Influence of Fitzpatrick Skin Phototype and Body Mass Index on Non-invasive Optoacoustic Imaging of Muscle During Vascular Restriction and Physical Activity

Melanin, a pigment found in the skin, has been reported to influence light-based measurements such as pulse oximetry or near-infrared spectroscopy (NIRS). Studies have shown measurements overestimation of darker skin tones or in ethnicities assumed to have darker skin tones compared to lighter skin tones. Even though optoacoustic imaging (OAI) has a different depth penetration than NIRS or pulse oximetry, the technology uses pulse laser light to assess tissue.

Multispectral Optoacoustic Tomography (MSOT) imaging is similar to conventional sonography: a transducer is placed on the skin, and instead of sound, energy is applied to the tissue by means of pulsed laser light. This leads to a constant change of minimal expansion and contraction of individual tissue components or molecules. The resulting sound waves can then be detected by the same device. Previous studies have already shown that the quantitative determination of hemoglobin can provide information on inflammatory activities or muscle hemodynamics. MSOT uses laser light between 660 and 1300nm to visualize and quantify different endogenous chromophores, such as hemoglobin, collagen, or melanin. Increase in melanin concentration (e.g. in melanomas or skin tags) has been previously assessed using the technology but never looked at signal at depth. Additionally, differences in body-mass-index (BMI) might influence light penetration, and therefore, the optoacoustic signal at depth. So far, no studies have looked at the influence of increased melanin concentration or subcutaneous fat on quantification of muscle perfusion and oxygenation.

In this first pilot study, the aim is to investigate the influence of different Fitzpatrick skin phenotypes (FSP) and BMI on muscle perfusion and oxygenation during arterial occlusion or muscle exercise and over time. This information is essential for further studies with a more diverse study population.

To gain insights into these differences, healthy volunteers with different skin tone (defined by FSP) and body-mass-index will be recruited and subjected to a leg arterial occlusion and to perform a toe raise exercise. They will then be scanned on different body areas (arm, legs) to assess changes in muscle perfusion and oxygenation by MSOT.