Racemic ketamine and S-ketamine are used in clinical practice today. Little is known of their difference in effect on cerebral blood flow, volume and metabolism. cerebral blood flow (CBF) measuring techniques are limited in time so constant measurement to mirror a dynamic process is impossible or very difficult. A novel MRI application, arterial spin labeling, offers the possibility that without radiation or contrast, to measure semi-continuous CBF with measurements every 60-120 seconds. The investigators will give 14 healthy volunteers both study drugs in a randomised sequence with one week apart and measure regional CBF during the study period of 45 minutes after a sub-anaesthetic bolus dose of 0,6 mg/kg racemic ketamine and 0,3 mg/kg S-ketamine The investigators hypothesize that there is no difference between racemic ketamine and S(+)-ketamine with regards to Arterial Spin Labeling (ASL) measured cerebral blood flow.
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regional cerebral blood flow
Timeframe: - Measured every 30 seconds from baseline to 45 min after study drug injection