Comparability of Quantifying Relative Lung Ventilation with Inhaled ^99mTc-Technegas and ¹³³Xe in Patients Undergoing Evaluation for Lung Transplantation

^99mTc-Technegas was recently approved by the U.S. Food and Drug Administration as a radiopharmaceutical for ventilation scintigraphy. However, there are currently no data comparing the quantification of relative lung ventilation with ^99mTc-Technegas with that performed using the standard approach with inhaled ¹³³Xe. Methods: We performed a secondary analysis of data from prospectively recruited participants in a phase 3 trial undergoing evaluation for lung transplantation who received both ¹³³Xe and ^99mTc-Technegas ventilation imaging. The ¹³³Xe and ^99mTc-Technegas images were analyzed asynchronously using semiautomatic segmentation to extract the relative lung ventilation percentages. The anterior and posterior ^99mTc-Technegas images were analyzed to derive 3 sets of relative ventilation percentages (posterior, anterior, and geometric mean data) and compared with the values from posterior ¹³³Xe images. We evaluated for correlation and agreement between the relative lung ventilation percentages obtained using these 2 radiopharmaceuticals. Results: In a cohort of 74 participants, we found a strong positive correlation in the relative lung ventilation quantified using ¹³³Xe with that using ^99mTc-Technegas. A high level of agreement was demonstrated on the Bland–Altman plot comparing the 2 imaging modalities. Seventy-two of 74 participants (97.3%) had their relative ventilation percentage measurements within 615% for ¹³³Xe and ^99mTc-Technegas. The differences in relative ventilation measurements were within the 95% CI limits of the mean for 70 of 74 participants (94.6%) and within a narrower 610% threshold for 68 of 74 participants (91.9%), again reflecting the comparability of the 2 techniques. The strongest correlation coefficient (r 5 0.79) was observed between the relative ventilation percentages obtained from ¹³³Xe and posterior ^99mTc-Technegas images. The geometric mean method had a slightly lower but still comparable correlation (r 5 0.77), and as expected, the correlation with the anterior ^99mTc-Technegas images was worst (r 5 0.70). Conclusion: We showed a strong positive correlation and high agreement between the relative lung ventilation percentages obtained using ¹³³Xe and ^99mTc-Technegas. These data provide important clinical evidence supporting the use of ^99mTc-Technegas for quantification of relative lung ventilation.