Dynamic single-slice CT estimates whole-lung dual-energy CT variables in pigs with and without experimental lung injury

John N Cronin,Anders Larsson,Göran Hedenstierna,Luigi Camporota,Minh C Tran,João Batista Borges,Federico Formenti,Douglas C Crockett,Andrew D Farmery

doi:10.1186/s40635-019-0273-y

Abstract

BackgroundDynamic single-slice CT (dCT) is increasingly used to examine the intra-tidal, physiological variation in aeration and lung density in experimental lung injury. The ability of dCT to predict whole-lung values is unclear, especially for dual-energy CT (DECT) variables. Additionally, the effect of inspiration-related lung movement on CT variables has not yet been quantified.MethodsEight domestic pigs were studied under general anaesthesia, including four following saline-lavage surfactant depletion (lung injury model). DECT, dCT and whole-lung images were collected at 12 ventilatory settings. Whole-lung single energy scans images were collected during expiratory and inspiratory apnoeas at positive end-expiratory pressures from 0 to 20 cmH2O. Means and distributions of CT variables were calculated for both dCT and whole-lung images. The cranio-caudal displacement of the anatomical slice was measured from whole-lung images.ResultsMean CT density and volume fractions of soft tissue, gas, iodinated blood, atelectasis, poor aeration, normal aeration and overdistension correlated between dCT and the whole lung (r2 0.75–0.94) with agreement between CT density distributions (r 0.89–0.97). Inspiration increased the matching between dCT and whole-lung values and was associated with a movement of 32% (SD 15%) of the imaged slice out of the scanner field-of-view. This effect introduced an artefactual increase in dCT mean CT density during inspiration, opposite to that caused by the underlying physiology.ConclusionsOverall, dCT closely approximates whole-lung aeration and density. This approximation is improved by inspiration where a decrease in CT density and atelectasis can be interpreted as physiological rather than artefactual.

Highlights

Dynamic single-slice Computed tomography (CT) is increasingly used to examine the intratidal, physiological variation in aeration and lung density in experimental lung injury
Lung injury model In four randomly chosen animals, a saline-lavage surfactant-depletion lung injury model was created using the technique of Lachmann [17] aiming for a Arterial partial pressure of oxygen (PaO2)/Inspired oxygen concentration (FiO2) (P/F) ratio of 150–200 mmHg measured at a positive end-expiratory pressure (PEEP) level of 5 cmH2O and FiO2 of 0.7
Mean CT density and volume fractional differences between Dynamic single-slice CT (dCT) and whole-lung dual-energy CT (DECT) Single-slice dCT correlated with whole-lung DECT measures for mean CT density and soft tissue, gas, iodinated blood, atelectatic, poorly aerated, normally aerated and overdistended volume fractions (Fig. 2)

Summary

Introduction

Dynamic single-slice CT (dCT) is increasingly used to examine the intratidal, physiological variation in aeration and lung density in experimental lung injury. Intra-tidal changes in lung aeration and atelectasis are common in animal models of the acute respiratory distress syndrome (ARDS) [1, 2] Quantifying such intra-tidal events is important as cyclical atelectasis remains one of the key pathophysiological mechanisms underlying ventilator-induced lung injury (VILI) [3]. Most studies examining these rapid changes have used a ‘single-slice’ dynamic CT (dCT) approach: a fixed. CT scanner field-of-view images a slice of the thorax over time, whilst the lung moves during ventilation [1, 4,5,6,7] This approach allows sufficient temporal resolution to study intra-tidal changes, but is blind to what occurs outside the field-of-view. As the regions around the hila contain a larger volume of both blood within major vessels and air within major bronchi, an artificial inspiratory-related increase in both atelectatic and hyperinflated regions may be expected

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