UNIT 5

SPECIAL OPTICAL TECHNIQUES

PHOTOTHERPAY

Phototherapy (light treatment) is the process of using light to eliminate bilirubin in the
blood. Baby's skin and blood absorb these light waves. Light waves absorbed convert bilirubin
into products, which can pass through their system. Lamps emitting light between the
wavelengths of 400 - 500 nanometres (peak at 460nm) are specifically used for administering
phototherapy as bilirubin absorbs this wavelength of light. Visible blue light is used.

Mechanism

Bilirubin, are present in the interstitial spaces and superficial capillaries of the skin,
subcutaneous tissues. During the phototherapy, these molecules are exposed to light. Photons of
energy are absorbed by the pigment, bilirubin. Leads to a sequence of photochemical reactions;
configurational isomerisation, structural isomerisation and photo-oxidation.

Energy converts bilirubin into its nontoxic isomers such as photobilirubin ,lumilirubin which are
more polar and thus water soluble. Photo-isomers are eliminated from the body more easily
without undergoing the process of conjugation in the liver. As formation of lumirubin is the rate
limiting step, less amount of lumirubin is formed.

Lights
1. White Halogen lights -Positioned above the infant and can deliver 10 to 30 µ W/cm2
/nm. Quartz halogen bulb
Tendency to become hot
It is positioned at 52cm away from baby.
2. 2 Blue and 2 White Fluorescent lights -Blue light is the most effective light for reducing
the bilirubin.
It delivers 12µW/cm2 /nm.
Light should not be delivered from the side of the infant.
3. Biliblanket - Blue Halogen light -Uses a halogen bulb directed into a fiberoptic mat.
Filter removes the ultraviolet and infrared components and the eventual light is a blue-green
colour. Blanket to give double phototherapy and increases the surface area exposed.
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4. Bilibed – Blue Fluorescent light -Blue fluorescent tube is fitted into a plastic crib with a
stretched plastic cover over the top for the baby to lie on.
Baby is dressed in the Bilicombi baby suit and nursed on the soft plastic cover.
Suit attaches to the crib by Velcro attachments.
Irradiance delivered is up to 40 µ W/cm2 /nm.
Risks
Progressive and gradual damage to your skin on a molecular level
Risk of developing skin cancer
Lead to immunosuppression.
Eyes become more sensitive to light

PHOTODYNAMIC THERAPY
A treatment that uses a drug, called a photosensitizer or photosensitizing agent, and a particular
type of light. When photosensitizers are exposed to a specific wavelength of light,
photoactivation causes the formation of singlet oxygen, which produces peroxidative reactions
that can cause cell damage and death. Each photosensitizer is activated by light of a specific
wavelength. This wavelength determines how far the light can travel into the body.
Steps
Three steps : –
1. Application of photosensitizer drug
2. Incubation
3. Light activation
In the first step of PDT for cancer treatment, a photosensitizing agent is injected into the
bloodstream. Agent is absorbed by cells all over the body but stays in cancer cells longer than it
does in normal cells. Approximately 24 to 72 hours after injection, when most of the agent has
left normal cells but remains in cancer cells, the tumor is exposed to light. Photosensitizer in the
tumor absorbs the light and produces an active form of oxygen that destroys nearby cancer cells

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 Fig 5.1 PDT Mechanism
In addition to directly killing cancer cells, PDT appears to shrink or destroy tumors in two other
ways. The photosensitizer can damage blood vessels in the tumor, thereby preventing the cancer
from receiving necessary nutrients. PDT also may activate the immune system to attack the
tumor cells. Light used for PDT include laser, intense pulsed light, light-emitting diodes (LEDs),
blue light, red light, and many other visible lights (including natural sunlight). Laser light can be
directed through fiber optic cables (thin fibers that transmit light) to deliver light to areas inside
the body. A fiber optic cable can be inserted through an endoscope (a thin, lighted tube used to
look at tissues inside the body) into the lungs or esophagus to treat cancer in these organs. Other
light sources include light-emitting diodes (LEDs), which may be used for surface tumors, such
as skin cancer
Mechanism
Type I Reaction:-
Direct reaction with substrate (cell membrane or molecule)
Transfer of H atom to form radicals
Radical react either O2 to form oxygenated products
Type II reaction:-
Transfer of oxygen to form singlet oxygen
Drugs Used
Porfimer sodium
Benzoporphyrin derivative & Aminolevulinic
acid Methyl ester of ALA-
Advantages
No long term side effects when used
properly. Less invasive than surgery.

