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Comparison of wavelength-dependent penetration depths of lasers in different types of skin in photodynamic therapy

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The determination of the penetration depth of laser light with different sources wavelengths into human skin is one of the preconditions of improving the photodynamic therapy (PDT) procedure for skin diseases. This research is planned to explore which wavelengths would be the most advantageous for use in PDT for superficial skin diseases, and to demonstrate that the red laser exposure of 635 nm wavelength is a suitable choice for all skin types in PDT. A realistic skin model (RSM) in the Advanced Systems Analysis Program (ASAP) software has been used to create different types of skin and to simulate laser sources with wavelengths of 635, 532, 405, 365, 308 and 295 nm. The penetration depths of different kinds of laser into the skin as well as their transmission have been calculated. Comparison of the depth of penetration of different wavelengths for all types of skin has been made. A large variation is found in the penetration depth of laser lights in all skin types. The transmission of lasers on the epidermis and dermis in different skin types occur, and the transmission dose changes significantly with the skin depths. The results of the present study provide a basis for understanding the penetration depth of laser in various skin colors and the responses of the skin to laser to improve dose–drug activation in PDT. The differences in spectral transmission between the red laser and the other lasers suggest that the red laser could be a suitable laser for all skin types.
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ORIGINAL PAPER
Comparison of wavelength-dependent penetration depths of lasers
in different types of skin in photodynamic therapy
F H Mustafa
1
* and M S Jaafar
2
1
Medical Physics, College of Pharmacy, Hawler Medical University, 44001 Erbil, Erbil, Iraq-Kurdistan
2
Medical Laser Research Group, School of Physics, Universiti Sains Malaysia, 11800 Georgetown, Penang, Malaysia
Received: 29 August 2012 / Accepted: 19 October 2012 / Published online: 20 November 2012
Abstract: The determination of the penetration depth of laser light with different sources wavelengths into human skin is
one of the preconditions of improving the photodynamic therapy (PDT) procedure for skin diseases. This research is
planned to explore which wavelengths would be the most advantageous for use in PDT for superficial skin diseases, and to
demonstrate that the red laser exposure of 635 nm wavelength is a suitable choice for all skin types in PDT. A realistic skin
model (RSM) in the Advanced Systems Analysis Program (ASAP) software has been used to create different types of skin
and to simulate laser sources with wavelengths of 635, 532, 405, 365, 308 and 295 nm. The penetration depths of different
kinds of laser into the skin as well as their transmission have been calculated. Comparison of the depth of penetration of
different wavelengths for all types of skin has been made. A large variation is found in the penetration depth of laser lights
in all skin types. The transmission of lasers on the epidermis and dermis in different skin types occur, and the transmission
dose changes significantly with the skin depths. The results of the present study provide a basis for understanding the
penetration depth of laser in various skin colors and the responses of the skin to laser to improve dose–drug activation in
PDT. The differences in spectral transmission between the red laser and the other lasers suggest that the red laser could be a
suitable laser for all skin types.
Keywords: Simulation; Laser skin interaction; Propagation and skin optics
PACS No.: 87.50.wp
1. Introduction
Photodynamic therapy (PDT) combines a photosensitizer
with a specific type of light source, e.g. a laser, to kill
malignant or non-malignant cells [1]. Skin is a main target
organ for medical application by lasers such as PDT
(Basset-Seguin, 2010). This is due to the fact that skin
covers all the body, and it is the organ most exposed to the
environment. So, many problems in skin have been found.
The ability to predict the light dose delivery into the skin of
various tissue chromophores in living tissue by the means
of optical methods provides advantages in many different
applications in photomedicine [2]. Thus, the simulation
study in the medical physics department could be very
useful for determination of penetration depth and
transmission of light [3,4]. Therefore, more research need
to be done to clarify the skin types role as a fundamental
factor on minimizing laser dose. Many different types of
light sources have been shown to be effective for use in
PDT. A wide range of light doses has been used, but very
little information is available on dosimetry methods
employed in skin. Laser dose to the photodynamic dose
activation is related, for skin diseases, and it is a funda-
mental element in PDT [5]. The process of laser absorption
in the skin during laser irradiation was a critical point for
this application [6]. Investigation on the role of human skin
properties on light dose delivery in PDT is still in its early
stage. There exist a variation of light dose delivery, due to
absorption, scattering and reflection of photons in layers of
skin. The correct amount of laser light delivery is a critical
element [7]. The non uniform dose of an amount of light
makes a problem to enhance photodynamic dose procedure
in skin, and able to affect photodynamic activation [8,9].
*Corresponding author, E-mail: science_farhad@yahoo.com
Indian J Phys (March 2013) 87(3):203–209
DOI 10.1007/s12648-012-0213-0
Ó2012 IACS
Additionally, more amounts of laser light able to affect
tissues in the skin and makes an adverse effect of the skin
[10]. Resolving this issue becomes easier by taking account
a comparison for various sources that were used previously
and consideration laser skin interaction at various human
skin properties, for different sources in PDT. In this paper,
UV and visible laser is proposed for human skin therapy in
order to find the safest and efficient wavelength. Further-
more, the present study examined six sources of laser in
different wavelengths to observe the effect of skin tone on
penetration depth and transmission.
2. Experimental details
The realistic skin model (RSM) of the ASAP software was
used to simulate different skin types. The skin model used
has three simplified layers, namely, the stratum corneum,
epidermis and dermis as shown in Fig. 1, in a 20 mm
2
sur-
face area of the skin. Five types of human skin, i.e., very fair,
fair, light, medium and dark were used to investigate the
effect of typical chromophores, such as melanosomes and
melanin, on the absorption, i.e., the penetration depth of the
laser. To simulate various skin types, the volume fraction of
the melanosomes in the epidermis was changed. In the
present study, the volume fraction of melanosomes was set at
0.026, 0.0505, 0.086, 0.13 and 0.31 for very fair, fair, light,
medium, and dark skin respectively. The data library of the
ASAP software was used to simulate the skin layers. Table 1
shows detailed descriptions of the parameters input as the
chromophore concentrations for skin layers.
