The study aims to investigate gastrointestinal transit using multispectral optoacoustic tomography (MSOT) in a prospective diagnostic study involving patients suspected of primary or secondary lactose intolerance. These patients exhibit varying clinical symptoms and different results from the hydrogen breath test (H2 breath test).

Lactose intolerance is caused by a deficiency in the enzyme lactase, which is responsible for breaking down lactose into glucose and galactose. Without this breakdown, lactose is fermented by colon bacteria, leading to symptoms such as bloating and diarrhea. The prevalence of lactose intolerance is increasing, especially among children, and the current diagnostic gold standard is the hydrogen breath test, which, while specific, has limitations in sensitivity.

MSOT could fill this diagnostic gap by non-invasively measuring intestinal transit time and providing a more objective assessment of the condition.

The study will compare MSOT results with H2 breath test outcomes, particularly focusing on patients with varying disease durations and activity levels.

Additionally, participants are offered an optional MRI examination, which can be used to measure intestinal motility. This helps to further quantify the results of the MSOT examination and discover new findings regarding the extent of the disease.

MSOT could improve the sensitivity of lactose intolerance diagnosis, differentiate it from other conditions, and offer insights into disease management over time.

Inclusion Criteria:

• Written informed consent of the subject
• Written informed consent of the subject's legal guardian
• Suspicion or diagnosis of lactose intolerance
• Age 6 to 18 years

General Exclusion Criteria:

• Pregnancy
• Breastfeeding mothers
• Tattoo in the examination area
• Subcutaneous fat tissue over 3 cm
• Known hypersensitivity to ICG, sodium iodide, or iodine
• Hyperthyroidism, focal or diffuse thyroid autonomy
• Recent treatment for thyroid function assessment involving radioactive iodine (within two weeks before or after the study)
• Impaired renal function
• Use of the following medications: beta-blockers, anticonvulsants, cyclopropane, bisulfite compounds, haloperidol, heroin, meperidine, metamizole, methadone, morphine, nitrofurantoin, opium alkaloids, phenobarbital, phenylbutazone, probenecid, rifamycin, any injection containing sodium bisulfite

MRI Exclusion Criteria:

• General contraindications for MRI examinations (e.g., electrical implants such as pacemakers or infusion pumps, etc.)
• Severe claustrophobia