| Fluid dynamics has a wide range of applications including biomedical. Traditionally, experimental fluid mechanics has involved invasive techniques to study flow dynamics. The advent of magnetic resonance imaging (MRI) in the 1970's presented a powerful new noninvasive, diagnostic tool for biomedical applications. However, the slow acquisition times associated with MRI limited its usefulness in vivo for regions with flow and motion. Recent advances in ultra-fast MRI allow one to obtain quality images that are not affected by the typical degrading effects of flow. With the development of the Rotating Ultra-Fast Imaging Sequence (RUFIS) in 1995, it is possible to quantitatively measure flow rates at velocities typically seen in vivo. In addition, RUFIS allows one to verify older, invasive studies of fluid flows under various conditions.; In this work, we describe the application of RUFIS to study laminar and turbulent flows through straight channels, flow emerging from a stenosis, and flow through a curved tube. The results are compared to other invasive studies and applicable theory.; In order to implement RUFIS and obtain precise measurements, technological advancements are required in eddy current compensation, and gradient field and RF probe performance. In addition, pulse sequence design improvements are needed to minimize imaging errors and techniques for processing the MR data are required. We present our approaches to resolving the technical challenges associated with quantitative flow assessment and data processing. These approaches include a programmable pre-emphasis system and a Linear Algebra Method (LAM) for reconstructing oversampled, bandlimited Free Induction Decay (FID) data.; The challenges of applying our flow assessment techniques in vivo are delineated for various specimen sizes and imager types. Preliminary in vivo imaging results for the rat thorax using various preparation sequences in conjunction with RUFIS are demonstrated. Techniques for enhancing the signal-to-noise and image resolution are described including RF pulse flip angle optimization and refocused RUFIS magnetization. |
