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Real-Time Tracking of Endoscopic Ultrasound Guided Hydrogel Injection Using Template Matching

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P Huang

P Huang1,2, D Li1* , E Shin2 , S kim2 , L Su2 , A Rao2 , L Rosati2 , J Wong2 , A Narang2 , J Herman2 , K Ding2 , (1) Shandong Normal University, Jinan, Shandong Province, (2) Johns Hopkins University, Baltimore, Maryland


SU-K-601-17 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 601

Purpose: In radiotherapy for pancreatic cancer, duodenum is often the dose limiting structure adjacent to tumor. To achieve adequate dose coverage to the planning target volume (PTV), the dose to the duodenum usually exceeds the dose tolerance. Our previous study has shown it is feasible to spare the duodenum by injecting biodegradable hydrogel spacer under endoscopic ultrasound (EUS) between pancreas and duodenum. A 5 mm hydrogel induced separation can significantly lower the duodenum dose. In this study, we propose a fast template matching method to track the hydrogel injection induced separation in real time to assist the spacer implantation.

Methods: Biodegradable hydrogel spacer was injected into the interface between the head of pancreas and the duodenal wall in three cadavers under EUS guidance with 19-gauge FNA needle and linear ultrasound transducer. In the B-mode EUS, since US images are corrupted by speckle noise, which is a disruptive random pattern that obscures the features of interest. Reducing speckle noise is important for object extraction. Firstly, we utilized a probabilistic speckle model using the Fisher-Tippett distribution to enhance the hydrogel. Then the template matching using NCC was used to automatic measure the diameter of injected gel volume in each frame. Manually annotated landmarks at the interface of the hydrogel were used as ground truth to assess the tracking accuracy.

Results: The average tracking error between manual annotation and the location acquired through template matching is 0.98 ± 0.25 mm in the x-direction and 0.67 ± 0.39 mm in the y-direction. Furthermore, the measuring time per frame is 80 milliseconds, which is similar to the frame acquisition time.

Conclusion: Our fast template matching method can track the EUS guided hydrogel injection in real time. The automatic measurement of the hydrogel spacing can be used to assist the injection procedure to achieve the desired separation based on pre-injection planning.

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