Objectives: Confirmed diagnosis for rejection after kidney transplantation is histopathological findings with kidney graft biopsy．However, a graft biopsy is not able to be indicated for the patients depending on their conditions including just after transplantation, a use of anticoagulant agencies and poor physical status for these patients, contrast-enhanced ultrasonography (CEUS) may be of use because of its non-invasive procedure. CEUS is able to evaluate tissue blood flow of the graft in real-time, which may reflect endothelial cell injury and interstitial edem due to cellular infiltration observed in the rejection, in this study, we examined the utility of CEUS in terms of a diagnosis of rejection. 
Method: From August 2015 to May 2017 in our department, Fujita Health University Hospital, we have experienced the CEUS study for five patients developing the rejection after kidney transplantation. From the clinical findings including blood chemistry, antibody examination and graft biopsy, three patients were diagnosed as acute antibody mediated rejection (AAMR) and the other two patients were diagnosed as acute T-cell mediated rejection (ATMR). In each case, we compared the findings obtained from CEUS before and after the treatment for the rejection.
Result: In normal grafts, a tissue blood flow rapidly reaches to the subcapsular tissue. The delayed tissue flow was observed in the 4 patients with rejection (2 AAMR, 2 ATMR). In the other one patient with AAMR, the total defect of blood flow in the cortex in addition to the delayed tissue flow in the meduula of the graft. In the 5 patients showing the delayed tissue flow, 2 AAMR patients and 1 ATMR patient showed “to and fro” movement pattern of the arteries of the graft. These findings of CEUS observed in the rejection after kidney transplantation recovered to normal pattern by the rejection therapy including a steroid pulse therapy and an administration of anti-human thymocyte globulin for ATMR and a plasma exchange and an administration of rituximab. However, one patient with AAMR, showing filling defect of the cortex with CEUS, resulted in the graft failure in spite of the rejection therapy for AAMR. From these results, CEUS is able to reflect the disturbance of the arterial and tissue blood flow. The delayed tissue flow and “to and fro” movement pattern of the arteries reflect the graft’s rejection and useful for the evaluation of the rejection therapy. Further studies are needed concerning with the differential diagnosis of the rejection (AMR or TMR) and the evaluation of the severity of the rejection.
Conclusion: Contrast-enhanced ultrasonography (CEUS) may be of use for a diagnosis of the rejection in the kidney transplant recipients especially in the patients who can not be performed with graft’s biopsy.