Auxiliary positioning method for ultrasonic microscope based on optical imaging

An auxiliary positioning method for an ultrasonic microscope based on optical imaging, comprising a three-axis scanning driving device, an ultrasonic microscope and a first camera device and a second camera device for optical assisted positioning, mounting the first camera device directly above the ultrasonic microscope, and mounting the second camera device directly in front of the ultrasonic microscope and parallel to an XZ plane of a water tank;

• for the first camera device, realizing an XY plane positioning of an ultrasonic probe using a projection matrix, and moving the ultrasonic probe to a real position in an actual plane corresponding thereto by selecting a point on a displayed image of the first camera device;
• and selecting a point on a displayed image of the second camera device right in front, and obtaining a distance between the ultrasonic probe and a sample in real time;
• for the first camera device, realizing an XY plane positioning of an ultrasonic probe using a projection matrix, comprising the steps of:
• connecting an original image plane and a target image plane together by projection transformation to construct a Homography;
• constructing two linear equations covering all parameters of the Homography H by representing the projection change by a system of linear equations:
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• obtaining a projection matrix of a pixel coordinate system of a displayed image of the first camera device to a world coordinate system of an actual water tank platform plane to realize optical assisted positioning;
• adopting a singular value decomposition (SVD) method to minimize ∥A·h−b∥, and after converting the solved vector h into the Homography H, and obtaining a projection matrix from a pixel coordinate system of a displayed image of the camera to a world coordinate system of a water tank plane;
• selecting, for each set of corresponding points in the original image and the target image whose coordinates are (Xi, Yi) and (xi, yi), four sets of suitable points (Xi, Yi) and (xi, yi), where i=1, 2, 3, 4, constructing eight linear equations, and converting the equations into matrix form, expressed as A·h=b, where h is a column vector comprising all elements of the Homography H, b is a zero vector, and matrix A is an under-constrained system of 8×9;
• and
• selecting a position on a displayed image of the camera, acquiring a coordinate value of the position in a pixel coordinate system, and converting the coordinate value to a corresponding coordinate in the world coordinate system by using the projection matrix H.