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All right. Hello and welcome to Noon conference hosted by MRI online.

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In response to the changes happening around the world right now and the

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shutting down of in person events, we have decided to provide free noon

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conferences to all radiologists worldwide. Today we're joined by Dr. Lacey

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McIntosh. She is an assistant professor of radiology at UMass Medical School

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and specializes in cancer and molecular imaging. She currently serves as

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the director of oncology imaging at UMass Memorial Healthcare. She is teaching

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and working with residents. Just a reminder that we will have time at

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the end of the session for a Q&A part of that and you

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can feel free to use the Q&A feature to ask your questions.

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We'll get to as many as we can before our time is up.

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That being said, thanks for joining us today, Dr. McIntosh. I'll let you

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take it from here. Wonderful. Thank you for having me.

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This is a great program. I've myself logged into a couple of

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the Noon conferences to learn from some of these wonderful colleagues of

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ours. I'm coming to you guys today from Massachusetts, but

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I see from the participant list it looks like we have people from

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all over the world here, which is really

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a cool way to get the radiology or people interested in radiology community

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together. Thank you for having me. Today I'm gonna talk about pulmonary

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nodule characterization, diagnosis and staging. Really focusing on the pulmonary

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nodules that end up becoming lung cancer. The two modalities we're really

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gonna be talking about are CT and PET CT. I think it's important

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that if you are looking at pulmonary nodules, either from

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a general radiologist standpoint or if you're a dedicated

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cardiothoracic or thoracic imager, or if you're more on the nuclear medicine

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side where you're reading PET CT, it's really important to integrate the

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imaging to come up with the best interpretation. You really can't read either

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of these in isolation and you have to synthesize all the information that

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you have together. We're gonna look at using the two modalities together

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to get the best guess of what's going on with these patients.

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Disclosures, I work as a consultant for BioClinica, which does clinical

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trial reads. And mostly for cancer drugs and novel tracers, but nothing

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pertinent to this lecture. In terms of lung cancer imaging, we use CT

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to really characterize size, morphology, look at local invasion of structures.

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It's always helpful when you're evaluating pulmonary nodule if you have

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multiple time points and you can assess the behavior over time.

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Sometimes when you see a pulmonary nodule just on one study,

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it's really hard to know, is this something that's been there forever and

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it's unchanged or has this been slowly growing?

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Is this something that wasn't there a week ago? Because that really changes

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your differential. Behavior over time is a big one.

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When you're using PET CT... Today I'm only speaking about 18 fluorodeoxyglucose

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or FDG, which is basically a radioactive sugar molecule and is taken up

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by any metabolizing cells. Obviously, we have normal tissues that are going

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to have uptake like brain, sometimes myocardium, the GI tract.

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We see it being excreted renally in the renal collecting system,

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but we also see it with other things like infection, inflammation,

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and cancers. While it's not specific for cancer, this is the primary tracer

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right now that we use to look at the metabolic activity of certain

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cancers. Depending on what your institution or your center does, the CT

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portion can range from being a full contrast enhanced diagnostic CT to

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really just a non contrast CT that's utilized for localization and has a

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somewhat limited diagnostic value. I think that majority of cases,

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these are being done with non contrast, so they're not a full diagnostic

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value. The other issues are that we have a very large field of

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view. The slices are often thick, five millimeters. And to avoid misregistration,

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we usually take the CT with a tidal breathing technique. And so,

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we don't ask the patient to take a breath and hold it.

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We might take the CT portion as they're breathing or basically just ask

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them to stop breathing. The reason for that is that we collect the

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PET data over 20 to 30 to 40 minutes, and patient's obviously breathing

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through all of that. If you have the patient take a deep breath

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and do the CT portion, then you're gonna have a lot of misregistration.

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And that's very important for pulmonary nodules, especially in the lower

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lobes. PET CT provides functional information about the metabolic activity

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of tissues. So, not only are you getting an idea of what your

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nodule is doing, but sometimes more importantly, we're looking for evidence

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of spread to the nodes regionally as well as distant metastatic disease.

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As I mentioned, this isn't specific for cancer, but a positive PET doesn't

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always equal cancer. There's false positives, infection, inflammation

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being some of those. And then, a negative PET doesn't always equal no

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cancer, so we can have false negatives as well. And one of the

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areas that we really think about that are with slow growing lung cancers

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and very small findings. Things that are larger are gonna be more FDG

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avid. And the reason for that is they have more cells with GLUT1 transporters,

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and so they're able to take up more tracer.

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Small findings just don't have as many cells, and so

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your accumulation is gonna be different. What you define as positive and

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negative has to be taken into perspective about size of your finding.

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One of the things that PET can be really useful for is

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it can be helpful when your anatomic information is limited. If you have

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an endobronchial lesion and you have post obstructive collapse, it can sometimes

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be really hard to tell where your tumor is. And if you're trying

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to figure out how to biopsy it or how suspicious it is,

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PET can be really, really helpful. This is an example from the literature,

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which is showing collapse of the right upper lobe. And you can actually

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see this right upper lobe bronchus is basically cut off and it's filled

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with something. Is it mucus and just post obstructive collapse from that,

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or is it actually tumor? We see on the PET CT that this

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is very FDG avid. It's right in the location we're expecting,

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and so mucus is not gonna do this. This is a tumor with

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post obstructive collapse. And so now we actually know the size of it,

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which is important for T staging. We know the location, which is really

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important for biopsy planning. It can give you a lot of information and

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be very helpful when the anatomy is challenging.

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Here's a case from our institution which is showing left lower lobe collapse.