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NIRS Meta Data
Sean Mullen edited this page Dec 29, 2020
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If a stream has the content-type NIRS, we recommend that meta-data about the stream adheres to the structure and naming laid out below. While all meta-data is optional, we recommend that any stream should describe at least those tags marked with an * below (and their parent containers) .
<channels> # per-channel meta-data
<channel> # description of one channel (one per channel in the time series)
<label> # unique channel label; an example naming scheme that references
# the source, detector and wavelength is: Src23-Dct6:750
<type> # type of data measured in this channel.
# Typically Intensity, which is assumed if unspecified;
# but some devices may yield different or additional data types, e.g.:
# ** dOD: (delta) optical density
# ** HbO, HbR: oxyhemoglobin, deoxyhemoglobin concentration
# ** HbT: Total hemoglobin concentration
# ** H2O, Lipid, CCO: water / lipid / Cytochrome c oxidase concentration
# ** mua, musp: Absorption coefficient, Scattering coefficient
# ** BFi: Blood flow index
<measure> # the name of the quantity being measured in this channel, where applicable
# (depends on NIRS technology used). e.g.:
# ** Amplitude
# ** Phase (FD-NIRS)
# ** AC Amplitude (FD-NIRS)
# ** Fluorescence amplitude
# ** Fluorescence phase (FD-NIRS)
<unit> # measurement unit for this channel, e.g.: lumens, micromolars, nanovolts
<source>* # unique identifier of the source; should match a `<probe><label>` (under probes)
<detector>* # unique identifier of the detector; should match a `<probe><label>`
<wavelen>* # nominal (excitation) wavelength, in nanometers;
# matches a `<probe><wavelens><wavelen>` if latter is specified
<wavelen_measured> # the actual (excitation) wavelength if measured, in nanometers
<fluorescence> # information related to fluorescence
<wavelen> # nominal fluorescence emission wavelength, in nanometers
# matches a `<probe><fluorescence><wavelens><wavelen>` if latter is specified
<wavelen_measured> # actual fluorescence emission wavelength, if measured, in nanometers
</fluorescence>
<illumination> # illumination pattern used, matches an `<illumination><label>` if latter is specified
<fd> # information specific to Frequency Domain (FD) NIRS
<frequency> # channel frequency, in Hz (FD-NIRS);
# matches a frequency in `<probe><frequencies>` if latter is specified
</fd>
<td> # information specific to Time Domain (TD-Gated or TD-Moments) NIRS
<delay> # time delay, in picoseconds (for TD-Gated NIRS);
# matches a time delay in `<probe><time_delays>` if latter is specified
<width> # time delay width, in picoseconds (for TD-Gated NIRS);
# matches a width in `<probe><time_delays>` if latter is specified
<order> # moment order, as an integer representing an ordinal (for TD-Moments NIRS);
# matches an order moment in <probe><time_delays> if latter is specified
</td>
<dcs> # information specific to Diffuse Correlation Spectroscopy (DCS)
<delay> # time delay for DCS measurements, in picoseconds
<width> # time delay width for DCS measurements, in picoseconds
</dcs>
</channel>
</channels>
<probes> # per-probe meta-data;
<probe> # description of a single probe
<modality> # NIRS modality, e.g.:
# ** CW: Continuous Wave
# ** FD: Frequency Domain
# ** TD-G: Time Domain Gated
# ** TD-M: Time Domain Moments
# ** DCS: Diffuse Correlation Spectroscopy
# if unspecified, CW is assumed
<function>* # probe type based on its function:
# ** Source
# ** Detector
<label>* # source/detector label (i.e., a number)
# referenced in <channel><source> or <channel><detector>
<location>* # measured location, relative to the fiducials (landmarks) specified in <fiducials>
# may be repeated if both 3D and 2D positions are specified
# for 2D positions, the missing axis (<Z>) should be empty
<X> # coordinate axis pointing from the center of the head to the right, in millimeters
<Y> # coordinate axis pointing from the center of the head to the front, in millimeters
<Z> # coordinate axis pointing from the center of the head to the top, in millimeters
</location>
<source> # information specific to source probes; can include vendor-specific child tags
<power> # power for a given probe, in milliwatts
</source>
<detector> # information specific to detector probes; can include vendor-specific child tags
<gain> # power gain of a given detector, in decibels
</detector>
<wavelens> # list of wavelengths transmitted for this probe
<wavelen> # wavelength in nanometers; repeated for each wavelength
</wavelens>
<fluorescence> # information related to fluorescence
<wavelens> # list of fluorescence emission wavelengths
<wavelen> # fluorescence emission wavelength, in nanometers; repeated for each wavelength
</wavelens>
</fluorescence>
