Bronchology – Past, Present and Future Diagnostic Procedures
17
Early Detection
Basic Principles of the Physics of Light
The search for a window of opportunity for effective intervention and detection
of pre-invasive lesions has been most critical. One exciting discovery during
recent years is autofluorescence/fluorescence imaging during bronchoscopy
with spectroscopy. The techniques have provided the experienced broncho-
scopist with a “searchlight” for scanning and detection of mucosal, sub-muco-
sal, cancerous, pre-cancerous and non-cancerous pathological conditions.
In order to understand the application of light-induced fluorescence in the early-
detection, some understanding of the effects of light on body tissues and
fluorochromes is required. Light is non-ionizing radiation, partly visible to the
human eye and partly invisible in its ultra-violet (UV) or infrared (IR) regions. It is
unlike the ionizing X-rays, which have a much shorter wavelength and higher
energies. At all wavelengths, including UV and IR, light initiates photochemical
reactions if absorbed by a molecular system.
The LASER, an acronym for “Light Amplification by Stimulated Emission of
Radiation”, produces a beam of light of high intensity, coherence and mono-
chromaticity. In 1960, Maiman of Hughes Research Laboratory constructed the
first ruby laser. Since then, various substances have been used in lasers, includ-
ing solids, liquids and gases. These different lasers have different wavelengths
and can be used as precise tools for specific medical and surgical procedures.
Fig. 12
Wavelengths of Electromagnetic
Radiation.
Fig. 13
Operational Diagramm of a gas laser in action
CO2
Argon
Nd:YAG
l = 10,6 mm
High absorption/
low scatter
Surface
absorption
l = 0,5 mm
Medium absorption/
medium scatter
Volume absorption
low penetration
l = 1,06 mm
Low absorption/
high scatter
Volume absorption
high penetration
Fig. 14
Three different types of laser used for the treatment of
bronchial carcinoma
+
+
+
+
+
++
++
++
++
++
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Molecules at
level E2
Gas outlet
Laser
Beam
Out
Partially reflecting
mirror
Ground
state
Reflected
beam
Fully
reflecting
mirror
Molecules at
level E1
Gas intlet
Electrical pump
103
102
10
1
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
Cosmic rays
Long waves
Radio waves
Radar
Millimeter waves
Heat waves
„Light“
X rays
Gamma rays
Infrared
Visible
Ultraviolet
LW
SW
VHF
UHF
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