Collateral Ventilation Quantification Using Xenon-enhanced Dynamic Dual Energy CT

Abstract

Purpose: This study was conducted to evaluate whether the difference in the degree of collateral ventilation between canine and swine models of bronchial obstruction can be detected using xenon-enhanced, dynamic dual energy technique of dual source CT. Through this study, we wanted to evaluate the feasibility of xenon-enhanced, dynamic dual energy technique of dual source CT for the quantification of collateral ventilation. Methods: Eight adult Mongrel dogs (25~30 kg) and six pigs (25~30kg) were studied under general anesthesia. With fluoroscopic guidance, the posterior segmental bronchus of the caudal lobe was occluded with 11.5 mm standard occlusion balloon catheter. Dynamic dual energy scanning (51 eff. mAs/213 eff. mAs at 140 kV/80 kV) was performed with dual source CT (Somatom Definition, Siemens) at a 12-second interval for 2 minute washin period and 24-second interval for 3 minute washout period while animals were mechanically ventilated via an endotracheal tube (60% xenon). CT images and xenon maps were generated using dedicated software. Ventilation parameters of magnitude (A value), maximal slope, velocity (K value), and time-to-peak enhancement (TTP) were calculated from dynamic xenon map using exponential function of Kety model. Results: Pigs showed significant lower maximal enhancement in the occluded than in the patent parenchyma (8.3 ± 1.1 HU vs. 41.3 ± 5.9 HU, p =0.027) but dogs did not show any difference (44.4 ± 8.1 HU vs. 47.2 ± 6.0 HU, p =0.123). Bigger between-parenchyma difference in A value was observed in pigs than in dogs (absolute difference, -33.0 ± 5.0 HU vs. -2.8 ± 7.1 HU, p =0.001

normalized percentage difference, -79.8 ± 1.8% vs. -5.4 ± 16.4%, p =0.0007). Mean values of maximal slopes in both periods significantly decreased in the occluded parenchyma only in pigs (maximal slopewashin, 4.7 ± 1.9 vs. 6.3 ± 2.8 in dogs, p =0.068

maximal slopewashout, -10.6 ± 2.8 vs. -8.6 ± 2.8 in dogs, p =0.092

maximal slopewashin, 1.0 ± 0.2 vs. 5.1 ± 1.5 in pigs, p =0.027

maximal slopewashout, -1.6 ± 1.4 vs. -10.2 ± 1.7 in pigs, p =0.028). Between-parenchyma absolute and normalized percentage differences in maximal slopes were greater in pigs than in dogs but statistical difference reached only in the washin period (all, p <0.05). K values of both periods were not different in dogs (p =0.892). One the other hand, in pigs, significant difference was found only in washin period (0.0029 ± 0.0006 sec-1 for occluded vs. 0.0039 ± 0.0003 sec-1for patent, p =0.027). While TTP was not significantly different between the occluded and patent parenchyma in dogs (p =0.892), TTP was markedly delayed in the occluded parenchyma in pigs (absolute difference, 212 ± 53.5 s vs. 140 ± 9.8 s, p =0.027

normalized percentage difference, 51.1 ± 34.4% vs. 6.8 ± 33.5%, p =0.013). Conclusions: Xenon-enhanced, dynamic dual energy technique of dual source CT allows quantifying collateral ventilation and detecting its difference between canine and swine models of bronchial obstruction.