CARDIAC POSITRON EMISSION TOMOGRAPHY Flashcards
What is positron emission tomography?
A technique that uses positrons, which are positively charged particles, emitted from unstable atoms to generate images through annihilation reactions that produce gamma photons.
The photons are captured by a PET scanner and transformed into images via sophisticated electronics and software.
Which are the two most common PET radiopharmaceuticals used for myocardial perfusion imaging?
Rubidium-82 (Rb-82) and nitrogen-13 (N-13) ammonia.
An example of an N-13 ammonia PET stress test is provided in the text.
What are the characteristics of Rb-82?
Monovalent cation analog of potassium, commercially available as a strontium-82 generator, physical half-life of 75 seconds, extracted by myocardial cells through Na/K/ATPase pump, adult radiation dose varies from 1.75 to 7.5 mSv.
What are the characteristics of N-13 ammonia?
Extractable myocardial perfusion tracer, 10-minute half-life, requires an on-site cyclotron, retained in myocardial tissue as N-13 glutamine, adult radiation dose approximately 1.4 mSv.
What are the advantages of PET myocardial perfusion imaging over single-photon emission computed tomography?
- More sensitive (93%) and specific (92%)
- Cost effective
- Lower radiation dose to the patient
- Allows for absolute quantification in myocardial blood flow (MBF) in mL/min/g of tissue.
Can a PET myocardial perfusion study show severe ischemia while a coronary angiogram shows only nonobstructive coronary artery disease?
Yes, due to the weak and nonlinear correlation between stenosis severity and coronary flow reserve (CFR).
How is coronary flow reserve determined on a PET scan?
CFR is a ratio of maximum MBF to baseline MBF at rest in a coronary artery, derived from radionuclide activity data collected during vasodilator stress and resting PET scans.
What is the relationship between fractional flow reserve and coronary flow reserve?
FFR is the invasive gold standard for assessing coronary arterial stenosis significance, while CFR is the noninvasive gold standard; low CFR correlates with low FFR but they are not directly comparable.
Can CFR (or MFR) be incorporated into routine clinical decision making?
Yes, CFR or MFR adds robust diagnostic and prognostic information to myocardial perfusion PET scan images.
What is the radiopharmaceutical used in cardiac PET for the assessment of myocardial viability?
F-18 fluorodeoxyglucose (FDG).
What is meant by ‘glucose loading’ when performing a viability F-18 FDG cardiac PET?
Administering an oral or intravenous glucose load to promote accumulation of F-18 FDG in viable myocardial tissue, enhancing its uptake.
What is the most common approach to preparing a nondiabetic patient for FDG myocardial viability PET scan?
Fasting for 6 to 12 hours, followed by 25 to 100 g of oral glucose and supplemental intravenous insulin as needed.
What are common approaches to preparing a patient with diabetes for FDG myocardial viability PET scan?
- Oral glucose loading protocol with IV dextrose loading
- Euglycemic hyperinsulinemic clamping
- Administration of acipimox.
What is meant by perfusion/metabolism ‘mismatch’ on cardiac PET viability imaging?
An area of decreased perfusion demonstrating normal or increased FDG uptake, indicating viable hibernating myocardium.
Are there any other tracers that can be used for PET cardiac imaging?
- C-11 acetate (Krebs cycle)
- C-11 palmitate (fatty acid metabolism)
- C-11 lactate (myocardial lactate utilization)
- C-11 phenylephrine (presynaptic catecholamine uptake)
- F-18 fluorodopamine (presynaptic sympathetic function).
