Integrating QDEC with Slicer3 Click to add subtitle

Overview Slicer3 provides integrated file format support for the FreeSurfer geometry files, scalar overlays, and volume files. Through the QdecModule GUI, it also provides an interface to launch queries on subject populations that have been processed by FreeSurfer morphometry autosegmentation pipelines. Users can also load precomputed data sets and inspect the statistical processing results. These slides cover where to get data, how to load it, how to inspect it, and how to run your own analyses.

Sample Data Subject scans –Obtained from your local MRI scanner, processed using FreeSurfer –Place them in a subjects directory on disk –Add a qdec directory at the same level as the subjects –Create a qdec.table.dat file to describe the subject population

qdec.table.dat Sample file: ID Gender Age CSF OAS1_0001_MR1 F OAS1_0002_MR1 F OAS1_0003_MR1 F OAS1_0004_MR1 M OAS1_0005_MR1 M OAS1_0006_MR1 F

Factors The first column is the subject id, the directory name There are discrete and continuous factors in the following columns for the data table The levels that the discrete factors can take on are specified in a separate file, e.g. for the Gender column, the values can be either “M” or “F”.

Average Subject When the FreeSurfer analysis is done over a set of subjects, an average subject is computed The fsaverage directory holds an averaged brain on which the group statistics will be displayed

XNAT Subject populations also can be downloaded from the OASIS brains project stored in an XNAT database at Slicer3 can load.xar archive files direct from a web page download

XNAT - OASIS

Inspect a data set and select it for download

XNAT - OASIS

XNAT Once subjects are downloaded, run FreeSurfer processing pipelines locally and set up a qdec directory with a qdec.table.dat file

XNAT - QDEC XNAT also provides an interface to run QDEC analyses on the server, so large sets of subject scans do not have to be downloaded to your local machine

XNAT - QDEC

Set up an analysis using the web form, selecting discrete and continuous variables, and morphometric measures Click “Analyze”

XNAT - QDEC The server will start an analysis on the data you selected using the factors and measures you set up You will get an when your data is ready for download

XNAT - QDEC Select “Download XAR”, open with Slicer3

XNAT - QDEC Slicer3 will load the downloaded.xar file and extract it to a temporary directory Inside the temporary directory is a.qdec file and Slicer3's data loader interface will give you the option to load it into Slicer3

Slicer3 Slicer3 has a QDEC library that will unpack the.qdec file and load the contents –Average brain surface file –Brain curvature overlay –Statistical overlays corresponding to the contrast questions –Volume holding data for each subject

Slicer3 The.qdec archive holds a qdec.table.dat file that describes the subjects that were used in the group analysis, and that information is loaded in the QdecModule GUI (to the left in the previous slide) The discrete and continuous factors are also loaded in the GUI

Plotting When loading a.qdec file, the first point in the average brain is used to pop up a plot of all the subject values at that vertex, in this example, cortical thickness versus age for the two genders

Slicer3

Plotting The Slicer3 GUI provides a point and click interface to plot data at any point on the average brain

Plotting The next slide shows the toggle to switch to plot mode circled, and a fiducial placed on the brain where the vertex was chosen The plot window shows the RAS and index of the chosen vertex

Plotting

Inspecting Data You can inspect all the statistical results of the analysis by switching to different overlays using the “Questions” menu

GLM Fit On machines that have a FreeSurfer binary installation, you can use Slicer3 to set up queries and launch the mri_glmfit executable Slicer3 will automatically load the processing results for inspection

GLM Fit Load a qdec.table.dat that describes the subjects you wish to analyse

Subject ID and other variable values are loaded into the table Valid discrete and continuous factors are set up in the Design section

GLM Fit Select the factors that you wish to analyse, e.g. Age, and the measures, e.g. Using the left hemisphere of the brain, thickness, and smoothing of 10 If the original pipeline didn't calculate some of these values, Slicer will return an error

Set the Design Name, Click on “Age” as the first continuous factor Click on “Run GLM Fit”

GLM Fit Slicer launches mri_glmfit and loads results Average brain is loaded, and a default overlay is set up via the Questions menu A plot window is set up with vertex 0 data shown, and then the user can plot other data points

Query Atlas Once the average brain surface and statistical overlays are loaded into Slicer3, you can use the QueryAtlas module to load the brain region labels and browse the annotations