What is the difference between mris & pet scans?

Structure v Function: A pet scan tells us which cells are taking up glucose which is a measure of functioning. Cancer cells take up too much glucose and other illnesses like dementia have cells that do not take up enough glucose. An MRI scan is a structural test and shows the outlines of cells and how big they are. Mri's are often most useful for looking at soft tissue.

Anatomy: Mri is a picture of structure or anatomy, and does well demonstrating brain pathology with changes in normal anatomy. Pet scanning shows functional metabolic brain derangements, and can illustrate cancers, alzheimer's, various dementias, and abnormal brain handling of normal chemicals such as glucose. Pattens can be diagnostic.

Anatomy vs Physiolog: Mri and ct 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.