Comparison of superb microvascular imaging (SMI) technique with conventional doppler ultrasound techniques in the evaluation of kidney vascularity in renal transplant receivers

Chronic kidney failure is increasing rapidly all over the world. Renal transplantation is considered to be the best treatment for patients with kidney failure. It is very important to recognize post-transplant complications early and prolong the survival of the transplanted kidney. Renal biopsy is the gold standard diagnostic method for transplanted kidney with dysfunction. CADI (Chronic Allograft Damage Index) is a biopsy-based technique used to score malfunction in the transplanted kidney. However, biopsy has limitations and contraindications. We aimed to use Doppler examination methods and SMI technique, instead of biopsy, which is an invasive method, in predicting the CADI. In addition, we aimed to compare the SMI technique and conventional Doppler techniques in predicting biopsy results and preventing recurrent biopsies. In this study, we evaluated 68 renal transplant patients who underwent kidney biopsy with a pre-diagnosis of rejection between January 2020 and October 2020 in the Radiology Department of Akdeniz University Hospital, with renal Doppler USG before the biopsy procedure. In the examination, at the level of the lower pole of the transplanted kidney; The distance between the renal capsule and the vascular structure closest to the capsule was measured by color Doppler ultrasonography (CDUS), power Doppler ultrasonography (PDUS) and superb microvascular imaging (SMI) techniques. We also measured kidney longitudinal size, resistive index (RI) values from the arcuate artery level in the lower pole of the kidney, and renal artery flow velocities. We statistically compared the relationship between creatine values, RI values, CADI score depending on the time elapsed after transplantation. We investigated the statistical relationship between "capsule-vessel distances measured by conventional Doppler method and SMI technique" and "CADI score". In our study, we found that as the time elapsed after transplantation increases, the severity of chronic kidney damage increases. We observed that the severity of the injury increased significantly, especially one year after transplantation. The creatinine values of the cases with high CADI scores were found to be significantly higher. There was no statistically significant correlation between the CADI score and RI values. The mean value of the distance between the renal capsule and the vessel was 2.44 mm in color Doppler examination, 1.34 mm in power Doppler examination, 0.99 mm in cSMI technique and 0.86 mm in mSMI technique. In our study, the SMI technique is better than the color and power Doppler technique in showing the cortical microvesseling of the kidney. There is a strong relationship between "CADI score" and "graft survival and function" in the literature (42,43,79,82,83,84). However, there is no radiological examination used to predict the CADI score. In this study, we found that, according to statistical results, conventional Doppler examinations and SMI technique are effective methods of investigation in predicting CADI score. The test with the highest sensitivity is the power Doppler technique, and the highest specificity is the cSMI technique in distinguishing high and low CADI scores. Although the sensitivities of cSMI and mSMI techniques are similar, the specificity of the cSMI technique is higher. Color Doppler has the lowest specificity. In conclusion, our study revealed that the capsule-vessel distance measured by Doppler examination and SMI technique can be used to predict the CADI score, which is closely related to graft survival and function, and it is the first study in the literature on this subject. We think that our study will allow to reduce the need for recurrent renal biopsy, to calculate risk in cases where kidney biopsy cannot be performed, or to provide appropriate treatment before graft loss occurs in patients with kidney transplantation. In addition, we think that our study can be used in evaluating the response of patients with transplanted kidney to drug treatment. However, national or international studies covering more patients are needed on this subject. Key Words: Kidney transplantation, Superb microvascular imaging (SMI), Doppler US, Chronic Allograft Damage Index (CADI)