Advances in Environmental Biology, 8(11) Special 2014, Pages: 1031-1042 AENSI Journals Advances in Environmental Biology ISSN-1995-0756 EISSN-1998-1066 Journal home page: http://www.aensiweb.com/AEB/ Corresponding Author: Elham Soleimani, Islamic Azad University, Science and Research Branch, Tehran, Iran. E-mail: elh.soleimani@gmail.com Different Energy Mapping Methods in CT-Based Attenuation Correction in PET/CT Systems Elham Soleimani, Ali Soleymani, Shahla Ahmadi, Majid Pouladian Islamic Azad University, Science and Research Branch, Tehran, Iran. ARTICLE INFO ABSTRACT Article history: Received 15 June 2014 Received in revised form 8 July 2014 Accepted 4 September 2014 Available online 20 September 2014 Keywords: Energy Mapping Methods, CT-Based Attenuation, CT-Based Attenuation This paper presents the result of assessing different attenuation correction methods for PET data according to CT data (CTAC). These methods are intended for use with a combined PET/CT scanner. We discuss five possible methods of energy mapping from the CT energies to the required 511keV. CT images are obtained using a computerized whole body phantom, 4DXCAT, which is simulation of physically and anatomically of human body. Materials and methods: The aim of this study is to compare different energy-mapping techniques: scaling, segmentation, hybrid, bilinear calibration curve and dual energy approach through attenuation map generated from CT data through XCAT phantom. The CT images acquired from XCAT phantom is applied to generate μ-maps in 511keV.Then these generated μ-maps are compared to the image acquired from XCAT phantom in 511keV as the gold standard image. For comparing methods we use three ways: Assessing different ROIs, correlation coefficients and difference images for comparing pixel by pixel. Results and Discussion: Nearly all energy- mapping methods shown similar results in soft tissues. A noticeable relative difference is seen in lung tissues in Segmentation method which refers to the variability in densities. Also a bias in bone in the same method, which is due to the extended borders of the segments. In Scaling results for different tissues are acceptable beside bone as it has a high photoelectric ratio. Hybrid and Bilinear are somehow good. Dual Energy reports the best results. © 2014 AENSI Publisher All rights reserved. To Cite This Article: Elham Soleimani, Ali Soleymani, Shahla Ahmadi, Majid Pouladian, Different Energy Mapping Methods in CT-Based Attenuation Correction in PET/CT Systems. Adv. Environ. Biol., 8(11), 1031-1042 2014 INTRODUCTION Today, diagnostic imaging is consisting of various branches. The information of imaging is divided into anatomical and function groups. In some systems as CT, MRI imaging based on anatomical techniques, the tumor is detected when the tissue is physiologically changed but in some systems including PET,SPECT imaging based on physiological techniques, metabolic changes are detected in the early stage. It is obvious that there are many instances in which it would be desirable to integrate the information obtained from two modalities of the same patient. The combination of PET-CT was introduced in the early 1990s by Townsend. The first prototype of PET-CT scanner was made in 1998 [1-9]. In PET/CT systems, based on the data, CT is applied for attenuation correction of PET data. In CTAC, at first the patient undergoes CT scan and then at the same position, PET scan is taken of the patient [10, 11]. In converting CT attenuation to be used as data in PET image, there are two problems. The first problem is the high difference between the energy of CT, PET photons. As attenuation coefficient depends on energy and the main issue in attenuation correction by CT is conversion of the coefficients of CT energy, the energy at120 kVp to PET energy, energy at 511keV and the second problem is the difference between single energy spectrum in PET and extensive energy spectrum in CT. In PET imaging, annihilation photons at 511kev are applied while CT diffuses the photons with extensive energy spectrum 40 to140 kev. This photoelectric overcome in CT energies range and Compton overcome at 511keve create error in conversion of the images of CT energies to PET energy. There are various methods for energy mapping to convert attenuation coefficients in CT energy to PET energy. These methods are including scaling, segmentation, hybrid (scaling+ segmentation) [12], bilinear [9, 13] and dual energy approach [14, 15].