Table 2. Comparisons and Correlations between Percentages of CT Right Pulmonary Vascular Volumes Quantified with Adaptive Attenuation Thresholds and Nuclear Medicine Right Lung Perfusion Percentages.

Adaptive Threshold	PAavg/2.50	PAavg/2.00	PAavg/1.75*	PAavg/1.63*	PAavg/1.50*	PAavg/1.25
CT right pulmonary vascular volume percentage (%)	67.2 ± 14.8	68.0 ± 15.3	68.7 ± 15.9	69.3 ± 16.2	69.7 ± 16.6	71.1 ± 17.2
p-value of paired t test	< 0.03	> 0.2	> 0.6	> 0.8	> 0.5	> 0.05
Pearson correlation coefficient	0.92	0.92	0.91	0.91	0.91	0.91
Mean absolute difference (%)	4.9	4.7	4.8	4.9	5.0	5.5

^*Optimal thresholds for CT pulmonary vascular volume ratio showing smallest mean absolute difference (≤ 5.0%), lowest level of statistically significant difference compared to reference values measured by lung perfusion scintigraphy, and highest Pearson correlation coefficient; PA_avg/2.50 PA_avg divided by 2.50, PA_avg/2.00 PA_avg divided by 2.00, PA_avg/1.75 PA_avg divided by 1.75, PA_avg/1.63 PA_avg divided by 1.63, PA_avg/1.50 PA_avg divided by 1.50, PA_avg/1.25 PA_avg divided by 1.25. PA_avg = average pulmonary artery enhancement