MR-guided Focused Ultrasound Surgery (MRg-FUS) at UCSF


In July 2010, UCSF became the first site in the country to be awarded a high-end instrumentation grant from the National Institute of Health for purchase of an MRg-FUS system (1S10RR028911-01; Fergus Coakley, Principal Investigator). The installation of the NIH-funded Insightec system in early 2011 allowed UCSF to offer this cutting edge therapeutic technology to patients in Northern California and across the country.

Frequently Asked Questions

What is Focused Ultrasound Surgery (FUS)

FUSFUS (Focused Ultrasound Surgery) uses tightly focused high energy ultrasound waves to kill tissue. Sound waves passing through tissue are partially absorbed and converted to heat. With proper focusing and sustained energy input, a small and targeted focus of heating (temperatures of 65-850 C are produced in the focal zone) can be achieved at varying depth within tissues and adjusted to kill a small (size of a grain of rice) piece of a tumor. Larger volumes of tumor can be treated by killing piece by piece. The use of focused ultrasound waves to heat and kill a piece of tumor is like using a magnifying glass to focus the sun’s energy on a single spot and heat it.

The principle of using high energy ultrasound beams for disease treatment dates to 1954, but early efforts were limited by lack of image guidance and lack of accurate monitoring of treatment effects. In 1984, extracorporeal shockwave lithotripsy (fragmentation of urinary stones by targeted high energy ultrasound) became the first clinical application of high energy ultrasound for disease treatment to be approved by the FDA. Interest in FUS for tumor ablation re-emerged in the 1990s due to the convergence of advances in medical imaging, ultrasound technology, and focal therapy.

How is FUS (Focused UltraSound) different from standard ultrasound

Standard ultrasound (i.e. diagnostic ultrasound for imaging) uses transient low energy ultrasound waves to create images of structures within the body. The energy is not focused on a single spot and does not create high temperatures.

Is FUS the same as high intensity focused ultrasound (HIFU)?

Yes, Focused Ultrasound Surgery and High Intensity Focused Ultrasound are the same.

What are the benefits of focused ultrasound for tumor ablation (killing)?

FUS has several attractive features when compared to other methods for non-invasive or minimally invasive tumor ablation such as vascular embolization, radiofrequency ablation, cryotherapy, and targeted radiotherapy. These advantages include:

  • Unlike radiation therapy, the passage of ultrasound energy through intervening tissue has no cumulative effect on that tissue or tissue beyond the focus. Focused ultrasound treatment is extremely precise, with the boundary zone between necrotic treated and viable untreated tissue measuring less than 0.1 mm. Accordingly, FUS is easily repeatable, unlike radiotherapy where tissue toxicity makes repeated treatment problematic.
  • FUS produces in-depth precise tissue necrosis using an external applicator, with no need to insert an instrument into the target tissue or arterial system. That is, the procedure is completely incisionless and non-invasive and so carries negligible risks of inducing hemorrhage or infection.
  • The experience with uterine fibroids shows that MRg-FUS can be performed as an outpatient procedure, so patients can go home on the day of treatment and return to work the following day. These benefits increase productivity and reduce healthcare costs related to provider and hospital utilization.
  • Patients with painful bone metastases treated with FUS on an outpatient basis are also able to return home within an hour of their procedure, experience rapid and substantial pain relief within a few days, and are able to reduce or completely stop analgesic use shortly thereafter. For prostate patients the procedure will be performed as a day-case under epidural anesthesia and with a bladder catheter in place. The patient should be able to return to normal activities after two days, providing he can urinate spontaneously after trial removal of the catheter.
  • FUS requires just a single session of treatment, unlike the multiple sessions requires for traditionally fractionated radiotherapy.
  • FUS employs a near-instantaneous delivery of focused energy and does not depend on heat conduction to treat the tumor. Therefore, FUS can be used even in the presence of large adjacent vessels which can act as heat-sinks and limit tumor killing by other modalities such as radiofrequency ablation.
  • Coagulative necrosis is far less painful than the ischemic necrosis induced by transarterial embolization. These advantages are not simply theoretical; it has been shown that MRg-FUS provides symptomatic relief that is faster than competing procedures for fibroid and bone lesion ablation.
  • The tissue necrosis produced by FUS is immediate and efficacy can be checked by obtaining gadolinium enhanced MR images to show the non-perfused treatment volume at the end of the procedure.
  • Standard definitive therapy of prostate cancer by surgery or radiation are associated with significant morbidities, including incontinence, fatigue, and diarrhea. While MRg-FUS therapy of prostate cancer remains investigational and the associated risk of side effects is unknown, the precise targeting used during the treatment may help reduce these toxicities.

    What is MR-guided FUS (MRg-FUS)

    MRg-FUS refers to the performance of FUS within an MRI scanner. This setup allows tumor targeting and real-time treatment monitoring by MRI. MRg-FUS is an FDA approved and commercially available procedure for the treatment of fibroids. Other conditions may be treated as part of FDA approved clinical trials.

