Biomedical Engineering Reference
In-Depth Information
6
3D SHG Imaging and
Analysis of Fibrillar
Collagen Organization
6.1 Introduction ......................................................................................125
Limitations of Existing SHG Analysis Techniques
6.2 Methods..............................................................................................128
SHG Imaging System • 3D SHG Imaging
Measurements • Measurement of Bulk Optical Parameters • Monte
Carlo Simulations
6.3 SHG Phasematching in Tissues ...................................................... 131
Introduction to Phasematching • Heuristic Model of Phasematching
in Collagenous Tissues • Relaxed Phasematching Conditions and
SHG Directionality • Fiber Morphology
6.4 Results of 3D Imaging and Analysis..............................................137
SHG Imaging of the Murine Model of Osteogenesis
Imperfecta • Ovarian Cancer
6.5 Discussion .......................................................................................... 147
References......................................................................................................148
Paul J. Campagnola
University of
Wisconsin—Madison
6.1 introduction
Second harmonic generation (SHG) imaging microscopy has great potential for visualization of disease
states where there is change in collagen structure. This is because SHG, as a second-order nonlinear
optical process, requires a noncentrosymmetric environment, and tissue alterations modify the overall
symmetry of the collagen architecture. Specifically, SHG is an exquisitely sensitive probe of the fibrillar
structure in tissues as it directly visualizes the supramolecular assembly, over the size scale of collagen
fibrils to fibers, that is, from ~50 nm to a few microns. While there are approximately 20 isoforms of
collagen, type I collagen (also known as col I) is the most abundant one and in fact is the most abundant
protein in the body. It is either the primary component or at least a component of the structure in the
matrix in diverse tissues such as tendon [1-3], skin [4,5], cornea [6,7], blood vessels [8], and bone and
also in internal organs such as lung [9], liver [10], and kidney [11]. Given this range of tissues, it is pos-
sible that SHG could be used to image collagen changes in a wide range of pathologies. For example,
many connective tissue disorders including osteogenesis imperfecta (OI) and scleroderma are charac-
terized by abnormal collagen assembly and SHG may reveal differences in the morphology of diseased
fibers not possible by other optical methods [12]. In addition, it is becoming increasingly documented
that extracellular matrix (ECM) changes occur in most cancers. Similarly, fibrosis, that is, an increase
in collagen, secretion is associated with several diseases and is further associated with poor prognoses.
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