  This paper presents a closed-loop magnetic manipulation framework for robotic
transesophageal echocardiography (TEE) acquisitions. Different from previous
work on intracorporeal robotic ultrasound acquisitions that focus on continuum
robot control, we first investigate the use of magnetic control methods for
more direct, intuitive, and accurate manipulation of the distal tip of the
probe. We modify a standard TEE probe by attaching a permanent magnet and an
inertial measurement unit sensor to the probe tip and replacing the flexible
gastroscope with a soft tether containing only wires for transmitting
ultrasound signals, and show that 6-DOF localization and 5-DOF closed-loop
control of the probe can be achieved with an external permanent magnet based on
the fusion of internal inertial measurement and external magnetic field sensing
data. The proposed method does not require complex structures or motions of the
actuator and the probe compared with existing magnetic manipulation methods. We
have conducted extensive experiments to validate the effectiveness of the
framework in terms of localization accuracy, update rate, workspace size, and
tracking accuracy. In addition, our results obtained on a realistic cardiac
tissue-mimicking phantom show that the proposed framework is applicable in real
conditions and can generally meet the requirements for tele-operated TEE
acquisitions.
