Table 2.

A variant of the COPDGene phantom (Fig. 2, top panel), with “trachea” and “lung” like regions as well as air, water, and acrylic regions, was scanned in SS and modes at 80, 100 and 140 kVp. The resultant mean values of the 80 and 140 kVp scans are listed for each region, in addition to the difference in values between the two modes and the level of significance using a two-tailed paired difference test. The results from the 100 kVp showed similar HU shifts between SS and DSDE scans.

		80 kVp		140 kVp
		SS	DSDE	SS	DSDE
“Trachea”	Mean	−987	−1003	−987	−1004
	|Difference| ± SD	16 ± 2		17 ± 2
	T-Test	p < 0.001 (n = 10)		p < 0.001 (n = 10)
Air	Mean	−999	−1002	−998	−1004
	|Difference| ± SD	3 ± 4		6 ± 2
	T-Test	p < 0.05 (n = 10)		P < 0.001 (n = 10)
“Lung”	Mean	−858	−860	−856	−863
	|Difference| ± SD	2 ± 5		7 ± 3
	T-Test	p = 0.1701 (n = 10)		p < 0.001 (n = 10)
Water	Mean	−2	2	−2	2
	|Difference| ± SD	4 ± 8		4 ± 6
	T-Test	p = 0.1816 (n = 10)		p = 0.0972 (n = 10)
Acrylic	Mean	94	111	125	154
	|Difference| ± SD	17 ± 15		29 ± 8
	T-Test	p < 0.01 (n = 10)		p < 0.001 (n = 10)

Note: Reference CT number for internal “trachea” air is −1000 HU; internal air is −1000 HU; “lung” is −860 HU; water is 0 HU; acrylic is 120 HU.