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: Unknown
Most sensitive investigation for preoperative localization of abnormal parathyroid glands is: 
Select and explain. 
A. Neck ultrasound, B. (99mTc) labelled Sestamibi isotope scan, C. CT scan, D. MRI
B: (99mTc) labelled Sestamibi isotope scan
Answer: B: (99mTc) labelled Sestamibi isotope scan 
Explanation: Neck ultrasound locates glands in approximately 75% of cases. (99mTc) labeled Sestamibi isotope scans identify approximately 80% of abnormal parathyroid glands.
CT & MRI is not indicated prior to first time neck exploration.