Table 3. Vascular attenuation, SNR, and CNR in monochromatic and conventional CT.

Location and parameter		40-keV	50-keV	Conventional	P-value (overall)	P-value in pairwise comparison*
						40-keV vs. 50-keV	40-keV vs. conventional	50-keV vs. conventional
LVOT
	Vascular attenuation, HU	544.5 (421.8–693.0)	364.0 (285.8–467.8)	199.0 (159.5–256.0)	< 0.001	< 0.001	< 0.001	< 0.001
	CNR	19.1 (15.2–29.7)	17.2 (12.9–24.2)	13.0 (9.0–17.4)	< 0.001	< 0.001	< 0.001	< 0.001
	SNR	10.0 (7.4–11.7)	10.0 (7.5–12.0)	10.0 (7.7–12.5)	0.018	0.445	0.013	0.445
Ascending aorta
	Vascular attenuation, HU	669.0 (510.0–814.0)	449.0 (344.3–545.5)	240 (193.5–298.5)	< 0.001	< 0.001	< 0.001	< 0.001
	CNR	24.3 (17.7–33.4)	21.1 (15.3–30.2)	15.6 (10.7–21.7)	< 0.001	< 0.001	< 0.001	< 0.001
	SNR	15.0 (12.1–18.5)	15.6 (12.3–18.6)	15.9 (12.3–18.8)	0.029	0.107	0.037	> 0.999
Descending thoracic aorta
	Vascular attenuation, HU	664.5 (522.8–82.0)	449.0 (353.8–55.0)	241.0 (195.0–29.0)	< 0.001	< 0.001	< 0.001	< 0.001
	CNR	25.8 (17.2–37.5)	22.6 (15.0–32.2)	15.15 (10.5–21.8)	< 0.001	< 0.001	< 0.001	< 0.001
	SNR	12.6 (10.3–16.5)	12.95 (10.1–16.8)	12.85 (10.4–16.4)	0.004	0.008	0.010	> 0.999

Values are median (Q1–Q3).

^*Adjusted P-value with Bonferroni correction.

SNR = signal-to-noise ratio, CNR = contrast-to-noise ratio, LVOT = left ventricular outflow tract, HU = Hounsfield units