computer methods and programs in biomedicine 87 ( 2 0 0 7 ) 112–122 journal homepage: www.intl.elsevierhealth.com/journals/cmpb Evaluation of amplitude-based sorting algorithm to reduce lung tumor blurring in PET images using 4D NCAT phantom Jiali Wang a,* , James Byrne a , Juan Franquiz b , Anthony McGoron a a Department of Biomedical Engineering, Florida International University, 10555 West Flagler Street EC 2610, Miami, FL 33174, USA b Radiological Physics of South Florida, Inc., Miami, FL, USA article info Article history: Received 1 January 2007 Received in revised form 4 May 2007 Accepted 4 May 2007 Keywords: Respiratory gating PET CT Cancer NCAT phantom abstract Purpose: develop and validate a PET sorting algorithm based on the respiratory amplitude to correct for abnormal respiratory cycles. Method and materials: using the 4D NCAT phantom model, 3D PET images were simulated in lung and other structures at different times within a respiratory cycle and noise was added. To validate the amplitude binning algorithm, NCAT phantom was used to simulate one case of five different respiratory periods and another case of five respiratory periods alone with five respiratory amplitudes. Comparison was performed for gated and un-gated images and for the new amplitude binning algorithm with the time binning algorithm by calculating the mean number of counts in the ROI (region of interest). Results: an average of 8.87 ± 5.10% improvement was reported for total 16 tumors with different tumor sizes and different T/B (tumor to background) ratios using the new sorting algorithm. As both the T/B ratio and tumor size decreases, image degradation due to respiration increases. The greater benefit for smaller diameter tumor and lower T/B ratio indicates a potential improvement in detecting more problematic tumors. © 2007 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Lung cancer is one of the most common types of cancers in the United States, with more than 175,000 deaths per year [1]. The early and most probable curable stage of the disease in all histological types is the solitary pulmonary nodule (SPN) [2,3]. Five-year survival for post operation of stage I lung cancer and nodules smaller than 3 cm has been reported to be over 80% [4]. Since the early treatment of a small SPN has a high probability of curability, accurate definition of tumor volume and posi- tion is especially important [5]. Computed tomography (CT) is the most common imaging technique for providing anatom- ical and morphological information of tumors in the body. However, a vast majority of small SPNs appear on CT as inde- terminate tumors [6,7]. Molecular imaging with 18 FDG-PET can provide significantly higher sensitivity (87%) and speci- ∗ Corresponding author. Tel.: +1 305 348 6950. E-mail address: Jiali.Wang@fiu.edu (J. Wang). ficity (91%) than CT (68% and 61%, respectively) in detection and characterization of malignant lung nodules [8–10]. It has become a popular imaging modality for lung cancer diagnosis, staging, and for differentiating tumor recurrence from scar- ring and other benign structures. The advantage of PET has also lead to the proposed use of molecular imaging fused with CT for defining a more accurate delineation of tumor volume. New hybrid PET/CT scanners provide an accurate anatomical framework for molecular imaging and a noise free CT map for more accurate attenuation correction and conse- quently, quantitation of 18 FDG uptake [11]. Even with these advances, only about 15% of SPNs are being detected at an early stage. One major inconvenience of 18 FDG-PET imaging is the relatively long scan time (from 5 to 7 min) compared to the shorter CT collection time (less than 1s), produces PET- CT mis-registration as consequence of the respiratory motion. 0169-2607/$ – see front matter © 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.cmpb.2007.05.004