Rotating Frame Relaxation Times for Off-Resonant MRI Pulses

Rotating Frame Relaxation Times for Off-Resonant MRI Pulses

Vermeulen, Mark (TU Delft Applied Sciences)

Coletti, C. (mentor)
Weingärtner, S.D. (mentor)
Vos, F.M. (graduation committee)
Menzel, Miriam (graduation committee)

Delft University of Technology

Applied Physics

2024-03-15

Magnetic Resonance Imaging (MRI) is an important imaging modality, since it can create high-resolution cross-sectional images of the human body. In MRI scanners, the nuclear spin magnetization is excited using radio-frequency pulses. Images are created based on the time-evolution of this magnetization, which is characterized by relaxation times (T₁,T₂,T_1ρ,…). These relaxation times change from tissue to tissue, and between healthy and diseased tissue.

Rotating frame (T_1ρ) relaxation measurements are a promising technique for assessing slow molecular interactions in tissue. This has applications in articular cartilage imaging, and cardiac imaging without contrast agent injection. T_1ρ measurements require continuous application of an electromagnetic excitation field. Variations of both the main magnetic field and the excitation field strength cause this excitation to be off-resonant. This in turn leads to contrast loss in the final images.

Adiabatic pulses, whose orientation changes slowly in time, are resistant to these off-resonance effects. Their effectiveness is dependent on their parameters, such as the peak sharpness β or the frequency modulation amplitude A. Conventional optimization techniques for these parameters neglect off-resonance effects.

In this project Redfield theory was used to create a pulse optimization algorithm that can take this off-resonance behaviour into account.

Magnetic Resonance Imaging
relaxation time
rotating frame relaxation
off-resonance

http://resolver.tudelft.nl/uuid:962239e4-5c3d-4e94-a6e1-5577c96820e7

Student theses

master thesis

© 2024 Mark Vermeulen