Table 2.

Comparison of computed tomography (CT) numbers between water phantom and Plastic Water ^a phantom

Position	Water phantom		Plastic Water phantom		Ratio
	HU	σ(HU)	HU	σ(HU)	Rel waterb	σ
80‐kVp CT slice measurements
Center of phantom	$-2.46$	32.84	0.43	15.94	1.003	0.037
Midplane of phantom, right edge	8.81	61.16	2.85	15.00	0.994	0.062
Midplane of phantom, left edge	9.87	23.20	2.87	16.20	0.993	0.028
Top of phantom, center	$-1.84$	32.00	$-5.65$	10.64	0.996	0.034
Top of phantom, right edge	5.91	62.91	$-0.63$	16.67	0.993	0.064
Top of phantom, left edge	4.31	26.45	$-0.54$	13.99	0.995	0.030
Bottom of phantom, center	5.20	30.41	3.99	14.52	0.999	0.033
Bottom of phantom, right edge	15.28	62.39	5.91	21.69	0.991	0.065
Bottom of phantom, left edge	14.70	34.61	5.56	23.63	0.991	0.041
100‐kVp CT slice measurements
Center of phantom	2.69	22.65	$-1.96$	10.41	0.995	0.025
Midplane of phantom, right edge	11.09	19.23	4.69	8.23	0.994	0.021
Midplane of phantom, left edge	9.93	28.38	5.10	8.31	0.995	0.029
Top of phantom, center	0.05	17.16	$-4.94$	7.26	0.995	0.019
Top of phantom, right edge	10.90	15.29	1.21	7.76	0.990	0.017
Top of phantom, left edge	4.61	24.77	1.59	9.80	0.997	0.026
Bottom of phantom, center	2.74	23.78	$-0.55$	8.85	0.997	0.025
Bottom of phantom, right edge	11.99	19.66	8.26	11.00	0.996	0.022
Bottom of phantom, left edge	14.93	39.65	7.52	13.70	0.993	0.041
120‐kVp CT slice measurements
Center of phantom	2.24	15.29	$-2.14$	6.16	0.996	0.016
Midplane of phantom, right edge	11.19	14.05	2.27	6.81	0.991	0.015
Midplane of phantom, left edge	7.82	18.23	3.74	5.26	0.996	0.019
Top of phantom, center	11.92	12.91	$-6.03$	5.40	0.982	0.014
Top of phantom, right edge	$-0.27$	12.13	$-0.21$	6.50	1.000	0.014
Top of phantom, left edge	4.21	14.29	0.97	5.35	0.997	0.015
Bottom of phantom, center	5.57	15.28	$-0.71$	6.25	0.994	0.016
Bottom of phantom, right edge	13.00	15.01	6.21	8.95	0.993	0.017
Bottom of phantom, left edge	12.50	26.95	7.36	7.28	0.995	0.027
140‐kVp CT slice measurements
Center of phantom	3.49	13.83	$-3.33$	5.35	0.993	0.015
Midplane of phantom, right edge	12.83	10.04	1.64	5.20	0.989	0.011
Midplane of phantom, left edge	8.06	13.42	2.05	5.47	0.994	0.014
Top of phantom, center	$-0.16$	9.12	$-6.86$	4.13	0.993	0.010
Top of phantom, right edge	13.10	10.00	0.50	4.70	0.988	0.011
Top of phantom, left edge	5.43	14.04	0.36	5.20	0.995	0.015
Bottom of phantom, center	4.19	14.97	$-1.70$	5.26	0.994	0.016
Bottom of phantom, right edge	13.51	11.53	6.68	7.19	0.993	0.013
Bottom of phantom, left edge	12.92	22.11	6.78	7.31	0.994	0.023

^aCIRS, Norfolk, VA

^b

$Rel\hspace{0.17em}Water=\frac{HU(PWDT)+1000}{HU(Water)+1000}$

$\mathrm{H}\mathrm{U}=\mathrm{H}\mathrm{o}\mathrm{u}\mathrm{n}\mathrm{s}\mathrm{f}\mathrm{i}\mathrm{e}\mathrm{l}\mathrm{d}\hspace{0.17em}\mathrm{u}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{s}$.