Alignment and Calibration of high frequency ultrasound (HFUS) and optical coherence tomography (OCT) 1D transducers using a dual wedge-tri step phantom

This paper introduces a novel alignment and calibration method for high frequency ultrasound (HFUS) and optical coherence tomography (OCT) 1D transducers. 2D images are constructed by means of translation of the transducers using a linear motor stage. Physical alignment of the transducers is needed in order to capture images of the same cross-sectional plane, and calibration is needed to determine the relative coordinates of the images, including the image skew. A dual wedge-tri step phantom is created for both alignment and calibration. This phantom includes two symmetrical wedges and three steps that provide the user with visual feedback on how well the scan plane is aligned with the midplane of the phantom. The phantom image consists of five line segments, each of which corresponds to one of the wedges or steps. The slopes and positions of the lines are extracted from the image and compared with the phantom model. The scan plane parameters are found so that the difference between the model and extracted features is minimized. The main advantage of this phantom is that only one frame is required to determine translations, orientations, and skew parameters of the scan plane with respect to the phantom. Experimental results with ocular imaging show the ability to achieve alignment based on this method and its potential for medical applications.