Sam power

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sam_power computes the Hilbert envelope of power for continuous data and outputs a 3D+time image. It does not compute event-related power (like sam_ers and sam_ersc or sam_4d and sam_4dc. sam_power is intended for use in connectivity studies of the correlation of the envelope of power among voxels — e.g., by using ICA or the AFNI function “Instacorr”.

sam_power applies the beamformer coefficients to the filtered MEG data (specified by ImageBand) to compute the estimated source timeseries. It then applies the Hibert transform to obtain the envelope of power. This is followed by a lowpass filter (specified by SmoothBand) and resampling at the interval specified by TimeStep. The smoothed, resampled Hilbert envelope of power is written out to each voxel.


 sam_power -r <dataset_name> -m <parameter_file_name> [options]

The -r flag is followed by the dataset name (with or without the .ds suffix). The -m flag is followed by the parameter file name (with or without .param).

Other options:

 -v  verbose mode
 -h  show help

Required parameters (either in the .param file or on the command line):

 RemoveBaseline: designates which option is used for baseline removal
 CovBand: Bandpass for covariance matrix, also specifies subdirectory for weights
 ImageBand: designates the bandpass for imaging the power
 SmoothBand: designates the lowpass filter for smoothing the Hilbert envelope
 TimeStep: Sampling interval for output image
 ImageMetric: Hilbert is always used
 NumMarkers: must be 0 (zero)
 CovType: must be GLOBAL

Optional parameters:

 ImageFormat: Designates whether the weights are in +orig or +tlrc space
 ImageDirectory: Directory where the output images are written, default is the SAM directory
 PrefixLength: Number of characters in the MEG dataset name used for naming MRI files.

Output Files

The output consists of a single 3D+time NIFTI format image, downsampled to the sampling interval specified by TimeStep.