This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Radiology
[{'content': 'What is the gold standard investigation of choice for deep vein thrombosis? \nSelect and explain. \nA. Double contrast duplex, B. Venography, C. CT scan, D. MRI', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B. Venography* Duplex ultrasound is the initial investigation of choice in nearly all patients with suspected DVT.* Its reliability is dependent upon the skill of the user.* Major axial veins of the lower limb are well displayed.* It has a sensitivity of 98.7% and specificity of 100% for above-knee DVT and a sensitivity of 85.2% and specificity of 98.2% for below-knee DVT.* Gold standard/Best test for venous occlusion is invasive venography.', 'role': 'assistant'}]