Deep learning-based magnetic resonance imaging reconstruction for improving the image quality of reduced-field-of-view diffusion-weighted imaging of the pancreas

Table 1 Details of imaging parameters

Parameters	FOCUS-DLR+/–	FOCUS-conv
Repetition time, ms	3000–10000	3500–15000
Echo time, ms	60	60
Flip angle, degree	90	90
FOV, mm2	220 × 110	220 × 110
Matrix	120 × 64	130 × 40
FOV reduction	Anterior-posterior	Anterior-posterior
Slice thickness, mm	3	4
Slice gap, mm	3	5
Number of slices	20–30	15–20
Number of excitations	4	8
b-values, s/mm2	0 and 600	0 and 600
Band width, Hz/pixel	1950	1300
Respiratory compensation	Respiratory-triggered with navigator echo	Respiratory-triggered with or without navigator echo
Deep learning reconstruction factor	Moderate	N/A
Scan time, min	2–5	3–10

The repetition time, number of slices and scan time varied depending on the patients' condition. DLR: Deep learning-based reconstruction; FOCUS: Field-of-view optimized and constrained undistorted single-shot; FOCUS-conv: Conventional field-of-view optimized and constrained undistorted single-shot; FOV: Field of view; N/A: Not applicable.

Table 2 Image-quality scores in the qualitative assessment

Qualitative assessment	1	2	3	4
Sharpness of the pancreas contour	Entire pancreas contour is unclear	< 50% of the pancreas contour is clear	≥ 50% of the pancreas contour is clear	Entire pancreas contour is clear
Image noise	Severe noise; no visualization of any organs	Moderate noise; compromised diagnostic capability of FOCUS is more than ≥ 50% of the image	Mild noise; compromised the diagnostic capability of FOCUS is < 50% of the image	No or slight noise on the image
Distortion of the pancreas	Severe distortion; no visualization of the whole pancreas	Moderate distortion; no visualization is ≥ 50% of the pancreas	Mild distortion; no visualization is < 50% of the pancreas	No distortion of the pancreas
Visualization of pancreas cystic lesion	No visualization of pancreas cystic lesion	Pancreas cystic lesion is visible, but its SI is low	Pancreas cystic lesion is visible with high SI, but its contour is unclear	Pancreas cystic lesion is clearly visible with high SI and clear contour
Visualization of MPD on ADC map	No visualization of MPD	Visible MPD is < 50% of the pancreas	Visible MPD is ≥ 50% of the pancreas	Whole MPD is visible

MPD: Main pancreatic duct; ADC: Apparent diffusion coefficient; SI: Signal intensity; FOCUS: Field-of-view optimized and constrained undistorted single-shot.

Table 3 The results of the two radiologists' qualitative assessments

Qualitative assessment	Reader	Mean image-quality score			P value
					Friedman test	Bonferroni post-hoc test
		FOCUS-DLR+	FOCUS-DLR-	FOCUS-conv		FOCUS-DLR+ vs FOCUS-DLR-	FOCUS-DLR+ vs FOCUS-conv	FOCUS-DLR- vs FOCUS-conv
Sharpness of pancreas contour	R1	3.32	3	2.24	< 0.0011	0.31	< 0.0011	0.0011
	R2	3.32	3.03	2.05	< 0.0011	0.49	< 0.0011	< 0.0011
Image noise	R1	3.65	2.7	2.86	< 0.00 11	< 0.0011	< 0.0011	1
	R2	3.59	2.54	2.7	< 0.0011	< 0.0011	< 0.0011	0.97
Distortion of pancreas	R1	3.16	3.11	3.05	0.05	N/A	N/A	N/A
	R2	3.11	3.18	3.05	0.73	N/A	N/A	N/A
Visualization of pancreas cystic lesion	R1	3.7	3.49	2.89	< 0.0011	0.67	0.0161	0.35
	R2	3.62	3.32	2.7	< 0.0011	0.24	0.0011	0.17
Visualization of MPD on ADC map	R1	2.97	2.54	2.19	< 0.0011	0.17	0.0031	0.49
	R2	2.73	2.24	1.99	< 0.0011	0.11	0.0011	0.35

¹A significant difference.

DLR: Deep learning-based reconstruction; FOCUS: Field-of-view optimized and constrained undistorted single-shot; FOCUS-conv: Conventional field-of-view optimized and constrained undistorted single-shot; ADC: Apparent diffusion coefficient; MPD: Main pancreatic duct; N/A: Not available.

