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

Microwave Ovens

All sorts of rumors abound about the dangers of microwave ovens leaking and microwaved food being harmful. I think it must be that some people are disturbed because they don’t know what’s going on in the oven and how it works. I hope then that my attempt at explanation is understandable and allays any concerns.

First of all you must know that microwaves are part of the electromagnetic radiation [EMR] spectrum just like radio waves and visible light and x-rays - they are rays of energy that pulse positive, negative, positive, negative, etc. through space and travel at the speed of light.

If the frequency at which the EMR changes from positive to negative is in the visible light region it affects our eyes so we can ‘see’ it as light. When the EMR comes from the sun, the part of it in the microwave region we feel as heat on our skin and think nothing of it. The remote control to turn a TV on and off is in the radio frequency region. X rays are pulses that change positive negative with such high frequency that mostly they pass through the body but the waves are partly absorbed by flesh and bones so give us an ‘x-image' of them.

To understand then how microwaves heat food, you have to know four things:

- 1. Positive is attracted to negative and repulsed by positive – something like the poles of a magnet. - 2. Lots of molecules have charges on them and we’re interested especially in charged water molecules here. - 3. Microwave pulses are slow enough to push and pull charged molecules, like water, around by attractive and repulsive forces as the waves, go past them, just like stick in the water bobs up and down as a wave goes by. - 4. We feel faster moving molecules as heat - the faster they go, the hotter they feel.

So essentially, all microwaves are doing is making charged molecules move faster. Since most plastics and pottery and glass have no charged molecules, they don’t react and stay cool in a microwave oven. Food, on the other hand, mostly has charged water molecules in it and heats up. Actually, microwaving has benefits because, by not heating food too long or too hot, many of the nutrients are preserved!

As far as microwaves leaking out of the oven, unless there is poor seal on the door - as an old, much used oven might have - no microwaves can escape. It’s like a box with a light in it in a dark room, if there are no cracks in the box, no light can escape.

So rest easy – microwave ovens have been around commercially since 1967 and when you look up the hazards, examples have to do with whole eggs in their shells and potatoes with skins intact which tend to explode and splatter because off the pressure of steam formed inside. You can’t heat water to more than 100 degrees C because it then just uses extra heat to form steam - but fats can be heated easily to very high temperatures and splatter so take care in heating them. Otherwise, rest easy – nothing unusual is going on in your microwave oven so just enjoy its wonderful convenience! Rie