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What is the difference between an MRI and  CAT scan?

Sat, 21 Oct 1995 00:17:27 GMT

A CAT scan uses X-rays (ionizing radiation) to create images of the
body. A MRI scan uses nuclear magnetic resonance signals from water to
create images. NMR signals are e{*filter*}d by radio-frequency waves (the
frequencies are close to the commercial FM radio band) or non-ionizing
radiation. The magnetic spin-states of the H nuclei must be coherent to
generate NMR signals. The patient is placed in a large (25 to 100
thousand times stronger than the earth's magnetic field) ***STATIC***
magnetic field. Since this is a DC field the controversy about AC fields
generated by power lines is not relevant. In order to create a 3D image
magnetic gradients are generated to suppliment the main field.
These gradients create eddy currrents that mechanicly shock coils in the
magnet. These shocks are the source of the noise heard during
the image creation process.

Unlike CAT scans MRI contains information about the local molecular
dynamics of the H nuclei in the water molecules. This information
(called relaxation effects) can be used to identify malignant tissue. It
seems that water molecules in the vicinity of transformed cells
relax differently than water near normal cells. This means a
relaxation weighted MRI image is the only non-invasive way to detect
malignant tissue BEFORE a gross structural change occurs. Of course CAT
scans only detect enlarged/deformed tissues.

This is the{*filter*}&Jane answer to your question.

Sat, 21 Oct 1995 23:19:33 GMT


>What is the difference between an MRI and  CAT scan?

CAT scans are made using x-rays and MRI scans are made by using
a giant magnet to align all the little water molecules in your
body and then watching them decay back to their ground state.
MRI requires no radiation and thus is safer.  Different tissues
show up better on one scan or another.  CT is better for bone,
MRI for soft tissues.

Gordon Banks  N3JXP      | "Skepticism is the chastity of the intellect, and


Sat, 21 Oct 1995 23:47:51 GMT
 [ 3 post ] 

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