Magnetic resonance-guided focused ultrasound surgery (MRgFUS) treatment for uterine fibroids
1 Department of Biomedical Imaging, University of Malaya, Kuala Lumpur, Malaysia
2 Department of Obstetrics and Gynaecology, University of Malaya, Kuala Lumpur, Malaysia
3 Insightec, United States
Magnetic Resonance-guided focused Ultrasound Surgery
(MRgFUS) is gaining popularity as an alternative to medical and surgical
interventions in the management of symptomatic uterine fibroids. Studies have shown
that it is an effective non-invasive treatment with minimal associated risks as
compared to myomectomy and hysterectomy. MRgFUS can be offered to a majority of
patients suffering from symptomatic uterine fibroids. It has been suggested
that the use of broader inclusion criteria as well as the mitigation techniques
makes it possible to offer MRgFUS to a much larger subset of patients than
previously believed. This paper will describe how MRgFUS treatment for uterine
fibroids is performed at the University of Malaya Medical Centre, Kuala Lumpur , Malaysia. © 2010 Biomedical Imaging and Intervention Journal. All
Keywords: MRgFUS, fibroids, technique
Fibroids are benign growths in the uterus, which are
symptomatic in up to 25 percent of women of childbearing age . Symptoms can
include heavy and prolonged menstrual bleeding, severe pain, bloating and
constipation or urinary complaints. The most common treatment is hysterectomy,
a highly invasive surgical procedure to remove the uterus, which is associated
with the usual surgical risks and complications, requires a three- to four-day
hospital stay and results in patient recovery time of six weeks or more [2,3].
All other techniques including uterine artery embolisation , involve some
level of incision, hospitalization and recovery time. For example, myomectomy
requires a hospital stay of several days and recovery time of two to four weeks
. A number of noninvasive alternatives to hysterectomy have become available
as treatments for uterine fibroids [5-9].
MRgFUS is so disruptive that it will very likely overturn
the other dominant current “technologies” e.g. surgery . Clinical studies
demonstrate that MRgFUS is a safe and effective treatment for symptomatic
uterine fibroids [11-13]. Several studies have shown that MRgFUS significantly
improves clinical symptoms in 70% to 80% of women with uterine myomas [13-16].
Studies have also demonstrated a correlation between the treated volume of the
myomas, improvement in symptoms, and lesion shrinkage . The results
demonstrate that successful and durable treatment of uterine fibroids with
MRgFUS necessitates selecting those patients for whom higher non-perfused
volumes can be attained using the MRgFUS system.
In contrast to other invasive treatments for uterine
fibroids, the relatively non-invasive MRgFUS can be performed as an outpatient
procedure and requires no general anaesthesia. The ExAblate 2000 (InSightec
Ltd., Haifa, Israel) is the first device to combine magnetic resonance imaging
(MRI) with high-intensity focused ultrasound to destroy tumours non-invasively.
In contrast to other options, the non-invasiveness of the MRgFUS technique is
associated with minimal risks and complications, requires no overnight hospital
stay and allows most patients to return to work and their normal activities in
one to two days.
Safety data from these studies consistently show that
there are few serious FDA-reportable adverse events related to MRgFUS. The only
device-related adverse events reported especially early on were skin burns
(secondary to poor coupling from hair and scars on the skin) and nerve damage
following MRgFUS, which resolved within a year . Damage to adjacent organs,
such as bowel perforation, is also possible during treatment but rare . To
date, no immediate emergency surgical interventions, unexpected short-term
adverse events or long-term complications have been observed after MRgFUS.
Based on the prospective registry of all known pregnancies
occurring after MrgFUS, and maintained by the device manufacturer and reported
to the FDA, 54 pregnancies in 51 women have occurred. The mean time to
conception was 8 months after treatment. Live births occurred in 41% of
pregnancies. There was a 28% spontaneous abortion rate, an 11% rate elective
pregnancy termination rate and 20% ongoing pregnancies beyond 20 gestational
weeks. The mean birth weight was 3.3 kg, and the vaginal delivery rate was 64%.
It also has been suggested that for the NHS in the UK, a treatment strategy for symptomatic uterine fibroids starting with MRgFUS is likely to
be cost-effective . It also remains cost-effective under alternative
assumptions regarding current practice, health utility estimates before and
after treatment, and the effectiveness of alternative treatments (complication
rates, recurrence rates and procedural death rates).
