Translation of Intravascular Optical Ultrasound Imaging

ances in the field of intravascular imaging have provided clinicians with power ful tools to aid in the assessment and treatment of vascular pathology. Optical Ultra sound (OpUS) is an emerging modality with the potential to offer significant bene fits over existing commercial technologies such as intravascular ultrasound (IVUS) or optical coherence tomography (OCT). With this paradigm ultrasound (US) is generated using pulsed or modulated light and received by a miniaturised fibre-optic hydrophone (FOH). The US generation is facilitated through the use of engineered optically-absorbing nanocomposite materials. To date pre-clinical benchtop stud ies of OpUS have shown significant promise however further study is needed to facilitate clinical translation. The overall aim of this PhD was to develop a pathway to clinical translation of OpUS, enabled by the development of a catheter-based device capable of high resolution vascular tissue imaging during an in-vivo setting. A forward-viewing OpUS imaging probe was developed using a 400 µm mul timode optical fibre, dip-coated in a multi-walled carbon nanotube-PDMS com posite, paired with a FOH comprising a 125 µm single mode fibre tipped with a Fabry-Perot cavity. With this high US pressures were generated (21.5 MPa at the transducer surface) and broad corresponding bandwidths were achieved (−6 dB of 39.8MHz). Using this probe, OpUS imaging was performed of an ex-vivo human coronary artery. The results demonstrated excellent correspondence, in the detec tion of calcification and lipid infiltration, with IVUS, OCT and histological analysis. A side-viewing OpUS imaging probe, employing a reflective 45 °angle at the dis tal fibre surface, was used to demonstrate rotational B-mode imaging of a vascular structure for the first time. This provided high-resolution imaging (54 µm axial resolution) with deep depth penetration (>10.5 mm). Finally the clinical utility of this technology was demonstrated during an in-vivo endovascular procedure. An OpUS imaging probe, incorporated into an interventional device, allowed guidance of in-situ fenestration of an endograft during a complex abdominal aortic aneurysm repair. Through this work the potential clinical utility of OpUS, to assess pathology and guide vascular intervention, has been demonstrated. These results pave the way for translation of this technology and a first in man study

A patient-specific multi-modality abdominal aortic aneurysm imaging phantom

PURPOSE: Multimodality imaging of the vascular system is a rapidly growing area of innovation and research, which is increasing with awareness of the dangers of ionizing radiation. Phantom models that are applicable across multiple imaging modalities facilitate testing and comparisons in pre-clinical studies of new devices. Additionally, phantom models are of benefit to surgical trainees for gaining experience with new techniques. We propose a temperature-stable, high-fidelity method for creating complex abdominal aortic aneurysm phantoms that are compatible with both radiation-based, and ultrasound-based imaging modalities, using low cost materials. METHODS: Volumetric CT data of an abdominal aortic aneurysm were acquired. Regions of interest were segmented to form a model compatible with 3D printing. The novel phantom fabrication method comprised a hybrid approach of using 3D printing of water-soluble materials to create wall-less, patient-derived vascular structures embedded within tailored tissue-mimicking materials to create realistic surrounding tissues. A non-soluble 3-D printed spine was included to provide a radiological landmark. RESULTS: The phantom was found to provide realistic appearances with intravascular ultrasound, computed tomography and transcutaneous ultrasound. Furthermore, the utility of this phantom as a training model was demonstrated during a simulated endovascular aneurysm repair procedure with image fusion. CONCLUSION: With the hybrid fabrication method demonstrated here, complex multimodality imaging patient-derived vascular phantoms can be successfully fabricated. These have potential roles in the benchtop development of emerging imaging technologies, refinement of novel minimally invasive surgical techniques and as clinical training tools

Morphological and Physiological Characteristics of Ruptured Plaques in Native Arteries and Neoatherosclerotic Segments: An OCT-Based and Computational Fluid Dynamics Study.

Background Intravascular imaging has been used to assess the morphology of lesions causing an acute coronary syndrome (ACS) in native vessels (NV) and identify differences between plaques that ruptured (PR) and caused an event and those that ruptured without clinical manifestations. However, there is no data about the morphological and physiological characteristics of neoatherosclerotic plaques that ruptured (PR-NA) which constitute a common cause of stent failure. Methods We retrospectively analyzed data from patients admitted with an acute myocardial infarction that had optical coherence tomography (OCT) imaging of the culprit vessel before balloon pre-dilation. OCT pullbacks showing PR were segmented at every 0.4 mm. The extent of the formed cavity, lipid and calcific tissue, thrombus, and macrophages were measured, and the fibrous cap thickness (FCT) and the incidence of micro-channels and cholesterol crystals were reported. These data were used to reconstruct a representative model of the native and neoatherosclerotic lesion geometry that was processed with computational fluid dynamics (CFD) techniques to estimate the distribution of the endothelial shear stress and plaque structural stress. Result Eighty patients were included in the present analysis: 56 had PR in NV (PR-NV group) and 24 in NA segments (PR-NA group). The PR-NV group had a larger minimum lumen area (2.93 ± 2.03 vs. 2.00 ± 1.26 mm2, p = 0.015) but similar lesion length and area stenosis compared to PR-NA group. The mean FCT (186 ± 65 vs. 232 ± 80 μm, p = 0.009) and the lipid index was smaller (16.7 ± 13.8 vs. 25.9 ± 14.1, p = 0.008) while the of calcific index (8.3 ± 9.5 vs. 2.2 ± 1.6%, p = 0.002) and the incidence of micro-channels (41.4 vs. 12.5%, p = 0.013) was higher in the PR-NV group. Conversely, there was no difference in the incidence of cholesterol crystals, thrombus burden or the location of the rupture site between groups. CFD analysis revealed higher maximum endothelial shear stress (19.1 vs. 11.0 Pa) and lower maximum plaque structural stress (38.8 vs. 95.1 kPa) in the PR-NA compared to the PR-NV model. Conclusion We reported significant morphological and physiological differences between culprit ruptured plaques in native and stented segments. Further research is needed to better understand the causes of these differences and the mechanisms regulating neoatherosclerotic lesion destabilization

All-optical dual photoacoustic and optical coherence tomography intravascular probe

Intravascular imaging in percutaneous coronary interventions can be an invaluable tool in the treatment of coronary artery disease. It is of significant interest to provide molecular imaging contrast that is complementary to structural contrast provided by optical coherence tomography (OCT) and intravascular ultrasound imaging (IVUS). In this study, we developed a dual-modality intravascular imaging probe comprising a commercial OCT catheter and a high sensitivity fiber optic ultrasound sensor, to provide both photoacoustic (PA) and OCT imaging. With PA imaging, the lateral resolution varied from 18 μm to 40 μm; the axial resolution was consistently in the vicinity of 45 μm. We demonstrated the clinical potential of the probe with 2-D circumferential PA and OCT imaging, and with multispectral PA imaging