Acoustic radiation force impulse elastography for evaluating renal parenchymal stiffness in children

Clinical perspective on renal elasticity quantification by acoustic radiation force impulse: Where we are and where we are going

Recent interests have focused on the exploration of the mechanical properties (elasticity, stiffness and deformity) of parenchymatous organs using tissue strain imaging techniques and elastosonography. Measures of the mechanical properties of the kidneys have given conflicting results. There are various conditions that affect the variability of renal parenchymal measures, the main target of the investigations. They can be classified as intrinsic (depending upon the patient), extrinsic (depending upon the operator) and mixed (both intrinsic and extrinsic). Indeed, the mechanical properties of the kidney depend on various conditions that alter its histology, mainly the amount of fibrosis in the renal parenchymal interstitium. Anatomical factors play an important role because the kidney is a highly anisotropic organ with important differences when considering the cortex and the medulla. Physical factors include the frequency of the probe, compression and distance from source to target. Many factors can affect measurements and it is necessary to find an accurate technique in order to avoid mistakes and to obtain reproducible data. Indeed, it is imperative to define a standardized examination technique in order to get comparable results. Therefore, the utility of acoustic radiation force imaging technique to predict only renal fibrosis or progression of chronic kidney disease is of dubious value because several variables - blood perfusion and urinary pressure - can contribute to a given measure, even with a standardized method able to minimize intra- and inter-operator variability.

Evaluation of kidney allograft status using novel ultrasonic technologies

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.