The relevance of CT densitometry decline in never and ex-smokers with alpha one antitrypsin deficiency (AATD) and chronic obstructive pulmonary disease (COPD) : a systematic review and validation study in untreated patients

CT densitometry is the method of quantifying emphysema using specialised software programs, and its ability to assess emphysema has been validated clinically and pathologically. However, the technique has yet to be standardised and its clinical utility remains unclear. The systematic review performed highlighted the strong relationship to clinically relevant parameters, but demonstrated that vast heterogeneity that exists between studies using CT Density. This heterogeneity was overcome when only studies using the same software program, reconstruction algorithm and slice thickness were meta-analysed. The variability the two leading software programs, PULMO and Pulmonary Workstation was calculated, and showed that where the same slickness and reconstruction algorithms were used, the two programs showed directly comparable results for volume and PD15. The difference between -910HU and -950HU is likely clinically negligible but requires further consensus, and the difference between different slice thicknesses will require adjustment. Analysis of CT scans performed within the Birmingham AAT registry confirmed the strong relationship between CT and lung function and quality of life measures. For the first time it was also shown that PD15 and -950HU whole lung are both predictive of mortality. Through a variety of methods the MCID for annual CT density decline was proposed as 2.89g/l/year.