N-13 AMMONIA

Although currently in limited supply due to the location proximity needed for conventional cyclotrons, 13N-ammonia is well understood and recognized as a gold standard for cardiac perfusion imaging. It is used at prominent cardiac programs at Mayo Clinic, Brigham & Women’s, Massachusetts General, UCLA, and the University of Texas.

N-13 AMMONIA CARDIAC PET RADIOPHARMACEUTICAL

N-13 Ammonia imaging offers many advantages over the dominant 99mTc-SPECT radiopharmaceutical, as well as another cardiac PET tracer, 82Rb-chloride. The table below highlights the differences between N-13 Ammonia and 82Rb-chloride.

Tracer Comparison

N-13 Ammonia, due to the low mean positron length associated before the proton annihilates, has been shown to provide clearer images potentially allowing for an improved diagnostic certainty. The following PET scan images is an example 1N-13 Ammonia compared to 82Rb-chloride.

Physical properties 13N-ammonia 82Rb-chloride
Half life (min) 9.97 1.27
Positron decay 100% 95.5%
Positron energy (MeV) 1.19 95.5%
Positron range (mm) 0.57 2.60
System Resolution (mm) 6.03-6.15 6.54-8.56
Effective radiation dose per study (msv) 1.5 3.8
Raw material High Purity O-16 water and methane gas Sr-82/Sr-85
Supplied Unit Dose Generator
Physiological properties 13N-ammonia Rest flow 82Rb-chloride
Physiology Diffusible/retained Extracted/retained
Rest Stress Rest Stress
Extraction fraction 0.98 0.93 0.70 0.40
Retention fraction 0.87-0.97 0.56-0.65 0.47-0.55 0.27-0.28
deKemp et. al. "Will 3-dimensional PET-CT enable the routine quantification of myocardial blood flow?" J. Nucl Cardiol 2007; 14:380-97. Sabin J Nucl Med 2008; 49:1555-1563

Tracer Comparison Example Images

Abnormal N-13 Ammonia PET from a patient with a 90% right coronary artery stenosis
Abnormal 82Rb PET from a patient with a 90% Proximal left anterior descending artery stenosis
Natazota et al. “Myocardical perfusion imaging with PET” Imaging Med. 2013 February 1; 5(1): 35-46.

Example Rest/Stress Protocol

Protocols for 13N-ammonia imaging can be as efficient as 82Rb-chloride if a low dose / high dose protocol is used.

Rest scan
Pharmaceutical stress
Stress scan
0 min
Scan
complete
30 min

Delay of at least 18 min between injection. This is necessary in order to insure rest contamination of less than 12%, which is consistent with a conventional rest/stress 99mTc myocardial perfusion study protocol.

  • 1 min CT
    transmission
    scan
  • Rest 9 mCi
    13N ammonia
    injection
    3 min
  • 2.5 min
    dynamic
    scan (CFR)
  • 5 min
    gated rest
    emission scan
  • Stress
    agent
    injection
  • Stress 20 mCi 13N
    ammonia
    injection
    21 min
  • 2.5 min
    dynamic
    scan (CFR)
  • 5 min
    gated stress
    emission scan
  • 1 min CT
    transmission
    scan

N-13 TREADMILL PET

The longer half-life of N-13 A-ammonia can allow for patients to be treadmill exercised as an alternative to pharmacologic stress. This provides additional imaging options for your cardiac PET program.

Recent studies utilizing treadmill N-13 A-ammonia stress testing have demonstrated:

  • Reliable diagnostic accuracy and image quality in obese and non-obese patients. 1
  • Annual event rate is consistent with previously published SPECT and PET data. 2
  • Produces larger, more severe defects compared to dipyridamole stress. 3

References & Articles

References

  1. Aggarwal NR, Drozdova A, Askew JW, Kemp BJ, Chareonthaitawee P. Feasibility and diagnostic accuracy of exercise treadmill nitrogen-N-13 Ammonia PET myocardial perfusion imaging of obese patients. Journal of Nuclear Cardiology. 2015 Dec 1;22(6):1273-80.
  2. Chow BJ, Al Shammeri OM, Beanlands RS, Chen L, DaSilva J, Ruddy TD. Prognostic value of treadmill exercise and dobutamine stress positron emission tomography. Canadian Journal of Cardiology. 2009 Jul 1;25(7):e220-4.
  3. Chow BJ, Beanlands RS, Lee A, DaSilva JN, Alkahtani A, Ruddy TD. Treadmill exercise produces larger perfusion defects than dipyridamole stress N-13 ammonia positron emission tomography. Journal of the American College of Cardiology. 2006 Jan 17;47(2):411-6.

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