Currently, MRgFUS has been used for breast tumours,
painful bony metastases, and liver tumours. For the brain, it has been used for
the ablation of glioblastomas and for functional neurosurgery. Future
applications for prostate cancer and acute stroke treatment are being explored.
All MRgFUS procedures were performed using the ExAblate
2000 (InSightec, Haifa, Israel), which is fully integrated with a 1.5 Tesla MR
scanner (GE Medical Systems, Milwaukee, WI). ExAblate uses a ‘sonication’
process wherein focused ultrasound (FUS) destroys tissues by concentrating a
high-energy beam on a specific point and raising its temperature to 60°-85°C.
Multiple sonications (focal delivery of energy) are required to ablate a
specific tissue. The MRI system provides critical data such as high-resolution
3D imaging of the location of the tumour and internal organs as well as
real-time temperature feedback that indicates the degree of tissue heating and
coagulation. Thus, this integration of FUS with MRI provides a “closed-loop
therapy and feedback system” that enables the physician to adjust treatment
parameters and control the treatment, helping to ensure a high level of safety and
efficacy. This is currently not commercially possible on the ultrasound- based
focused ultrasound systems.
If the patient is clinically eligible and interested in
MRgFUS, she is referred for a screening MRI scan. Screening is performed in the
prone position to flatten the abdomen (on a 1 cm gel pad similar to that used
for treatment) and to allow the pelvic structures to fall into the position
they would be in during a potential treatment. Imaging consists of several
sequences. To identify anatomical structures within the pelvis, T2-weighted
fast spin echo images in axial, sagittal and coronal orientations are acquired.
To evaluate the presence of hemorrhagic or fatty tissues, T1-weighted fast
spoiled gradient echo (FSPGR) images are acquired in the sagittal orientation
followed by T1-weighted fat suppressed FSPGR images post gadolinium injection
in order to evaluate the hemodynamic characteristics of the fibroids and to
assess their potential viability.
The first, and probably, the most important inclusion
criterion for selecting MRgFUS as a treatment is the existence of uterine
fibroid(s) and the relevance of the fibroid(s) to the patient’s symptoms. The
location and size of the fibroids must correlate with the patient’s symptoms.
However, if a patient’s symptoms do not correlate with the size and location of
the leiomyomas, MRgFUS may not be the appropriate treatment, for example,
subserosal leiomyomas associated with uterine bleeding instead of compression
symptoms to adjacent organs i.e. bladder and intestines 
The exclusion criteria are as listed in Table 1 
As bone absorbs ultrasound waves more readily than soft
tissue, low energies are sufficient to heat a bone surface to high
temperatures. Consequently, nerves lying adjacent to a heated bone surface may
be heated resulting in pain and, in extreme cases, even result in nerve damage
. It is now recommended that sonications are performed at least 4 cm from
bony structures to minimize the amount of heating of the bone  (Figure 1),
which can in turn heat the fat surrounding the nerves and lead to stimulation
or potentially damage of the nerve. Such stimulation of the adjacent sacral
nerves may result in incomplete treatment with reduced efficacy of the procedure
if the pain is severe. Therefore, fibroids lying close to the lumbosacral
plexus or to any bone surface require special care in MRgFUS treatment. Several
mitigation techniques such as tilting the beam path to avoid bone, increasing
the frequency of the ultrasound beam, rectal filling to push the fibroid away
from the bone  (Figure 2) or partial treatment to change the subsequent
orientation/location of fibroid are available.
Patients are deemed technically suitable for MRgFUS if
their fibroids mass seems accessible by the system (Figure 3) and is not deemed
too large in volume. A significant proportion of the fibroids mass should be no
more than 12 cm depth away from the skin line (which is the maximum depth of
penetration of the sound). Fibroids with more than 50% of their volume beyond
the maximum focus are generally excluded unless mitigation techniques are used,
for example using a thinner acoustic coupling gel pad (reducing the distance
between the patient and the transducer) or filling the rectum with ultrasound
gel to push the uterus and the fibroids towards the anterior.
