The Thermal Ablation with MRgFUS: From Physics to Oncological Applications

Abstract

The growing interest in minimal and non-invasive therapies, especially in the field of cancer treatment, highlights a significant shift toward safer and more effective options. Ablative therapies are well-established tools in cancer treatment, with known effects including locoregional control, while their role as modulators of the systemic immune response against cancer is emerging. The HIFU developed with magnetic resonance imaging (MRI) guidance enables treatment precision, improves real-time procedural control, and ensures accurate outcome assessment. Magnetic Resonance-guided Focused Ultrasound (MRgFUS) induces deep coagulation necrosis within an elliptical focal area, effectively encompassing the entire tumor site and allowing for highly targeted radical ablation. The applications of MRgFUS in oncology are rapidly expanding, offering pain relief and curative treatment options for bone metastatic lesions. Additionally, the MRgFUS plays an effective role in targeted optional therapies for early prostate and breast cancers. Emerging research also focuses on the potential uses in treating abdominal cancers and harnessing capabilities to stimulate immune responses against tumors or to facilitate the delivery of anticancer drugs. This evolving landscape presents exciting opportunities for improving patient outcomes and advancing cancer treatment methodologies. In neuro-oncology, MRgFUS utilizes low-intensity focused ultrasound (LIFU) along with intravenous microbubbles to open the blood-brain barrier (BBB) and enhance the intra-tumoral delivery of chemotherapy drugs.

Keywords: HIFU; LIFU; MRgFUS; oncology; thermal ablation.

Figure 1

The diagram illustrates an MRI scanner equipped with a high-intensity focused ultrasound (HIFU) transducer on the patient table. It showcases the configuration of the MR-guided Focused Ultrasound (MRgFUS) system, which includes an integrated focused ultrasound unit within the MRI bed. Patients are positioned carefully to ensure that the area of interest aligns directly above the FUS transducer. The concave transducer, submerged in degassed water and using a coupling gel pad, effectively transmits acoustic waves through the patient’s body. This multi-element ultrasonic transducer focuses ultrasound waves on the targeted area (focal zone), generating heat that leads to precise tissue ablation via necrosis. This advanced procedure is performed while the patient is inside the bore-MRI, always adhering to strict treatment planning protocols.

Figure 2

Schematic drawing of the sonication and thermal cytotoxic effects of the HIFU in the focal zone. The necrotic post-ablative lesions are elliptical; multiple sonications without gaps are necessary to target the entire lesion and achieve radical tumor ablation.

Figure 3

The thermo-mechanical effect of HIFU can be exploited to improve drug distribution and absorption by promoting the release of anticancer molecules encapsulated in a carrier (liposome) within the target tumor site.

Figure 4

HIFU ablation can induce an immune response. The generation of tumor debris in situ increases the circulation of tumor-associated antigens. This activates the immune response mediated by the interaction between antigen-presenting cells (APCs) and T lymphocytes (T cells) and will target cancer cells that expose that specific antigen. The activated T lymphocytes can infiltrate the tumor site and attack tumor cells by passing through the systemic circulation.