diff --git a/Plugins/org.mitk.gui.qt.diffusionimaging/documentation/UserManual/QmitkFiberfoxViewUserManual.dox b/Plugins/org.mitk.gui.qt.diffusionimaging/documentation/UserManual/QmitkFiberfoxViewUserManual.dox index f005dc1776..46f20aa809 100644 --- a/Plugins/org.mitk.gui.qt.diffusionimaging/documentation/UserManual/QmitkFiberfoxViewUserManual.dox +++ b/Plugins/org.mitk.gui.qt.diffusionimaging/documentation/UserManual/QmitkFiberfoxViewUserManual.dox @@ -1,115 +1,115 @@ /** \page org_mitk_views_fiberfoxview Fiberfox This view provides the user interface for Fiberfox [1,2,3], an interactive simulation tool for defining artificial white matter fibers and generating corresponding diffusion weighted images. Arbitrary fiber configurations like bent, crossing, kissing, twisting, and fanning bundles can be intuitively defined by positioning only a few 3D waypoints to trigger the automated generation of synthetic fibers. From these fibers a diffusion weighted signal is simulated using a flexible combination of various diffusion models. It can be modified using specified acquisition settings such as gradient direction, b-value, signal-to-noise ratio, image size, and resolution. Additionally it enables the simulation of magnetic resonance artifacts including thermal noise, Gibbs ringing, N/2 ghosting, susceptibility distortions and motion artifacts. The employed parameters can be saved and loaded as xml file with the ending ".ffp" (Fiberfox parameters). Available sections: - \ref QmitkFiberfoxViewUserManualFiberDefinition - \ref QmitkFiberfoxViewUserManualSignalGeneration - \ref QmitkFiberfoxViewUserManualKnownIssues - \ref QmitkFiberfoxViewUserManualReferences \imageMacro{Fiberfox.png, "Fig. 1: Screenshot of the Fiberfox framework. The four render windows display an axial (top left)\, sagittal (top right) and coronal (bottom left) 2D cut as well as a 3D view of a synthetic fiber helix and the fiducials used to define its shape. In the 2D views the helix is superimposing the baseline volume of the corresponding diffusion weighted image. The sagittal render window shows a close-up view on one of the circular fiducials.",16} \section QmitkFiberfoxViewUserManualFiberDefinition Fiber Definition Fiber strands are defined simply by placing markers in a 3D image volume. The fibers are then interpolated between these fiducials. Example: \li Chose an image volume to place the markers used to define the fiber pathway. If you don't have such an image available switch to the "Signal Generation" tab, define the size and spacing of the desired image and click "Generate Image". If no fiber bundle is selected, this will generate a dummy image that can be used to place the fiducials. \li Start placing fiducials at the desired positions to define the fiber pathway. To do that, click on the button with the circle pictogram, then click at the desired position and plane in the image volume and drag your mouse while keeping the button pressed to generate a circular shape. Adjust the shape using the control points (Fig. 2). The position of control point D introduces a twist of the fibers between two successive fiducials. The actual fiber generation is triggered automatically as soon as you place the second control point. \li In some cases the fibers are entangled in a way that can't be resolved by introducing an additional fiber twist. Fiberfox tries to avoid these situations, which arise from different normal orientations of succeeding fiducials, automatically. In rare cases this is not successful. Use the double-arrow button to flip the fiber positions of the selected fiducial in one dimension. Either the problem is resolved now or you can resolve it manually by adjusting the twist-control point. \li To create non elliptical fiber profile shapes switch to the Fiber Extraction View. This view provides tools to extract subesets of fibers from fiber bundles and enables to cut out arbitrary polygonal fiber shapes from existing bundles. -\imageMacro{Fiberfox-Fiducial.png, "Fig. 2: Control points defining the actual shape of the fiducial. A specifies the fiducials position in space\, B and C the two ellipse radii and D the twisting angle between two successive fiducials.",16} +\imageMacro{Fiberfox-Fiducial.png, "Fig. 2: Control points defining the actual shape of the fiducial. A specifies the fiducials position in space\, B and C the two ellipse radii and D the twisting angle between two successive fiducials.",10} Fiber Options: \li Real Time Fibers: If checked, each parameter adjustment (fiducial position, number of fibers, ...) will be directly applied to the selected fiber bundle. If unchecked, the fibers will only be generated if the corresponding button "Generate Fibers" is clicked. \li Advanced Options: Show/hide advanced options \li #Fibers: Specifies the number of fibers that will be generated for the selected bundle. \li Fiber Sampling: Adjusts the distenace of the fiber sampling points (in mm). A higher sampling rate is needed if high curvatures are modeled. \li Tension, Continuity, Bias: Parameters controlling the shape of the splines interpolation