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Diagrammatic TZ assessment

6 min.
Pomeranz, Stephen
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
CME Eligible

Dr. P., here talking about the assessment of TZ or transitional zone lesions on MRI. Now on the top here, I don't want you to get confused at all. These are scores as they relate to T2. In other words, T2 score of 1, T2 score of 2. These are DWI scores, 1, 2, 3, 4, 5 and simulate the ADC map. These are not PI-RADS designations. The PI-RADS designations, which you see at the bottom here, is a summation of each of these classifications as they relate to T2, DWI and ADC map, taken together to give you the PI-RADS score.

Let's dive into the T2 score first, which you've heard about in various vignettes. I would give a T2 score of 1. In other words, inconsequential, when I have a TZ lesion, the gray is the TZ area, and it's a nodule that's gray with a nice well-defined capsule all the way around. So we consider that normal in the aging male.

A T2 score of 2 would consist of maybe a nodule that's a little bit darker, like this one right here, not very encapsulated, hard to see a capsule. Or you have a nodule that's sort of gray or intermediate and only a part of it is encapsulated, so that would get a T2 score of 2. This is the same thing. These are both the same, but we're going to add them to two different scenarios in DWI. And the same thing is true over here on the right- hand side. So these three things are all the same. These three things are when we would assign a T2 designation of 2, 2, and 2. These are the same.

And here's when we would assign a designation of 1, heavily encapsulated, completely encapsulated nodule. Now what if we had a DWI scenario where there's little to no change in diffusion restriction, and we can see just a slight diminution in the parametric map, the ADC map, on the axial image? So we might say, okay, combine that together with just very slight changes in diffusion, barely perceptible, and we've got a nodule that's not encapsulated but well-defined, or a partially encapsulated nodule, that would equal a PI-RADS score of 2.

Now let's take exactly the same scenario, a well-defined nodule, discrete from the background of the rest of the TZ, not encapsulated, or partially encapsulated, and now add a little more diffusion restriction, a little slightly higher signal intensity relative to background on DWI, and slightly lower on the ADC map. That also would be given a total PI-RADS assessment of 2. Pretty easy.

Let's go back to this scenario. Same scenario, T2, designation of 2, discrete nodule, different than the background but not encapsulated, or partially encapsulated. There could be three, four, five, six of them, but this time the diffusion restriction is pronounced. It gets assigned the designation of 4 or 5, as opposed to 3 where it's kind of intermediate, as opposed to 1, 2, where it's barely perceptible. Now, the DWI is intense and on the ADC map, the parametric map, it's very dark. We take these three things together, T2 designation 2, DWI designation 4/5 and then the ADC map and that gives us a PI-RADS designation of 3.

One final caveat. When you're measuring your DWI, I want you to do it a unique way, a little bit different than what you've been doing before. And I want to elaborate on something I said earlier. I want you to have a B value of 50. So some people say you can get a B value of 0 to 100 as your lowest B value. I do not want you to use 0. There are a number of reasons for this that relate to vascular artifacts.

I think your first B values should be 50. Your next be value can be anything from 600 to 1,000. You pick. 800 seems pretty good. So if you've got a 50 and you have an 800, that's a pretty good day. That is what you're going to use to make your ADC map. Now, I know what you're thinking, "Where's the B value of 1,400, or 1,500, or 1,600?" That stands on its own. That does not get included in the calculation for the ADC map. We're going to look at the diffusion intensity by itself and maybe use it for measuring the size of the lesion on the B 14, 15, or 1,600.

You're going to have a minimum of three values, 50, let's say 800 for the second one. Use those two for the ADC map, and then the B value of 1,400 or greater is going to stand on its own to look at the DWI intensity to determine whether you're going to give it a designation of 2, 3, or 4, or 4/5.

That concludes our diagrammatic discussion of PI-RADS designations for TZ lesions that are encapsulated, not encapsulated but well-defined, or partially encapsulated.

LESSON 2, TOPIC 17

Mastery Series: PI-RADS 2.1 Update

Mastery Series

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Content reviewed: December 29, 2021

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