Frequency-domain optical coherence tomography assessment of human carotid atherosclerosis using saline flush for blood clearance without balloon occlusion

Hemodynamics of Saline Flushing in Endoscopic Imaging of Partially Occluded Coronary Arteries

PURPOSE

Intravascular endoscopy can aid in the diagnosis of coronary atherosclerosis by providing direct color images of coronary plaques. The procedure requires a blood-free optical path between the catheter and plaque, and achieving clearance safely remains an engineering challenge. In this study, we investigate the hemodynamics of saline flushing in partially occluded coronary arteries to advance the development of intravascular forward-imaging catheters that do not require balloon occlusion.

METHODS

In-vitro experiments and CFD simulations are used to quantify the influence of plaque size, catheter stand-off distance, saline injection flowrate, and injection orientation on the time required to achieve blood clearance.

RESULTS

Experiments and simulation of saline injection from a dual-lumen catheter demonstrated that flushing times increase both as injection flow rate (Reynolds number) decreases and as the catheter moves distally away from the plaque. CFD simulations demonstrated that successful flushing was achieved regardless of lumen axial orientation in a 95% occluded artery. Flushing time was also found to increase as plaque size decreases for a set injection flowrate, and a lower limit for injection flowrate was found to exist for each plaques size, below which clearance was not achieved. For the three occlusion sizes investigated (90, 95, 97% by area), successful occlusion was achieved in less than 1.2 s. Investigation of the pressure fields developed during injection, highlight that rapid clearance can be achieved while keeping the arterial overpressure to < 1 mmHg.

CONCLUSIONS

A dual lumen saline injection catheter was shown to produce clearance safely and effectively in models of partially occluded coronary arteries. Clearance was achieved across a range of engineering and clinical parameters without the use of a balloon occlusion, providing development guideposts for a fluid injection system in forward-imaging coronary endoscopes.

Assessing the efficacy of saline flush in frequency-domain optical coherence tomography for intracoronary imaging

BACKGROUND

The increased amount of contrast media in frequency-domain optical coherence tomography (FD-OCT) imaging during percutaneous coronary intervention (PCI) has raised potential concerns regarding impairment of renal function.

OBJECTIVES

This study aimed to evaluate the effectiveness of heparinized saline flush in FD-OCT-guided PCI and identify clinical factors contributing to optimal image quality.

METHODS

We retrospectively collected 100 lesions from 90 consecutive patients, and a total of 200 pullbacks were analyzed for the initial and final evaluation in which saline was used as the flushing medium.

RESULTS

The study population had a mean age of 73, with 52% having chronic kidney disease (CKD). The median amount of contrast used was 28 ml, and no complications were observed associated with saline flush OCT. Imaging quality was then categorized as excellent, good, or unacceptable. Among the total runs, 87% demonstrated clinically acceptable image quality, with 66.5% classified as excellent images and 20.5% classified as good images. Independent predictors of excellent images included lumen area stenosis ≥ 70% (adjusted odds ratio [OR] 2.37, 95% confidence interval [CI] 1.02-5.47, P = 0.044), and the use of intensive flushing (adjusted OR 2.06, 95% CI 1.11-3.86, P = 0.023) defined as a deep engagement of guiding catheter (GC) or a selective insertion of guide extension catheter (GE). Intensive flushing was performed in 60% of the total pullbacks, and it was particularly effective in improving image quality in the left coronary artery (LCA).

CONCLUSION

The use of saline flush during FD-OCT imaging was safe and feasible, which had a benefit in renal protection with adequate imaging quality.

