Purpose: To evaluate whether the extent of COVID-19 pneumonia on CT scans using quantitative CT imaging obtained early in the illness can predict its future severity .
Methods: We conducted a retrospective single-center study on confirmed COVID-19 patients between January 18 , 2020 and March 5 , 2020 . A quantitative AI algorithm was used to evaluate each patient's CT scan to determine the proportion of the lungs with pneumonia (VR) and the rate of change (RAR) in VR from scan to scan . Patients were classified as being in the severe or non-severe group based on their final symptoms . Penalized B-splines regression modeling was used to examine the relationship between mean VR and days from onset of symptoms in the two groups, with 95% and 99% confidence intervals .
Results: Median VR max was 18.6% (IQR 9.1–32.7 %) in 21 patients in the severe group, significantly higher (P <0.0001) than in the 53 patients in non-severe group (1.8% (IQR 0.4–5.7 %) ). RAR was increasing with a median RAR of 2.1% (IQR 0.4–5.5 %) in severe and 0.4% (IQR 0.1–0.9 %) in non-severe group, which was significantly different (P <0.0001). Penalized B-spline analyses showed positive relationships between VR and days from onset of symptom . The 95% confidence limits of the predicted means for the two groups diverged 5 days after the onset of initial symptoms with a threshold of 11.9% . Conclusion: Five days after the initial onset of symptoms, CT could predict the patients who later developed severe symptoms with 95% confidence.