Detection of emphysema progression in alpha 1-antitrypsin deficiency using CT densitometry; Methodological advances

Table 4 Densitometric progression adjusted for lung volume using random coefficient model

Variable	Annual change, mean ± SE (95% CI)	t	p value for annual rate	p value for volume
Whole lung analysis
WL Perc15	-2.13 ± 0.44 (-3.01, -1.24)	-4.82	< 0.0001	< 0.0001
WL VI-950	0.90 ± 0.19 (0.52, 1.29)	4.72	< 0.0001	< 0.0001
WL VI-910	1.16 ± 0.25 (0.66, 1.65)	4.67	< 0.0001	< 0.0001
Single slice analysis
UZPerc15	-2.02 ± 0.53 (-3.08, -0.97)	-3.82	0.0003	< 0.0001
UZ VI-950	0.60 ± 0.21 (0.18, 1.02)	2.84	0.0057	< 0.0001
UZ VI-910	0.94 ± 0.33 (0.29, 1.59)	2.88	0.0051	< 0.0001
LZ Perc15	-1.93 ± 0.58 (-3.07, -0.78)	-3.34	0.0013	< 0.0001
LZ VI-950	1.02 ± 0.32 (0.39, 1.65)	3.22	0.0019	< 0.0001
LZ VI-910	1.34 ± 0.38 (0.58, 2.1)	3.52	0.0007	< 0.0001
Targeted sampling
UT Perc15	-2.54 ± 0.62 (-3.77, -1.32)	4.13	< .0001	< 0.0001
UT VI-950	0.67 ± 0.22 (0.24, 1.10)	3.11	0.0027	< 0.0001
UT VI-910	1.28 ± 0.44 (0.42, 2.15)	2.95	0.0042	< 0.0001
MT Perc15	-2.94 ± 0.49 (-3.91, -1.97)	-6.04	< 0.0001	< 0.0001
MT VI-950	1.20 ± 0.24 (0.73, 1.67)	5.08	< 0.0001	< 0.0001
MT VI-910	1.78 ± 0.35 (1.08, 2.47)	5.12	< 0.0001	< 0.0001
LT Perc15	2.85 ± 0.61 (-4.07, -1.64)	-4.68	< 0.0001	< 0.0001
LT VI-950	1.28 ± 0.26 (0.76, 1.80)	4.96	< 0.0001	< 0.0001
LT VI-910	1.57 ± 0.29 (0.99, 2.15)	5.37	< 0.0001	< 0.0001

WL, whole lung; UZ, upper zone single slice; LZ, lower zone single slice; ATl, apical third; MT, middle third; LT, lower third; SE, standard error; Perc15, 15^th percentile point (measured in Hounsfield Units); VI-950, voxel index at a threshold of -950HU (measured in %); VI-910, voxel index at a threshold of -910HU (measured in %). The random coefficient model consists of outcome measurement as the dependent variable, time (year) as the fixed effect, volume as a time-dependent covariate, intercept and time (year) as random effects. The slope (coefficient for time variable) from the model is the estimated annual change adjusted for volume.

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