Dual-energy computed tomography derived pulmonary blood volume: association with pulmonary blood flow

Distribution of ventilation and pulmonary perfusion are the major determinants of pulmonary gas exchange. To study and compare strategies of mechanical ventilation in respiratory research accurate and high-resolution methods are needed to derive distribution of ventilation and perfusion with minimal additional intervention or radiation allowing repeated measurements. Dual-energy computed tomography (DECT) is an imaging technique allowing for the derivation of regional pulmonary perfused blood volume, as a surrogate for pulmonary perfusion (PP_DECT). Here accuracy of PP_DECT is evaluated in comparison to pulmonary blood flow measured with fluorescence-labeled microspheres (PP_FLM). Its feasibility of repeated measurements is evaluated.

Agreement between PP_FLM and PP_DECT was assessed by regression as well as Bland-Altman analysis in three anesthetized pigs using DECT and fluorescence labelled microspheres, respectively. Measurements were performed in two-lung and, after right sided thoracotomy, at one-lung ventilation with inhaled nitric oxide. PP_FLM and PP_DECT were assessed in three different regions of interest (ROI): the right (non-ventilated) and left (ventilated) upper and lower lung, yielding a total of 45 paired measurements over four hours. Persistent iodine accumulation was assessed by additional DECT scans before each contrast administration.

Regression analysis revealed a good overall association (R2 = 0.81) between PP_FLM and PP_DECT, with PP_DECT substantially overestimating PP_FLM up to 30%, with limits of agreement of -18 and 18%, Low PP_FLM was underestimated, while high PP_FLM was overestimated by PP_DECT, indicating a higher sensitivity of the later. Changes of PP_DECT and PP_FLM had a concordance of 69.4% for all measurements. Agreement and concordance were highest in ventilated and lowest in non-ventilated ROIs. No persistent iodine enhancement was detected in the lung parenchyma after repetitive measurements per hour.

Dual-energy CT based measurement of pulmonary perfusion shows promising results indicating its feasibility in translational research on strategies of mechanical ventilation.