b1_afi map: Actual Flip-Angle Imaging for B1+ mapping¶
- 1. Print b1_afi information
- 2. Setting model parameters
- 2.a. Create b1_afi object
- 2.b. Set protocol and options
- 2.b.1 Set protocol the CLI way
- 2.b.2 Set protocol and options the GUI way
- 3. Fit MRI data
- 3.a. Load input data
- 3.b. Execute fitting process
- 3.c. Display FitResults
- 3.d. Save fit results
- 3.e. Re-use or share fit configuration files
- 4. Simulations
- 4.a. Single Voxel Curve
- 4.b. Sensitivity Analysis
- 5. Notes
- 5.a. Notes specific to b1_afi
- 5.a.1 BIDS
- 5.b. Generic notes
- 5.b.1. Batch friendly option and protocol conventions
- 5.b.2 Parallelization:
- 6. Citations
% This m-file has been automatically generated using qMRgenBatch(b1_afi) % for publishing documentation. % Command Line Interface (CLI) is well-suited for automatization % purposes and Octave. % % Please execute this m-file section by section to get familiar with batch % processing for b1_afi on CLI. % % Demo files are downloaded into b1_afi_data folder. % % Written by: Agah Karakuzu, 2017 % ==============================================================================
1. Print b1_afi information
b1_afi map: Actual Flip-Angle Imaging for B1+ mapping Assumptions: Compute a B1map Smoothing can be done with different filters and optional size Spurious B1 values and those outside the mask (optional) are set to a constant before smoothing Inputs: AFIData1 3D Actual Flip Imaging (AFI) data 1 AFIData2 3D Actual Flip Imaging (AFI) data 2 (Mask) Binary mask to exclude non-brain voxels Outputs: B1map_raw Actual/Nominal FA field map (B1+) B1map_filtered Smoothed B1+ field map using Gaussian, Median, Spline or polynomial filter (see FilterClass.m for more info) Spurious Map of datapoints that were set to 1 prior to smoothing Reference page in Doc Center doc b1_afi
2. Setting model parameters
2.a. Create b1_afi object
Model = b1_afi;
2.b. Set protocol and options
Protocol: MRI acquisition parameters that are accounted for by the respective model.
For example: TE, TR, FA FieldStrength. The assigned protocol values are subjected to a sanity check to ensure that they are in agreement with the data attributes.
Options: Fitting preferences that are left at user's discretion.
For example: linear fit, exponential fit, drop first echo.
2.b.1 Set protocol the CLI way
If you are using Octave, or would like to serialize your operations any without GUI involvement, you can assign protocol directly in CLI:
nomFA = 60; TR1 = 20; TR2 = 100; Model.Prot.Sequence.Mat = [ nomFA TR1 TR2];
See the generic notes section below for further information.
2.b.2 Set protocol and options the GUI way
The following command opens a panel to set protocol and options (if GUI is available to the user):
Model = Custom_OptionsGUI(Model);
If available, you need to close this panel for the remaining of the script to proceed.
Using this panel, you can save qMRLab protocol files that can be used in both interfaces. See the generic notes section below for details.
3. Fit MRI data
3.a. Load input data
This section shows how you can load data into a(n) b1_afi object.
- At the CLI level, qMRLab accepts structs containing (double) data in the fields named in accordance with a qMRLab model.
See the generic notes section below for BIDS compatible wrappers and scalable
% |- b1_afi object needs 3 data input(s) to be assigned: % |- AFIData1 % |- AFIData2 % |- Mask data = struct(); % AFIData1.nii.gz contains [88 128 32] data. data.AFIData1=double(load_nii_data('b1_afi_data/AFIData1.nii.gz')); % AFIData2.nii.gz contains [88 128 32] data. data.AFIData2=double(load_nii_data('b1_afi_data/AFIData2.nii.gz'));
3.b. Execute fitting process
This section will fit the loaded data.
FitResults = FitData(data,Model,0);
Visit the generic notes section below for instructions to accelerate fitting by
3.c. Display FitResults
You can display the current outputs by:
A representative fit curve will be plotted if available.
