makeArbitraryGrad

Creates a gradient event with an arbitrary waveform. The function ensures the waveform adheres to the specified gradient hardware constraints (maximum slew rate and amplitude). It allows for oversampling and extrapolation to handle waveform edges.

Syntax

function grad=makeArbitraryGrad(channel,varargin)

Calling Pattern

mr.makeArbitraryGrad(...)
mr.makeArbitraryGrad('ParameterName', value, ...)

Parameters

This function accepts both positional parameters and name-value pairs.

Required Parameters

Parameter Name	Value Type	Description	Example	Units
channel	char	The gradient channel ('x', 'y', or 'z') for the waveform.	'x'
waveform	double	A vector representing the desired gradient waveform amplitude at each time point.	[0.1, 0.2, 0.3, 0.2, 0.1]	Hz/m

Name-Value Pair Arguments

Parameter Name (string)	Value Type	Default	Description	Example
system	struct	[]	A structure containing system parameters (e.g., maxSlew, maxGrad, gradRasterTime). If empty, defaults to mr.opts().	mr.opts()
'oversampling'	logical	false	Specifies whether oversampling is used. If true, the waveform is sampled at twice the resolution.	true
'maxGrad'	double	0	The maximum allowed gradient amplitude. If 0, the system's maxGrad is used. (Units: Hz/m)	1000
'maxSlew'	double	0	The maximum allowed gradient slew rate. If 0, the system's maxSlew is used. (Units: Hz/m/s)	100000
'delay'	double	0	Delay before the gradient waveform starts. (Units: seconds)	0.001
'first'	double	NaN	The gradient amplitude at the very beginning (before the first sample in 'waveform'). If NaN, it's extrapolated. (Units: Hz/m)	0
'last'	double	NaN	The gradient amplitude at the very end (after the last sample in 'waveform'). If NaN, it's extrapolated. (Units: Hz/m)	0

Returns

Output	Value Type	Description
grad	struct	A structure containing the gradient event details: type, channel, waveform, delay, area, and tt (time points).

Examples

% Create spiral gradient waveforms with oversampling
gx = mr.makeArbitraryGrad('x', spiral_grad_shape(1,:), 'Delay', mr.calcDuration(gzReph), ...
    'first', 0, 'last', spiral_grad_shape(1,end), 'system', sys, 'oversampling', gradOversampling);
gy = mr.makeArbitraryGrad('y', spiral_grad_shape(2,:), 'Delay', mr.calcDuration(gzReph), ...
    'first', 0, 'last', spiral_grad_shape(2,end), 'system', sys, 'oversampling', gradOversampling);

% Create selective RF gradient waveforms from k-space trajectory
gxRf = mr.makeArbitraryGrad('x', mr.traj2grad(kx, 'RasterTime', dTG), ...
    'first', 0, 'last', 0, 'oversampling', gradOversampling);
gyRf = mr.makeArbitraryGrad('y', mr.traj2grad(ky, 'RasterTime', dTG), ...
    'first', 0, 'last', 0, 'oversampling', gradOversampling);

See Also

Sequence.addBlock, mr.opts