Interactive Transcript
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The post-contrast, T1-weighted,
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fat-saturated images are performed using the
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same parameters as the pre-contrast image.
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However, we do these at three different time points, which
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takes into account the dual blood supply to the liver.
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The liver gets about 75 percent of its blood supply from the
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portal vein and about 25 percent from the hepatic artery.
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Now, the timing can be performed using a fixed delay or an
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individual delay utilizing a test bolus or bolus tracking.
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Here we have the first phase that we get,
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which is often known as a late arterial phase.
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We obtain this approximately about 30 seconds
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after intravenous injection of contrast.
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And you know you have a good late arterial phase
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images if you see enhancement of the hepatic
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artery over here as well as early enhancement
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of the portal vein that you can see over here.
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This is a very important sequence to get
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right because it allows stratification of
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liver lesions into one of four categories:
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whether they're hypervascular or enhanced very
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avidly early on, whether they're isovascular,
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whether they're hypovascular, or avascular.
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The next phase is the portal venous phase.
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This is obtained at about 70
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seconds after injecting contrast.
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And in this one you're going to see very homogeneous
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opacification of the liver, as well as opacification
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of all the vessels in the liver, including the
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portal veins over here, as well as the hepatic veins,
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the right hepatic vein, the middle hepatic vein,
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and the left hepatic vein.
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The final phase that we get is known as a
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delayed equilibrium or interstitial phase.
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You'll see it used differently
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depending on who's talking about it.
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And we typically obtain these at about
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three minutes after intravenous injection.
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Now depending on the case, we may obtain a
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fourth post-contrast image at about ten minutes.
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This is typically used if you're suspecting a
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malignant liver lesion called a cholangiocarcinoma.
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And if you're using an agent with partial
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hepatobiliary excretion, we're going to
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obtain a final phase at about twenty minutes.
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As we go through the cases today, we'll
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certainly come across cases where we
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utilize that twenty minutes delayed phase.
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