text: Post Acute Sequelae of COVID 19 Pneumonia Six month Chest CT Follow up Background The long term post acute pulmonary sequelae of COVID 19 remain unknown Purpose To evaluate lung injury in patients affected by COVID 19 pneumonia at the 6 month follow up CT examination compared with the baseline chest CT examination Materials and Methods From March 19 2020 to May 24 2020 patients with moderate to severe COVID 19 pneumonia who had undergone baseline chest CT were prospectively enrolled at their 6 month follow up The CT qualitative findings semiquantitative Lung Severity Score LSS and the well aerated lung volume at quantitative chest CT QCCT analysis were analyzed The performance of the baseline LSS and QCCT findings for predicting fibrosis like changes reticular pattern and or honeycombing at the 6 month follow up chest CT examination was tested by using receiver operating characteristic curves Univariable and multivariable logistic regression analyses were used to test clinical and radiologic features that were predictive of fibrosis like changes The multivariable analysis was performed with clinical parameters alone clinical model radiologic parameters alone radiologic model and the combination of clinical and radiologic parameters combined model Results One hundred eighteen patients who had undergone baseline chest CT and agreed to undergo follow up chest CT at 6 months were included in the study 62 women mean age 65 years 12 standard deviation At follow up chest CT 85 of 118 72 patients showed fibrosis like changes and 49 of 118 42 showed ground glass opacities The baseline LSS 14 and QCCT findings 3 75 L and 80 showed excellent performance for predicting fibrosis like changes at follow up chest CT In the multivariable analysis the areas under the curve were 0 89 95 CI 0 77 0 96 for the clinical model 0 81 95 CI 0 68 0 9 for the radiologic model and 0 92 95 CI 0 81 0 98 for the combined model Conclusion At 6 month follow up chest CT 72 of patients showed late sequelae in particular fibrosis like changes The baseline Lung Severity Score and the well aerated lung volume at quantitative chest CT QCCT analysis showed excellent performance for predicting fibrosis like changes at the 6 month chest CT area under the curve 0 88 Male sex cough lymphocytosis and the well aerated lung volume at QCCT analysis were significant predictors of fibrosis like changes at 6 months demonstrating an inverse correlation area under the curve 0 92 RSNA 2021 See also the editorial by Wells and Devaraj in this issue 