Data inputs to the container: raw BIDS files

This page provides details on the raw sensor data in BIDS format for the calibration and 72-hour files for the right leg and the left leg, which are provided as data inputs to the processing container.

Downloading from LASSO

When you try to download the raw BIDS files, you will see a screen below:

Under ‘Raw’, choose motion. You will see three categories - acq, task, and tracksys. Clicking any of the options once will deselect the category. See the example image below (CALIBRATION and RIGHTLEGMOVEMENT are not selected):

To understand what each of acq, task, and tracksys means, see Naming conventions.

BIDS directory

The BIDS directory should have one folder for each subject whose session data will be processed.

Each subject’s folder should contain raw data files, along with metadata files. The expected names of the files (with *denoting wildcard) are as follows:

bids_dir/
|-- participants.tsv
|-- participants.json
|-- sub-<label>/
|   |-- sub-<label>_sessions.tsv
|   |-- sub-<label>_sessions.json
|   |-- ses-<label>/
|   |   |-- sub-<label>_ses-<label>_scans.tsv
|   |   |-- sub-<label>_ses-<label>_scans.json
|   |   |-- motion/
|   |   |   |-- sub-<label>_ses-<label>_task-<label>_tracksys-imu_acq-<label>_motion.tsv
|   |   |   |-- sub-<label>_ses-<label>_task-<label>_tracksys-imu_acq-<label>_motion.json
|   |   |   |-- sub-<label>_ses-<label>_task-<label>_tracksys-imu_acq-<label>_channels.tsv
|   |   |   |-- sub-<label>_ses-<label>_task-<label>_tracksys-imu_acq-<label>_channels.json

sub-<label>_ses-<label>_scans.tsv will have the age of the subject at the data collection.

The age is in years (represented up to 3 decimal places).

Naming conventions

Calibration files will have the acquisition (acq-) label: calibration.

72-hour files will have the acq- label: primary.

Files that contain left leg movements will have the task label: LeftLegMovement.

Files that contain right leg movements will have the task label: RightLegMovement.

For each combination (ex. task-LeftLegMovement & acq-calibration) there will be 4 associated files.

In total, 16 files (4 combinations * 4 files) are expected.

tracksys-imu indicates that inertial measurement units (IMUs) were used to measure leg movements.

Raw time-series data (*_motion.tsv)

A *_motion.tsv is a recording of either calibration dataset or 72 hours of leg movement. There should be four *_motion.tsv files:

# Calibration files
a] sub-<label>_ses-<label>_task-LeftLegMovement_tracksys-imu_acq-calibration_motion.tsv
b] sub-<label>_ses-<label>_task-RightLegMovement_tracksys-imu_acq-calibration_motion.tsv

# Raw data, 72-hour files
c] sub-<label>_ses-<label>_task-LeftLegMovement_tracksys-imu_acq-primary_motion.tsv
d] sub-<label>_ses-<label>_task-RightLegMovement_tracksys-imu_acq-primary_motion.tsv

Each *_motion.tsv file will have seven columns:

t₀	a_x(t₀)	a_y(t₀)	a_z(t₀)	ω_x(t₀)	ω_y(t₀)	ω_z(t₀)
t₁	a_x(t₁)	a_y(t₁)	a_z(t₁)	ω_x(t₁)	ω_y(t₁)	ω_z(t₁)
…	…	…	…	…	…	…
t_N	a_x(t_N)	a_y(t_N)	a_z(t_N)	ω_x(t_N)	ω_y(t_N)	ω_z(t_N)

ti is the elapsed time from the start of a recording, where i is the index of a data point.
ax(ti), ay(ti),
az(ti) are the accelerometer readings at time ti,
along the three measurement axes.
ωx(ti), ωy(ti), ωz(ti)
are the gyroscope readings at time ti along its three measurement axes.
Further information about each column can be found in *_channels.tsv.

Note

Users interested in conducting their own analyses and not using the processing container first need to calibrate c] and d] using a] and b], respectively. They can then use calibrated c] and d] to proceed with their custom analyses.

