Assessment of coronary plaque with optical coherence tomography and high-frequency ultrasound

Quantitative optical coherence tomographic elastography: method for assessing arterial mechanical properties

Optical coherence tomography elastography represents a potentially attractive new technique for measuring elastic properties of tissues on a micron scale. In this study, the feasibility of optical coherence tomography (OCT) to study the mechanical properties of phantoms and atherosclerotic arterial samples is reported. The elastic modulus of tissue-mimicking phantoms was measured using OCT and correlated with mechanical measurements. The results indicate that elastography based on OCT represents an attractive technique for evaluating the mechanical properties of tissues.

Optical coherence tomography of laryngeal cancer

OBJECTIVES

Optical coherence tomography (OCT) is a high-resolution optical imaging technique that produces cross-sectional images of living tissues using light in a manner similar to ultrasound. This prospective study evaluated the ability of OCT to identify the characteristics of laryngeal cancer and measure changes in the basement membrane, tissue microstructure, and the transition zone at the edge of tumors.

MATERIALS AND METHODS

One hundred thirty-three patients underwent OCT examination during surgical endoscopy of the head and neck. Twenty-two patients with laryngeal cancer or a history of laryngeal cancer were imaged with a fiberoptic OCT system. Tumor and adjacent transition zones were imaged along with uninvolved subsites. OCT images were correlated with histopathology.

RESULTS

Twenty-six OCT examinations were performed in 22 patients. Basement membrane disruption was seen in 18 subjects, all of whom had histology showing classic features of cancer. A transition zone to uninvolved epithelium at the tumor periphery was also often observed. In six studies, benign or premalignant processes were histologically confirmed. In three thin, superficial lesions, an intact basement membrane was observed. The basement membrane could not be identified in three other bulky exophytic, premalignant lesions, primarily because of increased superficial signal backscattering observed in pathologic tissues.

CONCLUSIONS

OCT clearly identifies basement membrane violation from laryngeal cancer and can identify transition zones at the cancer margin. In bulky exophytic lesions, OCT signal may not penetrate deeply enough to show the basement membrane, but for many suspicious lesions that require exclusion of cancer, OCT shows potential for assisting in diagnostic assessment.

Sources of error and interpretation of plaque morphology by optical coherence tomography

This study was performed to assess the strengths and weaknesses of optical coherence tomography (OCT) intravascular imaging in identifying plaque morphology. Seventy-nine postmortem human coronary arterial sections classified as fibrous-cap atheromas, calcific plaques, fibrous plaques, and complicated lesions were studied. OCT was able to identify 45% of fibrous-cap atheromas (kappa=0.27, p<0.01), 68% of fibrocalcific plaques (kappa=0.40, p<0.001), 83% of fibrous plaques (kappa=0.37, p<0.001), and 100% of complicated lesions (all thrombi; kappa=1, p<0.001). Misinterpretation was caused mainly by the low OCT signal penetration, which could not detect lipid pools or calcium behind thick fibrous caps, and by an inability to distinguish calcium deposits from lipid pools or the opposite. Lesions with thick (>150 microm) caps were histologically identified as 25 thick fibrous-cap atheromas, 8 fibrocalcific plaques, and 5 fibrous plaques; all these lesions were relatively "stable." In contrast, lesions with fibrous caps<150 microm were either vulnerable or stable lesions (11 thin-fibrous-cap atheromas and 11 fibrocalcific plaques). In conclusion, although OCT images may give an indication of the overall composition of large homogenous signal-poor regions, such as lipids or calcified areas, they could be unreliable in differentiating areas with heterogenous compositions. OCT may easily recognize relatively stable lesions.

Prevalence of noncalcified coronary plaques by 64-slice computed tomography in patients with an intermediate risk for significant coronary artery disease

OBJECTIVES

In this prospective study, we investigated the prevalence and characteristics of clearly discernible noncalcified coronary plaques in a patient population with suspected significant coronary artery disease (CAD) by using 64-slice computed tomography (CT).

