In vivo T1 measurements of canine brain for deep tissue temperature measurements with MRI.
The possibility of deep tissue temperature imaging with a magnetic resonance (MR) imager was studied in 30 mongrel dogs. The coronary view of the brain of a dog anesthetized with muscle relaxant and pentobarbital and ventilated automatically with air was taken with a special head coil by a 0.1 Tesla MR imager, Asahi Mark-J, driven by a spin warp pulse sequence. T1s in the imaging of the right and left white matter, grey matter, thalamus and caudate nucleus were measured with rectal temperature in group I (10 dogs) for a control study every 30 min until 120 min without intervention, in group II (10 dogs) for hyperthermia with extracorporeal bypass method, before heating, at 41 and 42 degrees C, in group III (10 dogs) for hypothermia, before cooling, at 35 and 30 degrees C and after rewarming, respectively. In groups I, II and III, the T1s at all sites except the white matter at 42 degrees C did not change significantly at any rectal temperature. T1 prolongation in the white matter at 42 degrees C may be due to edema, probably because of biological reaction to hyperthermia. The present study suggests that deep tissue temperature imaging in vivo by T1s measured with the MR imager may be impossible in spite of obvious evidence of T1 dependance on temperature in theoretical, in vitro and ex vivo studies already achieved.