MRI is based on gyromagnetic
property of protons.
Proton density and relaxation time are assesed by radiofrequency pulse and computer generates a gray scale image from this data.
Types OF MRI :-
A. T1W (T 1-weighted MRI) :
Spin-lattice relaxation time : Time taken by proton to return to
original axis.
1. basic scan, in particular
differentiating fat from water -
with water darker and fat
brighter.
2. In the brain T 1-weighted scans
provide good gray matter/white
matter contrast.
3. It highlight fat deposition
4.used to find out normal
anatomical details of tissues
B.T2-weighted MRI
(Spin-spin relaxation time) : Time taken by proton to displace
1. fat is differentiated from water -
but in this case fat shows darker,
and water lighter
2. in the case of cerebral and spinal
study, the CSF (cerebrospinal fluid)
will be lighter in T2-weighted
images
3. It is particularly well suited to
imaging edema
used to assess pathological
process
CONTRAST AGENTS :
A.PARAMAGNETIC
1.gadolinium :MC used
2.manganese : MnDPDP/DPDP
B.SUPERPARAMAGNETIC
1.Iron oxide (SPIO/USPIO)
2.iron platinum (SIPPs)
CONTRAIDICATIONS :
1.PROSTHESIS
2.METALLIC FOREIGN BODY
3.PACEMAKER
4.CHOCHLEAR IMPLANT
5.ANEURYSMAL CLIPS
6.CLOSTROPHOBIA
SUPIRIOR to CT in
1.Middle cranial fossa imaging
2.skull base
3.neural canal
4.intaspinal content
5.cerebral edema
6.chronic hemorrhages
INFERIOR to CT in
1.detecting calcification
2.hyperostosis a/w brain tumour
(meningioma)
3.acute hemorrhage
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