To determine the effects of laser wavelengths and skin
colour on the laser penetration depth into human skin, optical
simulations in normal human skin were performed. For each
type of human skin, tests of each source with different laser
wavelength were conducted to determine the source fluence
rate and laser transmission. The laser source was placed
perpendicular to the surface of skin layers. Each skin model
was exposed to 6 different sources of UV lasers (295, 308
and 365 nm), diode laser (405 and 635 nm) and laser-diode
pumped solid-state green laser (532 nm) with 5 mW of
power and a laser beam diameter of 1.6 mm as shown in
Fig. 1. The power injection, the angle of directing beam and
beam diameter were same for all sources.
The light detector contains voxel elements to detect the
fluence rate of photons, which were launched within the
skin when the voxel faces a laser with a certain amount of
power. The 1,000,000 rays entering the sample were traced
and propagated in slices. Layers of the sample with the
z-direction were divided in 150 layers, and each layer
consisted of a set of voxels.
Where nis refractive index of skin layers, gis an iso-
tropic factor, dis the thickness, V
fw
is the volume fraction
of water, C
bc
is the beta carotene concentrations, C
ph
is the
pheomelanin concentrations, C
eu
is the eumelanin con-
centrations, C
hb
is the concentration of hemoglobin in
blood, V
fox
is the volume fraction of oxyhemoglobin and
V
fb
is the volume fraction of blood in d.
3. Results and discussion
Figure 2shows fluence rate spectra of two ranges; UV and
Visible wavelength and several types of skin. There are
significant differences between the UV and Visible lasers
in each types of skin used. The results suggested that the
diode laser at 635 nm was the most effective in reaching
fluence rate amongst all the wavelengths laser. In the
present study, the effects of UV lasers of three different
wavelengths on various human skin types were investi-
gated. We obtained the fluence rate of different kinds of
laser into the skin as well as their transmission. A large
variation was found in the fluence rate of lasers in all skin
Fig. 1 Basic structure of human skin in various skin colours and the
corresponding three layers of the stratum corneum, epidermis, and
dermis layer, of six different laser wavelengths: (a) UVB laser of 295
and 308 nm, (b) UVA laser of 365 nm wavelength, (c)blue laser of
405 nm wavelength, (d)green laser of 532 nm wavelength, and
(e)red laser of 635 nm
Table 1 Setting of optical properties of the different skin layers; stratum corneum, epidermis and dermis
Layer of skin ng d (mm) V
fw
C
bc
(g/L) C
eu
(g/L) C
ph
(g/L) C
hb
(g/L) V
fox
V
fb
Stratum corneum 1.55 0.9 0.01 0.13 0.00021 – – – –
Epidermis 1.5 0.79 0.08 0.67 0.00021 80 12
Dermis 1.8 0.82 1.8 0.8 0.00007 150 0.75 0.01
204 F H Mustafa and M S Jaafar
00.1 0.2 0.3 0.4 0.5 0.6 0.7
0
500
1000
1500
2000
2500
Skin depth (z) mm
Fluence rate mW . mm -3
635 nm
Exponential fiting
532 nm
Exponential fiting
405 nm
Exponential fiting
365 nm
Exponential fiting
308 nm
Exponential fiting
295 nm
Exponential fiting
(a)
Very fair skin
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0
500
1000
1500
2000
2500
Skin depth (z) mm
Fluence rate mW . mm -3
635 nm
Exponential fiting
532 nm
Exponential fiting
405 nm
Exponential fiting
356 nm
Exponential fiting
308 nm
Exponential fiting
295 nm
Exponential fiting
(b)
Fair skin
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0
500
1000
1500
2000
2500
Skin depth (z) mm
Fluence rate mW . mm -3
635 nm
Exponential fiting
532 nm
Exponential fiting
405 nm
Exponential fiting
365 nm
Exponential fiting
308 nm
Exponential fiting
295 nm
Exponential fiting
(c)
Light skin
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0
500
1000
1500
2000
2500
3000
Skin depth (z) mm
Fluence rate mW . mm
-3
635 nm
Exponential fit
532 nm
Exponential fit
405 nm
Exponential fit
365 nm
Exponential fit
308 nm
Exponential fit
295 nm
Exponential fit
(d)
Medium skin
00.1 0.2 0.3 0.4 0.5 0.6 0.7
0
500
1000
1500
2000
Skin depth (z) mm
Fluence rate mW .mm
-3
635 nm
Exponential fit
532 nm
Exponential fit
405 nm
Exponential fit
365 nm
Exponential fit
308 nm
Exponential fit
295 nm
Exponential fit
(e)
Dark skin
Fig. 2 Different fluence rates of lasers in various wavelengths as a function of skin depth for (a) very fair, (b) fair, (c) light, (d) medium and
(e) dark skin
Comparison of wavelength-dependent penetration depths 205
types. We can see that the comparative fluence rate of laser
of 365 nm wavelength correlates with the absorption of
skin colour. However, at 295 and 308 nm this correlation
disappears.
Figure 2demonstrates the simulated result of the fluence
rate and skin depth of all laser wavelengths on very fair,
fair, light, medium and dark skin types. Relationships for
all curves are exponential, and large variations between the
curves can be seen. The figures clearly show that the darker
skin type leads to larger power absorption. This occurrence
applies to all laser wavelengths. There is also a reasonable
correlation between 635 nm and all skin types, due to less
losses of laser delivery with the biology of tissue as com-
pared with the other source. However, a decrease in laser
dose delivery was found with the blue and green laser in all
skin types. A significant change on laser dose delivery was
found in medium and dark skin types. In very fair and fair
skin types, there was a slight change caused by the small
volume of melanosomes found. Thus, a significant asso-
ciation between the irradiation and skin types was obtained
for different wavelengths of laser.
