Magnetoencephalography
Support for Magnetoencephalography (MEG) was developed as a BIDS Extension Proposal. Please see Citing BIDS on how to appropriately credit this extension when referring to it in the context of the academic literature.
MEG recording data
Template:
sub-<label>/
[ses-<label>/]
meg/
sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>][_proc-<label>][_split-<index>]_meg.<extension>
sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>][_proc-<label>][_split-<index>]_meg.json
sub-<label>[_ses-<label>][_task-<label>][_acq-<label>][_space-<label>]_markers.mrk
sub-<label>[_ses-<label>][_task-<label>][_acq-<label>][_space-<label>]_markers.sqd
sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>]_events.json
sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>]_events.tsv
Unprocessed MEG data MUST be stored in the native file format of the MEG instrument with which the data was collected. With the MEG specification of BIDS, we wish to promote the adoption of good practices in the management of scientific data. Hence, the emphasis is not to impose a new, generic data format for the modality, but rather to standardize the way data is stored in repositories. Further, there is currently no widely accepted standard file format for MEG, but major software applications, including free and open-source solutions for MEG data analysis, provide readers of such raw files.
Some software readers may skip important metadata that is specific to MEG system manufacturers. It is therefore RECOMMENDED that users provide additional meta information extracted from the manufacturer raw data files in a sidecar JSON file. This allows for easy searching and indexing of key metadata elements without the need to parse files in proprietary data format. Other relevant files MAY be included alongside the MEG data; examples are provided below.
This template is for MEG data of any kind, including but not limited to
task-based, resting-state, and noise recordings.
If multiple Tasks were performed within a single Run,
the task description can be set to task-multitask.
The *_meg.json file SHOULD contain details on the Tasks.
Some manufacturers' data storage conventions use folders which contain data
files of various nature: for example, CTF's .ds format, or BTi/4D's data folder.
Yet other manufacturers split their files once they exceed a certain size
limit.
For example Neuromag/Elekta/Megin, which can produce several files
for a single recording.
Both some_file.fif and some_file-1.fif would belong to a single recording.
In BIDS, the split entity is RECOMMENDED to deal with split files.
Another manufacturer-specific detail pertains to the KIT/Yokogawa/Ricoh sytem,
which saves the MEG sensor coil positions in a separate file with two possible filename extensions (.sqd, .mrk).
For these files, the markers suffix MUST be used.
For example: sub-01_task-nback_markers.sqd
Please refer to Appendix VI for general information on how to deal with such manufacturer specifics and to see more examples.
The proc-<label> entity is analogous to the
rec-<label> entity for MRI,
and denotes a variant of a file that was a result of particular processing performed on the device.
This is useful for files produced in particular by Elekta's MaxFilter
(for example, sss, tsss, trans, quat, mc),
which some installations impose to be run on raw data prior to analysis.
Such processing steps are needed for example because of active shielding software corrections
that have to be performed to before the MEG data can actually be exploited.
Recording EEG simultaneously with MEG
Note that if EEG is recorded with a separate amplifier,
it SHOULD be stored separately under a new /eeg data type
(see the EEG specification).
If however EEG is recorded simultaneously with the same MEG system,
it MAY be stored under the /meg data type.
In that case, it SHOULD have the same sampling frequency as MEG (see SamplingFrequency field below).
Furthermore, the EEG sensor coordinates SHOULD be specified using MEG-specific coordinate
systems (see coordinates section below and Appendix VIII).
Sidecar JSON (*_meg.json)
Generic fields MUST be present:
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| TaskName | REQUIRED | string | Name of the task. No two tasks should have the same name. The task label included in the file name is derived from this TaskName field by removing all non-alphanumeric ([a-zA-Z0-9]) characters. For example TaskName faces n-back will correspond to task label facesnback. A RECOMMENDED convention is to name resting state task using labels beginning with rest. |
SHOULD be present: For consistency between studies and institutions, we encourage users to extract the values of these fields from the actual raw data. Whenever possible, please avoid using ad-hoc wording.
