MRgHIFU and USgHIFU treatments for uterine fibroids
A Chinese study in the July-August 2018 issue of the Korean Journal of Radiology comparing magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) and ultrasound-guided high-intensity focused ultrasound (USgHIFU) showed equivalent data with respect to feasibility, safety, and effectiveness for complete ablation of T2 hypo-intense fibroids. USgHIFU procedures, however, were much more efficient, taking about an hour less than MRgHIFU procedures, the researchers found.
HIFU offers a noninvasive alternative to surgical removal of uterine fibroids. A high-energy ultrasound transducer focuses sound waves and releases sonication energy to a target region to increase local temperature to 60-100º C, causing coagulative necrosis. Guidance by MRI or ultrasound targets treatment at a precise focal point in the tissue, without harming overlying and adjacent structures.
A key advantage of MRgHIFU over USgHIFU is that the former provides real-time temperature mapping at the target region, providing immediate feedback to record and adjust the sonication energy and power. This capability predicts the ablation effect of the treatment and is a critical safety feature to prevent excess tissue heating. The advantages of USgHIFU over MRgHIFU are greater accessibility to patients, a shorter treatment time, and lower cost.
The researchers at the Institute of Ultrasound Engineering in Medicine at Chongqing Medical University and at the Zhongshan-Xuhui Hospital of Fudan University in Shanghai evaluated treatment and outcomes of 43 patients who were treated with MRgHIFU for 44 symptomatic uterine fibroids and 51 patients who were treated with USgHIFU for 68 symptomatic uterine fibroids. All procedures were performed by a single interventional radiologist with more than 10 years of experience in image-guided tumor ablation therapy during a 12- month period.
During the MRgHIFU sonication procedures, acoustic power and energy were adjusted based on real-time temperature elevations and feedback. The duration of each acoustic exposure was 2 seconds to achieve a temperature in the focal region of 60º C or higher, followed by an interval of 2-3 seconds as the cooling period before starting again. Acoustic power and energy would be decreased when a focal temperature was recorded at higher than 70º C. The average treatment time for the 43 patients was 175 minutes, with a range of 133 to 317 minutes.
Interventional radiologists Yong-Hua Xu, MD, PhD, of the Department of Imaging and Interventional Radiology at Zhongshan-Xuhui Hospital, and co-researchers reported that the USgHIFU procedures were conducted under the ultrasound monitoring mode, with the acoustic power and energy determined by feedback from patients and changes in gray scale on ultrasound imaging during the procedure. A contrast medium was administered intravenously to assess the response for terminating the treatment when changes in the gray scale covered the region of the treated fibroid. The average treatment time for the 51 patients was 114 minutes, with a range of 75 to 153 minutes.
Patients who received both treatments did not have any major complications. Between 5% and 10% experienced abnormal vaginal discharge or mild pain in the lower abdomen. Non-perfused volume (NPV) ratio rates differed but not significantly.
Interestingly, 43% of USgHIFU-treated patients had a 100% ratio and 18% had a ratio of 90%-99%. By comparison, this ratio for MRgHIFU-treated patients was 23% and 23% respectively. The authors speculated, “The ultrasound contrast imaging conducted to detect the enhanced portion of treated fibroid for allowing supplementary sonication may contribute to improve the NPV ratio during the USgHIFU procedure.”
“The mean total released ultrasonic energy was close between MRgHIFU and USgHIFU,” the authors wrote. “Therefore, USgHIFU had the acoustic energy release within the range of safety for treatment of the uterine fibroids as MRgHIFU.” They concluded that both treatments were feasible, safe, and effective for complete ablation of T2 hypo-intense fibroids.
REFERENCE
- Wang Y, Wang ZB, Xu YH. Efficacy, efficiency, and safety of magnetic resonance-guided high-intensity focused ultrasound for ablation of uterine fibroids: Comparison with ultrasound-guided method. Korean J Radiol. 2018;19(4):724-732.