Tumor Detection with PET and CT: A Comparative Physical Review

Abstract : Positron emission tomography (PET) is an important molecular imaging modality in oncology because it provides functional and metabolic information that complements the anatomical information obtained from computed tomography (CT). However, the ability of PET to detect tumors is fundamentally determined by several physical characteristics of the imaging system, including spatial resolution, sensitivity, image contrast, noise, photon attenuation, scatter, random coincidences, and partial-volume effects. This review aims to examine the physical basis of PET for tumor detection and to compare its principal imaging characteristics with those of CT. A comparative narrative review was conducted using relevant literature on PET physics, detector instrumentation, image formation, image-quality determinants, tumor detectability, and the physical principles of CT. The reviewed evidence indicates that PET provides high sensitivity to radiotracer distribution and functional abnormalities, making it particularly valuable for detecting metabolically active tumors. However, its relatively limited spatial resolution and susceptibility to attenuation, scatter, noise, and partial-volume effects can restrict the detection and accurate characterization of small or low-contrast lesions. In contrast, CT provides superior anatomical detail and spatial resolution through X-ray attenuation measurements but offers substantially less direct functional information. The evidence therefore indicates that PET and CT possess complementary physical capabilities: PET is primarily advantageous for functional and metabolic tumor characterization, whereas CT is superior for anatomical localization and structural delineation. Understanding these physical differences is essential for interpreting the respective strengths and limitations of PET and CT in tumor detection and for optimizing their complementary use in hybrid PET/CT imaging.