High resolution optical imaging modalities such as optical coherence tomography (OCT), confocal and multiphoton microscopy continue to show promise for diagnostic imaging. These imaging modalities commonly employ 2D scanning mechanisms that scan the sample in regular, pre-defined patterns. However, these scanners can often have limited in field-of-view and can be susceptible to artefacts due to patient or clinician motion. We have recently demonstrated a new imaging paradigm called dual-beam manually-actuated distortion-corrected imaging (DMDI) that overcomes these limitations. DMDI exploits the predictable path and spatial separation of two beams to calculate and correct the scanning distortion caused by manual actuation of the probe or the sample. DMDI was first implemented using a dual-beam micromotor catheter (DBMC) which could be useful for in vivo imaging of internal vessels, air ways, or tubular organs. Here, we present a new implementation of DMDI using a single axis galvanometer scanner.
OCT imaging is used to demonstrate this implementation of DMDI. A single 1310nm swept source laser is split into two independent OCT interferometers. The two samples arms of the interferometers are aligned at different angles onto a single-axis galvo-mirror which is driven synchronously by the swept source. After passing through a scan lens, the scan pattern traced by the two beams is a pair of roughly parallel lines. A one-time calibration procedure is performed by imaging a phantom to precisely determine the beam separation and scanning pattern.
Samples were scanned by manually moving them approximately perpendicular to the scan lines, acquiring two images. Using common, unique features in both of the images, the recorded time difference between the imaging of the features, and the calibrated relationship between the two beams, the image distortion caused by manually actuating the sample can be discerned, and the distortion-corrected images can be produced.
To validate the galvanometer implementation of DMDI, we first imaged a phantom with a defined flat pattern. Image restoration was performed on the en face OCT images and showed distortion correction was feasible both perpendicular and parallel to the scan beam axis over a range of speeds. We also demonstrate correction for en face OCT images of a biological sample.
DMDI is demonstrated as a versatile imaging modality as it can be adapted for different implementations. Although a bench top galvanometer scanner setup was used in this study this implementation could be adapted for imaging body sites such as the oral cavity or skin. Furthermore, OCT was chosen due to its availability in our lab, however in principle any point-scanning modality could be used for DMDI.