Prolonged general anesthesia in MR studies of rats

Magnetic resonance (MR) imaging of laboratory animals may require general anesthesia to minimize body movements over many hours. The anesthetization technique should allow physiologic parameters to remain as close to normal as possible, permit fast recovery, allow safe, repeated 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.

In 15 rats (280-483-g body weight), general anesthesia was induced (with intramuscular ketamine hydrochloride, xylazine hydrochloride, acepromazine maleate, and atropine), a tail vein catheter was inserted, and preimaging surgical procedures were performed. A face mask was applied, the animal was positioned in a dorsal recumbent position on an acrylic 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 placed in the bore of a 4.7-T horizontal-bore magnet. The face mask was connected to a non-rebreathing gaseous anesthetic system, and anesthesia was maintained with 1.5-2.0 L/min oxygen and 0.25%-1.50% isoflurane. Oxygen saturation, heart rate, and rectal temperature were continuously monitored.

The duration of intramuscular anesthesia was 110 minutes +/- 12, and the duration of gaseous anesthesia was 106 minutes +/- 43. The monitoring equipment permitted display of vital signs.

The method appeared safe, was easy to perform, maintained a stable physiologic state for the parameters monitored, and could be used for repeated anesthesia in the same animal.