Imaging module

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Spinach contains a very general implementation of the Fokker-Planck formalism that is able to treat 3D diffusion and hydrodynamics simultaneously with Liouville-space spin dynamics, relaxation and chemical kinetics. This is a result of our in-house research, and it is dictated by the direction in which the field is moving: many emerging magnetic resonance methods (ultrafast NMR, singlet state imaging, spatially encoded NMR, metabolite-selective MRI, catalyst MRI, hyperpolarised imaging, etc.) fall in between the established simulation frameworks: on the one hand, they require accurate simulation of three-dimensional diffusion, hydrodynamics and chemical processes; on the other, it is essential that the spin evolution in every molecule is treated quantum mechanically in a way that accurately describes spin relaxation processes. At the same time, sophisticated spatially and temporally modulated radiofrequency pulses must be accounted for. Within the Fokker-Planck formalism, things like three-dimensional diffusion, hydrodynamics and off-resonance radiofrequency appear in a very simple way – each of these is just another constant matrix to add to the background evolution Hamiltonian.

Setting up the imaging context

For detailed instructions on setting up the imaging context, see imaging.m

Pre-programmed pulse sequences

basic_1d_hard.m - basic 1D imaging with a hard pulse and a gradient

cpmg_dec.m - CPMG echo train

dwi.m - 2D (spatial) diffusion weighted imaging sequence

epi.m - 2D (spatial) echo planar imaging sequence

fse.m - 2D (spatial) fast spin echo sequence

grad_echo.m - simple gradient echo pulse sequence

phase_enc.m - 2D (spatial) phase encoded imaging.

press_1d.m - 1D (spatial) PRESS sequence

press_2d.m - 2D (spatial) PRESS sequence

press_voxel_1d.m - voxel selection diagnostics for 1D (spatial) PRESS pulse sequence

press_voxel_2d.m - voxel selection diagnostics for 2D (spatial) PRESS pulse sequence

press_voxel_3d.m - voxel selection diagnostics for 2D (spatial) PRESS pulse sequence

slice_phase_enc.m - 3D (spatial) imaging with slice selection followed by phase-encoded acquisition

slice_select_1d.m - slice selection diagnostics

spin_echo.m - simple spin echo pulse sequence

spiral.m - 2D (spatial) imaging with spiral readout

udd_dec.m - Uhrig Dynamic Decoupling (UDD) echo train

uhrig_times.m - timing sequence for UDD echo train

Other relevant functions

g2fplanck.m - returns magnetic field gradient operators.

hydrodynamics.m - first derivative operators with respect to spatial coordinates.

mri_2d_plot.m - MRI image plotting with a black-and-white colour map.

ngridpts.m - estimates the minimum number of spatial grid points necessary to have a valid treatment of gradient driven experiments with explicit digitization of spatial dimensions.

phantoms.m - MRI phantoms library.

v2fplanck.m - converts diffusion and velocity fields into Fokker-Planck operators.

Version 2.1, authors: Ilya Kuprov, Ahmed Allami, Maria Grazia Concilio