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Hair
Transplant:
Hair Mass Index &
Hair Mass Transferred
by
Dr. John P. Cole |
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Courtesy
of Dr. John P. Cole
www.forhair.com
continued
from page 1...
We
are quite lucky that our creator used cylinders to cover our
spherical scalp. Archimedes
pointed out that the sphere is "inscribed" in the
cylinder. It's north pole just touches the top of the cylinder; the
south pole just touches the bottom. And the cylinder and sphere just
barely make contact all along the equator. If the cylinder were the
least bit shorter or skinnier, the sphere would not fit inside. If r
= the radius of the sphere and the radius of the cylinder, then 2r =
the height of the cylinder, Vc = volume of the cylinder
=(¼r2)(height) = 2¼r3, and Vs =
volume of the sphere = (4/3)¼r3. Therefore, Vc/Vs
= 3/2, the ratio Archimedes was most proud of. The can will hold 50%
more soda pop than the ball.
It is interesting to note that the ratio of the cylinder's area to
the sphere's area is the same as the ratio of their volumes: Ac
= area of top + area of bottom + area of side = ¼r2 + ¼r2
+ (2¼r)(2r) = 6¼r2 and As = 4¼r2,
so Ac/As = 3/2. It takes 50% more paint to
decorate the can than to decorate the ball.
It follows that it requires 50% less cylindrical hair to
cover the spherical scalp. Interestingly,
these follicular groups are arranged in mathematical spirals,
another complex calculation developed by Archimedes, but this is
beyond the scope of our discussion.
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The
term mass is actually a measure of volume. A mass of 1 gm is a cubic
centimeter of water. It follows that hair mass and hair volume are
essentially the same. In 1998, Dr. John Cole introduced Hair Mass
Transferred and Total Hair Volume Transferred as a predictor of hair
transplant coverage. The problem with the Cole method was it relied
on the mean hair diameter, a variable that required tedious
measurements with potentially costly equipment. In May 2001 Dr.
James Arnold presented Hair Mass Index (HMI) as an ingenious means
to quickly and inexpensively asses Hair Mass. He measured HMI in
both the donor area and recipient areas of his patients. The Arnold
method may not be as precise as the Cole method and does not
evaluate the actual mass of hair that is transferred at the time of
surgery. Rather, it assesses the individual’s hair mass before
surgery and after re-growth of the transplanted grafts.
Interestingly, he noted a lower than expected HMI in the recipient
area than was predicted based on the number of grafts and hairs he
transferred in many of his former patients. This was the forefather
to objective efficiency evaluations. Dr. Frank Neidel wrote a
chapter about HMI in the most recent edition of Hair Transplantation
of Dr. Walter Unger and Dr. Ron Shapiro. HMI measures the hair mass
in the donor area and recipient area, but it does not measure what
is actually transferred.
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Cole has stated
that scalp hairs may be classified according to the following table:
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Very fine
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Fine
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Medium-Fine
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Medium
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Medium-Coarse
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Coarse
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<60um
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60-65um
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65-70um
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70-75um
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75-80um
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80um>
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It should be noted that hair on other parts of the body has a much
different diameter than scalp hair. This characteristic offers great
potential coverage from coarse hair sources such as from the chest.
Neidel notes that HMI can be classified according to table below: |
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Optical
effect of fine hair
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Optical
effect of normal hair
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Optical
effect of thick hair
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0.18-0.32
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0.32-0.5
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0.5-0.72
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METHODS
Measurement of mean hair diameter requires a sample size of 20
hairs. We have found in multiple evaluations that this sample size
results in a more precise average hair diameter. The hair is
measured with the help a micrometer. The measurements are very
precise with an error of about 1 micron. Mean hair diameter is equal
to the sum of 20 hair diameters divided by 20. Hair diameters are
measured in micrometers. Cole recognizes the extreme variability of
hair diameters. For this reason, he believes that when one measures
only 20 hairs, you should not include hair diameters that are
particularly small or extremely large so that you get a more
accurate estimate of the average diameter.
This measurement allows us to calculate the mean surface area and
mean hair volume for any patient provided the length of hair is
known. Hair length varies from one individual to another. Therefore,
we introduce the term hair mass transfer index (HMTI) to compensate
for hair length. HMTI assumes a standard length of 1 cm. It is easy
to compensate for any length of hair as we will show. While cutting
the grafts, assistants examine and write down the number of hairs
contained in each graft. The grafts may be individual follicular
units, double follicular units (DFU), multiple follicular units,
(MUG). In addition, you may include fractionated follicular units
that may include a variety of combinations to include three hair
follicular units fractionated into three one hair grafts. The
objective is to assess the total number of hairs that are
transferred of a particular graft type or size. On a statistical
point of view, it is worth using this method for the first 200
grafts of any particular type (FU, MUG, etc.) and then it is
possible to proceed to an extrapolation. Single hair grafts that are
obtained by fractionation should always be counted in their
entirety. This sum is the Total Hairs Transferred (THT). Mean hair
radius is the quotient of the mean hair diameter divided by 2.
Mean hair volume
index (MHVI) is the product of the square of the mean hair radius,
p, and a hair length of 1 cm.
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MHVI
= ( r 2 ) ( p ) ( 1 )
Hair mass
transferred index is the total hairs transferred (THT) and mean hair
volume index (MHVI).
HMTI
= (THT) ( MHVI)
The expected actual
hair mass you have transferred (HMT) may be easily calculated based
on any hair length. One simply multiplies the HMTI by the actual
length of hair on the patient. Now one has the capacity to evaluate
efficiency of their hair transplant. One can calculate the hair mass
index in the recipient area and compare it to the actual HMT
calculated at the time of surgery. This method allows one to
evaluate efficiency on multiple regions of the scalp.
These are two
old and two recent examples of predicted Hair Mass Transferred:
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Example
no.1:
Before
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After
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Example
no.2:
Before
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After
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Courtesy
of Dr. John P. Cole
www.forhair.com
Email hairsite@aol.com
if you would like to schedule
a FREE online consultation with Dr. Cole.
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