Purpose: To prospectively investigate the effects of radiation dose and section thickness on quantitative multidetector computed tomographic (CT) indexes of pulmonary emphysema.
Materials and methods: The institutional review board approved this protocol. Written informed consent was obtained from all patients. Seventy patients (49 men, 21 women; age range, 38-79 years) referred for surgical resection of a lung tumor underwent multidetector CT with 4 x 1-mm collimation, 120 kVp, and 20 and 120 effective mAs. At each radiation dose, 1.25-, 5.0-, and 10.0-mm-thick sections were reconstructed at 10-mm intervals. From scans of the lobe or whole lung to be resected, relative areas (RAs) of lung with attenuation coefficients lower than nine thresholds and eight percentiles of the distribution of attenuation coefficients were compared with the histopathologic extent of emphysema, which was measured microscopically--by using the corrected mean interwall distance (MIWD) and the corrected mean perimeter (MP)--and macroscopically. Correlations between the data obtained by using attenuation thresholds and percentiles and the parameters macroscopic extent of emphysema, MIWD, and MP were investigated by using Spearman coefficients.
Results: The 1st percentile (r range, -0.394 to -0.675; P < .001) and attenuation coefficients of -980, -970, and -960 HU (r range, 0.478-0.664; P < .001) yielded the strongest correlations with macroscopic extent, MIWD, and MP, regardless of radiation dose or section thickness. The effects of radiation dose and section thickness on RAs of lung with attenuation coefficients lower than -960 HU (P = .007 and P < .001, respectively) and lower than -970 HU (P = .001 and P < .001, respectively) were significant. The effect of section thickness on the 1st percentile was significant (P < .001), whereas the effect of dose was not (P = .910).
Conclusion: At CT quantification of pulmonary emphysema, the tube current-time product can be reduced to 20 mAs, but both tube current-time product and section thickness should be kept constant in follow-up examinations.