Quantification of glomerular number and size distribution in normal rat kidneys using magnetic resonance imaging

Background. Glomerular number and size are important risk factors for chronic kidney disease (CKD) and cardiovascular disease and have traditionally been estimated using invasive techniques. Here, we report a novel technique to count and size every glomerulus in the rat kidney using magnetic resonance imaging (MRI). Methods. The ferromagnetic nature of cationized ferritin allowed visualization of single glomeruli in high-resolution susceptibility-weighted MRI. A segmentation algorithm was used to identify and count all glomeruli within the whole kidney. To prove our concept, we estimated total glomerular number and mean glomerular volume of each kidney using design-based stereology. Results. The glomerular counts obtained with MRI agreed well with estimates obtained using traditional methods [MRI, 32 785 (3117); stereology, 35 132 (3123)]. For the first time, the glomerular volume distribution for the entire kidney is shown. Additionally, the method is substantially faster than the current methods. Conclusions. MRI provides a new method for measuring these important microanatomical markers of disease risk and leads the way to in vivo analysis of these parameters, including longitudinal studies of animal models of CKD.