US-12616374-B2 - Intraoral scanner with a scanning reflector and a method for calibration of a scanning reflector

US12616374B2US 12616374 B2US12616374 B2US 12616374B2US-12616374-B2

Abstract

An intraoral scanner is disclosed for use with a dental optical coherence tomography system. The scanner has a scanning reflector that is energizable to direct a scanning beam in a raster pattern toward a sample surface. The scanning reflector is further to direct a reflected beam from the sample surface toward a detector. The scanning reflector is calibrated to direct the scanning and reflected beams in an open-loop control mode. A dental optical coherence tomography system and a method for calibration of a scanning reflector are also disclosed.

Inventors

Xiaodong Tao
Chuanmao Fan

Assignees

DENTAL IMAGING TECHNOLOGIES CORPORATION

Dates

Publication Date: 20260505
Application Date: 20240806

Claims (20)

1 . An intraoral scanner for use with a dental optical coherence tomography system, the intraoral scanner comprising: a scanning reflector that is energizable to direct a scanning beam toward a surface, wherein the scanning reflector further directs a reflected beam from the surface toward a detector, and wherein the scanning reflector is calibrated to direct the scanning and reflected beams in an open-loop control mode by operating the scanning reflector at a tuned natural frequency.
2 . The intraoral scanner of claim 1 , wherein a raster pattern disposes the scanning beam to discrete, uniformly spaced positions along the surface.
3 . The intraoral scanner of claim 1 , wherein the scanning reflector is a micro-electromechanical systems (MEMS) device.
4 . The intraoral scanner of claim 1 , wherein the scanning reflector further has an inverse system filter that is configured to improve stability of the scanning reflector.
5 . The intraoral scanner of claim 1 , wherein the detector is in signal communication with a processor that is programmed to execute instructions for calibration according to variations in the reflected beam from a scanned calibration target.
6 . The intraoral scanner of claim 5 , wherein a scanner nonlinearity is calculated according to a linear fitting error of a measured scanning trajectory determined according to optical coherence tomography images of the scanned calibration target.
7 . The intraoral scanner of claim 6 , wherein the scanning reflector is configured to operate at a natural frequency tuned according to the calculated scanner nonlinearity.
8 . A dental optical coherence tomography system, comprising: an intraoral probe having: (a) a micro-electromechanical scanning reflector that is energizable to direct a scanning beam toward a sample surface, wherein the scanning reflector further re-directs reflected light from the sample surface toward a detector; and (b) control logic that is in signal communication with the detector and that is configured to provide a drive signal to the scanning reflector that directs the scanning beam toward spaced-apart positions along the sample surface according to a tuned natural frequency of the scanning reflector determined from optical coherence tomography images of a calibration pattern previously sensed by the detector, wherein the calibration pattern has a sequence of alternating reflective and absorbing linear features.
9 . The dental optical coherence tomography system of claim 8 , wherein the calibration pattern of alternating features has a periodic distribution.
10 . The dental optical coherence tomography system of claim 8 , wherein the control logic is further conditioned by an inverse filter generated to improve scanning stability.
11 . The dental optical coherence tomography system of claim 8 , wherein the control logic is further conditioned by tuning a natural frequency of the scanning reflector to obtain the tuned natural frequency to reduce nonlinearity.
12 . The dental optical coherence tomography system of claim 8 , wherein a raster drive signal provides open-loop control of the scanning reflector.
13 . The dental optical coherence tomography system of claim 8 , wherein the probe further comprises a time-domain dental optical coherence tomography system.
14 . The dental optical coherence tomography system of claim 8 , wherein the probe further comprises a spectrum-domain dental optical coherence tomography system.
15 . The dental optical coherence tomography system of claim 8 , wherein the probe further comprises a swept-source dental optical coherence tomography system.
16 . The dental optical coherence tomography system of claim 8 , wherein the alternating reflective and absorbing features are linear in a direction orthogonal to scanning direction.
17 . The dental optical coherence tomography system of claim 8 , wherein spacing of the alternating reflective and absorbing linear features is at twice a resolution of the system.
18 . A method for calibration of a scanning reflector in an optical coherence tomography system, the method comprising the steps of: scanning a light along a calibration target, wherein the calibration target has a plurality of linear features, and wherein the calibration target features are paired and the features in each pair alternate between a light-absorbing feature and a reflective or scattering feature; and optimizing a cost function defined by a linear fitting error of a measured scanning trajectory determined according to optical coherence tomography images from the scanning of the calibration target.
