In vitro characterization of an Fe 8 cluster as potential MRI contrast agent

The complex [(tacn) 6 Fe 8 (µ 3 ‐O) 2 (µ 2 ‐OH) 12 ]Br 8 ·9H 2 O (Fe 8 ) was evaluated in vitro as a new kind of possible MRI contrast agent. Relaxivities were measured at 1.41 and 9.4 T for Fe 8 and commercial Gd‐DTPA dissolved in PBS. There was significant difference for r 1 and r 2 values between Fe 8 and Gd‐DTPA at high field (9.4 T) and for r 1 at low field (1.4 T) ( p <0.05). Phantom studies with T 1 ‐weighted MRI at 9.4 T suggest T 1 contrast potential for Fe 8 . That is, up to 5.2 times higher intensity enhancement with respect to that of equimolar Gd‐DTPA was obtained with an Fe 8 concentration, referred to the whole molecule, of 0.2 m M , for which no toxicity on C6 cells could be detected. No toxic effects on cultured C6 cells were observed up to a concentration of 1 m M Fe 8 . Copyright © 2005 John Wiley & Sons, Ltd.