It depends. MRI and to an even larger extent CT scans are "targeted" to an area. People are very very rarely scanned "totally".

E.g. you want to look at the cervical spine and therefore only examine this area. While you will also see neighbouring regions these are not necessarily full resolution (only if they can have an impact). So if the imaging run is being done for an area that is not affected much by the fat tissue it won't produce more data necessarily (a cardio MRI is a good example). If you do a abdominal or pelvis MRI/CT is normally does include all tissue and therefore will produce more data.

(Take this with a grain of salt though, while I worked inhospital for a while I am primarily a paramedic and more into repairing vital signs than radiology. While we have mobile CTs nowadays they are brain only and not my area of expertise)

There is an exception for the real complicated cases like the one I mentioned, though. As we didn't want to do the whole transport effort 4 weeks later again because another speciality found another issue the patient was indeed scanned almost completely" (with breaks in-between as that gets uncomfortable fast).

(Sadly enough the whole thing was done 6 weeks later again,indeed, as the patient had suffered from an acute stroke which later killed them. Sad story,really. Never had a chance in life)