[How I explore … Crohn's disease by various imaging modalities].

Crohn's disease is a chronic inflammatory condition characterized by recurrent and/or chronic lesions, leading to cumulative structural bowel damage. It is established that the correlation between symptoms and intestinal lesions is weak. Therefore, monitoring by frequent cross-sectional imaging is proposed to assess the disease activity. There is no consensus about the preferred imaging option. Priority is given to non-radiating modalities, such as ultrasonography and MRI. Tomodensitometry will be reserved for emergency cases. Ultrasonography can be useful, in emergency as well as for the monitoring of lesions of known topography. Entero-MRI is henceforth considered the standard imaging technique for the diagnosis and follow-up of Crohn's disease. Its high contrast resolution allows an accurate assessment of disease activity, therapeutic efficacy, cumulative structural bowel damage and complications.