ABSTRACT
Since both the chemical environment and relaxation properties of the nuclei that are the
source of the signal in magnetic resonance (MR) are sensitive to Brownian motion and
the associated molecular tumbling rates, MR imaging (MRI) techniques are intrinsically
sensitive to temperature. Of the many MR parameters that can provide temperature-
sensitive contrast, the temperature dependence and sensitivity of several parameters in
particular, have proven useful for monitoring temperature changes in soft tissue during
delivery of hyperthermia or thermal therapies: the apparent diffusion constant of water
(D), the spin-lattice relaxation time (T1), and the water proton resonance frequency (PRF). The temperature sensitivities associated with each of these parameters are large
enough to allow temperature-dependent changes to be observed quantitatively using
either direct or indirect measurements using standard MRI devices over a range of
temperatures relevant for thermal therapy. The development of these techniques to
noninvasively measure temperature changes in tissue has brought renewed interest in
using these techniques to enhance the guidance of thermal therapy treatments.