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Takes only a short time and is most often done as an outpatient.
Targeted very precisely.
PDT can be repeated many times at the same site if
needed. Little or no scarring after the site heals.
Costs less than other cancer treatments.
Limitations
Light needed to activate most photosensitizers cannot pass through more than about one-third of
an inch of tissue (1 centimeter).
PDT is usually used to treat tumors on or just under the skin or on the lining of internal organs or
cavities.
PDT is also less effective in treating other tumors, because the light cannot pass far into these
tumors.
PDT is a local treatment and generally cannot be used to treat cancer that has spread
Side Effects
Skin and eyes sensitive to light for approximately 6 weeks after treatment
Photosensitizers tend to build up in tumors and the activating light is focused on the tumor. As a
result, damage to healthy tissue is minimal.
PDT can cause burns, swelling, pain, and scarring in nearby healthy tissue.
Other side effects include coughing, painful breathing, trouble swallowing, stomach pain, or
shortness of breath; these side effects are usually temporary.

ONCOLOGICAL APPLICATIONS
1. Obstructive Esophageal Cancer-
Palliation of partially or totally obstructing tumors in the
esophagus Photofrin powder, is dissolved in 5% dextrose for
injection.
48 h post injection the photosensitizer localized to the tumor is activated by light at 630 nm
(laser) that is directed via a single-quartz fiber optic and delivered to the tumor through the
biopsy channel of an endoscope. Light is scattered laterally to the tumor on the wall of the
esophagus or the fiber may be inserted directly into the tumor. Experience mild to severe chest
pain

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2. Early Stage Endobronchial Tumors –

Treatment of microinvasive, nonsmall cell endobronchial tumors using Photofrin-PDT

Patients received 2 mg/kg Photofrin and 2 d later were treated endoscopically using a diffuser
fiber (usually 1 to 2.5 cm) delivering 200 J/cm of diffuser length at 630 nm.
Because these lesions are very thin, the fiber was held in the lumen adjacent to the lesion.
Patients were rescoped 2 days following treatment,and treated area was debrided.
3. Obstructing Endobronchial Tumors (Nonsmall Cell Lung
Cancer)- Palliative treatment of obstructive endobronchial tumors.
Photofrin, 630 nm light treatment 48 h later
2 days following treatment patients are re-endoscoped, and all necrotic tumor debris and exudate
must be removed because they can further obstruct the airway.
Adverse reactions included photosensitivity reaction hemoptysis, cough, dyspnea, chest pain, and
fever
4. Early Stage Esophageal Cancer- Barrett’s esophagus
Endoscopic PDT was applied using a specially designed balloon light applicator.
Balloon is inserted, deflated and then inflated in place to an appropriate pressure to allow
“unfolding” of the esophageal wall without shutting down the blood flow.
5. Cholangiocarcinoma- Bile duct cancer
6. Head and Neck Cancer- adjuvant to surgery in an attempt to “clean up” the remaining cancer
cells in the operative bed.
7. Brain Tumors- glioblastoma or
astrocytoma. 8.Mesothelioma - asbestos-
induced disease

BIOSTIMULATION EFFECTS
Biostimulation, also known as LILT or LLLT Low Intensity(Level) Laser Therapy, improves
post operative healing and yields excellent antalgic effects. It also called photobiology.
Biostimulation is obtained using a defocalised beam with low energy density. Light energy is
absorbed by tissues, and stimulates the metabolic processes inducing tissue regeneration. It emits
no heat, sound, or vibration. Another name is cold laser therapy. Low levels of light does not
heat the body tissue. Level of light is low when compared to other forms of laser therapy, such as
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those used to destroy tumors and coagulate tissue. Superficial tissue is commonly treated with

