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Dr. P. back with our 72 year old woman with

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3 00:00:01,140 --> 00:00:03,789

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an exophytic antero-inferior pole left renal mass to demonstrate

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two points: the signal intensity index and the

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signal intensity ratio, which sound like they're the

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same thing, but we're going to separate them out.

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The signal intensity ratio is actually a comparison

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between the early aspect of enhancement and the later

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aspect of enhancement. Classically, AMLs wash

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out, although you've heard in other vignettes that

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there's a tremendous amount of washout variability.

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So when we compare what's happening early

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to what's happening late, we see that the

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intensity is higher early and lower late.

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So that would produce a ratio that is higher

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for angiomyolipoma than many other lesions.

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I don't find this particularly helpful to

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exclude renal cell carcinoma from a lipid-poor

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AML or angiomyolipoma, so I

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don't use it frequently.

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Here's another ratio that is helpful,

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though, in patients with lipid-poor AMLs.

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They tend to have a higher signal intensity index

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than renal cell carcinomas with microscopic fat.

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So how do you calculate this?

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Well, you get the signal intensity, you get the signal

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intensity on the end phase, and here's the end phase.

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So we call this IP, signal intensity, IP end phase.

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of this lesion, and you can take it in regions

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of interest, you can take it for the whole lesion

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by tracing the lesion, and then you subtract

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the signal intensity of the out-of-phase image.

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So you have SI in-phase minus SI opposed

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phase, and this is the opposed or out-of-phase

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image as evidenced by this India ink phenomenon

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around many structures that are bordered by fat.

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Then what goes on the denominator?

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So it's this minus this, and then you got a

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denominator. I can draw my line all the way across,

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and the denominator is going to be the in-phase,

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the signal intensity in phase on the denominator.

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Signal intensity IP on the bottom.

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And then you multiply the whole thing by 100.

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And that gives you your signal intensity

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index for lipid AML, but a nice

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demonstration of what you want to do.

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So for lipid-poor AMLs, the signal

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intensity index may be of value to you.

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And it's typically higher than the microscopic

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fat-containing renal cell carcinoma.

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Dr. P out.