Magnetic
Resonance Imaging (MRI) Scans for Mesothelioma Lung Cancer - How
It Works, Magnetic Resonance?, Superconducting Magnets & Precautions
(August 11th, 2008)
Magnetic Resonance Imaging (MRI) is a medical imaging technique
used to take pictures of the lungs, structures of the body and organs.
It can provide detailed visuals of the body in any plane. The advantage
of using MRI over Computed Tomography (CT) scans is that MRI scans
provide greater contrast between different tissues of the body making
it easier to detect malignant cancerous cells & tumors. While
CT scans use ionizing radiation or X-rays to acquire images of the
lungs, MRI scans use non-ionizing radio frequency (RF) signals to
output images of internal organs of the body. To determine extent
& development of tumors in the lungs, Magnetic Resonance Imaging
(MRI) scans use strong magnets & radio waves from which the
energy released is formed in a pattern. A specialized computer translates
these patterns of radio waves emitted from the tissues into very
detailed images of the body. Not only does this produce cross sectional
slices of the lungs or the body, it can also output slices that
are parallel with the length of the body. MRI scans are also used
to visualize the diaphragm (thin muscle at the bottom of the lungs
that helps the body respirate) where malignant mesothelioma tumors
could easily spread to.
How Magnetic Resonance Imaging (MRI) Works
 When
the patient lies on the MRI scanner, the protons or hydrogen nuclei
found in water molecules in the body, align with the strong magnetic
fields contained on the MRI scanner. A second electromagnetic field
which is perpendicular to the main field pushes protons out of alignment
with the main field. These protons with the force of energy then
push back to align with the main fields, emitting a measurable radiofrequency
signal. Since protons in different tissues of the body realign at
different speeds, distinguished structures of the body can be easily
revealed. Contrast agents such as barium sulfate or iodine could
also be added (intraveously injected into the body) to make more
clearer the appearance of malignant tumors, blood vessels, lungs
or any inflammation caused by asbestos fibers. Since MRI does not
use ionizing radiation, adding any contrast agents to the body has
no dangerous effects and is a very safe procedure. Magnetic resonance
imaging is the #1 technique used to detect any malignant tumors
or abnormalities in the heart or blood vessels. MRI can also help
detect tumors in other reproductive organs of the body such as the
uterus, testicles, prostrate and ovaries as well as abdomen, pelvis
or the chest.
How the Process Works
The patient is asked to lie down on a mobile MRI examination table
& straps and bolsters are tied to the table to ensure you stay
still and do not move while the examination is taking place. The
examination cube could be as big as 7 feet tall by 7 feet wide.
A small radio device with the ability to send/receive radio waves
is placed opposite your body to ensure there is proper communication
between the MRI scanner and specialized computers located in another
room. The part of the body that is to be examined (the heart, abdomen
or the chest, etc) has to be placed on the 'isocenter' which is
the center of the magnetic fields. The function of the radio waves
energy is to examine the type of tissues that reside in the lungs,
are they normal or abnormal? The MRI mapping system will go over
the lungs or chest or the entire body piece by piece building up
2D or 3D maps of tissue types. All this is then tabulated at the
end to create one full diagram for the radiologist to view.
To enable blood transfusion, the patient is given contrast agents
injected via an intravenous line into the veins on your hands or
arms. You will then be placed on the MRI scanner under the electronic
magnets and the radiologist will leave the room. This entire process
could take between 45 minutes to 1 hour.
 Magnetic
Resonance?
The essence behind Magnetic Resonance Imaging (MRI) is the use
of magnets. The magnets are measured using a unit known as 'tesla.'
Today's magnets come in the 0.5-tesla to 2.0-tesla range. Tesla
helps radiologists measure the strength of the magnetic forces,
for example a 0.6 tesla is conservative while a 2.0 tesla magnetic
force is very high or the extreme. The magnetic force exerted on
a body increases exponentially as it nears the object. At 0.5 tesla,
the patient may be closer to the magnetic surface of the MRI scanner.
At a magnetic force of 2.0 tesla, the radiologist may position the
patient a little farther away from the magnetic strip.
The type of magnet most commonly used in MRI machines is the Superconducting
magnet (picture above). A superconducting magnet contains coils
& wires throuch which electricity is passed to create the radiofrequency
signals. The wires are bathed in liquid helium at 452.4 degrees
below zero, which is extremely cold! Not to worry though, you will
not feel this cold because the helium liquid is placed inside a
vacuum flask (shown as Seawater Duct in the diagram). Thanks to
the extreme cold, any resistance that this magnet faces is reduced
to 0.
Precautions
Objects such as pens, keys, paperclips, scissors, credit cards,
bank cards or anything else with a magnetic strip on it should NOT
be taken into the MRI scanner room. This is because the MRI scanner
could easily pull these objects into the scanner and hurt the patient
or anyone else in the room. The MRI scanner could also erase any
magnetic strip on credit or bank cards.
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