The 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  have shown both the mean positional error and the RMS trial-to-trial error to be under 0.2mm.
4D Phantom Customers
Abstracts Highlighting the 4D Phantom at AAPM 2007
Parag Parikh, MD