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- Optimizing Canine MRA: Slower Contrast Injection Improves Imaging Clarity and Reduces Artifacts
Optimizing Canine MRA: Slower Contrast Injection Improves Imaging Clarity and Reduces Artifacts
VRU 2026
Obi Veterinary Education
March 26, 2026
Sunghwa Hong, Eunji Kim, Junghee Yoon, Jihye Choi
Background
Time-resolved magnetic resonance angiography (MRA) improves vascular imaging by capturing dynamic contrast passage, but optimal contrast injection protocols in dogs remain poorly defined. Injection rate and contrast volume critically influence arterial enhancement, venous contamination, and imaging artifacts. Due to physiological differences between humans and dogs, established human protocols may not translate effectively, necessitating species-specific optimization to improve diagnostic performance.
Methods
This prospective experimental study evaluated four contrast injection protocols in five healthy Beagle dogs, combining two injection rates (0.2 vs. 2.0 mL/s) and two contrast volumes (0.2 vs. 0.4 mL/kg). Time-resolved MRA imaging was performed under general anesthesia. Quantitative metrics included maximum signal-to-noise ratio (SNR), peak enhancement time, diagnostic imaging window (dwMRA), and signal homogeneity. Qualitative assessments evaluated vessel visibility, margin clarity, venous contamination, and artifact presence. Statistical analyses included Friedman and Wilcoxon signed-rank tests.
Results
Injection rate significantly affected peak enhancement timing, with higher rates producing earlier peaks, while contrast volume primarily influenced the duration of arterial enhancement and diagnostic window. The low-flow–high-volume protocol (0.2 mL/s, 0.4 mL/kg) yielded the longest diagnostic window, superior vessel visibility, and minimal venous contamination. Maximum SNR did not differ significantly across protocols. High-flow protocols were associated with increased artifacts, including ringing and intravoxel dephasing, whereas low-flow protocols demonstrated better temporal vessel delineation and reduced artifact susceptibility.
Limitations
The study was limited by a small sample size (five dogs) of a single breed with similar body weights, restricting generalizability. Only two injection rates and volumes were tested due to logistical constraints. Physiological variability under repeated anesthesia and focus on extracranial vessels (rather than intracranial vasculature) may also affect applicability. Additionally, inherent limitations of time-resolved MRA, such as reduced spatial resolution, were noted.
Conclusions
A low injection rate combined with a higher contrast volume provides the optimal balance of image quality, vascular visibility, and artifact reduction in canine time-resolved MRA. This protocol is recommended for clinical and research applications, as it enhances diagnostic performance while minimizing common imaging artifacts.
Dorsal images from low-flow–high-volume protocol using time-resolved imaging of contrast kinetics with maximum intensity projection reconstruction. (A) Phase 11 and (B) Phase 15. A red circular region of interest (ROI) for signal intensity was placed at the center of the right common carotid artery in (A), and a blue ROI of identical size was placed at the center of the right external jugular vein in (B). To measure the standard deviation of background noise, identical circular ROIs (white circles) were placed in the air regions on both the left and right sides in (A). A rectangular ROI (yellow rectangle) was also placed at the same level to measure the coefficient of variation. (C) Time–intensity curves generated from circular ROIs placed within the artery and vein. The red and blue lines represent the arterial and venous signal-to-noise ratio (SNR) values, respectively. Colored squares indicate the peak SNR values for each vessel. The diagnostic imaging window for MRA (dwMRA), illustrated as a shaded light red area, corresponds to the area under the arterial SNR area under curve up to the point just before the venous SNR surpasses the arterial SNR.
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