Defining the Ideal CT Pancreatic Phase in Dogs: Evidence-Based Scan Timing for Peak Enhancement

Optimal Scan Delay for Computed Tomographic Evaluation of the Canine Pancreas Using a Fixed Injection Duration Technique

Kimberly Lim, Timothy Foo, Evelyn Hall, Mariano Makara

Background:
Accurate computed tomographic (CT) assessment of the canine pancreas is essential for diagnosing inflammatory and neoplastic conditions. Multiphase contrast-enhanced CT is widely used, yet no consensus exists regarding optimal scan timing in dogs. Establishing reproducible enhancement patterns of the normal pancreas is critical to maximize lesion detection. This study aimed to determine the optimal CT scan delay for peak enhancement of the pancreatic parenchyma, aorta, and portal vein using a fixed 20-second contrast injection duration and bolus tracking technique. The authors hypothesized that peak pancreatic enhancement would occur between peak aortic and portal venous enhancement and would remain consistent regardless of body weight.

Methods:
This mixed retrospective–prospective analytical study included 69 client-owned dogs undergoing abdominal CT. All dogs received 2 mL/kg of iohexol (350 mg iodine/mL) intravenously over a fixed 20-second injection duration. Bolus tracking detected contrast arrival in the abdominal aorta (threshold 150 HU), and diagnostic scans were obtained at post-aortic arrival delays of 5, 10, 15, 20, 25, 30, 35, 40, and 180 seconds. Circular regions of interest (ROIs) were placed in the aorta, portal vein, and three pancreatic regions (body, left lobe, right lobe). Mean pancreatic enhancement was calculated from the three regions. Univariable linear modeling assessed the effects of scan delay, body weight, age, and sex on attenuation values.

Results:
Scan delay significantly influenced enhancement of the aorta, pancreas, and portal vein (p < 0.001), whereas body weight, age, and sex had no significant effect. Peak mean aortic enhancement (569.9 HU) occurred at 5 seconds and declined thereafter. Peak mean pancreatic enhancement (137.8 HU) occurred at 15 seconds, with no significant difference between 15 and 20 seconds, defining a 15–20 second pancreatic phase. Peak portal vein enhancement (257.8 HU) occurred at 20 seconds, with sustained high enhancement from 20–30 seconds. Enhancement patterns were homogeneous across pancreatic regions and consistent across body weight categories. The arterial, pancreatic, and portovenous phases occurred sequentially at 5–10, 15–20, and 20–35 seconds, respectively.

Limitations:
Pancreatic normalcy was presumed based on CT morphology without biochemical or histopathologic confirmation. Some dogs had concurrent intra-abdominal disease, which may have influenced perfusion. Anesthetic protocols were not standardized. Sample sizes for certain delay groups (20 and 25 seconds) were smaller. A single unblinded reviewer performed ROI selection, introducing potential observer bias.

Conclusions:
Using a fixed 20-second injection duration and bolus tracking, a 15–20 second scan delay after aortic contrast arrival optimally achieves peak pancreatic parenchymal enhancement in dogs. This timing is consistent across body weights and enables clear differentiation from arterial and portal venous structures. Defined phases include arterial (5–10 s), pancreatic (15–20 s), and portovenous (20–35 s). These findings support standardized CT protocols for improved pancreatic evaluation in canine patients.

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