Biomedical Engineering Reference
In-Depth Information
The use of light for therapeutic and diagnostic procedures in medicine has evolved from
the use of sunlight for heat therapy and as a simple tool for the inspection of eyes, skin, and
wounds to the current use of lasers and endoscopy in various medical procedures. The
introduction of photonic technology into medicine over the last decade has revolutionized
many clinical procedures and has the potential to continue to greatly impact health care.
For example, coherent fiber optic bundles have been applied in laparoscopy cholecys-
tectomy (minimally invasive removal of the gallbladder) to transform a once painful
and expensive surgery into virtually an outpatient procedure. In the process, biomedical
engineers have been instrumental in defining and demonstrating the engineering funda-
mentals of the interaction of light and heat with biological media, resulting in advances
in dermatology, ophthalmology, cardiology, and urology.
Optical engineering has traditionally been taught as part of an electrical engineering
curriculum and has been primarily applied in the development of defense and communica-
tions technologies. In biomedical optics applications, however, there are many issues
related to the interaction of light with participating biological tissue/media that classical
optics topics and curricula do not cover. Therefore, the goal of this chapter is to provide
students with a better understanding of the fundamental principles associated with the
growing field of biomedical optics as well as advances in optically based therapeutic,
diagnostic, and monitoring devices.
17.1 IN
TRODUCTION TO ESSENTIAL OPTICAL PRIN
CIPLES
Throughout the ages, great minds, including those of Galileo, Newton, Huygens,
Fresnel, Maxwell, Planck, and Einstein, have studied the nature of light. Initially it was
believed that light was either corpuscular or particle-like in nature or that it behaved as
waves. After much debate and research, however, it has been concluded that there are
circumstances where light behaves like waves and those where it behaves like particles.
In this section, an overview of the behavior of light is described, beginning with the
wave equation, which is commonly derived from Maxwell's equations. In addition, the
optical spectrum and the fundamental governing equations for light absorption, scatter-
ing, and polarization are covered.
17.1.1 Electromagnetic Waves and the Optical Spectrum
It was in the late 1800s that J. Clerk Maxwell showed conclusively that light waves
were electromagnetic in nature. This was accomplished by expressing the basic laws of
electromagnetism and deriving from them the wave equation. The key to validating this
derivation was that the free space solutions to the wave equation corresponded to electro-
magnetic waves with a velocity equal to the known experimental value of the velocity of
light. Many introductory optics texts (such as the works of Hecht and Pedrotti) begin with
the vectorial form for Maxwell's equations
2
E
2
E
t
2
r
¼ e
0
m
0
@
=@
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17
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1
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