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Cardiac positron emission tomography


1

What is positron emission tomography?

  • A positron, as its name implies, is a positively charged particle that is ejected from the nucleus of an unstable atom. It is identical in mass to an electron. Strictly speaking it is “antimatter,” and very shortly after leaving the nucleus, it collides with an electron in what is called an annihilation reaction. This reaction generates two 511-keV gamma photons that are emitted almost diametrically opposite from each other. The energy of these photons is captured by a special positron emission tomography (PET) scanner, and through a sophisticated network of electronics as well as computer software and hardware, it is transformed into an image.

2

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 shown in Fig. 9.1 .

    Fig. 9.1, Nitrogen-13 ammonia cardiac positron emission tomography-computed tomography revealing inducible ischemia of left anterior descending territory as well as global subendocardial ischemia as demonstrated by the presence of transient ischemic dilatation. The multivessel nature of this patient’s coronary artery disease was corroborated by coronary flow measurements (not shown) where patient’s peak hyperemic stress flow was actually lower than resting coronary flow (coronary steal phenomenon).

3

What are the characteristics of Rb-82?

  • Rb-82 is a monovalent cation analog of potassium. It is commercially available as a strontium-82 generator. Its physical half-life is 75 seconds. It is extracted with high efficiency by myocardial cells through the Na/K/ATPase pump. The adult radiation dose from a Rb-82 myocardial perfusion scan (MPS) varies from 1.75 to 7.5 mSv.

4

What are the characteristics of N-13 ammonia?

  • N-13 ammonia is an extractable myocardial perfusion tracer, which due to its 10-minute half-life, requires an on-site cyclotron. It is retained in myocardial tissue as N-13 glutamine by the action of glutamine synthetase. The adult radiation dose from an N-13 ammonia MPS is approximately 1.4 mSv.

5

What are the advantages of PET myocardial perfusion imaging over single-photon emission computed tomography?

  • It is more sensitive and specific (93% and 92%, respectively).

  • It is cost effective. This is primarily due to a reduction in unnecessary coronary angiographies.

  • It results in lower radiation dose to the patient.

  • It allows for absolute quantification in myocardial blood flow (MBF) in mL/min/g of tissue.

6

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