X-rays have been widely
used for in medical diagnostic imaging for over
a hundred years. For the most part X-rays are
safe, effective and appropriate. However, every
time a human is exposed to an X-ray there is
some risk encountered.
Early in the development
of X-rays, it was learned that they could cause
cancers and birth defects. For this reason,
whenever X-rays are used, efforts are made to
reduce the risk due to X-ray exposure.
We accept the risk of
death from driving a car because we choose to
enjoy the benefits of driving. Similarly, we
choose to be subjected to medical X-rays because
of the health benefits gained from diagnostic
imaging and the relatively low risk of harm.
In addition, we routinely
do everything reasonable to reduce the risk
from necessary medical X-ray exposure. The risk
is usually reduced in two ways, firstly, through
the use of the most advanced equipment that
can make good quality images with tiniest amount
of X-ray irradiation and secondly, through the
use of shielding.
Reduced X-ray
Dose and Shielding: A good example
of these two principals is seen in the most
advanced dental practices. Firstly, the old
X-ray machine and film are replaced by advanced
electronic X-ray sensors exposed by digitally
controlled X-ray machines. Secondly, you are
provided with lead shields to protect you at
your two most X-ray sensitive areas, the thyroid
gland in the neck and the genital/gonadal region
in the pelvis.
The thyroid is shielded
to prevent thyroid cancer and the pelvis is
shielded to prevent the risk of reduced fertility
and birth defects in future children.
Higher Unshielded
Doses for Image Guided Injections:
The "one-shot" X-ray machines used
in a dental office or for a chest X-ray are
turned on a single time for a fraction of a
second. At the other extreme are the higher
exposures from the types of X-rays used for
image guided injections:
- "Fluoroscopy"
in which hundreds of X-rays are taken (ten
to twenty per second) for as much time as
the doctor needs to get the job done (ten
seconds to ten minutes or more).
- CT scanning in which
dozens of X-ray beams are directed through
you for as long as it takes to complete the
image (typically for about ten to a hundred
seconds or longer depending on the machine).
Unfortunately, despite
the much higher X-ray dose during image guided
injections, shielding can't be used. When an
injection is done in the cervical spine, a lead
thyroid shield would prevent the doctor from
seeing the bones of the neck. When an injection
is done in the lumbar spine or pelvis, there
can be no genital/gonadal shielding because,
once again, such shielding would prevent the
doctor from seeing the bones of the lumbar spine.
Iodine Contrast
Allergy: When image guided injections
are done, it is usually necessary to provide
some sort of injectable image contrast. For
X-rays, this requires an injected iodine compound.
Older iodine compounds have caused severe problems
with nerve adhesions or "arachnoiditis"
in the spinal canal, but newer "non-ionic"
iodine agents are essentially completely safe
from this point of view. Unfortunately, these
agents still carry the risk of death due to
allergic reaction. Whenever iodine contrast
agents are administered, a physician must be
present with immediate accesss to a "crash
cart" with an array of injectable medications
to reverse acute allergic reactions. An iodine
allergy is often discovered only once the contrast
has been administered for the first time (the
original exposure can come from shellfish).
For spinal and nerve MRI
guided injections, adequate contrast is provided
by the water in the injection. For some MRI
contrast studies, gadolinium agents need to
be injected. Gadolinium carries a much lower
risk of allergic reaction than iodine, and has
proven completely safe when administered appropriately.
However, no iodine or gadolinium are needed
in the production of bright, sharp, effective
injected water contrast as used for Open MR
guided injections at the Institute for Nerve
Medicine.
Avoidable Risks:
Currently, though, the greatest concern about
the risk of X-rays for image guided injections
is that the advent of MR guided injections has
made any risk from X-rays completely unnecessary.
This is particularly so since MR guidance provides
the doctor with greater accuracy, improved overall
patient safety, and greater comfort for the
patient.
As with X-ray risk in
general, the use of iodine may be reasonable
when the risk is necessary to achieve a definite
benefit. However, with the advent of Open MR
guided injections and water contrast, it is
difficult to justify accepting any risk at all
from iodine contrast.
