Prolonged general anesthesia in MR studies of rats

Rationale and Objectives. Magnetic resonance (MR) imaging of laboratory ani mals may require general anesthesia to minimize body movements over many ho urs. The anesthetization technique should allow physiologic parameters to r emain as close to normal as possible, permit fast recovery, allow safe, rep eated use, and avoid attachment of ferrous metal components to the animal. The purpose of this study was to evaluate an anesthetization technique that was developed to meet each of these qualifications. Materials and Methods. In 15 rats (280-483-g body weight), general anesthes ia was induced (with intramuscular ketamine hydrochloride, xylazine hydroch loride, acepromazine maleate, and atropine), a tail vein catheter was inser ted, and preimaging surgical procedures were performed. A face mask was app lied, the animal was positioned in a dorsal recumbent position on an acryli c board, and an isothermal heating pad was placed on the ventral aspect of the abdominal wall. The rat, on the board, was then inserted into a trough that contained a custom-built, linearly polarized birdcage head coil and pl aced in the bore of a 4.7-T horizontal-bore magnet. The face mask was conne cted to a non-rebreathing gaseous anesthetic system, and anesthesia was mai ntained with 1.5-2.0 L/min oxygen and 0.25%-1.50% isoflurane. Oxygen satura tion, heart rate, and rectal temperature were continuously monitored. Results. The duration of intramuscular anesthesia was 110 minutes +/- 12, a nd the duration of gaseous anesthesia was 106 minutes +/- 43. The monitorin g equipment permitted display of vital signs. Conclusion. The method appeared safe, was easy to perform, maintained a sta ble physiologic state for the parameters monitored, and could be used for r epeated anesthesia in the same animal.