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Sunday, October 7, 2012

CT Scans

There are many different imaging techniques that are used by doctors these days to be able to determine what is going on inside our bodies. Available are Ultrasounds, Angiograms, CT (or CAT) scans, MRI’s and PET scans, each with own diagnostic characteristics.  Some are totally non invasive but others involve X-rays and contrasting agents that are injected into the patient to make the images obtained more revealing and useful.

It’s an important subject and one that everyone should be familiar with as more and more use is being made of these very valuable techniques that help in the diagnosis of cancer, blockages in our arteries, sinus problems or any number of ailments. This week a young child in my immediate family had a CT scan of his head and it gave the doctor and his family a very clear picture of a congenital problem and how it could be corrected with surgery. My concern is that in taking the CT scan, multiple X-rays were taken so they could be combined in a computer to give 2-dimensional slices through the head – see picture on left. 

X-rays are just like any other kind of light (called electromagnetic radiation) but our eyes are only sensitive to the visible part of the spectrum and, as shown, x-rays are in the invisible range with short wavelengths and very high energy. Ordinary light doesn’t have enough energy to penetrate flesh but x-rays do.  Notice in the x-ray of the hand, however, that the x-rays are stopped by bone and partly absorbed as they pass through the flesh.

We know that when X-rays are absorbed in the body, their energy is released and it is transferred to an electron that can rip through a cell, tearing electrons from all sorts of atoms it meets, like a billiard ball spreading its energy to other balls on the table. Usually the human body is good at repairing itself but on rare occasions the damage may create the starting point where cancer can develop.  

When digital technology became available it eliminated some of the risk associated with x-rays because a much lower radiation dose could be used and the digital images had sufficient resolution so that they could be manipulated on a computer to obtain detailed information from them.

Thus it is now really quite safe to have the infrequent low dose x-rays taken at the dentists or in hospital? However, studies show that children are more sensitive to radiation, and they should have a CT scan only if it is essential for making a diagnosis and they should not have repeated CTscan unless absolutely necessary.

I plan to write another post next week to look into other types of medical imaging and what risks are associated with them.   Rie

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