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Heterogeneity of regional nitrogen 13-labeled ammonia tracer distribution in the normal human heart: Comparison with rubidium 82 and copper 62-labeled PTSM

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Recent reports on13N-labeled ammonia (13N-ammonia) positron emission tomographic (PET) imaging have suggested a relative reduction of measured tracer activity in the posterolateral wall. Such inhomogeneity of tracer distribution could potentially affect accuracy for detection of disease. The aim of this study was to compare the regional distribution of13N-ammonia with82Rb and62Cu-labeled PTSM (62Cu-PTSM) to identify tracer-specific patterns that may be important in the clinical interpretation of cardiac flow studies.

Methods and Results

Twenty-eight healthy volunteers underwent PET imaging at rest with either13N-ammonia (n=14),82Rb (n=8), or62Cu-PTSM (n=6). Eight subjects given13N-ammonia also underwent imaging after adenosine. Activity measured in the posterolateral wall on transaxial images was significantly lower than in the septum for13N-ammonia, both at rest (p<0.005) and after adenosine (p<0.05). No differences were detected for82Rb or62Cu-PTSM. The septum/posterolateral wall activity ratios for13N-ammonia,82Rb, and62Cu-PTSM were 1.15±0.07, 1.00±0.06, and 0.97±0.08, respectively (p<0.001). Regional analysis of image data showed the percent of maximal activity data for13N-ammonia in the lateral wall to be less than that of other regions (p<0.001) and in the inferior wall to be greater than in the anterior and lateral walls (p<0.001). For62Cu-PTSM, activity in the inferior wall was greater than that in other regions (p<0.005). No regional differences were detected for82Rb.


The relatively increased wall activity with13N-ammonia and62Cu-PTSM is most likely due to cross-contamination of activity from the liver. The significant reduction in activity in the lateral wall with13N-ammonia, which persists after adenosine, is most likely related to regional heterogeneity in13N-ammonia retention and may reflect regional differences in metabolic-trapping mechanisms for13N-ammonia. Further investigation is required to elucidate the underlying mechanism of this phenomenon. Reduced tracer retention in the lateral wall segment as a normal variant must be considered when evaluating clinical13N-ammonia PET studies.

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Author information

Correspondence to Rob S. B. Beanlands MD or Markus Schwaiger MD.

Additional information

This work was carried out during the tenure of Dr. Schwaiger as an established investigator of the American Heart Association, Dallas, Texas, and was supported in part by National Institutes of Health grant RO1HL41047-01. Dr. Beanlands was a research fellow supported by the Heart and Stroke Foundation of Canada (Ottawa, Canada) until June 30, 1991, and by the Medical Research Council of Canada (Ottawa, Canada) Centennial Fellowship Award from July 1, 1991, to Sept. 30, 1992. Dr. Muzik was supported in part by the Austrian Erwin Schroedinger Foundation Project No. J0473-MED (Vienna, Austria).

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Beanlands, R.S.B., Muzik, O., Hutchins, G.D. et al. Heterogeneity of regional nitrogen 13-labeled ammonia tracer distribution in the normal human heart: Comparison with rubidium 82 and copper 62-labeled PTSM. J. Nucl. Cardiol. 1, 225–235 (1994). https://doi.org/10.1007/BF02940336

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Key Words

  • nitrogen 13-labeled ammonia
  • rubidium 82
  • copper 62-labeled PTSM
  • positron emission tomography
  • myocardium
  • retention