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ConcentrationsToOpticalDensity

Infer NIRS (delta-)optical density from chormophore (HbO, HbR) concentration changes.

This node implements the reverse process of the EstimateConcentrations node, and is therefore less frequently used. One use case is to work backwards from concentration data to optical density at different wavelengths in order to then image the optical density using tomographic imaging methods such as HD-DOT. This node uses the modified Beer-Lambert Law (MBLL) which relies on the fact that the different chromophores have different light absorption spectra. The calculation depends on a number of parameters, notably the differential pathlength factor and the partial volume correction, which can be looked up from textbooks. Both of these are configurable as parameters to this node. Incorrect assumptions will mostly result in incorrect scaling of the estimated optical density changes. Version 0.5.0

Ports/Properties

data

Data to process.

  • verbose name: Data
  • default value: None
  • port type: DataPort
  • value type: Packet (can be None)
  • data direction: INOUT

dpf

Differential Pathlength Factor (DPF). This is a factor, often between 4-9, which relates optical pathlength through some tissue (e.g., bone, skin, brain) to the distance between optodes.

  • verbose name: Differential Pathlength Factor
  • default value: 6
  • port type: FloatPort
  • value type: float (can be None)

pvc

Partial Volume Correction (PVC). A correction term that quantifies what fraction of the optical path is subject to concentration changes -- for fNIRS this is typically on the other of 40-90. The DPF is divided by the PVC to yield the Partial Pathlength Factor (PPF), which is often loosely around 0.1.

  • verbose name: Partial Volume Correction
  • default value: 60
  • port type: FloatPort
  • value type: float (can be None)

wavelengths

List of NIRS wavelengths at which to estimate concentrations. Given in nanometers.

  • verbose name: Wavelengths
  • default value: []
  • port type: ListPort
  • value type: list (can be None)

coords_unit

Unit of the channel positions. Typically this would be m for meters, but some data may have it wrong.

  • verbose name: Coordinates Unit
  • default value: m
  • port type: EnumPort
  • value type: str (can be None)

set_breakpoint

Set a breakpoint on this node. If this is enabled, your debugger (if one is attached) will trigger a breakpoint.

  • verbose name: Set Breakpoint (Debug Only)
  • default value: False
  • port type: BoolPort
  • value type: bool (can be None)

metadata

User-definable meta-data associated with the node. Usually reserved for technical purposes.

  • verbose name: Metadata
  • default value: {}
  • port type: DictPort
  • value type: dict (can be None)