Geoffrey Hohert

A high-efficiency fiber-based imaging system for co-registered autofluorescence and optical coherence tomography

We present a power-efficient fiber-based imaging system capable of co-registered autofluorescence imaging and optical coherence tomography (AF/OCT). The system employs a custom fiber optic rotary joint (FORJ) with an embedded dichroic mirror to efficiently combine the OCT and AF pathways. This three-port wavelength multiplexing FORJ setup has a throughput of more than 83% for collected AF emission, significantly more efficient compared to previously reported fiber-based methods. A custom 900 µm diameter catheter ‒ consisting of a rotating lens assembly, double-clad fiber (DCF), and torque cable in a stationary plastic tube ‒ was fabricated to allow AF/OCT imaging of small airways in vivo. We demonstrate the performance of this system ex vivo in resected porcine airway specimens and in vivo in human on fingers, in the oral cavity, and in peripheral airways.

Endoscopic Doppler optical coherence tomography and autofluorescence imaging of peripheral pulmonary nodules and vasculature

We present the first endoscopic Doppler optical coherence tomography and co-registered autofluorescence imaging (DOCT-AFI) of peripheral pulmonary nodules and vascular networks in vivo using a small 0.9 mm diameter catheter. Using exemplary images from volumetric data sets collected from 31 patients during flexible bronchoscopy, we demonstrate how DOCT and AFI offer complementary information that may increase the ability to locate and characterize pulmonary nodules. AFI offers a sensitive visual presentation for the rapid identification of suspicious airway sites, while co-registered OCT provides detailed structural information to assess the airway morphology. We demonstrate the ability of AFI to visualize vascular networks in vivo and validate this finding using Doppler and structural OCT. Given the advantages of higher resolution, smaller probe size, and ability to visualize vasculature, DOCT-AFI has the potential to increase diagnostic accuracy and minimize bleeding to guide biopsy of pulmonary nodules compared to radial endobronchial ultrasound, the current standard of care.

Endoscopic high-resolution autofluorescence imaging and OCT of pulmonary vascular networks.

High-resolution imaging from within airways may allow new methods for studying lung disease. In this work, we report an endoscopic imaging system capable of high-resolution autofluorescence imaging (AFI) and optical coherence tomography (OCT) in peripheral airways using a 0.9 mm diameter double-clad fiber (DCF) catheter. In this system, AFI excitation light is coupled into the core of the DCF, enabling tightly focused excitation light while maintaining efficient collection of autofluorescence emission through the large diameter inner cladding of the DCF. We demonstrate the ability of this imaging system to visualize pulmonary vasculature as small as 12 μm in vivo.

3D-printed phantom for the characterization of non-uniform rotational distortion(Conference Presentation)

Endoscopic catheter-based imaging systems that employ a 2-dimensional rotary or 3-dimensional rotary-pullback scanning mechanism require constant angular velocity at the distal tip to ensure correct angular registration of the collected signal. Non-uniform rotational distortion (NURD) – often present due to a variety of mechanical issues – can result in inconsistent position and velocity profiles at the tip, limiting the accuracy of any measurements. Since artifacts like NURD are difficult to identify and characterize during tissue imaging, phantoms with well-defined patterns have been used to quantify position and/or velocity error. In this work we present a fast, versatile, and cost-effective method for making fused deposition modeling 3D printed phantoms for identifying and quantifying NURD errors along an arbitrary user-defined pullback path. Eight evenly-spaced features are present at the same orientation at all points on the path such that deviations from expected geometry can be quantified for the imaging catheter. The features are printed vertically and then folded together around the path to avoid issues with printer head resolution. This method can be adapted for probes of various diameters and for complex imaging paths with multiple bends. We demonstrate imaging using the 3D printed phantoms with a 1mm diameter rotary-pullback OCT catheter and system as a means of objectively evaluating the mechanical performance of similarly constructed probes.

Correction of motion artifacts in endoscopic optical coherence tomography and autofluorescence images based on azimuthal en face image registration

Abstract. We present a method for the correction of motion artifacts present in two- and three-dimensional in vivo endoscopic images produced by rotary-pullback catheters. This method can correct for cardiac/breathing-based motion artifacts and catheter-based motion artifacts such as nonuniform rotational distortion (NURD). This method assumes that en face tissue imaging contains slowly varying structures that are roughly parallel to the pullback axis. The method reduces motion artifacts using a dynamic time warping solution through a cost matrix that measures similarities between adjacent frames in en face images. We optimize and demonstrate the suitability of this method using a real and simulated NURD phantom and in vivo endoscopic pulmonary optical coherence tomography and autofluorescence images. Qualitative and quantitative evaluations of the method show an enhancement of the image quality.

