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Effect of Brachytherapy Seed Artifacts in T2 and Proton Density Maps in MR Images

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S Mashouf

S Mashouf1,2*, A Fatemi-Ardekani1,3 , W Song1,2,3 , (1) Sunnybrook Odette Cancer Centre, Toronto, Ontario, (2) University of Toronto, Dept of Radiation Oncology, Toronto, Ontario, (3) Sunnybrook Research Institute, Toronto, Ontario


SU-E-J-233 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This study aims at investigating the influence of brachytherapy seeds on T2 and proton density (PD) maps generated from MR images. Proton density maps can be used to extract water content. Since dose absorbed in tissue surrounding low energy brachytherapy seeds are highly influenced by tissue composition, knowing the water content is a first step towards implementing a heterogeneity correction algorithm using MR images.

Methods: An LDR brachytherapy (IsoAid Advantage Pd-103) seed was placed in the middle of an agar-based gel phantom and imaged using a 3T Philips MR scanner with a 168-channel head coil. A multiple echo sequence with TE=20, 40, 60, 80, 100 (ms) with large repetition time (TR=6259ms) was used to extract T2 and PD maps.

Results: Seed artifacts were considerably reduced on T2 maps compared to PD maps. The variation of PD around the mean was obtained as -97% to 125% (±1%) while for T2 it was recorded as -71% to 24% (±1%).

Conclusion: PD maps which are required for heterogeneity corrections are susceptible to artifacts from seeds. Seed artifacts on T2 maps, however, are significantly reduced due to not being sensitive to B0 field variation.

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