High intensity focused ultrasound (HIFU)
Focused ultrasound therapy, also known as high intensity focused ultrasound (HIFU), is a new therapeutic technique which has been recognized for enormous medical applications including cancer treatment and thrombolysis. In principle, HIFU induces local heating and temperature rise for the treatment of abnormalities by focusing acoustic energies to targeted areas from an extracorporeal source of ultrasound. When the acoustic waves propagate through the tissue, the medium particles start to vibrate, resulting in alternating cycles of compression and rarefaction pressure inside the tissue.
Due to the concave shape of transducer, the ultrasound beams converge into a focal area where the resulting acoustic pressure reaches the highest amplitude. This process induces tissue heating and corresponding temperature rise in the focal region that would be associated with irreversible biological effects such as necrosis and cell apoptosis.
HIFU has gained increasing attention as a new non-invasive therapeutic technique for the treatment of solid tumors. In last decade, many engineers and researchers have focused on different aspects of HIFU to helps surgeons with feasible use of HIFU for real clinical applications. To this end, we have designed and assemble an experimental setup for HIFU that allows us to monitor the HIFU mechanism in a tissue-mimicking phantom.
Currently we are currently working on two significant aspects of HIFU in our lab: nanoparticle (NP)-assisted focused ultrasound therapy and monitoring HIFU with thermography.
Nanoparticle-assisted focused ultrasound therapy
Despite the great potential of HIFU for cancer treatment, its mechanism has not been yet approved by the Food and Drug Administration (FDA), and there are several concerns about using extra-corporeal HIFU. Since a single HIFU exposure can just ablate a small volume of a tumor, the thermal ablating procedure is relatively long, as many of these ablating lesions must be placed side by side to paint out the entire tumor.
In addition, highly vascularized tissues such as liver are more resistant to HIFU than poorly perfused one, as blood flow in a vascular region can act as a heat sink for the generated heat by HIFU. Theoretically, increasing ultrasound power or exposure time can address some challenges of HIFU such as the blood perfusion effect, however, it can result in several major problems such as damage to surrounding tissues and skin burns. One possible strategy to reduce the required ultrasonic intensity and consequently to reduce the likelihood of adverse effects of HIFU is to use absorption enhancing agents during HIFU procedure.
Currently, we are working to study the use of nanoparticles (NP) as an ultrasound agent to locally enhance heating at relatively low powers, and to investigate the influence of NPs’ characteristics such as size and volume friction on the HIFU ablating mechanism.
Monitoring HIFU using intelligent thermography: with application in breast surgery
Breast cancer is the most common malignancy among women. More than one million new cases of invasive breast cancer are diagnosed each year worldwide. Traditionally, the surgical techniques such as the mastectomy and the breast conservation surgery have been considered as the major therapies for breast cancer.
In recent years, medical advancements have brought a shift away from open surgeries to minimally invasive therapeutic methods including laparoscopic and robot-assisted surgery, and even as far as to the energy-based techniques involving interstitial laser coagulation, radiofrequency, cryoablation and HIFU. Among them, HIFU is truly a non-invasive technique, and thus can be used to locally treat the breast cancer with excellent cosmetic results.
In principle, focused ultrasound (FUS) allows the local treatment of breast cancer by focusing acoustic energies to the target area from an extracorporeal source of ultrasound. To achieve the complete thermal treatment of breast cancer, the acoustic energies must be precisely guided to the target region. Monitoring of HIFU process allows minimizing damage to adjacent structures and helps surgeons make suitable therapeutic decisions.
Thermography is a revolutionary technique that has been successfully utilized as an alternative means for intraoperative detection and localization of breast cancer, brain tumor, and skin cancer. The ability to provide real-time temperature data of tissue’s surface with high resolution makes the thermography an attractive option as a safe and non-invasive imaging tool for breast cancer.
Currently, we are trying to propose the breast thermography as a feasible noninvasive method for monitoring HIFU during breast cancer therapy.
