High Intensity Focused Ultrasound – HIFU From Cosmetic to Prostate Cancer Treatment
When asked about the use of ultrasound in medicine most non-medical people will immediately respond with, “it takes cute pictures of the pre-born baby.” In actual clinical practice the use of ultrasound is bifurcated into either diagnostic or therapeutic applications. Diagnostic ultrasound gives us the cute baby images, therapeutic ultrasound cooks things. Historically, therapeutic ultrasound has been used to treat muscle aches and cramps by slightly elevating the temperature of muscle tissue to produce more blood flow in the heated area (volume) which accelerates the recovery process. High intensity focused ultrasound (HIFU) takes that paradigm to a much greater level in order to destroy cancer cells in vivo. For example, one clinical application for HIFU is in the treatment of prostate cancer. To kill a cancer cell (or any human cell) with heat the cell must be exposed to an acoustic field that will raise the temperature of that cell to ~60°C and keep it at that temperature for ~ two seconds or longer. This temperature rise will cause coagulation necrosis of the targeted volume thereby non-invasively destroying the cancerous tumor (often obviating the need for surgery or brachytherapy). To imagine how this is done with ultrasound think back to those lazy summer days when you were a kid playing outside with a magnifying glass. We learned that if we held the magnifying glass at a certain distance from a piece of paper, we could ignite it. It turns out that using focused ultrasound instead of the sun as an energy source we can do the same thing with a cell. A magnifying glass uses a converging lens, HIFU uses a focused ultrasound beam.
For reference, diagnostic ultrasound imaging and Doppler generally uses acoustic fields that range in intensity (spatial peak temporal average of SPTA) from ~ 90 to 650mW/cm2. HIFU on the other hand, using a 1MHz transducer, can generate as much as 20,000W/cm2 focal peak intensity: Hence the term high-intensity focused ultrasound.
The use of ultrasound is ever expanding in the medical field, and we are just at the beginning of what can be done with this amazing technology. HIFU is also starting to be used in treating pancreatic cancer as well treating facial skin wrinkles (albeit using significantly less energy!). Next month we will look at recent advances in Low Intensity Pulsating Ultrasound and its use in opening the blood brain barrier.
Until next month,