Visualization of thermal washout due to spatiotemporally heterogenous perfusion in the application of a model-based control algorithm for MR-HIFU mediated hyperthermia

Purpose This article will report results from the in-vivo application of a previously published model-predictive control algorithm for MR-HIFU hyperthermia. The purpose of the investigation was to test the controller's in-vivo performance and behavior in the presence of heterogeneous perfusion. Materials and methods Hyperthermia at 42 degrees C was induced and maintained for up to 30 min in a circular section of a thermometry slice in the biceps femoris of German landrace pigs (n=5) using a commercial MR-HIFU system and a recently developed MPC algorithm. The heating power allocation was correlated with heat sink maps and contrast-enhanced MRI images. The temporal change in perfusion was estimated based on the power required to maintain hyperthermia. Results The controller performed well throughout the treatments with an absolute average tracking error of 0.27 +/- 0.15 degrees C and an average difference of 1.25 +/- 0.22 degrees C between T 10 and T 90 . The MPC algorithm allocates additional heating power to sub-volumes with elevated heat sink effects, which are colocalized with blood vessels visible on contrast-enhanced MRI. The perfusion appeared to have increased by at least a factor of similar to 1.86 on average. Conclusions The MPC controller generates temperature distributions with a narrow spectrum of voxel temperatures inside the target ROI despite the presence of spatiotemporally heterogeneous perfusion due to the rapid thermometry feedback available with MR-HIFU and the flexible allocation of heating power. The visualization of spatiotemporally heterogeneous perfusion presents new research opportunities for the investigation of stimulated perfusion in hypoxic tumor regions.

Automated summary

This study reports the in-vivo application of a model-predictive control algorithm for MR-HIFU hyperthermia and investigates its performance in the presence of heterogeneous perfusion. Results show that the MPC algorithm performed well, allocating heating power based on the blood vessel distribution visible on contrast-enhanced MRI images. The rapid thermometry feedback and flexible power allocation allowed for temperature distributions with a narrow spectrum inside the target ROI despite the spatiotemporal heterogeneity in perfusion.