Decreased Perfusion in the Lateral Wall of the Left Ventricle in PET/CT Studies with 13N-Ammonia: Evaluation in Healthy Adults

Abstract

This study evaluated the causes of the frequently observed decreased myocardial perfusion in the lateral wall of the left ventricle in PET/CT studies with (13)N-ammonia in healthy adults. Thirty-two adults who were undergoing PET/CT of the heart with (13)N-ammonia as part of a study of the effects of posttraumatic stress disorder in American Indians were included. Participants who had evidence of heart disease by a physician-administered questionnaire or by pharmacologic stress during the myocardial perfusion study were excluded. The ratio of counts in the lateral wall relative to the septum at stress and rest were compared with the degree of misalignment between the PET and CT images at the left border of the heart and at the right hemidiaphragm. No participant had evidence of heart disease. For the left heart border, 41% of participants showed misalignment at rest and 62% showed misalignment at stress. For the right hemidiaphragm, 28% showed misalignment at rest and 53% showed misalignment at stress. Among all participants, the decrease in lateral wall counts relative to the septum correlated with the degree of misalignment of the PET and CT images at the left heart border at rest using both average (P = 0.01) and maximum (P < 0.01) counts per pixel and at stress using maximum counts per pixel (P = 0.02) but not average counts per pixel (P = 0.14). There was also a correlation between the degree of misalignment of the PET and CT images at the left heart border and at the right hemidiaphragm at stress (P = 0.01) but not at rest (P = 0.09). The decreased counts in the lateral wall relative to the septum and the misalignment of the PET and CT images at the left heart border and at the right hemidiaphragm were all greater at stress than at rest (all P < 0.05). In those participants who had no misalignment of the PET and CT images at the left heart border, there was still a residual decrease in relative counts in the lateral wall at both stress and rest, using both average and maximum counts (all P < 0.05). Relative decreased counts in the lateral wall of the heart in PET/CT studies with (13)N-ammonia are commonly seen in healthy adults. The decreased counts in the lateral wall appear to be caused by an attenuation artifact from misalignment at the left border of the heart between the PET and CT images, possibly related to differences in respiratory motion during acquisition of the PET and CT images. In addition, there was a small, but significant, decrease in relative counts in the lateral wall even in participants without misalignment at the left heart border or at the right hemidiaphragm.