The amount of the dose of light increases or decreases
observed in skin strongly correlates with the laser wave-
length and skin colour, as presented in the figures and
results. Based on these biological responses, we anticipated
the improvement of the irradiation of the photosensitizer
enhancement as well as the fluence rates in PDT. When
comparing the efficiency of penetration into skin of lasers;
red, green, and blue as seen in findings, it is noted that the
cases were not directly equivalent. The different tissue
depths and associated amounts of laser fluence rates indi-
cate that the overall form of the photodynamic activation
processes can vary with all laser wavelengths. For PDT to
be effective there must be an adequate dose of both pho-
tosensitizer and light to produce a phototoxic reaction [11].
The fluence rate difference among the six curves in skin
types in Fig. 2is due to the wavelength dependence of the
skin. Changing the sources from 405 to 635 nm led to a
huge increase in the photon transmission of the skin sur-
face. As presented in the curves of Fig. 2, a wavelength of
405 nm is not useful for targeting a 0.1 mm-thick skin for
darker skin types, such as medium and dark. At 635 nm,
the fluence rate efficacy at 0.1 mm depth is about 9–10
times greater than that in the blue laser. However, with
lighter skin, such as very fair and fair, the fluence rate
efficacy at 635 nm is about 3–4 times greater than the
405 nm. Thus, both sources for lighter skin are useful for
targeting 0.1 mm-thick skin. As a result, the wavelength
hardly influences the response of the skin depths in the
PDT procedure. UV lasers and blue and green lasers in
visible regions could not be used for more depths because
of the large absorptions of the chromophores. Moreover,
compared with the UV, blue and green lasers as mentioned
above, are noted that the red lasers are normally more user
friendly. Their characteristics make red lasers well suited
for the treatment of accessible.
Figure 3shows the calculated amount of transmission
curves in the six sources with varying skin depths for all
skin types. It was obtained by equation below:
T¼/=/o100 %ð1Þ
where Tis the percentage transmission (Transmittance), /
is the total fluence rate through the skin of thickness z, and
/is the incident fluence rate on the volume of the skin
surface.
A comparison of the transmission spectrum of the dif-
ferent laser wavelengths is exhibited for visible lasers, and
there is a big difference in the spectrum shape depending
on the skin types, as noted in curves. The figures illustrate
that the transmissions–skin depth curve is exponential. The
average transmission value of each laser is found for all
skin types and shows the comparison between the amounts
of transmission. We calculated the average transmission
ratio of the red laser to the blue and the green lasers. The
amount of transmission obtained at an average depth can
vary up to a factor of 3.5–9 from lighter skin to darker skin
based on the ratio between the red and the blue laser.
However, variations of the ratio of the amount of average
transmission of red laser to green laser at an average skin
depth can vary by a factor of 1.2–2.5. Thus, optical
transmittance depends on the skin type, as seen in Fig. 3,
where the very fair skin shows the highest transmittance of
light for all sources of laser. Conversely, dark skin has the
lowest transmittance.
Comparison of the transmission ratio of UV and visible
lasers in different wavelengths for all types of skin is
studied. A large variation is found in the transmission ratio
of laser in two types of skin, as illustrated in Table 2.
Irradiations by several laser wavelengths have been studied
within the range of 308, 295 and 365 nm, to show the
ability of short-wavelength radiations, and to show the
power uptake effect in chromophore cell in human skin.
The transmission light for very fair skin was 2, 9 and 33 %
with 295, 308 and 365 nm, respectively at a skin depth
0.08 mm, and 0, 1 and 1.4 % for dark skin. The trans-
mission of lasers on the epidermis and dermis in different
skin types occurred, and the transmission dose changed
significantly with the skin depths. The transmission of light
into the skin was 55, 85, and 93 % with 405, 532 and
635 nm respectively, at a skin depth of 0.08 mm in the
very fair skin type. However, in the dark skin type, with the
same depth and sources of laser, the transmission of blue,
green, and red lasers photons into the skin was 2.5, 10 and
29 % respectively. As such, the red laser at 635 nm is the
most effective in promoting drug activating among all the
wavelengths used. Moreover, the dark skin type may have
206 F H Mustafa and M S Jaafar
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
10
20
30
40
50
60
70
80
90
100
Skin depth (z) mm
Skin depth (z) mm
Transmission (T) %
635 nm
532 nm
405 nm
365 nm
308 nm
295 nm
(a) Very fair skin
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
10
20
30
40
50
60
70
80
90
100
Transmission (T) %
635 nm
532 nm
405 nm
365 nm
308 nm
295 nm
(b) Fair skin
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
10
20
30
40
50
60
70
80
90
100
Skin depth (z) mm
Transmission (T) %
635 nm
532 nm
405 nm
365 nm
308 nm
295 nm
(c) Light skin
00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
10
20
30
40
50
60
70
80
90
100
Skin depth (z) mm
Transmission ( T ) %
635 nm
532 nm
405 nm
365 nm
308 nm
295 nm
(d) Medium skin
00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
10
20
30
40
50
60
70
80
90
100
Skin depth (z) mm
Transmission ( T ) %
635 nm
532 nm
405 nm
365 nm
308 nm
295 nm
(e) Dark skin
Fig. 3 Variation in laser transmission in various wavelengths for skin types (a) very fair, (b) fair, (c) light, (d) medium and (e) dark skin
Comparison of wavelength-dependent penetration depths 207
a minimal amount of transmission for sources of laser
compared with the other skin types. However, the very fair
skin obtains a maximal amount of transmission of light.
Furthermore, the most efficient laser for all skin types is the
red laser, whereas blue and UV laser is the least efficient.
This behavior corresponds mainly to the optical absorption
spectrum of melanosomes contained in these skins. The
different volumes of melanosomes and the optical charac-
teristics of each sample gives different rates of fluence as a
results.