the fiducials. See Wikipedia for details. Fiducial Options: \li Use Constant Fiducial Radius: If checked, all fiducials are treated as circles with the same radius. The first fiducial of the bundle defines the radius of all other fiducials. \li Align with grid: Click to shift all fiducial center points to the next voxel center. Operations: \li Rotation: Define the rotation of the selected fiber bundle around each axis (in degree). \li Translation: Define the translation of the selected fiber bundle along each axis (in mm). \li Scaling: Define a scaling factor for the selected fiber bundle in each dimension. \li Transform Selection: Apply specified rotation, translation and scaling to the selected Bundle/Fiducial \li Copy Bundles: Add copies of the selected fiber bundles to the datamanager. \li Join Bundles: Add new bundle to the datamanager that contains all fibers from the selected bundles. \li Include Fiducials: If checked, the specified transformation is also applied to the fiducials belonging to the selected fiber bundle and the fiducials are also copied. -\imageMacro{FiberfoxExamples.png, "Fig. 3: Examples of artificial crossing (a\,b)\, fanning (c\,d)\, highly curved (e\,f)\, kissing (g\,h) and twisting (i\,j) fibers as well as of the corresponding tensor images generated with Fiberfox.",16} +\imageMacro{FiberfoxExamples.png, "Fig. 3: Examples of artificial crossing (a\,b)\, fanning (c\,d)\, highly curved (e\,f)\, kissing (g\,h) and twisting (i\,j) fibers as well as of the corresponding tensor images generated with Fiberfox.",6} \section QmitkFiberfoxViewUserManualSignalGeneration Signal Generation To generate an artificial signal from the input fibers we follow the concepts recently presented by Panagiotaki et al. in a review and taxonomy of different compartment models: a flexible model combining multiple compartments is used to simulate the anisotropic diffusion inside (intra-axonal compartment) and between axons (inter-axonal compartment), isotropic diffusion outside of the axons (extra-axonal compartment 1) and the restricted diffusion in other cell types (extra-axonal compartment 2) weighted according to their respective volume fraction. A diffusion weighted image is generated from the fibers by selecting the according fiber bundle in the datamanager and clicking "Generate Image". If some other diffusion weighted image is selected together with the fiber bundle, Fiberfox directly uses the parameters of the selected image (size, spacing, gradient directions, b-values) for the signal generation process. Additionally a binary image can be selected that defines the tissue area. Voxels outside of this mask will contain no signal, only noise. Basic Image Settings: \li Image Dimensions: Specifies actual image size (number of voxels in each dimension). \li Image Spacing: Specifies voxel size in mm. Beware that changing the voxel size also changes the signal strength, e.g. increasing the resolution from 2x2x2 mm to 1x1x1 mm decreases the signal obtained for each voxel by a factor 8. \li Gradient Directions: Number of gradients directions distributed equally over the half sphere. 10% baseline images are automatically added. \li b-Value: Diffusion weighting in s/mm². If an existing diffusion weighted image is used to set the basic parameters, the b-value is defined by the gradient direction magnitudes of this image, which also enables the use of multiple b-values. Advanced Image Settings (activate checkbox "Advanced Options"): \li Repetitions: Specifies the number of averages used for the acquisition to reduce noise. \li Signal Scale: Additional scaling factor for the signal in each voxel. The default value of 125 results in a maximum signal amplitude of 1000 for 2x2x2 mm voxels. Beware that changing this value without changing the noise variance results in a changed SNR. Adjustment of this value might be needed if the overall signal values are much too high or much too low (depends on a variety of factors like voxel size and relaxation times). \li Echo Time TE: Time between the 90° excitation pulse and the first spin echo. Increasing this time results in a stronger T2-relaxation effect (Wikipedia). \li Line Readout Time: Time to read one line in k-space. Increasing this time results in a stronger T2* effect which causes an attenuation of the higher frequencies in phase direction (here along y-axis) which again results in a blurring effect of sharp edges perpendicular to the phase direction. \li Tinhom Relaxation: Time constant specifying the signal decay due to magnetic field inhomogeneities (also called T2'). Together with the tissue specific relaxation time constant T2 this defines the T2* decay constant: T2*=(T2 T2')/(T2+T2') \li Fiber Radius (in µm): Used to calculate the volume fractions of the used compartments (fiber, water, etc.). If set to 0 (default) the fiber radius is set automatically so that the voxel containing the most fibers is filled completely. A realistic axon radius ranges from about 5 to 20 microns. Using the automatic estimation the resulting value might very well be much larger or smaller than