Introduction
Magnetic Resonance Imaging-guided focused ultrasound ablation (MRgFUS) is a completely non-invasive method for the treatment of women with symptomatic uterine fibroids. KK Women’s and Children’s Hospital’s Department of Diagnostic Imaging is currently the only facility in SE Asia that provides this treatment.

What it is
Whilst the ultrasound energy used in imaging is dispersed over a wide area, it is concentrated into a small target during focused ultrasound ablation to produce a precise volume of coagulative necrosis.

Unlike conventional surgery, the fibroids are not removed during the process, but are left in the body to undergo gradual involution.

Studies of uterine artery embolisation suggest that volume reduction is not essential for symptom resolution, and that the coagulation of angiogenic growth factors stored in myomas is an alternate explanation for symptomatic reduction of menorrhagia^1.

The ultrasound device is coupled to a compatible Magnetic Resonance Imaging (MRI) scanner, allowing real-time monitoring of uterine position and temperature changes throughout the treatment. There is good correlation between thermal dose estimates and ablation of tissues².

The treatment is performed on an FDA approved system (ExAblate 2000 Insightec, Haifa Israel) that is integrated to a 1.5Tesla MRI unit (GE Medical Systems, Milwaukee). It is currently the only system available for clinical use.

Patient selection
Not all patients are suitable for this procedure. Patients with pacemakers, some surgical implants, or other MR-incompatible devices cannot undergo the procedure. The procedure is also contraindicated in those with extensive abdominal scars. It is off ered to pre-menopausal women who have completed their families, and who have fibroids that range between 3cm to 10cm in diameter. The location and number of fibroids present may also aff ect the success rate of the procedure. The patients are assessed and counselled by a gynaecologist and radiologist at the hospital’s specialist clinic. Selected patients undergo an MRI scan to determine if their fi broids can be treated. In general, only about 30% of women are suitable for treatment after the MRI assessment.

How it is done
The patient is asked to fast overnight. On the day of the procedure, a urinary catheter is inserted. The patient lies prone on the table where the ultrasound transducer is located (figures 1a & b). A water bath and gel pad provides the coupling medium for the ultrasound to be transmitted from the transducer to the patient’s body.

Intravenous sedation and analgesia are administered during the treatment that is carried out in the MRI suite. Immediately before treatment, pelvic MR images were obtained to enable the radiologist to mark out the sensitive structures such as bowel and the lumbosacral nerves, and the area of treatment (figure 2). Prior to each sonication, the path of the ultrasound beam (figure 3) is displayed, and further adjustments may be made to steer it away from the sensitive structures, when necessary. During each sonication, which lasts about 20 seconds, active feedback on temperature rise in the targeted areas are shown on line diagrams (figure 4). Adequate treatment is based on the demonstration of a non-enhancing volume of at least 30% of the fibroid on the post-treatment study (figures 5 & 6). Non-enhancement in the fibroid basically indicates non-perfusion.

The patient is given a switch that she could use to turn off the sonication when she feels excessive heating or unusual sensations in her lower limbs or lower back. Most patients feel some amount of heating on their lower abdomen during the sonication. The temperature at the skin can go up to about 40 degrees Centigrade. Within the fibroid, temperatures go up to between 65 to 85 degrees Centigrade. In between sonications, there is a cooling time of between 70 to 90 seconds. The treatment usually takes between 2 to 4 hours. With the time taken for preparation and recovery, it is necessary for the patient to spend at least 6 hours, or more, in the hospital. The patient is discharged on the same day. Most patients are able to resume normal activities after one or two days.

Fig.1b shows set up of ultrasound table.

Fig. 3 shows the ultrasound beam path (blue).
Rectangle: target volume.

Fig. 4 Line graphs showing temperature rise in targeted tissue

Fig. 5 Pretreatment MR image of uterine fibroid (F). Arrows – uterus. P – pubic bone

Fig. 6 Post treatment MR image showing non-perfused area (arrows)

Complications
Complications from MRgFUS are uncommon and mostly minor. The most common complication is burns on the anterior abdominal wall. Surgical scars on the abdomen carry a higher risk of burns as patients often have diminished sensation around the scars. The more serious complications include bowel perforation and nerve injury. Bowel perforation can occur from accidental sonication of bowel that goes between the abdominal wall and the uterus. Nerve injury occurs when the bone at the back of the uterus is overheated. The most serious eff ect was sciatic nerve palsy in a patient who eventually recovered after a year³. In our experience with 22 patients treated at KK Women’s and Children’s Hospital (KK), none of the patients suff ered burns. The most signifi cant complication was in a patient who complained of some pain in the foot that lasted about 3 months, and was attributed to neuropraxia. She was able to continue her normal activities, including exercising. She has since recovered.

Other minor problems encountered were low-grade fever for a day, mild abdominal cramps, vaginal discharge and dysuria.

Outcome and conclusion
Preliminary results from a study conducted in KK to evaluate the efficacy of the treatment showed that 7 out of 10 of those with significant symptoms had greater improvement at 6 months follow-up. Some showed improvement at the first menstrual period after the treatment. This is similar to that reported in the literature^3-4, where 70-90% of patients showed improvement in their symptoms. Our experience with the procedure has shown that it is considerably safer than other treatment options available, and that the patients recover faster. Elsewhere, outside of Singapore, treatment applications using MRguided focused ultrasound continue to grow, with treatments on breast cancer, bone metastases, liver tumours, and currently still under research, brain tumours.

References
1. Spies JB, Roth AR, Jha RC, Gomez-Jorge J, Levy EB, Chang TC, et al. Leiomyomata treated with uterine artery embolization: factors associated with successful symptom and imaging outcome. Radiology 2002; 222: 45–52.

2. McDannold N., et al. Uterine leiomyomas: MR imaging-based thermometry and thermal dosimetry during focused ultrasound thermal ablation. Radiology 2006; 240: 263-72

3. Stewart EA, Rabinovici J, Tempany CM, et al. Clinical outcomes of focused ultrasound surgery for the treatment of uterine fibroids. Fertil Steril 2006; 85(1): 22–29.

4. Fennessy FM, Tempany CM, McDannold NJ, et al. Uterine Leiomyomas: MR Imaging-guided Focused Ultrasound Surgery – Results of Different Treatment Protocols. Radiology 2007; 243(3): 885-93.