Ultrasound 3D Volume Reconstruction from an Optically Tracked Endorectal Ultrasound (TERUS) Probe

ABSTRACT Endorectal Ultrasound (ERUS) is essential for the accurate staging of rectal cancer. Staging is important to the treatment of patients with rectal cancer because it will determine whether the patient r eceives preoperative radiotherapy for the purpose of tumor downstaging. ERUS images are intrinsically different from images taken by Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) in that ultrasound provides 2D images while CT and MRI provide 3D data sets that can be rendered into volumes and then re-sliced and viewed as 2D images in any desired orientation. This fundamental difference between ultrasound and tomographic imaging modalities creates a problem when a direct comparison between ultrasound and CT or MRI is desired. To accomplish the goal of following tumor volume over time, an accurate ultrasound volume must be constructed. By optically tracking the ERUS probe as data is collected, the intensity value for each pixel is saved and then inserted into the nearest voxel in the ERUS volume matrix. We validate the accuracy of volume reconstruction by finding the 3D coordinates of targets that are inside of the ERUS volume and comparing them to their known physical locations. Keywords : Image-Guided Procedures, 3-D Ultrasound, Endorectal Ultrasound, Freehand Ultrasound, Rectal Cancer