Development and optical characterization of a multilayered head phantom for optical brain monitoring

Optical techniques are promising tools for non-invasive cerebral monitoring; however, optical measurements acquired from the forehead can be influenced by extracranial tissues and skin pigmentation, potentially complicating interpretation of cerebral signals. Tissue-mimicking phantoms provide controlled platforms for studying these effects; however, existing head phantoms employ simplified geometries and lack the features required for cerebral photoplethysmography (PPG) investigations.

We present the development and characterization of a multilayer head phantom reproducing key anatomical, optical, and hemodynamic features relevant to optical brain monitoring while enabling future investigation of confounding factors.

The phantom incorporates a custom-made silicone brain with embedded vessels, a three-dimensional-printed skull, a vascularized scalp, and interchangeable skin layers representing different pigmentation levels, integrated with an in vitro cardiovascular system enabling selective perfusion of cerebral and extracranial compartments. The optical and colorimetric properties of the tissue-mimicking layers were assessed.

The scalp and skin layers exhibited absorption and reduced scattering coefficients within ranges reported for human tissues. Colorimetric assessment confirmed physiologically relevant pigmentation characteristics across the skin layers. Using the pale skin, the phantom generated measurable PPG signals across multiple wavelengths and source-detector separations.

The multilayer head phantom provides an anatomically and optically representative platform for optical brain monitoring research. Its interchangeable skin layers and independently perfusable cerebral and extracranial compartments enable future controlled investigations of skin pigmentation and extracranial hemodynamics as confounding factors in cerebral optical measurements.