Passive Ultrasound Sensor Out-of-Plane Positioning
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Solution Overview
Problem
Current ultrasound tracking systems for interventional medical devices using passive ultrasound sensors struggle to determine the side of the imaging plane and out-of-plane distance accurately, leading to errors in motion estimation and volume reconstruction due to relative measurements and lack of a reliable reference marker.
Innovation Solution
A system that combines voltage measurements from passive ultrasound sensors with inertial motion unit and image-based measurements to determine the directionality and distance of the sensor relative to the imaging plane, using a controller to process data from a position and orientation sensor attached to the ultrasound probe, thereby providing a quantitative indication of out-of-plane distance and direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If passive ultrasound sensor voltage measurements are used for tracking, then cost is reduced compared to absolute tracking sensors, but measurement precision deteriorates due to inability to determine side of imaging plane and out-of-plane distance
Solution Approach 1:
The patent combines passive ultrasound sensor voltage measurements with inertial motion unit (IMU) measurements and image-based measurements into an integrated system. The IMU provides relative motion data while the passive sensor provides voltage readings, and image-based methods provide additional constraints. By merging these multiple measurement sources, the system achieves accurate out-of-plane distance determination without requiring expensive absolute tracking sensors, thus resolving the contradiction between cost reduction and measurement precision.
Solution Approach 2:
The patent introduces image-based measurements as an intermediary to bridge the gap between passive sensor voltage readings and accurate position determination. The image-based method provides reference information about tissue features and probe position that helps disambiguate the symmetric voltage responses from the passive sensor, enabling the system to determine which side of the imaging plane the sensor is on and calculate out-of-plane distance accurately.
2Device complexity
If relative measurement methods (IMU sensors) are used for probe tracking, then device complexity is reduced, but reliability deteriorates due to drift and incremental error build-up
Solution Approach 1:
The patent implements a feedback mechanism where passive ultrasound sensor voltage measurements and image-based measurements continuously provide information about the actual probe position and orientation relative to the passive sensor. This feedback is used to correct drift and cumulative errors in the IMU-based relative measurements. The system constantly compares the predicted position from IMU integration with the observed position from passive sensor and image data, and adjusts the pose estimates accordingly, thereby maintaining reliability without increasing device complexity.
Solution Approach 2:
The patent performs preliminary calibration and registration of the IMU sensor with the ultrasound probe and passive sensor before the actual tracking procedure. This preliminary action establishes accurate initial transformations and relationships between the different measurement systems, which provides a solid foundation for the subsequent combined measurement and correction process, reducing the impact of drift and errors throughout the procedure.
3Device complexity
If passive ultrasound sensor response is used alone for position determination, then device complexity is minimized, but measurement precision deteriorates due to symmetric response around imaging plane
Solution Approach 1:
The patent transitions from using only passive sensor voltage measurements (2D information insufficient for 3D position) to incorporating image-based measurements that provide additional dimensional information. The image-based method analyzes tissue features and acoustic speckle patterns across multiple image frames, adding depth and lateral position information that complements the passive sensor data. This dimensional enhancement allows the system to resolve the symmetry ambiguity and determine lateral position accurately while maintaining relatively simple device architecture.
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
This approach enhances the accuracy of motion estimation and volume reconstruction, reducing errors and costs associated with absolute tracking sensors while maintaining high precision, even without additional reference markers.
Implementation Method 1
A passive ultrasound sensor is an acoustic pressure sensor
Implementation Method 2
an ultrasound probe emits an imaging beam that sweeps across a passive ultrasound sensor
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A controller (250) for identifying out-of-plane motion of a passive ultrasound sensor (S1) relative to an imaging plane from an ultrasound imaging probe includes a memory (391) that stores instructions and a processor (392) that executes the instructions. When executed by the processor, the instructions cause a system that includes the controller (250) to implement a process that includes obtaining (S710), from a position and orientation sensor (212) fixed to the ultrasound imaging probe (210), measurements of motion of the ultrasound imaging probe (210) between a first point in time and a second point in time. The process implemented by the controller (250) also includes obtaining (S720) intensity of signals received by the passive ultrasound sensor (S1) at the first point in time and at the second point in time based on emissions of beams from the ultrasound imaging probe (210), and determining (S730), based on the measurements of motion and the intensity of signals, directionality of and distance from the passive ultrasound sensor (S1) to the imaging plane.