The power relationship between the transmission ratio
of lasers and wavelength for all skin types are illustrated in
Fig. 4. The correlation factor is 0.988–0.99. One of the
most useful quantitative parameters for characterizing
absorption spectra is the transmission ratio, (Fig. 4) which
depends of the ability of a chromophore to absorb light as
well as the lasers wavelength. The transmission ratio is
useful for predicting amount of light that reached into the
skin. Comparisons data on laser transmission ratio as a
function of wavelengths in epidermis and dermis layer are
demonstrated in Fig. 4(a) and (b). However, the difference
in results between the laser transmission with UV and
visible wavelengths in epidermis layer and dermis layer
was highly significant. Two different areas could be cal-
culated, one with the epidermis at z=0.02 mm and the
other one with the dermis layer at z=0.2 mm. From the
result in both layers with the visible laser wavelength show
a big difference in transmission for the skin types, whereas
the results with the UV laser was a little variation.
Figure 5shows the penetration depth versus wave-
lengths of laser for various skin types. As the wavelength
increases its penetration depths, and the transmission of
light into the skin increases as well [12]. Therefore, the
penetration depth into the skin is strongly dependent on
wavelength. Few changes were observed in the spectral
shape of dark skin by changing the laser wavelength,
especially in the region between the blue and green
wavelengths. There was a big variation of the penetration
depth of the other skin types with the increase in laser
wavelength of all sources, especially red laser. In addition,
the penetration depth for the red laser in very fair skin
(&0.5 mm) was almost 7 times greater than the penetration
depth in dark skin (&0.07 mm). Therefore, most amounts
Table 2 Comparison of laser transmission ratio at different wave-
length for two types of skin at skin depth z=0.08 mm
Skin
types
Laser transmission ratio (T) %
295 nm 308 nm 365 nm 405 nm 532 nm 635 nm
Very
fair
2 9 33 55 85 93
Dark 0 1 1.4 2.5 10 29
300 350 400 450 500 550 600
10
20
30
40
50
60
70
80
90
100
Laser wavelength (
λ
) nm
Laser wavelength (
λ
) nm
Transmission ration ( T ) %
Very fair
Power fit
Fair
Power fit
Light
Power fit
Medium
Power fit
Dark
Power fit
(a) at epidermis layer z=0.05 mm
UV Lasers Visible Lasers
300 350 400 450 500 550 600
0
10
20
30
40
50
60
70
80
90
100
Transmission ratio ( T ) %
Very fair
Power fit
Fair
Power fit
Light
Power fit
Medium
Power fit
Dark
Power fit
(b) at dermis layer z=0.2 mm
UV Lasers Visible Lasers
Fig. 4 Relationship between the ratio of laser transmission and
wavelength for every type of skin colour, in two layers of skin
(a) epidermis at z=0.02 mm and (b) dermis at z=0.2 mm
300 350 400 450 500 550 600
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
Laser wavelength (
λ
) nm
Penetration depth (
δ
) mm
Very fair
Cubic fit
Fair
Cubic fit
Light
Cubic fit
Medium
Cubic fit
Dark
Cubic fit
Fig. 5 Relationship between the penetration depth and lasers wave-
length, for various skin types
208 F H Mustafa and M S Jaafar
of light were minimized and also there is variation for skin
types, because of the differences in melanosome volume,
which could also indicate why the recorded absorption is
lower in lighter skin than in darker skin. Thus, the maxi-
mum amount of light that reached the target decreased with
depth. In addition, it was a good opportunity to select the
optimum wavelength in PDT.
As wavelength increases, the scattering power goes
down, and the absorption power varies with wavelength
depending on the composition. However, for sources with
UV wavelength, the penetration depth tends to increase
slightly. But, for lasers with visible wavelength, the pen-
etration depth will tend to increase highly with wavelength.
The difference in the physics makes for substantial
differences in the absorption properties. Thus, that
parameter should to consider each spectral region sepa-
rately, to know how it behaves, there’s no single rule that
covers the entire electromagnetic spectrum in skin. There is
still different physics that is operative, and the behavior of
UV laser is still different from any of lasers at longer-
wavelength regions. In fact, the result found that lasers in
visible region have higher penetrating power as compared
with the UV lasers.
There are many technical challenges related to the
physics and clinics problems in applying PDT [13]. The
wavelength-dependent penetration depth of UV and visible
laser into human skin in PDT is a fundamental parameter
for the estimation of the possible photobiological effect of
red, green, and blue laser lights. In the blue and green
spectral region, where absorption in chromophore is nota-
ble, absorption and scattering of skin tissue decreased with
the increase in laser wavelength. The average depth of
penetration is defined as the layer of tissue that reduces the
power of irradiation to 1/e (i.e., 36.8 %). A limitation of
the current light sources in PDT is the depth of penetration.
Guidelines for the optimal disease-specific irradiance,
wavelength, and total dose characteristics for different light
sources have yet to be established [14].
The interpretation of the present study should consider
the penetration depth to clarify the role of skin colour and
laser wavelength into the human skin during irradiation.
Furthermore, data are required to establish the correlation
of both parameters with the adverse effects and optimal
dose. Thus, colour backgrounds of human skin are an
important consideration when irradiating target for treating
skin diseases in PDT and when evaluating laser outcomes
in PDT [15]. The amount of energy effectively delivered to
the dermal tissue is reduced because of the concentration of
pigment. This phenomenon illustrates two limitations in
PDT: the reduction of the efficacy of laser in PDT for
epidermal diseases treatment and the destruction of the
epidermal layer with more radiation. Thus, PDT using
green and blue lasers can be considered the best candidate
for those with lighter, very fair, and fair skin. Green and
blue lasers are not effective for people with darker skin
types. However, PDT using red laser light is applicable to
all skin types. In Amsterdam, the Academic Medical
Centre reported that, whether the use of laser is for treat-
ment or for diagnostic probe, its optical and thermal
interactions with the tissue must be understood [16].
