Laser depth math question!!

[lehughes]

Hi.
In the laser section of modalities 1, there is an (very appreciated) equation on calculating the amount of time that will be required (and dose required) to treat not just a cm2 area but incorporating the depth of the target area as well.

your page says ((DxA/P) x (1+d) = time in seconds to treat
*I assume there is one ')' missing at the end of that, but no matter.

but when I do your example problem of wanting to tx a 2cm2 area with dose of 8 J/cm2 at a depth of 2cm I am confused.

The final product 48 I get is the J total dose not the seconds to treat.?
if I leave off the divide by P then I get the 96 seconds to treat (but that only works if the laser being used is a 500mW laser).

Please let me know if I have misunderstood something.
cheers.
LP

[lehughes]

Hi L!

Sorry for the delay.  It got side tracked because it would require greater brain power.  But today, I have time and greater brain power!!!

So I think I know where the trouble may be coming from.

1) You are correct that there needs to be another bracket at the end of the equation.
2) and...

So for the equation, you would have 
((8 x 2)/.5) x (1 + 2))
(16/.5) x 3)
32 x 3
= 96
(Thus delivering 48J/cm2 at the surface with a 500mW laser)

I can’t figure out where your math went sideways…. I’m guessing it has to do with the D or the d  or the divide by 0.5 Watt laser.

If you have a different powered laser, then you’d have to put a different number in for P.

So if you were using a 250mW laser, it would be 

((8 x 2)/.25) x (1+2))
((16/.25) x 3)
(64 x 3)
= 192 seconds
(Again delivering 48J at the surface with a 250mw laser)

Remembering 1 Joule = 1 Watt x 1 Second

So ??Joules = .25 x 192 seconds
Thus 48 Joules

Sense or nonsense?

Laurie

[lehughes]

Hi.

Thanks for confirming the missing extra '()'.
I figured out where my math went awry.
I looked at the 0.5 and in my head said 1/2.  so divided by 2 instead of 0.5.  
so that's sorted.  

new question.
I thought I understood that laser depth of tissue penetration has mostly to do with the wavelength being used, so a calculation that considers depth of target tissue (or figuring in 3 dimensions vs 2 dimensions) wasn't really applicable? 
any more light to shed on that (sorry, couldn't help myself)?  or someone I can bother about it ( I tried CSU, but was told laser calculations for 3D were not applicable)?

much thanks for helping me sort out my silly question.

cheers.
LP

[lehughes]

I figured it had to be something to do with the 0.5.  Glad that is sorted.

So the calculation comes from the text The Laser Handbook and was created by Jan Tuner - one of the Godfathers of laser.
It is only applicable to lasers in the 800 - 900 nm range.  Yes, you are correct about depth being determined by wavelength.  (i.e. you could not get a 600 nm laser to even penetrate 2cm)
However, if you have a laser capable of depth penetration, then this is an acceptable method for predetermining depth.

MY laser guru is Peter Jenkins.  He has never let me down in regards to laser knowledge.  He owns Spectravet laser, but is the smartest guy I know regarding laser - and he’s friends with the laser research Gods  - ie. Tuner & Hode - and Roberta Chow as well I believe.

Anyways, many other company reps, I can poke holes in their BS, but Peter, a(s an owner, a guy who builds them, and participant in research projects) is right up there with his scientific knowledge.  His e-mail is spectra@spectravet.com.

Cheers,

Laurie