Dr. Sharma used a brain imaging method to look at sleep patterns of teenagers who suffered from insomnia. This brain imaging method allowed her to know when something was happening (meaning she was able to see brain waves), however, she could not tell what was causing it. What brain imaging method did Dr. Sharma most likely use?

a. Electroencephalography (EEG)
b. Functional magnetic resonance imaging (fMRI)
c. Positron emission tomography (PET) scan
d. Computerized tomography (CT) scan