Cone Beam Simulation

Simulates cone beam projection data from CT volume.

Input

  1. One 3D CT volume.
  2. (optional) A reference cone beam projection dataset from which the geometry settings should be copied.

Output

Cone beam projections with the geometry settings for each frame.

Description

A new cone beam projection dataset is created through the simulation of X-ray images from the input 3D CT volume. If a reference projection dataset was provided, then the image size as well as the geometry settings will be set from this reference. Otherwise, the cone beam geometry needs to be defined. Geometry and motion settings are disabled when the algorithm is opened with a reference projection dataset, since there is no need to define the cone beam geometry again.

The cone beam projections are created and displayed in the source-to-detector direction. Geometry presets are used to define the standard cone beam geometry settings. The user can further change the cone beam geometry settings under the controller of Cone Beam Geometry. Motion presets are used to apply transformation on each frame with respect to the motion parameters under Advanced motion parameters.

Geometry:

  • Half scan: Gantry angle range is 90°.
  • Full scan: Gantry angle range is 180°.
  • Short scan: Gantry angle range is 200°.
  • Single X-Ray shot: One cone beam projection is simulated with the rotational angle offset of 180°, which corresponds to the AP front-to-back X-ray projection.
  • Biplanar shot: Two cone beam projections are simulated with the angle difference of 90°, rotational angle offset of the first cone beam projection is 180°. This means that these projections are in the direction of AP front-to-back and right-to-left.

Motion:

  • No motion: Default mode with no motion.
  • Following detector: Rotational back-and-forward motion when the CT device reaches at 25% of the scan trajectory.
  • Nod after 25%: Up-down motion at 25% of the scan trajectory.
  • Nod after 50%: Up-down motion at 50% of the scan trajectory.
  • Nod after 75%: Up-down motion at 75% of the scan trajectory.
  • Device jitter: Simulating jittery movements of the device due to mechanical instabilities.
  • Ramp: Ramp motion when the CT device reaches at 25% of the scan trajectory.
  • Iso-jitter: Simulating small movements of the patient.

Warning

Width, height, and frame parameters are updated with each selection of geometry preset. Motion parameters are reset and updated by changing the frame numbers.

Projection:

  • Photon count projection: Simulates the regular X-ray projections by directly counting the number of photons that reach the detector after passing through the 3D CT volume.
  • Log-converted attenuation projection: Simulates the attenuation projections, i.e. the projections which are reconstructed from the linear attenuation coefficients. The acquired data after cone beam simulation is log-converted according to the Beer Lambert Law. Changing air value intensity does not affect log-converted attenuation projections.

Parameters:

  • width: Width of the projection images in pixels, default value is 512.

  • height: Height of the projection images in pixels, default value is 512.

  • frames: Number of frames to be simulated, default value is 400.

  • data type: Data type of the projection images, default type is Float.

  • air value intensity: The maximum X-ray beam intensity after passing through the input CT volume. If you select photon count projection under Projection, then you can set the air value intensity to any value from 0.1 to 1 with the step size of 0.1. If you select log-converted attenuation projection, then the air value intensity is not taken into computation.

  • Poisson noise: Add Poisson noise if photon count projections are simulated. No Poisson noise is added with the log-converted attenuation projections. When the air value intensity is lower, the expected Poisson noise with the photon count projections is stronger.

  • Show geometry visualization: Shows the cone beam geometry by drawing the source-to-detector connecting lines for each frame.

  • Advanced motion parameter settings: Motion can be modified by the parameters position, amplitude, offset, and par.

    • position: Frame number at start, turning point, and end of the motion. Note that position values should be consecutive or equal. The motion preset Jitter requires no position parameters.
    • amplitude: Amplitude of motion at start, turning point and end of the motion in mm or degrees (depending on par). Only for the motion preset Jitter, the first parameter is the percentage likelihood. The second and third parameters are the minimum and maximum of possible amplitude values.
    • offset: Offset in case of a rotation parameter par.
    • par: Parameter to define translation or rotational motion. 0 if motion shall be disabled, 1-3 for translational motion, 4-6 for rotational motion.