Measuring glomerular number and size in perfused kidneys using MRI

Area of Science:

• Nephrology
• Biomedical Imaging
• Medical Physics

Background:

• Glomerular number and size variations are implicated in renal and systemic diseases.
• Accurate quantification of glomeruli is crucial for understanding kidney health and disease.
• Existing histological methods for counting glomeruli are destructive and provide limited volumetric data.

Purpose of the Study:

• To develop and validate a non-destructive magnetic resonance imaging (MRI) technique for measuring whole-kidney glomerular number and volume.
• To establish a robust method for assessing variations in glomeruli linked to renal diseases.
• To enable in vivo measurements of glomerular parameters in animal models and potentially humans.

Main Methods:

• Intravenous injection of cationic ferritin (CF) as a contrast agent for MRI.
• High-field (19 Tesla) gradient-echo MRI to visualize and label individual glomeruli.
• Development of a 3D image-processing algorithm for automated glomerulus counting.
• Comparison of MRI-based counts and volumes with traditional methods like acid maceration and stereology.

Main Results:

• The MRI technique successfully labeled and enabled counting of individual glomeruli throughout the rat kidney.
• MRI-based glomerular counts (33,786 ± 3,753) closely matched counts from acid maceration (30,585 ± 2,053) and stereology (34,963).
• MRI accurately measured apparent glomerular volume (4.89 × 10(-4) mm(3)) comparable to stereology (4.99 × 10(-4) mm(3)) and provided intrarenal volume distribution.

Conclusions:

• A non-destructive MRI technique using CF allows accurate quantification of whole-kidney glomerular number and volume.
• This novel imaging approach overcomes limitations of destructive histological methods.
• The technique holds promise for advancing research into renal diseases and enabling in vivo glomerular assessments.