I have never heard of a person being scanned wearing a protective apron. The protective aprons for x-rays are for the personnel handling the machine and taking the scans, on a daily basis.
For the person being x-rayed of course no lead aprons!!otherwise the purpose would be defeated, as you state. Th dose he/she gets is very small, for the one off scan.
Edit after comment:
as pointed out in a link in the comments, radiation protection can also be used for patients
A lead (or lead equivalent) apron is a protective garment which is designed to shield the body from harmful radiation, usually in the context of medical imaging. Both patients and medical personnel utilize lead aprons, which are customized for a wide range of usages.
This part of the question then has to be answered
X-rays are projected to the rear of that person, and the rays are meant to pass through the person's body and hit the screen which is in front of the person.
Obviously the protection for the patient apron must be designed to protect areas of the body that need not be scanned . The ones under study can not be shielded from radiation, because of the obvious objection
So how do the x-rays find their way to hit the screen
So the shielded areas must be areas not of interest for the medical observation under study.