Biomedical Engineering Reference
In-Depth Information
18
Application of Gold Nanoparticles
(GNP) in Laser Thermal Therapy
18.1 Introduction .............................................................................................................................319
18.2 Overview of Laser-Tissue Interactions ................................................................................ 320
Tissue Optical Properties and the Therapeutic Window • Biomedical Lasers and Laser Tissue
Interactions with and without GNPs • Applying Laser to the Tumor
18.3 Laser Fluence Estimation in Tissues .................................................................................... 322
18.4 Optical Properties of GNPs ................................................................................................... 323
What Is the Ideal Absorber? • Optical Properties of GNPs
18.5 Laser GNP Effects I—Thermal Response at Multiple Scales ............................................ 325
Heat Generation and Scaling • Thermal Response of GNP Heating • The Concept of Thermal
Confinement • SAR Estimation
18.6 Laser GNP Effects II—Physical and Biological Responses at Multiple Scales ...............329
Nanoscale Effects •
In Vitro
Cellular Level Efects •
In Vivo
Effects
18.7 Clinical Studies ........................................................................................................................333
18.8 Conclusion and Future Studies..............................................................................................333
Acknowledgments .............................................................................................................................. 334
References ............................................................................................................................................ 334
Zhenpeng Qin
University of Minnesota
John C. Bischof
University of Minnesota
18.1 Introduction
The Pennes bioheat equation is widely used for the prediction
of temperature change during thermal therapies (Pennes 1948).
Although more sophisticated models incorporating the vascu-
lature of the tissue are available, they require more parameters
that are usually not readily available (Baish 2000). The Pennes
bioheat equation can be written as
A compelling vision for nanoparticles (NPs) in medicine involves
their use to selectively diagnose, image, and destroy disease by
throwing a noninvasive “switch.” This chapter explores the abil-
ity of laser light to be a switch that activates NPs accumulated in
tissue to heat and destroy disease. NPs can be locally or systemi-
cally delivered such that they accumulate within the cellular and
extracellular spaces of diseased tissue such as tumors. How NPs
distribute throughout the body and tumors will be briefly dis-
cussed, and comprehensive reviews will be noted. When present,
the
scattering
of light by the NP can yield contrast for imaging,
while light
absorption
by the NP can be used for therapeutic heat-
ing and photothermal imaging. While the advantages of using
NPs for image contrast have been extensively reviewed by others
(Qian 2008, Hu 2006, Zharov 2007), this chapter will focus on the
ability and effects of NP laser heat generation at multiple scales.
The potential advantages over traditional thermal therapies in
terms of tumor specific destruction will be discussed. While vari-
ous NPs are under investigation and some are in clinical trials,
gold nanoparticles (GNP) are among the most mature for this
technique due to the fact that they are among the strongest NP
absorbers of laser light and are already being used clinically for
photothermal treatment of cancer.
∂
∂
T
t
ρ
C
=
(
kT
)
+ ρω−++
()(
CTTq
)
SAR.
(18 .1)
b
b
m
The terms on the right hand side (W/m
3
) are heat diffusion,
blood perfusion (denoted by subscript
b
), metabolic heat genera-
tion (denoted by subscript
m
), and external heat source (specific
absorption rate - SAR), respectively.
The presence of GNP in the tumor can increase the selective
absorption of energy (i.e., laser) and therefore heating within the
tumor compared with traditional thermal therapies. The temper-
ature increase of laser photothermal therapy using GNPs comes
from the heat generated by a large amount of individual GNPs.
The heat generation of single GNP (
Q
nano
) under laser light can
be written as the product of absorption cross section area (
C
abs
,
m
2
) and laser fluence (
I
, W/m
2
) in Equation 18.2. The absorption
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