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Sagittal Plane: Field of View

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Focusing on the sagittal projection for

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the ankle, T1 on the left, gradient echo

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in the middle, 3D gradient echo, and on

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the far right, T2 with fat suppression.

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Now, you've got to have a practical

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approach to ankle imaging.

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So you can't have all these

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sequences plus more in every plane.

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You've got to choose, and

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you've got to choose wisely.

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So here I have three sequences, which

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I normally wouldn't get in every ankle.

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But if I am interested in a tendon, or a

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structure that's very long, like the plantar

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fascia, then I might focus all my effort, all

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my energy, into a specific plane of acquisition.

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For instance, in the Achilles, I'm focusing

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most of my energy and my pulsing sequences in

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the sagittal, and I will get three different

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sequences in that plane, and maybe one in

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the other two planes, for a maximum of five.

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If you're doing more than five planes of

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acquisition in an ankle, then you're either

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insecure, you're doing too many pulsing

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sequences, and you're taking up too much time.

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Now I'm talking in practical, everyday radiology.

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Not talking research.

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Another decision that you have to

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make in the sagittal projection is

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how much do you really want to see?

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For instance, if the Achilles

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was my interest, it's not in this

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case, then I need to see up higher.

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I should have moved my coil up higher

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to see the myotendinous junction and

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the watershed zone of the Achilles.

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Peace.

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I didn't because I'm interested

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in the ankle, not the Achilles.

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If I was interested in the

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plantar fascia, terrific.

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Let's scroll.

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I've got the entire plantar fascia on here.

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It's gorgeous.

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There it is.

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There it is.

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There it is.

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If I was interested in the medial flexor

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group, the posterior tibial tendon, the

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flexor hallucis, and the digitorum, fantastic.

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Then the field of view is great.

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But if you said to me, you know, ankle sprain,

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rule out osteochondral defect of the talar dome,

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I'm really interested in the talar dome and

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the collaterals that surround the ankle joint.

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I don't need all this midfoot anatomy.

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I need spatial detail.

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I'm bringing the field of view down to

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something on the order of 12 centimeters.

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This is more on the order of 16 to 18 centimeters.

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So, you control the horizontal, you control

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the vertical, you control the spatial detail.

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What about slice thickness?

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Slice thickness should be in the foot.

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I like four and under.

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Here you can see I've done

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three millimeters for the T1.

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Seven millimeters for the 3D, and

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three millimeters for the PD spur.

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And for each of these, there's

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a little bit of overlap.

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In fact, for this one, there's 50 percent overlap.

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There's a reason for this.

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I'm going to reconstruct this to look

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at the tendons in greater detail.

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What about the matrix?

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Well, there you've got a decision

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to make based on your scanner.

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Lower field systems, somewhere

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around 192 by 256 to 256 squared.

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Higher field systems, you can go up pretty easily

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to 512 by 512, which has been done here on this 1.

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5 Tesla scanner.

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So, that kind of gives you a rough

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overview of the sagittal projection.

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Its real strength is when you want to see

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length, but you have to know where that length is.

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If you're interested in length down here, then you

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want to have your field of view extend this way.

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If you're interested in length up here,

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for instance, an extensor tendon tear up

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higher, or an Achilles tear, then you've

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got to center up more proximally.

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And that is part of your job, part of

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training your technologist, and hopefully

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you don't have to go in there for every case.

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Your technologist is educated enough

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to make that judgment for you.

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Let's move on, shall we?

Report

Description

Faculty

Stephen J Pomeranz, MD

Chief Medical Officer, ProScan Imaging. Founder, MRI Online

ProScan Imaging

Tags

Musculoskeletal (MSK)

MSK

MRI

Foot & Ankle

Acquired/Developmental

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