Presentation Sam

7/30/2019 Presentation Sam

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PET/CTBy Sam McNulty



What is PET/CT

An imaging modality that allows theclinician to better differentiate benignvs malignant structural abnormalities

seen on CT as well as see possiblemalignancies where no structuralabnormalities are seen.



PET

Stands for positron emissiontomography

Fluorine-18-deoxyglucose (FDG), aradionuclide labeled glucoseanalogue is injected and the pt isimaged



Indications

Breast cancer: staging of distant metastasis, restaging,and monitoring response to treatment (when a change intherapy is anticipated based on results)

Cervical cancer: staging as adjunct to conventionalimaging

Colorectal cancer: diagnosis, staging, and restaging Esophageal cancer: diagnosis, staging, and restaging Head and neck cancer (non-thyroid, non-CNS): diagnosis,

staging, and restaging Lymphoma: diagnosis, staging, and restaging



Indications con’t

Melanoma: diagnosis, staging, and restaging Non small cell lung cancer: diagnosis, staging, and

restaging Solitary pulmonary nodules: characterization Follicular cell thyroid cancer: restaging of recurrent or

residual disease previously treated by thyroidectomy andradioiodine ablation in the setting of serum thyroglobulin> 10 ng/ml and a negative I-131 whole body scan

Myocardial viability: primary or initial diagnosis orfollowing an inconclusive SPECT prior to revascularization

Refractory seizures (brain): pre-surgical evaluation only



How does it work?

In the FDG decay process, positrons are emitted. When apositron is emitted it travels for a short distance from thesite of origin (on the order of 1-3 millimeters) graduallylosing energy to the tissue through which it passes. Whenmost of the positron’s kinetic energy has been lost, itundergoes a process called annihilation. In annihilation, the

positron reacts with an electron in the immediate area andthe result is the emission of two very high energy (511 keVeach) photons. The two 511 keV photons are emitted inopposite directions at approximately 180 degrees from eachother. These two photons interact with the PET detectorring at near opposite sites which define a line within thebody along which the annihilation occurred. With computerprocessing, this line between the two emitted photonspermits fairly precise localization of the annihilationreaction and thus defines a tissue site in the body wherethe positron emission occurred (i.e. an area of FDGactivity).



Huh?

Malignant cells take inherently have ahigher metabolism than non-malignantcells. They have a higher mitotic rate as

well as more ineffecient aerobicmetabolism leading to more anaerobicmetabolism

Through these mechanisms they will take

up the FDG at a faster rate and this willcan be seen on the scan as the FDGdecays.



PET/CT

PET and CT scans are now often done atthe same time.

The CT and PET data sets are fused or “coregistered” electronically by the

scanner’s computer system and presentedto the interpreter on a work station. Thedata can then be simultaneously andinteractively viewed as CT data, PET data,and superimposed CT and PET data in anypercentage combination of these data setsdesired (e.g. 100% PET data, 100% CTdata, 50% CT / 50% PET data).



PET/CT

Doing both scans at the same timeoffers the advantage over just thePET scan alone because the CT gives

exquisite anatomic detail as well asphysiologic information.





Fused PET/CT images



SUV

When a PET camera is appropriatelycalibrated, it is able to assess the amountof FDG activity per volume(millicuries/millileter or mCi/mL) of tissueand this can be expressed in “SUV” units

SUV=Mean region of interest activity(mCi/mL) =administered activity(mCi)/body weight (g) expressed in g/mL

SUV over 2.5 is considered suspicious formalignancy



Limitations of PET/CT

FDG is not cancer specific and willaccumulate in any areas of high rates of metabolism and glycolysis.

Therefore, increased uptake can be

expected in all sites of hyperactivity at thetime of FDG administration (e.g. musclesand nervous system tissues); at sites of active inflammation or infection (e.g.sarcoidosis, arthritis, infection etc.); andat sites of active tissue repair (e.g.surgical or traumatic wounds, healingfractures, etc.).



Brain/CNS

Brain tissue is always highly metabolicallyactive so detection of brain malignancies,particularly in gray matter, is limited withFGD PET.

Hypometabolism is also typical inepileptogenic foci during the interictalperiod. FDG activity may also bedecreased in one or bothfrontotemporoparietal associationcomplexes in Alzheimer’s dementia.

http://www.med-ed.virginia.edu/courses/rad/PETCT/Interpretation.html








Cardiac

When compared to conventionalSPECT imaging, PET/CT usingRubidium- 82 coupled with a 64-slice

CT scanner is a faster, easier, andmore accurate method to measuremyocardial blood flow.



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