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The 4D Phantom

A uniquely capable QA system

  • for validating imaging, radiation therapy, gating, and motion tracking systems
  • 3D stage for simulating internal tissue motion
  • 1D stage for respiratory surrogate system control
  • accurate static and dynamic positioning
  • custom ellipsoidal and non-uniform trajectories
  • smooth, precise motion
  • for use with standard QA phantoms
4D Phantom

Overview & Applications

The Washington University 4D Phantom is a QA tool designed to position a radiological phantom with sub-millimeter accuracy. Years of development have given rise to an advanced hardware control system that is run by practical, user-friendly software.

Whereas other systems are limited to ellipsoidal or other simple preset motion paths, the 4D Phantom is capable of moving a radiological phantom and a respiratory surrogate device through custom trajectories at fifty specified positions per second. Thus, the 4D Phantom can reproduce concurrent, patient-specific internal and external tissue motion. The 4D Phantom can also generate user-defined linear and ellipsoidal trajectories.

Additionally, the 4D Phantom can perform highly accurate static positioning. It can be used to position a radiological phantom at a single location or through a series of individual points.

Motion: Slides, Motors, & Encoders

The 4D Phantom has separate slides and motors for each dimension of motion, allowing for completely arbitrary 4D (x, y, z, and time) positioning. Closed-loop control is achieved by encoders on each motor that verify positioning and correct for discrepancies in real time.

An Advanced Control System

The 4D Phantom’s motion is directed by a sophisticated motion controller card, which synchronizes the motion of all axes. Additionally, as the 4D Phantom progresses through a dynamic trajectory, the controller card contours the path of motion between commanded points. Because velocities and intermediate positions are calculated at the level of hardware, rather than software, the motion is smooth and reliable.

Accuracy & Precision

The 4D Phantom is able to produce highly accurate motion. External validation tests [1] have shown both the mean positional error and the RMS trial-to-trial error to be under 0.2mm.

4D Phantom Customers

  • Ross Beberco, PhD, Brigham & Women's Hospital
  • Jonathan Ha, PhD, University of Maryland
  • Michael Kissick, PhD, University of Wisconsin

Abstracts Highlighting the 4D Phantom at AAPM 2007

  • Breathing motion-induced dose delivery error evaluations as applied to Tomotherapy dose delivery (Chaudhari, TU-D-M100F-9)
  • Reduction of in-plane breathing motion artifacts using optimized angle sonogram reconstruction (Low, SU-FF-I-38)
  • Use of the 4D Phantom to test real-time targeted radiation therapy device accuracy (Malinowski, WE-E-BRA-2)
  • The effect of mid-scan changes of breathing frequency and amplitude on 4D CT quality (Noel, TU-D-L100J-9)
  • Dosimetric effects of a 4D magnetic localization system for LINAC beam gating on prostate and lung radiation therapy (Parikh, TH-C-M100J-8)
  • Initial phantom evaluation of a surface imaging system (GateCT®) for a 4D CT (H. Zhao, TU-D-L100J-3)
  • PET free breathing motion artifact reduction using list-mode data (T. Zhao, SU-FF-J-130)

Contact Information


Parag Parikh, MD

Kate Malinowski
Research Assistant