Reprint of: Voxel-Wise Longitudinal Parametric Response Mapping Analysis of Chest Computed Tomography in Smokers

Abstract

Rationale and objectives: Chronic obstructive pulmonary disease is a heterogeneous disease characterized by small airway abnormality and emphysema. We hypothesized that a voxel-wise computed tomography analytic approach would identify patterns of disease progression in smokers.

Materials and methods: We analyzed 725 smokers in spirometric GOLD stages 0-4 with two chest CTs 5 years apart. Baseline inspiration, follow-up inspiration and follow-up expiration images were spatially registered to baseline expiration so that each voxel had correspondences across all time points and respiratory phases. Voxel-wise Parametric Response Mapping (PRM) was then generated for the baseline and follow-up scans. PRM classifies lung as normal, functional small airway disease (PRM^fSAD), and emphysema (PRM^EMPH).

Results: Subjects with low baseline PRM^fSAD and PRM^EMPH predominantly had an increase in PRM^fSAD on follow-up; those with higher baseline PRM^fSAD and PRM^EMPH mostly had increases in PRM^EMPH. For GOLD 0 participants (n = 419), mean 5-year increases in PRM^fSAD and PRM^EMPH were 0.3% for both; for GOLD 1-4 participants (n = 306), they were 0.6% and 1.6%, respectively. Eighty GOLD 0 subjects (19.1%) had overall radiologic progression (30.0% to PRM^fSAD, 52.5% to PRM^EMPH, and 17.5% to both); 153 GOLD 1-4 subjects (50.0%) experienced progression (17.6% to PRM^fSAD, 48.4% to PRM^EMPH, and 34.0% to both). In a multivariable model, both baseline PRM^fSAD and PRM^EMPH were associated with development of PRM^EMPH on follow-up, although this relationship was diminished at higher levels of baseline PRM^EMPH.

Conclusion: A voxel-wise longitudinal PRM analytic approach can identify patterns of disease progression in smokers with and without chronic obstructive pulmonary disease.

Keywords: Chronic obstructive pulmonary disease; Computed tomography; Emphysema; Parametric Response Mapping; Small airway disease.

Figure 1:. Five-year change of chest CT Parametric Response Mapping metrics in GOLD 0 and GOLD 1–4 progressors

The center of each circle represents the mean coordinates % (PRM^EMPH and % PRM^fSAD) for each type of progression (to fSAD [A], emphysema [B] or both [C]) at the baseline and follow-up visits (identified by the direction of the arrows). The area of each circle is proportional to the number of subjects with a given type of progression (A, B or C) within their GOLD category (0 or 1–4).

Figure 2:. Illustration of Parametric Response Mapping (PRM) changes on chest CT of a 58-year old man with COPD

(A) Longitudinal PRM changes on representative coronal CT slices showing normal lung parenchyma (green), functional small airway disease [fSAD] (yellow) and emphysema (red). (B) CT slices highlighting individual voxels that were classified as fSAD at baseline and became emphysema 5 years later in that same subject.