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Why does the doctor ask you for a CAT scan, and how does it work?

The CT test allows you to see the inside of the organs. Its excessive use carries risks, although it has been improved to make them minimal. Let’s see what it is and what it is used for.


Computerised Axial Tomography, better known as CAT, CT or scanner, is one of the tests that doctors use to see inside the body.

It is a system related to radiology (popularly called radiography) and uses ionising radiation (X-rays).


It is a machine that sends X-rays through the body and then hits a plate. In this way, an image of the inside of the body is made.

The difference with an X-ray is that in this, a single radiation hit is produced, while in the CT, a better vision is sought, and a whole sequence of images is given, which can be hundreds.

We could say that a CT scan combines many x-rays taken simultaneously from different angles to obtain a larger and more detailed image.

Are X-rays risky?

” CT scans have advanced to offer volume images that were unthinkable fifteen years ago “, explains Dr Alfonsa Friera, member of the Spanish Society of Radiology.

The new models are already called only Computerized Tomography because it does not rotate on a cut (axial) in two dimensions, but now it is a three-dimensional photo.


It is used to diagnose fractures, cancer screening, blood clots within the body’s organs, internal bleeding, or heart problems.

Compared to the information provided by a single X-ray, with the CT, the data collection is much more fantastic. The organ can be seen better and even detect problems (some types of cancer) that a single X-ray would not catch.

A three-dimensional impression of the analysed organ can be created.

With the images obtained, it is also possible to later create a three-dimensional impression of the organ or bone, for example, if it is going to have to be operated on. The surgeon will thus have an exact reproduction and can see how to proceed in advance.


As there are dozens of small X-rays, it can be thought that there is excessive patient irradiation.

However, today, through digital techniques, the dose received by the person undergoing this test is significantly adjusted.

The difference, however, is still essential and must be taken into account: a CT scan can involve up to 400 times more radiation than an X-ray.

It also depends on the part of the body. Different tissues and organs have different tolerance to X-rays.

For example, radiation to the head is five times less than radiation to the stomach.

Some parts of the body tolerate radiation better, such as the head.

However, the quantity is always significant. We can compare it, to understand it better, with the radiation that humans receive for the simple fact of living on Earth :

A cranial CT scan is equivalent to receiving all the radiation we would receive naturally for a year at one time.


“ The detrimental effect is not cumulative -clarifies Dr Friera-. However, radiation is indeed capable of altering cells and causing changes in them that may be the origin of a presumed disease. Thus, logically, the more radiation received throughout life, the options for this cellular alteration increase ”.

In any case, the risk of exposure “ is shallow”, reassures the doctor.

Special care must be taken when deciding to do a CT scan on children since they have many years ahead of them and may be forced to take other X-rays throughout their lives.

It is estimated that 30% of scanners are unnecessary.

” One of the current debates among the medical community is precise that CT scans are requested in excess, and it is estimated that 30% of the tests are not justified “, admits Dr Friera.


The debate is critical if you consider that there are other tests, especially in magnetic resonance imaging, which also serve to see the inside of the body and are harmless.

Both CT and MRI can be used interchangeably in some instances. “ As the images obtained with MRI improve, we will increasingly put CT aside,” says Dr Friera.

However, at the moment, the view provided by CT of the lungs, heart or digestive system is still much better.

Each specialist knows which device will offer the best vision, and the patient must trust that the test will be the most appropriate for their case.


There is also a time factor to consider.

The MRI can take almost an hour; in urgent cases, the CT scan will be done in just a few seconds.

Minimal patient preparation. The technician limits himself to check that he is not wearing metal objects (jewellery, glasses, fillings) that could alter the image.

Logically, a pregnant woman must also notify it if you take any type of medication or even herbal products.

The patient lies down on a stretcher attached to the machine that performs the image and is turned in the technician’s direction so that the scanner captures the entire contour of the organ.

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