Improved diagnosis of early kidney allograft dysfunction by ultrasound with echo enhancer—a new method for the diagnosis of renal perfusion

Background. Conventional ultrasound parameters such as the resistance index (RI) are only of limited use in the diagnosis of early allograft dysfunction. We, therefore, performed a prospective study to compare the value of ultrasound contrast media (USCM) with conventional US in the diagnosis of early allograft dysfunction. Methods. A total of 48 consecutive kidney recipients underwent US examination after USCM administration 4–10 days after transplantation. Arterial inflow was determined in the interlobar artery and renal cortex using time–intensity curve (TIC) software. The difference in time-to-peak intensity between these two vascular territories was determined, and a perfusion quotient (PQ) was defined as the ratio of TIC increase of interlobar artery to renal cortex. Three patients with segmental loss of renal perfusion demonstrated by Doppler US were excluded. Results. Nineteen patients had an uneventful clinical course (control group); PQ was 1.2 ± 0.4. Seven patients with a large perirenal haematoma, without rejection had an increased PQ (P < 0.05) and a prolonged time difference (P < 0.05). Based on clinical and histological criteria, the remaining patients were classified as acute tubular necrosis (ATN) (n = 7), non-vascular rejection (n = 7) or vascular rejection (n = 5). RI determination could not discriminate these groups. Patients with ATN (PQ = 1.6 ± 0.7) or non-vascular rejection (PQ = 1.1 ± 0.6) had a lower PQ than patients with vascular rejection (PQ = 2.2 ± 0.8, P < 0.05). The time difference in all three subgroups was longer compared with controls. Conclusions. USCM might be superior in the diagnosis of early kidney allograft dysfunction compared with conventional US by means of RI determination. Perirenal haematoma, ATN and vascular rejection are associated with characteristic changes of the TIC.