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: Radiology
Which is of the following is used in investigating a parathyroid pathology? 
Select and explain. 
A. CT scan, B. Gallium scan, C. Thallium scan, D. T.C thallium subtraction scan
D: T.C thallium subtraction scan
Answer: D: T.C thallium subtraction scan 
Explanation: Gallium scan is used for tumors. Thallium scan is used to study myocardial perfusion.