Figure 1

Thermal environments.

(a) Schematic of the conventional head radio frequency coil (CONV) and CryoProbe (CRYO) mouse cradles (view from above) illustrating their heating system – a warm water circulation loop (red) – and indicating the ventral temperature measurement sites (loop, mid, front). (b) Schematic of the ROCKET setup (top: view from above; bottom: view from side) illustrating geometry and temperature measurement locations for ambient air temperature, dorsal and ventral trunk, scalp temperature and ambient air temperature around the head (head space) in all setups. The suspended grid for placing the animal allows for non-contact warming of the animal. The insulating sheet between head and coil surface is illustrated in magenta. The thermostimulation system (TS) is shown from above in the top panel. (c) Body temperatures of awake (n = 9) and isoflurane anesthetized mice in three fMRI setups: CONV (n = 5), CRYO (n = 5) and ROCKET (n = 6) setup. Rectal temperature and body surface temperatures – scalp, dorsal and ventral trunk at different locations (loop, middle (mid) and front) – were plotted (mean (s.d.)); see measuring locations in panels (a,b). Range of circadian CBT variation (gray shading); temporal mean (gray dotted line)²³. The red gradient indicates cumulative equivalent minutes at 43 °C (red dotted line) beginning at 39 °C²⁷. (d) Temperature differences of respective body sites referenced against rectal temperature measured in the ROCKET (mean ± s.e.m.). (e) Thermal gradient of the CryoProbe surface with thermal shield set to 38 °C and 48 °C (measured outside the scanner at room temperature (20 °C)). Note the marked increase in surface temperature towards the internal heater located 8 cm distal from experimental head position (see (b)). (f,g) Color-coded temperature difference matrices illustrate body temperature distribution (at 36.3 °C ± 0.5 °C rectal temperature) within the tested experimental setups versus awake mice. The ROCKET setup resembles the situation of awake mice, except for the ambient air temperature, which must be raised to CBT in the ROCKET setup. (a–g) Ambient air temperatures were 20.0 °C (awake), 28.2 °C (CONV), 30.6 °C (CRYO) and 36.0 °C (ROCKET).