Transcranial high intensity focused ultrasound therapy guided by 7 TESLA MRI in a rat brain tumour model: a feasibility study.
OBJECTIVE
Transcranial high intensity focused ultrasound (HIFU) therapy guided by magnetic resonance imaging (MRI) is a promising approach for the treatment of brain tumours. Our objective is to validate a dedicated therapy monitoring system for rodents for transcranial HIFU therapy under MRI guidance in an in vivo brain tumour model.


METHODS
A dedicated MR-compatible ultrasound therapy system and positioning frame was developed. Three MR-compatible prefocused ultrasonic monoelement transducers were designed, operating at 1.5 MHz and 2.5 MHz with different geometries. A full protocol of transcranial HIFU brain therapy under MRI guidance was applied in n = 19 rats without and n = 6 rats with transplanted tumours (RG2). Different heating strategies were tested. After treatment, histological study of the brain was performed in order to confirm thermal lesions.


RESULTS
Relying on a larger aperture and a higher frequency, the 2.5 MHz transducer was found to give better results than other ones. This single element transducer optimised the ratio of the temperature elevation at the focus to the one at the skull surface. Using optimised transducer and heating strategies enabled thermal necrosis both in normal and tumour tissues as verified by histology while limiting overheating in the tissues in contact with the skull.


CONCLUSIONS
In this study, a system for transcranial HIFU therapy guided by MRI was developed and tested in an in vivo rat brain tumour model. The feasibility of this therapy set-up to induce thermal lesions within brain tumours was demonstrated.
Centre de Recherche de l'Institut du Cerveau et de la Moelle Épinière, INSERM - UMRS 975, CNRS 7225, Hôpital de la Pitié-Salpêtrière, Paris.
Elvis
E
Dervishi
Benoit
B
Larrat
Mathieu
M
Pernot
Clovis
C
Adam
Yannick
Y
Marie
Mathias
M
Fink
Jean-Yves
JY
Delattre
Ann-Laure
AL
Boch
Mickael
M
Tanter
Jean-Francois
JF
Aubry
D000818:Animals; D001921:Brain / Q000473:pathology; D001932:Brain Neoplasms / Q000473:pathology / Q000628:therapy*; D045744:Cell Line, Tumor; D005240:Feasibility Studies; D005910:Glioma / Q000473:pathology / Q000628:therapy*; D057086:High-Intensity Focused Ultrasound Ablation; D008279:Magnetic Resonance Imaging; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D014159:Transducers