| AVS 59th Annual International Symposium and Exhibition | |
| Biointerphases Focus Topic: Bioimaging | Wednesday Sessions |
| Session BN+AS-WeA |
| Session: | Bioimaging |
| Presenter: | A. Liberman, University of California San Diego |
| Authors: | A. Liberman, University of California San Diego H.P. Martinez, University of California San Diego Z. Wu, University of California San Diego C.V. Barback, University of California San Diego S.L. Blair, University of California San Diego Y. Kono, University of California San Diego R.F. Mattrey, University of California San Diego W.C. Trogler, University of California San Diego A.C. Kummel, University of California San Diego |
| Correspondent: | Click to Email |
The reported positive margin rate from wire localized excisions of breast cancers is approximately 20-50%; however, by preoperatively injecting a radio active seed into the tumor under CT guidance, the excision rate is halved because the surgeon can constantly reorient the dissection to place the seed in the center of the specimen. Unfortunately, radioactive seed localization has several safety challenges , only single foci can be localized, and incisions are required to implant the seeds, so it is rarely employed. As a safe alternative, gas-filled hollow Fe-doped silica particles have been developed, which can be used for ultrasound-guided surgery even for multiple focii. The function of the Fe doping is to render the silica shells biodegradable. The particles are synthesized through a sol-gel method on a polystyrene template, and subsequently calcined to create hollow, rigid microspheres. The Fe-doped silica shell is derived from tetramethoxy orthosilicate (TMOS) and iron (III) ethoxide, which forms a rigid, mesoporous shell upon calcination. The microshells are filled with perfluoropentane (PFP) vapor or liquid. The flourous phase is contained within the porous shell due to its extremely low solubility in water. Considerable testing of particle functionality, signal persistence and acoustical properties have been performed in various phantoms including ultrasound gel, chicken breast, and excised human mastectomy tissue. In vitro studies have shown that continuous particle imaging time is up to approximately 45 minutes, and will persist for over five days. Furthermore, preliminary in vivo particle injection longevity studies have been performed in a rabbit model which are consistent with in vitro data showing signal presence even five days post injection. These silica spheres may be used a sensitizing agent in high intensity focused ultrasound (HIFU). Traditional ultrasound agents pose several potential drawbacks such as poor in vivo persistence (minutes) and high risk (cardiac complications) during continuous perfusion. Preliminary in vitro results in HIFU ablation in an agar tissue phantom model suggest that very few particles are needed in order to develop a sensitizing effect to HIFU (approx. 1-10 μg/ml particles/agar varying by particle size). A novel technique has been developed to fill the particles with perfluorocarbon liquid which vaporizes upon exposure to HIFU thereby increasing the sensitivity compared to gas filled particles.