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| InstitutionName | RECOMMENDED | string | The name of the institution in charge of the equipment that produced the composite instances. |
| InstitutionAddress | RECOMMENDED | string | The address of the institution in charge of the equipment that produced the composite instances. |
| Manufacturer | RECOMMENDED | string | Manufacturer of the MEG system (CTF, Elekta/Neuromag, BTi/4D, KIT/Yokogawa, ITAB, KRISS, Other). See Appendix VII with preferred names. |
| ManufacturersModelName | RECOMMENDED | string | Manufacturer’s designation of the MEG scanner model (for example, CTF-275). See Appendix VII with preferred names. |
| SoftwareVersions | RECOMMENDED | string | Manufacturer’s designation of the acquisition software. |
| TaskDescription | RECOMMENDED | string | Description of the task. |
| Instructions | RECOMMENDED | string | Text of the instructions given to participants before the scan. This is not only important for behavioral or cognitive tasks but also in resting state paradigms (for example, to distinguish between eyes open and eyes closed). |
| CogAtlasID | RECOMMENDED | string | URI of the corresponding Cognitive Atlas term that describes the task (for example, Resting State with eyes closed "https://www.cognitiveatlas.org/task/id/trm_54e69c642d89b"). |
| CogPOID | RECOMMENDED | string | URI of the corresponding CogPO term that describes the task (for example, Rest "http://wiki.cogpo.org/index.php?title=Rest"). |
| DeviceSerialNumber | RECOMMENDED | string | The serial number of the equipment that produced the composite instances. A pseudonym can also be used to prevent the equipment from being identifiable, as long as each pseudonym is unique within the dataset. |
Specific MEG fields MUST be present:
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| SamplingFrequency | REQUIRED | number | Sampling frequency (in Hz) of all the data in the recording, regardless of their type (for example, 2400). |
| PowerLineFrequency | REQUIRED | number or "n/a" |
Frequency (in Hz) of the power grid at the geographical location of the MEG instrument (for example, 50 or 60). |
| DewarPosition | REQUIRED | string | Position of the dewar during the MEG scan: upright, supine or degrees of angle from vertical: for example on CTF systems, upright=15°, supine=90°. |
| SoftwareFilters | REQUIRED | object of objects or "n/a" |
Object of temporal software filters applied, or "n/a" if the data is not available. Each key:value pair in the JSON object is a name of the filter and an object in which its parameters are defined as key:value pairs (for example, {"SSS": {"frame": "head", "badlimit": 7}, "SpatialCompensation": {"GradientOrder": "Order of the gradient compensation"}}). |
| DigitizedLandmarks | REQUIRED | boolean | true or false value indicating whether anatomical landmark points (fiducials) are contained within this recording. |
| DigitizedHeadPoints | REQUIRED | boolean | true or false value indicating whether head points outlining the scalp/face surface are contained within this recording. |
SHOULD be present:
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| MEGChannelCount | RECOMMENDED | integer | Number of MEG channels (for example, 275). |
| MEGREFChannelCount | RECOMMENDED | integer | Number of MEG reference channels (for example, 23). For systems without such channels (for example, Neuromag Vectorview), MEGREFChannelCount should be set to 0. |
| EEGChannelCount | RECOMMENDED | integer | Number of EEG channels recorded simultaneously (for example, 21). |
| ECOGChannelCount | RECOMMENDED | integer | Number of ECoG channels. |
| SEEGChannelCount | RECOMMENDED | integer | Number of SEEG channels. |
| EOGChannelCount | RECOMMENDED | integer | Number of EOG channels. |
| ECGChannelCount | RECOMMENDED | integer | Number of ECG channels. |
| EMGChannelCount | RECOMMENDED | integer | Number of EMG channels. |
| MiscChannelCount | RECOMMENDED | integer | Number of miscellaneous analog channels for auxiliary signals. |
| TriggerChannelCount | RECOMMENDED | integer | Number of channels for digital (TTL bit level) triggers. |
| RecordingDuration | RECOMMENDED | number | Length of the recording in seconds (for example, 3600). |
| RecordingType | RECOMMENDED | string | Defines whether the recording is "continuous", "discontinuous" or "epoched", where "epoched" is limited to time windows about events of interest (for example, stimulus presentations or subject responses). |
| EpochLength | RECOMMENDED | number | Duration of individual epochs in seconds (for example, 1) in case of epoched data. |
| ContinuousHeadLocalization | RECOMMENDED | boolean | true or false value indicating whether continuous head localisation was performed. |
| HeadCoilFrequency | RECOMMENDED | number or array of numbers | List of frequencies (in Hz) used by the head localisation coils (‘HLC’ in CTF systems, ‘HPI’ in Elekta, ‘COH’ in BTi/4D) that track the subject’s head position in the MEG helmet (for example, [293, 307, 314, 321]). |
| MaxMovement | RECOMMENDED | number | Maximum head movement (in mm) detected during the recording, as measured by the head localisation coils (for example, 4.8). |
| SubjectArtefactDescription | RECOMMENDED | string | Freeform description of the observed subject artefact and its possible cause (for example, "Vagus Nerve Stimulator", "non-removable implant"). If this field is set to n/a, it will be interpreted as absence of major source of artifacts except cardiac and blinks. |
