IOP PUBLISHING PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 53 (2008) 3099–3112 doi:10.1088/0031-9155/53/12/002 Quantitative SPECT reconstruction using CT-derived corrections Kathy Willowson 1,2 , Dale L Bailey 1,2,3 and Clive Baldock 1 1 Institute of Medical Physics, School of Physics, University of Sydney, Camperdown, NSW 2006, Australia 2 Department of Nuclear Medicine, Royal North Shore Hospital, St Leonards, NSW 2065, Australia 3 Faculty of Medicine and Discipline of Medical Radiation Sciences, Faculties of Health, University of Sydney, Lidcombe, NSW 2141, Australia E-mail: K.Willowson@physics.usyd.edu.au Received 24 January 2008, in final form 25 March 2008 Published 21 May 2008 Online at stacks.iop.org/PMB/53/3099 Abstract A method for achieving quantitative single-photon emission computed tomography (SPECT) based upon corrections derived from x-ray computed tomography (CT) data is presented. A CT-derived attenuation map is used to perform transmission-dependent scatter correction (TDSC) in conjunction with non-uniform attenuation correction. The original CT data are also utilized to correct for partial volume effects in small volumes of interest. The accuracy of the quantitative technique has been evaluated with phantom experiments and clinical lung ventilation/perfusion SPECT/CT studies. A comparison of calculated values with the known total activities and concentrations in a mixed-material cylindrical phantom, and in liver and cardiac inserts within an anthropomorphic torso phantom, produced accurate results. The total activity in corrected ventilation-subtracted perfusion images was compared to the calibrated injected dose of [ 99m Tc]-MAA (macro-aggregated albumin). The average difference over 12 studies between the known and calculated activities was found to be −1%, with a range of ±7%. (Some figures in this article are in colour only in the electronic version) 1. Introduction In quantitative single-photon emission computed tomography (SPECT), the calculation of absolute radionuclide concentrations allows useful information to be obtained regarding in vivo function. Such data have not been readily available from SPECT studies, due primarily to the degrading effects of attenuated and scattered photons. In addition, quantitative values from structures that have a diameter less than approximately three times the total system 0031-9155/08/123099+14$30.00 © 2008 Institute of Physics and Engineering in Medicine Printed in the UK 3099