Optical Coherence Tomography in Cerebrovascular Disease: Open up New Horizons

Optical coherence tomography (OCT), based on the backscattering or reflection of near-infrared light, enables an ultra-high resolution of up to 10 μm. The successful application of OCT in coronary artery diseases has sparked increasing interest in its implementation in cerebrovascular diseases. OCT has shown promising potential in the atherosclerotic plaque structure characterization, plaque rupture risk stratification, pre-stenting and post-stenting evaluation, and long-term follow-up in extracranial and intracranial atherosclerotic stenosis (ICAS). In hemorrhagic cerebrovascular diseases, OCT plays an important role in the structure evaluation, rupture risk stratification, and healing and occlusion evaluation following initial treatment in intracranial aneurysms (IAs). In this study, we summarized the applications of OCT in the diagnosis, treatment, and follow-up of cerebrovascular diseases, especially in ICAS and IAs. The current limitations and future directions of OCT in the endovascular treatment of cerebrovascular diseases were also discussed.

Optical Coherence Tomography Evaluation of Carotid Artery Stenosis and Stenting in Patients With Previous Cervical Radiotherapy

Objectives

Cervical radiotherapy can lead to accelerated carotid artery stenosis, increased incidence of stroke, and a higher rate of in-stent restenosis in irradiated patients. Our objective was to reveal the morphological characteristics of radiation-induced carotid stenosis (RICS) and the stent–vessel interactions in patients with previous cervical radiotherapy by optical coherence tomography (OCT).

Materials and Methods

Between November 2017 and March 2019, five patients with a history of cervical radiotherapy were diagnosed with severe carotid artery stenosis and underwent carotid artery stenting (CAS). OCT was conducted before and immediately after the carotid stent implantation. Two patients received OCT evaluation of carotid stenting at 6- or 13-month follow-up.

Results

The tumor types indicating cervical radiotherapy were nasopharyngeal carcinoma (n = 3), cervical esophageal carcinoma (n = 1), and cervical lymphoma (n = 1). The median interval from the radiotherapy to the diagnosis of RICS was 8 years (range 4–36 years). Lesion characteristics of RICS were detected with heterogeneous signal-rich tissue, dissection, and advanced atherosclerosis upon OCT evaluation. Post-interventional OCT revealed 18.2–57.1% tissue protrusion and 3.3–13.8% stent strut malapposition. Follow-up OCT detected homogeneous signal-rich neointima and signal-poor regions around stent struts. In the patient with high rates of tissue protrusion and stent strut malapposition, the 6-month neointima burden reached 48.9% and microvessels were detected.

Conclusion

The morphological features of RICS were heterogeneous, including heterogeneous signal-rich tissue, dissection, and advanced atherosclerosis. Stenting was successful in all 5 patients with severe RICS. One patient, with high rates of tissue protrusion and stent strut malapposition immediately after stenting, received in-stent neointimal hyperplasia at a 6-month follow-up.

Saline as an alternative to radio-contrast for optical coherence tomography guided percutaneous coronary intervention: A prospective comparison

OBJECTIVES

To do a quantitative comparison of saline and contrast Frequency domain optical coherence tomography (FD-OCT) during percutaneous coronary intervention (PCI) optimisation.

METHODS

13 pairs of OCT runs were analysed, wherein each pair consisted of a contrast run and a heparinized saline run taken in the same coronary artery at the same position. Quantitative analysis was done comparing minimal lumen area (MLA), proximal reference diameter (PRD), distal reference diameter (DRD) and percentage area stenosis (AS) at the same anatomical location. Lesion morphologies, rendered stent view and 3D reconstruction were compared for image clarity.

RESULT

The saline OCT runs resulted in comparable MLA (3.88 ± 2.59 mm² with saline run vs 3.88 ± 2.71 mm² with contrast run; p = 0.650), PRD (3.66 ± 0.52 mm with saline vs 3.65 ± 0.52 mm with contrast; p = 0.463), DRD (2.97 ± 0.22 mm with saline vs 2.99 ± 0.88 mm with contrast; p = 0.433), and AS (59.60 ± 18.62% with saline vs 59.18 ± 19.11% with contrast; p = 0.753) with respect to the contrast runs. The Bland Altman plots of the measured parameters indicate good agreement between saline and contrast OCT. Linear regression analysis indicated the absence of proportional bias All lesion morphologies (calcified, fibrotic, thin cap fibroatheroma, macrophages, cholesterol crystals and edge dissection), 3D reconstruction and rendered stent view were clearly demonstrable in the saline OCT runs.

