Other: Cardiac surgery with cardiopulmonary bypass patients

Patients will be enrolled before cardiac surgery with cardiopulmonary bypass (CPB) and monitored until after the surgery. Patients enrolled will undergo diffusion weighted magnetic resonance imaging and will be administered with cognitive tests one day before surgery and within one week after surgery. Cerebral blood flow velocity as derived from transcranial Doppler recordings will be acquired from the middle cerebral artery synchronously with arterial pressure, invasively derived from the radial artery, and with the electrocardiogram as derived from patient's monitor. Signals will be acquired before anesthesia induction (BASAL), after anesthesia induction and intubation of the chest (ANESTH) and during CPB (CPB). Each acquisition will last at least 5 minutes and will be prolonged to the maximum possible length in keeping with clinical scheduling. Partial pressure of carbon dioxide and other clinical parameters will be acquired too during the intervention.