Towards MR-guided high intensity focused ultrasound ablation of liver tumors

Abstract

Magnetic Resonance-guided High Intensity Focused Ultrasound (MR-HIFU) is a promising technique which can be used for completely non-invasive tissue ablation. The converging ultrasound beam penetrates the skin and subcutaneous tissues with damage, while heating the tissue only in the focal point. The MRI guidance provides accurate treatment planning and real-time temperature feedback during the procedure (thermometry). The preclinical work in this PhD thesis investigates the possibilities for application of MR-HIFU ablation for the treatment of liver tumors. First, an overview is provided of the challenges which have to be overcome for clinical translation of this treatment technique. Subsequent chapters focus on each of these individual aspects. The next chapter describes the evolution of the ablation zone after MR-HIFU treatment. It is concluded that the optimal time point for imaging evaluation of the treatment is three to seven days after the procedure. Then, a technique is described which allows for MR-HIFU ablation in the liver dome, which is not possible under normal circumstances due to the lungs obstructing the HIFU beam. Next, methods for reducing and monitoring near-field heating are presented, which is a potential source of complications after MR-HIFU ablation. The results not only help in preventing complications but also help in decreasing the overall treatment time. The next study investigated the possibilities for MR-HIFU ablation of tumors which are located behind the rib cage. Is was demonstrated that intercostal ablation of superficially located tumors is feasible. The last study incorporates the previous techniques into one clinically-feasible treatment protocol, using respiratory-gated ablation and MR thermometry. It was demonstrated that it is feasible and safe to ablate a volume of liver tissue the size of a small metastasis. It is concluded that MR-HIFU for ablation in the liver is now ready for clinical translation. Since the expected impact of this treatment on quality of life is low, MR-HIFU may be a valuable treatment for patients who are not eligible for surgical treatment.