Custom Trajectories

The SPI readout module offers three options for the design of k-space trajectories, which can be selected by setting the variable SPI.geo.traj_mode to one of the following three options before running the SPI_init() function:

  • 'standard': calls SPI_traj_standard.m to create a spiral trajectory based on geometric parameters, following the formulation by Kai Tobias Block1.
  • 'vds': calls SPI_traj_vds.m to create a variable-density spiral based on geometric parameters and system specifications, using Brian Hargreaves' VDS toolbox 2.
  • 'import': calls SPI_traj_import.m to allow the import of custom trajectories. In order to use this feature, the parameter SPI.geo.path must be set to the path of a .mat file containing two variables: dur (the desired duration of the readout in seconds), and either gxy (the gradient waveform as a complex array) or kxy (the k-space trajectory as a complex array).

Warning

Importing custom trajectories is an experimental feature - use with care, desired performance cannot be guaranteed. Will likely be updated in future versions.

  1. KT Block. Spiralförmige Abtastung des k-Raumes bei der Magnetresonanz-Tomographie. Diploma thesis, Georg-August-Universität zu Göttingen. 2004. https://www.mpinat.mpg.de/597698/tblock_diploma.pdf (accessed November 30, 2025). ↩

  2. The original toolbox used to be available under http://mrsrl.stanford.edu/~brian/vdspiral/, but this link seems to not be active anymore. Parts of it can be found in https://github.com/mribri999/MRSignalsSeqs/tree/master/Matlab. ↩