Artifacts in two-dimensional shear wave elastography of liver

Table 1 Patient characteristics (n = 151)

Characteristic	Value
Age (yr)	46.2 ± 13.1 (19-75)
Liver stiffness value (kPa)	9.7 ± 7.8 (3.8-34.9)
Liver cirrhosis, n (%)	17 (11.3)
Subcutaneous fat thickness (cm)	0.4 ± 0.3 (0.1-2.4)
Sex, n (%)
Male	72 (47.7)
Female	79 (52.3)
Body mass index (kg/m2)	23.3 ± 3.4 (17.2-36.3)
Normal (< 25 kg/m2), n (%)	101 (66.9)
Overweight (25-30 kg/m2), n (%)	41 (27.2)
Obese (> 30 kg/m2), n (%)	9 (5.9)
Etiology of chronic liver disease, n (%)
Hepatitis B virus	122 (80.8)
Hepatitis C virus	8 (5.3)
Alcoholic liver disease	10 (6.6)
Nonalcoholic fatty liver disease	6 (4)
Autoimmune disease	5 (3.3)

Table 2 Artifacts at different locations of the two operators

Locations	Expert, n (%)	Novice, n (%)	P value
Top-left	40 (21.5)	120 (20.5)	0.769
Bottom-left	102 (54.8)	309 (52.8)	0.634
Top-right	7 (3.8)	42 (7.2)	0.098
Bottom-right	37 (19.9)	114 (19.5)	0.904

Qualitative data are expressed as n (%).

Table 3 Compare the percentage of artifacts at different locations

Locations of artifacts	P1 value	P2 value
Top-left vs bottom-left	< 0.001	< 0.001
Top-left vs top-right	< 0.001	< 0.001
Top-left vs bottom-right	0.703	0.669
Bottom-left vs top-right	< 0.001	< 0.001
Bottom-left vs bottom-right	< 0.001	< 0.001
Top-right vs bottom-right	< 0.001	< 0.001

¹Compare the percentage of artifacts at different locations of the expert.

²Compare the percentage of artifacts at different locations of the novice.

Table 4 Comparison of liver stiffness values of elastograms with different area artifacts for two operators

	Expert	Novice	P1 value
LSVs of EMAs (kPa)	10.2 ± 8.3	11.0 ± 8.7	0.006
LSVs of ELAs (kPa)	9.5 ± 7.4	9.8 ± 7.7	0.051
P2 value	< 0.001	< 0.001	N/A

¹Compare the liver stiffness values (LSVs) of the two operators.

²Compare the LSVs of elastograms with the most artifacts and elastograms with the least artifacts.

LSVs: Liver stiffness values; EMAs: Elastograms with the most artifacts; ELAs: Elastograms with the least artifacts; N/A: Not applicable.

Table 5 Standard deviation and stability index of the elastograms with different area artifacts for two operators

	SD of EMAs (kPa)	SD of ELAs (kPa)	P1 value	SI of EMAs	SI of ELAs	P2 value
Expert	1.2 ± 1.2	0.8 ± 0.6	< 0.001	92% ± 12%	95% ± 5%	0.135
Novice	2.1 ± 1.7	1.1 ± 1.1	< 0.001	89% ± 8%	93% ± 6%	0.002

¹Compare the standard deviation values of elastograms with the most artifacts (EMAs) and elastograms with the least artifacts (ELAs).

²Compare the stability index values of EMAs and ELAs.

SD: Standard deviation; SI: Stability index; EMAs: Elastograms with the most artifacts; ELAs: Elastograms with the least artifacts.

Table 6 Comparison of Q-Box parameters measured at different positions of the elastograms with artifacts

	Number	Q-Box in the center of the sampling frame			Q-Box away from the artifacts
		LSV	SD	SI	LSV	SD	SI
Expert	141	14.6 ± 9.5	1.7 ± 1.1	93% ± 6%	14.1 ± 9.3	0.8 ± 0.6	94% ± 7%
Novice	372	12.1 ± 9.5	1.9 ± 1.3	90% ± 7%	11.6 ± 9.4	0.9 ± 0.7	93% ± 6%

LSV: Liver stiffness value; SD: Standard deviation; SI: Stability index.