WE-G-BRF-09: Force- and Image-Adaptive Strategies for Robotised Placement of 4D Ultrasound Probes

Abstract

Purpose: To allow continuous acquisition of high quality 4D ultrasound images for non‐invasive live tracking of tumours for IGRT, image‐ and force‐adaptive strategies for robotised placement of 4D ultrasound probes are developed and evaluated. Methods: The developed robotised ultrasound system is based on a 6‐axes industrial robot (adept Viper s850) carrying a 4D ultrasound transducer with a mounted force‐torque sensor. The force‐adaptive placement strategies include probe position control using artificial potential fields and contact pressure regulation by a PD controller strategy. The basis for live target tracking is a continuous minimum contact pressure to ensure good image quality and high patient comfort. This contact pressure can be significantly disturbed by respiratory movements and has to be compensated. All measurements were performed on human subjects under realistic conditions. When performing cardiac ultrasound, rib‐ and lung shadows are a common source of interference and can disrupt the tracking. To ensure continuous tracking, these artefacts had to be detected to automatically realign the probe. The detection is realised by multiple algorithms based on entropy calculations as well as a determination of the image quality. Results: Through active contact pressure regulation it was possible to reduce the variance of the contact pressure by 89.79% despite respiratory motion of the chest. The results regarding the image processing clearly demonstrate the feasibility to detect image artefacts like rib shadows in real‐time. Conclusion: In all cases, it was possible to stabilise the image quality by active contact pressure control and automatically detected image artefacts. This fact enables the possibility to compensate for such interferences by realigning the probe and thus continuously optimising the ultrasound images. This is a huge step towards fully automated transducer positioning and opens the possibility for stable target tracking in ultrasoundguided radiation therapy requiring contact pressure of 5–10 N. This work was supported by the Graduate School for Computing in Medicine and Life Sciences funded by Germany's Excellence Initiative [DFG GSC 235/1].

Cooperative Control with Ultrasound Guidance for Radiation Therapy

“…Another telerobotic research system for US monitoring of radiotherapy was developed at Lubeck University by Kuhlemann (2013) and has been tested on the hearts of healthy human subjects. The two Stanford University systems and the system at Lubeck University are detailed in the studies by Western et al (2015) and Ammann (2012).…”

Confidence-driven control of an ultrasound probe: Target-specific acoustic window optimization

“…On the other hand, the impact of the probe placement on the image quality has received little attention up to now. Recently, Kuhlemann et al [13] have proposed a robotic system to avoid shadowed areas based on entropy as a measure of quality. Entropy, and other statistical image analysis techniques [2], [14], are easy to estimate and can provide a first insight into the quality of ultrasound images.…”

System integration and preliminary in-vivo experiments of a robot for ultrasound guidance and monitoring during radiotherapy

“…This has motivated the development of passive probe holders [4] and at least one telerobotic system [5], [6] for US monitoring during radiotherapy. Robotic systems for ultrasonography have also been developed for other applications [7]–[15]. Because US imaging requires contact between the probe and patient, all of these robotic systems include a force sensor for monitoring and/or controlling the contact force.…”