Osman O. Ahsen

Characterization of buried glands before and after radiofrequency ablation by using 3-dimensional optical coherence tomography (with videos)

BACKGROUND Radiofrequency ablation (RFA) is an endoscopic technique used to eradicate Barretts esophagus (BE). However, such ablation can commonly lead to neosquamous epithelium overlying residual BE glands not visible by conventional endoscopy and may evade detection on random biopsy samples. OBJECTIVE To demonstrate the capability of endoscopic 3-dimensional optical coherence tomography (3D-OCT) for the identification and characterization of buried glands before and after RFA therapy. DESIGN Cross-sectional study. SETTING Single teaching hospital. PATIENTS Twenty-six male and 1 female white patients with BE undergoing RFA treatment. INTERVENTIONS 3D-OCT was performed at the gastroesophageal junction in 18 patients before attaining complete eradication of intestinal metaplasia (pre-CE-IM group) and in 16 patients after CE-IM (post-CE-IM group). MAIN OUTCOME MEASUREMENTS Prevalence, size, and location of buried glands relative to the squamocolumnar junction. RESULTS 3D-OCT provided an approximately 30 to 60 times larger field of view compared with jumbo and standard biopsy and sufficient imaging depth for detecting buried glands. Based on 3D-OCT results, buried glands were found in 72% of patients (13/18) in the pre-CE-IM group and 63% of patients (10/16) in the post-CE-IM group. The number (mean [standard deviation]) of buried glands per patient in the post-CE-IM group (7.1 [9.3]) was significantly lower compared with the pre-CE-IM group (34.4 [44.6]; P = .02). The buried gland size (P = .69) and distribution (P = .54) were not significantly different before and after CE-IM. LIMITATIONS A single-center, cross-sectional study comparing patients at different time points in treatment. Lack of 1-to-1 coregistered histology for all OCT data sets obtained in vivo. CONCLUSION Buried glands were frequently detected with 3D-OCT near the gastroesophageal junction before and after radiofrequency ablation.

Assessment of breast pathologies using nonlinear microscopy

Significance Development of methods for rapid intraoperative assessment of breast pathologies is important for decreasing the rate of surgical reexcisions during breast-conserving therapy. Frozen-section analysis is the most widely used method for intraoperative margin assessment but is time consuming, has limited diagnostic accuracy, and produces freezing artifacts. This manuscript demonstrates nonlinear microscopy for rapid assessment of surgical breast specimens without need for fixation, embedding, and sectioning required for conventional histology. Blinded reading of nonlinear microscopy images by three pathologists achieved 95.4% sensitivity, 93.3% specificity, and 94.1% overall accuracy compared with histology for identifying invasive cancer and ductal carcinoma in situ versus benign breast tissue. The results suggest that nonlinear microscopy is a promising method for intraoperative assessment of breast surgical excision specimens. Rapid intraoperative assessment of breast excision specimens is clinically important because up to 40% of patients undergoing breast-conserving cancer surgery require reexcision for positive or close margins. We demonstrate nonlinear microscopy (NLM) for the assessment of benign and malignant breast pathologies in fresh surgical specimens. A total of 179 specimens from 50 patients was imaged with NLM using rapid extrinsic nuclear staining with acridine orange and intrinsic second harmonic contrast generation from collagen. Imaging was performed on fresh, intact specimens without the need for fixation, embedding, and sectioning required for conventional histopathology. A visualization method to aid pathological interpretation is presented that maps NLM contrast from two-photon fluorescence and second harmonic signals to features closely resembling histopathology using hematoxylin and eosin staining. Mosaicking is used to overcome trade-offs between resolution and field of view, enabling imaging of subcellular features over square-centimeter specimens. After NLM examination, specimens were processed for standard paraffin-embedded histology using a protocol that coregistered histological sections to NLM images for paired assessment. Blinded NLM reading by three pathologists achieved 95.4% sensitivity and 93.3% specificity, compared with paraffin-embedded histology, for identifying invasive cancer and ductal carcinoma in situ versus benign breast tissue. Interobserver agreement was κ = 0.88 for NLM and κ = 0.89 for histology. These results show that NLM achieves high diagnostic accuracy, can be rapidly performed on unfixed specimens, and is a promising method for intraoperative margin assessment.

