The clinical course of inflammatory bowel disease (IBD) is characterized by relapses and spontaneous or drug-induced remissions, but it cannot be predicted by currently known parameters. The priority of this thesis was to improve the accuracy of IBD diagnostics and to find methods in evaluating the course and the prognosis of IBD to facilitate individualized medication and to improve the outcome of the disease.

Positron emission tomography and magnetic resonance imaging (PET/MRI) is a hybrid imaging modality in which MRI provides high spatial resolution and soft tissue contrast while PET using fluorodeoxyglucose (18F-FDG) detects metabolic activity related to inflammation. We compared the data of PET/MRI of altogether ten ulcerative colitis (UC) and Crohn’s disease (CD) patients to intestinal histological samples to find out the ability of PET/MRI to detect and grade the inflammation activity of bowel wall. The analysis showed that the glucose uptake in bowel wall had significant association to inflammation activity. Also, the standardized uptake values from areas of severe inflammation activity emerged significantly from the background. Consequently, 18F-FDG-PET/MRI is a promising method to detect especially severe inflammatory lesions non-invasively.

The second aim was to investigate the expression of keratin 7 (K7) in IBD affected intestinal epithelial cells, and to evaluate its potential as prognostic biomarker of IBD. The study showed that K7 was expressed in the colonic epithelium of patients suffering from UC and CD, but not in healthy colon. The expression of K7 was the most pronounced in drug-resistant colitis. The analyses suggested also that K7 expression varies based on the anatomical location in colon. To evaluate the prognostic value of K7, the state of 16 patients was followed for three years. As a result, the severity of the disease during the following three years was not related to expression of K7 at the time of enrollment. Consequently, K7 could be used as a specific diagnostic marker for severe IBD, indicating especially disease with poor drug response and major pathological changes in epithelium.