Let's think about the processes behind the apparent slowness. The same logic applies to many areas of work - including woodworking!
The actual time needed to look at an x-ray and decide what it means can be very short - let's say one minute. Typing up a report is pretty quick too - in fact most radiology departments use voice recognition to speed this up further. Maybe another minute. Double that for the quality control checking. Add on transmission to the GP - which is generally electronic unless you've gone somewhere unusual for the exam. So maybe five minutes total actual work. You might expect the result to be with your GP within two hours. Reasonable? No.
The work of interpreting x-rays does not come in an even, predictable stream. It varies with the time of day, day of the week, time of year, weather conditions, and other unpredictable factors. Sometimes there will be a lot at once, then nothing for a while, then another peak. If every job had to be turned round in under two hours, the staffing would have to be at a level to meet the periods of highest demand. The staff would then have to wait around at non-peak times ready for some more work to come in.
Staffing to that level would be impractical and hugely expensive.
It makes far more sense to have enough people to cope with all the work - so no backlog builds up - averaged out over a fortnight or so.
(Also, for some lab tests, it really does take several days for a chemical reaction to complete, or a culture to grow to observable size. The diagnostic devices used on Star Trek are fictional!)