IOP PUBLISHING PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 52 (2007) 5187–5204 doi:10.1088/0031-9155/52/17/006 List-mode-based reconstruction for respiratory motion correction in PET using non-rigid body transformations F Lamare 1,2 , M J Ledesma Carbayo 3 , T Cresson 1 , G Kontaxakis 3 , A Santos 3 , C Cheze Le Rest 1 , A J Reader 4 and D Visvikis 1 1 INSERM, U650, Laboratoire du Traitement de l’Information M´ edicale (LaTIM), Brest, F-29200 France 2 MRC Clinical Sciences Centre, Imperial College, Faculty of Medicine, Hammersmith Hospital, London, UK 3 ETSI Telecomunicacion Universidad Politecnica de Madrid, Ciudad Universitaria s/n 28040, Madrid, Spain 4 School of Chemical Engineering & Analytical Science, The University of Manchester, Manchester, UK Received 14 March 2007, in final form 2 July 2007 Published 9 August 2007 Online at stacks.iop.org/PMB/52/5187 Abstract Respiratory motion in emission tomography leads to reduced image quality. Developed correction methodology has been concentrating on the use of respiratory synchronized acquisitions leading to gated frames. Such frames, however, are of low signal-to-noise ratio as a result of containing reduced statistics. In this work, we describe the implementation of an elastic transformation within a list-mode-based reconstruction for the correction of respiratory motion over the thorax, allowing the use of all data available throughout a respiratory motion average acquisition. The developed algorithm was evaluated using datasets of the NCAT phantom generated at different points throughout the respiratory cycle. List-mode-data-based PET-simulated frames were subsequently produced by combining the NCAT datasets with Monte Carlo simulation. A non-rigid registration algorithm based on B-spline basis functions was employed to derive transformation parameters accounting for the respiratory motion using the NCAT dynamic CT images. The displacement matrices derived were subsequently applied during the image reconstruction of the original emission list mode data. Two different implementations for the incorporation of the elastic transformations within the one-pass list mode EM (OPL-EM) algorithm were developed and evaluated. The corrected images were compared with those produced using an affine transformation of list mode data prior to reconstruction, as well as with uncorrected respiratory motion average images. Results demonstrate that although both correction techniques considered lead to significant improvements in accounting for respiratory motion artefacts in the lung fields, the elastic-transformation-based correction 0031-9155/07/175187+18$30.00 © 2007 IOP Publishing Ltd Printed in the UK 5187