    Why not use diagnostic ultrasound to guide and monitor FUS (HIFU)

    MRI provides two distinct advantages for guiding focused ultrasound. First, the ability to rapidly obtain multiplanar and multiparametric images allows for accurate and contemporaneous tumor localization, improving FUS targeting. Second, MR thermometry allows for real-time pixel-by-pixel temperature monitoring during the sonication, so that the extent and degree of tissue heating can be controlled and monitored. That is, MR thermal feedback during FUS treatment provides non-invasive monitoring for a non-invasive treatment. Other methods of guiding FUS, primarily the use of endorectal ultrasound for prostate therapy do not provide these advantages of precise tumor localization and treatment monitoring. Ultrasound does not have any thermal imaging capabilities, and ultrasound guided FUS depends on visualization of imprecise secondary changes in echogenicity. Accurate anatomic localization is particularly important in the prostate because of the proximity of the rectal wall, urethra, and neurovascular bundles. MRI provided superior visualization of these sensitive structures, for which inadvertent damage results in substantial patient morbidity. The distressing side effects (impotence, incontinence, and anorectal dysfunction) of prostatectomy and radiotherapy are primarily due to injury to the neurovascular bundle, urethral sphincter, and rectum. It is hoped that the ability to directly visualize and protect these structures while precisely targeting and ablating cancer will be an advantage of MR guidance and monitoring when compared to the relatively crude guidance and monitoring provided by ultrasound, whether for delivery of cryosurgery or focused ultrasound.  However, rigorous studies will be required to investigate the true risks and outcomes of MR-guided treatment of prostate cancer.  In summary, the combination of MR guidance and thermometry for focused ultrasound therapy provides a unique method of accurate and real-time targeting and treatment monitoring of a minimally invasive and precise method of tissue ablation; such rigorous monitoring will hopefully minimize side-effects related to unintended ablation of adjacent tissues.

    What conditions can be treated at UCSF by MRg-FUS

    We plan to offer MRg-FUS to patient groups, once the system has been installed and appropriate regulatory approval has been obtained:

    • Patients with fibroids who are eligible for research recruitment. UCSF is now providing MRgFUS for women enrolled in a randomized clinical trial. For more information, please visit the National Center of Excellence in Women's Health website.
    • Patients with painful bone cancer who are eligible for research recruitment. UCSF is participating in an FDA-approved research trial entitled “A Pivotal Study to Evaluate the Effectiveness and Safety of MR-Guided Focused Ultrasound Treatment of Metastatic Bone Tumors for the Palliation of Pain in Patients Who are not Candidates for Radiation Therapy”. If you may be interested in participating in this study or have questions, please contact Dr. Thomas Link.
    • Patients with prostate cancer who are eligible for research recruitment. UCSF is participating in a research trial entitled “Focal MR-Guided Focused Ultrasound Treatment of Localized Low-Risk Prostate Cancer: Feasibility Study”, once the trial has received FDA and UCSF CHR approval. If you may be interested in participating in this study or have questions, please call Dr. Andrew Taylor.

    What happens before an MRg-FUS procedure

    Several tests and discussions are required before performing an MRg-FUS procedure, in order to make sure that only appropriate patients who are likely to benefit from the procedure and who do not have any risk factors that would be a contra-indication to performing the procedure are selected. The exact requirements vary with the condition being treated, but at a minimum MRI of the treatment target (uterus, bone, or prostate) is required in all cases. It is preferable but not always essential for this MRI to be performed at UCSF.

    What happens during an MRg-FUS procedure

    The length of the procedure is variable, depending on what condition is being treated, but most cases last at least 3 hours. For women with fibroids, the patient lies on their stomach within the MRI scanner. Mild sedation and pain medicine are used to reduce discomfort and anxiety during the procedure, but patients remain conscious and are able to communicate throughout the treatment. Initial images are obtained to confirm the target is still accessible and appropriate. Then separate pulses of focused ultrasound energy are applied through the skin using a transducer that is in the table top of the MRI scanner, each known as a sonication and lasting about 20 seconds, are used to kill the fibroid in a piece by piece fashion. It is normal to feel a warming sensation during the sonications. Patients are given a safety stop button that allows them to immediately stop the sonication in the unlikely event that the treatment becomes painful. At the end of the study, an injection of an MRI contrast dye (“gadolinium”) is injected to confirm that the target fibroid(s) has been successfully destroyed.

    MRg-FUG procedure

    What happens after an MRg-FUS procedure

    After MRg-FUS, patients are allowed to rest comfortably while the effects of any medication given are allowed to wear off. Occasionally, patients with fibroids may experience some abdominal pain or discomfort or menstrual-like cramping, and if needed, the physician will provide instructions or a prescription for pain-relieving medication after discharge (often only over-the-counter pain relief medication is required). Most women are able to return to work the next day or the day after. Patients who are part of a clinical trial may be asked to fill up questionnaires or other forms in the weeks and months after the procedure to determine treatment outcome and evaluate if MRg-FUS is an effective treatment that should be offered to other patients.