Background: The aim of this study was the assessment of kidney morphology and glomerular filtration rate (GFR) in rat models of polycystic kidney disease and a healthy control group of Sprague-Dawley rats (SD rats). The performance of two non-invasive GFR estimation methods-3.0 Tesla magnetic resonance imaging (MRI) and optical imaging were investigated. Data of GFR assessment was compared to surrogate markers of kidney function and renal histology.
Methods: Optical imaging of GFR was performed transcutaneously in a small animal imaging system with the fluorescent renal marker fluorescein-isothiocyanate-labelled-sinistrin. Morphologic and dynamic renal imaging was done on a clinical 3.0T MR scanner. Renal perfusion analysis was performed with a two-compartment filtration model.
Results: The healthy SD rats showed physiological levels of creatinine and urea, indicating normal kidney function. These parameters were elevated in the small animal groups of polycystic kidney disease. For the calculation of perfusion and filtration parameters of kidney function in MRI, a 2D turbo FLASH sequence was performed and allowed to distinguish between normal GFR of healthy rats and reduced GFR of rats with polycystic kidney disease. Also, MRI GFR varied among two different rat strains of polycystic kidney disease, according to their status of renal function impairment. Optical imaging GFR confirmed higher GFR values in healthy rats compared to ill rats but did not show different results among the two rat strains of polycystic kidney disease. For this reason, MRI and optical imaging GFR estimation presented an intra-method bias.
Conclusions: Both non-invasive estimation methods of GFR, MRI and optical imaging, can differentiate between healthy rats and animals with limited kidney function. Furthermore, optical imaging, unlike MRI, seems to consider that disease progression with increase of renal polycystic deterioration does not correlate with decrease of GFR in the initial stage of compensatory hyperfiltration.