Nitrogen-13-labeled ammonia for myocardial imaging

Area of Science:

• Nuclear Medicine
• Cardiology
• Medical Imaging

Background:

• Nitrogen-13 ammonia (13NH4+) is a cyclotron-produced radiotracer with a short half-life (10 min).
• Regional myocardial uptake of 13NH4+ correlates with tissue perfusion in animal models.
• 13NH4+ is rapidly cleared from circulation, with extraction by various organs including the myocardium.

Purpose of the Study:

• To evaluate cyclotron-produced nitrogen-13 ammonia (13NH4+) as a myocardial perfusion imaging agent.
• To establish the efficacy of 13NH4+ for assessing regional myocardial perfusion in patients with heart disease.

Main Methods:

• 13NH4+ was administered intravenously and imaged using a scintillation camera with specialized collimators.
• Reproducible, high-quality myocardial images were obtained after overcoming initial technical challenges.
• Positron annihilation irradiation (511 keV) from 13N was utilized for imaging.

Main Results:

• Normal myocardial images exhibited a homogeneous "doughnut" configuration.
• Patients with ischemic and valvular heart disease showed a high incidence of localized perfusion defects.
• Sequential studies in acute myocardial infarction patients correlated perfusion changes with clinical course.

Conclusions:

• Myocardial imaging with 13NH4+ and a scintillation camera is a valid, noninvasive method for assessing regional myocardial perfusion.
• This technique is particularly suitable for sequential studies in acute cardiac patients.
• Coincidence imaging offers tomographic and potentially quantitative assessment of myocardial 13NH4+ uptake.