Program Information
Characterizing Low-Contrast Resolution for Non-Circular CBCT Trajectories
A Davis1*, E Pearson2 , X Pan1 , C Pelizzari1 , (1) The University of Chicago, Chicago, IL, (2) The Princess Margaret Cancer Centre - UHN, Toronto, ON
Presentations
SU-E-I-2 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: The use of non-circular scanning trajectories with optimization-based
reconstruction algorithms can be used in conjunction with non-planar
acquisition geometries for axial field-of-view (FOV) extension in
cone-beam CT (CBCT). To evaluate the utility of these trajectories,
quantitative image quality metrics should be evaluated. Low-contrast
resolution (LCR) and CT number accuracy are significant challenges for
CBCT. With unprecedented axial coverage provided by these
trajectories, measuring such metrics throughout the axial range is
critical. There are currently no phantoms designed to measure
low-contrast resolution over such an extended volume.
Methods: The CATPHAN (The Phantom Laboratory, Salem NY) is the current standard
for image quality evaluation. While providing several useful modules
for different evaluation metrics, each module was designed to be
evaluated in a single slice and not for comparison across axial
positions. To characterize the LCR and HU accuracy over an extended
axial length, we have designed and built a phantom with evaluation
modules at multiple and adjustable axial positions.
Results: The modules were made from a cast polyurethane resin. Holes ranging
from 1/8 to 5/8 inch were added at a constant radius from the module
center into which rods of two different plastic materials were pressed
to provide two nominal levels of contrast (1.0% and 0.5%). Larger
holes were bored to accept various RMI plugs with known electron
densities for HU accuracy evaluation. The modules can be inserted into
an acrylic tube long enough to cover the entire axial FOV and their
positions adjusted to desired evaluation points.
Conclusion: This phantom allows us to measure the LCR and HU accuracy across the
axial coverage within a single acquisition. These metrics can be used
to characterize the impact different trajectories and reconstruction
parameters have on clinically relevant image quality performance
metrics.
Funding Support, Disclosures, and Conflict of Interest: Funding was provided in part by Varian Medical Systems and NIH R01 Grants Nos. CA158446, CA182264, EB018102, and EB000225. The contents of this poster are solely the responsibility of the authors and do not necessarily represent the official view of any of the supporting organizations. .
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