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: Anaesthesia
A 40 year old female underwent surgery. Postoperatively she told the anaesthetist that she was aware of preoperative events. Individual intraoperative awareness is evaluated by – 
Select and explain. 
A. Pulse oximetry, B. Colour doppler, C. Bispectral imaging, D. End tidal CO2
C: Bispectral imaging
Answer: C: Bispectral imaging 
Explanation: Intraoperative awareness (depth of anaesthesia) is monitored by the Bispectral index.