Image analysis

The ultrasound sequences were output into digital imaging and communication in medicine (DICOM) format. Renal perfusion was analyzed in VueBox version 7.0 (Bracco SpA, Milan, Italy). Three regions of interest (ROIs) were defined: a reference ROI and two analysis ROIs. The segmental or interlobular arteries were set as the reference ROI in each kidney image and two ROI regions were set at the cortical zones in each image. The analysis ROI was placed on the middle pole to the lower pole of the renal cortex. The area of the ROI was 0.3 cm². Movement compensation was applied to all participants. The DICOM data of the ROI were converted into echo-power data. A time-intensity curve (TIC) of the ROI was generated, from which the analysis parameters were calculated (Table 1, Figure 1). The parameters included ratio of the peak enhancement to the reference ROI (PE%); wash-in area under the curve (WiAUC, a.u.); rise time (RT, s); mean transit time (mTTI, s); time to peak (TTP, s); wash-out AUC (WoAUC, a.u.); wash-in and wash-out area under the curve (WiWoAUC, a.u.). The values obtained in the two ROIs from the leftrenal cortical zones were averaged for the analysis. To guarantee the quality of the data analysis, the goodness of fit (GOF) in all analyses was not <75%.

A representative diagram of a curve fitting diagram of TIC. PE: peak enhancement; WiAUC: wash-in area under the curve; RT: rise time; mTTI: mean transit time local; TTP: time to peak; WoAUC: wash-out area under the curve; WiWoAUC: wash-in and wash-out area under the curve [18].

Time-intensity curve parameters in the CEUS analysis.

The unit a.u. indicates arbitrary unit, f(t) is the instantaneous signal of the time(t).