Using dual energy CT Scans to analyse blood perfusion compensation following resection of cancerous lobes

Introduction

Comparison of pulmonary perfusion before and after lung resection may provide a better understanding of compensation phenomena and, more importantly, additional clinical information for the inclusion of patients in these surgeries. To evaluate the pulmonary perfusion mechanisms in patients with lung diseases (COPD, nodule…), we used a novel approach using Dual energy CT scan (DECT). The aim is to produce a perfusion profile in surviving lobes, before and after surgery, allowing to quantize and localize potential changes in blood perfusion.

Methods

The CLIPPCAIR prospective study enrolls patients undergoing pulmonary resection due to non-small cell lung cancer, with the majority having pulmonary comorbidities such as COPD. 30 patients from this study were examinated. CLIPPCAIR focuses on patients scheduled for resection, excluding those with COPD stages 3 or 4. Patients performed a FEV1 (Forced Expiratory Volume in 1 second), and a FVC (Forced Vital Capacity) to assess their respiratory performances. The recording of these measurements provides elements to determine the COPD GOLD. For each patient, a DECT with an iodine injection (350 mg/mL, Iomeron, Bracco Imaging) is achieved and reconstructed by GE Revolution (KvP switch between 80 and 140.200 mA). Iodine concentration and lung parenchyma density maps were then generated. Iodine concentration is used as a biomarker for blood concentration. Lung blood vessels are segmented using Machine Learning. Then, the blood concentration is measured in voxels located in alveolar and small vessel areas, i.e. non large vessels areas. The “large” vessels are those segmented by the ML algorithm, meaning a diameter larger than the voxel resolution, giving a cross-sectional area of 2.6 mm². This perfusion metric is plotted against the distance to the nearest blood vessel of cross-sectional area greater than 5 mm² (BV5) (figure 1). This is done before and after surgery in all remaining lobes. It is then possible to compare the perfusion profile of the lobes before and after the resection.

Results

Patients from the CLIPPCAIR cohort lost on average 21 % (standard deviation: 5.2) of their volume, while only showing a slight decrease of their DLCO and FEV1 performances, respectively 7.2 (6.7)% and 5.9 (5.5)%. While these metrics are not a complete picture of respiratory performances, their moderate decrease highlights the existence of compensation mechanisms in the remaining lobes. Indeed, we observe a statistically significant increase of 5.1 (1.6)% in iodine concentration -a proxy for blood perfusion- in the remaining lobes post surgery (p-value < 0.05).

Conclusion

Patients undergoing lung resection show much better DLCO and FEV1 than expected. We show that there is an increase in blood perfusion in the remaining lung parenchyma, which could explain this favorable outcome for the patients regardless of the spirometric profile of the patients.