Distinct Functions of Activated Protein C Differentially Attenuate Acute Kidney Injury

http://jasn.asnjournals.org/cgi/content/full/20/2/267

Functional CT and Quantification of Perfusion Parameters
Perfusion CT imaging was utilized to measure renal blood flow as described previously.^55–58 Briefly, animals were placed in the center of the CT scanner (Locus Ultra; GE Medical Systems, Milwaukee, Wisconsin) and a tail-vein catheter was inserted (BD Biosciences) for contrast agent injection. Single-location multisection (80 rows) cine CT scanning was begun 3 s before a bolus of 300 µl of iodinated contrast medium (150 mg/ml, Omnipaque; Amersham, Princeton, New Jersey) was administered via the tail vein at a rate of 3 ml/min. All images were acquired by using an 80-kVp tube voltage, an 60-mA tube current, and a 1-Hz rotation speed. The data obtained at functional CT were then reconstructed into a 153- by 153- by 403-µm voxel matrix with an improved temporal resolution of 0.5 s between images. The reconstructed image data were then transferred to an image workstation (Advantage Windows; GE Medical Systems) for calculating perfusion parameters. Absolute values of perfusion parameters—blood flow (in milliliters per minute per 100 g of rat tissue weight) and blood volume (in milliliters per 100 g)—were measured by using perfusion software (Perfusion II; GE Medical Systems). Using the highest spatial resolution pixel-by-pixel calculation technique created the parametric map images. To quantify functional CT parameters, we first used cursors to indicate a six-pixel region of interest within the aorta to determine the enhancement value of arterial input. A region of interest was then drawn on the raw CT images, on which the whole kidney was delineated by contrast enhancement. In addition to measuring the entire kidney, we marked as functional hot spots on the parametric images the areas inside the kidney where the highest blood flow and blood volume were measured.