Accuracy of 190-keV Virtual Monoenergetic Dual-Energy CT for Determining the Presence or Absence of Intravitreal Silicone Oil

OBJECTIVE. We hypothesized that intravitreal silicone oil would show attenuation similar to that of fat on dual-energy CT 190-keV virtual monoenergetic images ( VMIs) with high frequency and that this appearance would enable confident determination of the presence or absence of intravitreal silicone oil. The purpose of the present study was to test our hypothesis in a blinded multireader study of selected patients with and without intravitreal silicone oil as well as in an unblinded ROI-based assessment. MATERIALS AND METHODS. In this retrospective study of 50 dual-energy CT examinations of the head that included 100 globes (64 that were normal, 19 that exhibited hyperattenuating mimics, and 17 that contained silicone oil), three neuroradiologists independently assessed anonymized 190-keV VMIs for intravitreal attenuation similar to that of fat. Interobserver agreement was calculated. The mean attenuation value on weighted-average images and 190-keV VMIs was recorded. RESULTS. The three readers identified intravitreal attenuation values similar to that of fat in 100% of globes that contained silicone oil and 0% of globes that did not contain silicone oil (100% sensitivity, specificity, PPV, and accuracy) with 100% agreement. The mean attenuation value of silicone oil on 190-keV VMIs was -55 HU, which was significantly less than the mean attenuation on 190-keV VMIs of normal globes and hyperattenuating mimics (p <.001 for both). CONCLUSION. Intravitreal silicone oil shows attenuation of -60 to - 49 HU on 190-keV VMIs. With the use of these images only, three neuroradiologists identified intravitreal silicone oil with 100% accuracy and perfect agreement.