4. Conclusions
Detailed knowledge of penetration depth is necessary to
obtain the desired therapeutic effect and to avoid the
unwanted side effects of PDT for dosimetry. The present
study reveals the large variability between the different
laser wavelengths and skin color, i.e., very fair, fair,
medium, and dark skin. The study also highlights the role
of red laser on skin color. The penetration depth of visible
laser into the human skin is highly dependent on wave-
length and skin color.
Acknowledgments The authors are grateful to the School of
Physics, Universiti Sains Malaysia for their technical assistance and
financial support.
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Comparison of wavelength-dependent penetration depths 209
... We usually conduct two different optical configuration measurements: i.e. (1) scattering configuration (by modifying the incident angle by tilting the PSG with respect to the optical tablewe usually use an incident angle of 56ºand maintaining PSA at 0º in order to avoid the ballistic reflection); and (2) transmission configuration (by placing both PSG and PSA at 90º). In addition, different illuminating wavelengths are also used, covering the visible range (625 nm, 530 nm and 470 nm), this allowing us to inspect different depths into the sample [55]. To build the experimental Mueller matrix, 36 images of the region of interest (1.1 × 1.1 cm 2 ) are taken in order to minimize the measurement noise (at least 16 images are needed): we use the 6 illumination (generators) states of polarization and the 6 analyzers proposed in [41]. ...
... In this section we perform a complete polarimetric analysis of two well-differentiated biological groups: on one hand, we measure the MM of three distinct ex-vivo chicken soft tissues (tendon, muscle and myotendinous junction), obtained from a collection of 20 different chicken leg sections, at scattering configuration. Because of different wavelengths provide different penetration lengths [55] these measurements have been repeated by using three distinct illumination channels (625 nm, 530 nm and 470 nm), covering the visible range. To not extend the work, we focus on presenting the results of muscle measurements but the same analysis on remain soft-tissues lead to similar conclusions. ...
... A region of interest (ROI) of 512 × 512 pixels (1.1 × 1.1 cm 2 ) is selected from the whole sample. By analyzing the output images from MM-metrics extraction (IPPs, R, D, and ∆ ) we point out, in agreement with many previous studies: i) retardance and depolarization constitute the polarimetric channels which provide the most significant amount of information [4,5,10-14, 22-24,42-47] in comparison with diattenuation and ii) blue wavelength illumination is appropriate when looking for surface details inspection [55]. Consequently, we choose the 470 nm channel to carry out the particular qualitative and quantitative analysis described in this proceeding. ...
... Although different optical leaf properties may play an important role in leaves spectral response 40 , as for example the spectral signature of a leaf, in the specimens studied in this work we have observed that longer wavelengths penetrate more into samples than shorter wavelengths, as they are less affected by scattering processes than shorter wavelengths. This result agrees with discussion provided in Ref. 47 . In fact, longer wavelengths may carry more information about microstructures present in the bulk of the sample than shorter wavelengths, which are more sensitive to features present in surface in a bulk region near the surface of the leaves. ...
... By taking advantage of the wide spectral response of the light source, which actually covers the visible spectrum (from 400 to 700 nm approx.), we use three different illuminating wavelengths (625 nm, 530 nm and 470 nm) for the consequently inspection of the sample at different depths 47 . The polarimeter consists of two independent optical systems based on Parallel Aligned Liquid Crystals (PA-LC) retarders, mounted into two compact mobile arms respectively. ...
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This paper highlights the potential of using polarimetric methods for the inspection of plant diseased tissues. We show how depolarizing observables are a suitable tool for the accurate discrimination between healthy and diseased tissues due to the pathogen infection of plant samples. The analysis is conducted on a set of different plant specimens showing various disease symptoms and infection stages. By means of a complete image Mueller polarimeter, we measure the experimental Mueller matrices of the samples, from which we calculate a set of metrics analyzing the depolarization content of the inspected leaves. From calculated metrics, we demonstrate, in a qualitative and quantitative way, how depolarizing information of vegetal tissues leads to the enhancement of image contrast between healthy and diseased tissues, as well as to the revelation of wounded regions which cannot be detected by means of regular visual inspections. Moreover, we also propose a pseudo-colored image method, based on the depolarizing metrics, capable to further enhance the visual image contrast between healthy and diseased regions in plants. The ability of proposed methods to characterize plant diseases (even at early stages of infection) may be of interest for preventing yield losses due to different plant pathogens.
... The final sample's intensity image is captured by means of a CCD camera. Regarding the illumination source, we use three different wavelengths in pursuit of achieve different depths into the sample [33] and cover the visible range (625 nm, 530 nm and 470 nm). This PSG-PSA set-up allows to perform two types of experimental measurements due to the different optical configurations. ...
... In this section we perform the complete statistical analysis of 9 polarimetric indicators, retrieved from the experimental Mueller matrix (MM) measurements of four distinct types of tissue (corresponding to 50 muscles, 34 tendons, 50 myotendinous junctions and 23 bones) from a collection of 25 different ex-vivo chicken thighs. The polarimetric measurements have been conducted by means of a complete image Mueller polarimeter, at scattering configuration, working at three illumination wavelengths covering the visible range (625 nm, 530 nm and 470 nm) [33]. The experimental MMs are encoded into a 512×512 pixels images which correspond to a sample area of 1.1×1.1 cm 2 . ...
