The study is intended to verify a newly developed method to measure the thickness of cranial soft tissue. In the study, a high-resolution MRI scan is used as ground truth for a laser scan of the forehead. The laser scan is acquired point by point with a prototype scanning unit developed at the University of Luebeck's Institute for Robotics.

The measured tissue thickness using the near-infrared scanning approach is validated against the ground truth obtained by the MRI scan. The average accuracy of the reconstruction method is then computed over all subjects from the individual study arms.

The required laser intensity and exposure time as well as the achieved measurement accuracy is evaluated with respect to the different skin types of the test subjects. Correlation between these features and the skin type according to the Fitzpatrick scale will be computed.

For 1/3 of the subjects, the laser and MRI scans are repeated after 2 and 8 weeks. The results of the scans are compared and time dependency is analysed.

Inclusion Criteria:

• male and female adults
• variations in skin type (at least 10 subjects with skin types I & II, at least 2 subjects with skin type III, at least 3 subjects with skin type IV, at least 3 subjects with skin types V & VI)
• optional: availability of high-resolution CT or CBCT (cone-beam CT) scan of the forehead

Exclusion Criteria:

• allergies or intolerances against ABS (acrylonitrile butadiene styrene), PMMA (polymethyl methacrylate) or alginate
• elevated light sensitivity of the skin
• exclusion criteria for MRI (claustrophobia, motoric disorders, tattoos, body piercings, metallic implants in the skull, epilepsy, cardiac pacemakers)