Magnetic Resonance Imaging Applications of Pseudo-Random Amplitude Modulation

Magnetic resonance imaging (MRI) is a medical imaging technique which can provide fine tissue contrast with relatively high image resolution in human. Besides the image quality, imaging speed is the other major concern in modern MRI, especially in human experiments where sufficient volumetric coverage is necessary. One approach to increase imaging speed is increasing image acquisition speed so that the same amount of volumetric coverage can be achieved within shorter time under conventional experiment paradigms.;In this dissertation, the application of pseudo-random amplitude modulation (PRAM) in MRI was explored to increase imaging speed by designing more efficient experiment paradigms for the human brain. Two relatively slow MRI studies were investigated. The first study was measuring longitudinal relaxation time. A novel method "Relaxation by Amplitude Modulation" (RLXAM) was invented. The RLXAM modulation code can be chosen from a large family of binary sequences. PRAM is a specific implementation using the maximum length sequence, also known as pseudo-random sequence. The other study was measuring transit time distribution in arterial spin labeling. The application of PRAM in transit time measurement was reported before on a 3T Philips Acheiva scanner using a single-slice protocol with standard gradient echo acquisition. The original theory was extended and multi-slice sequences with two different acquisition strategies were developed on a 3T Siemens Trio scanner. Both methods were applied to both phantom and human to demonstrate the theories and evaluate their performance.