In vivo monitoring of renal tubule volume fraction using dynamic parametric MRI

The increasing incidence of kidney diseases is a global concern, and current biomarkers and treatments are inadequate. Changes in renal tubule luminal volume fraction (TVF) serve as a rapid biomarker for kidney disease and improve understanding of renal (patho)physiology. This study uses the amplitude of the long T₂ component as a surrogate for TVF in rats, by applying multiexponential analysis of the T₂-driven signal decay to examine micromorphological changes in renal tissue.

Simulations were conducted to identify a low mean absolute error (MAE) protocol and an accelerated protocol customized for the in vivo study of T₂ mapping of the rat kidney at 9.4 T. We then validated our bi-exponential approach in a phantom mimicking the relaxation properties of renal tissue. This was followed by a proof-of-principle demonstration using in vivo data obtained during a transient increase of renal pelvis and tubular pressure.

Using the low MAE protocol, our approach achieved an accuracy of MAE < 1% on the mechanical phantom. The T₂ mapping protocol customized for in vivo study achieved an accuracy of MAE < 3%. Transiently increasing pressure in the renal pelvis and tubules led to significant changes in TVF in renal compartments: ΔTVF_cortex = 4.9%, ΔTVF_{outer_medulla} = 4.5%, and ΔTVF_{inner_medulla} = -14.6%.

These results demonstrate that our approach is promising for research into quantitative assessment of renal TVF in in vivo applications. Ultimately, these investigations have the potential to help reveal mechanism in acute renal injury that may lead to chronic kidney disease, which will support research into renal disorders.