Transplanted kidney’s functional evaluation with contrast-enhanced power Doppler ultrasound and time/intensity curves

Purpose: to evaluate the diagnostic capabilities of contrast-enhanced power Doppler ultrasound (CEUS) with time/intensity curves in the study of renal graft function in order to identify pathognomonic patterns of both physiologic and pathologic (acute tubular necrosis and chronic rejection) conditions. Materials and methods: 46 asymptomatic renal transplant patients (36 men and 20 women), 19 of whom had altered creatinine clearance levels, were studied by CEUS with time/intensity curves. US examinations were compared with renal biopsy available in all patients and considered as the gold standard. Ten asymptomatic patients with normal creatinine clearance levels were used as control group. Results: time/intensity curves allowed representation of the kidney’s wash-in and wash-out phases after intravenous administration of contrast agent US. Time/intensity curves analysis enabled identification of three groups of patients: group A (27 patients) showing peak enhancement between 50 and 65 seconds from intravenous administration of contrast agent US; group B (16 patients) with peak enhancement between 135 and 235 seconds; group C (3 patients) with peak enhancement between 100 and 130 seconds. The control group showed a peak enhancement between 50 and 65 seconds. Biopsy demonstrated absence of disease in group A; it permitted a diagnosis of chronic rejection in group B and acute tubular necrosis in group C. Conclusion: CEUS is a non-invasive imaging technique that allows a functional evaluation of the transplanted kidney. The presence of pathognomonic patterns in patients with chronic rejection and acute tubular necrosis could allow the identification of pathologic conditions avoiding renal biopsy.