ABSTRACT: Eleven patients with uterine fibroids were treated using MR guided high intensity focused ultrasound (MRgHIFUS) tissue ablation. Fibroid ablation temperature was monitored using phase sensitive MR mapping and treated tissue was defined by post contrast T1-weighted and diffusion weighted images (DWI). DWI exhibited hyperintense regions colocalized with the contrast T1 images. The mean Apparent Diffusion Coefficient (ADC) was decreased in the treated tissue compared to non-treated tissue. ADC mapping may provide a mechanism to assess the effectiveness of the MRGHIFUS in uterine fibroids.
INTRODUCTION: Non-invasive treatment of tumors is highly desirable and provides an alternative to surgery, one such method under active research is high intensity focused ultrasound[1-3], in particular, for the treatment of uterine fibroids[4]. The energy from the MRGHIFUS can be focused and with the goal of heating of the desired tissue and induce cell death and/or necrosis. While using MR guidance, large fibroids can be treated in one session. However, to date, there have been no published results applying DWI to MRGHIFUS treatment of uterine fibroids. Therefore, the diagnostic value of DWI and ADC maps was investigated after treatment with MRgHIFUS ablation for uterine fibroids.
METHODS: Eleven patients (mean age=45.3±3.8yrs) with uterine fibroids (mean size 32.7±16.7cm2) were treated with MRgHIFUS and guided MR imaging under conscious sedation monitored by a physician. Ultrasound treatment was performed using a modified MRgHIFUS system (InSightec, Haifa, Israel) coupled with a GE 1.5 T system. MR parameters consisted of calibration images and treatment planning T2-weighted (T2WI) images were acquired. T1 FSPGR phase sensitive (T1-PS; TR/TE=26/13ms,flip angle=30,256x128cm, 28x28, slice thickness=5mm) were acquired after each sonication by MRgHIFUS[5]. Each sonication lasted for aprox. 30s followed by a 60-90s cooling period where the temperature was monitored by the T1-PS. Optimal temperature for tissue ablation is 70C. Total MRgHIFUS treatment time was from 1-4 hrs, depending size and number of fibroids. After treatment, DWI (TR/TE=5000/90ms, b=0,500 1000,128x128, 28x28,ST=6mm) and T1 FSPGR (TR/TE=185/1.5ms, 256x100,28x28,ST=6mm) pre and post contrast images were acquired for verification of ablated tissue. Trace ADC maps were constructed for quantitative analysis. ROIs were drawn on the post contrast images and localized to the DWI hyperintensity. Quantitative statistics were obtainedfrom pre, post, and non-treated uterine tissue. Statistical analysis was performed using a paired t-test and significance was set at p<0.05.
RESULTS: All patients exhibited increased DWI signal intensity localized in the treated fibroid or fibroids region. Fig. 1 shows typical MR results after MRgHIFUS treatment on a 47 y/o patient. The top row consists of the pre MRgHIFUS treatment MR images: a) T1 post contrast, b-c) DWI d) ADC map. Similarly, the bottom row shows the post MRGHIFUS treatment same MR images. Note, the fibroids do not show any signal
intensity changes on the contrast T1, DWI, and ADC map before treatment. However, considerable signal intensity changes are noted in the treated areas. For example, increased signal in the DWI and in T2WI (edema formation). For all patients, lesion ADC (1179.8±306; Fig 2) was significantly (p<0.002) different than the non-treated post ADC(1751.9±460). In addition, the pre ADC (1375.04±460.8) was significantly different
(p=0.05) than the non-treated ADC value.
DISCUSSION: We have demonstrated that for the first time DWI and ADC mapping is feasible in MRgHIFUS treatment of uterine fibroids. The ADC was lower on average than the surrounding tissue that may indicate impending infarction. DWI has proven useful to define ischemic tissue in acute cerebral ischemia[6]. It measures cytotoxic edema and is very sensitive to the acute changes in tissue water and at later time points there are changes in the water content within the intracellular and extracellular spaces. During the transition from the subacute to chronic stages, the ADC pseudonormalizes, reflecting a probable loss of membrane integrity and cell necrosis as the tissue undergoes transformation from a state of edema to infarction[7]. The time course of change in the ADC in MRgHIFUS treated tissue may provide a measure to gauge the effectiveness of treatment.