Coherence gated doppler motion sensor and medical applications
Inventors
Tang, Cha-Min • Liang, Chia-Pin • Chen, Yu • Fouad, Ashraf • Schmitt, Joseph • Woolsey, Nicholas
Assignees
St Jude Medical LLC • University of Maryland Baltimore • US Department of Veterans Affairs • University of Maryland College Park
Publication Number
US-9486140-B2
Publication Date
2016-11-08
Expiration Date
2033-08-08
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Abstract
A motion sensor applicable to medical procedures includes a source of light with a wavelength bandwidth and an optical detector. A first optical coupler terminates in a first probe tip and couples the light into the first probe tip. A second optical coupler terminates in a second probe tip and directs onto the detector scattered light returning through the second probe tip. A presentation device outputs a signal that indicates motion in a target volume of a sample in a vicinity of the probe tips based on a Doppler shift of the scattered light. The volume depends on coherence distance determined by the bandwidth. In variations, the first and second tips are the same tip, a multimode fiber is included, the bandwidth is between 0.1% and 5% of a center wavelength, or the presentation device is a speaker, or some combination.
Core Innovation
The invention presents a coherence gated Doppler (CGD) motion sensor suitable for medical procedures. It uses an optical source of light with a controlled band of wavelengths and an optical detector. Light is directed through emission and return optical paths terminating in one or two probe tips, where scattered light returning through the probes is detected. The device outputs a signal indicating motion within a target volume of a sample based on Doppler shifts of the scattered light. The size and position of this target volume depend on the coherence distance determined by the bandwidth of the light source.
The problem addressed arises from limitations in existing motion sensor technologies used in medical applications, such as laser Doppler flowmetry (LDF) and Doppler optical coherence tomography (DOCT). LDF devices have low spatial resolution and low signal-to-noise ratio, which limits vessel localization during diagnosis and treatment. DOCT devices provide high resolution but are expensive, complicated, unwieldy, and not suitable for real-time guidance. Current motion sensors are also challenged by the difficulty of penetrating tissues like bone and the complexity of controlling detection volumes for accurate vessel localization.
The invention provides a sensing technique combining advantages of LDF and DOCT while mitigating their drawbacks. It employs a light source bandwidth optimized to control a coherence gated target volume that is smaller and more localized than LDF volumes but larger and less complex than DOCT volumes. This produces a simple, inexpensive, and reliable sensor with sufficient resolution to detect, locate, and distinguish blood vessels during medical procedures and other applications. The system supports embodiments with a single fiber or separate fibers for emission and return paths, and can include a presentation device such as an acoustic speaker for real-time audible feedback.
Claims Coverage
The claims cover three independent apparatuses featuring optical motion sensing using bandwidth-controlled light sources and coherence gated target volumes with various optical coupling configurations and output presentations.
Emission and return optical paths with bandwidth-controlled coherence gating
An apparatus includes an optical source with wavelength bandwidth between 0.1% and 2.9% of a center wavelength, an optical detector, a first optical coupler directing light to a single probe tip and a second optical coupler directing scattered light from that tip to the detector. A presentation device outputs a signal indicating motion in a target volume based on Doppler shift, where the volume is set by coherence distance determined by the bandwidth.
Use of a single multimode optical fiber with a single probe tip
The apparatus where the first and second optical couplers include a single multimode optical fiber connected to the single probe tip, enabling emission and return through the same fiber and tip, and the tip is configured to be handheld.
Dual balanced detection with reference optical path for heterodyne interference
Inclusion of a third optical coupler directing light through a reference optical path to the detector to produce an interference beat frequency with the scattered light; optionally the reference path length is adjustable or fixed; the presentation device can be an acoustic speaker producing acoustic frequency based on the interference beat frequency, driven directly by analog signals without analog to digital conversion.
Separate emission and return optical paths and probe tips with bandwidth-controlled gating
An apparatus with the optical source and detector as above, with a first optical coupler directing light through an emission path terminating at a first probe tip and a second optical coupler directing scattered light entering a different second probe tip through a return path to the detector. The presentation device indicates motion based on Doppler shift in a target volume defined by coherence distance. The tips can be the same or different and configured to be handheld.
Speaker output indicating motion based on interference signal
An apparatus as above with a speaker configured to output a signal indicating motion in a target volume based on interference at the detector. The second probe tip is the same as or different from the first, and the bandwidth is in the specified range. The analog speaker is driven by analog electronic signal from the detector without an intervening ADC.
The independent claims collectively cover apparatuses using an optical source with a bandwidth in a defined range to create a coherence gated target volume for motion detection through Doppler shifts. Various configurations include single or separate probe tips and fibers, balanced or unbalanced detection circuits, use of reference paths for heterodyne interference, and presentation of output via speakers or digital devices.
Stated Advantages
Simple, inexpensive, and reliable motion sensor suitable for medical procedures with better localization than laser Doppler flowmetry.
Sufficiently high resolution to detect, locate, and distinguish blood vessels during medical procedures without the complexity and cost of Doppler optical coherence tomography.
Enables real-time guidance with a handheld probe, providing audible feedback without need for complex imaging or extensive processing.
Robust against hand motion and orientation changes due to coherence gating and bandwidth selection.
Documented Applications
Detection of blood vessels during instrument insertion for stereotactic neurosurgery.
Detection and avoidance of large blood vessels during anesthesia injection, catheterization, cerebrospinal fluid collection, intravascular and non-vascular interventions.
Vessel avoidance in the brain during deep brain electrode placement.
Tooth pulp vitality detection with rejection of adjacent flow in gums.
Verification of flow cessation in ligated vessels during open surgical procedures.
Applications in machinery and robotics, microfluidics, micro-electro-mechanical systems (MEMS), and detection of fluid flow in engines or other instruments.
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