This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Investigation of choice in the early phase of renal transplant 
Select and explain. 
A. IVP, B. Retrograde cystourethrogram, C. Ultrasonogram, D. CT scan
C: Ultrasonogram
Answer: C: Ultrasonogram 
Explanation: • Vascular complications after renal transplantation are low, presents during the first week after transplantation with sudden pain and swelling at the site of the graft.
• Diagnosis is confirmed by Doppler ultrasonography.
• Urgent surgical exploration is indicated and, in most cases, transplant nephrectomy is required.