A method for MRI guidance of intercostal high intensity focused ultrasound ablation in the liver.
OBJECTIVE
High intensity focused ultrasound (HIFU) is a promising method for the noninvasive treatment of liver tumors. However, the presence of ribs in the HIFU beam path remains problematic since it may lead to adverse effects (skin burns) by absorption and reflection of the incident beam at or near the bone surface. This article presents a method based on magnetic resonance (MR) imaging for identification of the ribs in the HIFU beam, and for selection of the transducer elements to deactivate.


METHODS
The ribs are visualized on anatomical images acquired prior to heating and manually segmented. The resulting regions of interest surrounding the ribs are projected onto the transducer surface by ray tracing from the focal point. The transducer elements in the "shadow" of the ribs are then deactivated. The method was validated ex vivo and in vivo in pig liver during breathing under multislice real-time MR thermometry, using the proton resonance frequency shift method.


RESULTS
Ex vivo and in vivo temperature data showed that the temperature increase near the ribs was substantial when HIFU sonications were performed with all elements active, whereas the temperature was reduced with deactivation of the transducer elements located in front of the ribs. The temperature at the focal point was similar with and without deactivation of the transducer elements, indicative of no loss of heat efficiency with the proposed technique.


CONCLUSIONS
This method is simple, rapid, and reliable, and enables intercostal HIFU ablation while sparing ribs and their surrounding tissues.
Quesson
Bruno
B
Laboratory for Molecular and Functional Imaging, UMR5231, CNRS, University Victor Segalen Bordeaux 2, 33076 Bordeaux, France. b.quesson@imf.u-bordeaux2.fr
Merle
Mathilde
M
Köhler
Max O
MO
Mougenot
Charles
C
Roujol
Sebastien
S
de Senneville
Baudouin Denis
BD
Moonen
Chrit T
CT
D000818:Animals; D006498:Hepatectomy / Q000379:methods*; D057086:High-Intensity Focused Ultrasound Ablation / Q000379:methods*; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008099:Liver / Q000473:pathology* / Q000601:surgery*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012272:Ribs / Q000473:pathology / Q000601:surgery; D012680:Sensitivity and Specificity; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013552:Swine; D013817:Thermography / Q000379:methods*