Definitions
The RTE can mathematically model the transfer of energy as photons move inside a tissue. The flow of radiation energy through a small area element in the radiation field can be characterized by radiance . Radiance is defined as energy flow per unit normal area per unit solid angle per unit time. Here, denotes position, denotes unit direction vector and denotes time (Figure 1).
Several other important physical quantities are based on the definition of radiance:
- Fluence rate or intensity
- Fluence
- Current density (energy flux) . This is the vector counterpart of fluence rate pointing in the prevalent direction of energy flow.
Read more about this topic: Radiative Transfer Equation And Diffusion Theory For Photon Transport In Biological Tissue
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