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Next we're going to talk about T2*

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mapping cardiac MRI, which is used for direct quantitative

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measurement of the T2* time of tissue.

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It turns out that the T2* time becomes abnormal in patients with iron

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deposition, and it can cause signal loss at longer TE times.

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Why is it important?

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Well, cardiac iron deposition can lead

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to heart failure in a variety of different etiologies.

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This includes multiple transfusions in patients with sickle cell anemia or

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Beta Thalassemia, and then also patients who have abnormalities of iron handling

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in the body, particularly primary (hereditary) hemochromatosis.

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And in all these patients, you can end up with a lot of iron

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deposition in the heart, in the liver, in the spleen, and they can eventually

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develop heart failure due that iron deposition.

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T2* mapping is really important because it gives a direct quantitative

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measurement of the amount of iron in the myocardium.

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And from that amount of iron, you can tailor therapy to try and reduce

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the amount of iron circulating in the blood pool.

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Oftentimes, we'll have patients come

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on a yearly basis for annual T2* mapping.

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For instance, if they have sickle cell

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and iron overload, to monitor the amount of iron in the heart.

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And if they have increasing amounts

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of iron, they'll start chelation therapy to try and pull some of that iron out

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of the circulation before heart failure becomes a problem.

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So this slide actually does a nice job

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of showing you exactly what's going on with T2* mapping imaging.

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And it's really pretty simple.

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You acquire a bunch of images through the heart at the same portion

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of the cardiac cycle, and each image is exactly the same,

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except for one parameter, which is the echo time.

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And you can see on this image that the echo time is increasing from two

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milliseconds to four, six, eight, and so on, all the way up to 16 milliseconds.

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And what that's doing is allowing more

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time for susceptibility artifacts to occur.

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And you can see in this patient who has iron deposition, that you have relatively

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high signal to myocardium on the initial image.

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And then as the echo time increases,

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you start to have lower and lower myocardial signal.

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And so that is because of the iron

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deposition, which is creating the susceptibility artifacts.

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If you had a normal patient, you would see perhaps a little bit

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of signal loss, maybe on the TE of 16 milliseconds.

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It would look a little bit like this TE of four milliseconds.

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So it's not going to hold on to all the signal, but certainly you wouldn't

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have this dramatic loss in signal that you see at the TE of 16 milliseconds in this

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patient who does have iron deposition from Beta Thalassemia.

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So we can quantify this using specialized software.

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It turns out that if you have a TE time, or excuse me, a T2* time of less than

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ten milliseconds, then that correlates to a large amount

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of iron deposition, and those patients absolutely will get therapy.

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If you're at a T2* star time of roughly

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10 to 20 milliseconds, that's a bit of a gray area.

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They certainly have iron deposition in the myocardium.

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Whether or not they get treated is kind of up to the practitioner.

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They may monitor them or they may treat

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them, and then over 20 milliseconds is considered normal.