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Apply CLEARSWI in the command line without Julia programming experience. This repository contains the CLEARSWI algorithm and a command line interface.

Susceptibility Weighted Imaging (CLEAR-SWI)

Published as CLEAR-SWI. It provides magnetic resonance images with improved vein and iron contrast by weighting a combined magnitude image with a preprocessed phase image. This package has the additional capability of multi-echo SWI, intensity correction, contrast enhancement and improved phase processing. The reason for the development of this package was to solve artefacts at ultra-high field strength (7T), however, it also drastically improves the SWI quality at lower field strength.

Download standalone executables
This package contains binaries with dependencies.
For usage help, run the command line program in bin/clearswi without arguments or see below.

Usage - command line via Julia

Install Julia 1.9 or newer (
Copy the file clearswi.jl from this repository to a convenient location. An alias for clearswi as julia <path-to-file>/clearswi.jl might be useful.

    $ julia <path-to-file>/clearswi.jl -p phase.nii -m mag.nii -t [2.1,4.2,6.3] -o results

On the first run, the dependencies will be installed automatically.

For an extended explanation of the command line interface see below.

Usage - Julia


A Julia installation ≥ 1.6 (Official Julia Webpage)

Single-echo or multi-echo Magnitude and Phase images in NIfTI fileformat (4D images with echoes in the 4th dimension)


Run the following commands in Julia (either interactively in the REPL or as a script)

import Pkg; Pkg.add("CLEARSWI")

Function Reference


This is a simple multi-echo case without changing default behavior


TEs = [4,8,12] # change this to the Echo Time of your sequence. For multi-echoes, set a list of TE values, else set a list with a single TE value.
nifti_folder = CLEARSWI.dir("test","data","small") # replace with path to your folder e.g. nifti_folder="/data/clearswi"
magfile = joinpath(nifti_folder, "Mag.nii") # Path to the magnitude image in nifti format, must be .nii or .hdr
phasefile = joinpath(nifti_folder, "Phase.nii") # Path to the phase image

mag = readmag(magfile);
phase = readphase(phasefile);
data = Data(mag, phase, mag.header, TEs);

swi = calculateSWI(data);
# mip = createIntensityProjection(swi, minimum); # minimum intensity projection, other Julia functions can be used instead of minimum
mip = createMIP(swi); # shorthand for createIntensityProjection(swi, minimum)

savenii(swi, "<outputpath>/swi.nii"; header=mag.header) # change <outputpath> with the path where you want to save the reconstructed SWI
savenii(mip, "<outputpath>/mip.nii"; header=mag.header)

Available Options

To apply custom options use the following keyword syntax (example to apply 3D high-pass filtering for the phase with the given kernel size and deactivate softplus magnitude scaling):

options = Options(phase_hp_sigma=[10,10,5], mag_softplus=false)
swi = calculateSWI(data, options);

All the possible options with the default values are

  • mag_combine selects the echo combination for the magnitude. Options are

    • :SNR
    • :average
    • :last to select the last echo
    • (:CNR => (:gm, :wm)) to optimize the contrast between two selected tissues with the possible tissues classes to select in src\tissue.jl, currently only working for 7T
    • (:echo => 3) to select the 3rd echo
    • (:closest => 15.3) to select the echo that is closest to 15.3 ms
    • (:SE => 15.3) to simulate the contrast that would be achieved using a corresponding single-echo scan with 15.3 ms echo time.
  • If mag_sens is set to an array, it is used instead of CLEAR-SWI sensitivity estimation. This can also be set to mag_sens=[1] to use the constant sensitivity of 1 and effectively avoid sensitivity correction.

  • To deactivate scaling of the combined magnitude with the softplus function, use mag_softplus=false.

  • phase_unwrap is either :laplacian, :romeo, or :laplacianslice (slicewise laplacian unwrapping)

  • The phase_hp_sigma is used for high-pass filtering and is given in voxel for the [x,y,z]-dimension.

  • phase_scaling_type is the scaling function to create the phase mask and can be :tanh or :negativetanh for sigmoidal filtering, or :positive, :negative, and :triangular for traditional SWI application.

  • phase_scaling_strength adjusts the strength of the created phase mask. A higher phase_scaling_strength is a stronger phase appearance. With a traditional SWI phase_scaling_type it corresponds to the power or number of phase mask multiplications.

  • Set writesteps to the path, where intermediate steps should be saved, e.g. writesteps="/tmp/clearswi_steps". If set to nothing, intermediate steps won't be saved.