Dual-beam manually-actuated distortion-corrected imaging (DMDI) with micromotor catheters

We present a new paradigm for performing two-dimensional scanning called dual-beam manually-actuated distortion-corrected imaging (DMDI). DMDI operates by imaging the same object with two spatially-separated beams that are being mechanically scanned rapidly in one dimension with slower manual actuation along a second dimension. Registration of common features between the two imaging channels allows remapping of the images to correct for distortions due to manual actuation. We demonstrate DMDI using a 4.7 mm OD rotationally scanning dual-beam micromotor catheter (DBMC). The DBMC requires a simple, one-time calibration of the beam paths by imaging a patterned phantom. DMDI allows for distortion correction of non-uniform axial speed and rotational motion of the DBMC. We show the utility of this technique by demonstrating en face OCT image distortion correction of a manually-scanned checkerboard phantom and fingerprint scan.

Dual-beam manually-actuated distortion-corrected imaging (DMDI) using galvanometer scanner (Conference Presentation)

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.

OCT for lung transplantation monitoring: quantification of chronic lung allograft dysfunction (CLAD) biomarkers (Conference Presentation)

Chronic Lung Allograft Dysfunction (CLAD) remains a significant cause of morbidity and mortality following lung transplantation. Bronchiolitis obliterans Syndrome (BOS) is a predominant phenotype of CLAD primarily affecting the small and subsequently the large airways leading eventually to graft failure. In addition, the allograft airways are also involved in other types of CLAD such as Restrictive Allograft Syndrome (RAS). Freedom from BOS at five years post-transplant is only approximately 50 % among lung transplant recipients. The diagnosis of CLAD is primarily based on pulmonary function testing and radiographic findings on CT scan. Transbronchial biopsies have a low diagnostic yield due to the multifocal nature of CLAD and the frequent lack of bronchioles in the biopsy specimen. Thus, CLAD is often diagnosed after significant disease progression. We performed endoscopic OCT as a minimally invasive method to identify early CLAD biomarkers. During 65 routine surveillance and event-initiated bronchoscopies of lung transplant recipients at Vancouver General Hospital, OCT imaging was performed prior to acquiring biopsy samples, with multiple 3D volumetric scans taken at locations as close as possible to those biopsied. OCT has the potential to be advantageous over biopsy because multiple airways in the lung can be quickly surveyed. As a first step towards clinical utility we present our methods for quantifying observable biomarkers including luminal size and alveolar density. Ranges of values are established and correlated with airway generation, time since transplant, and infection status.

Motion artifacts in endoscopic catheter-based images: simulation and motion correction method

A model for motion artifacts for 3D/2D rotational catheter data and a motion correction method called azimuthal en face image registration is presented. Qualitative and quantitative evaluations of the method are analysed on optical coherence tomography (OCT) and AFI images.

Quantitative Evaluation of Correction Methods and Simulation of Motion Artifacts for Rotary Pullback Imaging Catheters

In this work, we present a quantitative study based on the ground truth image and artificial motion artifacts and its correction using azimuthal en face image registration (AEIR) method. Motion artifacts in the in vivo imaging make identification of features and structures like blood vessels challenging. Correction of distortions of tissue features resultant from motion artifacts may enhance image quality and interpretation of images. Optical coherence tomography (OCT) and autofluorescence imaging (AFI) has been reported for in vivo endoscopic imaging. Motion artifacts in pulmonary OCT-AFI data sets may be estimated from both AFI and OCT images based on azimuthal registration of slowly varying structures in the 2D en face image. In our previous work, we have described a simulation of motion artifacts for 3D or 2D rotational catheter data and AEIR method, correcting motion artifacts. Our simulated artifacts may be applied on a ground truth image to create an image with known artifacts for the quantitative evaluation of performance of the correction methods. Since there might be some non-visible motion artifacts in the original ground truth image, we need apply the correction method before applying the simulated artifacts. However, there is no guarantee that this process converges to a motion-free scan; also the pre-corrected ground truth image is subjected to the correction method for further quantitative analysis. Here, we present a study for quantitative evaluations on a ground truth image of in silico phantom, NURD phantom and in vivo OCT and AF images.