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Utilizing the Axial Sequence

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Let's look at the axial T1-weighted or fat-

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weighted appearance of the prostate on MR.

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I've got the axial

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T2-weighted up for a comparison.

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The T1-weighted image is not meant to help

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you evaluate the locus or to detect cancers

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and to put them in their proper zone.

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Its main function is to evaluate the periprostatic

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fat and the neurovascular bundles at 5 o'clock

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and 7 o'clock, which should be surrounded by fat.

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So, let's scroll it a little bit.

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And yeah, in some locations, it may be a little

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tough to, to separate or distinguish them.

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But there's no mass effect.

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The fat is pretty symmetric on both sides.

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Now, each vessel isn't going to be

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exactly identical to the other side.

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So if you're very OCD, then you're

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going to, you're going to tend to

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overcall invasion of this area.

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But, you know, if you're going to call invasion,

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you should have a mass that has capsular contact.

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And almost always, that mass that has

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capsular contact is somewhere between

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one and a half to two centimeters long.

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So if you simply see a little bit of asymmetry

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there, and there's no mass present, that's silly.

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Don't make that mistake.

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So it's not going to be exactly identical

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from side to side, and you'll notice that the

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signal is a little darker on the left than the

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right, and perhaps the flow rates are a little

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faster on the left than the right, which brings

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me to another role of the T1-weighted image.

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We've talked about the importance of fat,

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capsular invasion, including the pre-prostatic

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space of Retzius, which we'll inspect, but

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also the T1-weighted image, especially

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if they're, they're a little bit thinner,

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can help you look for nodes just like CT.

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know, I see nodules on MRI all the time."

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How do I know whether something

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is a nodule or a node?

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That takes a little bit of experience,

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but not a tremendous amount.

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There are a couple of ways.

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First of all, nodes are not tubular.

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So if the structure you're looking at

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is tubular, like that one, not a node.

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Nodes are going to be gray.

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So if the structure that you're looking

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at is very hyperintense or white,

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like that, it's not going to be a node.

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You know, it's probably going to be

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flow, like that flow right there.

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So signal intensity is also going to help you.

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Nodes that are involved by prostate

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metastasis tend to be gray, round,

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plump, and have no fatty hila.

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Size criteria helpful, about 1 centimeter.

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But morphology, plumpness,

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the absence of the fatty hila.

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Isolation, a node that's 1.2 centimeters

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that's round and gray,

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sitting all by itself in the iliac

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chain, that is a worrisome thing.

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Now it's very helpful to go back and

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forth between, say, the T1 and the T2,

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and that's why I have the T2 up here.

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For instance, this structure right

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here is tubular, okay, that's easy.

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But let's say it wasn't tubular.

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Let's say it was circuitous, like a vessel,

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and it didn't have a straight course.

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So it's hard to tell that it

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really is a linear structure.

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Well, you look over here and you see this

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round on the outside and gray on the inside?

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That is slow flow in a vessel with

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faster flow in the center of the vessel.

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So that ring-like appearance

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is another method you can use

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that tells you you're not dealing with a node.

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Now, don't forget to look at the, the

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obturator chain nodes and the obturator

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canal in a patient with prostate cancer.

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You, you, you do have a, a, a complement

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of an artery, a vein, and a nerve in there.

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Sometimes you may have some small

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nodes in there that are undersized,

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maybe 3 or 4 millimeters at best.

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But you shouldn't have anything that

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approaches a centimeter in the obturator canal.

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So that's how you use the T1-weighted image

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to look for neurovascular bundle invasion,

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anatomic capsular crossing into the surrounding

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periprostatic fat, and looking for nodes.

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Don't forget, the T1-weighted image is a

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very reliable, helpful sequence in prostate

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cancer to look for bone mets, right?

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The fat is white, and prostate cancer tends

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to be sclerotic; sclerosis is dark, so dark

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against the background of white, especially with

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round or irregular shape, easy in most cases

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of metastatic prostate carcinoma to the bone.

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That concludes our discussion of the axial

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T1-weighted image on MR and its role.

Report

Editorial Note

Faculty

Stephen J Pomeranz, MD

Chief Medical Officer, ProScan Imaging. Founder, MRI Online

ProScan Imaging

John F. Feller, MD

Chief Medical Officer, HALO Diagnostics. Medical Director & Founder, Desert Medical Imaging. Chief of Radiology, American Medical Center, Shanghai, China.

HALO Diagnostics

Tags

Prostate/seminal vesicles

Neoplastic

MRI

Genitourinary (GU)

Body

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