Taly Gilat Schmidt PhD, Presenter: Nothing to Disclose

Fatih Pektas, Abstract Co-Author: Nothing to Disclose

To investigate region-of-interest (ROI) material decomposition and basis image reconstruction from truncated energy-resolved CT data.  Acquiring energy-resolved data of a limited ROI may avoid pulse-pileup effects that occur at the periphery of objects.

One method is proposed to reconstruct images of basis functions that are primarily contained within the ROI, such as K-edge contrast agents. Material decomposition is performed independently for each ray in the truncated sinogram, followed by filtered backprojection. A second method is proposed for general basis decomposition, which uses a prior conventional energy-integrating image to estimate energy-resolved data outside the ROI. The measured and estimated energy-resolved data are decomposed into basis projections and merged into basis sinograms of the full FOV. Basis images of the ROI are then reconstructed through filtered backprojection. Simulations of a voxelized thorax phantom and a detector with five energy bins were performed. Full FOV, truncated, and truncated data merged with data estimated from the prior image were decomposed into Compton, photoelectric, and iodine basis functions. An empirical weighting factor was determined to blend the merged sinograms at the boundary of the truncated data. Basis images of the central 15 cm x 15 cm ROI containing the heart were reconstructed via filtered backprojection. Basis image accuracy was quantified relative to gold-standard basis images.

The error in the iodine basis image reconstructed from truncated energy-resolved data without prior information was less than 1% for the central 7 cm of the 7.5-cm-radius ROI and 3% at the edge of the ROI. When the truncated and estimated basis sinograms were blended, the error was below 1% throughout the ROI for the iodine and photoelectric basis images and ranged from 1% to 4% for the Compton basis image.

Results suggest that the density of localized K-edge contrast agents can be estimated to within 1% error using filtered backprojection of truncated data. General basis images can be reconstructed to within a few percent error using a prior energy-integrating image.

Energy-resolved CT has the potential to provide improved material decomposition. ROI imaging may avoid pulse-pileup effects and facilitate the use of available photon-counting detectors.

Schmidt, T, Pektas, F, Region-of-Interest Material Decomposition from Truncated Energy-resolved CT.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11011887.html