HIFU (high-Intensity Focused Ultrasound) (sometimes FUS or HIFUS) is a highly precise medical procedure using high-intensity focused ultrasound medical device to heat and destroy pathogenic tissue rapidly. It is one modality of therapeutic ultrasound, and, although it induces hyperthermia, it should not be confused with this technique, which heats much less rapidly and to much lower therapeutic temperatures (in general < 45°C).
This is under ultrasonography or computerized MRI. When MRI is used it is sometimes called Magnetic Resonance-guided Focused Ultrasound, often shortened to MRgFUS. When ultrasonography is used it is sometimes called Ultrasound-guided Focused Ultrasound, often shortened to USgFUS. Magnetic resonance imaging (MRI) is used to identify tumors or fibroids in the body, before they are destroyed by the ultrasound. MRgFUS is currently used in the United States, Canada, Israel, Europe, and Asia to treat uterine fibroids. And ultrasonography guided HIFU is currently used in the United Kingdom, Italy, Spain, Korea, Japan, Hong Kong, Malaysia, Russia, China, Romania and Bulgaria. Current clinical trials are underway, examining the possible use of the technique in the treatment of cancers of the brain, breast, liver, bone, and prostate.
Therapeutic ultrasound is a minimally invasive or non-invasive method to deposit acoustic energy into tissue. Applications include tissue ablation (HIFU) (for tumor treatments, for example), hyperthermia treatments (low-level heating combined with radiation or chemotherapy), or the activation or enhanced delivery of drugs.
Aiming
The ultrasound beam can be focused in these ways:
- Geometrically, for example with a lens or with a spherically curved transducer.
- Electronically, by adjusting the relative phases of elements in an array of transducers (a "phased array"). By dynamically adjusting the electronic signals to the elements of a phased array, the beam can be steered to different locations, and aberrations due to tissue structures can be corrected.
How HIFU works
As an acoustic wave propagates through the tissue, part of it is absorbed and converted to heat. With focused beams, a very small focus can be achieved deep in tissues. When hot enough, the tissue is thermally coagulated. By focusing at more than one place or by scanning the focus, a volume can be thermally ablated. At high enough acoustic intensities, cavitation (microbubbles forming and interacting with the ultrasound field) can occur. Microbubbles produced in the field oscillate and grow (due to factors including rectified diffusion), and eventually implode (inertial or transient cavitation). During inertial cavitation, very high temperatures inside the bubbles occur, and the collapse is associated with a shock wave and jets that can mechanically damage tissue. Because the onset of cavitation and the resulting tissue damage can be unpredictable, it has generally been avoided in clinical applications. However, cavitation is currently being investigated as a means to enhance HIFU ablation and for other applications.
Method of use
In HIFU therapy, ultrasound beams are focused on diseased tissue, and due to the significant energy deposition at the focus, temperature within the tissue rises to 65° to 85°C, destroying the diseased tissue by coagulation necrosis. Each sonication of the beams treats a precisely defined portion of the targeted tissue. The entire therapeutic target is treated by moving the applicator on its robotic arm in order to juxtapose multiple shots, according to a protocol designed by the physician. This technology can achieve precise ablation of diseased tissue, therefore it is called HIFU surgery. Because it destroys the diseased tissue non-invasively, it is also known as "Non-invasive HIFU surgery". Anesthesia is not required, but should be recommended. The treatment can be combined with radiotherapy or chemotherapy.
Uses
Uterine fibroids
Development of this therapy significantly broadened the range of treatment options for patients suffering from uterine fibroids. HIFU treatment for uterine fibroids was approved by the Food and Drug Administration (FDA) in October 2004.
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