Optimization of Contrast Injection Protocols for Time-Resolved MRA Technique in Dogs: A Comparative Study of Vascular Signal Characteristics and Artifacts.

This study aimed to optimize magnetic resonance angiography (MRA) protocols for time-resolved MRA imaging in dogs by using different injection rates and contrast volumes. In this experimental and prospective study, four protocols combining two flow rates (0.2 and 2.0 mL/s) and two contrast volumes (0.2 and 0.4 mL/kg, equivalent to 0.1 and 0.2 mmol/kg gadolinium) were applied in five healthy beagle dogs. Quantitative measurements, including maximum signal intensity, peak enhancement time, diagnostic window, and signal homogeneity, were obtained for the common carotid artery and external jugular vein. Qualitative assessment included arterial visibility persistence, wall margin clarity, and artifact evaluation. Statistical comparisons were performed using the Friedman and Wilcoxon signed-rank tests, and effect size analysis was used to further interpret nonsignificant trends. The low-flow-high-volume protocol (0.2 mL/s, 0.4 mL/kg) yielded the longest diagnostic window and superior vessel visibility with minimal venous contamination, while maintaining comparable maximum signal intensity to higher flow rate protocols. Artifact-related issues such as ringing and intravoxel dephasing were least observed in the low-flow-high-volume protocol. Although high-flow-high-volume protocol showed improved signal homogeneity, it was associated with greater artifact susceptibility. Interobserver agreement ranged from fair to substantial (κ = 0.457-0.681), with greater variability in artifact-related scores. These findings suggest that a slower injection rate with higher contrast volume, as seen in the low-flow-high-volume protocol, provides the best balance of image quality and diagnostic performance, supporting its recommendation as a preferred protocol for small-animal time-resolved MRA.