BACKGROUND

The assessment of noncalcified coronary plaques by noninvasive strategies may be important to improve cardiovascular risk stratification.

METHODS

To rule out significant stenosis, high-resolution 64-slice coronary CT (0.6-mm collimation, 330-ms gantry rotation time) was performed in 161 consecutive patients with an intermediate risk for having CAD. Computed tomography data sets were evaluated for presence of coronary calcifications, noncalcified plaques, and/or lumen narrowing.

RESULTS

Noncalcified coronary plaques were detected in 48 (29.8%) of 161 enrolled patients. Although noncalcified plaques together with coronary calcifications were present in 38 of 161 (23.6%) patients, the prevalence of noncalcified plaques as the only manifestation of CAD was 6.2% (10 of 161 patients). Patients with noncalcified plaques were characterized by significantly higher total cholesterol, low-density lipoprotein, and C-reactive protein levels as well as a trend for more diabetes mellitus. The majority of noncalcified plaques resulted in lumen narrowing of <50%. Of the remaining 113 patients, CAD and coronary calcifications were ruled out in 53 of 161 (32.9%) patients, whereas 60 of 161 (37.3%) patients presented with calcifications in the absence of noncalcified plaque.

CONCLUSIONS

With the use of 64-slice CT, clearly discernible noncalcified atherosclerotic coronary plaques can be detected in a large group of patients with an intermediate risk for having CAD. The assessment of these plaques by CT angiography may allow for improved cardiovascular risk stratification.

Plaque characterization with optical coherence tomography

The identification of unstable plaque is central in risk-stratifying patients for acute coronary events. Optical coherence tomography (OCT) is a recently introduced imaging modality that has shown considerable promise for the identification of high-risk plaques. Advantages of OCT include its high resolution (4 to 20 microm), high data acquisition rate, small and inexpensive guidewires/catheters, and ability to be combined with adjuvant optical techniques. This article summarizes the current state of intravascular OCT imaging, focusing on potential markers of instability and current limitations.

Optical coherence tomography for identifying unstable coronary plaque

This manuscript examines intravascular imaging with optical coherence tomography (OCT). OCT is a potentially attractive intravascular imaging technology due to its high resolution, small catheters/guidewires, and ability to be combined with spectroscopic techniques. Its potential disadvantages remain its limited penetration and signal attenuation by blood. The manuscript reviews unstable plaque, OCT principles, historical development, current challenges, and comparison with IVUS.

Intravascular Optical Coherence Tomography: Comparison with Histopathology in Atherosclerotic Peripheral Artery Specimens

PURPOSE

Intravascular optical coherence tomography (OCT) is a new imaging modality that provides microstructural information on atherosclerotic plaques and has an axial resolution of 10-20 microm. OCT of coronary arteries characterizes different atherosclerotic plaque components by their distinctive signal patterns. Peripheral human arteries were examined ex vivo by means of OCT, and attempts to distinguish among fibrous, lipid-rich, and calcified atherosclerotic plaques were made based on imaging criteria previously established for coronary arteries.

MATERIALS AND METHODS

One hundred fifty-one atherosclerotic arterial segments were obtained from 15 below-knee amputations. OCT imaging criteria for different plaque types (fibrous, lipid-rich, calcified) were established in a subset of 30 arterial segments. The remaining 121 OCT images were analyzed by two independent readers. Each segment was divided into four quadrants. Agreement between histopathology and OCT was quantified by the kappa test of concordance, as were interobserver, intraobserver, and inter-method variability.

RESULTS

Four hundred sixty-nine of 484 quadrants (97%) were available for comparison. Sensitivity and specificity for OCT criteria (consensus readers 1 and 2) were 86% and 86% for fibrous plaques, 78% and 93% for lipid-rich plaques, and 84% and 95% for calcified plaques, respectively (overall agreement, 84%). The interobserver and intraobserver reliabilities of OCT assessment were high (kappa values of 0.84 and 0.87, respectively). The inter-method agreement was 0.74 for consensus OCT versus consensus histology.

