addRamps¶

This function adds ramp segments to a k-space trajectory to ensure smooth transitions between zero and the desired trajectory. It prevents violations of gradient and slew rate limits. It can handle single or multiple k-space trajectories (provided as a cell array or matrix). It can also add corresponding zero-filled segments to an accompanying RF pulse.

Syntax¶

function varargout=addRamps(k,varargin)

Calling Pattern¶

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

Parameters¶

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

Required Parameters¶

Parameter Name	Value Type	Description	Example	Units
`k`	double	cell	The k-space trajectory. Can be a numeric array (single trajectory) or a cell array of numeric arrays (multiple trajectories). Each column represents a time point.	`[1;2;3]`

Name-Value Pair Arguments¶

Parameter Name (string)	Value Type	Default	Description	Example
`system`	struct	`[]`	A structure containing system limits (e.g., maxGrad, maxSlew). If empty, defaults to mr.opts().	`mr.opts()`
`'rf'`	double	`[]`	An RF pulse shape. If provided, segments of zeros are added to match the duration of the added ramps.	`[0.5 0.5 0.5]`
`'maxGrad'`	double	`0`	Maximum gradient amplitude. Overrides the value in the 'system' structure if greater than 0. (Units: Hz/m)	`30e6`
`'maxSlew'`	double	`0`	Maximum gradient slew rate. Overrides the value in the 'system' structure if greater than 0. (Units: Hz/m/s)	`100e6`
`'gradOversampling'`	logical	`false`	Logical flag indicating whether gradient oversampling is used during ramp calculation.	`true`

Returns¶

Output	Value Type	Description
`varargout`	double	cell

Examples¶

% Example 1: Adding ramps to spiral k-space trajectory with RF pulse
% Define spiral k-space trajectory
kMax = (2*n)/foe/2;       % Units of 1/m (not rad/m)
tk = 0:dTG:T-dTG;
kx = kMax*(1-tk/T).*cos(2*pi*n*tk/T);
ky = kMax*(1-tk/T).*sin(2*pi*n*tk/T);

% Add gradient ramps with RF signal
[kx, ky, signal] = mr.addRamps({kx, ky}, 'rf', signal, 'system', lims, 'gradOversampling', gradOversampling);

% Example 2: Adding ramps with system limits
k_space = [1; 2; 3];
[k_space_with_ramps] = mr.addRamps(k_space, 'maxGrad', 30e6, 'maxSlew', 100e6);

% Example 3: Multiple trajectories with RF pulse extension
k_space = {[1; 2; 3], [4; 5; 6]};
rf_pulse = [0.5 0.5 0.5];
[k_space_with_ramps1, k_space_with_ramps2, rf_with_zeros] = mr.addRamps(k_space, 'rf', rf_pulse, 'maxGrad', 30e6, 'maxSlew', 100e6);