LASERS in ENT, general, urology

Question 1

What is the tissue temperature for coagulation?

Answer 1

60 deg C

Question 2

What is the tissue temperature for vaporisation?

Answer 2

100 deg C

Question 3

What is the tissue temperature for carbonisation?

Answer 3

> 100 deg C

Question 4

What is the tissue temperature for melting?

Answer 4

> 200 degC

Question 5

Beer Lambert law

Answer 5

I=I0exp(-alpha.z)

Question 6

Penetration depth eqn

Answer 6

L=1/alpha

Question 7

Value for specific heat capacity of water?

Answer 7

4.2 J/g/degC

Question 8

Value for latent heat of vaporisation for water?

Answer 8

~2000 J/g

Question 9

Ablation eqn?

Answer 9

v = f.mu.k x I0.V/Q [cm/s]

Question 10

What is the thermal penetration depth?

Answer 10

Z(t)=sqrt(4kappat)

Distance over which T has reduced to 1/e of peak value in time t, due to diffusion.

Question 11

What lasers have a ZnSe lens and what does it pass?

Answer 11

CO2
passes vis + IR

Question 12

What is kappa in the equation for thermal penetration depth?

Answer 12

Temperature conductivity
kappa = k / rho c

k thermal conductivity Wm^-1K^-1
rho density
c specific heat capacity

Question 13

How to choose laser pulse length to minimise collateral thermal damage to tissue at depth?

Answer 13

Set optical penetration depth equal to thermal penetration depth, then rearrange for thermal relaxation time t.