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Kidney pathologies are often highly heterogeneous. To comprehensively understand kidney structure and pathology, it is critical to develop tools to map tissue microstructure in the context of the whole, intact organ. Magnetic resonance imaging (MRI) can provide a unique, three-dimensional view of the kidney and allows for measurements of multiple pathological features. Here, we developed a platform to systematically render and map gross and microstructural features of the human kidney based on three-dimensional MRI. These features include pyramid number and morphology as well as the associated medulla and cortex. In a subset of these kidneys, we also mapped individual glomeruli and glomerular volumes using cationic ferritin-enhanced MRI to report intrarenal heterogeneity in glomerular density and size. Finally, we rendered and measured 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 anatomic 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. NEW & NOTEWORTHY We report the application of cutting-edge image analysis approaches to characterize the pyramidal geometry, glomerular microstructure, and heterogeneity of the whole human kidney imaged using MRI. This work establishes a framework to improve the detection of microstructural pathology to potentially facilitate disease monitoring or transplant evaluation in the individual kidney.

number is highly variable in humans and is thought to play an important role in renal health. Chronic kidney disease (CKD) is the result of too few nephrons to maintain homeostasis. Currently, nephron number can only be determined invasively or as a terminal assessment. Due to a lack of tools to measure and track nephron number in the living, the early stages of CKD often go unrecognized, preventing early intervention that might halt the progression of CKD. In this work, we present a technique to directly measure glomerular number ( N glom ) and volume in vivo in the rat kidney ( n = 8) using MRI enhanced with the novel contrast agent cationized ferritin (CFE-MRI). Adult male rats were administered intravenous cationized ferritin (CF) and imaged in vivo with MRI. Glomerular number was measured and each glomerulus was spatially mapped in 3D in the image. Mean apparent glomerular volume (a V glom ) and intrarenal distribution of the individual glomerular volume (IGV), were also measured. These metrics were compared between images of the same kidneys scanned in vivo and ex vivo with CFE-MRI. In vivo N glom and a V glom correlated to ex vivo metrics within the same kidneys and were within 10% of N glom and a V glom previously validated by stereologic methods. This is the first report of direct in vivo measurements of N glom and a V glom , introducing an opportunity to investigate mechanisms of renal disease progression and therapeutic response over time.

Magnetic resonance imaging (MRI) is becoming important for whole-kidney assessment of glomerular morphology, both in vivo and ex vivo. MRI-based renal morphological measurements can be made in intact organs and allow direct measurements of every perfused glomerulus. Cationic ferritin (CF) is used as a superparamagnetic contrast agent for MRI. CF binds to the glomerular basement membrane after intravenous injection, allowing direct, whole-kidney measurements of glomerular number, volume, and volume distribution. Here we describe the production, testing, and use of CF as an MRI contrast agent for quantitative glomerular morphology in intact mouse, rat, and human kidneys.

Nephron number (N(glom)) and size (V(glom)) are correlated with risk for chronic cardiovascular and kidney disease and may be predictive of renal allograft viability. Unfortunately, there are no techniques to assess N(glom) and V(glom) in intact kidneys. This work demonstrates the use of cationized ferritin (CF) as a magnetic resonance imaging (MRI) contrast agent to measure N(glom) and V(glom) in viable human kidneys donated to science. The kidneys were obtained from patients with varying levels of cardiovascular and renal disease. CF was intravenously injected into three viable human kidneys. A fourth control kidney was perfused with saline. After fixation, immunofluorescence and electron microscopy confirmed binding of CF to the glomerulus. The intact kidneys were imaged with three-dimensional MRI and CF-labeled glomeruli appeared as punctate spots. Custom software identified, counted, and measured the apparent volumes of CF-labeled glomeruli, with an ~6% false positive rate. These measurements were comparable to stereological estimates. The MRI-based technique yielded a novel whole kidney distribution of glomerular volumes. Histopathology demonstrated that the distribution of CF-labeled glomeruli may be predictive of glomerular and vascular disease. Variations in CF distribution were quantified using image texture analyses, which be a useful marker of glomerular sclerosis. This is the first report of direct measurement of glomerular number and volume in intact human kidneys., (Copyright © 2014 the American Physiological Society.)

Techniques to measure morphological parameters, such as glomerular (and thereby nephron) number, glomerular size, and kidney volume, have been vital to understanding factors contributing to chronic kidney disease (CKD). These techniques have also been important to understanding the associations between CKD and other systemic and cardiovascular diseases and have led to the identification of developmental risk factors for these pathologies. However, existing techniques in quantitative kidney morphology are resource- and time-consuming and are destructive to the organ. This review discusses the emerging generation of techniques to study kidney morphology quantitatively using magnetic resonance imaging (MRI) using the intravenous injection of the superparamagnetic nanoparticle cationic ferritin, which binds to the glomerular basement membrane. A primary advantage of MRI over previously established techniques is the ability to quantify morphology in the intact organ with minimal sample preparation. We highlight areas of research where MRI-based morphological measurements will be helpful in animal models and possibly diagnostic clinical nephrology, discuss technical challenges in light of the progress in MRI techniques to date, and identify novel measurements that may be possible using MRI, both ex vivo and in vivo.

The goal of this work was to nondestructively measure glomerular (and thereby nephron) number in the whole kidney. Variations in the number and size of glomeruli have been linked to many renal and systemic diseases. Here, we develop a robust magnetic resonance imaging (MRI) technique based on injection of cationic ferritin (CF) to produce an accurate measurement of number and size of individual glomeruli. High-field (19 Tesla) gradient-echo MR images of perfused rat kidneys after in vivo intravenous injection of CF showed specific labeling of individual glomeruli with CF throughout the kidney. We developed a three-dimensional image-processing algorithm to count every labeled glomerulus. MRI-based counts yielded 33,786 ± 3,753 labeled glomeruli (n = 5 kidneys). Acid maceration counting of contralateral kidneys yielded an estimate of 30,585 ± 2,053 glomeruli (n = 6 kidneys). Disector/fractionator stereology counting yielded an estimate of 34,963 glomeruli (n = 2). MRI-based measurement of apparent glomerular volume of labeled glomeruli was 4.89 × 10(-4) mm(3) (n = 5) compared with the average stereological measurement of 4.99 × 10(-4) mm(3) (n = 2). The MRI-based technique also yielded the intrarenal distribution of apparent glomerular volume, a measurement previously unobtainable in histology. This work makes it possible to nondestructively measure whole-kidney glomerular number and apparent glomerular volumes to study susceptibility to renal diseases and opens the door to similar in vivo measurements in animals and humans.