Patients with more than six uterine fibroids of more than
4 cm in size each should also possibly be excluded. This is generally
associated with the fibroids being close to the sacrum or hidden behind the
bowel and, thus, will be inaccessible. Pre-treatment of large fibroids with a
gonadotropin-releasing hormone (GnRH) agonist helps to reduce fibroid volume
and increase fibroid tissue susceptibility to the treatment, which may improve
MRgFUS outcomes .
Presence of longitudinal scars in the beam path, including
those that could not be seen on the MR images are also reasons for exclusion.
Scar tissue may absorb the ultrasound energy and cause pain or result in a skin
burn. The St Mary’s group has developed an ingenious method of highlighting
transverse scars  where the scar is painted with a solution of nail varnish
and paramagnetic iron oxide particles. This provides an obvious artefact along
the line of the scar, which can easily be avoided by appropriate positioning
and angling of the ultrasound beam.
Other exclusion criteria include grossly calcified
fibroids i.e. the pseudo capsule of the fibroid becomes heavily calcified where
the ultrasound energy is disrupted by the capsular calcifications and cannot
pass into the body of the fibroid mass. Non-enhancing fibroids, which are
essentially non-viable, are also excluded. They may, however, be treated if
they cause symptoms such as mass effect (Figure 4). Pedunculated fibroids, when
attached by a small stalk, are another contraindication to MRgFUS as they may
detach into the abdominal cavity, thus requiring further surgical
interventions. Patients with other pelvic pathologies (such as adenomyosis)
should not be treated with MRgFUS.
As air bubbles or hard particles may be present in the
bowel and may reflect or absorb the ultrasonic energy, patients with bowel that
cannot be potentially shifted from the beam path (by bladder or rectal filling)
or beam angulation are also excluded from treatment.
What about adenomyosis? Symptoms of adenomyosis are very
similar to those of fibroid  and both can occur in the same patient. A
junctional zone width of more than 12 mm was defined as adenomyosis . It is
not uncommon to have patients referred for screening as fibroids but
subsequently found to have adenomyosis (35% to 55%) after MR imaging .
The MRgFUS procedure can ablate adenomyosis tissue
sufficiently and can improve symptoms significantly during a period of 3 to 6
months post-treatment  especially those with low-signal intensity
adenomyosis on T2-weighted MR images. They went on to classify the architecture
of the non-perfused lesions on contrast-enhanced T1-weighted MR images
immediately after MRgFUS into 3 types: lesions with round margins (type R)
(Figure 5), serrated margins (type S) (Figure 6), and honeycomb structures with
numerous small, non-perfused holes (type H). There is still no long-term
evidence currently available in print to demonstrate that treatment of
adenomyosis results in clinical benefit.
The patient’s abdomen is shaved and cleaned to remove any
hair and also checked for the presence of any moles or scars as these may
result in skin burns. A urinary catheter is inserted to control uterine
movement during the three-hour treatment. An IV line is necessary for the
administration of sedation. The patient lays prone over a water bath in which
the transducer is immersed. The patient’s abdomen is acoustically coupled with
the transducer via the water bath using a special gel pad. The patient's legs
may be wrapped with compression stockings to reduce the risk of deep vein
thrombosis but the authors do not practice this. Prior to starting the
treatment, 100 mg Diclofenac sodium is given as a suppository. The patient is
then positioned prone on the ExAblate treatment table with her abdomen over the
water bath containing the ultrasound transducer. Patient’s blood pressure,
heart rate, oxygenation, and comfort level are monitored throughout the
treatment. The position of the patient over the transducer is determined from a
3plane localizer and T2-weighted imaging. This is to maximise the window
available for the treatment of fibroids (images of poor positioning and images
of baseline and MRI showing good positioning). Midazolam 2 mg is given via IV
once the patient has been properly positioned on the FUS table. Pethidine 50 mg
and Maxolon 20 mg are administered just prior to performing the sonications.
