Amy White

Freehand 3D ultrasound calibration using an electromagnetically tracked needle

Freehand 3D ultrasound allows intra-operative imaging of volumes of interest in a fast and flexible way. However, the ultrasound device must be calibrated before it can be registered with other imaging modalities. We present a needle-fiducial based electromagnetic localization approach for calibrating freehand 3D ultrasound as a prerequisite for creating an intra-operative navigation system. Although most existing calibration methods require a complex and tedious experiment using a customized calibration phantom, our method does not. The calibration set-up requires only a container of water and only several frames (three to nine) to detect an electromagnetically tracked needle tip in a 2D ultrasound image. The tracked needle is dipped into the water and moved freehand to locate the tip in the ultrasound imaging plane. The images that show the needle tip are recorded and the coordinates are manually or automatically identified. For each frame, the pixel indices, as well as the discrete coordinates of the tracker and the needle, are used as the inputs, and the calibration matrix is reconstructed. Three group positions, each with nine frames, are recorded for calibration and validation. Despite the lower accuracy of the electromagnetic tracking device compared to optical tracking devices, the maximum RMS error for calibration is 1.22mm with six or more frames, which shows that our proposed approach is accurate and feasible.

Repeat Uterine Artery Embolization: Indications and Technical Findings

PURPOSE To determine the indications and technical aspects of procedures in patients undergoing repeat uterine artery embolization (UAE). MATERIALS AND METHODS At a single center, 24 patients underwent repeat embolization for recurrent or persistent symptoms. The magnetic resonance (MR) imaging findings before repeat embolization were compared with those of earlier studies. The extent of tumor infarction after the first procedure was determined, and the status of existing or new tumors before the second procedure was assessed. The angiographic studies from the initial and repeat embolization studies were reviewed and summarized. These findings were assessed with the use of summary statistics. RESULTS Twenty-four patients underwent repeat embolization 6-66 months after the initial embolization. The most common symptom at representation was pressure and/or bulk symptoms (n=15), followed by recurrent heavy bleeding (n=12) and pelvic pain or cramping (n=7). MR imaging studies before repeat embolization revealed incomplete infarction of tumors present before the first embolization in 22 of 24 patients. New tumors were identified in 12 patients, two of whom had new tumors only. During repeat embolization, nine patients (37%) required ovarian artery embolization to occlude ovarian supply to the uterus. Among 21 women with clinical follow-up after the second embolization, 19 (90%) had symptom control. CONCLUSIONS Repeat embolization prompted by recurrent uterine leiomyomas usually occurs in the setting of regrowth of incompletely infarcted tumors. Although ovarian embolization was often needed, on the basis of this limited experience, symptoms appear to respond well to repeat embolization.

Recent advances in uterine fibroid embolization.

Purpose of review To summarize the literature on uterine embolization for fibroids published in 2004 and 2005. Recent findings During the last two years, our understanding of the outcome of uterine fibroid embolization has increased. The outcomes are comparable to those that occur after hysterectomy. Health-related quality-of-life studies have confirmed the positive impact of the procedure. Improvement in menorrhagia has been quantified using the alkaline hematin method, objectively confirming the outcome. Recovery is also better understood and quantified, with most patients experiencing only moderate pain over the first few days after embolization. In two pregnancy-outcome studies, an increased frequency of cesarean section occurred and possibly a greater likelihood of abnormal placentation, although the data are too few to draw conclusions at this time. Contrast-enhanced magnetic resonance imaging (MRI) has emerged as the primary tool for assessing the potential of complications following the procedure, and our understanding of vaginal discharge and uterine infarction has been increased as a result of its use. Summary Within the last few years, uterine embolization has become an accepted therapy for uterine fibroids. The increase in understanding gained in recent years has helped to confirm the effectiveness and relative tolerability of this therapy.