A benefit of MR is that, unlike
conventional x-ray or CT imaging, it does
not use x-ray radiation. Magnetic resonance imaging is non-invasive and provides exquisite
images with excellent contrast detail of soft tissue and anatomic structures like gray and
white matter in the brain or small metastatic lesions (cancers) in the liver. In
comparison to MR, conventional x-ray provides images of dense structures like bones with
good resolution. The x-ray angiogram is the traditional
standard for imaging vessels like the carotid arteries in the neck, vessels in the brain,
peripheral arm and leg vessels, or the coronary arteries which supply blood to the heart.
But conventional angiographic imaging is very labor- and time-intensive and requires
administration of significant amounts of contrast to image the blood vessels. X-ray
angiography does not provide clear images of the soft tissue organs in the body like the
liver or brain (see section on MR Angiography).
Like MR, Computed
Tomography (CT) also creates detailed cross sectional images of the body. But, while CT
can depict soft tissue structures much better than conventional x-ray, it does not
have the contrast detail that MR provides. Many diseases, for example certain brain
tumors, are more readily apparent in MR images than in the corresponding CT images due to
the better contrast definition of MR.
MR imaging is unique in that it can
also create detailed images of blood vessels without the use of contrast media
(although there is a trend toward the use of special MR-contrast media called Gadolinium
when imaging the vessels as well as soft tissue like the brain).
Emerging
Applications and Clinical Benefits of MR Imaging
The use of MR imaging as a diagnostic
technique continues to grow, allowing the study of more and more body parts. Initially, MR
was mainly used to image the brain and spinal column, and each exam could last up to an
hour. However, MR scanners can now image a host of additional body parts including
injuries of the joints (such as the shoulder, knee, elbow, wrist), the blood vessels (for
instance, carotid arteries, renal arteries, peripheral leg arteries), the breast, as well
as abdominal and pelvic organs like the liver or male and female reproductive anatomy. MR
examinations have also become much faster, in some cases rivaling the speed of spiral CT.
Skilled MR operators with the latest equipment can now do complete routine studies (e.g.
brain or knee) in as little as ten minutes. In some cases, MR systems equipped with Echo
Planar Imaging (EPI) packages can use special emergency or fast protocols to do a basic
head study in as little as five to twenty seconds.
Click here to see a
dynamic MR CINE (movie) of the beating heart.
(106k Windows .avi file)
Note the aorta in the lower right corner of the image and the clear definition of the
heart's four chambers. (To start or stop the movie, click on the image with your mouse.
Explorer users double click on the image, Netscape users click once.)
Updated: June 10, 2008
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