19 . The method of claim 18 , wherein the method further comprises a step of operating the scanning reflector according to a natural frequency determined in optimizing the cost function.
20 . The method of claim 18 , wherein optimizing a cost function comprises minimizing scanner nonlinearity by tuning one or more scanning reflector parameters according to a natural frequency of the scanning reflector.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of and claims priority to U.S. patent application Ser. No. 17/431,750, filed on Aug. 18, 2021, which is a National Stage entry of PCT Application Serial No. PCT/US2020/022201, filed on Mar. 11, 2020, which claims priority to U.S. Provisional Application Ser. No. 62/817,054, filed on Mar. 12, 2019, the contents of each of which are hereby incorporated by reference in their entirety. FIELD OF THE INVENTION The present invention relates generally to intraoral optical coherence tomography (OCT) imaging and, more particularly, to calibration for open-loop control of an electromechanical scanner apparatus used within a handheld OCT imaging device. BACKGROUND Optical coherence tomography (OCT) is a non-invasive imaging technique that employs interferometric principles to obtain high resolution, cross-sectional tomographic images that characterize the depth structure of a sample. Particularly suitable for in vivo imaging of human tissue, OCT has shown its usefulness in a range of biomedical research and medical imaging applications, such as in ophthalmology, dermatology, oncology, and other fields, as well as in car-nose-throat (ENT) and dental imaging. OCT has been described as a type of “optical ultrasound” imaging reflected energy from within living tissue to obtain cross-sectional data. In an OCT imaging system, light from a wide-bandwidth source, such as a super luminescent diode (SLD) or other light source, is directed along two different optical paths: a reference arm of known length and a sample arm that illuminates the tissue or other subject under study. Reflected and back-scattered light from the reference and sample arms is then recombined in the OCT apparatus and interference effects are used to determine characteristics of the surface and near-surface underlying structure of the sample. Interference data can be acquired by rapidly scanning the illumination across the sample. At each of several thousand points along the sample surface, the OCT apparatus obtains an interference profile which can be used to reconstruct an A-scan with an axial depth into the material that is a factor of light source coherence. For most tissue imaging applications, OCT uses broadband illumination sources and can provide image content at depths of up to a few millimeters (mm). Hand-held intraoral scanners for use with dental optical coherence tomography (OCT) systems require a compact, fast two-dimensional (2D) scanner integrated into the intraoral scanning probe. Traditionally, galvanometers have been used in optical scanning systems to provide scanning functionality. More recently, because of their advantages with respect to bulk, weight, and complexity, MEMS-based devices are being used in hand-held optical scanning systems due to their low cost and compact size. Calibration of the MEMS scanner can be challenging; conventional techniques for calibration can add complexity and cost to the calibration task. For example, solutions that employ low-pass filtering can constrain MEMS bandwidth and performance. The relatively high Q-factor of MEMS devices further complicates the tasks of MEMS scanner calibration and control. More advanced closed-loop operation of MEMS-based devices often requires additional sensors for the generation of feedback signals. The increased complexity and the high cost required for closed-loop operation have thus far limited the use of such MEMS-based scanners in a hand-held device. Therefore, there is a need in the industry for a compact, fast, two-dimensional (2D) MEMS-based intraoral scanner that solves these and other problems, difficulties, and shortcomings. SUMMARY Broadly described, the present invention comprises apparatuses and methods for According to one example embodiment of the present invention, there is provided an intraoral scanner for use with a dental optical coherence tomography system that comprises a scanning reflector that is energizable to direct a scanning beam toward a surface in a raster pattern and to direct a beam reflected from the surface toward a detector. The scanning reflector is calibrated to direct the scanning and reflected beams in an open-loop control mode. Various advantages and benefits of the present invention will become apparent from reading the following more particular description of example embodiments thereof and as illustrated in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram displaying a swept-source OCT (SS-OCT) apparatus according to an example embodiment of the present invention. FIG. 2 is a schematic diagram displaying a probe configured for OCT imaging and having a swept-source light source according to an example embodiment of the present invention. FIG. 3A is a schematic representation displaying a method of scanning operation for obtaining a B-scan. FIG. 3B displays an OCT scanning pattern for C-scan acquisition. FIG. 4 displays