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 motion‐related image artifacts and inter‐image object displacement, leading to incorrect spatial temperature reference. Here, cyclic navigator echoes were incorporated in rapid gradient‐echo MRI sequences, used for temperature mapping based on the proton resonance frequency. On‐line evaluation of navigator information was used in three ways. First, motion artifacts were minimized in echo‐shifted (TE > TR) gradient‐echo images using the phase information of the navigator echo. Second, navigator profiles were matched for a quantitative evaluation of displacement. Together with a novel processing method, this information was employed to correct the reference temperature maps, thereby avoiding persistence of motion‐related temperature errors throughout the hyperthermic period. Third, on‐line visualization of displacement, together with temperature maps and thermal dose images, was developed, allowing physician intervention at all times. Examples are given of on‐line corrections during hyperthermia procedures with focused ultrasound and radiofrequency heat sources. Magn Reson Med 45:128–137, 2001. © 2001 Wiley‐Liss, Inc.