Correlation of dynamic contrast-enhanced ultrasonography and the Ki-67 labelling index in pancreatic ductal adenocarcinoma

Table 1 Explanations for quantitative parameters

Parameters	Explanations
Contrast agent arrival time (second)	Time from 0 to the start of enhancement
Peak enhancement (a.u.)	Maximum enhancement intensity during the arterial phase
Half-decrease time (second)	The time required to decrease from PE to 1/2 PE of the arterial phase
Fall time (second)	The time for the contrast agent intensity to decrease from 95% to 5% of PE during the arterial phase
Rise time (second)	The time it takes for the contrast agent intensity to go from 5% to 95% of PE during the arterial phase
Time to peak (second)	The time required to reach PE of the arterial phase after contrast agent injection
Wash-in area under the curve (a.u.)	Area under the TIC from the time of arrival to the PE of arterial phase
Wash-in perfusion index (a.u./second)	WiAUC/RT
Wash-in rate (a.u./second)	The maximum slope of the rising part of the TIC
Wash-out area under the curve (a.u.)	The area under the TIC from the PE of the arterial phase to the end of the curve
Wash-out rate (a.u./second)	The minimum slope of the descending part of the curve
Wash-in and wash-out area under the curve (a.u.)	WiAUC + WoAUC, representing the area under the entire curve
Mean transit time (second)	Time from the rising of the intensity up to decrease to 50% of maximum

TIC: Time-intensity curve; PE: Peak enhancement; WiAUC: Wash-in area under the curve; RT: Rise time; WoAUC: Wash-out area under the curve.