MO-D-213CD-02: Non-Contrast-Enhanced Magnetic Resonance Angiography Methods for Assessment of Morphology and Flow

Traditional clinical MR Angiography (MRA) provides volumetric datasets to characterize the vessel lumen. These MRA techniques can be generally separated into two categories: • contrast-enhanced MRA, which requires the venous injection of a paramagnetic contrast agent in form of a Gadolinium chelate and • non-contrast-enhanced MRA (NCE MRA), which relies on signal properties of the blood or the motion of the blood to create signal differences between the blood pool and the surrounding tissues. Time-of-Flight (TOF) and Phase- Contrast (PC) imaging have been developed as NCE techniques in the early days of MR imaging. However, widespread clinical adaptation of MRA did not occur until the introduction of CE-MRA in the mid-1990ies with significantly improved robustness. Recent developments have renewed the interest in imaging approaches that do not rely on any external contrast agents. Advances in hardware, especially gradient amplifiers and multi-channel coil technology, have reduced imaging times, improved the signal-to-noise ratio, and reduced artefacts so that NCE MRA is becoming competitive again. These approaches provide viable alternatives in patients that are at risk for nephrogenic systemic fibrosis (NSF) and should not receive a Gd-based contrast agent. In addition, some of those approaches provide insights in functional information beyond the standard luminography. For example, arterial spin labeling (ASL) imaging can be used as a 'pseudo arterial injection' by labeling blood in targeted volumes and tracking its distribution over time. Novel '4D MR Flow' imaging is an extension of traditional PC MRA to capture volumetric velocity vector fields throughout the cardiac cycle, thereby allowing for direct measures of hemdodynamic parameters such as pressure gradient, wall shear stress, pulse wave velocity, kinetic energy, and more. This lecture will provide an overview of the underlying contrast mechanisms of time-of-flight, phase-contrast, balanced steady state free precession (bSSFP), and ASL MRA. Current and potential future roles of these approaches in clinical imaging will also be discussed.

1. Understand the various origins of MRA contrast mechanisms that do not require a contrast agent. 2. Understand the issues related to NCE-MRA imaging including design, acquisition and processing. 3. Understand the benefits, pitfalls, and future potentials of these approaches. My research is sponsored by GE Healthcare.