Hybrid imaging in Crohn's disease: from SPECT/CT to PET/MR and new image interpretation criteria

Crohn's disease is a chronic relapsing disease characterized by mucosal inflammation, lymphocytes infiltration and fibrotic strictures. Usually, the assessment of location, extension, inflammatory activity and severity of intestinal lesions is complex and invasive with endoscopic methods or histological and biochemical investigations. Thus, the diagnosis remains a challenge for the management of patients. Nuclear medicine techniques, in particular hybrid and molecular imaging, might offer a valid option for the evaluation and determination of the prognosis of the disease. Indeed, imaging methods provide a non-invasive, reproducible and quantitative analysis. An overview of the currently available multimodality imaging techniques in Crohn's disease are reviewed, with particular regard to positron-emission tomography/magnetic resonance and the choice of the best evaluation Score, explaining advantages and disadvantages of each one, with particular regard to their potential role for the assessment of disease activity and extent of inflammation in order to improve the diagnosis. We propose new interpretation criteria for PET/MR images.