Table 4 Inter-reader agreement between the two radiologists

Qualitative assessment	Imaging	κ value (95%CI)	P value
Sharpness of pancreas contour	FOCUS-DLR+	0.73 (0.52–0.95)	< 0.0011
	FOCUS-DLR-	0.69 (0.45–0.93)	< 0.0011
	FOCUS-conv	0.66 (0.43–0.89)	< 0.0011
Image noise	FOCUS-DLR+	0.69 (0.46–0.92)	< 0.0011
	FOCUS-DLR-	0.70 (0.50–0.90)	< 0.0011
	FOCUS-conv	0.64 (0.42–0.87)	< 0.0011
Distortion of pancreas	FOCUS-DLR+	0.61 (0.40–0.82)	< 0.0011
	FOCUS-DLR-	0.71 (0.53–0.89)	< 0.0011
	FOCUS-conv	0.61 (0.41–0.82)	< 0.0011
Visualization of pancreas cystic lesion	FOCUS-DLR+	0.80 (0.56–1.03)	< 0.0011
	FOCUS-DLR-	0.76 (0.60–0.93)	< 0.0011
	FOCUS-conv	0.71 (0.51–0.91)	< 0.0011
Visualization of MPD on ADC map	FOCUS-DLR+	0.67 (0.51–0.83)	< 0.0011
	FOCUS-DLR-	0.75 (0.60–0.90)	< 0.0011
	FOCUS-conv	0.74 (0.54–0.94)	< 0.0011

¹A significant difference. P values were obtained by the weighted κ statistic.

κ values: < 0, no agreement; 0–0.20, slight agreement; 0.21–0.40, fair agreement; 0.41–0.60, moderate agreement; 0.61–0.80, substantial agreement; and 0.81–1.00, almost perfect agreement. 95%CI: 95% confidence intervals; DLR: Deep learning-based reconstruction; FOCUS: Field-of-view optimized and constrained undistorted single-shot; FOCUS-conv: Conventional field-of-view optimized and constrained undistorted single-shot; ADC: Apparent diffusion coefficient; MPD: Main pancreatic duct.

Table 5 The results of quantitative assessments

Quantitative assessments	mean ± SD			P values
				Friedman test	Bonferroni post-hoc test
	FOCUS-DLR+	FOCUS-DLR-	FOCUS-conv		FOCUS-DLR+ vs FOCUS-DLR-	FOCUS-DLR+ vs FOCUS-conv	FOCUS-DLR- vs FOCUS-conv
CRpancreas-fat on FOCUS with b value of 600 s/mm2	0.68 ± 0.08	0.49 ± 0.10	0.27 ± 0.11	< 0.0011	< 0.0011	< 0.0011	< 0.0011
CRpancreas-fat on FOCUS with b value of 0 s/mm2	0.72 ± 0.08	0.65 ± 0.08	0.40 ± 0.11	< 0.0011	< 0.0011	< 0.0011	< 0.0011
CRlesion-pancreas on FOCUS with b value of 600 s/mm2	0.51 ± 0.26	0.62 ± 0.21	0.01 ± 0.26	< 0.0011	< 0.0011	< 0.0011	< 0.0011
CRlesion-pancreas on FOCUS with b value of 0 s/mm2	0.53 ± 0.21	0.62 ± 0.21	0.17 ± 0.19	< 0.0011	< 0.0011	< 0.0011	< 0.0011
ADCpancreas+ (× 10-3 mm2/s)	1.44 ± 0.24	1.39 ± 0.22	1.84 ± 0.45	< 0.0011	< 0.0011	< 0.0011	< 0.0011
ADClesion (× 10-3 mm2/s)	3.00 ± 0.66	2.86 ± 0.61	3.32 ± 0.70	< 0.0011	< 0.0011	< 0.0011	< 0.0011

¹A significant difference.

mean ± SD were calculated from the combined data of two radiologists' measurements. All CRs are presented in absolute values. 95%CI: 95% confidence intervals; DLR: Deep learning-based reconstruction; FOCUS: Field-of-view optimized and constrained undistorted single-shot; FOCUS-conv: Conventional field-of-view optimized and constrained undistorted single-shot; ADC: Apparent diffusion coefficient; MPD: Main pancreatic duct; CR: Contrast ratio.