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Development of a Prospective Gating Algorithm for a Novel 4DCT Technique: Retrospective Data Analysis

D Low

D Low*, D Thomas, B White, S Gaudio, S Jani, P Lee, J Lamb, University of California, Los Angeles, Los Angeles, CA

SU-E-J-126 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To develop an algorithm for prospective CT scan selection to support a novel 4DCT acquisition technique

Methods: The new 4DCT acquisition protocol utilizes repeated rapid helical CT scans. Unless the CT scanner is synchronized with breathing, scans may be acquired at similar breathing phases, adding little to the breathing-motion characterization and therefore unnecessarily irradiating the patient. A retrospective patient dataset that consisted of 25 repeated CT scans and the accompanying breathing-motion model was used to evaluate possible algorithms. A single coronal slice through the lungs was used for the preliminary analysis. The mean model discrepancy for the 25 scans was 0.63mm. The model was fit using every subset of N scans out of the first 15. The discrepancies ranged from nearly 0.68mm to 9mm. The variation was hypothesized to be due to the level of redundancy in the scans used to generate the motion models. Scans were evaluated based on how the breathing depth and breathing rate (the two independent variables in the breathing motion model) differed at each CT slice. To maximize the variety of breaths selected from the 15, the mean square root difference D of the breathing depths and breathing rates were calculated and D correlated against the model discrepancies.

Results: The square-root difference function provided excellent separation between scan combinations that had small and large model errors. As expected, scans sets with small model errors were well spaced in breathing depth and rate. An optimal combination of breathing depth and rate was identified and shown to better select good scan combinations relative to separately analyzing depth or rate. The optimal scans had residual errors of 0.68mm compared with the baseline of 0.63mm.

Conclusion: The use of the mean square-root difference in breathing depth and rate will provide guidance for prospective scanning algorithm development.

Funding Support, Disclosures, and Conflict of Interest: Supported by NIH R01 CA096679

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