Autonomous animal heating and cooling system for temperature-regulated magnetic resonance experiments

Abstract

Temperature is a hallmark parameter influencing almost all magnetic resonance properties (e.g., T₁ , T₂ , proton density, and diffusion). In the preclinical setting, temperature has a large influence on animal physiology (e.g., respiration rate, heart rate, metabolism, and oxidative stress) and needs to be carefully regulated, especially when the animal is under anesthesia and thermoregulation is disrupted. We present an open-source heating and cooling system capable of regulating the temperature of the animal. The system was designed using Peltier modules capable of heating or cooling a circulating water bath with active temperature feedback. Feedback was obtained using a commercial thermistor, placed in the animal rectum, and a proportional-integral-derivative controller was used to modulate the temperature. Its operation was demonstrated in a phantom as well as in mouse and rat animal models, where the standard deviation of the temperature of the animal upon convergence was less than a 10th of a degree. An application where brain temperature of a mouse was modulated was demonstrated using an invasive optical probe and noninvasive magnetic resonance spectroscopic thermometry measurements.

Keywords: MR thermometry; animal temperature; animal thermoregulation; preclinical MRI.

Figure 1.

A. system architecture for the heating/cooling system and temperature measurement setup. Blue and green doted lines represent the collection of Peltier and fan modules, respectively. B. Front and back pictures of the designed box with fans mounted on the heat exchangers. C. 3D printed bed design schematic with water channels allowing water to flow within the bed.

Figure 2.

A. Comparison of temperature control with and without PID control in a liquid phantom. Reduction of temperature fluctuations was observed with the PID control. B. Infrared images of the thermal bed at 15, 30 and 45 °C.

Figure 3.

Comparison of B₁⁺ (A) and SNR (B) maps for axial, coronal, and sagittal slices with and without the temperature probe inserted inside the phantom.

Figure 4.

Time course of heating of the mouse (A) and rat (B) at 36 °C and 39 °C, respectively. Body temperature was measured using a fiber optic temperature probe placed in the rectum of the animal. Red blocks indicate the time at which the target temperatures were set and the yellow blocks show the time for which temperature stabilized.

Figure 5.

Comparison of body and brain temperature in an anesthetized mouse. T1–5 indicate the target temperatures at: 36, 34.1, 36.5, 38, and 35 °C, respectively. Note the absence of heating occurred in minute ~60 (yellow arrow) causing a drop in body temperature, while when heating resumed (at minute 90, green arrow), temperature elevated by ~3.6 °C in 15 minutes.

Figure 6.

Mouse MRS thermometry at two different target temperatures of 36 and 37 °C respectively. Average temperature computed from NAA, Cr, and Cho distances to water was 36.25 and 36.9 °C, respectively. Mean B₀ drift of 0.014 was observed between the two experiments.