To render images in this page, we will load the fit results that had been saved before. You can skip the following code block;
% Load FitResults that comes with the example dataset. FitResults_old = load('FitResults/FitResults.mat'); qMRshowOutput(FitResults_old,data,Model);
3.d. Save fit results
Outputs can be saved as *.nii.(gz) if NIfTI inputs are available:
% Generic function call to save nifti outputs FitResultsSave_nii(FitResults, 'reference/nifti/file.nii.(gz)');
If not, FitResults.mat file can be saved. This file contains all the outputs as workspace variables:
% Generic function call to save FitResults.mat FitResultsSave_mat(FitResults);
FitResults.mat files can be loaded to qMRLab
GUI for visualization and ROI
The section below will be dynamically generated in accordance with the example data format (mat or nii). You can substitute FitResults_old with FitResults if you executed the fitting using example dataset for this model in section 3.b..
3.e. Re-use or share fit configuration files
qMRLab's fit configuration files (b1_afi_Demo.qmrlab.mat) store all the options and protocol in relation to the used model and the release version.
*.qmrlab.mat files can be easily shared with collaborators to allow them fit their own
data or run simulations using identical
4.a. Single Voxel Curve
Simulates single voxel curves
Not available for the current model.
4.b. Sensitivity Analysis
Simulates sensitivity to fitted parameters
Not available for the current model.
5.a. Notes specific to b1_afi
|== sub-01/ |~~~~~~ fmap/ |---------- sub-01_acq-tr1_TB1AFI.json |---------- sub-01_acq-tr1_TB1AFI.nii.gz |---------- sub-01_acq-tr2_TB1AFI.json |---------- sub-01_acq-tr1_TB1AFI.nii.gz | |== derivatives/ |~~~~~~ qMRLab/ |---------- dataset_description.json |~~~~~~~~~~ sub-01/fmap/ |-------------- sub-01_TB1map.nii.gz |-------------- sub-01_TB1map.json
For further information, please visit BIDS qMRI Appendix.
5.b. Generic notes
5.b.1. Batch friendly option and protocol conventions
If you would like to load a desired set of options / protocols programatically, you can use *.qmrlab.mat files. To save a configuration from the protocol panel of b1_afi, first open the respective panel by running the following command in your MATLAB command window (MATLAB only):
In this panel, you can arrange available options and protocols according to your needs, then click the save button to save my_b1_afi.qmrlab.mat file. This file can be later loaded into a b1_afi object in batch by:
Model = b1_afi; Model = Model.loadObj('my_b1_afi.qmrlab.mat');
Model.loadObj('my_b1_afi.qmrlab.mat') call won't update the fields in the
Model object, unless the output is assigned to the object as shown above. This compromise on convenience is to retain Octave CLI compatibility.
If you don't have MATLAB, hence cannot access the GUI, two alternatives are available to populate options:
- Use qmrlab/mcrgui:latest Docker image to access GUI. The instructions are available here.
- Set options and protocols in CLI:
- List available option fields using tab completion in Octave's command prompt (or window)
Model = b1_afi; Model.option. % click the tab button on your keyboard and list the available fields.
- Assign the desired field. For example, for a mono_t2 object:
Model = mono_t2; Model.options.DropFirstEcho = true; Model.options.OffsetTerm = false;
Some option fields may be mutually exclusive or interdependent. Such cases are handled by the
GUI options panel; however, not exposed to the
CLI. Therefore, manual
options assignments may be challenging for some involved methods such as
qsm_sb. If above options are not working for you and you cannot infer how to set options solely in batch, please feel free to open an issue in qMRLab and request the protocol file you need.
Similarly, in CLI, you can inspect and assign the protocols:
Model = b1_afi; Model.Prot. % click the tab button on your keyboard and list the available fields.
Each protocol field has two subfields of Format and Mat. The first one is a cell indicating the name of the protocol parameter (such as EchoTime (ms)) and the latter one contains the respective values (such as 30 x 1 double array containing EchoTimes).
Mat protocol values are set according to the example datasets served via OSF.
The current model does not perform voxelwise fitting. Therefore, parallelization is not enabled.
qMRLab JOSS article
Karakuzu A., Boudreau M., Duval T.,Boshkovski T., Leppert I.R., Cabana J.F., Gagnon I., Beliveau P., Pike G.B., Cohen-Adad J., Stikov N. (2020), qMRLab: Quantitative MRI analysis, under one umbrella 10.21105/joss.02343
Reference article for b1_afi
Quantitative MRI, under one umbrella.
NeuroPoly Lab, Montreal, Canada