Optimal b value of diffusion-weighted imaging on a 3.0T magnetic resonance scanner in Crohn’s disease

Table 1 Crohn’s disease activity index

Signs and symptoms	Multiplication factor
Number of liquid or very soft stools per day in a week	2
Abdominal pain (0 = none; 1 = mild; 2 = moderate; 3 = severe)	5
Number of complications	20
Taking loperamide/opiates for diarrhea (0 = no, 1 = yes)	30
Abdominal mass (0 = none, 2 = questionable, 5 = definite)	10
Hematocrit: male (47-Hct); female (42-Hct)	6
Percentage below predicted body weight	1
Evaluation	< 150: remission
	150-450: moderate-severe
	> 450: very serious

Table 2 Mean contrast-to-noise ratios of four b value diffusion-weighted imaging sequences

	b = 800	b = 1500	b = 2000	b = 2500
b = 800	79.30 ± 34.59	P = 0.006	P < 0.01	P < 0.01
b = 1500	P = 0.006	57.66 ± 23.95	P = 0.007	P = 0.003
b = 2000	P < 0.01	P = 0.007	36.52 ± 14.95	P = 0.820
b = 2500	P < 0.01	P = 0.003	P = 0.820	34.78 ± 24.83

Unit of b value in diffusion-weighted imaging is s/mm².

Table 3 Mean signal-to-noise ratios of four b value diffusion-weighted imaging sequences

	b = 800	b = 1500	b = 2000	b = 2500
b = 800	113.98 ± 48.92	P = 0.007	P < 0.01	P < 0.01
b = 1500	P = 0.007	84.77 ± 33.24	P = 0.004	P = 0.001
b = 2000	P < 0.01	P = 0.004	53.58 ± 23.45	P = 0.567
b = 2500	P < 0.01	P = 0.001	P = 0.567	47.58 ± 29.67

Unit of b value in diffusion-weighted imaging is s/mm².

Table 4 Apparent diffusion coefficient values of four b value diffusion-weighted imaging sequences

b value (s/mm2)	ADC value (×10-3mm2/s)		P value
	Inflammatory segments	Normal segments
800	1.38 ± 0.28	2.00 ± 0.38	< 0.01
1500	1.09 ± 0.20	1.50 ± 0.28	< 0.01
2000	0.95 ± 0.19	1.34 ± 0.28	< 0.01
2500	0.88 ± 0.14	1.20 ± 0.21	< 0.01

ADC: Apparent diffusion coefficient.

Table 5 Overall diagnostic assessment of active Crohn's lesions on diffusion-weighted imaging

b value (s/mm2)	TP	FP	FN	TN	Sensitivity	Specificity	Lesion detection rate
800	71	20	12	145	83.53%	88.96%	87.10%
1500	69	8	16	155	81.18%	95.10%	90.32%
2000	62	9	23	154	72.94%	94.48%	87.10%
2500	55	8	30	155	64.71%	95.10%	84.68%

TP: True positive; FP: False positive; FN: False negative; TN: True negative. Unit of b value in diffusion-weighted imaging is s/mm².