Thesis

A novel method for detecting and recording movement and functional performance of cardiac valve prostheses exposed to the static magnetic field associated with magnetic resonance imaging

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Awarding institution
  • University of Strathclyde
Date of award
  • 2013
Thesis identifier
  • T13397
Qualification Level
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Department, School or Faculty
Abstract
  • Aging and disease processes are known to compromise tissue strength and consequently increase the risk of harmful movement or detachment of a heart valve prosthesis in vivo when exposed to strong magnetic forces associated with magnetic resonance imaging (MRI). Research however, has failed to fully assess prosthetic valve movement or functional valve impedance in the MR environment. This study seeks to design and evaluate an MR compatible device which aims to detect and measure ex vivo, frequency, direction and magnitude of movements and leaflet function in vitro of nine prosthetic heart valves in the static magnetic field (B₀) of a 1.5 Tesla (T) and a 3.0 T MR system. A valve holder incorporating strain gauges connected to a strain gauge recorder and laptop computer were used to detect and record displacement and rotational valve movements and, a hydro-pneumatic system recorded pressure changes across the valve indicative of any MR induced alteration in leaflet performance in vitro. The data confirms the compatibility of the test apparatus in the MR environment and its capacity to detect and record valve movement and changes in functional valve performance in field strengths ≤3.0 T. Real-time three-dimensional movements were detected in both B₀ fields in all valves, differences in entry and return profiles and static and dynamic measurements were recorded. Furthermore, applied magnetic forces leading to prosthesis movement were greater than previously reported. Functional valve impedance was detected in three valves but no commonality between valve types or sub-groups regarding this, type, frequency, magnitude or patterns of valve movements were noted. These data suggests magnetism is induced and retained in valve prostheses during exposure to the MR environment and patients with friable valvular tissue are at significantly increased risk of prosthetic valve movement and/or dehiscence. Furthermore, current uses of static measurements to assess risk are inadequate.
Resource Type
Note
  • This thesis was previously held under moratorium from 10th June 2013 until 10th June 2014.
DOI
Date Created
  • 2013
Former identifier
  • 989804

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