Is the lumbar CT scan with dye a risky thing to do?

Not too Risky. The biggest risk would be an allergy to the dye. It is rare, centers knows the cross allergies, that is, red flags about people who are increased risk for an allergic reaction. Centers are also prepared to take appropriate in case there is an allergic reaction. There is also the risk from the radiation associated with the ct.
No. Big risk is spinal fluid leak and headache under 2% routine procedure.