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Effect of CT Slice Thickness On Template Tracking Using Dual Energy Fluoroscopy

J Roeske1*, H Mostafavi2 , M Haytmyradov1 , M Surucu1 , A Wang2 , L Zhu2 , R Patel1 , M Harkenrider1 , (1) Loyola university Medical Center, Maywood, IL, (2) Varian Medical Systems, Palo Alto, CA


(Tuesday, 7/31/2018) 7:30 AM - 9:30 AM

Room: Room 205

Purpose: To evaluate the effect of reference CT slice thickness on the accuracy of markerless motion tracking (MMT) for single energy (SE) and dual energy (DE) fluoroscopy.

Methods: A fast-kV-switching DE imaging system was implemented on a bench top. SE and DE images were acquired on a static phantom with tumors ranging from 0.5-2.5cm, as well as with a programmable motion phantom. Bone-suppressed images, obtained from the DE fluoroscopic sequences, were created using logarithmic subtraction. Separately, a template-based matching algorithm was used to track tumor location on both sequences. Templates were generated using CT scans of each phantom. The CT reconstruction slice thickness was varied from 0.75-3.00mm. A match score surface was calculated by shifting the template across the image and calculating the normalized cross correlation (NCC). The offset at which the NCC has a maximum value represents the potential target position. The strength of this peak relative to NCC values away from the peak, called side lobe values, is quantified by the peak-to-side lobe ratio (PSR).

Results: The maximum slice thickness required to achieve a tracking success rate of > 90% was evaluated vs. tumor dimension for the static phantom. As expected smaller tumors required a finer slice thickness. However, the maximum slice thickness was generally larger for DE vs. SE. For SE imaging the tumor size/slice thickness ratio was nearly a constant of 10, whereas for DE imaging the ratio was ~7. For the motion phantom, DE images had a larger PSR vs. SE imaging, indicating a higher quality template match. For this target a slice thickness of ≤1.5 mm was needed to achieve a stable PSR value.

Conclusion: The maximum CT slice thickness for template tracking is a function of the tumor size. For most smaller tumors a CT slice thickness of ≤1.5-2.0mm is required for MMT.

Funding Support, Disclosures, and Conflict of Interest: Supported by NIH R01CA207483.


Dual-energy Imaging, Planar Imaging


IM- X-ray: Dual-energy and spectral

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