This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Magnetic Resonance Imaging, Subject name: Radiology
BOLD technique is used by which MRI sequence? 
Select and explain. 
A. T1WI, B. DWI, C. FLAIR, D. fMRI
D: fMRI
Answer: D: fMRI 
Explanation: Blood oxygenation level dependent (BOLD) Imaging Is the standard technique used to generate images in functional MRI (fMRI) studies, and relies on regional differences in cerebral blood flow to delineate regional activity. Blood flow in the brain is highly locally controlled in response to oxygen and carbon dioxide tension of coical tissue. When a specific region of the coex increases its activity in response to a task, the extraction fraction of oxygen from the local capillaries leads to an initial drop in oxygenated haemoglobin (oxyHb) and an increase in local carbon dioxide (CO2) and deoxygenated haemoglobin (deoxyHb). The reason fMRI is able to detect this change is due to a fundamental difference in the paramagnetic propeies of oxyHb and deoxyHb.