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wavelengths between 600 and 700 nanometers (nm). For deeper penetration, wavelengths
between 780 and 950 nm are used. It generates light of a single wavelength. No temperature
elevation within the tissue, but rather produce their effects from photobiostimulation effect
within the tissues. Low-level lasers do not cut or ablate the tissue.
LLLT devices include the gallium arsenide, gallium aluminum arsenide infrared semiconductor
(gallium-aluminum-arsenide), and helium-neon lasers. Output powers range from 50 to 500 mW
with wavelengths in the red and near infrared of the electromagnetic spectrum, from 630 to 980
nm with pulsed or continuous-wave emission.
Mechanism
Biostimulatory and inhibitory effects of LLLT are governed by the Arndt-Schulz law.
The law states that low-dose will increase physiologic processes, and strong stimuli will inhibit
physiological activity. It represents a set of structural, biochemical and functional changes in
living microorganisms. It acts directly on stimulating components of the so-called antenna
pigments of the respiratory chain and manifest as an immediate effect cell vitalization by
adenosine triphosphate (ATP) mitochondrial production increase. It Induces intracellular
metabolic changes, resulting in faster cell division, proliferation rate, migration of fibroblasts and
rapid matrix production.

Fig 5.2 Mechanism of Biostimulation

Benefits
Increases ATP synthesis
Stimulates cell growth

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Increases cell metabolism
Improves cell regeneration
Invokes an anti-inflammatory response
Promotes edema reduction
Reduces fibrous tissue formation
Stimulates nerve function
Laser used
Previously helium-neon (HeNe) laser of <1 mW was used.
Limited by the need for an optic fiber, the size of the machine and the still rather low power
option
Replaced by the indium-gallium-aluminum-phosphide laser, a diode producing red laser in the
range 600-700 nm and able to deliver as much as 500 mW.
Frequently used in dentistry is the gallium-aluminum-arsenide laser.
Operates in the spectrum between 780 and 830 nm. The output is typically between 10 and 500
mW.
Advantage of the diode lasers is the small size and option for battery operation, making them
rather handy and portable. T
Work in continuous mode, but can be mechanically or electronically pulsed.
Effects
Reduction of inflammation: It can occur within hours to
days. Pain relief
Accelerated tissue regeneration: LLLT stimulates cell proliferation of fibroblasts , keratinocytes ,
endothelial cells and lymphocytes.
Wound healing in a range of sites, like surgical wounds, extraction sites, recurrent aphthous
ulcerations - Dental
Applications
Minor injuries and sprains
Inflammation
Aches and Pain
Skin rejuvenation
Wound healing

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Acupuncture
LASER SAFETY PROCEDURES
Laser treatment increases the potential for laser accidents also increases.

Beam Hazards
Hazardous effects related to unintentional direct contact with the laser beam

⦿ Eye related
⦿ Interaction hazards (Plume and Fire)
⦿ Skin related

1. Eye Related
⦿ Corneal/Sclera Injury:caused by wavelengths that do not pass through fluid (roughly
above 1400 nm and below 400 nm)
⦿ Retinal Burns Injury: caused by wavelengths that do pass through fluid from (roughly
400-1400nm)
 Injury can result from exposure to:
 direct beam
 mirror reflection (surgical instruments)
 diffuse beam (tissue reflection)
⦿ Damage dependent on:
 intensity - lens of eye can focus beam onto the retina
 wavelength - absorbed by different parts of the eye
 duration - fraction of second, before you can blink

2. Interaction Hazards
⦿ Plume - Smoke from vaporization
Creates a visibility
problem Can cause nausea
⦿ Can be Carbon, Aerosolized blood, Gases – including benzene, toluene and
formaldehyde with particle size - 0.1 microns. Smoke evacuators is the preferred control
method
⦿ Fire and explosion

