No abstract

Acute kidney injury (AKI) in premature neonates is common due to the administration of life‐saving therapies. The impact of AKI on renal morphology and susceptibility to further renal damage is poorly understood. Recent advances in radiological imaging have allowed integration of soft tissue morphology in the intact organ, facilitating a more complete understanding of changes in tissue microstructure associated with pathology. Here, we applied magnetic resonance imaging (MRI) to detect both glomerular and vascular changes in a rabbit model of neonatal AKI, induced by indomethacin and gentamicin. Using combined spin‐echo MRI and cationic ferritin enhanced gradient‐echo MRI (CFE‐MRI), we observed (a) an increased cortical arterial diameter in the AKI cohort compared to healthy controls, and (b) focal loss of vascular density and glomerular loss in a circumferential band ~1 mm from the cortical surface. This combined use of vascular and glomerular imaging may give insight into the etiology of AKI and its impact on renal health later in life.

Background: Accumulating evidence supports an association between nephron number and susceptibility to kidney disease. However, it is not currently possible to directly measure nephron number in a clinical setting. Recent clinical studies have used glomerular density from a single biopsy and whole kidney cortical volume from imaging to estimate both nephron number and single nephron glomerular filtration rate. However, the accuracy of these estimates from individual subjects is unknown. Furthermore, it is not clear how sample size or biopsy location may influence these estimates. These questions are critical to study design and to the potential translation of these tools to estimate nephron number in individual subjects. Methods: We measured the variability in estimated nephron number derived from needle or virtual biopsies and cortical volume in human kidneys declined for transplantation. We performed multiple needle biopsies in the same kidney, and examined the three-dimensional spatial distribution of nephron density by magnetic resonance imaging. We determined the accuracy of a single kidney biopsy to predict the mean nephron number estimated from multiple biopsies from the same kidney. Results: A single needle biopsy had a 15% chance and virtual biopsy had a 60% chance of being within 20% of whole kidney nephron number. Single needle biopsies could be used to detect differences in nephron number between large cohorts of several hundred subjects. Conclusions: The number of subjects required to accurately detect differences in nephron number between populations can be predicted based on natural intra-kidney variability in glomerular density. A single biopsy is insufficient to accurately predict nephron number in individual subjects.

Kidney pathologies are often highly heterogenous. To comprehensively understand kidney structure and pathology, it is critical to develop tool to map tissue microstructure in the context of the whole, intact organ. Magnetic resonance imaging (MRI) can provide a unique, three-dimensional (3D) view of the kidney and allows for measurement of multiple pathologic features. Here, we develop a platform to systematically render and map gross and microstructural features of the human kidney based on 3D MRI. These features include pyramid number and morphology, and associated medulla and cortex. in a subset of these kidneys, we also map individual glomeruli and glomerular volumes using cationic ferritin enhance-MRI to report intra-renal heterogeneity in glomerular density and size. Finally, we render and measure regions of nephron loss due to pathology and individual glomerular volumes in each pyramidal unit. This work provides new tools to comprehensively evaluate the kidney across scales, with potential applications in anatomical and physiological research, transplant allograft evaluation, biomarker development, biopsy guidance, and therapeutic monitoring. These image rendering and analysis tools could eventually impact the field of transplantation medicine to improve longevity matching of donor allografts and recipients and reduce discard rates through the direct assessment of donor kidneys.