Substudy 1 (healthy adult volunteers)  Inclusion Criteria:  Healthy adult Signed informed consent  Exclusion Criteria:  Dense black hair at the location of measurement Neurological diseases.  Substudy 2 (preterm infants)  Inclusion Criteria:  Pre-term neonates (gestational age at birth less than 37 weeks) Signed informed consent by at least one parent  Exclusion Criteria:  Clinically instability Malformations