Image Guided Therapy Program -
Therapeutic Ultrasound Laboratory
Please visit us at http://www.harvard.focused-ultrasound.org/.
Nathan McDannold, PhD - Research Director
Greg Clement, PhD - Technical Director
The most intriguing and appealing thermal ablation method is Focused Ultrasound Surgery (FUS). This previously well-known method is based on primary acoustic energy deposition and secondary thermal effects. FUS is non-invasive, requires no probe insertion, and the appropriately targeted and focused high-energy US beam causes no tissue damage in front of or beyond the target.
The FUS Lab is supported by federal and private grants.
The main industrial partner of our FUS research is InSightec Inc. and its subsidiary, TXSONICS. The support is substantial and exclusive. It covers both engineering developments and clinical applications.
Focused Ultrasound Surgery (FUS)
It has long been recognized that among thermal ablation techniques, non-invasive FUS has the greatest potential. Therefore, even without the possibility of visualizing the high temperature focal spot, this technique was tested for the treatment of brain tumors and prostate cancer. These preliminary trials were essentially unsuccessful due to the lack of targeting and monitoring options. Introducing and integrating temperature-sensitive MRI-guidance into the targeting and energy-delivery process revived the method.
After MRI-based localization of the tumor target, a relatively low-power energy-deposition is used for targeting. The small, MRI-detectable temperature elevation within the focal spot (just a few millimeters in diameter) causes no permanent tissue damage but can be localized by MRI and moved on the target within the field of view. When targeting is accomplished, the power level can be increased to achieve a temperature elevation of more than 60o, which results in irreversible tissue damage. This method is now under clinical testing for the treatment of benign and malignant breast lesions.
The MRI-integrated system is semi-automated. The physician outlines the tumor volume, and the computer deposits a sufficient number of overlapping focal volumes within the defined contours of the lesion to treat the entire tumor. The temperature levels within the focal spots are defined using water-proton chemical-shift-based temperature imaging in order to determine the effective area for tumor killing. The current systems use appropriately shaped movable transducers for focusing, but electronically controlled phased-array systems are now under development. With this latter technology, the treatment times can be shortened, and the focal spot sizes can be changed. With phased-array systems, we may someday treat brain tumors without making craniotomies for acoustic window.
Besides tumor ablation, there are other potential applications of FUS. Relatively small power levels can functionally open the blood-brain-barrier, and chemo- or immunotherapy of brain tumors may become possible. Both thermal and non-thermal (cavitation) effects of FUS on cell membranes are applicable for targeted drug delivery or for local gene therapy. Also, systemic injection of drugs can be followed by local activation by heat or cavitation. The combination of MRI and FUS may have a great impact on the future of image-guided cancer treatment if such hypotheses can be developed into feasible clinical protocols.
Clinical Applications
FUS refers to the destruction of highly specific volumes of tissue (malignant tumors, benign fibroids, etc.) by generating tissue-killing levels of heat using narrowly targeted spots of ultrasonic waves. The focused use of these sound waves allows for the pathological tissue to be destroyed while at the same time preserving the normal tissues surrounding it. This non-invasive surgical procedure is well along in the development phase and has had what we perceive as successes in limited human trials. It is hoped that FUS will become a routine procedure within the next two to three years. Development is continuing under the auspices of an FDA IDE process. The technique has been tested on the following applications:
- Breast tumors
• Benign fibroadenoma
• Breast cancer
- Uterine fibroid
- Brain tumor
For further information contact:
Nathan McDannold, PhD at njm@bwh.harvard.edu
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