Development of a high-field MR-guided HIFU setup for thermal and mechanical ablation methods in small animals.
BACKGROUND
Thermal and mechanical high intensity focused ultrasound (HIFU) ablation techniques are in development for non-invasive treatment of cancer. However, knowledge of in vivo histopathologic and immunologic reactions after HIFU ablation is still limited. This study aims to create a setup for evaluation of different HIFU ablation methods in mouse tumors using high-field magnetic resonance (MR) guidance. An optimized MR-guided-HIFU setup could be used to increase knowledge of the different pathologic and immunologic reactions to different HIFU ablation methods.


METHODS
Three different HIFU treatment strategies were applied in mouse melanomas (B16): a thermal (continuous wave), a mechanical (5 ms pulsed wave), and an intermediate setting (20 ms pulsed wave) for HIFU ablation, all under MR guidance using a 7 tesla animal MR system. Histopathologic evaluation was performed 3 days after treatment.


RESULTS
The focus of the ultrasound transducer could accurately be positioned within the tumor under MR image guidance, without substantial damage to the surrounding tissue and skin. All mice retained complete use of the treated leg after treatment. Temperatures of >60, <50, and <44 °C were reached during thermal, intermediate, and mechanical HIFU ablation, respectively. Thermal-treated tumors showed large regions of coagulative necrosis. Tumors of both the mechanical and intermediate groups showed fractionated tissue with islands of necrosis and some pseudocysts with hemorrhage.


CONCLUSIONS
A stable small animal MR-guided HIFU setup was designed and evaluated for follow-up MR imaging and histopathologic responses of the treated tumors. This will facilitate further studies with a larger number of mice for detailed evaluation of the pathologic and immunologic response to different HIFU strategies.
Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Geert Grooteplein-Zuid 10, 6500 HB Nijmegen, The Netherlands.
Martijn
M
Hoogenboom
Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Geert Grooteplein-Zuid 10, 6500 HB Nijmegen, The Netherlands.
Martinus J
MJ
van Amerongen
Department of Tumor Immunology, Radboud University Medical Center, Nijmegen, The Netherlands.
Dylan C
DC
Eikelenboom
Department of Tumor Immunology, Radboud University Medical Center, Nijmegen, The Netherlands.
Melissa
M
Wassink
Department of Tumor Immunology, Radboud University Medical Center, Nijmegen, The Netherlands.
Martijn H
MH
den Brok
Department of Pathology, Radboud University Medical Center, Nijmegen, The Netherlands.
Christina
C
Hulsbergen-van de Kaa
Image Guided Therapy, Pessac, Bordeaux, France.
Erik
E
Dumont
Department of Tumor Immunology, Radboud University Medical Center, Nijmegen, The Netherlands.
Gosse J
GJ
Adema
Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Geert Grooteplein-Zuid 10, 6500 HB Nijmegen, The Netherlands.
Arend
A
Heerschap
Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Geert Grooteplein-Zuid 10, 6500 HB Nijmegen, The Netherlands.|MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, Netherlands.
Jurgen J
JJ
Fütterer