Dynamic ¹⁸F-fluoride small animal PET to noninvasively assess renal function in rats

Renal function can be quantified by both laboratory and scintigraphic methods. In the case of small animal diagnostics, scintigraphic image-based methods are ideal since they can assess split renal function, work noninvasively, and can be repeated. The aim of this study is to validate a ¹⁸F-PET-based method to quantify renal function in rats.

Fluoride clearance was calculated from a dynamic whole body listmode acquisition of 60 min length in a small animal PET scanner following an i.v. injection of 15 MBq ¹⁸F-fluoride. Volumes of interest (VOIs) were placed in the left ventricle and the bladder as well as traced around the kidney contours. The respective time–activity curves (TAC) were calculated. The renal ¹⁸F-clearance was calculated by the ratio of the total renal excreted activity (bladder VOI) and the integral of the blood TAC. PET-derived renal function was validated by intraindividual measurements of creatinine clearance (n = 23), urea clearance (n = 23), and tubular excretion rate (TER-MAG3). The split renal function was derived from the injection of the clinically available radionuclide ^99mTc-mercaptotriglycine by blood sampling and planar renography (n = 8).

In all animals studied, PET revealed high-quality TACs. PET-derived renal fluoride clearance was linearly correlated with intraindividual laboratory measures (PET vs. creatinine: r = 0.78; PET vs. urea: r = 0.73; PET vs. TER-MAG3: r = 0.73). Split function was comparable (¹⁸F-PET vs. MAG3-renography: r = 0.98). PET-derived measures were highly reproducible.

¹⁸F-PET is able to noninvasively assess renal function in rats and provides a significant potential for serial studies in different experimental scenarios.