CONCLUSIONS

OCT of peripheral human arteries ex vivo characterized different atherosclerotic plaque types with a high degree of agreement with histopathologic findings. Findings were comparable to those reported for coronary arteries. OCT promises to improve understanding of the progression or regression of peripheral atherosclerosis in vivo.

Assessment of coronary plaque collagen with polarization sensitive optical coherence tomography (PS-OCT)

INTRODUCTION

Current evidence indicates that most plaques classified as vulnerable or ruptured plaque do not lead to unstable angina or myocardial infarction. Improved methods are needed to risk stratify plaques to identify those which lead to most acute coronary syndromes. Collagen depletion in the intima overlying lipid collections appears to be a critical component of unstable plaques. In this study, we use polarization sensitive optical coherence tomography (PS-OCT) for the assessment of coronary plaque collagen. Collagen is birefringent, meaning that different polarization states travel through it at different velocities.

METHODS AND RESULTS

Changes in PS-OCT images are a measure of tissue birefringence. Twenty-two coronary artery segments were imaged with PS-OCT and analyzed by picrosirius staining (a measure of collagen intensity and fiber size) and trichrome blue. The regression plot between PS-OCT changes and measured collagen yielded a correlation coefficient value of 0.475 (p<0.002). The predictive value of a PS-OCT measurement of negligible birefringence (less than 33% change) for minimal collagen was 93% while the predictive value of high birefringence (greater than 66% change) for high collagen concentrations was 89%. The effect of fiber type (chemical composition) was minimal relative to the effect due to fiber concentration.

CONCLUSION

The capability of PS-OCT to assess plaque collagen content, in addition to its ability to generate high resolution structural assessments, make it a potentially powerful technology for identifying high risk plaques.

In vivo optical coherence tomography of the human larynx: normative and benign pathology in 82 patients

OBJECTIVES

Optical coherence tomography (OCT) is an emerging imaging modality that combines low-coherence light with interferometry to produce cross-sectional images of tissue with resolution about 10 mum. Patients undergoing surgical head and neck endoscopy were examined using a fiberoptic OCT imaging probe to study and characterize microstructural anatomy and features of the larynx and benign laryngeal pathology in vivo.

STUDY DESIGN

Prospective clinical trial.

MATERIALS AND METHODS

OCT imaging of the larynx was performed in 82 of 115 patients who underwent surgical endoscopy for various head and neck pathologies. The OCT device employs a 1.3 microm broadband light source (FWHM, 80 nm). The frame rate is 1 Hz. Imaging was performed using a handheld probe placed in near contact with the target site. The maximum axial and lateral dimensions for the region of interest imaged were 2.5 mm x 6 mm, with resolutions of 10 microm. Simultaneously, conventional endoscopic images were obtained to provide anatomic correlation with OCT images and histology. Optical micrometry was performed to measure the epithelium thickness.

RESULTS

Systematic OCT imaging of laryngeal structures and subsites provided information on the thickness of the epithelium, integrity of the basement membrane, and structure of the lamina propria. Microstructural features identified included glands, ducts, blood vessels, fluid collection/edema, and the transitions between pseudostratified columnar and stratified squamous epithelium. The mean epithelial thickness of laryngeal subsites was calculated: true vocal cord (129 microm), false vocal cords (124 microm), aryepiglottic fold (177 microm), subglottis (98 microm), and epiglottis (185 microm). True vocal cord pathology imaged included Reinke's edema, papillomatosis, polyps, mucous cysts, and granulation tissue. Subglottic imaging identified boundaries between epithelium, lamina propria, and cartilage. The OCT images compared favorably with conventional histopathology.