| AssociatedEmptyRoom | RECOMMENDED | string | Relative path in BIDS folder structure to empty-room file associated with the subject’s MEG recording. The path needs to use forward slashes instead of backward slashes (for example, sub-emptyroom/ses-/meg/sub-emptyroom_ses-_task-noise_run-_meg.ds). |
| HardwareFilters | RECOMMENDED | object of objects or "n/a" |
Object of temporal hardware filters applied, or "n/a" if the data is not available. Each key:value pair in the JSON object is a name of the filter and an object in which its parameters are defined as key:value pairs (for example, {"Highpass RC filter": {"Half amplitude cutoff (Hz)": 0.0159, "Roll-off": "6dB/Octave"}}). |
Specific EEG fields (if recorded with MEG, see Recording EEG simultaneously with MEG SHOULD be present:
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| EEGPlacementScheme | OPTIONAL | string | Placement scheme of EEG electrodes. Either the name of a standardised placement system (for example, "10-20") or a list of standardised electrode names (for example, ["Cz", "Pz"]). |
| CapManufacturer | OPTIONAL | string | Manufacturer of the EEG cap (for example, EasyCap). |
| CapManufacturersModelName | OPTIONAL | string | Manufacturer’s designation of the EEG cap model (for example, M10). |
| EEGReference | OPTIONAL | string | Description of the type of EEG reference used (for example, M1 for left mastoid, average, or longitudinal bipolar). |
Example:
{
"InstitutionName": "Stanford University",
"InstitutionAddress": "450 Serra Mall, Stanford, CA 94305-2004, USA",
"Manufacturer": "CTF",
"ManufacturersModelName": "CTF-275",
"DeviceSerialNumber": "11035",
"SoftwareVersions": "Acq 5.4.2-linux-20070507",
"PowerLineFrequency": 60,
"SamplingFrequency": 2400,
"MEGChannelCount": 270,
"MEGREFChannelCount": 26,
"EEGChannelCount": 0,
"EOGChannelCount": 2,
"ECGChannelCount": 1,
"EMGChannelCount": 0,
"DewarPosition": "upright",
"SoftwareFilters": {
"SpatialCompensation": {"GradientOrder": "3rd"}
},
"RecordingDuration": 600,
"RecordingType": "continuous",
"EpochLength": 0,
"TaskName": "rest",
"ContinuousHeadLocalization": true,
"HeadCoilFrequency": [1470,1530,1590],
"DigitizedLandmarks": true,
"DigitizedHeadPoints": true
}
Note that the date and time information SHOULD be stored in the Study key file
(scans.tsv), see Scans file.
Date time information MUST be expressed as indicated in Units
Channels description (*_channels.tsv)
Template:
sub-<label>/
[ses-<label>/]
meg/
sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>][_proc-<label>]_channels.json
sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>][_proc-<label>]_channels.tsv
This file is RECOMMENDED as it provides easily searchable information across
BIDS datasets for for example, general curation, response to queries or batch
analysis.
To avoid confusion, the channels SHOULD be listed in the order they
appear in the MEG data file.
Missing values MUST be indicated with n/a.
The columns of the Channels description table stored in *_channels.tsv are:
MUST be present:
| Column name | Requirement level | Description |
|---|---|---|
| name | REQUIRED | Channel name (for example, MRT012, MEG023). |
| type | REQUIRED | Type of channel; MUST use the channel types listed below. Note that the type MUST be in upper-case. |
| units | REQUIRED | Physical unit of the value represented in this channel, for example, V for Volt, or fT/cm for femto Tesla per centimeter (see Units). |
SHOULD be present:
| Column name | Requirement level | Description |
|---|---|---|
| description | OPTIONAL | Brief free-text description of the channel, or other information of interest. See examples below. |
| sampling_frequency | OPTIONAL | Sampling rate of the channel in Hz. |
| low_cutoff | OPTIONAL | Frequencies used for the high-pass filter applied to the channel in Hz. If no high-pass filter applied, use n/a. |
| high_cutoff | OPTIONAL | Frequencies used for the low-pass filter applied to the channel in Hz. If no low-pass filter applied, use n/a. Note that hardware anti-aliasing in A/D conversion of all MEG/EEG electronics applies a low-pass filter; specify its frequency here if applicable. |
| notch | OPTIONAL | Frequencies used for the notch filter applied to the channel, in Hz. If no notch filter applied, use n/a. |
| software_filters | OPTIONAL | List of temporal and/or spatial software filters applied (for example, "SSS", "SpatialCompensation"). Note that parameters should be defined in the general MEG sidecar .json file. Indicate n/a in the absence of software filters applied. |
| status | OPTIONAL | Data quality observed on the channel (good/bad). A channel is considered bad if its data quality is compromised by excessive noise. Description of noise type SHOULD be provided in [status_description]. |
| status_description | OPTIONAL | Freeform text description of noise or artifact affecting data quality on the channel. It is meant to explain why the channel was declared bad in [status]. |
Example:
name type units description sampling_frequency low_cutoff high_cutoff notch software_filters status
UDIO001 TRIG V analogue trigger 1200 0.1 300 0 n/a good
MLC11 MEGGRADAXIAL T sensor 1st-order grad 1200 0 n/a 50 SSS bad
Restricted keyword list for field type.
