Magnetic resonance imaging to assess renal flow distribution during ex vivo normothermic machine perfusion - It takes time to obtain cortical perfusion

R. Schutter, V.A. Lantinga, H.G.D. Leuvenink, R.J.H. Borra, C. Moers

Wednesday 4 march 2020

16:30 - 16:40h at Joep Nicolas zaal

Parallel session: Parallel sessie VII – Basale- en Klinische abstracts

Background: With increased use of renal grafts from suboptimal donors, the need for objective pre-transplant organ quality assessment has become more important than ever. Ex vivo normothermic machine perfusion (NMP) is a potentially promising method for evaluating kidney viability prior to transplantation. However, the exact physiological mechanisms that govern a kidney during NMP are unclear. Hence, it remains to be discovered which perfusion-based biomarkers are relevant for ex vivo organ evaluation and at which time point such assessment should be done. This study utilized functional magnetic resonance imaging (fMRI) to determine how regional flow distribution develops during NMP and indicates an appropriate window for on-pump viability assessment

Methods: Three viable porcine kidneys were retrieved from a slaughterhouse. NMP on a special MRI compatible setup was performed with a perfusate containing red blood cells, crystalloids and a colloid. Longitudinally, arterial spin labeling (ASL) sequences were performed. This technique is used to quantify blood perfusion without the use of an exogenous contrast agent. For each time point, we calculated the ratio of the average cortical and medullar signal intensity on the perfusion map (CM ratio). Absolute flow values for the whole kidney were externally measured with a flow sensor.

Results: During the first 30 minutes of NMP, cortical flow was extremely low compared to flow in the medulla, with an average CM ratio of 0.20. CM ratio gradually increased over time, with an average CM ratio of 0.42 after 60 minutes, 1.01 after 120 minutes and 1.14 after 180 minutes. It took approximately 2.5 hours before renal flow distribution reached a predominant cortical perfusion. Externally measured whole-kidney flow rates stabilized much earlier, after 60-90 minutes. At comparable whole-kidney flow rates within one experiment, completely different CM ratios were observed.

Conclusions: Externally measured flow values during renal NMP did not reliably correlate with cortico-medullar flow distribution. Perfusate flow distribution gradually shifted from mainly medullar to predominantly cortical during NMP. Only after approximately 2.5 hours, this pattern resembled a near-physiologic distribution. Since most functional units of the kidney are located in the cortex, ex vivo viability assessment should most likely be performed at time points past 2.5 hours from the start of NMP.