SU-E-U-06: MR-Guided Focused Ultrasound After Uterine Artery Embolization: What Happens to the Embosphere Microspheres?

Introduction: In order to select appropriate candidates for treatment of uterine fibroids using MR guided focused ultrasound (MRgFUS), a careful review of the patients' history and imaging is required. Not infrequently, patients with uterine fibroids seeking MRgFUS have previously undergone uterine artery embolization (UAE). The most common embolic agent used during UAE is Embosphere microspheres (Merit Medical Systems, INC, South Jordan, UT). Following UAE, the microspheres remain in the capillary beds of the fibroid vessels indefinitely. However, little is known regarding the nature of Embosphere microspheres in the setting of elevated temperatures (65–85degrees C) generated by high intensity focused ultrasound (HIFU). Embosphere microspheres are made of an acrylic co‐polymer (trisacryl), which is cross‐linked with gelatin. The aim of the present study was to evaluate for changes in Embosphere microspheres that underwent HIFU. Purpose: To evaluate for changes in shape and nature of Embosphere microspheres following MRgFUS.Materials and Methods: 10cc of 500–700micron Embosphere microspheres were injected into chicken breast. HIFU thermal ablation was performed, reaching high enough temperature to coagulate the chicken breast surrounding the microspheres. Additionally a vial containing microspheres was placed in a bath of heating water and temperature monitoring was performed until a maximum temperature of 100 degrees C. Gross and microscopic evaluation of the microspheres following HIFU and waterbath heating was performed. Results: The microspheres maintained their normal structure without evidence of denaturing or melting when targeted directly with HIFU (Figure 1). Additionally, the microspheres in boiling water did not alter their shape and structural integrity (Figure 2). Conclusion: HIFU of Embosphere microspheres does not change the structural integrity of the particles. As such, in the setting of prior UAE with Embosphere microspheres, MRgFUS may be safe without inducing particle denaturing or melting.