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So in this video we're gonna look at the technical aspects

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of PET CT imaging

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and we're gonna start defining what is PET ct?

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PET ct. It's a hybrid imaging system that combines

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functional and molecular imaging with morphologic imaging

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and it implies the use

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of radionuclides that we administer

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to the patient intravenously.

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And that allows us to see specific physiologic

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or pathological processes that are happening in the body

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but in vivo.

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So I'm showing this is a almost whole body picture

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of the pet system alone.

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Uh, and we can see that there are several organs

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and this is a labeled glucose.

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It's called FDG.

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This image will be combined to the CT

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that we will also acquire at the same time,

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and then the system will be able to show us a fuse image

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so we can correlate that an anatomically all the areas

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of abnormality seen on the PET portion.

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The advantages of PET imaging include that it's a system

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that has fairly good special resolution.

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It obviously, uh, evaluates the physiology of disease.

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We can calculate the degree

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of the tracer uptake compared to normal tissue.

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We can follow patients

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and see how disease is responding to treatment.

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And the other good advantage of PET CT as opposed

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to other techniques is that it gives us a good coverage

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and we can image the entire body in one study.

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What are the limitations?

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Well, because of the time that it's required

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to acquire the PET portion, it is not feasible

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that the patients hold their breath.

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So whenever we image the chest, for instance,

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the patients are breathing

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and that results in a little bit of breathing motion,

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which in most of the cases is not a problem,

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but it could be a limitation in certain occasions.

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So it's something to be aware of.

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The other thing is that the small lesions might not be seen

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on the PET portion or the CT

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because of the spatial resolution of the system.

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When we use, uh, CT is a low dose ct.

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Some systems have the capability

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of doing a high diagnostic ct, so

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that would be depend on the practice and your scanner.

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But in my experience, even the low dose CT is very good

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and it's enough to read p ct, uh, to a diagnostic level.

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Patient may move between the acquisition of the CT

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and the pet and that will result

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In some misregistration.

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The ability of detecting a small lesions will depend on the

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tracer and we will see several examples of that.

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Uh, later in the course, patients may have claustrophobia

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or anxiety, although, as I will show you,

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this system is a ring, but it's an open ring.

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We can have hardware artifacts

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and we can have some pitfalls that lead to, uh,

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limited study

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and we will also cover those uh, in the course.

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The radio nucleus that are used for PET imaging are

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positron emitters.

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This positron will decay

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and will release a positron,

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which is a positively charged

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particle that we have right here.

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This particle will move through the body

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and interact with the body,

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and at some point it will meet a free electron,

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which is a negatively charged particle.

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The result of this interaction will be the release

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of two photons

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with equal energy 511 kv

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in opposite directions.

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Along this line, what we're really imaging will be these

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photons that are released after the inhalation occurs.

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So PET imaging is based on

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what is called coincidence detection.

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As I have said, these photons will be released in opposite

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directions and our pet system is a ring scanner.

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This scanner has two components.

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One is the CT component

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and the other will be a ring of detectors

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that will detect these photons of 511 KUV.

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In order for the system to detect these photons have

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to be in a line of coincidence,

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and we have what is called a true coincidence.

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And this is when an event or an inhalation happens

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and the photons arrive along a line and they are detected

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and recorded as true events.

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But we have other events that happen that can lead to, um,

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a scatter and blurriness in the system.

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And these are the scatter coincidence in the

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random coincidence.

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In a scatter coincidence,

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both photons will be originated from the single event

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and will be detected,

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but one will go through Compton

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and will change a little bit

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direction and will be scattered.

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And so the system will detect

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that both photons have arrived,

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but the line of coincidence will be incorrectly assumed.

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Then we have the other event,

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which is the random coincidence in which

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there's two events happening and photons are released

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and they arrive to the ring.

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But the system will essentially take one photon from one

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event and another photon from another event

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and think that they come from the same line of coincidence.

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So all these happens

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and then it contributes to the quality of your image.