It is essential that the patient is comfortable in the
position for the procedure. The authors ensure there is support for the head
and arms, and provide headphones and ear plugs. Communication is provided
through the 2 way-intercom and an emergency button. Analgesia is topped up
regularly and the bladder, if filled to provide an acoustic window, is drained
by 30-40 ml every 30 minutes to minimise the displacement of the uterus
due to continued filling via the kidneys. The authors use updated MRI images to
visualise the location of the fibroid in relation to the intended target
fibroids (i.e. the center of the transducer) and make appropriate adjustments
to the patient's position. The MRI scans also provide information as to the
need to perform any mitigation techniques by changing the volume of the
bladder, or filling the rectum with ultrasound gel using Sengstaken-Blakemore
When the position of the patient has been finalised and
the patient is comfortable, there follows the acquisition of high-resolution
T2-weighted MR images of the pelvis in the three orthogonal planes i.e.
sagittal, axial and coronal. These images are used to define the location of
the fibroid, the volume to be ablated, the proximity of the sacrum and
lumbo-sacral spine as well as to determine the presence of any bowel lying
anterior to the fibroid which may lie in the beam path. The authors have found
that using a fat-suppressed T2-weighted imaging sequence assists in defining
the intestine much easier (Figure 7).
If the fibroid lies too close to the sacral area, then
ultrasound gel (approx 250cc) can be inserted rectally to displace the fibroids
away form the area. A safe distance of 4 cm is necessary. If bowel has migrated
anteriorly to the fibroid, then saline can be infused into the bladder. This
may need to be followed with insertion of rectal gel. The skin-gel pad
interface needs to be defined. This is followed by marking out the critical
structures i.e. the pubic bone, bowel and far field bone (the spine and sacrum)
using specific low-energy density region markers.
The region of treatment (ROT) is then defined on the
targeted fibroid. This ROT is placed on the coronal images. The ROT is drawn
such that a margin of at least 1 cm is kept from the serosal surfaces to
minimise the risk of ablating the serosa which causes severe pain. There is no
limit to the percentage of fibroid volume that can be treated though generally
a 60-70% of ablation is necessary for good outcomes . The operator then
chooses the treatment plan depending on the size and type of fibroid being
treated. For “white fibroids”, a nominal high-density plan should be selected,
otherwise a medium-density plan would be suitable. The length of the
sonications can then be selected and may vary from 10 mm to 45 mm. Based on the
treatment plan chosen, the FUS system automatically displays a series of
sonications to cover the region of treatment. Each spot is cylindrically
shaped, 25 to 45 mm in length and 5 mm in diameter for a nominal fibroid.
The sonication beam path is carefully checked to ensure
that it does not pass through any structures that should be avoided – such as
the small bowel that can fall in front of the uterus.
Generally, treating and ablating an 8 cm fibroid takes
approximately 3 h of sonications (that is excluding the patient preparation and
planning), depending on energy absorption and location of the fibroid. Fibroids
that are larger than 10 cm are less suitable for the treatment because of the
long treatment time. However two options are available:
- Treating the fibroid over two sessions performed preferably with the
fibroid volume being split into a superior and an inferior region for each of
the treatment. This is to avoid the ultrasound beam in the second treatment
from passing through already treated regions if an anterior-posterior division
- Or as mentioned previously, use pre-treatment with GnRH agonist prior to
MRgFUS to shrink the fibroid and improve treatment outcomes .
Before treatment, the patient is asked to press the
emergency button. One or more low-energy 'verification' sonications are then
delivered to calibrate the location of the actual target spot against the
planned target location (Figure 8). This is monitored on the temperature maps,
which are displayed real time during the course of the sonications. These
sonications also allow a titration of the energy to the patient progressively
rather than being treated with a large dose in a single step.
The system will display the total number of sonication
spots on the defined ROT. These spots are green, yellow or red (just like
traffic lights) to indicate the safety of each sonication spot. The green spots
can be safely treated while the yellow spots generally indicate that the energy
density reaching the marked out areas of the sacrum has exceeded a
system-defined lower safety limit. One can still treat these yellow spots but
should try to modify the sonication parameters appropriately and ensure post
sonication that the patients do not have discomfort in their back or radiation
down their lower limbs. However, when the spots turn red, the system will not
allow you to sonicate. This is generally due to areas of bowel, which lie
within the beam pass zone and pass through the pubic bone or the energy density
in the posterior pelvis reaching a system-defined upper margin. The beam must
be angled to avoid the bowel, parameters changed or the spot moved.
Each sonication duration varies from 20 to 30 seconds.
