Cephalic or Saphenous? New Data Define Optimal Contrast Timing for Equine Skull CT

Time Attenuation Curves for Equine Intravenous Contrast Enhanced Skull CT Using the Medial Saphenous and Cephalic Veins

Kahlina Frey; Michael Perlini; Rachel Reed

Background

Contrast-enhanced computed tomography (CT) of the equine head is routinely performed to improve lesion characterization; however, standardized intravenous (IV) contrast protocols for horses are lacking. Existing protocols are largely extrapolated from human and canine data, and the optimal timing of image acquisition and site of contrast administration remain undefined in equine patients. The objective of this prospective crossover pilot study was to generate time–attenuation curves for IV contrast administration via the medial saphenous vein and cephalic vein, assess artifacts, and compare symmetry and timing of vascular enhancement between the two sites.

Methods

Four clinically normal adult horses (400–500 kg) were enrolled in a prospective crossover design. Under general anesthesia, each horse received 400 mL of iohexol (350 mgI/mL) administered at 5 mL/s via power injector through both the cephalic vein and medial saphenous vein during the same anesthetic event, with an approximate 20-minute interval between injections to allow washout. Dynamic single-level transverse CT scans (100 acquisitions at 6-second intervals) were obtained at the level of the hyoid apparatus and sphenopalatine sinuses using a 64-slice multidetector CT scanner. Regions of interest (ROIs) included bilateral common carotid arteries, maxillary veins, cerebral parenchyma, masseter muscles, and lateral pterygoid muscles. Time–attenuation curves were generated, and peak enhancement times were recorded. Subjective artifact scoring was performed using a previously described five-point scale.

Results

All scans were diagnostic, and no adverse effects or contrast pooling artifacts were observed with either administration site. Peak arterial enhancement occurred earlier than venous enhancement for both injection routes. Mean peak enhancement times for the carotid arteries were approximately 109 seconds, whereas mean peak enhancement for the maxillary veins occurred at approximately 174 seconds. Results were similar between cephalic and saphenous administration. Mild asymmetric or heterogeneous venous enhancement was observed in some horses, more commonly following cephalic administration, and was suspected to result from reflux or flow turbulence. Cerebral parenchyma and masticatory muscles demonstrated minimal contrast enhancement.

Limitations

This was a pilot study with a small sample size (n = 4), limiting statistical power and generalizability. The single-level dynamic scan location restricted ROI placement, particularly within small carotid arteries. Centralized ROI placement to reduce beam-hardening artifact may have contributed to variability in attenuation measurements in cases of asymmetric enhancement.

Conclusions

Both medial saphenous and cephalic veins are effective sites for IV contrast administration in equine skull CT, with no pooling artifacts observed. Arterial enhancement precedes venous enhancement, with carotid artery peak enhancement occurring at approximately 1.8 minutes post-injection and maxillary vein enhancement at approximately 2.9 minutes. These findings provide foundational data to guide optimal timing of post-contrast image acquisition in horses and inform development of standardized contrast-enhanced CT protocols for the equine head.

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