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					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
In 1952 Felix Bloch and
Edward Purcell were awarded
the Nobel Prize when they
discovered the concepts
surrounding NMR/MRI.

During the time between
1950-1970, 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
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
MRI machines look like a large block with a tub
running through the middle of the machine, call
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 MR
machine creates a model of the tissue. This allow
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
To give perspective on
strengths from 5000 to 20,000 Gauss.
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
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
  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       These magnets
that is found   are
in all MRI      responsible for
machines,       altering the
called          magnetic field
gradient        in the area to
magnets         be scanned
                and can
                magnetically
                “slice” the
                tissue to be
                examined from
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
    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.

				
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posted:3/13/2013
language:English
pages:30