Validation of lung density indices by cardiac CT for quantification of lung emphysema

Figures & data

Table 1 Characteristics of study population

	Study participants (n=156)
Age groups
<35 years, n (%)	1 (0.6)
35–44 years, n (%)	18 (11.5)
45–54 years, n (%)	49 (31.4)
>55 years, n (%)	88 (56.4)
Male, n (%)	112 (71.8)
Caucasians, n (%)	146 (93.6)
BMI (kg/m^2), mean (SD)	24.4 (4.2)
HIV-infected, n (%)	105 (67.3)
Smoking status
Current smokers, n (%)	55 (35.3)
Former smokers, n (%)	55 (35.3)
Never-smokers, n (%)	42 (26.9)
Tobacco consumption in pack-years,a median (IQR)	15.5 (0.0–34.0)
Airflow limitation
FEV1/FVC <LLN, n (%)	49 (31.4)
FEV1/FVC <0.7,b n (%)	85 (54.5)
Severity of airflow limitation
FEV1 predicted >80%, n (%)	99 (63.5)
FEV1 predicted 50%–79%, n (%)	46 (29.5)
FEV1 predicted 30%–49%, n (%)	9 (5.8)
FEV1 predicted <30%, n (%)	2 (1.3)
%LAA-950 by chest CT, median (range)	2.2 (0.0–18.2)
%LAA-950 by cardiac CT, median (range)	0.0 (0.0–1.0)
PD15 (g/L) by chest CT, mean (SD)	107.9 (21.7)
PD15 (g/L) by cardiac CT, mean (SD)	147.9 (38.5)
%LAA-950 >5% by chest CT, n (%)	45 (29.2%)

Notes: Data are summarized as median and IQR or number (percent). If percentages in each category do not add to 100% it is due to missing values.

a Pack-year is calculated for entire cohort.

b Pre-bronchodilatory spirometric indices.

Abbreviations: BMI, body mass index; IQR, interquartile range; %LAA-950, percent low attenuation area ≤950 Hounsfield units; LLN, lower limit of normal.

Table 2 Correlation and agreement between lung emphysema by cardiac and chest CT (n=156)

	ρ	ρcorrecteda	P-valueb	CCC	P15 (%)	P30 (%)
%LAA-910 cardiac CT vs %LAA-950 chest CT	0.67	0.68	<0.0001	0.50	5.1	12.8
%LAA-920 cardiac CT vs %LAA-950 chest CT	0.63	0.65	<0.0001	0.61	5.1	16.2
%LAA-930 cardiac CT vs %LAA-950 chest CT	0.60	0.60	<0.0001	0.60	5.1	12.2
%LAA-940 cardiac CT vs %LAA-950 chest CT	0.50	0.50	<0.0001	0.45	3.9	6.4
%LAA-950 cardiac CT vs %LAA-950 chest CT	0.49	0.50	<0.0001	0.33	3.2	5.1
PD15 cardiac CT vs PD15 chest CT	0.71	0.61	<0.0001	0.34	17.3	37.8

Notes:

a Correlation coefficient where measurements obtained by cardiac CT were corrected for cardiac CT lung volume.

b P-value for Spearman’s correlation coefficient rho (ρ). P15/P30, relative accuracy.

Abbreviations: CCC, concordance correlation coefficient; %LAA, percent low attenuation area; PD15, 15th percentile density index.

Figure 1 Association between lung density indices measured by cardiac and chest CT.

Notes: (A) PD15 by chest CT vs PD15 by cardiac CT and (B) Bland–Altman plot of PD15 by chest CT vs PD15 by cardiac CT. Ninety-five percent limits of agreement (−12.7–93.1). The correlation between the difference of the two measures and the average of the two measures was assessed using Kendall’s rank correlation tau and found to be correlated (tau =−0.45, P<0.0001).
Abbreviations: CT, computed tomography; PD15, 15th percentile density index.

Figure 2 Association between lung density indices measured by chest (A) and cardiac (B) CT and FEV₁%-predicted.

Abbreviations: CT, computed tomography; %LAA-950, percent low attenuation area ≤950 Hounsfield units.

Figure 3 ROC curves for the ability of lung density indices to discriminate airflow limitation.

Notes: ROC curves for (A) %LAA-950 from chest CT with AUC 0.62 (95% CI: 0.51–0.73) and cardiac CT with AUC 0.66 (95% CI: 0.55–0.78) and (B) PD15 from chest CT with AUC 0.62 (95% CI: 0.51–0.73) and cardiac CT with AUC 0.64 (95% CI: 0.53–0.75). Airflow limitation was defined as FEV₁/FVC <LLN.
Abbreviations: AUC, area under the curve; %LAA-950, percent low attenuation area ≤950 Hounsfield units; LLN, lower limit of normal; PD15, 15th percentile density index; ROC, receiver operating characteristics.

Figure 4 Association between visually and quantitatively assessed lung emphysema by cardiac and chest CT.

Notes: (A) %LAA-950 from chest CT and cardiac CT and (B) PD15 from chest CT and cardiac CT. Data are presented as mean and standard errors. Wilcoxon rank–sum test was used for calculation of P-values. Visual lung emphysema was determined by a radiologist (author: TK) blinded from the quantitatively determined lung emphysema.
Abbreviations: CT, computed tomography; %LAA-950, percent low attenuation area ≤950 Hounsfield units; PD15, 15th percentile density index.

Figure S1 Emphysema quantification by cardiac CT.

Notes: Male aged 54 years with emphysema (cardiac CT %LAA-950 =14.6% and chest CT %LAA-950 =18.2%). (A) Lung segmentation by chest CT; (B) lung volume segmentation by cardiac CT; and (C) axial cardiac CT slice; red pixels indicate LAAs.

Abbreviations: CT, computed tomography; %LAA-950, percent low attenuation area ≤950 Hounsfield units.

Table S1 Correlation and agreement between lung emphysema by cardiac and chest CT for individuals without HIV infection (n=51)

	ρ	P-valuea	CCC	P15 (%)	P30 (%)
%LAA-910 cardiac CT vs %LAA-950 chest CT	0.62	<0.0001	0.61	7.8	11.8
%LAA-920 cardiac CT vs %LAA-950 chest CT	0.61	<0.0001	0.63	3.9	7.8
%LAA-930 cardiac CT vs %LAA-950 chest CT	0.50	<0.0001	0.42	3.9	3.9
%LAA-940 cardiac CT vs %LAA-950 chest CT	0.42	<0.0001	0.19	19.6	19.6
%LAA-950 cardiac CT vs %LAA-950 chest CT	0.40	<0.0001	0.10	3.9	3.9
PD15 cardiac CT vs PD15 chest CT	0.74	<0.0001	0.30	11.7	29.4

Notes:

a P-value for Spearman’s correlation coefficient ρ. P15/P30, relative accuracy measure.

Abbreviations: CCC, concordance correlation coefficient; CT, computed tomography; %LAA, percent low attenuation area; PD15, 15th percentile density index.