Effect of injection rate on contrast-enhanced MR angiography image quality: Modulation transfer function analysis
Contrast-enhanced (CE)-MRA optimization involves interactions of sequence duration, bolus timing, contrast recirculation, and both R1 relaxivity and R*2-related reduction of signal. Prior data suggest superior image quality with slower gadolinium injection rates than typically used.Methods
A computer-based model of CE-MRA was developed, with contrast injection, physiologic, and image acquisition parameters varied over a wide gamut. Gadolinium concentration was derived using Verhoeven's model with recirculation, R1 and R*2 calculated at each time point, and modulation transfer curves used to determine injection rates, resulting in optimal resolution and image contrast for renal and carotid artery CE-MRA. Validation was via a vessel stenosis phantom and example patients who underwent carotid CE-MRA with low effective injection rates.Results
Optimal resolution for renal and carotid CE-MRA is achieved with injection rates between 0.5 to 0.9 mL/s and 0.2 to 0.3 mL/s, respectively, dependent on contrast volume. Optimal image contrast requires slightly faster injection rates. Expected signal-to-noise ratio varies with both contrast volume and cardiac output. Simulated vessel phantom and clinical carotid CE-MRA exams at an effective contrast injection rate of 0.4 to 0.5 mL/s demonstrate increased resolution.Conclusion
Optimal image resolution is achieved at intuitively low, effective injection rates (0.2–0.9 mL/s, dependent on imaging parameters and contrast injection volume). Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.