Model predictive filtering MR thermometry: Effects of model inaccuracies, k-space reduction factor, and temperature increase rate.
OBJECTIVE
Evaluate effects of model parameter inaccuracies (thermal conductivity, k, and ultrasound power deposition density, Q), k-space reduction factor (R), and rate of temperature increase ( T˙) in a thermal model-based reconstruction for MR-thermometry during focused-ultrasound heating.


METHODS
Simulations and ex vivo experiments were performed to investigate the accuracy of the thermal model and the model predictive filtering (MPF) algorithm for varying R and T˙, and their sensitivity to errors in k and Q. Ex vivo data was acquired with a segmented EPI pulse sequence to achieve large field-of-view (192 × 162 × 96 mm) four-dimensional temperature maps with high spatiotemporal resolution (1.5 × 1.5 × 2.0 mm, 1.7 s).


RESULTS
In the simulations, 50% errors in k and Q resulted in maximum temperature root mean square errors (RMSE) of 6 °C for model only and 3 °C for MPF. Using recently developed methods, estimates of k and Q were accurate to within 3%. The RMSE between MPF and true temperature increased with R and T˙. In the ex vivo study the RMSE remained below 0.7 °C for R ranging from 4 to 12 and T˙ of 0.28-0.75 °C/s.


CONCLUSIONS
Errors in MPF temperatures occur due to errors in k and Q. These MPF temperature errors increase with increase in R and T˙, but are smaller than those obtained using the thermal model alone.
Department of Radiology, University of Utah, Salt Lake City, Utah, USA.|Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah, USA.
Henrik
H
Odéen
Department of Radiology, University of Utah, Salt Lake City, Utah, USA.
Nick
N
Todd
Department of Bioengineering, University of Utah, Salt Lake City, Utah, USA.
Christopher
C
Dillon
Department of Radiology, University of Utah, Salt Lake City, Utah, USA.
Allison
A
Payne
Department of Radiology, University of Utah, Salt Lake City, Utah, USA.
Dennis L
DL
Parker
D001831:Body Temperature / Q000502:physiology* / Q000528:radiation effects; D003198:Computer Simulation; D019220:High-Energy Shock Waves; D057086:High-Intensity Focused Ultrasound Ablation / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000502:physiology* / Q000528:radiation effects / Q000601:surgery; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D025321:Surgery, Computer-Assisted / Q000379:methods; D013696:Temperature; D013817:Thermography / Q000379:methods*
HIFU; MPF; MR thermometry; MRTI; PRF