Evaluation of kidney allograft status using novel ultrasonic technologies

Abstract

Early diagnosis of kidney allograft injury contributes to proper decisions regarding treatment strategy and promotes the long-term survival of both the recipients and the allografts. Although biopsy remains the gold standard, non-invasive methods of kidney allograft evaluation are required for clinical practice. Recently, novel ultrasonic technologies have been applied in the evaluation and diagnosis of kidney allograft status, including tissue elasticity quantification using acoustic radiation force impulse (ARFI) and contrast-enhanced ultrasonography (CEUS). In this review, we discuss current opinions on the application of ARFI and CEUS for evaluating kidney allograft function and their possible influencing factors, advantages and limitations. We also compare these two technologies with other non-invasive diagnostic methods, including nuclear medicine and radiology. While the role of novel non-invasive ultrasonic technologies in the assessment of kidney allografts requires further investigation, the use of such technologies remains highly promising.

Keywords: Acoustic radiation force impulse; Contrast-enhanced ultrasonography; Kidney transplantation; Non-invasive; Ultrasound.

Figure 1

The time-intensity curve (TIC) of CEUS in kidney allografts with different status. Adequate perfusion in the kidney grafts was observed in the stable group but not in the AR or ATN groups. In a stable kidney graft, the TIC had a positively skewed distribution with a smooth curve. It rose rapidly and then reached a peak, followed by an increase in contrast agents in the renal cortex. After a rapid decrease, it slowly increased when the contrast agent moved from the cortex to the medulla. Finally, it decreased after reaching a second peak. In AR and ATN kidneys, the TIC was coarse, particularly in the AR kidney, with apparent ups and downs. In addition, the ascending and descending rates of TIC were slow, compared with those instable kidney grafts. The solid yellow line indicates the peak time point in the stable kidney, and the solid red line indicates the resolution time of contrast agent in the cortex. The period between the yellow and red lines reflects the metabolism of contrast agent in the cortex. Compared to the stable group, the echo-power in the AR and ATN groups was much higher at the time when the contrast agent was excreted from the cortex. AR, acute rejection; ATN, acute tubular necrosis. This is a modified figure that came originally from our published article (Ref. [24]).