Lung shrinking assessment on HRCT with elastic registration technique for monitoring idiopathic pulmonary fibrosis

Objectives Evaluation and follow-up of idiopathic pulmonary fibrosis (IPF) mainly rely on high-resolution computed tomography (HRCT) and pulmonary function tests (PFTs). The elastic registration technique can quantitatively assess lung shrinkage. We aimed to investigate the correlation between lung shrinkage and morphological and functional deterioration in IPF. Methods Patients with IPF who underwent at least two HRCT scans and PFTs were retrospectively included. Elastic registration was performed on the baseline and follow-up HRCTs to obtain deformation maps of the whole lung. Jacobian determinants were calculated from the deformation fields and after logarithm transformation, log_jac values were represented on color maps to describe morphological deterioration, and to assess the correlation between log_jac values and PFTs. Results A total of 69 patients with IPF (male 66) were included. Jacobian maps demonstrated constriction of the lung parenchyma marked at the lung base in patients who were deteriorated on visual and PFT assessment. The log_jac values were significantly reduced in the deteriorated patients compared to the stable patients. Mean log_jac values showed positive correlation with baseline percentage of predicted vital capacity (VC%) ( r = 0.394, p < 0.05) and percentage of predicted forced vital capacity (FVC%) ( r = 0.395, p < 0.05). Additionally, the mean log_jac values were positively correlated with pulmonary vascular volume ( r = 0.438, p < 0.01) and the number of pulmonary vascular branches ( r = 0.326, p < 0.01). Conclusions Elastic registration between baseline and follow-up HRCT was helpful to quantitatively assess the morphological deterioration of lung shrinkage in IPF, and the quantitative indicator log_jac values were significantly correlated with PFTs. Key Points • The elastic registration on HRCT was helpful to quantitatively assess the deterioration of IPF . • Jacobian logarithm was significantly reduced in deteriorated patients and mean log_jac values were correlated with PFTs . • The mean log_jac values were related to the changes of pulmonary vascular volume and the number of vascular branches .