Relationship Between Simulated Gadolinium‐Based Contrast Agent Injection Profile and Achievable Resolution Metrics in Contrast‐Enhanced Magnetic Resonance Angiography

Abstract

Background Contrast bolus variation during contrast‐enhanced magnetic resonance angiography (CE‐MRA) acquisition may lead to vessel blurring. Purpose To combine knowledge of how contrast signal intensity (SI) evolves for different injection strategies with anatomically familiar parametric computer models to measure and visually assess the effects of a wide range of variables on modeled CE‐MRA, and in doing so develop contrast rate injection guidelines. Study Type Computer modeling. Phantom Digital three‐dimensional phantom consisting of orthogonal “aorta,” 7 mm diameter “renal arteries” (with 57% and 86% diameter stenoses), and 7 mm diameter “superior mesenteric artery” (with 57% diameter stenosis). Field Strength/Sequence One millimeter in‐plane resolution arterial CE‐MRA imaging at 3 T. Assessment “Background” (time invariant) and “vascular” (time varying) components of the phantom were each Fourier transformed into the spatial frequency domain, the latter modulated by the SI evolution of a contrast bolus of varying “plateau” lengths and “tail” heights. Data are presented as surface plots of stenosis measurement error and blurring vs. a reference‐standard injection. Statistical Tests Descriptive. Results Shorter plateau lengths and lower tail heights resulted in increased measured stenosis error and blurring vs. the reference standard. Under a 44‐second acquisition, full width half maximum stenosis error of the 86% stenosis with 25% plateau length and 25% tail height is 24% as compared to that from the reference standard. As plateau length and tail height approach 100%, stenosis error and blurring approach a floor defined by the MR acquisition's limitations. Data Conclusion We propose that to achieve minimal degradation with CE‐MRA, one can create a contrast bolus with either 60% plateau and 50% tail height or 80% plateau with any tail. These considerations may well prove to be of practical importance, possibly via manipulating the tail by means of multiphasic contrast injections. Level of Evidence 3 Technical Efficacy Stage 1

Efficacy of Whole‐Blood Model of Gadolinium‐Based Contrast Agent Relaxivity in Predicting Vascular MR Signal Intensity In Vivo

“…This suggests that there comes a point at which further increases in [GBCA] (i.e., by injecting more quickly or injecting a more concentrated GBCA) will not increase SI, but will instead shorten bolus duration, resulting in image blurring and degradation. [7][8][9][10] The aim of this study was to corroborate the in vitro findings described above by investigating the impact of increasing blood [GBCA] on R 1 and R 2 * in an in vivo animal model.…”

“…Applying these R 1 and R 2 * relationships to clinical imaging, specifically CE‐MRA, it is expected that as [GBCA] increases, first‐pass blood SI for a typical gradient echo sequence will rise, plateau, and ultimately diminish. This suggests that there comes a point at which further increases in [GBCA] (i.e., by injecting more quickly or injecting a more concentrated GBCA) will not increase SI, but will instead shorten bolus duration, resulting in image blurring and degradation 7–10 …”