This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urology, Subject name: Anatomy
[{'content': 'Trans rectal ultrasonogram in evaluation of carcinoma prostate most useful for: \nSelect and explain. \nA. Taking guided biopsy, B. Identifying seminal vesicle invasion, C. Nodal sampling, D. Measuring the extent of invasion', 'role': 'user'}, {'content': 'Answer: A \nExplanation: TRUS is the imaging technique most frequently used to assess the primary tumor, but its chief use is directing prostate biopsies, not staging" - Harrison Thus primary role of TRUS is guiding prostate biopsies Other uses are assessing extent of invasion if cancer is detected. measurement of prostate volume which is needed in the calculation of the PSA density. also used in performance of cryosurgery & brachytherapy. Ref :Smith\'s Urology 17/e p361', 'role': 'assistant'}]