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SOFT TISSUE CHARACTERIZATION FOR IMPROVING SURGICAL
PROCEDURES
by
Kinon Chen
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Ful llment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(BIOMEDICAL ENGINEERING)
August 2008
Copyright 2008 Kinon Chen
Object Description
| Title | Soft tissue characterization for improving surgical procedures |
| Author | Chen, Kinon |
| Author email | kinonche@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Biomedical Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2008-06-19 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-07-24 |
| Advisor (committee chair) | Weiland, James D. |
| Advisor (committee member) |
Meng, Ellis F. Bardet, Jean-Pierre |
| Abstract | Soft-tissue biomechanics (Chapter 1). This is just a brief introduction to soft-tissue mechanics for readers' convenience.; Vascular tissues (Chapter 2-5). We study whether an inverse modeling approach is applicable for characterizing blood-vessel tissue subjected to various levels of internal pressure and axial stretch that approximate in-vivo conditions. To compensate for the limitation of axial-displacement/pressure/diameter data typical of clinical data, which does not provide information about axial force, we propose to constrain the ratio of axial to circumferential elastic moduli to a typical range. Vessel wall constitutive behavior is modeled with a transversely isotropic hyperelastic equation that accounts for dispersed collagen fibers. A single-layer and a bi-layer approximation to vessel ultrastructure are examined, as is the possibility of obtaining the fiber orientation as part of the optimization. Characterization is validated against independent pipette-aspiration biaxial data on the same samples. It was found that the single-layer model based on homogeneous wall assumption could not reproduce the validation data. In contrast, the constrained bi-layer model was in excellent agreement with both types of experimental data. Due to covariance, estimations of fiber angle were slightly outside of the normal range, and it can be resolved by predefining the angles to normal values. Our approach is relatively invariant to a constant or a variable axial response. We believe that it is suitable for in-vivo characterization.; Ocular tissues (Chapter 6-9). We study the elastic properties of porcine posterior retina, choroid, and sclera. Almost all of the previous mechanical studies on the retina, choroid, and sclera neglected the fact that the particular water content and/or temperature in soft tissues in vivo may have significant biomechanical contribution to these tissues, and changing these conditions may alter their mechanical properties. Furthermore, only one of these studies in the past had measured the degree of anisotropy as well as the thickness of their samples. In the present study, we want to demonstrate the hydraulic and temperature effect in the retina, choroid, and sclera by characterizing and comparing their elastic properties in different testing environments. Furthermore, we hope to examine their degree of anisotropy and thickness variation between samples. We also want to compare the mechanical properties of each layer to the others. Strips of tissue samples were dissected from the eyes, and they were tested in a tensile machine in three testing environments: 1) room-temperature air, 2) room-temperature saline, and 3) body-temperature saline. Thickness of the adjacent samples was measured under a microscope to estimate the thickness of the actual testing samples.; It was found that the thickness of the retina, choroid, and sclera can vary between samples, and the standard deviation values were about 25 %, 21 %, and 18 % of the measured mean values in the retina, choroid, sclera respectively. The elastic properties of these layers were significantly different in room-temperature air versus room-temperature saline. Their properties were also significantly different in room-temperature saline versus body-temperature saline. The elastic properties of each layer were very different from the others. In addition, they were found to be significantly anisotropic in 10 % confidence level but not in 4 % level. These results suggest that each posterior layer has a very unique properties versus the others, the posterior retina, choroid,and sclera may be significantly anisotropic but will need further study to confirm, and there is a significant biomechanical dependency of these layers on water and temperature. In conclusion, the retina, choroid, and sclera should be tested in body-temperature saline, which is in general believed to a testing environment that is similar to the in-vivo habitat from bench-top testing. Thickness of each sample should be measured, and their anisotropic behavior should be put into consideration in future testing. |
| Keyword | blood vessel; retina; choroid; sclera; soft tissue; mechanical properties |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Type | texts |
| Legacy record ID | usctheses-m1404 |
| Contributing entity | University of Southern California |
| Rights | Chen, Kinon |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Chen-20080724 |
| Archival file | uscthesesreloadpub_Volume26/etd-Chen-20080724.pdf |
Description
| Title | Page 1 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | SOFT TISSUE CHARACTERIZATION FOR IMPROVING SURGICAL PROCEDURES by Kinon Chen A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Ful llment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (BIOMEDICAL ENGINEERING) August 2008 Copyright 2008 Kinon Chen |
