laser-skin interactions
• Laser induced skin autofluorescence photobleaching on focus
• This study:
o 405nm, 473nm, 532nm lasers
o Multi-spectral imaging (non-contact method)
o Single spot spectrometry (contact method)
o Power densities on skin 20 ÷ 120 mW/cm2
• Signatures of low power laser irradiation?
Skin surface
405 nm laser
473 nm laser
Laptops
Optical
fiber
𝜆1 𝜆2
𝜆3 𝜆4
𝜆, nm Pix
el (
x,y
) in
tensi
ty
Spectra
at pixel (x,y)
Pixel (x,y)
Hologen lamp
Multi-spectral imaging setup
Single Spot Spectrometry Setup • Spectral registration method
Laser
Probe
Y-shaped
optical fiber
bundle
SMA connectors
PC
Spectrometer
Skin
Filters
Light source
Skin autofluorescence photobleaching effects during cw laser excitation
5
𝐼𝜆=𝑐𝑜𝑛𝑠𝑡 = 𝑓(𝐼𝑜, 𝑡)
405 nm laser excitation (3 min)
𝐼 = 𝑓(𝜆, 𝑡)
Inte
nsi
ty
Wavelength
Laser excitation
Autofluorescence spectrum
t = 0
t = 3min
It=0 > It=3min
𝐼𝑡=𝑐𝑜𝑛𝑠𝑡 = 𝑓(𝐼𝑜, 𝜆)
Flu
ore
scen
ce I
nte
nsi
ty
Time, s
0
5
10
15
20
470 520 570 620 670 720
AF
In
ten
sity
(re
l.u
.)
Wavelength (nm)
3 min 405 nm
3 min 532 nm
AF intensity after 3 min
Initial AF intensity
Skin autofluorescence photo-bleaching effects
6
),( oconstt IfI
Impact of 3 min irradiation: 473nm-excited skin AF
0 120 240 360 480 600
0,6
0,8
1,0
Flu
ores
cenc
e in
tens
ity, r
el.u
.
Time, s
1- 680 nm
2- 600 nm
1
2
Skin photo-memory
7
Skin «photo-memory» - photo-induced irreversible processes in skin
),( tIfI oconst
Skin AF intensity recovery after low-power
532 nm laser irradiation (at 600nm ~ max)
0 25 50 75 100 1250
20
40
60
80
100
Rec
ov
ery
of
AF
in
ten
sity
(%
)
Time (Hours)
Relative optical density
9
500 550 600 650 700 750
0.00
0.05
0.10
0.15
0.20
Op
tica
l den
sity
Wavelength, nm
130 mW/cm2
115 mW/cm2
90 mW/cm2
532 nma)
500 550 600 650 700 750
0.00
0.05
0.10
0.15
0.20
Op
tica
l d
en
sity
Wavelength, nm
100 mW/cm2
45 mW/cm2
20 mW/cm2
473 nmb)
500 550 600 650 700 750
0.00
0.05
0.10
0.15
0.20
Op
tica
l den
sity
Wavelength, nm
70 mW/cm2
40 mW/cm2
20 mW/cm2
405 nmc)
532 nm
473 nm
405 nm
MSI results (optical density)
10
500 550 600 650 700 750
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Op
tica
l d
en
sity
Wavelength, nm
Irradiated skin
Not irradiated skin
473 nm473 nm
500 550 600 650 700 750
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Op
tica
l den
sity
Wavelength, nm
Irradiated skin
Not irradiated skin
405 nm405 nm
Hemoglobin absorption
• Hemoglobin absorption impact during and after
laser-irradiation
• Local skin heating – blood volume changes
• Arterial occlusion – blood flow after release
• Recovery after photobleaching:
o skin autofluorescence at the laser-irradiated spot
o diffuse reflectance spectra
Photobleaching Mechanisms
• Direct degradation of specific fluorophores (?)
• Changes in absorption properties, quenching (?)
• Photo-induced increase/generation of chromophores
(like UV-enhanced melanin) (?)
Conclusions
• Visible laser-excitated skin autofluorescence (AF) photo-
bleaching takes place even at irradiation power
densities well below the laser-skin safety limits
• Mechanism of skin AF photo-bleaching still under study;
seems like microcirculation is involved
• Future work will involve combined experiments of diffuse
reflectance, fluorescence emission spectrum and
fluorescence lifetime data.
• Interesting enough to continue ...
Thank you for your attention!
14
Institute of Atomic Physics and Spectroscopy
Riga, Latvia
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