In vivo measurements of relaxivities in the rat kidney cortex.
The aim of this study was to implement a novel noninvasive method to derive the in vivo T1 relaxivity (R1) and T2 relaxivity (R2) in the rat kidney cortex. A two-compartment gadolinium diethylene triamine pentaacetic acid (Gd-DTPA) distribution model was established to estimate the bolus and infusion dosages of Gd-DTPA necessary for obtaining the required steady-state concentration levels. After a single bolus injection of (99m)Tc-DTPA, several blood samples were collected. Based on considerations from the applied two-compartment model, a steady-state concentration was predicted approximately 5-10 minutes after the bolus injection. The plasma concentration levels of Gd-DTPA were measured by simultaneous injection of (99m)Tc-DTPA. Three regions in the cortex (upper, central, and lower) of both rat kidneys were used. A statistical evaluation resulted in the following in vivo relaxivities found at 7 T: R1 = 1.04 +/- 0.08 mM(-1)s(-1) and R2 = 10.78 +/- 0.83 mM(-1)s(-1). Using a 95% confidence interval, no intracortical differences were detected. The relaxivities R1 and R2 calculated in the intact rat kidney cortex were distinctly different from relaxivities found in human plasma: (22 degrees C) 4.42 +/- 0.07 mM(-1)s(-1) (r2> 0.98) and R2 = 5.75 +/- 0.17 mM(-1)s(-1) (r2> 0.98), respectively. The measurements showed a marked difference between in vitro and in vivo relaxivities. Comparison of the distribution rates in pig, human, and rats shows a distinct proportionality between size and renal function.
Pedersen
M
M
MR Research Center, Aarhus University Hospital, Denmark. michael@mr.mr.sks.auh.dk
Mørkenborg
J
J
Jensen
F T
FT
Stødkilde-Jørgensen
H
H
Djurhuus
J C
JC
Frokiaer
J
J
D000818:Animals; D003287:Contrast Media / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004305:Dose-Response Relationship, Drug; D019786:Gadolinium DTPA / Q000008:administration & dosage / Q000493:pharmacokinetics*; D007262:Infusions, Intravenous; D007275:Injections, Intravenous; D007672:Kidney Cortex / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D017556:Technetium Compounds
D003287:Contrast Media; D017556:Technetium Compounds; D019786:Gadolinium DTPA