CONCLUSION

OCT has the unique ability to image laryngeal tissue microstructure and can detail microanatomic changes in benign, premalignant, and malignant laryngeal pathologies. OCT holds the potential to guide surgical biopsies, direct therapy, and monitor disease, particularly when office-based systems are developed. This is a promising imaging modality to study the larynx.

Clinical imaging of the vulnerable plaque in the coronary arteries: new intracoronary diagnostic methods

Rupture of a vulnerable plaque is the main cause of acute coronary syndromes and myocardial infarction. The features of rupture-prone atherosclerotic plaques have been previously described by pathologists. However, identification of vulnerable plaques in vivo is essential to study their natural history and to evaluate potential treatment modalities. Coronary angiography is the gold standard for the diagnosis of coronary artery disease, but it is unable to distinguish between stable and unstable plaques and to accurately predict future cardiac events. This current perspective describes the recently developed invasive imaging techniques to detect atherosclerotic vulnerable plaques in the coronary tree.

In vivo volumetric analysis of coronary stent using optical coherence tomography with a novel balloon occlusion-flushing catheter: a comparison with intravascular ultrasound

Optical coherence tomography (OCT) is limited as an intravascular imaging tool because of interference with blood. This study tested a new balloon occlusion-flushing catheter for OCT scanning of stented coronary arteries and compared stent measurements between OCT and intravascular ultrasound (IVUS). Motorized pullback with OCT and IVUS was examined in coronary stents deployed in swine. Quantitative measurements were obtained and compared between both groups. In addition, stent strut thickness was compared among OCT, IVUS and actual measurement. The occlusion catheter successfully provided motorized pullback OCT images in the stented coronary arteries without any complications. There were no differences in calculated lumen volume. However, stent volumes were significantly smaller with OCT than with IVUS (p < 0.05). OCT significantly underestimated the stent strut thickness compared with the actual measurement. Although OCT underestimates the stent strut thickness, motorized pullback OCT imaging with the occlusion catheter can provide appropriate in-stent images in the porcine coronary arteries.

In vivo optical coherence tomography for the diagnosis of oral malignancy

BACKGROUND AND OBJECTIVE

Oral cancer results in 10,000 U.S. deaths annually. Improved highly sensitive diagnostics allowing early detection of oral cancer would benefit patient survival and quality of life. Objective was to investigate in vivo non-invasive optical coherence tomography (OCT) techniques for imaging and diagnosing neoplasia-related epithelial, sub-epithelial changes throughout carcinogenesis.

STUDY DESIGN/MATERIALS AND METHODS

In the standard hamster cheek pouch model for oral carcinogenesis (n = 36), in vivo OCT was used to image epithelial and sub-epithelial change. OCT- and histopathology-based diagnoses on a scale of 0 (healthy) to 6 (squamous cell carcinoma, SCC) were performed at all stages throughout carcinogenesis by two blinded investigators.

RESULTS

Epithelial, sub-epithelial structures were clearly discernible using OCT. OCT diagnosis agreed with the histopathological gold standard in 80% of readings.

CONCLUSION

In vivo OCT demonstrates excellent potential as a diagnostic tool in the oral cavity.

Noninvasive imaging of oral premalignancy and malignancy

Early detection of cancer and its precursors remains the best way to ensure patient survival and quality of life. Our specific aim is to test a multimodality approach to noninvasive diagnostics of oral premalignancy and malignancy. In the hamster cheek pouch model (120 hamsters), in vivo optical coherence tomography (OCT) and optical Doppler tomography (ODT) map epithelial, subepithelial, and vascular change throughout carcinogenesis. In vivo multiwavelength multiphoton (MPM) and second-harmonic generated (SHG) fluorescence techniques provided parallel data on surface and subsurface tissue structure, specifically collagen presence and structure, cellular presence, and vasculature. Images are diagnosed by two blinded, prestandardized investigators using a scale from 0 to 6 for all modalities. After sacrifice, histopathology is evaluated on a scale of 0 to 6. Imaging data are reproducibly obtained with good accuracy. Carcinogenesis-related structural and vascular changes are clearly visible to tissue depths of 2 mm. Sensitivity (OCT/ODT alone, 71 to 88%; OCT+MPMSHG, 79 to 91%) and specificity (OCT alone, 62 to 83%; OCT+MPMSHG, 67 to 90%) compare well with conventional techniques. Our conclusions are that OCT/ODT and MPM/SHG are promising noninvasive in vivo diagnostic modalities for oral dysplasia and malignancy.

