Inclusion Criteria:  Age over 18 years Written declaration of consent  Exclusion Criteria:  Generally valid:  Pregnancy Nursing mothers Tattoo in the field of investigation Subcutaneous fat tissue over 3 cm Chronic or acute diseases of the gastrointestinal tract or symptoms suggestive of such a disease Diseases requiring acute treatment Lack of written consent  ICG related:  Known hypersensitivity to ICG, sodium iodide or iodine Hyperthyroidism, focal or diffuse thyroid autonomy Treatment with radioactive iodine for the diagnostic examination of thyroid function within two weeks before or after the study Restricted renal function Intake of the following drugs: Beta-blockers, anticonvulsants, cyclopropane, bisulphite compounds, haloperidol, heroin, meperidine, metamizole, methadone, morphine, nitrofurantoin, opium alkaloids, phenobarbital, phenylbutazone, probenecid, rifamycin, any injection containing sodium bisulphite.