Abstract
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°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 °C and an average difference of 1.25 ± 0.22 °C between and 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 ∼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.
Highlights
Mild hyperthermia, that is, the heating of malignant tissue to temperatures between 40 and 43 C, sensitizes tumors for chemo- and radiotherapy (RT and CT) without introducing additional systemic toxicity [1,2]
The controller performed well throughout the treatments with an absolute average tracking error of 0.27 ± 0.15 C and an average difference of 1.25 ± 0.22 C between T10 and T90: The Model predictive control (MPC) algorithm allocates additional heating power to sub-volumes with elevated heat sink effects, which are colocalized with blood vessels visible on contrast-enhanced magnetic resonance imaging (MRI)
We showed that the MPC algorithm yields superior performance in-vitro via the targeted compensation of heat loss due to diffusion and local heat loss induced by an artificial blood vessel
Summary
That is, the heating of malignant tissue to temperatures between 40 and 43 C, sensitizes tumors for chemo- and radiotherapy (RT and CT) without introducing additional systemic toxicity [1,2] This thermal enhancement effect has already been demonstrated in several clinical trials targeting a wide variety of tumors [3,4,5,6,7,8,9]. Devices used for clinical hyperthermia applications are currently almost exclusively based on extracorporeal antenna systems emitting electromagnetic waves (EMW) in the radiofrequency and microwave range. These devices enable the application of energy across regions with diameters of tens of centimeters (regional hyperthermia, RHT), allowing to heat large tumor volumes. The systematic validation of a device for EMW-mediated RHT under MRI guidance is currently ongoing [34,35,41]
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