This is followed by cooling periods of 24 to 90 seconds. The cooling periods
allow time for the skin to cool down; otherwise patients may suffer skin burns.
Thermal feedback is generated by real-time PRF while magnitude images highlight
the temperature changes and the anatomy in the targeted area. A temperature
graph shows the temperature change on the temperature maps (Figure 9). Once the
targeted tissue reaches the desired temperature leading to thermal necrosis 
system automatically highlights the treated areas in blue (Figure 10). The
sonications can be monitored in axial, coronal or the sagittal plane.
For the patient’s safety, a cooling period between each
sonication is programmed into the treatment plan, to allow cooling of tissue
outside and anterior to the treatment zone. This cooling duration varies
depending on the output energy and how close the next sonication is to the area
just treated, but is generally between 40 and 70 seconds. Using an interleaved
mode in large fibroids shortens the cooling time and hastens the treatment time
where subsequent sonications anterior pass zones do not intersect.
Sonication parameters can be changed, if necessary,
including energy, duration, spot size and frequency depending on the response
seen in the previous treatment or due to pain or discomfort (Figure 11).
During each sonication, magnitude images, which display
the position of the uterus relative to the electronic 3D special markers
(fudicials) placed at the beginning of treatment on the T2 images, are
obtained, and allows for determination of any movement of the uterus and patient.
After all the sonications have been completed and the dose
volume is determined to be adequate for fibroid destruction, the treatment has
ended. Post-treatment fat-saturated T2WI are obtained to assess the skin and
abdominal muscles for the presence of any hyperemia (Figure 12).
DWI changes, which include changes in both T2 and ADC, may
be useful in many cases to delineate the treated region resulting from MRgFUS.
However, definite DWI changes are not always observed, and in some large
treatments, the area of the non-perfused region may be under estimated .
Despite these limitations, these same sequences may be performed anytime during
the treatment to assess damage or extent of ablation. The authors currently use
axial DWI images using B values of 600 to assess the size of ablation (Figure
A series of contrast-enhanced T1-weighted images are
acquired to determine the treatment outcome, which shows the treated fibroid as
non-enhancing (Figure 14). In the authors' practice, gadolinium contrast is not
given intra-procedurally because there is a possibility that the gadolinium
chelate will dissociate and the free gadolinium may become fixed in the
tissues. The long-term effects of such exposure are not known. Therefore in the
authors' centre, once the intravenous gadolinium has been given, the treatment
has to be terminated.
Immediately following treatment, the patient’s skin is
checked for the presence of any burns. In one study, approximately 11% of
patients developed some inflammatory changes in the near field but these
changes cause minimal if any post-treatment discomfort to the patients . It
is vital that the near field structures are monitored for heating on thermal
images acquired during sonications. Occasional in-treatment acquisition of
T2-weighted fat saturation images are helpful in detecting these changes early,
especially if there is an awareness of the location of patient discomfort
associated with sonications.
The authors do prescribe some post-procedure analgesics to
take should patients experience any pain. Patients are provided with the
contact phone number of the gynecologist should they need any assistance.
Following treatment, the patient generally remains in the MRI suite for one
hour to recover from the sedation. Then they are discharged and accompanied
home by their spouse or a relative.
On the day following treatment, they should be able to
return to their normal activities with no unusual events and no medication. The
authors subsequently plan for them to visit the interventional radiology clinic
in 2 weeks and see the gynecologist at the same time. Patients for whom
treatment could not be completed because of the large size or number, a repeat
treatment is planned anytime from 1 week onwards. Follow-up contrast-enhanced
MRI is performed after 6 months to assess the fibroid size (Figure 15).
Patient-reported outcomes of symptom severity and
Health-Related Quality of Life (HRQL) are becoming increasingly important for
evaluating treatment of uterine fibroids within the clinical setting. The
Uterine Fibroid Symptom and Health Related Quality of Life Questionnaire
(UFS-QOL) is a uterine fibroid-specific questionnaire developed specifically to
evaluate the symptoms of uterine fibroids and their impact on HRQL. The UFS-QOL
appears to be a useful evaluative tool for assessing symptoms and HRQL in
studies among patients with uterine fibroids . The authors screen their
patients using these criteria to assess response.
