Off-axis Coil EM Sensor for Roll Angle Measurement in Narrow Catheters
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Solution Overview
Problem
Minimally invasive medical devices, such as lung catheters, face challenges in manufacturing small diameter instruments that incorporate mechanical structures and sensors for robotic operation, particularly in measuring roll angles due to the limitations of existing electromagnetic (EM) sensors which require larger diameters to accommodate 6-DoF capabilities.
Innovation Solution
The development of an off-axis coil design for EM sensors, where the winding of the coil defines areas with a normal direction at a significant angle to the symmetry axis, allowing for roll angle measurement while maintaining a narrow diameter, and the use of secondary sensors to supplement orientation information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a 6-DoF EM sensor includes two coils with non-parallel symmetry axes to measure roll angle, then measurement precision is improved, but device complexity and package size increase significantly
Solution Approach 1:
The patent applies asymmetry by positioning the coil's symmetry axis at a non-zero angle relative to the instrument's roll axis. This asymmetric orientation allows a single coil to break the rotational symmetry that would otherwise prevent roll angle measurement, enabling 6-DoF capability without requiring multiple coils arranged in complex configurations.
Solution Approach 2:
The patent introduces a new dimensional approach by orienting the coil's magnetic axis in a direction that is not aligned with either the longitudinal or roll axis of the instrument. This three-dimensional arrangement allows the single coil to sense components of the magnetic field that correspond to roll angle, effectively adding measurement capability without adding physical components.
2Device complexity
If a 5-DoF EM sensor uses a single cylindrical coil with symmetry axis aligned with roll axis, then device complexity is reduced, but measurement precision is insufficient as roll angle cannot be measured
Solution Approach 1:
The patent resolves this contradiction by deliberately introducing asymmetry in the coil's orientation relative to the instrument axis. The coil's symmetry axis is positioned at a non-zero angle to the roll axis, which breaks the cylindrical symmetry that causes roll angle indeterminacy. This maintains structural simplicity while enabling the previously unmeasurable roll angle.
3Ease of operation
If a catheter diameter is reduced to 3 mm or less to fit within narrow body lumens, then ease of operation is improved, but manufacturing precision requirements increase due to smaller dimensions
Solution Approach 1:
The patent merges the electromagnetic sensing function with the existing structural constraints of the catheter by designing a single coil that simultaneously provides 6-DoF measurement capability and fits within the narrow 3 mm diameter. The coil's asymmetric orientation is integrated into the catheter's structural design, combining multiple functions (position sensing, orientation sensing, and roll angle measurement) in a single compact component.
Solution Approach 2:
The patent changes the critical parameter of coil orientation from the conventional aligned configuration to a non-zero angle configuration. This parameter change enables roll angle measurement while maintaining compatibility with narrow catheter diameters, effectively decoupling the manufacturing precision requirements from the functional capabilities.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the measurement of roll angles in small-diameter medical instruments, facilitating more precise robotic control and navigation within narrow body lumens, while maintaining a compact sensor package.
Implementation Method 1
During EM sensor operation, a generator external to a patient can produce a well-controlled, time-varying magnetic field, and in response, one or more coils of an EM sensor in or on a portion of the medical instrument produce induced electrical signals. In particular, time variations in the magnetic field induce currents in the coils of the EM sensor
Data Source
AI summary
A medical system comprises a probe comprising a coil and a terminal distal end. The medical system further comprises a guide instrument comprising a terminal distal end, a sensor, and a lumen sized to receive the probe. The probe is configured to be inserted through the lumen to reach a worksite. At the worksite, the terminal distal end of the probe is configured to reach at least the terminal distal end of the guide instrument. The medical system further comprises processing hardware configured to receive a first signal from the coil and to receive a second signal from the sensor.