CONCLUSIONS

Using heparinized saline as flushing media in coronary FD-OCT may result in vessel dimensions that are comparable with contrast. Heparinized saline may be used as a contrast saving alternative for FD-OCT during PCI optimization.

Study of saline optical coherence tomography-guided percutaneous coronary intervention (SOCT-PCI Study)

AIM

The aim of this study was to evaluate the feasibility of heparinised saline as flushing media for frequency-domain optical coherence tomography (FD-OCT) image acquisition during percutaneous coronary intervention (PCI) optimisation.

METHODS AND RESULTS

Twenty-seven patients undergoing FD-OCT-guided PCI were enrolled. Heparinised saline was injected into the coronary during FD-OCT image acquisition. A total of 118 runs were analysed for image quality and diagnostic value. FD-OCT runs were categorised as follows: good runs (GRs), clinically usable runs (CURs) and clinically not usable runs (NURs); GRs and CURs were combined as clinically effective runs (ERs). Saline FD-OCT enabled visualisation of all possible coronary lesions. Of the 118 runs analysed, 61%, 27.1%, 11.9% and 88.1% were GRs, CURs, NURs and ERs, respectively. Sixty-one percent of total runs were left coronary system (LCS) and 39% were right coronary system (RCS) runs. Among LCS runs, 55.6%, 30.6%, 13.8% and 86.2% were GRs, CURs, NURs and ERs, respectively. Among RCS runs, 69.6%, 21.7%, 8.7% and 91.3% were GRs, CURs, NURs and ERs, respectively.

CONCLUSION

This is the first study to demonstrate the technical feasibility of isolated saline FD-OCT for PCI optimisation.

Endovascular optical coherence tomography imaging in cerebrovascular disease

Endovascular optical coherence tomography (OCT) is the highest resolution imaging modality currently available with spatial resolution of 10 µm. Although originally developed for interventional cardiology, the ability to visualize the luminal environment and anatomy, along with the stent-vessel interaction could be of great utility for various cerebrovascular diseases, and the adoption of endovascular OCT imaging in the evolving field of interventional neuroradiology seems instinctive. The purpose of this study is to conduct a systematic review of the literature regarding applications of endovascular OCT in the diagnosis and treatment of cerebrovascular diseases. In addition, the authors report their institutional experience with the use of OCT in carotid atherosclerotic disease, cerebral aneurysms, and acute ischemic stroke. A systematic review of the literature was undertaken. Peer-reviewed articles were collected through MEDLINE, Embase, Scopus, and Cochrane Central Register of Controlled Trials (CENTRAL) searches through March 2020. A total of 34 studies with 598 patients were included in the qualitative synthesis. These include 23 studies of carotid atherosclerotic disease, 7 studies of cerebral aneurysms, and 4 studies of non-aneurysmal posterior circulation pathology. OCT imaging was feasible in 94% of patients with 0.6% complication rate. Endovascular OCT appears to be safe and feasible, allowing clinicians to visualize stent-vessel interactions, aneurysmal healing, and vulnerable atherosclerotic plaque features. OCT carries great promise, however additional investigations are needed before any imposing statement can be made about the role of OCT in cerebrovascular imaging.

A neurovascular high-frequency optical coherence tomography system enables in situ cerebrovascular volumetric microscopy

Intravascular imaging has emerged as a valuable tool for the treatment of coronary and peripheral artery disease; however, no solution is available for safe and reliable use in the tortuous vascular anatomy of the brain. Endovascular treatment of stroke is delivered under image guidance with insufficient resolution to adequately assess underlying arterial pathology and therapeutic devices. High-resolution imaging, enabling surgeons to visualize cerebral arteries' microstructure and micron-level features of neurovascular devices, would have a profound impact in the research, diagnosis, and treatment of cerebrovascular diseases. Here, we present a neurovascular high-frequency optical coherence tomography (HF-OCT) system, including an imaging console and an endoscopic probe designed to rapidly acquire volumetric microscopy data at a resolution approaching 10 microns in tortuous cerebrovascular anatomies. Using a combination of in vitro, ex vivo, and in vivo models, the feasibility of HF-OCT for cerebrovascular imaging was demonstrated.