Depth-encoded all-fiber swept source polarization sensitive OCT

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of conventional OCT and can assess depth-resolved tissue birefringence in addition to intensity. Most existing PS-OCT systems are relatively complex and their clinical translation remains difficult. We present a simple and robust all-fiber PS-OCT system based on swept source technology and polarization depth-encoding. Polarization multiplexing was achieved using a polarization maintaining fiber. Polarization sensitive signals were detected using fiber based polarization beam splitters and polarization controllers were used to remove the polarization ambiguity. A simplified post-processing algorithm was proposed for speckle noise reduction relaxing the demand for phase stability. We demonstrated systems design for both ophthalmic and catheter-based PS-OCT. For ophthalmic imaging, we used an optical clock frequency doubling method to extend the imaging range of a commercially available short cavity light source to improve polarization depth-encoding. For catheter based imaging, we demonstrated 200 kHz PS-OCT imaging using a MEMS-tunable vertical cavity surface emitting laser (VCSEL) and a high speed micromotor imaging catheter. The system was demonstrated in human retina, finger and lip imaging, as well as ex vivo swine esophagus and cardiovascular imaging. The all-fiber PS-OCT is easier to implement and maintain compared to previous PS-OCT systems and can be more easily translated to clinical applications due to its robust design.

Swept source optical coherence microscopy using a 1310 nm VCSEL light source

We demonstrate high speed, swept source optical coherence microscopy (OCM) using a MEMS tunable vertical cavity surface-emitting laser (VCSEL) light source. The light source had a sweep rate of 280 kHz, providing a bidirectional axial scan rate of 560 kHz. The sweep bandwidth was 117 nm centered at 1310 nm, corresponding to an axial resolution of 13.1 µm in air, corresponding to 8.1 µm (9.6 µm spectrally shaped) in tissue. Dispersion mismatch from different objectives was compensated numerically, enabling magnification and field of view to be easily changed. OCM images were acquired with transverse resolutions between 0.86 µm - 3.42 µm using interchangeable 40X, 20X and 10X objectives with ~600 µm x 600 µm, ~1 mm x 1 mm and ~2 mm x 2 mm field-of-view (FOV), respectively. Parasitic variations in path length with beam scanning were corrected numerically. These features enable swept source OCM to be integrated with a wide range of existing scanning microscopes. Large FOV mosaics were generated by serially acquiring adjacent overlapping microscopic fields and combining them in post-processing. Fresh human colon, thyroid and kidney specimens were imaged ex vivo and compared to matching histology sections, demonstrating the ability of OCM to image tissue specimens.

Ultrahigh speed en face OCT capsule for endoscopic imaging

Depth resolved and en face OCT visualization in vivo may have important clinical applications in endoscopy. We demonstrate a high speed, two-dimensional (2D) distal scanning capsule with a micromotor for fast rotary scanning and a pneumatic actuator for precision longitudinal scanning. Longitudinal position measurement and image registration were performed by optical tracking of the pneumatic scanner. The 2D scanning device enables high resolution imaging over a small field of view and is suitable for OCT as well as other scanning microscopies. Large field of view imaging for screening or surveillance applications can also be achieved by proximally pulling back or advancing the capsule while scanning the distal high-speed micromotor. Circumferential en face OCT was demonstrated in living swine at 250 Hz frame rate and 1 MHz A-scan rate using a MEMS tunable VCSEL light source at 1300 nm. Cross-sectional and en face OCT views of the upper and lower gastrointestinal tract were generated with precision distal pneumatic longitudinal actuation as well as proximal manual longitudinal actuation. These devices could enable clinical studies either as an adjunct to endoscopy, attached to an endoscope, or as a swallowed tethered capsule for non-endoscopic imaging without sedation. The combination of ultrahigh speed imaging and distal scanning capsule technology could enable both screening and surveillance applications.

Correction of rotational distortion for catheter-based en face OCT and OCT angiography

We demonstrate a computationally efficient method for correcting the nonuniform rotational distortion (NURD) in catheter-based imaging systems to improve endoscopic en face optical coherence tomography (OCT) and OCT angiography. The method performs nonrigid registration using fiducial markers on the catheter to correct rotational speed variations. Algorithm performance is investigated with an ultrahigh-speed endoscopic OCT system and micromotor catheter. Scan nonuniformity is quantitatively characterized, and artifacts from rotational speed variations are significantly reduced. Furthermore, we present endoscopic en face OCT and OCT angiography images of human gastrointestinal tract in vivo to demonstrate the image quality improvement using the correction algorithm.

