TH-C-217BCD-04: 3D Ultrasound Reconstruction from Freehand Scans Using an Optical Tracking System

Purpose: To develop a 3D-ultrasound image reconstruction method from scans collected with a freehand 2D-ultrasound probe and a tracking system affixed to the probe for coordinate determination. A freehand ultrasound probe can be used to obtain arbitrary volumes since the motion of the probe is unconstrained. However the 2D images are limited to a thin plane at an arbitrary angle in the volume of interest. The 3D-ultrasound image reconstruction overcomes this limitation and allows accurate correlation with other 3D imaging modalities. Methods: A tracking system (Polaris Vicra system) which measures the 3D positions of markers affixed to the freehand ultrasound probe was used to determine the coordinates of the transducer during the scanning procedure. The tracking tool was calibrated to determine the location of each ultrasound imaging frame. This allowed the relative position of each ultrasound image plane to its neighboring images to be determined. The image intensities of the new 3D ultrasound volume were calculated by linear interpolation as the weighted average of the pixel values of nearest neighbors among the embedded 2D image intensities. Results: 3D ultrasound reconstructed volumes from freehand scanning of breast tumors clearly demonstrates the location and size of the tumor. The reconstruction accuracy was evaluated by comparing known inclusion volumes in a dedicated brachytherapy and breast ultrasound phantoms with the volumes obtained from the ultrasound reconstruction. The inclusions were contoured on each 2D slices obtained from the ultrasound reconstruction. The known volumes versus the measured volumes were (9.0/8.6 cc; 4.0/4.1cc; 0.27/0.25 cc) with an overall relative error of 5%. Conclusions: Accurate 3D ultrasound image reconstruction is possible using a tracker tool attached to the ultrasound freehand probe. The method offers the freedom of scanning large volumes of interest in breast and allows registration with other 3D imaging modalities. Terry Fox New Frontiers Program Project in Ultrasound for Cancer Therapy Dr. Brock has financial interest in deformable registration technology through the licensing of Morfeus to RaySearch Laboratories.