We compared the effects of intravenous administration of @ % hydroxyethyl starch ( maize-derived ) in @ % saline ( Voluven ; Fresenius Kabi , Runcorn , United Kingdom ) and a `` balanced '' preparation of @ % hydroxyethyl starch ( potato-derived ) -LSB- Plasma Volume Redibag ( PVR ) ; Baxter Healthcare , Thetford , United Kingdom -RSB- on renal blood flow velocity and renal cortical tissue perfusion in humans using magnetic resonance imaging .