Magnetic Resonance-guided Focused Ultrasound Ablation of Uterine Fibroids
February 21, 2011 | Emerging Technology Reports
Proprietary names: Discovery MRI; ExAblate 2000; ExAblate 2100; ExAblate ONE; ExAblate OR System; Signa 1.5 Tesla Magnetic Resonance System; Signa 3 Tesla Magnetic Resonance System; Sonalleve MR-High Intensity Focused Ultrasound system. Generic names:acoustic surgery; acoustic therapy; focused ultrasound ablation (FUA); focused ultrasound tissue ablation; high-intensity focused ultrasound ablation (HIFUA); high-intensity focused ultrasound surgery (HIFUS); high-intensity focused ultrasound (HIFU) therapy; HIFU-MRI; image-guided acoustic therapy; image guided robotic acoustic surgery; image-guided surgery; incisionless surgery; magnetic resonance-guided focused ultrasound ablation (MRgFUA); magnetic resonance imaging (MRI)-guided high-intensity ultrasound ablation; magnetic resonance (MR) thermal ablation; therapeutic ultrasound; thermoablative therapy; ultrasound ablation; ultrasound surgery Related disease names: fibroleiomyomata; fibromyoma; leiomyoma; leiomyomata; myoma
Focused ultrasound ablation is a noninvasive surgical procedure used to treat uterine fibroids. During this outpatient procedure, the treating team (typically a gynecologist, an interventional radiologist, a nurse, and a technologist) delivers focused ultrasound waves to heat and destroy a patient's fibroids while sparing healthy tissue. In early research of focused ultrasound ablation to treat uterine fibroids, investigators used ultrasonic guidance to visualize fibroids but later began studying real-time guidance by magnetic resonance imaging (MRI). Proponents believe that magnetic resonance guidance provides the following advantages:
This report focuses on two commercially available magnetic resonance-guided focused ultrasound (MRgFUS) systems used to treat fibroids: the ExAblate System (InSightec Ltd, Tirat Carmel, Israel) and the Sonalleve MR-HIFU (magnetic resonance high-intensity focused ultrasound) Fibroid Therapy System (Phillips Healthcare, Andover, MA, USA). The ExAblate system consists of the following:
The Sonalleve MR-HIFU Fibroid Therapy System consists of the following:
To provide MRI guidance during MRgFUS, physicians must use a compatible MRI system, which includes a scanner and a workstation. Compatible MRI systems have a detachable patient table that the MRgFUS treatment table replaces during the procedure. Patients considered for treatment first undergo an MRI with gadolinium to determine the size, number, and location of fibroids. Review of these images is an important step in making appropriate patient selection decisions (see Indications and Contraindications). Treating the patient requires several steps. First, the team administers medication to induce conscious sedation. The sedation relaxes the patient and minimizes movement but allows communication with team members during the procedure. As the patient lies prone on the treatment table, a technologist applies ultrasound gel and a coupling pad to the skin over the fibroid target. The technologist then positions the patient so that the fibroid is directly over the treatment bath device. Next, the technologist provides ear protection, ensures that the patient can operate a "stop sonication" button (in case of pain), and moves the patient (on the treatment table) into the MRI scanner. The team calibrates the system, loads computer data, conducts pretreatment MRI, and plans the treatment using 3-D simulation and thermal mapping that verifies patient anatomy and the system's prescribed sonic dosing level. Treatment begins when a physician, guided by MRI, directs ultrasound waves (i.e., sonication) through the patient's body to the fibroid. The waves cause little or no tissue damage directly except where they converge—the "focal point"—to generate heat. MRI enables the physician to visualize temperature effects (i.e., monitor and assess sonicating accuracy and estimate effects on fibroids and healthy tissue). The physician focuses the waves at a point within the tumor. Tissue at the focal point reaches 60°C to 85°C; the heat causes cell death and extracellular protein destruction. With properly applied image-guided acoustic surgery, the tissue immediately surrounding the focal point also rises in temperature, but not to a level that directly causes tissue damage. The physician typically delivers 40 to 100 overlapping sonications (each lasting about 20 seconds, followed by 90 seconds of cooling) to ablate a fibroid. After each sonication, MRI indicates tissue temperature. A complete treatment session lasts two to four hours, depending on product specifications. After MRgFUS, patients rest for one to two hours because they may have pain, nausea, and/or other symptoms requiring medication. Patients usually resume normal activities 24 hours later.4 Normal physiologic processes remove ablated tissue over time. Some patients may require more than one treatment, but physicians must not treat a patient more than twice in a two-week period. Physicians typically order contrast-enhanced MR images six months after...