Your doctor may have ordered your exam stat instead of routine. This means that the test will be done as soon as possible and also read quicker then the routine exams by the radiologists. Usually stat exams are prioritized on the radiology work list as those that need to be read the fastest.
Stat exams in many cases are for patients who are the sickest or that the doctor is more concerned about. Your doctor wants a result fast because he is concerned that you may have a serious condition that will need treatment right away.
In our system, all exams done from the emergency room are stat. We also have many outpatient exams ordered as stat, mainly because your doctor wants the test to be done as soon as possible. The radiologist will often call your doctor with results, especially if there is a significant finding which needs to be addressed immediately.
Sometimes stat exams are done simply because your doctor wants to get you in. I see some stat exams done for conditions which are not urgent, but simply because they want to get you in and get results. This can delay exams on truly sick patients who need the test done sooner. There are only so many scanners to do tests on. If your exam is done after business hours, there may be one radiologist reading who may get backed up because of unnecessary stat exams.
I have seen stat exams ordered for many body parts and nearly all modalities such as ultrasound, CT or MR. While a head CT with a brain bleed is certainly an emergency, an exam done to look at the prostate is rarely truly an emergency. A stat exam of the chest to look for a clot is an emergency, while a chest CT looking for metastasis or spread of cancer is never one.
Therefore, a stat exam should be reserved for patients who are truly sick and need results to guide their management. Doing non emergent exams stat can delay the care of patients who truly have emergent conditions. Non emergent exams done stat can back up the radiologist reading the exams preventing timely results for patients who have truly emergent conditions.