This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
Gold standard investigation for recurrent gastrointestinal stromal tumor is 
Select and explain. 
A. MRI, B. MIBG, C. USG, D. PET CT
D: PET CT
Answer: D: PET CT 
Explanation: .Investigation: - Mainly CT scan - Tumour / molecular marker to differentiate it from sarcomas (immunohistochemistry). - Endosonography guided biopsy/guided FNAC are impoant to get histological confirmation. - 18 FDG PET scan is very useful adjunct to CT but reserved for difficult/equivocal cases. ref:SRB&;S manual of surgery,ed 3,pg no 792