CT Beam Width Measurement Using a CTDI Pencil Chamber
M Fadhel, K Grizzard, D Vergara, R Perez Franco, M Hoerner*, Yale University, New Haven, CT
Presentations
SU-I400-BReP-F1-4 (Sunday, 7/10/2022) 4:00 PM - 5:00 PM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 1
Purpose: Measurement of the CT beam width is required by the ACR and Joint Commission for annual physics evaluations. Methods for performing this measurement require either special hardware / software or consumable film. Currently, most 100mm pencil chambers used to evaluate CTDIvol have a high sampling rate to reconstruct a high resolution dose profile P(z) for a helical scan. The goal of this study is to measure the CT beam width from the dose profile of a single helical acquisition using a pencil chamber.
Methods: The dose profile of a CT scanner was measured for two helical scans with collimations of 20 and 40 mm using a pencil chamber. The dose profiles were corrected for table attenuation by extracting a table attenuation factor (TAF). The TAF repeats itself for every tube rotation, causing periodic dips in the measured profile P_meas(z) represented by a periodic function A_table(z). The measured profile was deconvolved with the function rect(z/Lc), representing the spatial integrating characteristics of the pencil chamber (L_c = 100mm for the chamber length). The beam width was defined by the full width half maximum of the resulting beam profile P_beam(z). Reference dose profiles were also measured and compared using a thimble ion chamber (0.6cc) and radiochromic film.
Results: The estimated beam widths using the proposed method of deconvolving P_meas(z) with rect(z/Lc) have a percent deviation of 2.6% and 2.8%, when compared to using an ion chamber and radiochromic film, respectively.
Conclusion: The proposed approach to deconvolve the pencil chamber response demonstrates the potential of obtaining the CT beam width at high accuracy without the need of extra equipment or film. This can improve the workflow for routine performance evaluation of CT systems.
Keywords
CT, Quality Control, Optimization
Taxonomy
IM- CT: Quality Control and Image Quality Assessment
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