Abdominal pelvic non-contrast magnetic resonance angiography

Abstract

MRI is a powerful modality that has the benefits of non-invasive, non radiative imaging in soft tissue, and it has become an indispensable imaging tool in modern medicine. Vascular diseases can cause blood obstruction and vessel rupture, which may be threatening to life. Modern clinical angiography techniques include Digital Subtraction Angiography (DSA), Computed Tomography Angiography (CTA), and Magnetic Resonance Angiography (MRA). The former two utilize radiation, and Contrast Enhanced MRA uses contrast agents that may cause renal damage, so these are not suitable for special groups such as children, pregnant women, and patients with renal impairment. Therefore, this study focuses on developing new Non-Contrast MRA techniques that can be more widely applied in the population.

In this thesis, two different blood labelling techniques combined with an acquisition sequence for vascular imaging are proposed. Firstly, a Non Subtractive Arterial Spin Labelling (NSASL) module is established based on pseudo-Continuous ASL (pCASL) and multiple Inversion Recovery (IR) theory with a saturation pulse. Simultaneous blood labelling and background suppression can be achieved without the need for control subtraction. Secondly, a central-out stack-of-star balanced Steady State Free Precession (bSSFP) has been adopted to match the 0-crossing point. To reduce severe eddy current artifacts and signal oscillations, a small remainder angle scheme derived from the golden angle and block-based acquisition is introduced for optimization. Then, Velocity Selective ASL (VSASL) has been implemented with the optimized bSSFP. Because of the global labelling mechanism, it supports a larger Field of View (FOV) imaging. Arteriovenous and background separation can be realized through velocity profile design. By combining a shifted Velocity Selective Inversion (VSI) and a Velocity Selective Saturation (VSS), arterial angiography is successfully acquired.

Phantoms and human experimental results demonstrate the feasibility and performance of the two proposed methods. Phantom experiments validated the effectiveness of blood labelling and background suppression. In human abdominal studies, both NSASL and VSASL bSSFP Maximum Intensity Projection (MIP) images clearly depicted distal small vessels, such as the interlobar artery in the renal. Compared with the clinical version of Inflow Inversion Recovery (IFIR), NSASL bSSFP exhibited superior stability and image quality for small-field abdominal and renal angiography. By contrast, VSASL enabled faster scanning time and reliable vascular depiction over a larger FOV.

Finally, the main contributions and limitations of the thesis are summarized, and future plans on research directions are discussed for further technical translation and generalized application.

Date of Award	15 Nov 2026
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Chengbo Wang (Supervisor), Liang Huang (Supervisor), Thomas Meersmann (Supervisor) & Galina E. Pavlovskaya (Supervisor)