Conference Paper
During the last decades, the attention on the application of polarimetric methods for biological tissues inspection has been increasing. Nowadays, organic tissue recognition algorithms are of potential interest in different research areas, as for instance, in biomedical applications for the early detection of diseases or the classification of biological structures. Based on the modifications in polarization that light-matter interactions produce, an exhaustive polarimetric analysis of the sample (extraction of dichroism, retardance and depolarization) may unveil the different tissue inherent characteristics and provide a complete description of how the biological structures interact with incident polarized light. By taking advantage of such polarimetric methods tissues characterization, we propose four predictive models corresponding to the recognition of four ex-vivo chicken tissue categories: bone, muscle, tendon and myotendinous junction tissue samples. The implemented multivariant probabilistic models are based on the logistic regression fit of the experimental Mueller matrixderived polarimetric observables (measured at three different wavelengths: 625 nm, 530 nm and 470nm): polarizance P, diattenuation D, depolarization content (Indices of Polarimetric Purity P1, P2, P3 and depolarization index 𝑃Δ), retardance (global, R, and linear δ) and optical rotation Ψ. As a result, we achieve stable predictive models whose output, in terms of sensitivity and specificity indicators, are of 82.6% and 80.6% for bone recognition, 85% and 93.5% for tendon, 86% and 88.8% for muscle and 82% and 71% for myotendinous junction, respectively. Obtained results suggest that these noninvasive methods could be applied in multiple biomedical scenarios such as for early diagnosis of pathologies.
... EM protects skin and increases with light exposure while PM causes the susceptibility of fair-skinned individuals to the deleterious effects of sunlight. In addition, of course, there is deeper penetration of light in such fair skin compared to dark/black skin [9]. ...
... Additionally, very old work by Knott [35] suggested that at least some of the beneficial effects of UV skin irradiation could be due to direct irradiation of the blood circulating in the skin's capillaries. Whilst this effect may not be directly related to any radical production from melanin, the amount of light penetrating paler skins is higher [9] meaning more will be able to reach the bloodstream. ...
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A hypothesis is proposed to explain the increased detrimental effect of COVID-19 for Black, Asian and Minority Ethnic (BAME) men and women compared to Caucasian individuals. This is based on the differing photochemistry of phaeomelanin in fair skin and eumelanin in dark/black skin. It is suggested that a range of reactive oxygen species, including, singlet oxygen and the superoxide radical anion, derived via direct photolysis of phaeomelanin, may escape the melanocyte and cause subsequent damage to the SARS-CoV-2 virus. It is further suggested that (large) carbon and sulphur peroxy radicals, from oxygen addition to radicals formed by carbon–sulphur bond cleavage, may assist via damage to the cell membranes. It is also speculated that light absorption by phaeomelanin and the subsequent C-S bond cleavage, leads to release of pre-absorbed reactive oxygen species, such as singlet oxygen and free radicals, which may also contribute to an enhanced protective effect for fair-skinned people.
... Skin, adipose tissue, striated muscle, vein, nerve, and blood were measured by THz spectroscopy [10]. The penetration depth of visible (laser) light into human skin tissue strongly depends on wavelength and skin pigmentation [11]. Similar finding was reported from the measurement of the optical properties of in vitro-pigmented human skin tissue models [12]. ...
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The transmission of THz, near-infrared (1030 nm), and green (515 nm) pulses through Eisenia andrei body wall is studied, which consists of epithelial layer and circular and longitudinal muscles. Samples with the full-body cross-section were also investigated. The transmitted power for the green pulses followed the Beer-Lambert law of exponential attenuation for all thicknesses and tissue structures. Different body wall and body center absorption coefficients were found in case of infrared pulses. In the THz range, the body wall absorption coefficient steadily increases from about 80 cm –1 at 0.2 THz to about 273 cm –1 at 2.5 THz. Numerical estimation indicates that THz pulses of 5-μJ energy and 1-kHz repetition rate (5-mW average power) cause only a small temperature increase of about 0.4 K, suggesting that heating has minor contribution to biological effectiveness.
... It is these processes that can cause the susceptibility of fair-skinned people to the serious deleterious effects of sunlight absorption. Moreover, of course, there is deeper penetration of light in fair-skinned individuals compared to those with dark skin [37]. It is these processes that have also been speculated to be linked to the incidence and/or severity of COVID-19. ...
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Reactive oxygen species comprise oxygen-based free radicals and non-radical species such as peroxynitrite and electronically excited (singlet) oxygen. These reactive species often have short lifetimes, and much of our understanding of their formation and reactivity in biological and especially medical environments has come from complimentary fast reaction methods involving pulsed lasers and high-energy radiation techniques. These and related methods, such as EPR, are discussed with particular reference to singlet oxygen, hydroxy radicals, the superoxide radical anion, and their roles in medical aspects, such as cancer, vision and skin disorders, and especially pro- and anti-oxidative processes.
... In the current study, the experimental Mueller matrices of 157 biological samples are measured at three different wavelengths covering the visible range (625 nm, 530 nm and 470 nm), since different wavelengths are associated with different light penetration capability in tissues [43]. Such measurements are performed in a scattering configuration (capturing diffuse light) by using a complete Mueller imaging polarimeter (described in section 1 of Supplement 1) based on parallel-aligned liquid crystal retarders [11,12,15,25]. ...
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We highlight the potential of a predictive optical model method for tissue recognition, based on the statistical analysis of different polarimetric indicators that retrieve complete polarimetric information (selective absorption, retardance and depolarization) of samples. The study is conducted on the experimental Mueller matrices of four biological tissues (bone, tendon, muscle and myotendinous junction) measured from a collection of 157 ex-vivo chicken samples. Moreover, we perform several non-parametric data distribution analyses to build a logistic regression-based algorithm capable to recognize, in a single and dynamic measurement, whether a sample corresponds (or not) to one of the four different tissue categories.
