Acoustic Radiation Force Impulse Imaging of the Transplant Kidney: Correlation Between Cortical Stiffness and Arterial Resistance in Early Post-transplant Period

Background: Acoustic radiation force impulse (ARFI) imaging is a noninvasive imaging modality for quantitative assessment of tissue stiffness. This study utilized ARFI imaging to assess the stiffness of a transplant renal cortex within the first month after renal transplantation and to explore the correlation between the cortical stiffness and arterial resistance of the transplant kidney.

Methods: Forty renal transplant recipients (male/female = 26/14; mean age: 45.3 years; deceased donor/living related donor = 27/13) were included in this study. ARFI imaging with virtual touch tissue imaging quantification was applied to assess the stiffness of the transplant renal cortex by using a linear ultrasound transducer. Arterial resistance was acquired by spectral Doppler examination of the main artery and intrarenal arteries of the transplant kidney using a curvilinear ultrasound transducer.

Results: The stiffness of transplant renal cortex was expressed as shear wave velocity (m/s). The mean value of cortical stiffness was 3.19 ± 1.01 m/s (range: 1.55-5.54). The stiffness of transplant renal cortex was positively correlated with the resistance index of the main renal artery (r = 0.55, P = .001), segmental artery (r = 0.43, P = .005), and interlobar artery (r = 0.42, P = .006).

Conclusion: The stiffness of a transplant renal cortex is positively correlated with the arterial resistance of the renal transplant in the early post-transplant period. This result indicates that, in addition to renal fibrosis, the stiffness of the transplant renal cortex is also influenced by the hemodynamics of the transplant kidney.