<fd> # information specific to Frequency-Domain NIRS (FD-NIRS)
<frequencies> # list of modulation or detection frequencies
<frequency> # a frequency modulated or detected by this probe, in Hz
</frequencies>
</fd>
<td> # information specific to Time-Domain NIRS (TD-Gated NIRS or TD-Moments NIRS)
<time_delays> # holds time delays, widths and moment orders
<time_delay> # description of a single time delay, may be repeated
<delay> # a time delay, in picoseconds
<width> # a time width, in picoseconds
<order> # a moment order of the temporal point spread function; integer (for TD-Moments)
</time_delay>
</time_delays>
</td>
<dcs> # information specific to Diffuse Correlation Spectroscopy (DCS)
<time_delays> # holds time delays, widths and moment orders
<time_delay> # description of a single time delay, may be repeated
<delay> # a time delay, in picoseconds
<width> # a time width, in picoseconds
</time_delay>
</time_delays>
</dcs>
<hardware> # references the name of a probe hardware defined in <hardwares>, if specified
<module> # references the name of a module/group defined in <modules>, if specified
</probe>
</probes>
<hardwares> # information about optode/probe hardware
<hardware> # describes one type of probe hardware;
# repeated for each type of source or detector hardware used on this device
# includes other vendor-specific tags as needed (e.g., spring type, light guide length
<label> # unique name of the hardware; referenced in <probe><hardware>
<function> # the function of the probe:
# ** Source
# ** Detector
<manufacturer> # manufacturer of the probe
<model> # model of the probe
<type> # type of source or detector hardware, e.g.:
# for sources: Laser, LED, Fluorescence (?)
# for detectors: SiPD, APD
<surface> # type of the contact surface (e.g., Plate, Pins, Bristle, Pad, Dual-Tip, Multi-Tip)
<mount> # type of probe mount used (e.g., Spring-Loaded, Dock)
</hardware>
</hardwares>
<modules> # a list of modules/groups of probes
<module> # information describing a module/group of probes
# (may correspond to, e.g., docks, amplifiers, sensor bundles)
# may include other vendor-specific tags as needed
<label> # the name of the module
</module>
</modules>
<illuminations> # information about device illumination patterns
<illumination> # describes an illumination pattern; may be repeated
<label> # unique name of an illumination pattern (i.e., “bilateral”, a number, etc.)
<num_steps> # the total number of steps in this illumination pattern
<duration> # the duration of each step in the pattern, in microseconds
<pulse> # duration of source pulse or oscillation, in picoseconds,
# if different the duration (e.g., for TD-NIRS)
<sources> # a list of sources firing simultaneously in this pattern
<source> # a source included in this pattern
<label> # the name of the source, should match a `<probe><label>`
<step> # the sequential step number when this source is fired, an integer (1-base)
</source>
</sources>
</illumination>
</illuminations>
<fiducials> # locations of fiducials/landmarks (in the same space as the signal-carrying channels)
<origin> # name of the coordinate system used to define the origin for all fiducials or channels
# common fiducials include:
# ** MNI (assumed if unspecified), Talairach, CTF
<fiducial> # information about a single fiducial/landmark (repeated for each one)
<label>* # name of the location, e.g.:
# ** Nasion, Inion
# ** Cz
# ** LPF, RPF
<location>* # measured location (same coordinate system as channel locations)
<X> # axis pointing from the center of the head (origin) to the right, in millimeters
<Y> # axis pointing from the center of the head (origin) to the front, in millimeters
<Z> # axis pointing from the center of the head (origin) to the top, in millimeters
</location>
</fiducial>
</fiducials>
<cap> # information about the NIRS cap
# may include additional vendor-specific tags describing the features of the cap
<manufacturer> # manufacturer of the cap
<label> # unique label of the cap
<size> # cap size (head circumference), in centimeters (e.g., 54, 56, 58)
<label_scheme> # the labelling scheme used for montages (e.g., 10-20)
</cap>
<acquisition> # information about the signal acquisition device (amplifier/hub)
<manufacturer> # manufacturer of the amplifier
<model> # model name of the amplifier
<label> # unique label of the amplifier (e.g., serial number)
<precision> # the theoretical number of bits precision delivered by the amplifier
# (typical values are 8, 16, 24, 32)
<compensated_lag> # amount of hardware/system lag that has been implicitly
# compensated for in the stream's time stamps (in seconds)
<settings> # vendor-specific settings of the amplifier
<setting> # a vendor-specific setting, may be repeated
<label> # name of the setting
<value> # value of the setting
</setting>
</settings>
</acquisition>