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Detection of biomarkers associated with body conditions provides in‐depth healthcare information and benefits to disease management, where the key challenge is to develop a minimally invasive platform with the ability to directly detect multiple biomarkers in body fluid. Dermal tattoo biosensor holds the potential to simultaneously detect multiple health‐related biomarkers in skin interstitial fluid because of the features of minimal invasion, easy operation, and equipment‐free result reading. Herein, a colorimetric dermal tattoo biosensor fabricated by a four‐area segmented microneedle patch is developed for multiplexed detection of health‐related biomarkers. The biosensor exhibits color changes in response to the change of biomarker concentration (i.e., pH, glucose, uric acid, and temperature), which can be directly read by naked eyes or captured by a camera for semi‐quantitative measurement. It is demonstrated that the colorimetric dermal tattoo biosensor can simultaneously detect multiple biomarkers in vitro, ex vivo, and in vivo, and monitor the changes of the biomarker concentration for at least 4 days, showing its great potential for long‐term health monitoring. Simultaneous detection of multiple biomarkers provides in‐depth healthcare information, where the key challenge is to develop a minimally invasive platform. To this end, a colorimetric dermal tattoo biosensor fabricated by a four‐area segmented microneedle patch is developed. The biosensor exhibits color changes in response to biomarker concentration variations, showing its great potential for health monitoring.
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Background: The prognosis of replanted teeth is depended on the vitality of periodontal ligament cells residual on the root surface. Photobiomodulation has photobiological effects that can promote cell vitality. The study aimed to explore the effect of photobiomodulation on the periodontal ligament cells under inflamed or starved conditions mimicking clinically damaged periodontal ligament cells of avulsed teeth and provide the adjuvant procedure for tooth replantation. Materials and methods: Normal, starved, or inflamed periodontal ligament cells were irradiated with an 808 nm laser at densities of 0, 1, 3, 5, or 10 J/cm2. The cell counting kit-8 (CCK-8) assay and scratch test were applied to determine the effects on the proliferation and migration of cells. Anti-inflammatory effects were assessed according to the mRNA expression of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) measured by reverse-transcription polymerase chain reaction. Osteogenic capacity was evaluated by alkaline phosphatase (ALP) staining, ALP activity assay, Alizarin Red S staining, and ALP and osteocalcin (OCN) mRNA expression. Results: The CCK-8 assay and scratch test demonstrated that the 808 nm laser significantly promoted proliferation and migration of normal condition periodontal ligament cells at a density of 3 J/cm2 versus 5 J/cm2 under the starved and inflamed conditions. Moreover, the 808 nm laser had anti-inflammatory effects and promoted osteogenesis of periodontal ligament cells at 3 J/cm2 under normal conditions, while photobiomodulation at 5 J/cm2 upregulated the osteogenesis of periodontal ligament cells under starved and inflamed conditions. Conclusions: The photobiomodulation of 808 nm laser reduced inflammation and improved the proliferation, migration, and osteogenesis of normal, starved, and inflamed periodontal ligament cells. These effects required a higher energy density under starved or inflamed conditions compared with normal conditions. The photobiomodulation of 808 nm has a potential application in root surface treatment for replanted teeth.
Chapter
Tuberculosis (TB) is an infectious communicable bacterial disease that has been a global health burden for many years, with an estimated one in four people infected with the disease. TB is an airborne disease caused by the bacillus Mycobacterium tuberculosis. It typically infects the lungs (pulmonary TB) but can also affect other sites, such as the brain and spine (extrapulmonary TB). The occurrence of drug-resistant TB (DR-TB) has greatly affected treatment outcomes. A novel alternative treatment for TB has emerged over the last few years called photodynamic therapy (PDT). Typically, PDT is used for the treatment of various cancers, but its use in the treatment of drug-resistant pathogenic microorganisms (antimicrobial PDT or antimicrobial photoinactivation) is gaining popularity. PDT is minimally invasive and involves the combination of a photosensitizer (PS), molecular oxygen, and laser light at a specific wavelength. The result is the production of reactive oxygen species (ROS) that selectively damage target cells in an athermic manner.
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This paper quantifies the role played by fiber dispersion in limiting the transmission distance in directly modulated gigabit optical fiber communication systems (OFCSs). The study is based on modeling and simulation of an OFCS deploying a directly modulated 1.55-lm distributed feedback InGaAsP laser diode, a single-mode fiber and a PIN photodetector. The repeater distance of the system is decided to correspond to a bit error rate of 10 -9 . The receiver sensitivity corresponding to the back-to-back configuration is calculated. Fiber attenuation was found to limit the maximum transmission distance to 162–202 km under bit rates ranging between 1 and 10 Gbps. This distance was found to be less affected by counting the chromatic dispersion of the fiber up to bit rate of 2 Gbps. A dramatic decrease in the transmission distance is predicted when the bit rate increases further and the system becomes dispersion limited. Influence of dispersion on the transmission distance is quantified in terms of the power penalty of the OFCS system associated with taking account of fiber dispersion. This power penalty is predicted to be within 7 dB for bit rates below 5 Gbps but jumps to values as high as 22 dB at higher bit rates.
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We describe three lessons learned about how tissue optics affect the dosimetry of red to near-infrared treatment light during PDT, based on working with Dr. Tayyaba Hasan. Lesson 1-The optical fluence rate φ near the tissue surface exceeds the delivered irradiance (E). A broad beam penetrates into tissue to a depth (z) as φ=Eke(-μz), with an attenuation constant μ and a backscatter term k. In tissues, k is typically in the range 3-5, and 1∕μ equals δ, the 1∕e optical penetration depth. Lesson 2-Edge losses at the periphery of a uniform treatment beam extend about 3δ from the beam edge. If the beam diameter exceeds 6δ, then there is a central zone of uniform fluence rate in the tissue. Lesson 3-The depth of treatment is linearly proportional to δ (and the melanin content of pigmented epidermis in skin) while proportional to the logarithm of all other factors, such as irradiance, exposure time, or the photosensitizer properties (concentration, extinction coefficient, quantum yield for oxidizing species). The lessons illustrate how tissue optics play a dominant role in specifying the treatment zone during PDT.
