T2*‐weighted imaging in the assessment of the non‐perfused volume of uterine fibroids following magnetic resonance‐guided high‐intensity focused ultrasound ablation

Abstract

Keywords:Fast field echo (FFE) T2*-weighted imaging (T2*WI) contrast-enhanced T1-weighted imaging (CE-T1WI) magnetic resonance-guided high-intensity focused ultrasound (HIFU) non-perfused volume (NPV) uterine fibroid Magnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU) is applied widely in the ablation of symptomatic uterine fibroids [1-4]. Contrast-enhanced T1-weighted imaging (CE-T1WI) has been used in the assessment of the ablated areas of uterine fibroid, called the non-perfused volume (NPV), immediately following HIFU ablation and during follow-up. The present study details a case employing fast field echo T2*-weighted imaging (T2*WI) without the use of contrast agent for assessing NPV of fibroids in response to HIFU therapy, making a comparison with CE-T1WI. To our knowledge, this is the first report of this nature. A 45-year-old woman presenting with abdominal pain with uterine fibroids was treated by HIFU ablation. MR scanning and HIFU therapy were conducted using an Achieva TX 3 T MR scanner (Philips Healthcare, Best, The Netherlands). T2*WI (repetition time/echo time: 837/24 ms; slice thickness: 5 mm with a 1-mm gap; field of view: 240 × 240 mm; matrix: 320 × 250; flip angle: 24°) and CE-T1WI techniques were applied before and 3 minutes after the injection of contrast agents, respectively. The geometric parameters of T2*WI and CE T1WI were the same, including the scanning location and number of slices. T2*WI and CE-T1WI were compared slice by slice at the same location in the patient. The images produced using T2*WI had a high image quality and the NPV inside uterine fibroids could be visualized with clear margins on each slice, both during ablation and during follow-up. The majority of the NPV margins were irregular, but the details around the margins were almost exactly the same when employing T2*WI as CE-T1WI (Fig. 1). Using T2*WI, a dark-line around the NPV margin can be seen clearly; this might be due to surrounding micro hemorrhage. This appearance seems to make the boundary between NPV and fibroid tissue clearer with T2*WI in comparison with CE-T1WI. Additionally, two radiologists were asked to independently calculate the NPV areas on each slice from both T2*WI and CE-T1WI of the fibroids, with a paired t-test used to analyze the results; a P value of b0.05 was considered statistically significant. The statistical analysis showed no significant differences in the radiologists' calculated NPVs between T2*WI and CE-T1WI of the fibroids (first fibroid: t 1 = -1.063, P 1 = 0.296; second fibroid: t 2 = 0.375, P 2 = 0.714). The present case demonstrated the feasibility of T2*WI in the assessment of the ablated volume of fibroids treated with HIFU. As an alternative to CE-T1WI, T2*WI without the use of a contrast agent might be a very promising method in assessing NPV inside uterine fibroids following HIFU ablation, both in real-time and during follow-up after the procedure.

A clinical investigation treating different types of fibroids identified by MRI-T2WI imaging with ultrasound guided high intensity focused ultrasound

“…Consistent with this trend, high-intensity focused ultrasound (HIFU) draws clinicians’ attention and patients’ acceptance due to its non-invasive features and minimal complications. The principle of HIFU ablation relies on high energy absorption in the focal area of a tumor, which is based on the hyperacoustic tissue penetrability and focalization characteristics 3 – 5 . The thermal effect generated by ultrasound in the lesion can raise the temperature of the target area rapidly to between 60 °C and 100 °C within 0.5–1.0 seconds, causing coagulation necrosis in the target tissue and leaving the surrounding normal tissue intact.…”