Interactive Transcript
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The third group of sequences that we utilize
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in evaluating liver lesions are the T1
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weighted in and out of phase sequences.
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These are performed without intravenous
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contrast and performed without fat saturation.
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So here we can see the T1 out of phase
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sequence and the in-phase sequence.
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These are gradient echo sequences
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performed with breath holds.
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The in-phase sequence is obtained at an echo time,
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at which fat and water protons are aligned with one
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another, while the out-of-phase sequence are obtained
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at an echo time where fat and water oppose one another.
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From a practical perspective, this means that
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anywhere where you have a fat and water interface,
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such as the edge of the liver with the adjacent
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fat, you're going to see this very, very dark line.
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And this is known as the India ink artifact.
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So what do we use these sequences for?
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Well, we use it to detect the presence of hepatic
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steatosis, and this is identified as a loss of signal
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within the liver parenchyma on the
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out-of-phase sequence versus the in-phase sequence.
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We can use the spleen or potentially the
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paraspinal muscles as an internal control.
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The latter two organs should not lose
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signal on the out-of-phase sequence.
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The in-phase sequences, because they're obtained
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at a longer echo time, will show increased
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susceptibility artifact associated with any
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eclipse, any metallic deposition, and even gas.
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So if you're looking for gas within a liver lesion,
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you're going to look at the in-phase sequence for that.
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These sequences can also be used to detect the presence
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of hyperintense T1 signal within any liver lesions,
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though this is better detected on the isotropic fat
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suppressed sequences, which we'll talk about next.
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