Emphysema quantification using chest CT: influence of radiation dose reduction and reconstruction technique

European Radiology Experimental

Table 1 Percentage of emphysema using the -950 HU threshold and the perc₁₅ method at different dose levels reconstructed with FBP, HIR and MIR

	-950 HU (%)	ICC (95% CI)	Perc₁₅ (HU-value)	ICC (95%CI)
Routine dose
FBP	5.1 (1.7–8.4)	NA	-923 (-936 – -895)	NA
HIR	1.5 (0.1–4.5)^a	0.63 (0.00–0.88)	-914 (-927 – -881)^a	0.91 (0.00–0.98)
MIR	0.9 (0.0–3.6)^a	0.50 (0.00–0.80)	-913 (-926 – -879)^a	0.88 (0.01–0.97)
45% reduced dose
FBP	8.0 (3.3–12.4)^a	0.83 (0.00–0.96)	-932 (-944 – -898)^a	0.93 (0.39–0.98)
HIR	2.5 (0.2–5.1)^a	0.79 (0.01–0.94)	-916 (-929 – -875)^a	0.89 (0.28–0.97)
MIR	1.2 (0.0–3.1)^a	0.51 (0.00–0.81)	-913 (-927 – -867)^a	0.83 (0.07–0.95)
60% reduced dose
FBP	10.2 (5.5–14.7)^a	0.63 (0.00–0.89)	-940 (-949 – -912)^a	0.77 (0.00–0.94)
HIR	2.7 (0.5–6.2)^a	0.83 (0.24–0.95)	-917 (-931 – -881)^a	0.87 (0.62–0.95)
MIR	1.3 (0.0–3.2)^a	0.49 (0.00–0.79)	-911 (-927 – -874)^a	0.80 (0.28–0.93)
75% reduced dose
FBP	14.3 (9.7–19.6)^a	0.42 (0.00–0.79)	-948 (-961 – -925)^a	0.59 (0.00–0.88)
HIR	3.5 (0.7–8.1)^a	0.92 (0.76–0.97)	-921 (-935 – -878)^a	0.94 (0.81–0.98)
MIR	0.9 (0.0–4.2)^a	0.47 (0.00–0.78)	-914 (-927 – -869)^a	0.84 (0.16–0.95)

Values represent the median (interquartile range). The ICC compares with the reference standard, namely FBP at routine dose
^aStatistically significant difference compared to FBP at routine dose with a Bonferroni corrected p value of 0.017
FBP filtered back projection, HIR hybrid iterative reconstruction, ICC intraclass correlation coefficient, MIR model-based iterative reconstruction