Spatial distribution and temporal changes of pulmonary thallium uptake in myocardial perfusion studies
Spatial distribution and temporal changes in pulmonary thallium uptake were assessed in 24 normal subjects and 35 patients with coronary artery disease (CAD). In studies carried out directly after stress and 3 h later, pulmonary T1 uptake was assessed as body surface area corrected absolute pulmonary uptake in the upper, middle and lower right lung regions, and in the total right lung and upper left lung. Pulmonary/myocardial (PM) uptake ratios for these 5 regions were calculated as mean pulmonary/mean background-corrected myocardial uptake. Additionally, wash-out was assessed for each region and for the myocardium. In normal subjects, the inital pulmonary T1 uptake, the PM ratios and T1 wash-out were greater in the lower lung regions than in the upper. In the late studies, no significant differences in T1 content or PM ratios were found among the regions. In patients with CAD, initial pulmonary T1 uptake and PM ratios were greater in the lower than in the upper regions, and higher than for the normal subjects in all pulmonary regions (P<0.001). T1 wash-out was significantly higher in the low and middle regions versus the upper region (P < 0.001) and higher in all regions than in normal subjects (P<0.001). In the late studies no significant differences in T1 content or PM ratios were found between any pulmonary regions. Pulmonary T1 content was, in all regions, higher in CAD than in normal subjects (P<0.01), as were the PM ratios (P<0.001). In conclusion, in normal subjects as well as in patients with CAD, pulmonary T1 uptake is greatest in the lower lung regions. Absolute pulmonary T1 uptake, PM ratios and pulmonary wash-out are greater in all lung regions in patients with CAD. Lower myocardial uptake may be the more important factor in producing the increased PM ratios in patients with CAD. Pulmonary redistribution is complete after 3–4 h. These characteristics strongly affect pulmonary T1 uptake ratios and wash-out assessments.