Note that upper-case is REQUIRED:
| Keyword | Description |
|---|---|
| MEGMAG | MEG magnetometer |
| MEGGRADAXIAL | MEG axial gradiometer |
| MEGGRADPLANAR | MEG planargradiometer |
| MEGREFMAG | MEG reference magnetometer |
| MEGREFGRADAXIAL | MEG reference axial gradiometer |
| MEGREFGRADPLANAR | MEG reference planar gradiometer |
| MEGOTHER | Any other type of MEG sensor |
| EEG | Electrode channel |
| ECOG | Electrode channel |
| SEEG | Electrode channel |
| DBS | Electrode channel |
| VEOG | Vertical EOG (electrooculogram) |
| HEOG | Horizontal EOG |
| EOG | Generic EOG channel |
| ECG | ElectroCardioGram (heart) |
| EMG | ElectroMyoGram (muscle) |
| TRIG | System Triggers |
| AUDIO | Audio signal |
| PD | Photodiode |
| EYEGAZE | Eye Tracker gaze |
| PUPIL | Eye Tracker pupil diameter |
| MISC | Miscellaneous |
| SYSCLOCK | System time showing elapsed time since trial started |
| ADC | Analog to Digital input |
| DAC | Digital to Analog output |
| HLU | Measured position of head and head coils |
| FITERR | Fit error signal from each head localization coil |
| OTHER | Any other type of channel |
Example of free text for field description:
- stimulus, response, vertical EOG, horizontal EOG, skin conductance, sats, intracranial, eyetracker
Example:
name type units description
VEOG VEOG V vertical EOG
FDI EMG V left first dorsal interosseous
UDIO001 TRIG V analog trigger signal
UADC001 AUDIO V envelope of audio signal presented to participant
Coordinate System JSON (*_coordsystem.json)
Template:
sub-<label>/
[ses-<label>/]
meg/
sub-<label>[_ses-<label>][_acq-<label>]_coordsystem.json
OPTIONAL. A JSON document specifying the coordinate system(s) used for the MEG, EEG, head localization coils, and anatomical landmarks.
MEG and EEG sensors:
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| MEGCoordinateSystem | REQUIRED | string | Defines the coordinate system for the MEG sensors. See Appendix VIII for a list of restricted keywords for coordinate systems. If Other, provide definition of the coordinate system in MEGCoordinateSystemDescription. |
| MEGCoordinateUnits | REQUIRED | string | Units of the coordinates of MEGCoordinateSystem. MUST be m, cm, or mm. |
| MEGCoordinateSystemDescription | OPTIONAL, but REQUIRED if MEGCoordinateSystem is Other |
string | Free-form text description of the coordinate system. May also include a link to a documentation page or paper describing the system in greater detail. |
| EEGCoordinateSystem | OPTIONAL | string | See Recording EEG simultaneously with MEG. Preferably the same as the MEGCoordinateSystem. Defines the coordinate system for the EEG sensors. See Appendix VIII for a list of restricted keywords for coordinate systems. If Other, provide definition of the coordinate system in EEGCoordinateSystemDescription. |
| EEGCoordinateUnits | OPTIONAL | string | Units of the coordinates of EEGCoordinateSystem. MUST be m, cm, or mm. |
| EEGCoordinateSystemDescription | OPTIONAL, but REQUIRED if EEGCoordinateSystem is Other |
string | See Recording EEG simultaneously with MEG. Free-form text description of the coordinate system. May also include a link to a documentation page or paper describing the system in greater detail. |
Head localization coils:
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| HeadCoilCoordinates | OPTIONAL | object of arrays | Key:value pairs describing head localization coil labels and their coordinates, interpreted following the HeadCoilCoordinateSystem (for example, {"NAS": [12.7,21.3,13.9], "LPA": [5.2,11.3,9.6], "RPA": [20.2,11.3,9.1]}). Note that coils are not always placed at locations that have a known anatomical name (for example, for Elekta, Yokogawa systems); in that case generic labels can be used (for example, {"coil1": [12.2,21.3,12.3], "coil2": [6.7,12.3,8.6], "coil3": [21.9,11.0,8.1]}). Each array MUST contain three numeric values corresponding to x, y, and z axis of the coordinate system in that exact order. |
