Evaluation of chronic allographt rejection in renal transplant patients with shear wave elastography

Allograft biopsy is the gold standard method for the evaluation of renal allograft function. Renal biopsy, which is an invasive procedure, has the risk of potential life-threatening complications such as haemorrhage. Therefore, noninvasive imaging methods have gained importance in the evaluation of renal allograft. USG and Doppler USG are easily accessible, cost-effective, rapid and non-nephrotoxic imaging modalities of first choice for the evaluation of renal allograft. Elastography is a newly developed and nowadays widespread application added to the USG device. SE is similar to palpation used in clinical examination and provides quantitative data about tissue stiffness. SWE, which is a dynamic SE method, can detect tissue stiffness more easily by simultaneously monitoring the propagation of shear waves under B mode USG guidance at many points in the image. In this study, we aimed to investigate the role of SWE method in the diagnosis of chronic allograft rejection with tubular atrophy and interstitial fibrosis in the pathology. Between November 2022 and January 2024, a total of 84 renal transplant patients, including 42 patients with stable renal function (control) and 42 patients with unstable renal function, were evaluated with SWE in the Radiology Department of Akdeniz University Hospital. We obtained elasticity data from the upper, middle and lower parts of the transplant kidney with a convex probe and from the area closest to the skin with a linear probe using the SWE technique. RI values were measured at the level of the arcuate artery from the upper, middle and lower parts of the transplant kidney. Renal artery and vein flow were evaluated by RDUS. We statistically investigated the relationship between transplant duration, donor type, renal function tests (creatinine, e-GFR and proteinuria), clinical status, grey scale USG findings and RI value with SWE data. We statistically evaluated the relationship between the diagnosis of chronic rejection and RI and SWE values. The mean age of the patients was 39.6 years and the mean Tx duration was 7.9 years. Transplantation was performed from living donors in 83.3% of the patients and from cadaveric donors in 16.7%. The mean creatinine value of the patients was 1.8, 51.2% had increased creatinine, 50.0% had unstable clinical status and 46.4% had a diagnosis of chronic rejection. No correlation was found between transplant duration and donor type and chronic rejection. There was no significant correlation between high RI values and chronic rejection, but there was a significant correlation between increased parenchymal echogenicity and chronic rejection. Significant correlation was found between laboratory parameters (creatinine, proteinuria ve e-GFR) which are important in clinical follow-up and SWE examination data performed with linear probe. In conclusion, SWE findings can be used to evaluate and predict renal allograft function. Our study demonstrated that SWE examination with a linear probe can play an important role in the early diagnosis and treatment of chronic rejection. In particular, there is a limited number of studies in the literature evaluating renal allografts with SWE technique using a linear probe. In addition, we concluded that SWE technique can provide guidance in patient selection for biopsy and determination of the biopsy site. In this context, we think that SWE examination may reduce unnecessary biopsies and biopsy repetitions. Key words: Renal transplantation, Sonoelastography, Shear Wave Elastography (SWE), Chronic allograft dysfunction, Chronic allograft rejection