Perspective review on applications of optics in cerebral endovascular neurosurgery

Cerebral endovascular neurosurgery has transformed the way we manage cerebrovascular disease. Several landmark trials have demonstrated the effectiveness of endovascular techniques leading to continued technological development and applications for various diseases. The utilization of optical technologies and devices is already underway in the field of endovascular neurosurgery. We discuss the contemporary paradigms, challenges, and current optical applications for the most common cerebrovascular diseases: carotid atherosclerotic disease, cerebral aneurysms, intracranial atherosclerosis, and dural arteriovenous fistulas. We also describe needs-based opportunities for future optical applications, with the goal of providing researchers a sense of where we feel optical technologies could impact the way we manage cerebral disease.

Ex Vivo Porcine Arterial and Chorioallantoic Membrane Acoustic Angiography Using Dual-Frequency Intravascular Ultrasound Probes

The presence of blood vessels within a developing atherosclerotic plaque has been found to be correlated with increased plaque vulnerability and ensuing cardiac events, however, detection of coronary intraplaque neovascularization poses a significant challenge in the clinic. We describe here a new in vivo intravascular ultrasound imaging method using a dual-frequency transducer to visualize contrast flow in microvessels with high specificity. This method uses a specialized transducer capable of exciting contrast agents at a low frequency (5.5 MHz) while detecting their nonlinear superhamonics at a much higher frequency (37 MHz). In vitro evaluation of the approach was performed in a microvascular phantom to produce 3-D renderings of simulated vessel patterns and to determine image quality metrics as a function of depth. Furthermore, we describe the ability of the system to detect microvessels both ex vivo using porcine arteries and in vivo using the chorioallantoic membrane of a developing chicken embryo with optical confirmation. Dual-frequency contrast-specific imaging was able to resolve vessels similar in size to those found in vulnerable atherosclerotic plaques at clinically relevant depths. The results of this study add to the support for further evaluation and translation of contrast-specific imaging in intravascular ultrasound for the detection of vulnerable plaques in atherosclerosis.

Adaptive windowing in contrast-enhanced intravascular ultrasound imaging

Intravascular ultrasound (IVUS) is one of the most commonly-used interventional imaging techniques and has seen recent innovations which attempt to characterize the risk posed by atherosclerotic plaques. One such development is the use of microbubble contrast agents to image vasa vasorum, fine vessels which supply oxygen and nutrients to the walls of coronary arteries and typically have diameters less than 200μm. The degree of vasa vasorum neovascularization within plaques is positively correlated with plaque vulnerability. Having recently presented a prototype dual-frequency transducer for contrast agent-specific intravascular imaging, here we describe signal processing approaches based on minimum variance (MV) beamforming and the phase coherence factor (PCF) for improving the spatial resolution and contrast-to-tissue ratio (CTR) in IVUS imaging. These approaches are examined through simulations, phantom studies, ex vivo studies in porcine arteries, and in vivo studies in chicken embryos. In phantom studies, PCF processing improved CTR by a mean of 4.2dB, while combined MV and PCF processing improved spatial resolution by 41.7%. Improvements of 2.2dB in CTR and 37.2% in resolution were observed in vivo. Applying these processing strategies can enhance image quality in conventional B-mode IVUS or in contrast-enhanced IVUS, where signal-to-noise ratio is relatively low and resolution is at a premium.

