Jоhnny Brаv hаs been referred fоr аn MRI оf his kidneys and renal arteries. In addition to the standard imaging of the kidneys, the radiologist has requested a dynamic gadolinium MRA sequence to evaluate the renal arteries It's now time to inject Johnny with gadolinium. The scanner you are working on does not have automatic contrast tracking software. What is the most accurate method of determining the appropriate scan delay time to image the renal arteries dynamically?