Diagnostic accuracy of dual-layer spectral computed tomography virtual monoenergetic imaging with multiplanar reformation for T-staging of colorectal cancer

Table 1 Dual-layer spectral computed tomography parameters

Scan parameters and contrast agent injection protocol	Details
Scan parameters
Range	Diaphragmatic dome to the inferior pubic symphysis
Tube voltage (kV)	120
Tube current	Automatic tube current modulation
Detector collimation (mm)	64 × 0.625
Gantry rotation speed (second)	0.4
Pitch	1.0
Contrast agent
Concentration (mg/mL)	350
Dose (mL/kg)	1.5
Rate (mL/s)	3.0
Monitoring
Monitoring method	Bolus tracking
Monitoring level	Abdominal aorta
Monitoring threshold (HU)	150
Scan phases	Arterial phase, venous phase (delayed by 40 seconds)

HU: Hounsfield units.

Table 2 Patient demographic characteristics

Characteristic	Percentage/cohort details
Sex, n (%)
Male	98 (62.4)
Female	59 (37.6)
Age (mean ± SD, year)	63.5 ± 12.1
Pathological stage, n (%)
T1	14 (8.9)
T2	17 (10.8)
T3	118 (75.2)
T4	8 (5.1)
Differentiation grade, n (%)
G1	9 (5.7)
G2	142 (90.4)
G3	6 (3.8)
Tumor location
Rectum	87 (55.4)
Sigmoid colon	31 (19.7)
Descending colon	11 (7.0)
Splenic flexure	1 (0.6)
Transverse colon	7 (4.5)
Hepatic flexure	1 (0.6)
Ascending colon	19 (12.1)

Table 3 Subjective and objective image quality assessments of 40-70 keV virtual monoenergetic images and polyenergetic images in colorectal cancer evaluation (n = 157)

Subjective/objective	PEIs	40 keV VMIs	50 keV VMIs	60 keV VMIs	70 keV VMIs	Z value	P value
Noise	8.53 ± 2.90	8.17 ± 3.63	7.27 ± 3.18	6.83 ± 2.73	6.57 ± 2.58	74.521	< 0.001
SNR	8.41 ± 2.45	18.13 ± 7.09	14.81 ± 5.09	12.60 ± 4.05	10.73 ± 3.26	427.420	< 0.001
CNR	23.09 ± 8.95	45.69 ± 22.76	37.85 ± 18.12	31.58 ± 13.60	27.89 ± 12.11	275.540	< 0.001
Subjective scores	3.97 ± 0.42	4.88 ± 0.33	4.85 ± 0.36	4.69 ± 0.50	4.11 ± 0.49	376.086	< 0.001

Objective image quality parameters (noise/contrast-to-noise ratio/signal-to-noise ratio): Reported as median ± interquartile range due to non-normal distribution. Subjective scores: Reported as mean ± SD. CNR: Contrast-to-noise ratio; SNR: Signal-to-noise ratio; PEI: Polyenergetic image; VMI: Virtual monoenergetic image.

Table 4 Intergroup comparisons of subjective and objective image quality parameters for 40-70 keV virtual monoenergetic images and polyenergetic images in colorectal cancer evaluation (n = 157)

Subjective/objective		PEIs	40 keV VMIs	50 keV VMIs	60 keV VMIs	70 keV VMIs
Noise	PEI	-	0.673	< 0.001	< 0.001	< 0.001
	40 keV VMIs	-	-	0.054	< 0.001	< 0.001
	50 keV VMIs	-	-	-	0.873	0.075
	60 keV VMIs	-	-	-	-	1.000
	70 keV VMIs	-	-	-	-	-
SNR	PEIs	-	< 0.001	< 0.001	< 0.001	< 0.001
	40 keV VMIs	-	-	< 0.001	< 0.001	< 0.001
	50 keV VMIs	-	-	-	< 0.001	< 0.001
	60 keV VMIs	-	-	-	-	< 0.001
	70 keV VMIs	-	-	-	-	-
CNR	PEIs	-	< 0.001	< 0.001	< 0.001	< 0.001
	40 keV VMIs	-	-	0.002	< 0.001	< 0.001
	50 keV VMIs	-	-	-	0.001	< 0.001
	60 keV VMIs	-	-	-	-	< 0.001
	70 keV VMIs	-	-	-	-	-
Subjective scores	PEIs	-	< 0.001	< 0.001	< 0.001	0.376
	40 keV VMIs	-	-	1.000	0.033	< 0.001
	50 keV VMIs	-	-	-	0.120	< 0.001
	60 keV VMIs	-	-	-	-	< 0.001
	70 keV VMIs	-	-	-	-	-

CNR: Contrast-to-noise ratio; SNR: Signal-to-noise ratio; PEI: Polyenergetic image; VMI: Virtual monoenergetic image.