this range. \li Simulate Signal Relaxation: If checked, the relaxation induced signal decay is simulated, other wise the parameters TE, Line Readout Time, Tinhom, and T2 are ignored. \li Disable Partial Volume Effects: If checked, the actual volume fractions of the single compartments are ignored. A voxel will either be filled by the intra axonal compartment completely or will contain no fiber at all. \li Output Volume Fractions: Output a double image for each compartment. The voxel values correspond to the volume fraction of the respective compartment. Compartment Settings: The group-boxes "Intra-axonal Compartment", "Inter-axonal Compartment" and "Extra-axonal Compartments" allow the specification which model to use and the corresponding model parameters. Currently the following models are implemented: \li Stick: The “stick” model describes diffusion in an idealized cylinder with zero radius. Parameter: Diffusivity d \li Zeppelin: Cylindrically symmetric diffusion tensor. Parameters: Parallel diffusivity d|| and perpendicular diffusivity d⊥ \li Tensor: Full diffusion tensor. Parameters: Parallel diffusivity d|| and perpendicular diffusivity constants d⊥1 and d⊥2 \li Ball: Isotropic compartment. Parameter: Diffusivity d \li Astrosticks: Consists of multiple stick models pointing in different directions. The single stick orientations can either be distributed equally over the sphere or are sampled randomly. The model represents signal coming from a type of glial cell called astrocytes, or populations of axons with arbitrary orientation. Parameters: randomization of the stick orientations and diffusivity of the sticks d. \li Dot: Isotropically restricted compartment. No parameter. For a detailed description of the single models, please refer to Panagiotaki et al. "Compartment models of the diffusion MR signal in brain white matter: A taxonomy and comparison". Additionally to the model parameters, each compartment has its own T2 signal relaxation constant (in ms). Noise and Artifacts: \li Noise: Add Rician or Chi-Square distributed noise with the specified variance to the signal. \li Spikes: Add signal spikes to the k-space signal resulting in stripe artifacts across the corresponding image slice. \li Aliasing: Aliasing artifacts occur if the FOV in phase direction is smaller than the imaged object. The parameter defines the percentage by which the FOV is shrunk. \li N/2 Ghosts: Specify the offset between successive lines in k-space. This offset causes ghost images in distance N/2 in phase direction due to the alternating EPI readout directions. \li Distortions: Simulate distortions due to magnetic field inhomogeneities. This is achieved by adding an additional phase during the readout process. The input is a frequency map specifying the inhomogeneities. The "Fieldmap Generator" view provides an interface to generate simple artificial frequency maps. \li Motion Artifacts: To simulate motion artifacts, the fiber configuration is moved between the signal simulation of the individual gradient volumes. The motion can be performed randomly, where the parameters are used to define the +/- maximum of the corresponding motion, or linearly, where the parameters define the maximum rotation/translation around/along the corresponding axis at the and of the simulated acquisition. \li Eddy Currents: EXPERIMENTAL! This feature is currently being tested and might not yet behave as expected! \li Gibbs Ringing: Ringing artifacts occurring on edges in the image due to the frequency low-pass filtering caused by the limited size of the k-space. \section QmitkFiberfoxViewUserManualKnownIssues Known Issues \li If fiducials are created in one of the marginal slices of the underlying image, a position change of the fiducial can be observed upon selection/deselection. If the fiducial is created in any other slice this bug does not occur. \li If a scaling factor is applied to the selcted fiber bundle, the corresponding fiducials are not scaled accordingly. \li In some cases the automatic update of the selected fiber bundle is not triggered even if "Real Time Fibers" is checked, e.g. if a fiducial is deleted. If this happens on can always force an update by pressing the "Generate Fibers" button. If any other issues or feature requests arises during the use of Fiberfox, please don't hesitate to send us an e-mail or directly report the issue in our bugtracker: http://bugs.mitk.org/ \section QmitkFiberfoxViewUserManualReferences References [1] Peter F. Neher, Frederik B. Laun, Bram Stieltjes, and Klaus H. Fritzsche: Fiberfox: Facilitating the creation of realistic white matter software phantoms, Magn Reson Med, DOI: 10.1002/mrm.25045. [2] Peter F. Neher, Frederik B. Laun, Bram Stieltjes, and Klaus H. Fritzsche: Fiberfox: An extensible system for generating realistic white matter software phantoms, MICCAI CDMRI Workshop, Nagoya; 09/2013 [3] Peter F. Neher, Bram Stieltjes, Frederik B. Laun, Hans-Peter Meinzer, and Klaus H. Fritzsche: Fiberfox: Fiberfox: A novel tool to generate software phantoms of complex fiber geometries, ISMRM, Salt Lake City; 04/2013 */