NONINVASIVE MEASUREMENT OF TEMPERATURE DISTRIBUTIONS WITH HIGH-SPATIAL-RESOLUTION USING QUANTITATIVE IMAGING OF NMR RELAXATION-TIMES

The steady-state temperature distribution within a block of cis-polybu tadiene has been mapped using quantitative magnetic resonance imaging. The experiment described makes use of the temperature dependence of t he nuclear magnetic longitudinal relaxation time (T1) of the polymer p rotons. Hot and cold water flowed through two axially mounted pipes in a cylindrical sample, creating a dipolar temperature distribution. A fast inversion recovery imaging sequence was used to map T1 values in the sample with a spatial resolution of 0.3 mm and random error of +/- 5% for individual pixels in the 128X128 image. The T1 values thus obta ined were converted into temperatures using an empirical calibration c urve, leading to a temperature resolution of +/-2 K for each pixel. Us ing a median filter (which reduces the image resolution by a variable factor of up to 3), the data are rendered smooth enough to obtain a cl ear contour plot. This is compared with a finite element solution of L aplace's equation over the same domain, demonstrating that the MRI tec hnique is reliable. A number of experimental problems limiting both th e exact comparison between theory and experiment and the long-term uti lity of the technique are discussed.