What is the difference between a cat scan and pet scan?

Anatomy / metabolism. CAT scan utilizes xrays for determination of anatomical structures in multiple planes coronal, sagittal, and transaxial. PET scan uses radioactivity with tracer FDG 18 a glucose metabolite to show metabolic areas . Usually malignant lesions are most active. Small metastatic lesions can be detected. Sometimes compared with anatomy with PT CT.
Anatomy vs Physiolog. Ct scans look at the structure of the body, the anatomy, and the way diseases change or distort it. Pet looks at the physiology, or how the body uses, or metabolizes something. For pet, the most common metabolism pathway looked at is how glucose is used. A low dose ct is often acquired at the same time as the pet (as in pet/ct scan), to correlate the pet findings with the ct anatomy.
Physiology. A ct scan is a static picture of anatomy. A pet/ct scan also shows you how metabolically active the " anatomy" is ...