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CNR Dependence On Spatial Resolution and Subject Contrast in Phase Contrast CT

B Nelson*, S Leng, C McCollough, Mayo Clinic, Rochester, MN

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To quantify spatial resolution transition points at which x-ray phase has improved CNR over attenuation in x-ray grating interferometry and to demonstrate that these crossover points are material specific in a preclinical lung imaging application.
Methods: Lungs and heart from a murine sample were removed intact and fixed at end inspiratory inflated volume. Attenuation, phase, and normalized visibility contrast CT images were acquired using a Talbot-Lau grating interferometer in a 1st Talbot order geometry at 40 keV effective energy with a p/2 phase shift grating and 6 phase steps of 1.5 seconds each per view angle. Grating interferometer CT acquisitions acquired with 720 views over 2p range were repeated at six different dose levels and four detector binning configurations. ROIs from a heart region and lung were selected and CNR was calculated with respect to a nearby air ROI. CNR was then plotted against binned detector size and a power function was fit to each curve to determine the detector size at which phase and normalized visibility CNR intersect attenuation CNR.
Results: Due to the different noise responses to spatial resolution of phase and attenuation we measured transition points at which smaller detector sizes yield superior phase CNR. Additionally we found these transitions in the lung to be at nearly half the detector size as that observed in the heart.
Conclusion: These results provide additional evidence supporting the use of phase contrast for high resolution soft tissue imaging tasks and larger detector sizes for normalized visibility. Measuring these system CNR transitions illustrates the interactions between noise and contrast in grating interferometry and its impact in preclinical lung imaging.

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Keywords

Phase Contrast, CT, Resolution

Taxonomy

IM- X-Ray: Phase contrast

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