Difference between Gentlelase &Cyn 9300?

Hair Removal Methods Laser hair removal
#1

I think I understand variable vs fixed pulse settings. So gentlase has a fixed pulse at 3msec and 9300 has variable from 20msec to 5msec approximately.
My understanding is coarse hair reacts to 20msec/10msec and thin hair is good with 3msec or similar number.
Should I have this lower(stronger) pulse of 3msec rather than messing with the bigger 10msec(weaker)?
All other settings aside, joules/spot size etc.

Type 2, back-shoulders, 4 treatments so far with last settings at 25j/10msec/15 spot with cynosure 9300.

How can gentlase treat coarse hair if it has a fixed pulsewidth at 3msec(normally just for thin hair?).

I would really like to get the most bang for my buck at my next treatment. Thanks.

#2

I believe shorter pulse is more effective period, on all types of hair. Longer pulse is useful for treating people with a bit darker skin as there is less chance of burning. I think I would ask to be treated at 5m/s next time. 25 joules and 15mm spot size should be fine.

#3

To really understand this, you have to understand the concept of thermal relaxation time. This is a theoretical concept that explains the speed at which a structure in the skin loses heat to the surrounding structures. The idea is that the large an object the slower it loses heat, while the smaller an object, the quicker it loses heat. The TRT is based on the time it takes for half of the heat to be lost to the surrounding tissue.

The evidence, based on theoretical models that have been tested in vitro (meaning bench research, not in living people) analysis, is that an individual skin cell has a TRT of about 1-2 ms. Coarse hair seems to have a TRT of around 30-100 ms depending on how coarse it is. Fine hair is somewhere around 3-5 ms depending on how fine it is.

When the laser pulse is on, you are pushing energy into the structure (hair and skin). At the same time the structure is losing heat (sort of like a funnel). So theoretically, if the time that the heat being pushed into the skin is longer than the TRT of the skin, then it is less likely that you will burn the skin. This is why a variable pulse laser is safer. You can treat at a longer pulse width and help protect the skin. This is also the reason why Candela, which made the decision to use a fixed pulse at 3 ms had to go with cryogen cooling. The cryogen helps to reduce the skin temperature and decreases the TRT for the skin significantly.

The problem for variable pulse has to do with the hair. You can always put the energy into hair quicker than the TRT, so it is is possible to treat coarse hair with a short pulsewidth. The problem is that you can’t treat fine hair (which has a short TRT) with a long pulse because what happens is that the hair loses the heat faster than you are putting it in.

So treating coarse hair doesn’t really matter. Treating very fine hair does. And when it comes to treating fine hair the difference between 3 ms and 5 ms is enough to have a impact on very very fine hair.

#4

Aha, thanks.

Last question, I promise. What determines depth of laser. I was reading a paper-“Monte Carlo” something and depth with deflection/scatter of light seemed to be important as well to killing follicles. Any opinions? Thanks again.

Would this be influenced by joules or other parameters?

#5

Aha, thanks.

Last question, I promise. What determines depth of laser. I was reading a paper-“Monte Carlo” something and depth with deflection/scatter of light seemed to be important as well to killing follicles. Any opinions? Thanks again.

Would this be influenced by joules or other parameters?

Not sure what the Monte Carlo would be unless you mean “monte carlo simulation” which is a process by which one tests a model by allowing parameters to randomly vary using specific distributions. It is a type of sensitivity analysis.

The depth to which a laser pulse will go is dependent on a number of parameters. First, it is dependent on the wavelength which really doesn’t say how deep the pulse will go but rather affects the amount of scatter and absorption. The more absorption and scatter the less depth the pulse will penetrate. The YAG wavelength for example has less absorption and scatter hence penetrates deeper. But of course, notice that with less absorption there is also less of an effect. There is usually no such thing as a free lunch and there isn’t one here either.

Second it is also strongly influenced by the size of the spot. The greater the spot size, the less the scatter. This is because the loss from scatter occurs at the edge of the pulse not in the middle and the larger the spot size the larger the middle in comparison to the edges. The volume of a cylinder (which is what a pulse is) grows faster than the surface area. So the larger the spot size, the deeper the effective penetration.

The effect of a more effective deeper penetration is that a) it can kill hairs that are deeper and b) and the width of the effective pulse at any depth is larger meaning that there are fewer hairs on the edges that may not receive a strong enough pulse to destroy them.

#6

That was exactly what I was wondering-thank you you’ve been extremely helpful.