Magnetic resonance imaging for the evaluation of rejection of a kindney allograft in the rat

Orthotopic DA (RT1^a) into Lewis (RT1¹) rat kidney allografts and control Lewis-into-Lewis grafts were assessed by magnetic resonance imaging (MRI) and perfusion measurement after intravenous injection of a superparamagnetic contrast agent. MRI anatomical scores (range 1–6) and perfusion rates were compared with graft histology (rank of rejection score 1–6). Not only acute rejection, but also chronic events were monitored after acute rejection was prevented by daily cyclosporine (Sandimmune) treatment during the first 2 weeks after transplantation. In acute allograft rejection (n=11), MRI scores reached the maximum value of 6 and perfusion rates were severely reduced within 5 days after transplantation; histology showed severe acute rejection (histologic score 5–6). In the chronic phase (100–130 days after transplantation), allografts (n=5) manifested rejection (in histology cellular rejection and vessel changes), accompanied by MRI scores of around 2–3 and reduced perfusion rates. Both in the acute and chronic phases, the MRI anatomical score correlated significantly with the histological score (Spearman rank correlation coefficient r _s 0.89, n=30, P<0.01), and perfusion rates correlated significantly with the MRI score or histological score (r _s values between-0.60 and -0.87, n=23, P<0.01). It is concluded that MRI represents an interesting tool for assessing the anatomical and hemodynamical status of a kidney allograft in the acute and chronic phases after transplantation.