  • [Experimental] Set qsm to true to use QSM processing for the phase contrast. This requires the additional use of a QSM package. Supported are either QSM or QuantitativeSusceptibilityMappingTGV. Before setting this option, you need load one of these packages with using.

Calculating T2* and B0 maps on multi-echo datasets

T2* and B0 maps can be calculated using the package MriResearchTools:


B0 and R2*/T2* calculation requires the package MriResearchTools

using Pkg


With the previously defined variables phase, mag and TEs

using MriResearchTools

unwrapped = romeo(phase; mag=mag, TEs=TEs) # type ?romeo in REPL for options
B0 = calculateB0_unwrapped(unwrapped, mag, TEs) # inverse variance weighted

t2s = NumART2star(mag, TEs)
r2s = r2s_from_t2s(t2s)

Command Line Help

$ .\bin\clearswi
usage: <PROGRAM> [-m MAGNITUDE] [-p PHASE] [-o OUTPUT]
                 [-t ECHO-TIMES [ECHO-TIMES...]] [--qsm]
                 [--mag-combine MAG-COMBINE [MAG-COMBINE...]]
                 [--mag-sensitivity-correction MAG-SENSITIVITY-CORRECTION]
                 [--mag-softplus-scaling MAG-SOFTPLUS-SCALING]
                 [--unwrapping-algorithm UNWRAPPING-ALGORITHM]
                 [--filter-size FILTER-SIZE [FILTER-SIZE...]]
                 [--phase-scaling-type PHASE-SCALING-TYPE]
                 [--phase-scaling-strength PHASE-SCALING-STRENGTH]
                 [-e ECHOES [ECHOES...]] [-N] [--no-phase-rescale]
                 [--writesteps WRITESTEPS] [-v] [--version] [-h]


optional arguments:
  -m, --magnitude MAGNITUDE
                        The magnitude image (single or multi-echo)
  -p, --phase PHASE     The phase image (single or multi-echo)
  -o, --output OUTPUT   The output path or filename (default:
  -t, --echo-times ECHO-TIMES [ECHO-TIMES...]
                        The echo times are required for multi-echo
                        datasets specified in array or range syntax
                        (eg. "[1.5,3.0]" or "3.5:3.5:14").
  --qsm                 When activated uses RTS QSM for phase weighting
  --mag-combine MAG-COMBINE [MAG-COMBINE...]
                        SNR | average | echo <n> | SE <te>. Magnitude
                        combination algorithm. echo <n> selects a
                        specific echo; SE <te> simulates a single echo
                        scan of the given echo time. (default:
  --mag-sensitivity-correction MAG-SENSITIVITY-CORRECTION
                        <filename> | on | off. Use the CLEAR-SWI
                        sensitivity correction. Alternatively, a
                        sensitivity map can be read from a file
                        (default: "on")
  --mag-softplus-scaling MAG-SOFTPLUS-SCALING
                        on | off. Set softplus scaling of the
                        magnitude (default: "on")
  --unwrapping-algorithm UNWRAPPING-ALGORITHM
                        laplacian | romeo | laplacianslice (default:
  --filter-size FILTER-SIZE [FILTER-SIZE...]
                        Size for the high-pass phase filter in voxels.
                        Can be given as <x> <y> <z> or in array syntax
                        (e.g. [2.2,3.1,0], which is effectively a 2D
                        filter). (default: ["[4,4,0]"])
  --phase-scaling-type PHASE-SCALING-TYPE
                        tanh | negativetanh | positive | negative |
                        triangular Select the type of phase scaling.
                        positive or negative with a strength of 3-6 is
                        used in standard SWI. (default: "tanh")
  --phase-scaling-strength PHASE-SCALING-STRENGTH
                        Sets the phase scaling strength. Corresponds
                        to power values for positive, negative and
                        triangular phase scaling type. (default: "4")
  -e, --echoes ECHOES [ECHOES...]
                        Load only the specified echoes from disk
                        (default: [":"])
  -N, --no-mmap         Deactivate memory mapping. Memory mapping
                        might cause problems on network storage
  --no-phase-rescale    Deactivate automatic rescaling of phase
                        images. By default the input phase is rescaled
                        to the range [-π;π].
  --writesteps WRITESTEPS
                        Set to the path of a folder, if intermediate
                        steps should be saved.
  -v, --verbose         verbose output messages
  --version             show version information and exit
  -h, --help            show this help message and exit


This project is licensed under the MIT License - see the LICENSE for details