| HeadCoilCoordinateSystem | OPTIONAL | string | Defines the coordinate system for the head coils. See Appendix VIII for a list of restricted keywords for coordinate systems. If Other, provide definition of the coordinate system in HeadCoilCoordinateSystemDescription. |
| HeadCoilCoordinateUnits | OPTIONAL | string | Units of the coordinates of HeadCoilCoordinateSystem. MUST be m, cm, or mm. |
| HeadCoilCoordinateSystemDescription | OPTIONAL, but REQUIRED if HeadCoilCoordinateSystem is Other |
string | Free-form text description of the coordinate system. May also include a link to a documentation page or paper describing the system in greater detail. |
Digitized head points:
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| DigitizedHeadPoints | OPTIONAL | string | Relative path to the file containing the locations of digitized head points collected during the session (for example, sub-01_headshape.pos). RECOMMENDED for all MEG systems, especially for CTF and BTi/4D. For Elekta/Neuromag the head points will be stored in the fif file. |
| DigitizedHeadPointsCoordinateSystem | OPTIONAL | string | Defines the coordinate system for the digitized head points. See Appendix VIII for a list of restricted keywords for coordinate systems. If Other, provide definition of the coordinate system in DigitizedHeadPointsCoordinateSystemDescription. |
| DigitizedHeadPointsCoordinateUnits | OPTIONAL | string | Units of the coordinates of DigitizedHeadPointsCoordinateSystem. MUST be m, cm, or mm. |
| DigitizedHeadPointsCoordinateSystemDescription | OPTIONAL, but REQUIRED if DigitizedHeadPointsCoordinateSystem is Other |
string | Free-form text description of the coordinate system. May also include a link to a documentation page or paper describing the system in greater detail. |
Anatomical MRI:
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| IntendedFor | OPTIONAL | string or array of strings | Path or list of path relative to the subject subfolder pointing to the structural MRI, possibly of different types if a list is specified, to be used with the MEG recording. The path(s) need(s) to use forward slashes instead of backward slashes (for example, ses-/anat/sub-01_T1w.nii.gz). |
Anatomical landmarks:
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| AnatomicalLandmarkCoordinates | OPTIONAL | object of arrays | Key:value pairs of the labels and 3-D digitized locations of anatomical landmarks, interpreted following the AnatomicalLandmarkCoordinateSystem (for example, {"NAS": [12.7,21.3,13.9], "LPA": [5.2,11.3,9.6], "RPA": [20.2,11.3,9.1]}. Each array MUST contain three numeric values corresponding to x, y, and z axis of the coordinate system in that exact order. |
| AnatomicalLandmarkCoordinateSystem | OPTIONAL | string | Defines the coordinate system for the anatomical landmarks. See Appendix VIII for a list of restricted keywords for coordinate systems. If Other, provide definition of the coordinate system in AnatomicalLandmarkCoordinateSystemDescription. |
| AnatomicalLandmarkCoordinateUnits | OPTIONAL | string | Units of the coordinates of AnatomicalLandmarkCoordinateSystem. MUST be m, cm, or mm. |
| AnatomicalLandmarkCoordinateSystemDescription | OPTIONAL, but REQUIRED if AnatomicalLandmarkCoordinateSystem is Other |
string | Free-form text description of the coordinate system. May also include a link to a documentation page or paper describing the system in greater detail. |
It is also RECOMMENDED that the MRI voxel coordinates of the actual anatomical
landmarks for co-registration of MEG with structural MRI are stored in the
AnatomicalLandmarkCoordinates field in the JSON sidecar of the corresponding
T1w MRI anatomical data of the subject seen in the MEG session
(see Anatomy Imaging Data).