Table 5 Interobserver agreement analysis of subjective quality scores between two radiologists for 40-70 keV virtual monoenergetic images and polyenergetic images (n = 157)

Subjective quality scores			Doctor B
			3	4	5	κ	P value
Doctor A	PEIs	3	14	0	0	0.913	< 0.001
		4	2	130	2
		5	0	0	9
	40 keV VMIs	3	0	0	0	0.812	< 0.001
		4	0	15	2
		5	0	4	136
	50 keV VMIs	3	0	0	0	0.813	< 0.001
		4	0	18	2
		5	0	5	132
	60 keV VMIs	3	2	1	0	0.766	< 0.001
		4	1	32	5
		5	0	9	107
	70 keV VMIs	3	11	0	0	0.789	< 0.001
		4	0	107	4
		5	0	11	24

SNR: Signal-to-noise ratio; PEI: Polyenergetic image; VMI: Virtual monoenergetic image.

Table 6 Interobserver agreement for T-staging assessments between two radiologists for 40-70 keV virtual monoenergetic images and polyenergetic images (n = 157)

	Images	T staging	Doctor B
			T1	T2	T3-4	κ	P value
Doctor A	Axial PEIs	T1	2	0	0	0.891	< 0.001
		T2	1	29	3
		T3-4	0	2	123
	OA PEIs	T1	2	0	0	0.899	< 0.001
		T2	1	33	2
		T3-4	0	3	116
	40 keV OA VMIs	T1	15	0	0	0.943	< 0.001
		T2	1	14	2
		T3-4	0	0	125
	50 keV OA VMIs	T1	13	0	0	0.924	< 0.001
		T2	2	15	2
		T3-4	0	0	125
	60 keV OA VMIs	T1	4	1	0	0.843	< 0.001
		T2	2	21	3
		T3-4	0	2	124
	70 keV OA VMIs	T1	3	0	0	0.906	< 0.001
		T2	1	27	3
		T3-4	0	1	122

PEI: Polyenergetic image; VMI: Virtual monoenergetic image; OA: Oblique axial.

Table 7 Diagnostic performance of 40-70 keV virtual monoenergetic images and polyenergetic images in preoperative staging of T1-2 and T3-4 colorectal cancer

Images	CT T-staging	Pathological staging		Accuracy (%)	Sensitivity (%)	Specificity (%)	Youden index
		T1-2 (n = 31)	T3-4 (n = 126)
Axial PEIs	T1-2	12	19	70.7	38.71	78.56	0.17
	T3-4	27	99
PFS	T1-2	17	14	68.79	54.84	72.22	0.27
	T3-4	35	91
Axial PEIs and PFS	T1-2	12	19	70.7	38.71	78.56	0.17
	T3-4	27	99
OA PEIs	T1-2	14	17	76.43	45.16	84.13	0.29
	T3-4	20	106
PFS	T1-2	25	6	73.89	80.65	72.22	0.53
	T3-4	35	91
OA PEIs and PFS	T1-2	14	17	77.07	45.16	84.92	0.30
	T3-4	19	107
40 keV OA VIMs	T1-2	26	5	94.27	83.87	96.83	0.81
	T3-4	4	122
PFS	T1-2	25	6	73.25	80.65	71.43	0.52
	T3-4	36	90
40 keV OA VMIs and PFS	T1-2	25	6	93.63	80.65	96.83	0.77
	T3-4	4	122
50 keV OA VMIs	T1-2	26	5	94.27	83.87	96.83	0.81
	T3-4	4	122
PFS	T1-2	25	6	76.43	80.65	76.19	0.57
	T3-4	36	96
50 keV OA VMIs and PFS	T1-2	25	6	93.63	80.65	96.83	0.77
	T3-4	4	122
60 keV OA VMIs	T1-2	18	13	84.08	58.06	90.48	0.49
	T3-4	12	114
PFS	T1-2	25	6	73.25	80.65	71.43	0.52
	T3-4	36	90
60 keV OA VMIs and PFS	T1-2	18	13	84.08	58.06	90.48	0.49
	T3-4	12	114
70 keV OA VMIs	T1-2	16	15	80.25	51.61	87.30	0.39
	T3-4	16	110
PFS	T1-2	25	6	73.25	80.65	71.43	0.52
	T3-4	36	90
70 keV OA VMIs and PFS	T1-2	16	15	80.25	51.61	87.30	0.39
	T3-4	16	110

PEI: Polyenergetic image; VMI: Virtual monoenergetic image; PFS: Peritumoral fat stranding; OA: Oblique axial.