Publications

@article{Setchfield2024-kl,

title = {Effect of skin color on optical properties and the implications  for medical optical technologies: a review},

author = {Kerry Setchfield and Alistair Gorman and A Hamish R W Simpson and Michael G Somekh and Amanda J Wright},

doi = {10.1117/1.JBO.29.1.010901},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {J. Biomed. Opt.},

volume = {29},

number = {1},

pages = {010901},

abstract = {Significance: Skin color affects light penetration leading to 

 differences in its absorption and scattering properties. COVID-19 

 highlighted the importance of understanding of the interaction of 

 light with different skin types, e.g., pulse oximetry (PO) 

 unreliably determined oxygen saturation levels in people from 

 Black and ethnic minority backgrounds. Furthermore, with 

 increased use of other medical wearables using light to provide 

 disease information and photodynamic therapies to treat skin 

 cancers, a thorough understanding of the effect skin color has on 

 light is important for reducing healthcare disparities. Aim: The 

 aim of this work is to perform a thorough review on the effect of 

 skin color on optical properties and the implication of variation 

 on optical medical technologies. Approach: Published in vivo 

 optical coefficients associated with different skin colors were 

 collated and their effects on optical penetration depth and 

 transport mean free path (TMFP) assessed. Results: Variation 

 among reported values is significant. We show that absorption 

 coefficients for dark skin are ∼6% to 74% greater than for 

 light skin in the 400 to 1000 nm spectrum. Beyond 600 nm, the 

 TMFP for light skin is greater than for dark skin. Maximum 

 transmission for all skin types was beyond 940 nm in this 

 spectrum. There are significant losses of light with increasing 

 skin depth; in this spectrum, depending upon Fitzpatrick skin 

 type (FST), on average 14% to 18% of light is lost by a depth 

 of 0.1 mm compared with 90% to 97% of the remaining light being 

 lost by a depth of 1.93 mm. Conclusions: Current published data 

 suggest that at wavelengths beyond 940 nm light transmission is 

 greatest for all FSTs. Data beyond 1000 nm are minimal and 

 further study is required. It is possible that the amount of 

 light transmitted through skin for all skin colors will converge 

 with increasing wavelength enabling optical medical technologies 

 to become independent of skin color.},

keywords = {absorption and scattering   coefficients, Fitzpatrick skin type scale, medical wearables, optical coherence tomography, optical imaging, photodynamic therapy, Racial bias, skin, transmission},

pubstate = {published},

tppubtype = {article}

}

@article{Setchfield2023-mi,

title = {Relevance and utility of the in-vivo and ex-vivo optical  properties of the skin reported in the literature: a review  [Invited]},

author = {Kerry Setchfield and Alistair Gorman and A Hamish R W Simpson and Michael G Somekh and Amanda J Wright},

year  = {2023},

date = {2023-07-01},

urldate = {2023-07-01},

journal = {Biomed. Opt. Express},

volume = {14},

number = {7},

pages = {3555\textendash3583},

publisher = {Optica Publishing Group},

abstract = {Imaging non-invasively into the human body is currently limited 

 by cost (MRI and CT scan), image resolution (ultrasound), 

 exposure to ionising radiation (CT scan and X-ray), and the 

 requirement for exogenous contrast agents (CT scan and PET 

 scan). Optical imaging has the potential to overcome all these 

 issues but is currently limited by imaging depth due to the 

 scattering and absorption properties of human tissue. Skin is 

 the first barrier encountered by light when imaging 

 non-invasively, and therefore a clear understanding of the way 

 that light interacts with skin is required for progress on 

 optical medical imaging to be made. Here we present a thorough 

 review of the optical properties of human skin measured in-vivo 

 and compare these to the previously collated ex-vivo 

 measurements. Both in-vivo and ex-vivo published data show high 

 inter- and intra-publication variability making definitive 

 answers regarding optical properties at given wavelengths 

 challenging. Overall, variability is highest for ex-vivo 

 absorption measurements with differences of up to 77-fold 

 compared with 9.6-fold for the in-vivo absorption case. The 

 impact of this variation on optical penetration depth and 

 transport mean free path is presented and potential causes of 

 these inconsistencies are discussed. We propose a set of 

 experimental controls and reporting requirements for future 

 measurements. We conclude that a robust in-vivo dataset, 

 measured across a broad spectrum of wavelengths, is required for 

 the development of future technologies that significantly 

 increase the depth of optical imaging.},

keywords = {optical imaging, optical properties, skin},

pubstate = {published},

tppubtype = {article}

}