An MRI-Compatible High Frequency AC Resistive Heating System for Homeothermic Maintenance in Small Animals

PURPOSE To develop an MRI-compatible resistive heater, using high frequency alternating current (AC), for temperature maintenance of anaesthetised animals. MATERIALS AND METHODS An MRI-compatible resistive electrical heater was formed from narrow gauge wire connected to a high frequency (10-100 kHz) AC power source. Multiple gradient echo images covering a range of echo times, and pulse-acquire spectra were acquired with the wire heater powered using high frequency AC or DC power sources and without any current flowing in order to assess the sensitivity of the MRI acquisitions to the presence of current flow through the heater wire. The efficacy of temperature maintenance using the AC heater was assessed by measuring rectal temperature immediately following induction of general anaesthesia for a period of 30 minutes in three different mice. RESULTS Images and spectra acquired in the presence and absence of 50-100 kHz AC through the wire heater were indistinguishable, whereas DC power created field shifts and lineshape distortions. Temperature lost during induction of anaesthesia was recovered within approximately 20 minutes and a stable temperature was reached as the mouse's temperature approached the set target. CONCLUSION The AC-powered wire heater maintains adequate heat input to the animal to maintain body temperature, and does not compromise image quality.