Table 1 Main component parameters of TIC

Qontraxt software to analyze ultrasonography time–intensity curve parameters

Time parameters

AT

Arrival time

s

Time after injection when ROI signal start to enhance

Determined by the blood flow velocity in renal cortical microvessels

Ma et al. [68]; Luo et al. [69]; Seo et al. [77]

TTP

Time to peak

s

Time after injection when ROI signal intensity reaches its maximum

It is the time from zero intensity to maximum intensity. This parameter is calculated from the fitted mathematical model and often is supplied in a closed form analytical expression

AS

Ascending slope

dB/s

Slope of ascending part of TIC

Representing the perfusion speed of the ROI

DT/2

Descending time/2

s

Half of descending time

Time needed after injection for intensity to decrease to half of PI

DS

Descending slope

dB/s

Slope of descending part of the TIC, representing the dilution speed of the ROI

Reflecting the total number of microbubbles clearing the vessels within the ROI, in response to renal perfusion

Intensity parameters

PI

Peak intensity

dB

The peak intensity is the difference between the maximum and minimum intensity

Reflecting the total number of microbubbles entering the vessels within the ROI, in response to renal perfusion

AUC

Area under the curve

dB/s

Area under the TIC curve

Influenced by blood flow velocity and blood distribution volume, it is proportional to the mean blood flow at the ROI, which reflects changes in intravascular blood flow volume

Sonotumor software analyses contrast time–intensity curve parameters

Time parameters

RT

Rise time

s

The time from injection until the peak of enhancement

Referring to the time interval between the first arrival of contrast and TTP

Schneider et at. [76]; Harrois et al. [10]; Liu et al. [78]; Nylund et al. [79]

MTT

Mean transit time

s

Describe the average time it takes for a microbubble to pass through the ROI

It is a measure of the time to recharge after contrast destruction, with shorter times indicating higher levels of perfusion

FT

Fall time

s

Referring to the duration of contrast wash-out

–

WIS

Wash in slope

dB/s

The speed from the beginning of enhancement to the peak of enhancement

Maximum of wash in slope of contrast agent

WIT

Wash-in time

dB/s

It is time from 5% intensity to 95% intensity

It is proportional to the time to peak but it is sometimes used with mathematical models that do not have closed form analytical expressions of TTP

WOT

Wash-out time

dB/s

It is the time from the peak of the TIC curve to the zero value again

The latter timepoint (zero enhancement) is rarely seen in the raw data as it may take a long time for the ROI to become completely black again. It is easily calculated from the fitted mathematical model (curve)

WiPI

Wash-in perfusion index

dB/s

Calculated as WiAUC divided by RT

–

Intensity parameters

RBV

Relative blood volume

a.u

Measure of maximum intensity of ROI after full recharge

RBV is proportional to the concentration of contrast agent within the ROI and increases with increasing perfusion levels

PI

Perfusion index

a.u

RBV/MTT

A measure of maximum CEUS signal intensity that is more variable than time to replenishment

PE

Peak enhancement

a.u

The maximum intensity of the TIC

WiWoAUC

Wash-in and wash-out area under the curve

dB/s

The total area under the curve of TIC

-

WiAUC

Wash-in area under the curve

dB/s

The area under the TIC from time of arrival to the PE

-

WoAUC

Wash-out area under the curve

dB/s

The area under the TIC from the PE to the end of the curve

–