[Nirfast] Positive Jacobian Values

Hamid Dehghani h.dehghani at cs.bham.ac.uk
Mon Feb 13 13:35:14 EST 2017

Are you looking at J.complete or J.complex?
If J.complete, remember that the values are rate of change of log 
intensity per a small change in mua.
So a positive value, just means a larger attenuation.

On 13/02/2017 17:32, Thomas Johnson wrote:
> Hello,
> I am performing single wavelength forward simulations (800nm) on a custom 6-layer head mesh that models skin, skull, meninges, CSF, WM and GM. At a new different fibre separation lengths I end up with a Jacobian that has mostly positive values, while most other separation lengths give negative values. To me, this indicates the tissue is generating light! Can anyone help me out on this one? Here are things I am thinking:
> - I have given each tissue type a separate index of refraction. Could this be reflection coming off the tissue boundary?
> - There is a large region of CSF in my model. Is this an artefact of the diffusion approximation being unable to accurately simulate low scattering media?
> Thank you,
> Thomas Johnson
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Hamid Dehghani, PhD, MIPEM
School of Computer Science
Acting Director, Physical Sciences for Health Doctoral Training Centre
University of Birmingham
B15 2TT
0121 414 8728

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