Ultrahigh speed endoscopic optical coherence tomography for gastroenterology

We describe an ultrahigh speed endoscopic swept source optical coherence tomography (OCT) system for clinical gastroenterology using a vertical-cavity surface-emitting laser (VCSEL) and micromotor imaging catheter. The system had a 600 kHz axial scan rate and 8 µm axial resolution in tissue. Imaging was performed with a 3.2 mm diameter imaging catheter at 400 frames per second with a 12 µm spot size. Three-dimensional OCT (3D-OCT) imaging was performed in patients with a cross section of pathologies undergoing upper and lower endoscopy. The use of distally actuated imaging catheters enabled OCT imaging with more flexibility, such as volumetric imaging in the small intestine and the assessment of hiatal hernia using retroflex imaging. The high rotational scanning stability of the micromotor enabled 3D volumetric imaging with micron scale volumetric accuracy for both en face OCT and cross-sectional imaging, as well as OCT angiography (OCTA) for 3D visualization of subsurface microvasculature. The ability to perform both structural and functional 3D OCT imaging in the GI tract with microscopic accuracy should enable a wide range of studies and enhance the sensitivity and specificity of OCT for detecting pathology.

Compact piezoelectric transducer fiber scanning probe for optical coherence tomography

We developed a compact, optical fiber scanning piezoelectric transducer (PZT) probe for endoscopic and minimally invasive optical coherence tomography (OCT). Compared with previous forward-mount fiber designs, we present a reverse-mount design that achieves a shorter rigid length. The fiber was mounted at the proximal end of a quadruple PZT tube and scanned inside the hollow PZT tube to reduce the probe length. The fiber resonant frequency was 338 Hz using a 17-mm-long fiber. A 0.9 mm fiber deflection was achieved with a driving amplitude of 35 V. Using a GRIN lens-based optical design with a 1.3× magnification, a ∼6 μm spot was scanned over a 1.2 mm diameter field. The probe was encased in a metal hypodermic tube with a ∼25 mm rigid length and covered with a 3.2 mm outer diameter (OD) plastic sheath. Imaging was performed with a swept source OCT system based on a Fourier domain modelocked laser (FDML) light source at a 240 kHz axial scan rate and 8 μm axial resolution (in air). En face OCT imaging of skin in vivo and human colon ex vivo was demonstrated.

Silencing of the Drosophila ortholog of SOX5 in heart leads to cardiac dysfunction as detected by optical coherence tomography

The SRY-related HMG-box 5 (SOX5) gene encodes a member of the SOX family of transcription factors. Recently, genome-wide association studies have implicated SOX5 as a candidate gene for susceptibility to four cardiac-related endophenotypes: higher resting heart rate (HR), the electrocardiographic PR interval, atrial fibrillation and left ventricular mass. We have determined that human SOX5 has a highly conserved Drosophila ortholog, Sox102F, and have employed transgenic Drosophila models to quantitatively measure cardiac function in adult flies. For this purpose, we have developed a high-speed and ultrahigh-resolution optical coherence tomography imaging system, which enables rapid cross-sectional imaging of the heart tube over various cardiac cycles for the measurement of cardiac structural and dynamical parameters such as HR, dimensions and areas of heart chambers, cardiac wall thickness and wall velocities. We have found that the silencing of Sox102F resulted in a significant decrease in HR, heart chamber size and cardiac wall velocities, and a significant increase in cardiac wall thickness that was accompanied by disrupted myofibril structure in adult flies. In addition, the silencing of Sox102F in the wing led to increased L2, L3 and wing marginal veins and increased and disorganized expression of wingless, the central component of the Wnt signaling pathway. Collectively, the silencing of Sox102F resulted in severe cardiac dysfunction and structural defects with disrupted Wnt signaling transduction in flies. This implicates an important functional role for SOX5 in heart and suggests that the alterations in SOX5 levels may contribute to the pathogenesis of multiple cardiac diseases or traits.

Comparison of Tissue Architectural Changes between Radiofrequency Ablation and Cryospray Ablation in Barrett's Esophagus Using Endoscopic Three-Dimensional Optical Coherence Tomography.

Two main nonsurgical endoscopic approaches for ablating dysplastic and early cancer lesions in the esophagus have gained popularity, namely, radiofrequency ablation (RFA) and cryospray ablation (CSA). We report a uniquely suited endoscopic and near-microscopic imaging modality, three-dimensional (3D) optical coherence tomography (OCT), to assess and compare the esophagus immediately after RFA and CSA. The maximum depths of architectural changes were measured and compared between the two treatment groups. RFA was observed to induce 230~260 μm depth of architectural changes after each set of ablations over a particular region, while CSA was observed to induce edema-like spongiform changes to ~640 μm depth within the ablated field. The ability to obtain micron-scale depth-resolved images of tissue structural changes following different ablation therapies makes 3D-OCT an ideal tool to assess treatment efficacy. Such information could be potentially used to provide real-time feedback for treatment dosing and to identify regions that need further retreatment.