Observation and correction of transient cavitation-induced PRFS thermometry artifacts during radiofrequency ablation, using simultaneous Ultrasound/MR imaging

Abstract

RFA induces dynamic changes in magnetic bulk susceptibility in biological tissue, resulting in large and spatially dependent errors of phase-subtraction-only PRFS MRT and unexploitable thermal dose maps. These thermometry artifacts were strongly correlated with the appearance of transient cavitation. A first-order dynamic model of susceptibility provided a useful method for minimizing these artifacts in phantom and ex vivo experiments.

Magnetic Resonance–Guided Shielding of Prefocal Acoustic Obstacles in Focused Ultrasound Therapy

“…Further details are provided in the study of Auboiroux et al 21 Proton Resonance Frequency Shift Temperature Monitoring and MR-ARFI Acquisition A conventional radiofrequency-spoiled segmented EPI gradient echo sequence (GRE-EPI) was used for time-referenced PRFS MR thermometry. 24,25 The main imaging parameters for this sequence were as follows: EPI factor, 11; asymmetric echo train with phase direction partial Fourier, 6/8; field of view (FOV), 128 mm  128 mm (ex vivo) or 200 mm  200 mm (in vivo); voxel size, 1.0  1.0  5.0 mm (ex vivo) or 1.56  1.56  5.0 mm (in vivo); 3 or 4 interleaved slices;, repetition time (TR)/echo time (TE)/field angle (FA), 50 to 70 milliseconds/9 milliseconds/15 degrees; bandwidth (BW), 738 hertz per pixel; echo spacing, 1.66 milliseconds; and temporal resolution, 2.5 to 3.5 seconds. Acquisition was accelerated using 75% partial Fourier reconstruction (neither rectangular FOV nor parallel imaging were used).…”

Arterial input function calculation in dynamic contrast-enhanced MRI: an in vivo validation study using co-registered contrast-enhanced ultrasound imaging

“…Imaging was performed with the rabbits in the lateral decubitus position, using an apparatus developed for coregistered ultrasound and MR imaging, described previously [33][34][35]. Briefly, ultrasound imaging was first performed to obtain 20 axial images (2 mm apart).…”

Correction of susceptibility-induced GRE phase shift for accurate PRFS thermometry proximal to cryoablation iceball

“…b Plot of the measured temperatures over time in the three positions visualized in frame a). c Illustration of the spatial profile of susceptibility-corrected temperature through the centre of the ice-ball (comprising positions 2 and 3 from above) tude several times smaller than the local field perturbation by thermal cavitation bubbles around an RF electrode, as described by Viallon et al [21]. With regard to the dipolar structure of the temperature artifacts and the physical source of magnetic field localized around the applicator, the two effects share similar features.…”