Services:
MR Angiography (MRA)
What is MR Angiography?
What are some common uses of the procedure?
How should I prepare for the procedure?
What does the equipment look like?
How does the procedure work?
How is the procedure performed?
What will I experience during the procedure?
Who interprets the results and how do I get them?
What are the benefits vs. risks?
What are the limitations of MR Angiography?
What is MR Angiography?
MR angiography (MRA) is an MRI study of the blood vessels. It
utilizes MR technology to detect, diagnose and aid the
treatment of heart disorders, stroke and blood vessel
diseases. MRA provides detailed images of blood vessels
without using any contrast material, although today a special
form of contrast usually is given to make the MR images even
clearer. The procedure is painless, and the magnetic field is
not known to cause tissue damage of any kind.
What are some common uses of the procedure?
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Many patients with arterial
disease now have it treated in the radiology department rather
than undergoing surgery in an operating room. MRA is a very
useful way of finding problems with blood vessels and
determining how to best to treat those problems.
-
The carotid arteries in the neck
that conduct blood to the brain are a common site of
atherosclerosis, which may severely narrow or block off an
artery, reducing blood flow to the brain and even causing a
stroke. If an ultrasound study shows that such disease is
present, many surgeons now will do the necessary operation
after confirmation by MRA, dispensing with the need for
catheter angiography.
-
MRA has found wide use in
checking patients for diseased intracranial (in the head)
arteries, so that only those with positive findings will have
to have a more invasive catheter study.
-
MRA also is used to detect
disease in the aorta and in blood vessels supplying the
kidneys, lungs and legs.
-
Patients with a family history of
arterial aneurysm, a ballooning out of a segment of the vessel
wall, can be screened by MRA to see if they have a similar
disorder that has not produced symptoms. If an aneurysm is
found, it may be eliminated surgically, possibly avoiding
serious or fatal bleeding.
How should I prepare for the procedure?
The magnetic field used for MRA will pull on any
iron-containing object in the body, such as a heart pacemaker,
intrauterine device, vascular access port, metal plate, or
pins, screws or staples. The technologist should know about
any such item and also whether you have ever had a bullet in
your body, whether you ever worked with metals, or if you have
had a joint replacement. An x-ray may be taken to detect metal
objects. The radiologist also should know if you have fillings
in your teeth, which could distort images of the facial region
or brain. Braces make it harder to properly adjust the MRI
unit. You will be asked to remove hairpins, jewelry,
eyeglasses, hearing aids, and any dental work that can be
taken out. Some wigs contain metal and must be removed. Red
dyes used in tattoos and permanent eyeliner may contain
metallic iron, but this is rarely a problem. You should report
any drug allergies to the technologist, and should mention if
there's any possibility that you might be pregnant.
You can eat normally before the exam (unless told
differently), but a young child should not eat or drink for
about four hours if they will receive a sedative. Medications
may be taken as usual. Some patients will feel uncomfortably
confined (claustrophobic) when enclosed in an MRI unit. If
necessary, you will be given a sedative to help put you at
ease, though probably less than one in every 20 patients will
need this.
What does the equipment look like?
The traditional MRI unit is a large tube surrounded by a
circular magnet, in which the patient lies without moving for
several seconds at a time. You will be placed on a wheeled bed
that is moved into the magnet. Our patient-friendly unit is
both shorter and wider than a conventional MRI unit.
How does the procedure work?
Exposing the patient to radio waves in a strong magnetic field
generates data that are used by a computer to create images of
tissue slices that may be viewed in any plane or from any
direction. The magnetic field lines up atomic particles called
protons in the tissues, which are then spun by a beam of radio
waves and produce signals that are picked up by a receiver in
the scanner. It is these signals that are processed by the
computer to produce images. The resulting images are very
sharp and detailed, and so are able to detect tiny changes
from the normal pattern that are caused by disease or injury.
Special settings are used to image various structures, such as
arteries in the case of MRA.
