Cardiovascular Magnetic Resonance Angiography

Noninvasive aortic imaging

“…At least two post-contrast datasets are then acquired, with an interval of approximately 10 seconds between the two during which the patient can freely breathe. Additional post contrast datasets help visualize structures such as large aneurysms which have slow flow, compensate for variable flow dynamics based on patient cardiac output, allow visualization of venous structures, and can be used for dynamic perfusion data (47). While CE-MRA mainly evaluates vascular lumen, MRA protocols for the aorta should include sequences to visualize vessel walls such as T1-weighted spin echo in the axial plane.…”

“…Repeated radiofrequency (RF) excitation is applied to a slice of interest to saturate the spins of stationary tissue, and inflowing blood which has not been exposed to the repeated RF will have fresh longitudinal magnetization resulting in high signal intensity (54). Sequences with a short repetition time (TR) will maximize flow related enhancement (47). The thickness of the imaging slice should be kept to a minimum and be oriented perpendicular to the direction of flow, to minimize artifactual loss of signal for in-plane flow.…”

“…One of the crucial breakthroughs which allowed high SNR images to be acquired quickly for MRA was the development of parallel imaging, which includes acquisition and reconstruction methods such as SMASH (SiMultaneous Acquisition of Spatial Harmonics) (44), SENSE (SENSitivity Encoding) (45), and GRAPPA (GeneRalized Autocalibrating Partially Parallel Acquisitions) (46). By utilizing phased array RF coils, parallel imaging accelerates acquisition time by encoding additional k-space lines for each line encoded by the magnetic field gradients, with acceleration factors ranging from 2-32 (47). The degree of acceleration is dependent on the degree of SNR that the imager is willing to trade off in the interest of decreased scan time.…”