All You Ever
Wanted To Know
About MRI
Kim Eriks and Katy Koukouras
MRI=Magnetic Resonance
Imaging
Allows the clinician to see
high quality images of the
inside of the body:
• Brain
• Heart
• Lungs
• Spine
• Knees
• Wrist
• Etc.
MRI is a very close relative of NMR, which allows
clinicians to obtain chemical and physical
information about certain molecules. In the
1970’s the name was changed from NMRI to MRI
due to the negative connotations associated with
the word “nuclear”. Many patients thought that
the exam would expose them to radiation.
In 1952 Felix Bloch and Edward
Purcell were awarded the Nobel
Prize when they discovered the
concepts surrounding NMR/MRI.
During the time between 19501970, the idea was used for
chemical and physical analysis
of molecules.
• In 1971, Raymond Damadian
discovered that NMR could be
used in the detection of diseases.
• In 1974, Damadian received a
patent for the design of his MRI
machine.
• In 1977, Damadian did his first
scan on a human, his assistant,
Larry Minkoff. He couldn’t go in
himself due to his enormous size.
Damadian’s first prototype
was called “Indomitable”,
due to criticism and the
seven years that it took to
complete.
In 1978, Damadian
established a new
corporation called FONAR,
which introduced the first
commercial MRI scanner in
1980.
Slide shows which
area of the brain is
responsible for touch.
MRI machines have come a long way since
Indomitable. Previously, it took up to five hours
to get an image, whereas today, it takes minutes.
In 1992, functional magnetic resonance imaging
(fMRI) was discovered, which allowed clinicians to
see various regions of the brain, their functions,
and their specific locations.
MRI machines look like a large block with a tube
running through the middle of the machine, called
the bore of the magnet.
The bore is where the patient is located for the
duration of the scan.
The MRI machine picks points
in the patients body, decides
what type of tissue the points
define, then compiles the
points into 2 dimensional and
3 dimensional images.
Once the 3 dimensional image is created, the MRI
machine creates a model of the tissue. This allows
the clinician to diagnose without the use of
invasive surgery.
The largest and most important components
of the MRI machine are the magnets.
The magnet strength is measured in units of
Tesla or Gauss (1 Tesla = 10,000 Gauss).
Today’s MRI machines have magnets with
strengths from 5000 to 20,000 Gauss.
To give perspective on the
strength of these magnets,
the earth’s magnetic field
is about .5 Gauss, making
the MRI machine 10,000
to 30,000 times stronger.
There are three types
of magnets:
1.Resistive Magnets
2.Permanent Magnets
3.Superconducting
Magnets
The resistive magnet has many coils of wire that
wrap around the bore, through which electrical
currents are passed, creating a magnetic field.
This particular magnet requires a large amount
of electricity to run, but are quite cheap to
produce.
The permanent magnet is one that delivers a
magnetic field, which is always on at full strength
and therefore, does not require electricity. The
cost to run the machine is low due to the
constant magnetic force. However, the major
drawback of these magnets is the weight in
relation to the magnetic field they produce.
The superconducting magnets are very similar
to the design of the resistive magnets, in that
they too have coils through which electricity is
passed creating a magnetic field. However, the
major difference between the resistive magnet
and the superconducting magnet is the fact that
the coils are constantly bathed in liquid helium at
-452.4ºC. This cold temperature causes the
resistance of the wire to be near zero, therefore
reducing the electrical requirement of the
system. All of these factors allow for the
machine to remain a manageable size, have the
ability to create high quality images, and still
operate at a reasonable cost.
The superconducting magnet is the most
commonly used in machines today, giving the
highest quality images of all three magnet types.
There is
another type of
magnet that is
found in all
MRI machines,
called gradient
magnets
These magnets
are responsible
for altering the
magnetic field in
the area to be
scanned and
can
magnetically
“slice” the tissue
to be examined
from every
angle.
MRI’s of the heart can be done to look at many
different areas including: vessels, chambers, and
valves.
The MRI can detect
problems associated with
different heart diseases
including plaque build up and
other blockages in blood
vessels due to coronary
artery disease or heart
attacks.
MRI’s of the brain can
evaluate how the brain is
working, whether normal
or abnormal.
Brain MRI’s can show damage resulting from
different problems such as: damage due to
stroke, abnormalities associated with dementia
and/or Alzheimer’s, seizures, and tumors.
fMRI are done prior to brain surgery,
to give a map of the brain, and help
plan the procedure.
MRI’s can be done on the
knee to evaluate damage to
the meniscus, ligaments, and
tendons.
Tears in the ligaments are
given a grade 1-3 depending
on their severity:
1-fluid around the ligament
2-fluid around the ligament with partial disruption
of the ligament fibers
3-complete disruption of the ligament fibers
Often prior to a MRI scan, a patient would need to
have a contrast dye, either injected or taken orally,
usually gadolinium as seen here.
The Procedure…
Once the contrast dye has been injected, the
patient enters the bore of the MRI machine on
their back lying on a special table.
The patient will enter the machine head first or
feet first, depending on the area to be scanned.
Once the target is
centered, the scan can
begin.
•The scan can last anywhere from 20-30
minutes.
•The patient has a coil that is placed in the target
area, to be scanned.
•A radio frequency is passed through the coils
that excites the hydrogen protons in the target
area.
•The gradient magnets are then activated in the
main magnet and alter the magnetic field in the
area that is being scanned.
The patient must hold completely still in
order to get a high quality image. (This is
hard for patients with claustrophobia, and
often times a sedative will be given, if
appropriate.)
The radio frequency is then turned-off and the
hydrogen protons slowly begin to return to
their natural state.
The magnetic field runs down the center of
the patient, causing the slowing hydrogen
protons to line-up.
The protons either align themselves
pointed towards the head or the feet of the
patient, and most cancel each other out.
The protons that are not cancelled create a
signal and are the ones responsible for the
image.
The contrast dye is what makes the
target area stand out and show any
irregularities that are present.
The dye blocks the X-Ray photons
from reaching the film, showing
different densities in the tissue.
The tissue is classified as normal or
abnormal based on its response to the
magnetic field.
The tissues with the help of the magnetic
field send a signal to the computer.
The different signals are sent and
modified into images that the clinician can
evaluate, and label as normal or
abnormal.
If the tissue is considered abnormal, the
clinician can often detect the abnormality,
and monitor progress and treatment of
the abnormality.
The MRI has allowed clinicians to treat,
monitor, and learn about many different
diseases and problems. As well as, to learn
how the body functions, normally, without
needing to resort to more invasive methods
like surgery.
MRI treatment is a wonderful option for most
patients, but there are some people who are not
candidates.
Those include:
1) Patients with pacemakers cannot have the scan
done as the magnet from the MRI interferes
with
the signal sent from the pacemaker, and
deactivates it.
2) Patients who are too tall, or too obese
3) Patients who have orthopedic hardware can get
distortion in the image, and the scan quality is
not as high.
THE FUTURE OF
MRI:
•The possibility of having very small machines
that scan specific parts of the body.
• The continuing improvements on seeing the
venous and arterial systems.
• Brain mapping while the patient does specific
tasks, allowing clinician’s to see what part of the
brain is responsible for that task/activity.
• Improvements on the ability to do MRI’s of the
lungs.
• ETC.