Hybrid positron detection and optical coherence tomography system: design, calibration, and experimental validation with rabbit atherosclerotic models

We evaluate the performance of our novel hybrid optical coherence tomography (OCT) and scintillating probe, demonstrate simultaneous OCT imaging and scintillating detection, and validate the system using an atherosclerotic rabbit model. Preliminary data obtained from the rabbit model suggest that our prototype positron probe detects local uptake of fluorodeoxyglucose (FDG) labeled with 18F positron (beta) radionuclide emitter, and the high-uptake regions correlate with sites of injury and extensive atherosclerosis areas. Preliminary data also suggest that coregistered high-resolution OCT images provide imaging of detailed plaque microstructures, which cannot be resolved by positron detection.

High-resolution optical coherence tomographic imaging of osteoarthritic cartilage during open knee surgery

This study demonstrates the first real-time imaging in vivo of human cartilage in normal and osteoarthritic knee joints at a resolution of micrometers, using optical coherence tomography (OCT). This recently developed high-resolution imaging technology is analogous to B-mode ultrasound except that it uses infrared light rather than sound. Real-time imaging with 11-microm resolution at four frames per second was performed on six patients using a portable OCT system with a handheld imaging probe during open knee surgery. Tissue registration was achieved by marking sites before imaging, and then histologic processing was performed. Structural changes including cartilage thinning, fissures, and fibrillations were observed at a resolution substantially higher than is achieved with any current clinical imaging technology. The structural features detected with OCT were evident in the corresponding histology. In addition to changes in architectural morphology, changes in the birefringent or the polarization properties of the articular cartilage were observed with OCT, suggesting collagen disorganization, an early indicator of osteoarthritis. Furthermore, this study supports the hypothesis that polarization-sensitive OCT may allow osteoarthritis to be diagnosed before cartilage thinning. This study illustrates that OCT, which can eventually be developed for use in offices or through an arthroscope, has considerable potential for assessing early osteoarthritic cartilage and monitoring therapeutic effects for cartilage repair with resolution in real time on a scale of micrometers.

Visualization of Neointima Formation by Optical Coherence Tomography

Optical coherence tomography (OCT) has recently been proposed as a high-resolution imaging method. Our male patient, who had been treated with a coronary stent, died due to acute leukemia. Coronary artery images using intravascular ultrasound (IVUS) and OCT were obtained postmortem. We also compared the image of neointima formation after stent implantation evaluated by histopathological examination with that evaluated by IVUS and OCT. OCT visualized well-apposed stent struts and neointima formation, which could not be visualized completely by IVUS. OCT may be useful for monitoring structural changes after stent implantation.

Assessment of Coronary Intima - Media Thickness by Optical Coherence Tomography Comparison With Intravascular Ultrasound

BACKGROUND

Optical coherence tomography (OCT) is a new imaging method. With a resolution of approximately 10-20 Em, which is approximately 10-fold higher than that of intravascular ultrasound (IVUS).

METHODS AND RESULTS

This study compared the coronary intima - media thickness (IMT) and the intimal thickness of 54 coronary arterial segments evaluated by histological examination with the results of OCT and IVUS. There was better agreement in IMT between OCT and histological examination than between IVUS and histological examination (r = 0.95, p < 0.001, mean difference = -0.01+/-0.07 mm for OCT; r = 0.88, p < 0.001, mean difference = -0.03+/-0.10 mm for IVUS). There was good agreement in the intimal thickness between OCT and histological examination (r = 0.98, p < 0.001, mean difference = 0.01+/-0.04 mm).

