Perfusion measurement is routinely used in human patients to diagnose, stage, and assess the prognosis and therapeutic response associated with conditions such as obstructive or stenotic lesions and vascular deformities.1–3 Various noninvasive perfusion imaging modalities have been developed to estimate variables such as tissue blood flow and the exchange of fluids between the blood and extravascular space.4 Among these modalities, CT perfusion analysis offers several advantages to human patients, including wide availability, short imaging time, and the positive correlation between the tissue contrast medium concentration and CT-based estimates of tissue perfusion.
Veterinary reports5,6 have described the use of CT perfusion analysis to estimate pancreatic and hepatic perfusion in dogs, including those with and without portal vascular anomalies and with hepatic fibrosis. To the authors’ knowledge, there are no published reports of renal CT perfusion analysis in dogs. However, given the demonstrated utility of renal CT perfusion analysis in humans,7–10 this modality could be useful in veterinary patients for applications such as evaluating glomerular filtration rate and tissue viability following renal transplantation, grading and assessing the therapeutic response of renal tumors, and evaluating renal arterial stenosis and ureteral obstruction.
Estimates of tissue perfusion by CT perfusion analysis are based on temporal changes in tissue enhancement attributable to circulation of contrast medium.4 Analytic approaches for computing these estimates include compartmental, deconvolution, and maximum slope methods, of which the maximum slope method is the most widely used in human clinical practice.11 The maximum slope method is a single-compartment model based on the assumption that there is no venous outflow or recycling of the contrast medium during perfusion analysis.12,a The single-compartment model requires that the contrast medium achieve peak arterial enhancement before venous outflow of that medium occurs.12 The assumption of no venous outflow of contrast medium depends on a short scanning time, typically until peak tissue enhancement is achieved, which also reduces the chance of motion artifacts.
Because the contrast medium takes only a few seconds to circulate from the injection site to the target tissues, a short injection duration is recommended to minimize underestimation of perfusion measures.11 Recommendations from studies13,14,a involving humans include using an injection duration < 4 to 6 seconds and a contrast medium injection rate > 5 mL/s when performing cerebral CT perfusion analysis with the maximum slope method.
There are several factors to consider when performing CT perfusion analysis with the maximum slope method in veterinary patients. The use of large catheters to achieve high injection rates may be contraindicated in some patients, such as small dogs or cats, or those that are emaciated or have fragile veins (eg, cancer patients). High injection rates can also result in a shorter time to peak enhancement, making accurate image timing difficult because of the decreased temporal window.15 Because the contrast medium dose is based on body weight, the volume required for small patients may permit a low injection rate that still results in a sufficiently short injection duration for CT perfusion analysis with the maximum slope method. The purpose of the study reported here was to evaluate different contrast medium injection rates in small dogs to determine whether a low injection rate would meet the assumption of the maximum slope method for CT perfusion analysis in this population.
Supported by the Animal Medical Institute of Chonnam National University and the Basic Science Research Program through the National Research Foundation of Korea, funded by the Ministry of Science, ICT, and Future Planning (grant No. 2018R1A2B6006775).
The authors declare that there were no conflicts of interest.
Time to initial renal venous enhancement
Time to peak aortic enhancement
Fisher JA. Improvements in computed tomography perfusion output using complex singular value decomposition and the maximum slope algorithm. MS thesis, School of Medicine, Boston University, Boston, Mass, 2014.
Zoletil (25 mg of zolazepam and 25 mg of tiletamine/mL), Virbac, Carros, France.
Domitor (1 mg of medetomidine/mL), Orion Corp, Espoo, Finland.
Terrell, Piramal Critical Care, Bethlehem, Pa.
Siemens Emotion 16, Siemens, Forchheim, Germany.
Omnipaque 300, GE Healthcare, Oslo, Norway.
Medrad Vistron CT injection system, Medrad, Warrendale, Pa.
Syngo Dynamic Evaluation, Siemens, Forchheim, Germany.
Syngo Body Perfusion CT, Siemens, Forchheim, Germany.
SPSS Statistics, version 20, IBM Corp, New York, NY.
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