Daniel Kolditz Dipl Eng, PhD, Presenter: Nothing to Disclose

Yiannis Kyriakou PhD, Abstract Co-Author: Nothing to Disclose

Willi A. Kalender PhD, Abstract Co-Author: Consultant, Siemens AG Consultant, Bayer AG Founder, CT Imaging GmbH Scientific Advisor, CT Imaging GmbH Shareholder, CT Imaging GmbH Founder, Artemis Imaging GmbH CEO, Artemis Imaging GmbH Shareholder, Artemis Imaging GmbH

In C-arm based flat-detector CT (FDCT) it frequently happens that the patient exceeds the scan field of view (SFOV) in transaxial direction which causes raw-data truncation and CT image artifacts. The aim of this study was to develop and evaluate a truncation correction for extended field-of-view (EFOV) reconstructions based on patient size and shape information from an optical camera system.

The patient outline was sampled with an optical camera system to obtain size and shape information outside the SFOV. This estimate was used to appropriately extrapolate the truncated projections by an elliptical extrapolation function. A smooth transition from original to extrapolated raw-data was ensured and the extrapolation yielded zero at the estimated object width. The detruncated projections were reconstructed with a standard Feldkamp-type algorithm. In simulations, performance was evaluated for voxelized anthropomorphic phantoms by calculation of root-mean-square differences (RMSD) between truncation-free reconstructions and corrected/uncorrected reconstructions. Measurements with the C-arm FDCT system Artis Zeego (Siemens AG, Healthcare Sector, Erlangen, Germany) and the optical tracking system NDI Polaris (Northern Digital Inc., Waterloo, Canada) were used to validate the applicability for realistic applications. The anthropomorphic phantoms which were used caused truncation in all projections.

The proposed approach enlarged the FOV, e.g. from 240 mm to 400 mm, and improved the image quality inside and outside the SFOV. It was possible to cover larger patient cross-sections in transaxial direction. For simulations, the relative RMSD was less than 5 % for the SFOV and less than 16 % for the EFOV, depending on the phantom. Truncation-induced cupping artifacts in simulated and measured data were significantly reduced.

The algorithm improves the image quality inside and outside the SFOV, enables the imaging of the complete patient circumference and simultaneously reduces the dose. The correction can be used regardless of the number of truncated projections.

The proposed truncation correction is useful for extended field-of-view reconstructions in C-arm FDCT for various applications, e.g. image guided radiotherapy.

Kolditz, D, Kyriakou, Y, Kalender, W, Extended Field-of-View Reconstruction in C-arm Flat-Detector CT by Using Patient Size and Shape Information from an Optical Camera System.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9007058.html