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The Effects of Radiation Dose and Computed Tomography Manufacturer on Measurements of Lung Densitometry

¹James Hogg iCAPTURE Centre for Cardiovascular and Pulmonary Research, St. Paul's Hospital ²Department of Radiology, Vancouver General Hospital ³British Columbia Cancer Agency; Vancouver, British Columbia, Canada

harvey.coxson{at}vch.ca

Abstract

BackgroundTo evaluate the effect of radiation dose and scanner manufacturer on quantitative CT measurements of lung morphology in smokers.

MethodsLow and high dose inspiratory multi-slice CT scans were obtained in 50 subjects at an approximate six-month interval (0.5 ± 0.2 years). In another 30 subjects, multi-slice CT scans were acquired first using a GE LightSpeed Ultra followed 1.2 ± 0.4 years later by a Siemens Sensation 16 scanner. Custom software was used to measure lung volume, mass, mean density, and the extent of emphysema using threshold cut-offs of -950 -910, and -856 HU and the lowest 15^th and 5^th percentile points.

ResultsThe change in x-ray dose significantly affected measurements of emphysema assessed using mean lung density, threshold or percentile methods. There were also interactions between dose and total lung volume for all the measurements except the -950 HU threshold and lowest 5^th percentile point. These two emphysema measurements suggest that there is more emphysema in the CT scans obtained using a lower x-ray dose. Only the mean lung density and -856 HU threshold showed significant effects between CT scanner manufacturer and interactions between total lung volume and scanner. All other measures of lung structure were not different between the two CT scanners.

ConclusionCT measurements of very low density lung structures are significantly affected by radiation dose, but less sensitive to the lung volume. Image acquisition parameters including radiation dose and scanner type, and the subject's breath size should be standardized to estimate emphysema severity in longitudinal studies.

Key Words: Emphysema • Computed tomography • Radiation dose • Lung expansion