OBJECTIVE To assess the effects of 3 contrast medium injection techniques on attenuation values for canine adrenal glands during contrast-enhanced CT.
ANIMALS 9 healthy Beagles.
PROCEDURES 3 protocols were evaluated in a randomized cross-over design study: 700 mg of iodine/kg at a constant injection rate over 20 seconds (full-dose constant rate), the same dose at a rate following an exponential decay curve over 20 seconds (full-dose decelerated rate), and 350 mg of iodine/kg at a constant injection rate over 10 seconds (half-dose constant rate). Multislice CT images were obtained before and at predetermined time points after the start of contrast medium injection.
RESULTS Median peak attenuation values were 129, 133, and 87 Hounsfield units with the full-dose constant rate, full-dose decelerated rate, and half-dose constant rate injection protocols, respectively. Peak attenuation differed significantly between the full-dose constant rate and half-dose constant rate injection protocols and between the full-dose decelerated rate and half-dose constant rate injection protocols. Median time to peak attenuation did not differ significantly among injection methods and was 30, 23, and 15 seconds for the full-dose constant rate, full-dose decelerated rate, and half-dose constant rate injections, respectively.
CONCLUSIONS AND CLINICAL RELEVANCE The dose of contrast medium and the timing of postinjection CT scanning were main determinants of peak attenuation for adrenal glands in healthy dogs; effects of the 3 injection protocols on attenuation were minor. The exponentially decelerated injection method was subjectively complex. A constant injection protocol delivering 700 mg of iodine/kg over 20 seconds, with scans obtained approximately 30 seconds after starting contrast medium injection, provided images with maximum adrenal gland attenuation values. (Am J Vet Res 2016;77:144–150)
PROCEDURES Each dog underwent 3 iohexol-injection protocols (700 mg of iodine/kg administered at a constant rate over 20 seconds, 700 mg of iodine/kg administered following an exponentially decelerated injection over 20 seconds, and 350 mg of iodine/kg at a constant rate over 10 seconds) during dynamic, whole renal-volume CT in randomized order with an interval of ≥ 7 days between experiments. Values of GFR determined from Patlak plots derived by use of 4 measurement techniques (standard transverse section, optimized transverse section, dorsal reconstruction, and volume calculation techniques) were compared.
RESULTS The measurement technique influenced the mean ± SD GFR results (standard transverse section technique, 2.49 ± 0.54 mL/kg/min; optimized transverse section technique, 2.72 ± 0.52 mL/kg/min; dorsal reconstruction technique, 3.00 ± 0.60 mL/kg/min, and volume calculation technique, 2.48 ± 0.51 mL/kg/min). The lower iodine dose resulted in a significantly higher GFR value (3.00 ± 0.65 mL/kg/min), compared with that achieved with either higher dose administration (constant rate injection, 2.54 ± 0.45 mL/kg/min and exponentially decelerated injection, 2.47 ± 0.48 mL/kg/min).
CONCLUSIONS AND CLINICAL RELEVANCE In healthy Beagles, the CT-derived GFR measurements obtained after injection of a full dose of contrast medium were reduced, compared with measurements obtained after injection of a half dose. This finding is important with regard to potential nephrotoxicosis in dogs with impaired renal function and for GFR measurement with CT-contrast medium protocols.