WE-G-217BCD-11: A New Phantom to Study Combined Effects of In-Plane (x,y) and Z Axis Resolution for 3-D Imaging.

PURPOSE

The aim of this work is to develop phantoms that can be used to sample the radial and 3D properties of a CT image, including in-plane (x,y) and z-axis information. The Phantom is amenable to mathematical analysis of the x, y, and z axis resolution properties separately and combined.

METHODS

A periodic pattern of a pair of opposed (30°) angled ramps is configured to produce a waveform profile across the CT image. A perfect CT image (with no loss of resolution) of the test object would produce a consistent geometric pattern of the intersection of a line with the pair of angled ramps. However, due to the finite resolution (x, y and z), the CT waveform profile will not yield the perfect profile; rather it will be influenced by slice thickness, and in-plane resolution (PSF, MTF), as well as noise limitations, and other sources of non-uniformity such as beam hardening etc. Various characteristics of the waveform profile including, amplitude, frequency, and slope (rate of climb) of the peaks, can be studied using mathematical analysis such as the Fourier transform. It will be shown how these performance characteristics are encoded in the wave pattern.

RESULTS

The waveform profiles are visually examined and mathematically analyzed, to demonstrate the effect of Slice Thickness (z axis) and changes of In-Plane (x,y) Resolution and non-uniformity across the image field; moreover, the harmonic analysis of the waveform is used to predict, either the in-plane resolution (MTF), or the z-axis MTF when one of the two is already known.

CONCLUSIONS

The Wave pattern phantom offers a way to consider 3-D imaging characteristics of a CT scanner by scanning a single repetitive test object that encodes both in-plane resolution and z-axis resolution and also offers a way to study non-uniformity effects throughout the CT plane (volume). DJG is a consultant to The Phantom Laboratory and Image OWL, Salem, NY. Funding of other authors is supplied by Image OWL Salem, NY.