Cardiovascular magnetic resonance imaging: Error sources in phase contrast flow measurements

Juha Peltonen

    Research output: ThesisLicenciate's thesis

    Abstract

    Phase contrast velocity encoded flow measurement was first introduced 30 years ago and have been subject to constant evolution since. The method has been validated repeatedly to be suitable for numerous clinical applications. It is capable to visualize and quantify dynamic phenomena such as blood flow in any part of the human body without being invasive or using ionizing radiation. Recent publications even suggest that velocity encoded imaging should be used as a gold standard in the flow measurements of great arteries. Despite of numerous possibilities, the method remains underused. However, phase contrast flow imaging carries some challenges that are limiting clinical applicability. First of all, magnetic resonance imaging is expensive and time consuming imaging modality. Currently velocity encoded flow imaging can be seen as a secondary modality which is used if necessary after alternative methods such as ultrasound. Also, phase contrast flow imaging includes numerous physical and physiological error sources affecting the accuracy of flow measurements. The understanding of these error sources is important to be able to estimate the accuracy of obtained results. An overview on these error sources is presented in this work. Essential theoretical basis to understand the physics underlying the error mechanisms are presented and means to minimize the error are addressed. The dimensions of human arteries are varying considerably along the flow track beyond the ventricles. Changing geometrical dimension and individual characteristics of cardiac valves are giving a raise to several spatially alternating flow phenomena such as acceleration artefact and voxel dephasing. In this work a research is presented where optimal measurement plane to quantify stroke volume is studied. The importance of optimal measurement plane is studied in both healthy controls and patients with accelerated flow velocities. In the work it was found that optimal location to measure arterial flow is approximately 2 cm distal from the aortic or pulmonal valve in case of accelerated flow. In controls no such relation was found between the measurement plane and the stroke volume. We are also considering the amount of hardware velocity offset in our measurement system and discussing how it affects to the results.
    Original languageEnglish
    QualificationLicentiate's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Ilmoniemi, Risto, Supervising Professor
    • Sipilä, Outi, Thesis Advisor
    Publisher
    Publication statusPublished - 2013
    MoE publication typeG3 Licentiate thesis

    Keywords

    • MRI
    • Phase contrast flow imaging

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