Abstract
PurposeTo develop an MRI-compatible resistive heater, using high frequency alternating current (AC), for temperature maintenance of anaesthetised animals.Materials and MethodsAn 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.ResultsImages 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.ConclusionThe AC-powered wire heater maintains adequate heat input to the animal to maintain body temperature, and does not compromise image quality.
Highlights
It is well-known that the thermoregulatory mechanisms in mice are suppressed during general anaesthesia [1,2,3]
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
We recently described the use of an MRI compatible electrical resistive heater for thermoregulation in mice for MRI applications where space is limited [9]
Summary
It is well-known that the thermoregulatory mechanisms in mice are suppressed during general anaesthesia [1,2,3]. We present an improved design in which a single wire electrical heating element is used in combination with a high frequency AC power source to form an MRI-compatible heating system which uses a temporal, rather than a spatial self-cancellation of stray magnetic fields. This is directly analogous to the application of the refocusing gradient pulses that are applied in MRI and MRS, for example, to maximise signal that is lost during RF excitations, and to allow echo centering during acquisition periods
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