Consolidated lung on contrast-enhanced chest CT: the use of spectral-detector computed tomography parameters in differentiating atelectasis and pneumonia.

Objectives: To investigate the value of spectral-detector computed tomography (SDCT) parameters for the quantitative differentiation between atelectasis and pneumonia on contrast-enhanced chest CT.

Material And Methods: Sixty-three patients, 22 clinically diagnosed with pneumonia and 41 with atelectasis, underwent contrast-enhanced SDCT scans during the venous phase. CT numbers (Hounsfield Units [HU]) were measured on conventional reconstructions (CON) and the iodine concentration (C, [mg/ml]), and effective atomic number (Z) on spectral reconstructions, using region-of-interest (ROI) analysis. Receiver operating characteristics (ROC) and contrast-to-noise ratios (CNRs) were calculated to assess each reconstruction's potential to differentiate between atelectasis and pneumonia.

Results: On contrast-enhanced SDCT, the difference between atelectasis and pneumonia was significant on CON, C, and Z images (p < 0.001). On CON images, a threshold of 81 HU achieved a sensitivity of 93 % and a specificity of 95 % for identifying pneumonia, while C and Z images reached the same sensitivity but lower specificities of 85 % and 83 %. CON images showed significantly higher CNRs between normal lung and atelectasis or pneumonia with 30.63 and 27.69 compared to C images with 3.54 and 1.27 and Z images with 4.22 and 7.63 (p < 0.001). None of the parameters could differentiate atelectasis and pneumonia without contrast media.

Conclusions: Contrast-enhanced SDCT can differentiate atelectasis and pneumonia based on the spectral parameters C, and Z However, they had no added value compared to CT number measurement on CON images. Furthermore, contrast media is still needed for a differentiation based on quantitative SDCT parameters.