Paul GREILLIER PhD Defense

Wednesday 20 December 2017

Thesis title: Evaluation of a transoesophageal HIFU probe on beating hearts
Summary: Transesophageal HIFU was proposed as an alternative to the cardiac arrhythmias treatments. The work presented in this thesis describes the feasibility of transoeso- phageal thermal ablation of hearts in silico, in vivo and ex vivo, as well as the use of passive elastography as a method of treatment follow-up.
An endoscope integrating a 5MHz 64-element commercial transesophageal echo- cardiography probe and a 8-element HIFU transducer was built. The transducer was cooled at 5°C and ultrasonic beam could be steered over a 15 to 55 mm range.
The first part demonstrates the ability of passive elastoraphy to be used for mo- nitoring thermal injury. The technique has been demonstrated on a simple model of thermosensitive hydrogel, then on biological samples of liver and heart. One study showed the influence of motion on passive elastography.
The prototype was tested on three 30 kg male baboons. Left atrium and ventricles were exposed to repeated continuous sonications (4-15 times during 16s). Passive elastography showed a hardening in the left ventricle after shooting in one of the subjects. T1-weighted and contrast MRI sequences show contradictory results that do not confirm the presence of this lesion.
After a numerical study simulating the influence of motion on the creation of thermal lesions in ultrasound treatment, ultrasound parameters were optimized on a model of isolated beating heart using the Langendorff procedure.
Place: Salle des Thèses (1) de la Faculté de médecine de Rockfeller