How is the procedure performed?
You will be placed on a sliding table and a radio antenna
device called a surface coil is positioned around the part of
your body being imaged. After positioning you inside the MRI
gantry, the technologist leaves the room and the individual
sequences are performed. You are able to communicate with the
technologist at any time using the intercom. Carvel Imaging
Center allows a friend or, if a child is being is examined, a
parent, into the room. Depending on how may images are needed,
the exam will generally take from 15 to 45 minutes, although a
very detailed study may take longer. You will be asked not to
move during the actual imaging process, but between sequences
some movement is allowed. Patients are generally required to
remain still for only a few seconds at a time. Some patients
will require an injection of a contrast material to enhance
the visibility of certain tissues or blood vessels. A small
needle is placed in an arm or hand vein.
When the exam is over you will be asked to wait until the
images are examined to determine if more images are needed.
What will I experience during the procedure?
The technologist will make you as comfortable as possible, but
at times the magnet may be within a few inches of your face.
For those who become very uncomfortable when enclosed in a
small space, a mild sedative is nearly always effective. You
may notice a warm feeling in the area being studied. This is
normal, but do not hesitate to report it if it bothers you. If
you receive a contrast material injection there may be some
local discomfort at the IV site. The loud tapping or knocking
noises that are heard during certain parts of the exam disturb
some patients; earplugs may help. You may bring your favorite
CD to listen to during the exam or we can tune in to your
favorite radio station.
Who interprets the results and how do I get them?
Our radiologist will analyze the results and fax a signed
report with the interpretation to your physician. Your
physician's office will inform you on how to obtain their
results.
What are the benefits vs. risks?
Benefits
- Detailed images of blood vessels and blood flow are obtained
without having to insert a catheter directly into the area of
interest, so that there is no risk of damaging an artery.
- The procedure itself and the time needed to recover are
shorter than after a traditional catheter angiogram.
- MRA is less costly than catheter angiography.
- There is no exposure to x-rays during an MRI study.
- Contrast material may be injected, but unlike catheter
angiography or CT angiography, which make use of iodine-based
contrast material, the risk of an allergic reaction from MRA
contrast is extremely low and kidney damage does not occur.
Even without using contrast material, MRA can provide
high-quality images of many blood vessels, making it very
useful for patients prone to allergic reactions.
- As with catheter-based angiography or CT angiography, it
frequently is possible to defer surgery after getting the
results of an MRA study. If surgery remains necessary, it can
be performed with more accuracy.
Risks
- There are no definite side effects from any type of MRI
study including MR angiography. However, Claustrophobia may be
a problem. When it is severe and not relieved by giving a
sedative, an alternative imaging method may have to be tried.
If a metal implant is present but goes undetected, it may be
affected by the strong magnetic field to which the patient is
exposed. In addition, if the implant is close to the
examination site it may be hard to get high-quality images.
- MRI generally is avoided during the first three months of
pregnancy. Ultrasound is preferred at this time unless the
woman might have a very serious condition that is best
detected by MRA. The effects of MRA on the fetus, if any,
remain to be determined. The general rule for MR imaging and
other diagnostic studies in pregnancy is that they should be
avoided unless there is substantial risk from missing the
correct diagnosis because the procedure is not done. Women who
are breast-feeding should inform the radiologist and ask how
to proceed. They may pump breast milk before the exam for use
until gadolinium contrast material has cleared from the body.
What are the limitations of MR Angiography?
MRA does not image calcium, as does CT angiography. The
procedure should be avoided in any patient having a pacemaker,
implanted neurostimulator, metallic ear implant, or metallic
object within the eye socket. It should also be avoided if
there is a bullet fragment or if the patient has a port for
delivering insulin or chemotherapy.
The clearness of MRA images does not match those obtained by
conventional angiography. Furthermore, images are acquired
more slowly by MRA than by catheter angiography. Sometimes it
may be difficult to separate images of arteries from veins by
MRA.
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