For example: sub-01/ses-mri/anat/sub-01_ses-mri_acq-mprage_T1w.json
In principle, these locations are those of absolute anatomical markers. However,
the marking of NAS, LPA and RPA is more ambiguous than that of for example, AC and PC.
This may result in some variability in their 3-D digitization from session to
session, even for the same participant. The solution would be to use only one
T1w file and populate the AnatomicalLandmarkCoordinates field with
session-specific labels for example, "NAS-session1": [127,213,139],"NAS-session2":
[123,220,142].
Fiducials information:
| Key name | Requirement level | Data type | Description |
|---|---|---|---|
| FiducialsDescription | OPTIONAL | string | A freeform text field documenting the anatomical landmarks that were used and how the head localization coils were placed relative to these. This field can describe, for instance, whether the true anatomical locations of the left and right pre-auricular points were used and digitized, or rather whether they were defined as the intersection between the tragus and the helix (the entry of the ear canal), or any other anatomical description of selected points in the vicinity of the ears. |
For more information on the definition of anatomical landmarks, please visit: http://www.fieldtriptoolbox.org/faq/how_are_the_lpa_and_rpa_points_defined
For more information on typical coordinate systems for MEG-MRI coregistration: http://www.fieldtriptoolbox.org/faq/how_are_the_different_head_and_mri_coordinate_systems_defined, or: http://neuroimage.usc.edu/brainstorm/CoordinateSystems
Landmark photos (*_photo.jpg)
Photos of the anatomical landmarks and/or head localization coils
(*_photo.jpg)
Template:
sub-<label>/
[ses-<label>/]
meg/
sub-<label>[_ses-<label>][_acq-<label>]_photo.jpg
Photos of the anatomical landmarks and/or head localization coils on the subject’s head are RECOMMENDED. If the coils are not placed at the location of actual anatomical landmarks, these latter may be marked with a piece of felt-tip taped to the skin. Please note that the photos may need to be cropped or blurred to conceal identifying features prior to sharing, depending on the terms of the consent given by the participant.
The acq-<label> entity can be used to indicate acquisition of different photos of
the same face (or other body part in different angles to show, for example, the
location of the nasion (NAS) as opposed to the right periauricular point (RPA)).
Example of the NAS fiducial placed between the eyebrows, rather than at the
actual anatomical nasion: sub-0001_ses-001_acq-NAS_photo.jpg
Head shape and electrode description (*_headshape.<ext>)
Template:
sub-<label>/
[ses-<label>/]
meg/
sub-<label>[_ses-<label>][_acq-<label>]_headshape.<extension>
This file is RECOMMENDED.
The 3-D locations of points that describe the head shape and/or EEG
electrode locations can be digitized and stored in separate files. The
acq-<label> entity can be used when more than one type of digitization in done for
a session, for example when the head points are in a separate file from the EEG
locations. These files are stored in the specific format of the 3-D digitizer’s
manufacturer (see Appendix VI).
Example:
sub-control01
ses-01
sub-control01_ses-01_acq-HEAD_headshape.pos
sub-control01_ses-01_acq-ECG_headshape.pos
Note that the *_headshape file(s) is shared by all the runs and tasks in a
session. If the subject needs to be taken out of the scanner and the head-shape
has to be updated, then for MEG it could be considered to be a new session.
Empty-room MEG recordings
Empty-room MEG recordings capture the environmental and recording system's
noise.
In the context of BIDS it is RECOMMENDED to perform an empty-room recording for
each experimental session.
It is RECOMMENDED to store the empty-room recording inside a subject folder
named sub-emptyroom.
The label for the task-<label> entity in the empty-room recording SHOULD be
set to noise.
If a session-<label> entity is present, its label SHOULD be the date of the
empty-room recording in the format YYYYMMDD, that is ses-YYYYMMDD.
The scans.tsv file containing the date and time of the acquisition SHOULD
also be included.
The rationale is that this naming scheme will allow users to easily retrieve the
empty-room recording that best matches a particular experimental session, based
on date and time of the recording.
It should be possible to query empty-room recordings just like usual subject
recordings, hence all metadata sidecar files (such as the channels.tsv) file
SHOULD be present as well.
Example:
sub-control01/
sub-control02/
sub-emptyroom/
ses-20170801/
sub-emptyroom_ses-20170801_scans.tsv
meg/
sub-emptyroom_ses-20170801_task-noise_meg.ds
sub-emptyroom_ses-20170801_task-noise_meg.json
sub-emptyroom_ses-20170801_task-noise_channels.tsv