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Dosimetry for photodynamic therapy (PDT) is becoming increasingly complex as more factors are identified which may influence the effectiveness of a given treatment. The simple prescription of a PDT treatment in terms of the administered photosensitizer dose, the incident light and the drug-light time interval does not account for patient-to-patient variability in either the photosensitizer uptake, tissue optical properties or tissue oxygenation, nor for the interdependence of the photosensitizer-light-tissue factors. This interdependence is examined and the implications for developing adequate dosimetry for PDT are considered. The traditional dosimetric approach, measuring each dose factor independently, and termed here 'explicit dosimetry', may be contrasted with the recent trend to use photosensitizer photobleaching as an index of the effective delivered dose, termed here 'implicit dosimetry'. The advantages and limitations of each approach are discussed, and the need to understand the degree to which the photobleaching mechanism is linked, or 'coupled', to the photosensitizing mechanism is analysed. Finally, the influence of the tissue-response endpoints on the optimal dosimetry methods is considered.
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Monte Carlo Simulation for light propagation in different types of human and animal tissues has been performed using programming methods. During the simulation we have recorded the photon reflectance, transmittance and absorption in lung and dermis tissues of human, pig and rabbit and compared. Average values of total diffuse reflectance, transmittance and absorption have been calculated by the 10 simulations of 100,000 photons for these tissues at 633 nm. We have found that transmittance, reflectance and absorption are strongly dependent on tissue type and diffuse reflectance increases as the scattering coefficient (μ s ), increases or anisotropy (g), decreases, while diffuse transmittance increases as absorption coefficient (μ a ) or (μ s ) decreases, or as (g) increases.
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Objective: Retrospective analysis of clinical effects of vascular acting photodynamic therapy (PDT) for the treatment of port wine stains (PWS). Methods: Between September 1997 and June 2003, a total of 238 PWS cases (2-56 years old) were treated with Photocarcinorin-mediated PDT using a copper vapour laser. Among them, 20 cases were pink lesions (Type I), 44 cases red lesions (Type II), 99 cases dark red lesions (Type III), 51 cases purple lesions (Type IV), and 24 cases nodular or thickened lesions (Type V), respectively. Patient received a slow intravenous injection of Photocarcinorin (4-5mg/kg b.w.) and light was delivered during the drug injection at dose levels of 160-260J/cm(2) at fluence rates of 70-100mW/cm(2). The same procedure was repeated 2-4 times for some patients. All patients were followed up for 6 months to 4 years. Results: Sixty-eight cases (28.6%) showed excellent response, 76 cases (31.9%) good response, 87 cases (36.6%) fair response and 7 cases (2.9%) poor or no response. Secondary scar formation was reported in three cases. Highest good to excellent response rates were seen in patients of 5-20 years old. PDT-induced transitional hyperpigmentation was reported in some patients but disappeared without the need of treatment within 3-6 months. Conclusion: Copper vapour laser PDT can selectively destroy PWS vessels without damage to the normal skin. If the technique is applied properly, it can cure superficial lesions and greatly improve thick lesions.
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Irradiation of He-Ne LASER beam on polystyrene (PS) and poly vinyl chloride (PVC) polyblend sample for different time intervals viz. 3, 5,7, 10 and 15 min. Structural and electrical properties have been studied before and after irradiation. It has been found that irradiation increases the dc electrical conductivity due to creation of new charge carriers in the polyblend sample.
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Laser light is frequently used in both diagnostics and treatment of patients. For any laser treatment to be effective it is important to deliver the correct dose at the treatment site. Human skin scatters and absorbs laser light in the visible wavelength region, which results in a decrease in fluence some distance into the skin. Computer simulations can be used to predict the fluence at the treatment site. Liquid and solid phantoms were prepared and the optical properties were measured. These values were then used as input values to a commercial software package simulating the different layers of skin representing phantoms. The transmission and reflected fractions of the different phantoms were measured with an integrating sphere and compared with the computer simulations. The results showed very good agreement with the measured values and the model can therefore be used with confidence to predict fluence at any treatment site inside the skin.
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This article is a review of laboratory and clinical research undertaken in Poland in PDD and PDT over the past 20 years. These are divided into two parallel research areas. The first is based on clinical trials where new modalities of photosensitizer synthesis, molecular mechanisms of PDT and other aspects are investigated. The second is concerned with clinical aspects of PDD and PDT in both pre-neoplastic and malignant disease. In Poland there were 2 National Congresses in 2006 and 2008 with 100 and 400 participants respectively. One of the oldest centers of Photodynamic Diagnostics and Therapy is located in Bytom. For about 10 years it has led clinical research in Poland with PDD and PDT in such medical disciplines as dermatology, gastroenterology, laryngology, pulmonology, gynecology, and orthopedics.
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The introduction of drug consumption in the model of dose as the product of light dose together with the existence of thresholds for tissue necrosis results in a profound alteration in the perception of PDT dosimetry. Light doses had been limited by normal tissue toxicities which were the result of levels of drug. The consequence of that thought process was the dose of light (when limited to that which spares normal tissue) falls off sharply with depth [4,5]. Based upon the theories presented the consideration of consumption of drug can increase the effective photodynamic depth greater that twofold. The maximum injected drug dose which allows normal tissue to fully recover from an unlimited light dose appears from studies conducted in human patients with various cutaneous malignancies, to be 1 mg/kg. There is however, no reason a priori, to assume that for other tissues or specific applications (i.e., obstructing tumors vs. superficial disease) this is the optimum value. The gap between the current clinical practice of employing PDT using the simplest parameters of drug dose administered, light dose applied and the timeframe between them and a more concise description of specific dosimetry factors is presumably wide. However, in practice, based upon empirical data the drug and light dosage prescribed is sufficient to produce the desired clinical effect particularly in the approved indications. The challenge of developing methods and instrumentation in order to achieve a more effective dosing scheme which will allow for a more personalized dose modification based upon various factors to produce clinically relevant tissue response endpoints is yet to be accomplished. While promising for the future of PDT the concept of dosimetry ultimately needs to be determined and evaluated via clinical trials.