MEDRADSC 3DE3 Lecture Notes - Lecture 11: Ferromagnetism, Superparamagnetism, Chelation
18 Jun 2018
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Contrast Agents
Most of chapter 11– read
ď‚·MRI contrast agents change the relaxation properties of blood (changes blood composition)
ď‚·Axial t1: 3 different shades of grey
ored is the actual tumour within the lesion
oblue arrow: cystic component
oyellow area: surround edema
ď‚·T2 weighted image:
ocontrast, differences between margins, patho weighting because it better allows us to
see mobile water protons
ď‚·Bottom image:
otumour itself enhanced brightly with contrast media, we see the vasculature in the
tumour enhancing, has reduced the relaxation time of H spins/ more efficient, we can
catch it on a t1 weighted image because we’ve changed the composition (usually water
has a long relax time)
Introduction
ď‚·Which weighting has high contrast between pathology and normal tissue in most cases? T2
ď‚·When high intrinsic contrast is not enough:
ocontrast agents used
ď‚·Selectively change T1 and T2 relaxation times of certain tissues
oIntrinsic contrast parameters (can’t change, but with adding contrast we look to
manipulate it), proton density is a 3rd instirc contrast parameter that we can’t change, t1
and t2 relaxation time that we look to manipulate
when high intrinsic contrast isn’t enough, we need to know more– introduce
contrast (affects the t1 and t2 times of tissues)
Typically affecting t1 time, impossible for us to affect only the t1 time (it is also
reducing our t2 time)
oExtrinsic contrast parameters (TR, excitation time, inversion time, flip angle)
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Magnetic Susceptibility
ď‚·
ď‚·
ď‚·Diamagnetic:
ogold, silver - mild : not positively affected by B0 (no unpaired electrons), negative effects
on local field w/I the nucelus
oIntroducing something with high mag susceptible– material able to be affected by B0
oDiamagnetic: titanium and copper
ď‚· Paramagnetic:
oGd chelates – positive effect on B0, has unpaired electrons, can be affected by B0
because of composition
GD chelate: gadolinium combined with chelates to ensure it can be excreted by
pt
ď‚·Superparamagnetic:
oiron oxides - greater positive, disruptions
ď‚·Ferromagnetic:
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oiron- high positive, retain magnetization, extremely affected by B0– retain
magnetization after they’ve been removed, can kill you, become projectiles
T1 Agents
ď‚·Water/pathology: inefficient relaxation on its own
ď‚·Gadolinium (Gad)
oIf not bound to chelates, they are ferromagnetic: extreme potential to be toxic, can
accumulate in different areas in your body
orare earth metal ion
oseven unpaired electrons (large magnetic moment), extreme impact on local mag field,
the impact= shortening the t1 times water, affects the molecular tumbling rate in H
spins in water- matches the Larmour frequency more
Don’t do t2 times post gado injection– miss the signal because it shortens the t1
times
When you slow down the molecular tumbling rate it is closer to the larmour
frequency
olarge magnetic moment at or near Larmour frequency- efficiency met, relaxation times
shortened, even water
ď‚·Manganese- IV t1 agent, not currently used
o
oHelp demo liver lesions only
oT1 weighting before and after contrast
oNormal liver tissue is enhancing an abnormal is not
ď‚·Hyper-polarized helium gas: used in the lungs
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find more resources at oneclass.com
Document Summary
Mri contrast agents change the relaxation properties of blood (changes blood composition) Axial t1: 3 different shades of grey: red is the actual tumour within the lesion, blue arrow: cystic component, yellow area: surround edema. T2 weighted image: contrast, differences between margins, patho weighting because it better allows us to see mobile water protons. When high intrinsic contrast is not enough: contrast agents used. When high intrinsic contrast isn"t enough, we need to know more introduce contrast (affects the t1 and t2 times of tissues) Typically affecting t1 time, impossible for us to affect only the t1 time (it is also reducing our t2 time: extrinsic contrast parameters (tr, excitation time, inversion time, flip angle) Paramagnetic: gd chelates positive effect on b0, has unpaired electrons, can be affected by b0 because of composition. Gd chelate: gadolinium combined with chelates to ensure it can be excreted by pt. Superparamagnetic: iron oxides - greater positive, disruptions.
