Affiliation:
1. University of Edinburgh
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.
Funder
Engineering and Physical Sciences
Research Council
Subject
Atomic and Molecular Physics, and Optics,Biotechnology