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Radiology and medical imaging when carried out correctly, can aid your doctor
in diagnosing and treating your problem. As our imaging technology can utilize
the use of x-rays, dye injections and other imaging aids, many patients are
concerned about the potential side effects. The articles below help cover some
of the safety aspects of medical imaging and may help in allaying any concerns
that you may have about a particular procedure. Please do not hesitate to
contact us if you have any questions.
If you feel that a particular topic should be covered here in this section,
then please let us know and we will endeavour to have it added to our safety
guide as soon as possible.
Are X-rays dangerous?
We are all continuously exposed to many kinds of radiation from our
environment. This includes ultra violet light - which causes skin cancer, and
x-rays and gamma rays. These come from natural radioactivity in the rock and
soil around us, as well as the sun.
Medical X-rays are only one of many sources of radiation, and account for about
10% of the total radiation to which we are all exposed over a lifetime.
In most places in NZ this background radiation dose is about 2mSv per year. A
chest x-ray uses less than a tenth of that. People living in stone or concrete
houses receive more than those in wooden houses, and people living in some
geothermal areas can be exposed to radioactive gas from the ground. Much of the
harmful radiation from the sun is filtered by the atmosphere, but flying high
in a commercial airplane exposes you to a greater dose. Because of this there
are restrictions on the number of flights pregnant flight crew can make.
High doses of radiation such as from atomic bomb blasts can damage our cells
and cause cancer. If the damage affects the genetic material in the ovaries and
testicles, the abnormalities can be passed on to later children. That is why we
use lead shields, whenever possible, to protect the ovaries and testicles when
x-rays are taken. It is not certain if damage can be caused by the very low
doses used in radiology, but all doctors and radiologists are well aware of the
potential risk and x-rays are only performed for significant medical reasons
Contrast Medium
Some types of x-ray examination require us to inject a clear fluid called
contrast medium or dye to enhance the outline of organs and blood vessels. It
can be injected intravenously through an arm vein for CT scans and kidney
x-rays, or injected into the arteries of the heart, brain and legs to check for
blockages (angiography).
Over the years there have been major advances in the safety of contrast medium,
but it still carries a very small risk of an allergic reaction. The latest
contrast is nearly four times the cost of the older material but at Mercy, we
only use the new, safest contrast medium.
A reaction is quite uncommon, and usually consists of an itchy rash. On rare
occasions a severe allergic reaction can occur, and this may be bad enough to
cause a cardiac arrest. The risk of such a severe reaction is very low - about
1 in 100,000 patients - which is similar to many other risks we willingly take
in our day to day life. Patients with asthma are at slightly higher risk.
Unfortunately there is no way of testing people in advance to detect those who
are sensitive to contrast, and we always have emergency equipment on hand when
injecting it.
Magnetic Resonance Imaging (MRI)
This uses very strong magnetic fields, combined with radio waves to create
pictures of the internal organs, brain, spine and joints.
The only risk with this technique occurs when someone has steel fragments - eg
shrapnel, or implants - like surgical clips, in their body. The strong magnetic
field can cause these to move, and possibly tear the nearby flesh. Most modern
surgical clips and joint replacements and all artificial heart valves do not
have steel in them so are quite safe.
The magnet is so strong that a small nail will be pulled into the magnet with
the force of a bullet, so you need to empty everything out of your pockets
before going near the magnet.
Remember to leave your credit cards and watch in the changing room as well,
because the strong magnetic fields will scramble the information in the
magnetic stripe on the credit card, and permanently damage the internal watch
mechanism.
Before you have an MRI scan our radiographers will discuss these issues with
you.
Radiation dose from x-rays
The x-ray exposure from common diagnostic x-rays is small - and similar to the
exposure we all get from the natural background radiation, which is about 2mSv
per year. The exposures from most x-ray procedures range from 0.2 - 10mSv.
Eg Chest x-ray - 0.2, mammography 0.3, back x-ray 2.5, CT scan of head 2.3, CT
scan of abdomen 12mSv.
One long haul airplane trip in the upper atmosphere exposes you to about the
same dose as a chest x-ray.
In most x-ray tests the x-rays are made outside the body by the x-ray machine. For
some procedures, called scintigraphy or nuclear scans, a very small amount of
special radioactive fluid which makes its own xays is injected into the
patient’s bloodstream. This sounds a bit scary, but the amount of radiation
used is very similar to the dose from other common types of x-ray, and this
special type of radioactivity wears off quickly. The most common of these scans
is a bone scan, which is a very sensitive test to detect bone damage before it
can be seen on ordinary x-rays.
Remember, there is little risk from medical x-rays, and much to be gained from
them - like diagnosing broken bones, pneumonia, and detecting early cancers. A
normal x-ray can also be very important in excluding disease. The medical
community still treats x-rays with a great deal of respect and we only take
x-rays when they will really contribute to improving patient care.
See also Risks in perspective, and Are x-rays dangerous?
Risks in perspective
Most things we do in our day to day lives carry risks, and medical procedures,
from blood tests and chest x-rays to brain surgery and cancer treatment are no
exception.
The following list of activities have one thing in common - they all increase
the risk of death by about one chance in a million:
Smoking 1 and half cigarettes ( cancer, heart disease),
Drinking 1/2 a litre of wine (liver disease),
Long distance air travel (accident, cancer from cosmic radiation),
One chest x-ray (cancer from medical radiation),
Living for 2 months (cancer from natural background radiation),
Eating 40 tablespoons of peanut butter (liver cancer).
Medical tests often carry a small risk, but remember that not having the test
also carries risks - such as delayed or incorrect diagnosis. In radiology the
main thing people worry about is the risk of getting a cancer from the x-rays.
This risk is very small. Driving your car is probably more dangerous than
having an x-ray. Our other imaging tests which use ultrasound are completely
risk free.
Ultrasound
This is an imaging test which uses the echoes of high frequency sound waves to
create pictures of the body. The sound waves used are not very strong and
ultrasound is considered to be very safe. After much research into its action
on the human body, no bad effects have been found. That is why it is widely
used in obstetrics to monitor the growth and well being of the unborn baby.
Contrary to what you may read in some magazines, the baby can neither feel nor
hear the sound waves, and does not react to them.
X-ray workers.
Those of us who work with x-rays all day could receive quite high doses if we
were not careful. This is why the radiographer who takes the x-rays will shelter
behind a lead screen when a film is being taken. For some procedures, such as
when x-rays are used during an operation, we cannot leave the room, so we have
to wear a lead coat to protect us. And they are very heavy I can assure you!
We will ask a parent to wear a lead apron as well if they need to stay with a
child as an x-ray is taken.
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