The problem to the femoral line is that you will not have any clue on extravasation should it occur. the risk is the extension of the morbidity to the patient where gangrene can happen if not carefully treated

moreover,

the line is crucial for patient medication, if the line was corrupted by the contrast, the patient will loss their precious line to be facilitated by iv medications.

if the clinician was confident, they must be present should the line has to be utilized