Room: Exhibit Hall | Forum 6
Purpose: To evaluate the effect of image acquisition rate on the accuracy of markerless motion tracking (MMT) for single energy (SE) and dual energy (DE) fluoroscopy using a fast-kV-switching imaging system.
Methods: A fast-kV-switching DE imaging system was implemented on a bench top. SE and DE imaging were performed using a programmable motion phantom, with bones, simulated lung and tumor. The image acquisition rate was varied from 3-15 frames per sec (fps). Soft tissue images, obtained from the DE fluoroscopic sequences, were created using a frame-by-frame weighted logarithmic subtraction. Separately, a template-based matching algorithm (using a template from a CT scan of the phantom) was used to track tumor location on SE and DE sequences. This algorithm shifts the template across the image and calculates the normalized cross correlation (NCC), resulting in a match score surface. 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 accuracy of motion tracking was assessed by comparing the tracked coordinates with the programmed motion function. Overall, DE resulted in a significantly smaller root mean square (RMS) tracking error vs. SE tracking. Moreover, the overall success rate of MMT for DE vs. SE was 100% vs. 74% (p=0.0001). Of interest, the PSR value was consistently larger for DE vs. SE (p=0.0001). However, at the highest fps, the DE-PSR value was lower than slower frame rates, corresponding to potential image lag. Similarly, the DE weighting factors increased with increasing frame rate.
Conclusion: For all frame rates considered, DE tracking was more accurate than SE tracking. However, DE image lag may play a role in determining the optimal imaging energies and acquisition rate.
Funding Support, Disclosures, and Conflict of Interest: Supported by NIH R01CA207483