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
[{'content': 'Which of the following is the investigation of choice for assessment of depth of penetration and perirectal nodes in rectal cancer \nSelect and explain. \nA. Trans rectal ultrasound, B. CT Scan pelvis, C. MRI Scan, D. Double contrast Barium enema', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Investigations for Rectal Carcinoma \nFor Diagnosis -\n\nBest diagnosed by sigmoidoscopy (rigid, not flexible) & Biopsy of tumor\nBarium enema\n\nFor staging\n\nTRUS (transrectal ultrasonography)\nCT\nMRI\n\nTRUS — (transrectal ultrasonography)\n\nThe depth of tumor invasion can be accurately determined by TRUS\nBut it cannot detect cancer metastasis in lymph node (though it can detect enlarged lymph node, but it cannot predict if — cancer infiltration is present or not).\n\nCT\n\nCT scan is also helpful for evaluation of cancer extension.\nBut again, CT also cannot tell clearly about lymph node invasion by cancer cell.\n\nMRI\n\nIt has become the most useful investigation tool (especially with the use of transrectal coils) for rectal carcinoma.\nIt can very well predict the invasion of tumor in the rectal wall as well as lymph node invasion with high accuracy.', 'role': 'assistant'}]