Metadata to a specific tracking system (*_motion.json)

A *_motion.json contains metadata to the sensor used for preparing either a calibration file or a 72-hour file. There should be four *_motion.json files:

# Calibration files
e] sub-<label>_ses-<label>_task-LeftLegMovement_tracksys-imu_acq-calibration_motion.json
f] sub-<label>_ses-<label>_task-RightLegMovement_tracksys-imu_acq-calibration_motion.json

# Raw data, 72-hour files
g] sub-<label>_ses-<label>_task-LeftLegMovement_tracksys-imu_acq-primary_motion.json
h] sub-<label>_ses-<label>_task-RightLegMovement_tracksys-imu_acq-primary_motion.json

Items listed in each file are:

sampling frequency
effective sampling frequency
task name (primary or calibration)
task description
tracking system name
recording duration
accelerometer channel count
gyroscope channel count
latency channel count
manufacturer
sensor name
sensor serial number

Metadata to the recorded channels (*_channels.tsv)

A *_channels.tsv provides details about each column of *_motion.tsv. There should be four *_channels.tsv files:

# Calibration files
i] sub-<label>_ses-<label>_task-LeftLegMovement_tracksys-imu_acq-calibratioin_channels.tsv
j] sub-<label>_ses-<label>_task-RightLegMovement_tracksys-imu_acq-calibratioin_channels.tsv

# Raw data, 72-hour files
k] sub-<label>_ses-<label>_task-LeftLegMovement_tracksys-imu_acq-primary_channels.tsv
l] sub-<label>_ses-<label>_task-RightLegMovement_tracksys-imu_acq-primary_channels.tsv

Each *_channels.tsv file will have seven rows and seven columns. For example, i] for one subject is:

name	component	type	tracked_point	units	sampling_frequency	reference_frame
imu_latency	n/a	LATENCY	n/a	seconds	25.70383751213197	local
LeftAnkle_ACCEL_x	x	ACCEL	LeftAnkle	m/s^2	25.70383751213197	local
…	…	…	…	…	…	…
LeftAnkle_GYRO_z	z	GYRO	LeftAnkle	rad/s	25.70383751213197	local

Columns

name: the description of each column
component: the measurement axis (x, y, or z)
type: the type of sensor (LATENCY, ACCEL, or GYRO)
tracked_point: the location of the sensor (LeftAnkle or RightAnkle)
units: measurement unit (seconds, m/s^2 or rad/s)
sampling_frequency: effective sampling frequency in Hz
reference_frame: local (sensor-oriented)

Rows

imu_latency: latency information of the sensor used
LeftAnkle (or RightAnkle) ACCEL_x: accelerometer’s x-axis
LeftAnkle (or RightAnkle) ACCEL_y: accelerometer’s y-axis
LeftAnkle (or RightAnkle) ACCEL_z: accelerometer’s z-axis
LeftAnkle (or RightAnkle) GYRO_x: gyroscope’s x-axis
LeftAnkle (or RightAnkle) GYRO_y: gyroscope’s y-axis
LeftAnkle (or RightAnkle) GYRO_z: gyroscope’s z-axis

Metadata complementing _channels.tsv (_channels.json)

A *_channels.json describes the spatial properties of the reference frame used to prepare sensor movement dataset are represented. Positive X, Y, and Z sensor axes correspond to anterior, right, superior, respectively. There should be four *_channels.json files:

# Calibration files
m] sub-<label>_ses-<label>_task-LeftLegMovement_tracksys-imu_acq-calibratioin_channels.json
n] sub-<label>_ses-<label>_task-RightLegMovement_tracksys-imu_acq-calibratioin_channels.json

# Raw data, 72-hour files
o] sub-<label>_ses-<label>_task-LeftLegMovement_tracksys-imu_acq-primary_channels.json
p] sub-<label>_ses-<label>_task-RightLegMovement_tracksys-imu_acq-primary_channels.json