Development of an MRI fiducial marker prototype for automated MR-US fusion of abdominal images

External MRI fiducial marker devices are expected to facilitate robust, accurate, and efficient image fusion between MRI and other modalities. Automating of this process requires careful selection of a suitable marker size and material visible across a variety of pulse sequences, design of an appropriate fiducial device, and a robust segmentation algorithm. A set of routine clinical abdominal MRI pulse sequences was used to image a variety of marker materials and range of marker sizes. The most successfully detected marker was 12.7 mm diameter cylindrical reservoir filled with 1 g/L copper sulfate solution. A fiducial device was designed and fabricated from four such markers arranged in a tetrahedral orientation. MRI examinations were performed with the device attached to phantom and a volunteer, and custom developed algorithm was used to detect and segment the individual markers. The individual markers were accurately segmented in all sequences for both the phantom and volunteer. The measured intra-marker spacings matched well with the dimensions of the fiducial device. The average deviations from the actual physical spacings were 0.45± 0.40 mm and 0.52 ± 0.36 mm for the phantom and the volunteer data, respectively. These preliminary results suggest that this general fiducial design and detection algorithm could be used for MRI multimodality fusion applications.