Flow mediated dilatation (FMD) assessment via an MRI integrated signal intensity (IntSI) approach: A comparison with ultrasound
Year: 2017
Type: dissertation
Abstract: Endothelial dysfunction is a precursor of atherosclerosis. Flow mediated dilatation (FMD) is a measure of endothelial function. Ultrasound (US) is often used during FMD studies, but US- FMD is technically challenging. MRI methods for FMD rely on high spatial resolution but this entails a trade off involving temporal resolution and SNR. An adequate temporal sampling frequency is however required to detect the peak dilatation. In this thesis, concepts in hemodynamics and MRI physics were explored in order to develop a reliable MRI-FMD technique that is comparable with US-FMD. The approach was to measure the luminal area as a function of the integrated signal intensity (IntSI) of the lumen, since signal intensity increases with area. An equation was derived to account for concurrent velocity based increases in signal intensity. Phantom studies showed the IntSI technique as a reliable means of measuring the luminal area, provided that certain assumptions are not violated. Next, the IntSI technique was adapted for in vivo application. The popliteal artery was the artery of choice based on its anatomical advantages. The velocity profile and time averaged velocities of the popliteal artery were determined from spectral Doppler analysis, in order to design an in vivo technique that is compatible with the assumptions on which the IntSI technique is based. When applied in vivo, the IntSI technique overestimated luminal area measurements compared to a conventional MRI approach. Numerical optimization was used to obtain a correction factor to account for the bias. Subsequently, the IntSI technique was applied for measuring the luminal area during MRI-FMD and compared with US-FMD. The IntSI technique provided repeatable FMD measurements. Although the thesis did not demonstrate that the popliteal MRI-FMD using the IntSI technique was superior to US-FMD, it was non-inferior to US-FMD.
Source: TSpace (University of Toronto)
Author: Omodele Olowoyeye
Language: English
Subfield: Cardiology and Cardiovascular Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2788008607