Skin imaging involves a non-invasive digital technique
which produces better images of the skin. These high
quality images make assessment of the skin condition
easier. Additionally, digital imaging makes storage
and retrieval of data much easier. It also enables
objective computer analysis and quicker evaluation
Non-invasive skin imaging is now widely used by researchers,
dermatologists and the cosmetics industry. The objective
study of skin properties is of great interest to the
Skin imaging is used for four purposes.
For studying the normal skin
For examining the diseased skin
For noninvasive monitoring of the skin during treatment
For use as a diagnostic tool in the dermatology clinic.
Skin imaging devices
Various imaging devices examine various aspects of
the skin surface, sub surface and skin sections, but
almost all depend on the optical and sonographic properties
of the skin.
A magnifying glass is the simplest device where a
magnified image is examined by eye. Great reliance
is still placed on such visual examination since the
superiority of computer analysis is yet to be established.
Surface photography is the most widely used device
for detecting melanoma skin cancer, often making biopsy
unnecessary. It is also used for evaluating many other
kinds of skin lesion. Polaroid and ultra violet filters
are used to magnify the surface image to reveal wrinkles,
erythema and pigmentation for example.
Profilometry is the assessment of the topography
or the natural and unnatural features of the skin
surface. Optical profilometry is a rapid procedure
and exploits the different ways oblique light is reflected
from various surface features. A computer image of
the surface topography is then generated detailing
parameters such as skin roughness and depth of skin
defects. Laser profilometry is excellent for assessing
skin wrinkle line disorders.
Optical profilometry is most widely used for evaluating
hydrating or anti-wrinkle creams. It can also be used
to understand how skin ages and the consequences of
photoaging due to UV light exposure.
Dermatoscopy: Reflected light from the skin surface
interferes with images of the deeper skin structures.
Dermatoscopy is a technique where this problem is
partially resolved by reducing the surface reflection
thereby increasing light penetration. Fluid immersion
dermatoscopy does this by inserting a liquid-glass
interface between the light source and the epidermis.
Some dermatoscopes also use a cross-polarized lens
to absorb the surface light reflection.
With the advent of image digitization, mole scanners
are being increasingly used in dermatoscopy for clinical
observation, monitoring, automatic lesion identification
and even automatic diagnosis, tasks traditionally
performed by dermatologists. However, superiority
of mole scanners over dermatologists is not yet established.
Dermatoscopy is currently the most popular skin imaging
Spectroscopy: Chromophores are skin components that
variably absorb light. After some time period of light
absorption, some chromophores, called fluorophores,
emit radiation of different wavelengths, which a spectroscope
can separate into its component radiations. Each component
is then separately analysed. Spectroscopy is currently
used mostly in research.
Diuse reflectance spectroscopy or DRS examines the
absorption characteristics of the 320nm to 1100nm
range of wave lengths. The major chromophores here
are hemaglobins, melanins, keratins and water. Differences
in absorption can distinguish a melanoma from benign
In fluorescence spectroscopy, a specific emitted
wavelength is sought after scanning with a particular
range of wavelengths. The method requires knowledge
of fluorophores. It is useful in detecting basal cell
Raman spectroscopy uses the phenomenon of Raman scattering
where monochromatic light from the infrared region
falling on the skin is reflected back as light of
different wavelengths. The scattering is caused by
molecular structures, which have their own particular
spectral signatures. Healthy and diseased skin have
different molecular structures and this may make diagnostic
raman imaging possible in the future.
Optical coherence tomography or OCT: All methods
described so far have the common limitation that different
skin layers cannot be separated. Therefore descriptive
morphology is not possible.
OCT produces interference patterns that correspond
to different skin layers. OCT was first used for retinal
imaging in 1991 and the image resembled an unstained
histology section. While currently only the upper
layers can be studied, in future the technique may
approach the cellular level making it a potential
High-resolution ultra sonography or HRU: HRU relies
on different tissues having different impedance. As
with OCT it is possible to use HRU to obtain images
of a histology section. HRU can be used to monitor
and assess inflammatory conditions.
Currently dermatoscopy with mole scanners is the
best technique in skin imaging although some doubt
the usefulness of automated computer mole scanners.
Generally, the diagnostic capabilities of all skin
imaging devices need to be accurately studied and
compared to that of clinicians before making any firm
conclusions about their usefulness.