Volumetric MR-HIFU ablation of uterine fibroids

Abstract

Over the past two decades, magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) has increasingly been used as a non-invasive treatment option for symptomatic uterine fibroids. In this thesis, a volumetric MR-HIFU ablation technique of uterine fibroids is investigated. The first part assesses the implementation of this treatment in clinical practice. The second part explores the use of diffusion-weighted magnetic resonance imaging (DWI) for the measurement and prediction of treatment effect of volumetric MR-HIFU ablation.

Part I. Clinical treatment evaluation Chapter 2 describes the mid-term clinical efficacy of volumetric MR-HIFU ablation for the treatment of uterine fibroids. This study shows that at 6 months, significant symptom improvement was obtained in 54% of the patients. In chapter 3, the effectiveness of volumetric MR-HIFU is compared with that of uterine artery embolisation (UAE) for the treatment of uterine fibroids. Patients were retrospectively selected and had to meet the eligibility criteria for both radiological treatment options. The results show that both volumetric MR-HIFU and UAE lead to significant symptom relief and improvement in health-related quality of life. However, within 12 months of follow-up, patients treated with MR-HIFU had a significantly higher risk of reintervention compared to the reintervention risk of patients treated with UAE (35% versus 4.5%, respectively). Chapter 4 demonstrates the clinical use of a direct skin cooling (DISC) device added to the MR-HIFU system to maintain a constant temperature (T≈20°C) at the interface between the MR-HIFU table top and the abdominal skin during volumetric ablation of uterine fibroids. This proof of concept study shows that it is safe and technically feasible to perform a volumetric MR-HIFU ablation with DISC for reducing the risk of thermal damage to the abdominal wall.

Part II. MRI for prediction and measurement of treatment effect In Chapter 5 we assess the value of DWI and apparent diffusion coefficient (ADC) mapping with different b-value combinations for treatment evaluation after volumetric MR-HIFU of uterine fibroids. The results show that DWI can become a helpful non-contrast-enhanced tool to assess the extent of tissue ablation (non-perfused volume) immediately after MR-HIFU ablation. A decrease in contrast agent uptake within the ablated region on contrast-enhanced T1-weighted (CE-T1w) MRI resulted in a uniform increased DWI signal intensity with a corresponding decrease in ADC when the lowest b-values (0, 200 s/mm2) were used for ADC mapping. In Chapter 6, a pre-treatment intravoxel incoherent motion (IVIM) model is investigated for tissue characterisation to predict the heating effectiveness of volumetric MR-HIFU ablation. The mean diffusion coefficient D, the mean pseudodiffusion coefficient D* and the mean perfusion fraction f in fibroid tissue were measured. The results show a high f of over 0.4, but were not able to show correlations between the IVIM parameters and the thermal response and ablation efficacy of MR-HIFU.

Increased experience and further advances in technological developments may allow for further improvements in clinical efficacy of volumetric MR-HIFU ablation.