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The Effect of Reconstruction and Volume Preset Parameters On Low-Contrast Visibility for KV CBCT

H Lee1, M Goss2*, D Pavord3, S Palefsky4, J Sohn5, (1) Allegheny Health Network, Pittsburgh, PA, (2) Allegheny Health Network, Pittsburgh, PA, (3) Allegheny General Hospital, Pittsburgh, PA, (4) Elekta, Inc., Atlanta, GA, (5) Allegheny Health Network, Pittsburgh, PA

Presentations

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

Room: AAPM ePoster Library

Purpose: To investigate the optimal combination of volume and reconstruction kV CBCT presets for soft tissue contrast and visualization of the abdominal organs to allow for dose escalation techniques.

Methods: Using the onboard XVI system on an Elekta Versa HD, image quality metric low contrast visibility % was analyzed for different combinations of volume and reconstruction CBCT presets used on the Catphan CTP 503 phantom. Higher low contrast visibility % corresponds to higher noise. Custom volume and reconstruction presets were used to compare the resulting images from varying mA, collimator, filter, slice averaging, and interpolation.

Results: Increasing slice averaging from three to nine resulted in reduced low contrast visibility %. Decreasing mA with constant mS and collimator/filter resulted in decreasing low contrast visibility %. Decreasing the collimator size and not using a bowtie filter in the volume presets also resulted in decreasing low contrast visibility %. Comparisons between reconstruction presets showed that in every case the highest low contrast visibility % was observed with the Bilinear interpolation, while the lowest was when reconstruction used the Partial2 interpolation.

Conclusion: Using trends inferred from the study data, the recommended optimal combination should utilize a low mA, smallest collimator size, no use of a bowtie filter, high slice averaging, and Partial2 interpolation. Caution should be exercised with parameter changes that deviate significantly from clinical presets, especially mA when applied to a patient as opposed to this proof-of-concept phantom study.

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Keywords

Low Contrast Detectability, Image-guided Therapy, SNR

Taxonomy

IM/TH- Cone Beam CT: Image Reconstruction

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