Dextran or Saline Can Replace Contrast for Intravascular Optical Coherence Tomography in Lower Extremity Arteries

PURPOSE

To examine the hypothesis that alternative flush media could be used for lower extremity optical coherence tomography (OCT) imaging in long lesions that would normally require excessive use of contrast.

METHODS

The OPTical Imaging Measurement of Intravascular Solution Efficacy (OPTIMISE) trial was a single-center, prospective study (ClinicalTrials.gov identifier NCT01743872) that enrolled 23 patients (mean age 68±11 years; 14 men) undergoing endovascular intervention involving the superficial femoral artery. Four flush media (heparinized saline, dextran, carbon dioxide, and contrast) were used in succession in random order for each image pullback. Quality was defined as ≥270° visualization of vessel wall layers from each axial image. Mean proportions (± standard deviation) of image quality for each flush medium were assessed using 1-way analysis of variance and are reported with the 95% confidence intervals (CI).

RESULTS

Four OCT catheters failed, leaving 19 patients who completed the OCT imaging protocol; from this cohort, 51 highest quality runs were selected for analysis. Average vessel diameter was 3.99±1.01 mm. OCT imaging allowed 10- to 15-μm resolution of the lumen border, with diminishing quality as vessel diameter increased. Plaque characterization revealed fibrotic lesions. Mean proportions of image quality were dextran 87.2%±12% (95% CI 0.81 to 0.94), heparinized saline 74.3%±24.8% (95% CI 0.66 to 0.93), contrast 70.1%±30.5% (95% CI 0.52 to 0.88), and carbon dioxide 10.0%±10.4% (95% CI 0.00 to 0.26). Dextran, saline, and contrast provided better quality than carbon dioxide (p<0.001).

CONCLUSION

OCT is feasible in peripheral vessels <5 mm in diameter. Dextran or saline flush media can allow lesion characterization, avoiding iodinated contrast. Carbon dioxide is inadequate for peripheral OCT imaging. Axial imaging may aid in enhancing durability of peripheral endovascular interventions.

Optical coherence tomography of traumatic aneurysms of the internal carotid artery: report of 2 cases

The pathophysiology of extracranial traumatic aneurysm formation has not been fully elucidated. Intraarterial optical coherence tomography (OCT), an imaging modality capable of micrometer cross-sectional resolution, was used to evaluate patients presenting with saccular traumatic aneurysms of the internal carotid artery (ICA). Two consecutive trauma patients diagnosed with saccular traumatic aneurysms of the cervical ICA, per the institutional screening protocol for traumatic cerebrovascular injury, underwent digital subtraction angiography (DSA) with OCT. Optical coherence tomography demonstrated disruption of the intima with preservation and stretching of the more peripheral layers. In 1 patient the traumatic aneurysm was associated with thrombus formation and a separate, more proximal dissection not visible on CT angiography (CTA) or DSA. Imaging with OCT indicates that saccular traumatic aneurysms may develop from disruption of the intima with at least partial preservation of the media and adventitia. This provides in vivo evidence that saccular traumatic aneurysms result from a partial arterial wall tear rather than complete disruption. Interestingly, OCT was also able to detect arterial injury and thrombi not visible on CTA or DSA.

Optical coherence tomography of the intracranial vasculature and Wingspan stent in a patient

A 67-year-old man with medically refractory vertebrobasilar insufficiency and short segment occlusions of the intracranial vertebral arteries was treated with angioplasty and stent placement. Fifteen hours after the procedure the patient developed symptoms of posterior fossa ischemia and repeat angiography showed thrombus formation within the stent which was treated with thrombolytic and aggressive antiplatelet therapy. Angiography revealed lysis of the clot, but concerns regarding the mechanism of the thrombotic phenomenon prompted frequency-domain optical coherence tomography (FDOCT) assessment. FDOCT provided excellent visualization of the stent and vessel wall interactions, as well as excluding residual flow-limiting stenosis, obviating the need for further intervention. The potential utility of FDOCT in the evaluation of intracranial atherosclerotic disease and additional intracranial applications are discussed.