Tantalum sedimentation in Onyx® syringes: An in-vitro study of agitation strategies to maintain fluoroscopic visibility

BACKGROUND AND PURPOSE: During Onyx® plug formation, pauses in injection can lead to tantalum powder sedimentation, reducing fluoroscopic visibility and increasing the risk of reflux and non-target embolization. Syringe agitation is commonly used to counteract this effect. This study aimed to assess sedimentation time and identify the most effective agitation method. MATERIALS AND METHODS: Standardized preparations of 1 mL syringes were subjected to nine agitation methods (no agitation, automated/manual; fast/slow, rotary/horizontal) at 3, 5, 7, and 10 min. Optical (absorbance, transmittance) and fluoroscopic measurements (visibility, signal-to-noise ratio [SNR]) were performed. A 3D-printed intracranial artery model was also used to assess fluoroscopy visibility. RESULTS: Tantalum sedimentation progressed gradually, with visible deposits after 35.3 ± 7.32 min. Transmittance remained stable for 150 ± 4.12 min before decreasing. All agitation methods significantly improved SNR and visibility versus no agitation. The most effective methods were observed with automatic slow rotary and manual fast rotary agitation, which consistently maintained higher SNR and visibility (p < 0.001). In the 3D model, time had less impact, and rotary agitation did not significantly impact visibility. CONCLUSIONS: Agitation during waiting periods is necessary to preserve visibility. Awareness of early fluoroscopy visibility loss is critical - injecting visually opaque but fluoroscopically invisible Onyx® poses procedural risks. During prolonged procedures, preloaded syringes should be regularly agitated to ensure safe embolization.