Parameter estimation in reconstructing temperature fields during hyperthermia.

Persistent Link:
http://hdl.handle.net/10150/185613
Title:
Parameter estimation in reconstructing temperature fields during hyperthermia.
Author:
Liauh, Chihng-Tsung.
Issue Date:
1991
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
In this dissertation, a state and parameter estimation algorithm is implemented and modified to predict the blood perfusions and thus the complete steady-state temperature fields based on input from a limited number of temperature measurements taken during simulated hyperthermia treatments. Several fundamental phenomena related to this inverse problem are investigated from simple direct models. The general conditions under which these multiple minima occur are shown to be solely due to the existence of symmetries in the inverse problem formulation. Both an adjoint formulation and a sensitivity equation method are derived and used to determine the elements in the Jacobian matrix associated with the inverse problem of estimating the blood perfusion and temperature fields during hyperthermia cancer treatments. These methods and a previously developed influence coefficient method for obtaining that matrix are comparatively evaluated by solving a set of numerically simulated inverse hyperthermia problems. An improved state and parameter estimation algorithm has been developed to reduce the total computational time required. If the change of the unknown perfusion parameters is small a linear approximation scheme is implemented in which the old Jacobian matrix (or sensitivity matrix) is used, instead of recalculating the new Jacobian matrix for the next iteration. Results show that if the temperature is approximated as a linear (or quasi-linear) function of the blood perfusion, the linearizing approach considerably reduces the CPU time required to accurately reconstruct the temperature field. One of the model mismatch problems between the actual tumor and the simulated models is selected and investigated for the one-dimensional case. The model mismatch present in this dissertation is caused by the discretization of a perfusion field into several discrete zones. It is our attempt to understand the effects of the model mismatch problems from a simple model, and then generalize to more complicated three-dimensional cases which could occur during hyperthermia treatments. To simulate the ultrasound hyperthermia treatments, a scanned focussed ultrasound power field is generated and then used to create the transient power-on data and the steady-state temperature field. The feasibility of using the transient power-on data to estimate the attenuation coefficient and the blood perfusion and thus reconstruct the steady-state temperature field is presented.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Dissertations, Academic; Biomedical engineering.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Aerospace and Mechanical Engineering; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Roemer, Robert B.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleParameter estimation in reconstructing temperature fields during hyperthermia.en_US
dc.creatorLiauh, Chihng-Tsung.en_US
dc.contributor.authorLiauh, Chihng-Tsung.en_US
dc.date.issued1991en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractIn this dissertation, a state and parameter estimation algorithm is implemented and modified to predict the blood perfusions and thus the complete steady-state temperature fields based on input from a limited number of temperature measurements taken during simulated hyperthermia treatments. Several fundamental phenomena related to this inverse problem are investigated from simple direct models. The general conditions under which these multiple minima occur are shown to be solely due to the existence of symmetries in the inverse problem formulation. Both an adjoint formulation and a sensitivity equation method are derived and used to determine the elements in the Jacobian matrix associated with the inverse problem of estimating the blood perfusion and temperature fields during hyperthermia cancer treatments. These methods and a previously developed influence coefficient method for obtaining that matrix are comparatively evaluated by solving a set of numerically simulated inverse hyperthermia problems. An improved state and parameter estimation algorithm has been developed to reduce the total computational time required. If the change of the unknown perfusion parameters is small a linear approximation scheme is implemented in which the old Jacobian matrix (or sensitivity matrix) is used, instead of recalculating the new Jacobian matrix for the next iteration. Results show that if the temperature is approximated as a linear (or quasi-linear) function of the blood perfusion, the linearizing approach considerably reduces the CPU time required to accurately reconstruct the temperature field. One of the model mismatch problems between the actual tumor and the simulated models is selected and investigated for the one-dimensional case. The model mismatch present in this dissertation is caused by the discretization of a perfusion field into several discrete zones. It is our attempt to understand the effects of the model mismatch problems from a simple model, and then generalize to more complicated three-dimensional cases which could occur during hyperthermia treatments. To simulate the ultrasound hyperthermia treatments, a scanned focussed ultrasound power field is generated and then used to create the transient power-on data and the steady-state temperature field. The feasibility of using the transient power-on data to estimate the attenuation coefficient and the blood perfusion and thus reconstruct the steady-state temperature field is presented.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectDissertations, Academicen_US
dc.subjectBiomedical engineering.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineAerospace and Mechanical Engineeringen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorRoemer, Robert B.en_US
dc.contributor.committeememberChan, Choliken_US
dc.contributor.committeememberTharp, Hal S.en_US
dc.identifier.proquest9202084en_US
dc.identifier.oclc711788664en_US
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