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Ellipsoid Volume

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

I'm here with a live case T2 weighted image acquisition, axial, sagittal, coronal, all orthogonal. Going to focus on three things, two more important than the third, the axial angle of acquisition, how to measure volume, and we'll talk just briefly about some new sector mapping.

Let's begin with the axial. If you look to the left, look at how we're scrolling, orthogonal, a straight axial or in other words, if I draw it, it is straight across from posterior to anterior. On the other hand, you could acquire the axial by looking at the long axis of the prostate, and that long axis can be determined from the opening of the urethra at the level of the bladder, straight on down to the bottom of the peripheral zone. That is not the bottom of the prostate right there, that is the surgical capsule. This is all PZ tissue, so you come all the way down to get your longitudinal measurement, but also your axial acquisition could be perpendicular to that, a so-called axial oblique. Either this one right here or this one right here is fine. I don't mind. As long as when you measure your transverse measurement you're at the level of maximal prostate width, which is right here. We're going to go from the patient's right capsule to the patient's left capsule, and that gives us our transverse width.

Now what about the anteroposterior length? That one is tricky. Or anteroposterior dimension. We're going to have length times width, times height. Let's go with length, which is AP. To measure length I'm going to use my pointer again and my colored pencil. I'm going to go from the opening of the urethra down perpendicular to the axis of the prostate. And see I'm not going like this, I'm going like this. And I'm not stopping here, I'm going all the way down to the peripheral zone.

Now here is an important point. If you're directly in the midline you may not see this tissue here, so you may have to go slightly off the midline to include this apical portion of the peripheral zone. This is how you're going to get your height. The AP dimension, so-called length, is going to be perpendicular to that. Now if you go directly to the midline, this is the midline, look at how thinned out the peripheral zone is anatomically. I like to go one slice off that, right there, and then I'm going to go perpendicular to the long axis of the prostate. I'm going to go right from the back of the capsule to the anterior fibromuscular stroma, right at the mid level. And that is going to be my AP length.

I got AP length, I've got height, don't forget to include the inferior aspect or apical portion of the peripheral zone. And I've got transverse dimension or width this times this, times this, multiplied by PI, divided by six gives you your ellipsoid volume.

We've addressed angle of T2 acquisition and the axial projection, the ellipsoid measurement. And finally, one more caveat, we've got some new sector map zones, including something called PZ, PM to be discussed in another vignette. Let's move on. Shall we? Dr. P out.

LESSON 2, TOPIC 6

Mastery Series: PI-RADS 2.1 Update

Mastery Series

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Content reviewed: December 29, 2021

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