Image quality and diagnostic performance of free-breathing diffusion-weighted imaging for hepatocellular carcinoma

Table 1 Details of magnetic resonance parameters

Imaging technique	FB-DWI	RT-DWI
	Spin echo single-shot EPI	Spin echo single-shot EPI
SENSE factor	2	2
TR/TE (ms)	6250/56	1877/55
Flip angle (degree)	90°	90°
Field of view (mm2)	380 × 299	380 × 299
Matrix (frequency × phase)	112 × 176	112 × 68
Slice thickness (mm)	7	7
Slice gap (mm)	1	1
No. of slice	25	25
No. of excitations	2	2
b-value (s/mm2)	0.500 and 1.000	0.500 and 1.000
Respiratory compensation	Free-breathing without navigator echo	Respiratory-triggered with navigator echo
Fat-suppression	SPAIR	SPIR
SPAIR delay (ms)	100
SPAIR TR (ms)	250
Frequency offset (Hz)	250	180
EPI factor	75	25
Band width (Hz/pixel)	4050.4	4438.5
Scan time (min:s)	3:32	3:201

¹The mean scan time of RT-DWI, because these values vary depending on the subjects’ respiration condition. FB-DWI: Diffusion-weighted imaging with modified MR parameter settings for image improvement by referring to the literature[18]; RT-DWI: Respiratory-triggered diffusion-weighted imaging without modified MR parameter settings for the image improvement; EPI: Echo planar imaging; TR: Repetition time; TE: Echo time; SPAIR: Spectral attenuation with inversion recovery; SPIR: Spectral presaturation with inversion recovery; SPAIR delay: Inversion time from exposure of SPAIR pulse; SPAIR TR: TR between SPAIR pulses during the scan; Frequency offset: Bandwidth from the frequency of fat tissue; EPI factor: The number of k-space profiles collected per excitation.

Table 2 Image quality scores of sharpness of the liver contour, distortion and chemical shift artifacts

Score	Sharpness of the liver contour	Distortion and chemical shift artifacts
1	Unclear liver contour	Severe distortion or artifacts compromise the diagnostic capability of DWI in the whole liver
2	The liver contour is partially unclear	Distortion or artifacts are moderate, and they compromise the diagnostic capability of DWI in 50% or more of the liver
3	The liver contour is mostly clear	Distortion or artifacts are mild, and they compromise the diagnostic capability of DWI in less than 50% of the liver
4	The entire liver contour is clear	No distortion or artifacts; the diagnostic capability of DWI is not compromised

DWI: Diffusion-weighted imaging.

Table 3 Results of qualitative assessment of the free-breathing diffusion-weighted imaging and respiratory-triggering-diffusion-weighted imaging results

	Sharpness of the liver contour		Distortion		Chemical shift artifacts
	FB-DWI	RT-DWI	FB-DWI	RT-DWI	FB-DWI	RT-DWI
Observer 1	3.08 ± 0.81	2.33 ± 0.65a	2.94 ± 0.50	2.81 ± 0.56a	3.38 ± 0.60	2.92 ± 0.59a
Observer 2	2.98 ± 0.73	2.37 ± 0.74a	2.71 ± 0.70	2.25 ± 0.74a	3.15 ± 1.07	2.21 ± 0.85a
Observer 3	3.54 ± 0.75	2.75 ± 0.81a	3.27 ± 0.53	2.96 ± 0.71a	3.21 ± 0.85	2.77 ± 1.08a

Data are the average ± SD.

^aP < 0.05 by the Wilcoxon signed-rank test. FB-DWI: Diffusion-weighted imaging with modified MR parameter settings for image improvement by referring to the literature[18]; RT-DWI: Navigator-echo-based, real-time respiratory-gating and respiratory-triggered diffusion-weighted imaging without modified MR parameter settings.