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 🗉 Can occur if the laser beam comes into contact with combustible or volatile materials,
such as: gauge pads ,surgical drapes ,gowns ,alcohol ,anesthetic gases

3. Skin related
🗉 Thermal burn
🗉 Laser effects on tissue are dependent on 4 factors: power density of laser beam
,wavelength ,duration of exposure ,effects of circulation and conduction

Non beam hazards

 Hazards associated with the generation of the laser beam
 Electrical - High voltage – many lasers require high voltage to generate
the laser beam.
 Accidental exposure can result in electrical shock or death
 Chemical
 Dye lasers use hazardous dyes to generate the laser beam (hazardous
waste)
Control Measure
⦿ Engineering- control measures that are built into the laser system, such as: enclosing the
electrical system, within a cabinet , enclosing the beam within fiber optics or
mechanical arms
⦿ Administrative Control
a. Controlled Entry- Closing doors and covering windows (when required) ,Posting of
the PROPER “Laser in Use” signs outside all entries.
⦿ b.Education-All personnel that may be exposed to the laser shall be required to attend
regular “in-services” on operating the laser and laser safety.
⦿ c.Standards- Each medical facility should develop their own set of operating standards
Personal Protection
⦿ Eyewear - Each laser requires specific eyewear that is capable of absorbing laser light of
that specific wavelength. Everyone in the laser OR must wear eye protection including
the patient. Patient eye’s can be protected by covering with moist towels, goggles, intra-
ocular shields . The surgeon must have eye protection, even during microscopic and
endoscopic procedures. Lens filters that fit over the eyepiece can be used.

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 ⦿ Skin Protection- Clothing , Gloves , Fire resistant gowns , Fire resistant surgical
drapes , Moist gauze and drapes around surgical area . All gauze and drapes
around the surgical area should be moistened with sterile saline. Smoke
evacuators filter out the smallest particles (0.1 µ) found in the laser plume.
Smoke evacuator suction tube must be placed as near to the site of laser ablation
as possible

Near field Imaging of biological structures

Near-field scanning optical microscopy (NSOM) or scanning near-field optical microscopy (SNOM) is
a microscopy technique for nanostructure investigation that breaks the far field resolution limit by
exploiting the properties of evanescent waves. In SNOM, the excitation laser light is focused through an
aperture with a diameter smaller than the excitation wavelength, resulting in an evanescent field (or near-
field) on the far side of the aperture. When the sample is scanned at a small distance below the aperture,
the optical resolution of transmitted or reflected light is limited only by the diameter of the aperture. In
particular, lateral resolution of 20 nm and vertical resolution of 2–5 nm have been demonstrated.

As in optical microscopy, the contrast mechanism can be easily adapted to study different properties,
such as refractive index, chemical structure and local stress. Dynamic properties can also be studied at a
sub-wavelength scale using this technique.

NSOM/SNOM is a form of scanning probe microscopy.

Instrumentation and standard setup

The primary components of an NSOM setup are the light source, feedback mechanism, the scanning tip,
the detector and the piezoelectric sample stage. The light source is usually a laser focused into an optical
fiber through a polarizer, a beam splitter and a couple. The polarizer and the beam splitter would serve to
remove stray light from the returning reflected light. The scanning tip, depending upon the operation
mode, is usually a pulled or stretched optical fiber coated with metal except at the tip or just a standard
AFM cantilever with a hole in the center of the pyramidal tip. Standard optical detectors, such
as avalanche photodiode, photomultiplier tube (PMT) or CCD, can be used. Highly specialized NSOM
techniques, Raman NSOM for example, have much more stringent detector requirements

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Biological applications

Aperture near field scanning optical microscopy (NSOM) with fluorescence detection gives biochemical
specificity and orientational information, in addition to the simultaneously acquired force image. This
technique has large potential for DNA sequencing, molecular organization in monolayers, and study of
the role of the cytoskeleton in cellular mobility in cell growth, cell migration, formation of protrusions,
etc.

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