MR-guided focused Ultrasound provides an important new
non-invasive and effective treatment for uterine fibroids. MRgFUS can be
offered to the majority of patients suffering from symptomatic uterine fibroids
. They suggest that the use of broader inclusion criteria as well as the mitigation
techniques makes it possible to offer MRgFUS to a much larger subset of
patients than previously believed (Table 2). Recovery from the treatment is
almost immediate and symptom relief is generally noticed sooner than
alternative therapies. This is a tremendous advantage over existing options,
which place a large burden on patients. Additional applications e.g. drug
deliveries are under investigation and hold the promise of transforming the
surgical arena to benefit millions of patients.
Figure 1 Sagittal T2-WI shows a “black” fibroid which is very close to the LS spine (blue arrows) and cannot be treated safely unless the bladder is drained or other mitigation techniques performed.
Figure 10 (a) The areas in dark blue are previous treatment areas that have achieved the desired thermal dose. The rectangular box (lighter blue) shows the current sonications application while the green area shows the current sonications dose map. (b) The inverted light blue cones show the beam path which can be angulated to avoid critical structures. The rectangular box (yellow) shows the current sonication has exceeded the recommended dose but can still be delivered. The areas of red are phase shift artefacts.
Figure 11 The system allows changes to the energy, frequency, spot parameters depending on the patient comfort and the response of the fibroids to the sonications. The system also displays the spot length, diameter of the sonication spot along with the angulation of the beam (roll and pitch).
Figure 12 Post-contrast T1WI in sagittal plane showing enhancement of the subcutaneous tissue (arrow) and ablated region of fibroid (asterisk).
Figure 13 (a) Coronal DWI images compared to (b) post-contrast fat suppressed T1WI to assess the extent of ablation (arrows) at the same level.
Figure 14 T1W post contrast enhanced images showing (a) poor (b) average and (c) good ablation (arrows).
Figure 15 Fat saturated post-contrast T1WI (a) at baseline prior to treatment (b) following completion of ablation with area of non perfusion seen centrally and (c) at 6 months follow-up.
Figure 2 Sagittal T2-WI of the pelvis. Use of rectal filling (arrows) to displace the uterus away from the sacrum.
Figure 3 (a) Sagittal T2-WI shows no acoustic window (blue triangle represents the FUS beam path) secondary to bowel (asterisks) lying anterior to fibroid (may be overcome by filling the bladder and/or rectum) while (b) axial T2-WI shows a good acoustic window.
Figure 4 (a) Sagittal T2-WI shows multiple dark fibroids which on the (b) post contrast T1-WI shows some of the fibroids to be non-enhancing (*) and therefore need not be treated.
Figure 5 (a) Type A multiple area of focal adenomyosis (round) (blue dotted ring) seen in both anterior and posterior walls on the sagittal T2-WI; (b) and (c) post-contrast T1-WI following MRgFUS showing good response.
Figure 6 (a) Type B (serrated) area of focal adenomyosis seen in the posterior wall on the sagittal T2-WI; (b) axial and (c) sagittal post-contrast T1-WI following MRgFUS showing poor treatment (arrows) response with serrated margins.
Figure 7 Defining the bowel on treatment planning (a) T2 WI in sagittal plane followed by T2WI with fat saturation shows the bowel (arrow) clearly against the suppressed intra-peritoneal fat.
Figure 8 The verification sonication (blue ring) on the coronal image. The red crosses “X” are the fudicial markers to identify the uterus, pelvic bones, and bladder to ascertain if the patient has moved during the treatment.
Figure 9 The post sonication temperature display of the tissue temperature in the fibroid after the treatment has been delivered.
Table 1 Patient exclusion criteria.
Table 2 Comparison of assessment criteria used in earlier studies and the current St. Mary’s centre .
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|Received 12 August 2009; received in revised form 19 January
2010, accepted 24 January 2010
Correspondence: Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia. Tel.: +603-79492069; Fax: +603-79581973; E-mail: firstname.lastname@example.org (Basri J.J. Abdullah).
Please cite as: Abdullah BJJ, Subramaniam RV, Omar SS, Wragg P, Ramli N, Wui AL, Lee CC, Yusof Y,
Magnetic resonance-guided focused ultrasound surgery (MRgFUS) treatment for uterine fibroids, Biomed Imaging Interv J 2010; 6(2):e15