MR guided Focused Ultrasound Surgery (MRgFUS) For Uterine Fibroids

July 8, 2011

What is different with the MRI diagnostic test the doctor’s order to help them determine if a uterine fibroid patient is a candidate for the ExAblate procedure?

What is different with the MRI diagnostic test the doctor’s order to help them determine if a uterine fibroid patient is a candidate for the ExAblate procedure?

Answer:  To diagnose uterine fibroids physicians sometimes depend on ultrasound tests.  Many of the doctors rely on Magnetic Resonance Imaging (MRI) tests to diagnose uterine fibroids.  With many of the fibroid procedures an Open MRI with or without contrast is allowed.  The patient is restricted from eating food or drinking fluids four (4) hours before the medical test.  

With the ExAblate (MR guided Focused Ultrasound Surgery) procedure the test must be done in a Closed MRI with and without contrast.  The patient is not allowed to eat or drink for six (6) hours before the test.  Patient positioning is feet first, prone, and an empty bladder. The scan should cover the entirety of the uterus; clearly showing the fibroid and uterus boundaries, and images should clearly show sacral bones, pubic bones, and bowel loops. 

Dr. Gordon Goldman said, "My understanding is that the ExAblate MRI must be done in the manner described, only in a 'closed MRI because of the

lesser resolution of an 'open' MRI. The positioning as described is correct, and is key because this is the position in which the treatment is delivered. This positioning allows maximal anterior placement of the fibroid to the anterior abdominal wall and at the same time may move any bowel away from the proposed treatment regions. The 'beam path' of the ultrasound energy has a maximal therapeutic penetration of only 12.5 cm. If the MRI were to be done in a supine position, the mobile uterus would possibly be lying against the sacrum and appear to be out of range of the therapeutic parameters of the ultrasound 'beam path'. Similarly, the ultrasound treatment area must be a minimum of 4.0 cm from the sacral nerve plexuses, which lie along both sides of the sacrum, anteriorly. Again, in the supine position, the mobile uterus may be lying against the sacrum. That may give the appearance of being too close to the sacrum, thereby giving the false impression that it would be out of range of the treatment parameters.

The reason for contrast is to see the 'viability' of the fibroids. Viable fibroids will show up as bright (enhanced) images when contrast is used during MRI. If they do not enhance, they may not be viable. Many fibroids have undergone spontaneous necrosis and/or cystic degeneration. Treatment of non-enhanced fibroids is of no benefit and indeed, could be obstructive to treatment of fibroids lying behind them (in their shadow), as the former may absorb too much of the energy aimed at those enhanced fibroids in their 'shadow'."
 

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Medical Articles

Mid-term outcome of magnetic resonance-guided focused ultrasound surgery for uterine myomas: From six to twelve months after volume reduction. Funaki K, Fukunishi H, Funaki T, Kawakami C. J Minim Invasive Gynecol 2007 Sep-Oct,14(5):616-21. 

Features influencing patient selection for fibroid treatment with magnetic resonance-guided focused ultrasound. Arleo EK, Khilnani NM, Ng A, Min RJ. J Vasc Interv Radiol. 2007 May;18(5):681-5.

Does the phase of menstrual cycle affect MR-guided focused ultrasound surgery of uterine leiomyomas? So MJ, Fennessy FM, Zou KH, McDonald N, Hynynen K, Jolesz FA, Stewart EA, Rybicki FJ, Tempany CM. Eur J Radiol. 2006 Aug;59(2):203-7

Clinical outcomes of focused ultrasound surgery for the treatment of uterine fibroids. Stewart EA, Rabinovici J, Tempany CM, Inbar Y, Regan L, Gostout B, Hesley G, Kim HS, Hengst S, Gedroyc WM. Fertil Steril. 2006 Jan;85(1):22-9.