DSX Definitions

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In the DSX Suite documentation there are some terms which are specific to the technology and/or programs. A list of these terms and their definitions are provided below.

Asynchronous X-ray Data
X-ray data in which it is not the case that every frame in one view has a frame in the other view at the same time.
Calibration Object
Coordinate Systems
Sometimes referred to as reference frames or frames.
Object's CT coordinate system
The coordinate system implicitly defined by an object's segmented CT data file. The origin is in the lower-left corner of the first slice, with X to the right, Y going up, and Z increasing through the slices.
Object's local coordinate system (LCS)
The user-specified coordinate system for the object. It is usually calculated in Orient3D, but can also be specified directly in xManager. When the object is an anatomical object (e.g., bone), it is often called the anatomical coordinate system (ACS). It is stored in the subject file as a transform from the object's CT coordinate system to its local coordinate system. All tracking results output from Locate3D and X4D are stored as transforms between the X-ray lab coordinate system and the LCS.
X-ray lab coordinate system
The coordinate system of the X-ray imaging system. It is implicitly defined by the 3D coordinates of the beads in the calibration object.
Mocap coordinate system
The coordinate system of the motion-capture system. Its definition is dependent on the motion-capture software, but is usually defined by an L-frame during mocap calibration.
Digitally Reconstructed Radiograph (DRR)
Simulated X-ray image obtained by ray casting through CT data.
Dock Widgets
The dockable widgets allow for some flexibility in the graphical interface of most of the DSX applications. These widgets can be made visible or hidden using the View menu. The widgets can be dragged across the screen as a normal dialog window and can be docked in predefined locations (normally the sides, top, or bottom) in the main window.
A point identified in the voxel data or on the surface model of an object (e.g., ligament attachment). Once the object has been tracked in the X-ray data (using either points of interest in Locate3D or DRR-based tracking in X4D), the position of the landmark at the reporting times can be calculated and output.
Subject Object
A 3D object (e.g., bone, implant) that can be tracked in multiple motion trials. It must have voxel data associated with it in order to be tracked in the X-ray data with X4D, or three or more beads embedded in it to be tracked with Locate3D. It must also have a polygonal surface model with a local coordinate system in order to be used in kinematic analyses in Visual3D.
Tracked Object
A subject object that is tracked in a particular motion trial or reference trial. Once subject objects have been created from voxel data, any subset of them can be chosen for tracking in each motion trial. The ones chosen for a trial are that trial’s tracked objects. Each tracked object has a link to its subject object and a pose map containing tracking data.
Each DSX application has its own application-specific parameters that are displayed, and can be edited, in a dockable widget. The parameter values are stored in the subject file.
Point of Interest (POI)
A point of interest (usually a bead) that is tracked in X-ray data. If three or more POIs are identified in voxel data and then tracked in the X-ray images, they can then be used to calculate the pose of a 3D object (e.g., bone).
Pose for Objects
A set of 6 degrees of freedom (DOFs) that define the object's position and orientation (the pose of the object's local coordinate system in the X-ray lab frame). Objects can be bones or implants.
Pose for POI
A set of 3 translations that define the POIs position in the X-ray lab frame.
Pose Map
A set of poses, each with its own time stamp during a trial, that are interpolated by a cubic spline.
Region of Interest (ROI)
A region of interest is a geometric primitive that is used to mark a region of the surface model of an object. This region is used by Visual3D to calculate distance maps between the object and another object.
Subject File
All of the DSX applications use a single subject file (*.dsx) for holding all of the information about a single subject, which can include multiple data-collection sessions. The subject file contains the following information:
  • the subject details,
  • the X-ray configurations,
  • links to all of the data files (both raw and processed), and
  • links to all of the results files.
Each application loads the subject file to import the information that it needs and updates the file with the results of the analyses performed.
Surface Model
Triangulated representation of the segmented image data of an object. It is defined in the object's CT coordinate system.
ROI Surface Model
Triangulated representation of the segmented image data of an object after processing in Orient3D. It is defined in the object's local coordinate system (LCS).
Synchronous X-ray Data
X-ray data in which every frame in one view has a matching frame in the other view with the same time stamp.
Temporary Subject File
All of the DSX applications maintain a temporary subject file while you are working. This file is always kept up-to-date and can be used in case of a crash or inadvertent overwrite of the original file. When you load a subject file, each application will check to see if there is a temporary version of the file. If there is, you will be asked if you want to load the temporary or the original. Each application has a file menu which allows you to save the currently loaded subject file to the existing file or to a new file. When an application is closed, it checks whether the temporary subject file has changed since the last save and, if so, asks you to save or discard the changes.
Frame Time
The time stamp for a single frame of X-ray data in one view.
Reporting Time
A user-specified time point which is used to calculate and output tracking data. The reporting times do not have to match the frame times in either view. However, in most cases the X-ray images are synchronous in both views and the reporting times are the same as the X-ray frame times.
Calibration Trial
An X-ray trial used for calibrating the DSX system. There are three types: uniformity (white), grid (distortion), and calibration object. The uniformity trial, sometimes called a white trial, is used to correct for non-uniformity in the X-ray intensity levels across the images. Uniformity images should be taken at a lower kV setting than normal, so that none of the image is saturated. The grid trial is used for distortion correction, and consists of images of a grid of regularly spaced beads on a radiotranslucent surface or regularly spaced holes in a radiopaque sheet. The kV setting used to collect these images should be that same as the one used for the uniformity trial. The calibration object trial is used to calculate the 3D configuration of the X-ray equipment.
Motion Trial
An X-ray trial of an activity for which you want to track objects and/or points of interest.
Reference Trial
An X-ray trial that is used to help process and analyze motion trials. They are usually static trials in which the subject is stationary. Reference trials are needed in order to create Visual3D linked models, which are used to generate object poses from motion capture data.
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