PET Scans and CT Scans Are Fundamentally Different Imaging Technologies
Yes, PET scans and CT scans (CAT scans) are completely different imaging modalities that provide distinct types of information—PET provides functional/metabolic data while CT provides anatomical/structural data. 1
Core Differences Between the Technologies
CT (Computed Axial Tomography) Scanning
- CT provides excellent morphologic information by using X-rays to create three-dimensional images of the body that reflect variations in tissue density 1
- CT excels at showing anatomical structures with high spatial resolution 2
- CT has significant limitations in differentiating between benign and malignant lesions in organs or lymph nodes based on anatomy alone 1
PET (Positron Emission Tomography) Scanning
- PET provides metabolic/functional information rather than anatomical detail 1
- PET uses radioactive tracers (most commonly F-18 fluorodeoxyglucose/FDG) that accumulate in areas of high glucose metabolism 3
- PET moves beyond anatomy and characterizes tissue based on metabolic function 2
- The primary limitation of PET is that it provides little information on exact anatomic localization of lesions 1
Why PET/CT Combined Scanners Were Developed
Modern clinical practice now predominantly uses combined PET/CT scanners that merge both technologies in a single device 1:
- PET/CT scanners have both a PET and CT scanner in the same gantry, allowing precise co-registration of molecular (PET) and anatomic (CT) imaging 1
- Almost all current clinical PET imaging is performed using combined PET/CT devices 1
- The combined approach is superior to PET alone, CT alone, or visual correlation of both techniques performed separately 1
Important Clinical Caveat
When ordering a "PET/CT," understand that the CT component can vary significantly 1:
- Many centers perform low-dose CT as part of PET/CT (primarily for attenuation correction and anatomic localization, without diagnostic quality) 1
- Diagnostic CT requires higher radiation doses, breath-holding, and often intravenous contrast 1
- Referring physicians must understand whether they are getting diagnostic-quality CT or just low-dose CT with their PET scan 1
The complementary nature of these technologies—CT showing "form" and PET showing "function"—is why they are now routinely combined in clinical oncology practice 4.