Use of segmented CT transmission map to avoid metal artifacts in PET images by a PET-CT device

Background: Attenuation correction is generally used to PET images to achieve count rate values independent from tissue densities. The goal of this study was to provide a qualitative comparison of attenuation corrected PET images produced by a PET-CT device (CT, 120 kV, 40 mAs, FOV 600 mm) with and without segmentation of transmission data (ACseg(+ )and ACseg(-)respectively). Methods: The reconstructed images were compared to attenuation corrected images obtained with a high-energy transmission source (Cs-137 – 662 keV). Thirty oncologic patients were studied using CT and (137)Cs for attenuation correction. All image data were acquired using the Gemini PET-CT scanner (Philips Medical Systems). It is an open PET-CT system that consists of the MX8000 multislice CT and the Allegro PET scanner arranged in a separable configuration. Images with ACseg(+ )and ACseg(- )were analyzed simultaneously in coronal, sagittal and transaxial planes. Two nuclear medicine physicians reviewed the image sets. Results: The image quality in the area of metal implants was better with ACseg(+ )than ACseg(-), without metal induced artifacts generally observed in CT corrected images. Further the images with ACseg(+ )were qualitatively comparable to those obtained with (137)Cs attenuation correction. Conclusions: In case of metal implants, PET studies corrected by CT should preferably use the ACseg(+ )method to avoid the image artifacts.