Description du projet :
Magnetic resonance-guided high-intensity focused ultrasound is considered to be a promising
treatment for localized cancer. Depending on the anatomical target, commonly recognized challenges
for the transfer of this technology towards the clinical routine are: acoustic obstacles
(bones, air filled cavities, calcifications, scars), tissue motion (respiratory and cardiac) and heat
sink in perfused organs (requiring sustained sonication). An increasing number of recent publications
tried to address these issues, individually or simultaneously. However, based on our own
solid experience with MRgHIFU in vivo studies with upper abdomen applications, it appears that a
challenging complication of HIFU ablation is the far field heating of hard acoustic interfaces, for
instance spinal bone structures or tissue-to-air interfaces, that represent a severe and frequent
side effect. Indeed, any HIFU transducer forms an energy beam that is first concentrated at a focus
then continues its post-focal propagation while losing the spatial controllability as a consequence
of diffraction. That is, the spatial profile of the acoustic intensity in the far field loses its
correlation with the emission pattern at the surface of the transducer and there is little or no possibility
of manipulating the HIFU source in order to directly reduce the far field energy deposition,
unlike the near field situation. Therefore, to reduce this side effect there is an urgent need to
search for new methods to enhance the thermal contrast achievable between the focus and the far
field areas. Various attempts to solve this problem are known: use of shock waves with non-linear
enhancement of focal absorption, thermally induced boiling core of water steam, or use of ultrasound
contrast agents as adjuvants. Each suggested approach has demonstrated some potential
interest, whilst exhibiting drawbacks that prevent it being applied 'as is' in a realistic clinical
scenario. We propose an alternative method that does not have the same drawbacks as previously
published approaches. It consists of using exogenous microparticles as a source of in situ boiling
core induction, only at the focal point of the HIFU beam. These microparticles are perfluorocarbon
droplets stabilized by fluorinated surfactants, whose evaporation is triggered using low to moderate
HIFU energy, as a joint effect of temperature and acoustic pressure. The evaporation process
will induce a cascade of positive-feedback ('chain reaction', or 'self-amplified') energy deposition
that will result in the use of lower energy to perform ablation and reduced HIFU side effects. Indeed,
the vaporized microparticles will act as a strong reflector for the incident beam. This will
protect organs or bones located in the far field by partly blocking the forward propagation of the
wave. The superposition of the incident and reflected wave at the distal frontier of the boiling core
will yield enhanced absorption and heating. This will finally re-trigger the evaporation of new particles
freshly supplied by the blood flow and the process will be self-maintained until the sonication
stops or the renewal of the particles stops. Our goal in this project is to achieve a proof-ofconcept
for this cascade-amplified focal ultrasound ablation, first in tissue mimicking gels, then
in ex vivo perfused kidney, and eventually in living animal liver. This joint application between
Swiss and French work groups will take advantage of the complementary skills and available resources
of the involved partners, covering the chemistry and physics of microparticle synthesis
and characterization, hybrid ultrasonography and MR imaging and thermometry for simultaneous
monitoring of cascade-amplified focal ultrasound ablation treatments, and animal research facilities
for in vivo proof of concept.
Equipe de recherche au sein de la HES-SO:
Hyacinthe Jean-Noël
Partenaires académiques: Santé
Durée du projet:
15.12.2014 - 31.01.2015
Montant global du projet: 11'000 CHF
Statut: Terminé
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