<p>This thesis explores the
implementation of an electromagnetic positioning system to track medical
instruments used in minimally invasive surgeries. The end application is for catheter
cardiac ablation. Cardiac ablation is a low-risk procedure that can correct
arrhythmia. In the procedure, a diagnostic mapping catheter is inserted into
the heart to identify locations causing incorrect heartbeat, and an ablation
catheter applies radiofrequency (RF) thermal energy, which burns tissue that
emits abnormal heart rhythm. Current techniques which determine the mapping
catheter’s tip position while a patient is undergoing heart surgery are usually
invasive, often inaccurate, and require some forms of imaging. </p><p><br></p>
<p>Most existing electromagnetic (EM)
tracking systems track a tiny sensing coil on the catheter tip by placing
planar magnetic transmitters in reference locations around a patient. However,
the tracking speed of these systems is extremely limited apart from deficiency
in positioning accuracy due to poor sensitivity of the small sensor. In this
study, we develop a unique real-time tracking system which can track the
position and orientation of a medical catheter tip inside a human heart. A
configuration of a small transmitting coil on the catheter tip with multiple
larger receiving coils placed at reference locations is investigated. </p><p><br></p>
<p>We propose a novel tracking system
based on a single uniaxial transmitter (1.5 mm diameter) placed on a medical
catheter tip and two triaxial receivers placed in reference locations. The
electromagnetic field generated by the uniaxial transmitter is controlled by an
operational amplifier LC tank driver with a unique active feedback sensing
system in the form of a digital phased lock loop (DPLL), which <a>generates a low noise low distortion</a> AC signal for the
LC circuit. Such control is vital because the small transmitting coil has a
relatively large DC resistance, resulting in copious amounts of heat. This
unique transmitter driver active feedback system is optimized to ensure a
stable magnetic field transmitted with minimal noise and distortion.</p><p><br></p>
<p>Precise and efficient calibration
and compensation techniques are developed for the proposed system. The
calibration techniques include mutual coupling correction, which rectifies one
of the main limitations of a triaxial coil-based implementation. In addition, a
novel divergence mitigation method for the position algorithm is developed in
the form of a software-based reference sensing coil distance offset. This is
advantageous compared to a hardware-based solution, which involves adding more
coils to the system, in turn, leading to decreased tracking speed and higher
risk of interference among coils. Because of its simplicity, the proposed EM
tracking system also has the advantage of supporting a wide dynamic range,
multiple catheters, and can be applied to other medical systems in need of
real-time positioning.</p><p><br></p>
<p>This EM tracking system is
demonstrated on a test bench in a research lab and in a pre-clinical
environment with a 3D-printed heart inside a phantom. The tested system
features a fast update rate of 200 Hz and an average position error of 1.6 mm,
which indicates that the proposed system can successfully track a catheter RF
tip with millimeter precision. </p><p><br></p>
<p> This
dissertation presents the proposed EM tracking system. First, the motivation of
this research and a review of existing tracking methodologies used in the
medical field are presented. Then, the hardware design of individual modules
and magnetic positioning firmware are described, which is followed by
discussions of full system integration and calibration, as well as system test
results. A summary, highlighting novelties of the tracking system, and
discussion of future research directions are included in the final chapter.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/19443128 |
| Date | 19 April 2022 |
| Creators | Rubing Jin (12311240) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Magnetic_Tracking_for_Medical_Applications/19443128 |
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