Table 1.

Recommendations for accurately measuring renal blood flow by phase-contrast MRI

Patient preparation
Hydration	Potential confounder Control by hydrating the patient whenever possible
Data acquisition
Slice orientation	Perpendicular to the vessel direction, prior to any bifurcations Good survey scan (e.g., angiography) needed
TR, TE (ms)	Minimum to reduce acquisition time and flow-induced artifacts
Flip angle (°)	Low to reduce acquisition time, but slightly higher than the optimal flip angle to increase inflow enhancement [(10–30) range]
Velocity encoding (cm/s)	Higher than the peak velocity to avoid aliasing Low enough not to compromise SNR (around 100)
Spatial resolution	Not too high-few pixels are enough Not too low to reliably identify vessels
Motion compensation	Breath-hold or respiratory gating
Cardiac gating	Recommended for arterial flow measurements Either prospective or retrospective ECG
Acquisition time	Below few minutes (to be compatible with multi-parametric MRI protocol)
Image post-processing
Offset correction	Fit background plane to stationary regions (unless correction already integrated in the scanner)
ROI definition	Circular or elliptic, covering the lumen but not the vessel wall By manual, semi-automatic or automatic segmentation tools To be adjusted to account for movement of the vessels during the cardiac cycle
Quality control	Careful visual inspection Scan to be discarded in case of artifacts (even in few voxels of a single time frame)