1276 AJVR, Vol 72, No. 9, September 2011 C ats provide special companionship to humans, and general management of their health is important because of their long life span. Evaluation of kidney function is especially important in cats because chronic renal disease appears to be a major cause of illness and death in middle-aged to older cats. Clinical assessment of early kidney dysfunction benefits clients and patients by allowing determination of the long-term prognosis and timely institution of renal protective treatments. 1 The traditional criterion-referenced standard for mea- suring the GFR is determination of exogenous inulin clearance; however, this method is technically difficult, which renders it impractical for clinical use. 1 Therefore, additional clinical methods have been investigated, such as use of plasma clearance of radioactive agents Evaluation of glomerular filtration rate by use of dynamic computed tomography and Patlak analysis in clinically normal cats Jinhwa Chang, DVM, PhD; Sejoon Ahn, DVM, PhD; Sooyoung Choi, DVM, MS; Heechun Lee, DVM, PhD; Dongwoo Chang, DVM, PhD; Hojung Choi, DVM, PhD; Youngwon Lee, DVM, PhD Objective—To obtain quantitative variables of the abdominal aorta and both kidneys on the basis of time-attenuation curves (TACs) and to measure glomerular filtration rate (GFR) for each kidney and the global GFR in clinically normal cats by use of dynamic computed tomography (CT) and Patlak analysis. Animals—9 healthy cats. Procedures—All the cats were anesthetized with propofol. Anesthesia was maintained by administration of isoflurane, and CT examination was performed in the anesthetized cats. The TACs and renal volume were measured by use of the baseline precontrast and single- slice dynamic scans. The CT-GFR of each kidney and the global CT-GFRs were calculated via Patlak plot analysis. Results—CT-GFR results from 7 cats were valid. Peak aortic enhancement was detected between 9.0 and 14.0 seconds after iohexol injection, and the initial peak time of renal parenchymal enhancement was 15 to 24 seconds after iohexol injection. Mean ± SD global GFR was 2.06 ± 0.62 mL/min/kg. Mean ± SD CT-GFR of the right and left kidneys was 0.97 ± 0.32 mL/min/kg and 1.05 ± 0.31 mL/min/kg, respectively. Conclusions and Clinical Relevance—The CT-GFR method can be rapidly and conve- niently performed in clinically normal cats. This combined structural-functional approach provided physiologic and morphological information on the kidneys of cats. (Am J Vet Res 2011;72:1276–1282) or contrast media and renal scintigraphy. 2–4 However, these techniques reflect only renal function. A com- bined structural and functional assessment of the kid- neys has been made possible as a result of a new appli- cation of dynamic CT that involves the use of contrast medium. 5 The most notable aspect is that CT-GFR can be measured because of advances in CT technology and the application of a specific kinetic model. 6–9 A high- speed CT scanner is suitable for use in performing a functional CT scan. 10 An autoinjector is used to admin- ister contrast medium at a constant flow rate during a single-slice dynamic CT scan. 11 In several previous studies, 11–15 a positive correlation was found between CT-GFR and the inulin-based GFR, and CT-GFR was found to be a more practical substitute for evaluation of renal function. Received March 11, 2010. Accepted July 26, 2010. From the Department of Diagnostic Imaging, College of Veterinary Medicine, Chungnam National University, Daejeon, 305-764, South Korea (J Chang, Ahn, S Choi, H Choi, Y Lee); Department of Medi- cal Imaging, College of Veterinary Medicine, Gyeongsang National University, Jinju, 600-701, South Korea (H Lee); and the Department of Medical Imaging, College of Veterinary Medicine, Chungbuk National University, Cheongju-si, 361-763, South Korea (D Chang). Address correspondence to Dr. Youngwon Lee (lywon@cnu.ac.kr). ABBREVIATIONS CT Computed tomography GFR Glomerular filtration rate HU Hounsfield unit ROI Region of interest TAC Time-attenuation curve USG Urine specific gravity