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Prospective Free-Breathing CT Scan Selection for 5DCT

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D O'Connell

D O'Connell*, D Thomas, T Dou, L Yang, J Lamb, J Lewis, D Ruan, P Lee, D Low UCLA, Los Angeles, CA


SU-D-202-6 (Sunday, July 31, 2016) 2:05 PM - 3:00 PM Room: 202

Purpose: 5DCT employs 25 fast helical scans and breathing surrogate monitoring to sample the respiratory cycle. Deformable image registration is used to fit a correspondence model between tissue motion and breathing amplitude and rate. The number of scans was chosen to ensure a high probability that tissues were imaged at sufficiently distinct breathing phases for accurate modeling of the entire breathing cycle. This work describes a method to prospectively select scan start times and reduce the protocol's number of scans from 25 to 6.

Methods: Breathing traces from 7 patients imaged with 5DCT were used to simulate acquisition of 6 scans. Breathing phase was estimated using only observations from previous time points. Cross-correlation between the representative breath and the most recent half period was continuously computed. If phase and cross-correlation criteria were met, scans were triggered with a 2 second delay before acquisition. Blind acquisition, 6 scans separated by a fixed delay, was modeled at staggered start times. The spread of prospectively and blindly sampled breathing waveforms was characterized using a previously published objective function.

Results: Prospectively selected scans ranked on average in the 84th percentile of objective function values obtained by blind acquisition at staggered start times for 7 patient breathing traces.

Conclusion: A method to prospectively determine scan start times for 5DCT was developed and tested by simulating acquisition on patient breathing traces. The method is computationally inexpensive enough for real-time implementation and would result in an imaging dose of less than one quarter of the current 5DCT protocol.

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