Propofol-based deep sedation is the most common sedation technique used in pediatric MRI [1]. It has been shown that propofol based sedation has both cardiovascular and respiratory side effects [2, 3], and alternative sedation concepts like the combination of propofol with ketamine have been used to perform paediatric MRI [4]. Anaesthetics such as those used for sedation in pediatric MRI affect cerebral blood flow and hemodynamics to varying degrees. The purpose of this investigation was to assess whether there is any difference between these 2 techniques with regard to brain blood flow. A randomized double blinded investigation was initiated on a large cohort of 110 children who've been sedated for brain MRI. Children underwent anaesthetic deep sedation with or without ketamine (1 mg/kg) at induction, followed by propofol 10 vs. 5 mg/kg/hour for maintenance. Irrespective of the sedation regime used, induction was performed either with intravenous propofol boluses or inhalational Sevoflurane until an intravenous line was established. We performed a single slice 2D cine phase-contrast MRI about 5 min after injection of either propopfol (Pr) or a combination of propofol and ketamine (PrK) to assess brain blood flow. The slice was prescribed at the level of the spine (C2/C3) and angulated to include the jugular veins, the internal carotid arteries and the vertebral arteries. The imaging parameters are: Xres x Yres=256 x 160, 2 Nex, 2 VPS, flip-angle = 20°, 32 cardiac phases, peripheral gating, Venc=100 cm/s, FOV=140 mm x 105mm. Among these patients, 58 were diagnostic with negative MRI finding (no lesions, normal ventricle enlargement, no hemorrhage, no histroy of epilepsy, trauma, etc...) and were selected for this study. The mean age at MRI was 59 ± 31 months (range: 3 - 112 months, median 49.5), 35 boys, 23 girls. We used tidam software (www.tidam.fr) to measure both arterial and venous blood flow [5,6]. Multivariate analysis of covariance was performed (SPSS 21.0) to compare drug sedation effect on both arterial and venous blood flow. There was significant age difference between the 2 groups (Pr: 50 ± 34 Mo, PfK: 52 ± 29 Mon, p = 0.002), thus age was included as covariate in the analysis. Arterial flow (estimated marginal mean controlling for age) was equal to 14.29 ml/s in the Pr group and 15.34 in the PrK group. We also measured a 14.34 ml/s venous blood flow in the Pr group and 15.68 ml/s in the PrK group. Comparison of the 2 groups did not show any significant difference neither in the artery (p = 0.37) nor the vein (p = 0.26). We repeated the analysis by subgroup of age under/over 36 months. The propofol group included 13 children (Pr1) under 36 months of age and 19 over 36 months (Pr2). The combined "propofol + ketamine" has 8 children under 36 months (PrK1) and 18 over 36 months. Between group difference (Pr1 vs PrK1) did not reveal any significant difference neither in arterial flow (p=0.22) nor in venous flow (p=0.22). Similarly, we did n to recorded any significant difference between Pr2 and PrK2 (arterial flow p = 0.89, venous flow p = 0.90). Propofol alone and the combination of a single dose ketamine added to propofol are similar in terms of blood flow to and from the brain as measured by phase-contrast MRI. While previous reports on the impact of ketamine on cerebral hemodynamics exist [7], an effect of ketamine on the global cerebral blood flow could not be detected in this group of sedated children.