CT quantification of interstitial lung abnormalities: a prospective comparison between supine and prone positions

To prospectively evaluate positional variability in quantitative CT (qCT)-derived measurements of interstitial lung abnormality (ILA) using the same-day supine and prone CT.

In this prospective study (February 2024-February 2025), participants with ILA underwent sequential non-contrast supine and prone CT scans using identical acquisition parameters. A commercially available deep learning-based software quantified fibrotic (reticulation and honeycombing) and nonfibrotic (ground-glass opacity) ILA components in accordance with Fleischner Society definitions. qCT differences between supine and prone measurements were assessed using paired t tests, Bland-Altman analysis with 95% limits of agreement (LOA), and concordance correlation coefficients (CCC).

Of 47 consented participants, 38 (mean age, 70.9 ± 6.4 years; 27 men) were included in the final analysis. Mean total ILA extent was greater on supine than on prone scans (1.76% vs 1.39%, p = 0.02), largely due to a greater extent of fibrotic ILAs on supine images (1.43% vs 1.12%, p = 0.007). The 95% LOA between supine and prone scans were -1.49% to 2.23% for total ILA extent, -0.97% to 1.58% for the fibrotic component, and -0.89% to 1.03% for the nonfibrotic component. Agreement between positions was moderate for the fibrotic component (CCC = 0.770), and poor for the nonfibrotic component (CCC = 0.431), with the lowest reproducibility observed in dependent lung zones.

The measurement variability of qCT result of ILA between supine and prone scans was approximately 1.9%, with moderate agreement for the fibrotic component but poor agreement for the nonfibrotic component between the same-day supine and prone CT scans.

Question Whether qCT-derived measurements of ILA are interchangeable between supine and prone CT scans remains unknown. Findings qCT measurements showed approximately 1.9% positional variability, with moderate agreement for fibrotic components but poor agreement for nonfibrotic components, especially in dependent lung zones. Clinical relevance Supine and prone scans should not be used interchangeably for qCT analysis of ILA. Consistent patient positioning is essential to ensure accurate longitudinal assessment.