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So there are two different techniques for finding

0:04

that Z for a biopsy.

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The two different techniques are stereotactic imaging

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and tomosynthesis.

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So we're going to start discussing stereotactic imaging

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where Z is determined

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by the targets apparent change in position relative

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to a reference point when seen on angled views.

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That's a mouthful. That is

0:27

what parallax shift is to start with.

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Uh, two images are acquired

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with the x-ray tube in different positions.

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So here's the scout view at zero degrees

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and here's a target of grouped microcalcifications.

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We get a view at positive 15 degrees

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and a view at negative 15 degrees.

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The target of the lesion appears

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to change position in the X dimension

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between the two projections.

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You can see it looks more towards the left here

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and more towards the right here.

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Z or depth in the breast is determined

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by the target's Apparent change in position relative

1:13

to a reference point.

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You don't have to know this calculation, uh,

1:20

but there is an actual mathematical formula

1:22

that the computer does

1:24

and it shows the change in x divided by two.

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Tangent of 15 degrees gives the change in Z,

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meaning the difference in Z

1:33

between the target and the reference.

1:38

Going back to our patient with new grouped calcifications,

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we would obtain an image at positive 15,

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an image at negative 15.

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There's positive, there's negative at the workstation.

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We place our cursor on the target manually selecting X

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and Y by placing the cursor on those targets

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and then the computer will do the calculation and provide Z

2:08

or depth on the workstation.

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This is what it looks like.

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We're going to see after we choose our target X, Y,

2:17

and Z here, and we click check here

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and it magically transfers the coordinates over

2:27

to the stage of the needle.

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This is what's right below the needle next to the patient.

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And here we can see the target, the X,

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the Y, and the Z.

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And when you're doing the biopsy,

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the needle should be at the same coordinates, X, Y, and Z.

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And so you know you're at the appropriate position

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because the difference between what the target is

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and where your needle is, is zero.

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We take pre-fire images and on these images

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The needle should point directly at the target.

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On both views, there is a button

3:06

to press where the needle fires or advances.

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The throw on many

3:11

of the needles is approximately two centimeters.

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On those post biopsy images, the trough should align

3:19

with the target on both views.

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In this case, the target calcifications align

3:25

with the trough, although they are towards the nipple.

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This would be chest wall in the patient,

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and then this would be the nipple

3:32

down towards the bottom of the screen.

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And so we would orient our trough towards the nipple

3:39

and sample in that direction.

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We would obtain a specimen radiograph.

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Here are the specimens, um,

3:47

array in a core biopsy specimen container.

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Um, and this is the radiograph of those same samples.

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The reason we do specifically in this, uh, core container is

3:59

that our pathologists like to have our specimens separated

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between those that have calcifications

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and those that do not, they do look at everything,

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but they like to do their own rad path correlation

4:12

and make sure they know

4:13

that they are looking at the target Calcifications

4:17

over here on the top left is just

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what these specimens look like in the container

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that's attached to the needle.