X-rays or CT scans: when they are needed and which emit more radiation

At a diagnostic level, x-rays and CT scans are now essential for the evaluation of many pathologies and injuries. On the other hand, these are tools characterized by the use of ionizing radiations, which may cause concern for patients. For this reason, the Dr. Luca BalzariniDirector of the Diagnostic Imaging Department of the IRCCS Humanitas Clinical Institute, explained how each choice is thoroughly considered and justified and how each radiologist decides on the most appropriate intervention based on the pathology.

Doctor, how do you decide whether to have x-rays or a CT scan?
“The choice is made based on the pathology. Let’s take an example: if there is a suspected fracture of a bone in a sports injury, the first thing to do is a traditional radiological study. In a polytrauma from a road accidentwhere there may also be a risk of involvement of internal viscera or lungs, the transition to CT scanning is essentialbecause it has as its fundamental characteristic compared to radiology ‘latitude of contrasts’that is, the possibility of representing organs that have completely different densities through images.”
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So is the CT scan more appropriate when it is necessary to check the condition of the organs?
​“With the CT scan we see and judge the presence of pathologies of the lungs, vessels, liver parenchyma, together with the bone, something that we cannot do with a traditional radiological study. The other great advantage of the CT scan consists in the possibility of using the contrast medium to verify the vascularization, the liver, the spleen, the kidneys, and understand how the lesions of these organs are vascularized”.

What are the risks associated with the use of radiation?
​“The risks associated with doses are the same for both radiology and CT, clearly with different dosages. Let’s say that the ratio goes from 1-6 to 1-8 between rays and CT scan, so the latter gives radiation doses 6 to 8 times higher compared to traditional radiology. The risks linked to radiation are of two different levels: one we do not consider because it is linked to very high quantities, as in nuclear disasterswe are interested in the diagnostic risk which is probabilistic and does not have a real threshold. A bit like the smoker’s risk: theoretically even a single cigarette can cause a genetic transformation that leads to cancer, but it is clear that if you smoke a lot the risk is higher.”

So it’s up to the radiologist to understand how to act?
​“There is no minimum threshold, and this is the reason why every time it is decided to use ionizing radiation the radiologist must take into account the ‘justification’: in summary, every radiological examination must be justified. Let’s take an example: if we take the car to go to Bologna to Milan, we are not absolutely certain of getting there, the car could turn off, or there could be an accident, but we still use the car because we recognize that the risk is much lower than our need. It’s the same thing with radiation: I decide to use them because I have to solve a diagnostic problem, for example evaluating the condition of a lung. The radiologist must not be afraid of doing too many tests: think for example of cancer patients, or the Covid period, where it was necessary to do many CT scans of the lungs in a short space of time. In that case we assume a necessary risk due to the pathology. The important thing is to avoid doing unnecessary tests and always choose the most suitable and least risky instrument. For example, if I have to evaluate a liver angioma I can do it with both a CT scan and an MRI, and given the choice I will opt for the MRI, because it doesn’t use radiation.”