ESTIMATING GLOMERULAR NUMBER IN-SITU USING MAGNETIC-RESONANCE-IMAGINGAND BIOPSY

In the past researchers have used an estimate of one million as the nu mber of glomeruli in each human kidney. However, recent work on excise d kidneys has demonstrated a large variation in glomerular number from one person to another (330,000 to 1,400,000) per kidney. Theoreticall y an in situ estimate of glomerular number could be obtained if renal cortical volume, volume density of glomeruli per cortex [Vv(glom/corte x)] and mean glomerular volume are known. We used a dog model to demon strate that an accurate estimate of cortical volume could be obtained in situ using magnetic resonance imaging (MRI). Vv(glom/cortex) and me an glomerular volume were obtained from needle biopsies. An independen t and more direct method (the fractionator) was used to validate the e stimate of glomerular number obtained using MRI and renal biopsy. On a verage there was very good agreement between the fractionator method ( 379,000 +/- 40,000) and the MRI/renal biopsy method (376,000 +/- 108,0 00) for the 10 dog kidneys measured; however we found up to a 36% diff erence between the two methods in an individual kidney. Nonetheless, t he estimate from the MRI/renal biopsy method has more precision than t he assumption that there are one million glomeruli per human kidney.