Counting glomeruli in human kidney specimens using ex vivo MRI without contrast agents
Nyoman D. Kurniawan, Aurel J. Amar, Luise A. Cullen‐McEwen, Alexander N. Combes, Raeesah Hayatudin, Andrew J. Kassianos, Jiaxin Du, Sarah E. Gazzard, Helen Grania Healy, Wendy E. Hoy, John F. Bertram, David C. Reutens · Magnetic Resonance in Medicine · 2025
PURPOSE: The total number of glomeruli is an important indicator of kidney function and susceptibility to disease. Glomeruli, however, are difficult to image using MRI without contrast enhancement. For this reason, previous studies have used cationic ferritin as a contrast agent to detect glomeruli in ex vivo and in vivo perfused kidneys. This study aimed to develop a new technique using MR microimaging at ultrahigh field, without contrast agents, to visualize and quantify glomeruli in human nephrectomy samples. METHODS: . A segmentation pipeline based on shape recognition and clustering was developed to count glomeruli on MR images at 30-μm isotropic resolution. Glomerular number and density were estimated after MRI using unbiased stereology, and glomerular distribution was visualized using a subset of samples imaged using confocal microscopy. RESULTS: Glomeruli were identified in the MR images as hypointense spheres. High spatial concordance between glomeruli identified by MRI, histology, and confocal microscopy was observed. Statistical analyses showed that glomerular counts from stereology and MR images were similar, with Pearson correlation and intraclass correlation coefficients of 0.98. CONCLUSION: High-resolution microimaging at 16.4 T combined with automated segmentation allowed identification and quantitation of human glomeruli ex vivo without the need for contrast agents. The results showed strong agreement with the gold-standard stereological method for glomerular counting.