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In this video we are gonna talk about quantification

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of the tracer uptake

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and also what factors will affect the

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accuracy in these measurements.

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PET imaging doesn't have a way to absolutely

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quantify the degree of uptake, at least not with the tracers

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that are used in oncology.

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But we do have a tool, uh, to quantify the uptake

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and it's called a standardized uptake value,

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which is a relative measurement.

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This will give us an idea of

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how much tracer is accumulated in the area

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that we want to investigate.

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The SUV formula I have put here

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takes into account the activity concentration in the tissue,

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how much activity we've given and what is the body size.

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And there are different ways to arrive to these measurement,

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but we commonly use the body size as patient's body.

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You could also use the limb body mass

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or the body surface area.

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So now we're gonna see some examples.

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This is a case of FDG Petina patient

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with diffuse malignancy involving bone,

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and as we will see, uh, novel disease as well.

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But we're gonna center our

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topic into calculation of this activity.

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When you read PET ct, you will be able to create regions

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of interest and each software will give you several options.

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In my case, I can just select with this button,

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you will be able to control how big

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or how small your region of interest is

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and you could either select it

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as a circle in a single image

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or you'd be able to create a sphere.

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As you can see, my region

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of interest includes this abnormality in the anterior

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mediastinum, but it also is a sphere

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that way I make sure

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that I include the entire lesion in my calculation.

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We get several measurements

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and you can select how much or how little you want to see.

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But the one that is most commonly used

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for PET CT is SUV max.

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What does that mean?

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SUV max is the highest value within a voxel

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that is included in your region of interest

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or volume of interest independently of the size.

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So whether you include more

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or less, it will tell you what is the pixel

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with highest uptake.

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This will be obviously more susceptible to noise as noise

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and scatter activity may also give you counts.

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The other measurement that we less commonly use

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Is SUB mean this incorporate all the information from the

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multiple boxes that are included in your region of interest

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or volume of interest.

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And it is less sensitive to image noise

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but it will depend on your region heavily and

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therefore is less commonly used.

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We're gonna see some examples in this case

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with the anterior mediastinal mass you can see

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that there is an intense uptick

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peripherally less uptick in the center.

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And when I place my ROII normally get

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a little cross where it tells me where is the pixel

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with highest uptake

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and this would be the one that has an SUV max of 13.6.

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Look how my mean is 4.26.

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Let's move on that same ROI to another area

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of the body without changing the size.

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And look how the values have changed.

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Now we have an SUV max of 2.2

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and an SUV mean of 0.5, so you can see

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how things change when you change your ROIs.

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Let's make the ROI smaller, for instance.

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Let's place it here where you have an SUV max of 10.5

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and an SUV mean of 4.2.

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Again, the software is telling me where is the pixel

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with highest uptake

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and if I include that no matter where it is, if I move it

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around, my SUV max is not changing.

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But my SUV mean is

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because within the ROI I'm averaging different

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amount of activity.

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In this case, I include more non FDG AVID tissue

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and when I include more FDG Avid tissue, my numbers go up.

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So the most consistent value would be the SUV max.

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The only thing is to make sure that the entire lesion,

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or at least visually you can select the area

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of highest uptake.

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It's included in your region of interest.