processing.fid

processing.fid

Functions¶

Name	Description
apodize_exp	Apply an exponential weighting filter function for line broadening.
apodize_lg	Apply a Lorentzian-to-Gaussian transformation filter.
to_fid	Convert a frequency-domain spectrum back to a time-domain FID.
to_spectrum	Convert a time-domain Free Induction Decay (FID) to a frequency-domain spectrum.
zero_fill	Pad the specified dimension with zero amplitude points.

apodize_exp¶

processing.fid.apodize_exp(da, dim=DIMS.time, lb=1.0)

Apply an exponential weighting filter function for line broadening.

During apodization, the time-domain FID signal $f(t)$ is multiplied with a filter function $f_{filter}(t) = e^{-t/T_L}$ . This improves the Signal-to-Noise Ratio (SNR) because data points at the end of the FID, which primarily contain noise, are attenuated. The time constant $T_L$ is calculated from the desired line broadening in Hz.

Parameters¶

Name	Type	Description	Default
da	xr.DataArray	The input time-domain data.	required
dim	str	The dimension corresponding to time, by default `DIMS.time`.	`DIMS.time`
lb	float	The desired line broadening factor in Hz, by default 1.0.	`1.0`

Returns¶

Name	Type	Description
	xr.DataArray	A new apodized DataArray, preserving coordinates and attributes.

apodize_lg¶

processing.fid.apodize_lg(da, dim=DIMS.time, lb=1.0, gb=1.0)

Apply a Lorentzian-to-Gaussian transformation filter.

This filter converts a Lorentzian line shape to a Gaussian line shape, which decays to the baseline in a narrower frequency range. The time-domain FID is multiplied by $e^{+t/T_L}e^{-t^2/T_G^2}$ . The time constants $T_L$ and $T_G$ are derived from the lb and gb frequency-domain parameters.

Parameters¶

Name	Type	Description	Default
da	xr.DataArray	The input time-domain data.	required
dim	str	The dimension corresponding to time, by default `DIMS.time`.	`DIMS.time`
lb	float	The Lorentzian line broadening to cancel in Hz, by default 1.0.	`1.0`
gb	float	The Gaussian line broadening to apply in Hz, by default 1.0.	`1.0`

Returns¶

Name	Type	Description
	xr.DataArray	A new apodized DataArray, preserving coordinates and attributes.

to_fid¶

processing.fid.to_fid(da, dim=DIMS.frequency, out_dim=DIMS.time)

Convert a frequency-domain spectrum back to a time-domain FID.

This is the mathematical inverse of to_spectrum. It inverse-shifts the data to position 0 Hz at the array boundary, computes the IFFT, and reconstructs strictly positive time coordinates.

Parameters¶

Name	Type	Description	Default
da	xr.DataArray	The input frequency-domain data.	required
dim	str	The frequency dimension to transform, by default `DIMS.frequency`.	`DIMS.frequency`
out_dim	str	The name of the resulting time dimension, by default `DIMS.time`.	`DIMS.time`

Returns¶

Name	Type	Description
	xr.DataArray	The reconstructed time-domain FID.

to_spectrum¶

processing.fid.to_spectrum(da, dim=DIMS.time, out_dim=DIMS.frequency)

Convert a time-domain Free Induction Decay (FID) to a frequency-domain spectrum.

The stored, digital FID signal can be processed by a discrete Fourier transformation (DFT) to produce a digital MR spectrum. This function applies the FFT along the specified time dimension and shifts the zero-frequency component to the center of the spectrum.

Parameters¶

Name	Type	Description	Default
da	xr.DataArray	The input time-domain FID data.	required
dim	str	The time dimension to transform, by default `DIMS.time`.	`DIMS.time`
out_dim	str	The name of the resulting frequency dimension, by default `DIMS.frequency`.	`DIMS.frequency`

Returns¶

Name	Type	Description
	xr.DataArray	The frequency-domain spectrum with centered zero-frequency coordinates.

zero_fill¶

processing.fid.zero_fill(da, dim=DIMS.time, target_points=1024, position='end')

Pad the specified dimension with zero amplitude points.

Artificially extends the data with zeros to interpolate and increase the apparent digital resolution of the resulting spectrum.

Parameters¶

Name	Type	Description	Default
da	xr.DataArray	The input data.	required
dim	str	The dimension along which to pad zeros, by default `DIMS.time`.	`DIMS.time`
target_points	int	The total number of points desired after padding, by default 1024.	`1024`
position	(end, symmetric)	Where to apply the zeros. Use “end” for time-domain FIDs, and “symmetric” for spatial frequency domains like k-space. By default “end”.	`"end"`

Returns¶

Name	Type	Description
	xr.DataArray	A new DataArray padded with zeros to the target length, preserving metadata.