On-line correction and visualization of motion during MRI-controlled hyperthermia

Displacement of tissue during MRI-controlled hyperthermia therapy can cause significant problems. Errors in calculated temperature may result from mot ion-related image artifacts and inter-image object displacement, leading to incorrect spatial temperature reference. Here, cyclic navigator echoes wer e incorporated in rapid gradient-echo MRI sequences, used for temperature m apping based on the proton resonance frequency. On-line evaluation of navig ator information was used in three ways. First, motion artifacts were minim ized in echo-shifted (TE > TR) gradient-echo images using the phase informa tion of the navigator echo. Second, navigator profiles were matched for a q uantitative evaluation of displacement. Together with a novel processing me thod, this information was employed to correct the reference temperature ma ps, thereby avoiding persistence of motion-related temperature errors throu ghout the hyperthermic period. Third, on-line visualization of displacement , together with temperature maps and thermal dose images, was developed, al lowing physician intervention at ail times. Examples are given of on-line c orrections during hyperthermia procedures with focused ultrasound and radio frequency heat sources. Magn Reson Med 45:128-137, 2001, (C) 2001 Wiley-Lis s, Inc.