[18F]-sodium fluoride autoradiography imaging of nephrocalcinosis in donor kidneys and explanted kidney allografts

Nephrocalcinosis is present in up to 43% of kidney allograft biopsies at one-year after transplantation and is associated with inferior graft function and poor graft survival. We studied [F-18]-sodium fluoride ([F-18]-NaF) imaging of microcalcifications in donor kidneys (n=7) and explanted kidney allografts (n=13). Three mu m paraffin-embedded serial sections were used for histological evaluation of calcification (Alizarin Red; Von Kossa staining) and ex-vivo [F-18]-NaF autoradiography. The images were fused to evaluate if microcalcification areas corresponded with [F-18]-NaF uptake areas. Based on histological analyses, tubulointerstitial and glomerular microcalcifications were present in 19/20 and 7/20 samples, respectively. Using autoradiography, [F-18]-NaF uptake was found in 19/20 samples, with significantly more tracer activity in kidney allograft compared to deceased donor kidney samples (p=0.019). Alizarin Red staining of active microcalcifications demonstrated good correlation (Spearman's rho of 0.81, p<0.001) and Von Kossa staining of consolidated calcifications demonstrated significant but weak correlation (0.62, p=0.003) with [F-18]-NaF activity. This correlation between ex-vivo [F-18]-NaF uptake and histology-proven microcalcifications, is the first step towards an imaging method to identify microcalcifications in active nephrocalcinosis. This may lead to better understanding of the etiology of microcalcifications and its impact on kidney transplant function.

Automated summary

Nephrocalcinosis is common in kidney transplant recipients and is associated with poor graft outcomes. In this study, [F-18]-sodium fluoride imaging was used to detect microcalcifications in donor and transplanted kidneys, revealing higher tracer activity in transplanted kidneys. The correlation between [F-18]-NaF uptake and histology-proven microcalcifications could potentially lead to a better understanding of the impact of microcalcifications on kidney transplant function.