CT scan, MRI and PET scan are three common diagnostic tests. But how do they differ and when do you resort to one or the other? Professor Arturo Chiti, Head of Nuclear Medicine at Humanitas, spoke about this in a video interview with Corriere della Sera.

“We have several exams because none of them can be considered the best of them all: each exam has the ability to see our body differently.

CT (Computed Axial Tomography) is perhaps the best-known examination and through the use of X-rays it is possible to observe differences in terms of organ density and shape. Magnetic resonance imaging (MRI) provides an idea of how water molecules are distributed in our bodies. PET (positron-emitting tomography) uses specific substances, called radiopharmaceuticals, which allow observing some particular structures or organs and it is able to recognize some metabolic processes.

CT therefore gives us an idea of form, Resonance gives us not only an idea of form but also adds a functional component, PET instead gives us an idea of function: a tissue may appear more functional because it consumes more energy (or more sugar) and therefore could be tumor, or has certain metabolic characteristics that can be defined using radiopharmaceuticals,” explained the specialist.


PET and the various radiopharmaceuticals

“PET does not exist as a single method because, depending on the radiopharmaceutical used, different things can be observed. For example, the brain is the organ in our body that consumes more sugar and if there are areas that work less we can see a decrease in sugar consumption. How do we see it? We inject a substance that is taken from the cells as if it was sugar and that has attacked a bulb that emits positrons. However, we could also see what the flow of blood to the brain is like, for example by injecting radioactive water, or we could observe the deposits of amyloid, which could be increased in patients with Alzheimer’s disease.

If with CT (also with contrast medium) we only have an image of density and with Resonance we better see the soft tissues because they are rich in water, with PET we have more possibilities depending on the radiopharmaceutical used: the consumption of sugar, amyloid deposits, bone remodeling or the expression of particular receptors of certain tumors. PET is therefore an examination that is defined as functional because it allows us to see some peculiar characteristics of the tissues”, continued Professor Chiti.


Are there any tests that merge the different methods?

“We are currently talking about hybrid or multimodal imaging: PET machines perform PET and CT because PET is a functional examination and therefore does not give an idea of the exact anatomy of the lesion or alteration that we can locate, while CT is a method that gives us a peculiar and precise assessment of the anatomy and therefore PET-CT allows us to have the best of both methods. Machines are also available that run PET and MRI at the same time.

In fact, a single image method is almost never sufficient to obtain all the information you need”, concluded Professor Chiti.


Watch the full interview with Professor Chiti, click here.