It depends on many factors. One of the most important is where you are located when the CT scan is done. Another factor is the priority which which your doctor ordered the CT scan- stat or routine. Another important factor is how backed up the radiologist reading list is. There are facility specific factors as well.
Location of patient
Where you are located when the CT scan is done is one of the most important factors that will determine when your CT report is available. By this I mean, the emergency room, hospital wards, outpatient clinic or coming from home for a CT appointment (outpatient).
When you get a CT scan from the emergency room, it is treated like an emergency read. The scan will usually be read within an hour and often even faster. The CT is read quickly because it helps the emergency room doctor with your treatment. The emergency doctor will use the CT read along with other information to decide how to care for you.
In the hospital
A CT scan done if you are in the hospital is also given priority. Often these CT scans will be read within hours if not faster. These are often the sickest patients and will be given priority after the emergency room patients.
A CT scan done from the outpatient clinic can be ordered as routine or stat. The stat CT will be read within an hour or so, while routine cases will take longer. This depends on what priority your doctor has placed on the order.
Usually stat orders are done when your doctor feels that an urgent or life threatening condition may be present. He wants the results within an hour instead of being in the cue with routine patients.
Routine orders for CT scans will often depend on how backed up the radiologists work list is. Often the case will be read before the end of the day if done during normal business hours. Sometimes faster if the radiologists are caught up or have little backup. Those done in the late evening may be read the next day.
I have seen scenarios where order priority changes based on the patient or doctors request. At times, patients who are outpatients end up in the emergency room. In these cases, the outpatient routine CT may be requested to be read by the emergency room doctor stat.
There are therefore many factors which determine how fast a CT report is read. The priority of the exam order, the location of the patient when the CT is ordered and how backed up the radiology work list is are some of the most important factors. Some orders are changed from routine to stat. Patients also change their locations at times.