|
Global
photographs
The phototrichogram technique yields a quantitative measure of
the ratio of anagen to telogen phase hairs. It is often used in
tandem with global photographic assessment, which is useful for
determining overall clinical changes in the patient over time in
a standardized manner. Global photographs are head shots taken a
short distance away from the patient and are different from the
up close photographs used in the phototrichogram technique.
For the average dermatology clinic where the requirement is just
to monitor the overall changes in scalp hair coverage in a patient
and where accuracy does not need to be one hundred percent, the
patient is is usually seated in front of a plain color cloth or
other non reflective surface on a wall and then photographed from
a few feet away. The patient is usually photographed from the front
with their hair down to show the frontal hair line and crown and
also from the back to show the vertex (center of the scalp whorl).
If there are other features like patchy hair loss on the sides of
the scalp then these will be photographed too.
The photographer should use a good quality single reflex lens camera
with either a ring light flash (the flash is attached around the
lens at the front and give an even light to the photograph) or,
and much better, professional flash photography lights mounted on
stands either side of the patient. A standard flash mounted on top
of a camera generally gives poor lighting with a lot of reflection
from the skin. This is not good when photographs of hair are desired.
This basic photographic set up gives some good, clear photographs
suitable for recording a patient's progress with their hair loss
and hair growth during treatment. However, this photographic set
up is not good enough for use in clinical trials and other studies
where scalp hair coverage needs to be evaluated in a consistent
and quantitative manner.
For clinical and research studies, global photographs are taken
with a fixed photographic system. The same camera design must be
used throughout the study, the same lighting must also be used.
The photographs must all be taken with the same type of film from
the same manufacturer and the camera must have a fixed time exposure,
lens focal length and lens aperture. Usually a framework is built
to which the camera and the lighting is permanently attached. This
framework has a stand with a forehead brace and a cup underneath.
The study volunteer places his/her chin in the cup and their forehead
up against the brace. Because the brace and the chin cup is a fixed
distance from the camera and the lighting is also fixed in relation
to the position of the volunteers head in the framework, the photographs
produced are very consistent. They have the same degree of lighting,
the hair is at the same magnification on the photograph, and the
same area of hair is visible in the photograph. In this way, over
time multiple photographs can be taken of the same person in exactly
the same way so that photographs at different time points in a study
can be directly compared.
This attempt to be consistent is very important when using global
photographs in clinical studies and research projects. It is very
easy to falsify the result of global photographs. If you take a two
photographs of the same person form the same position one after the
other, but with a different degree of flash lighting for each photograph
the resulting pictures will have different degrees of light reflectivity
from the skin and hair. More light reflectance can give the impression
of less hair while correspondingly less lighting can give the impression
of more hair. Lighting can be varied in a similar way by changing
the time exposure, or the lens aperture when the photograph is taken.
As a result, photographs taken without fixing the photographic system
and maintaining consistency in the way the photographs are taken can
look very different and this can bias the results of a study where
global photographs are compared and statistically analyzed for changes
in hair density over time.
Really good studies using global photographs must be conducted
in a very strict manner. The volunteers must agree not to change
their hairstyle much as different hairstyles can change how thin
the hair looks. They should also not use cosmetic treatments like
having a perm (it thickens the hair fibers) or use hair thickening
shampoos (they coat the hair in protein to make the larger). Studies
should always be conducted with the photograph takers being unaware
of who has received treatment and who is in the comparative control
group. Without this blinding of the study operatives, it is possible
they may consciously or unconsciously influence the photographs
taken to make the treated group look better. The photographs themselves
must be evaluated by people who are unaware which photos are taken
of people using a treatment and those who are comparative controls
taking a placebo as the photo evaluators may also unconsciously
give different scores to photos of people taking a treatment compared
to those taking a placebo - it is only human nature to do so.
These frames to which cameras and lighting can be attached to get
consistent pictures for hair loss studies can be bought ready made.
The primary supplier of this kind of equipment is Canfield Scientific
who have a virtual monopoly in providing these products to dermatologists
and pharmaceutical companies studying hair growth treatments. Studies
on Rogaine and Propecia both used photographic apparatus from Canfield
Scientific. Canfield scientific also provide a complete global photograph
evaluation service. If you send them the photographs, coded so that
the company does not know which photos are from which volunteer
and whether the volunteer was using a hair growth treatment or not,
then their professional evaluators will study the photos and score
them for the degree of hair loss or hair growth in a standardized
manner. This independent scoring by a company completely seperate
from another company testing a hair growth product is a very good
way to ensure consistency and accuracy in recording changes in hair
growth with an experimental treatment.
 |
| The
photographs above were taken of an individual with diffuse
pattern baldness. The head is at a fixed distance form the
camera and held in place by a brace which can be seen at
the bottom of the picture. However, while the pictures were
taken one after the other, the lower picture gives the impression
of more hair loss. This is because the second photograph
was taken with more intense lighting. More light reflectance
makes the hair look thinner. This is why global photographs
of hair loss must be taken in a very consistent manner. |
Global
photographs references
- Canfield D. Photographic documentation
of hair growth in androgenetic alopecia. Dermatol Clin. 1996 Oct;14(4):713-21.
- DiBernardo BE, Giampapa VC, Vogel J. Standardized
hair photography. Dermatol Surg. 1996 Nov;22(11):945-52.
|
