The primary objective of this study is to prospectively validate a novel intestinal ultrasound (IUS) Crohn's disease (CD) activity index and component items, correlating CD activity and responsiveness to therapy as evaluated by IUS with evaluations by ileocolonoscopy (IC) (Simple Endoscopic Score for Crohn's disease [SES-CD]) and magnetic resonance enterography (MRE) (Simplified Magnetic Resonance Index of Activity [MaRIA] score).