CONCLUSIONS

IMT could be measured more accurately by OCT than IVUS. In addition, the intimal thickness could be evaluated by OCT and correlated well with the histological examination.

3-D optical coherence tomography of the laryngeal mucosa*

Laryngeal carcinoma is one of the commonest primary head and neck malignancy and the need for early identification is very important for successful treatment. Outpatient fibreoptic examination of the larynx is unreliable in differentiating benign, pre-malignant and malignant lesions, and therefore surgeons have to rely on biopsies for a definitive diagnosis. This is an invasive procedure requiring general anaesthesia and may have a detrimental effect on the patient's voice. Conventional imaging modalities (ultrasound, computed tomography and magnetic resonance imaging) have a limited resolution and hence cannot give sufficient information on the extent or nature of laryngeal lesions. The aim of our study is to investigate the feasibility of optical coherence tomography (OCT) in imaging the normal larynx, to lay the foundations for an investigation of its ability to differentiate between benign and malignant disease. Ten tissue specimens from normal larynges were imaged with an 850 nm OCT system that was capable of providing both B-scan (longitudinal or cross-section) images as well as C-scan (en-face or images at constant depth). The en-face OCT mode allowed us to reconstruct 3-D OCT images of the tissue examined. Imaged specimens were processed with standard histopathological techniques and sectioned in the plane of the B-scan OCT images. Haematoxylin-eosin stained specimens were compared with the OCT images thus collected. Preliminary results showed good correlation between OCT images and histology sections in normal tissue.

Tissue pH determination for the detection of metabolically active, inflamed vulnerable plaques using near-infrared spectroscopy: an in-vitro feasibility study

Detection of vulnerable plaques as the underlying cause of myocardial infarction is at the center of attention in cardiology. We have previously shown that infiltration of inflammatory cells in atherosclerotic plaques renders these plaques relatively hot and acidic, with substantial plaque temperature and pH variation. The objective of this investigation was to determine whether near-infrared diffuse reflectance spectroscopy (NIRS) could be used to non-destructively measure the tissue pH in atherosclerotic plaques. NIRS and tissue pH electrode measurements were taken on freshly excised carotid plaques maintained under physiological conditions. The coefficient of determination between NIRS and the pH microelectrode measurement was 0.75 using 17 different areas. The estimated accuracy of the NIRS measurement was 0.09 pH units. These results demonstrate the feasibility of using NIRS tissue pH in freshly excised atherosclerotic plaques in light of marked pH heterogeneity and warrants future in-vivo investigations on pH measurement of atherosclerotic plaques.

Review of the Ability of Optical Coherence Tomography to Characterize Plaque, Including a Comparison with Intravascular Ultrasound

Over the last 50 years the introduction of several imaging technologies have been pivotal in reducing mortality associated with coronary artery disease. However coronary disease continues to be the leading cause of mortality in the industrialized world. Optical coherence tomography (OCT) has recently been introduced for micron scale intravascular imaging. It is analogous to ultrasound, measuring the intensity of back-reflected infrared light instead of sound. Some of the advantages of OCT include its resolution, which is higher than any currently available imaging technology and acquisition rates are near video speed. Unlike ultrasound, OCT catheters consist of simple fiber optics and contain no transducers within their frame, thereby making imaging catheters both inexpensive and small. Currently, the smallest catheters have a cross-sectional diameter of 0.014". OCT systems are compact and portable and can be combined with a range of spectroscopic techniques. We review the application of OCT to intracoronary imaging.

Group velocity dispersion effects with water and lipid in 1.3 microm optical coherence tomography system

Optical coherence tomography (OCT) has been introduced for the diagnosis of vulnerable plaques in the coronary arteries. When an OCT system images through tissue and biological liquids, group velocity dispersion (GVD) will occur, which may be useful in tissue characterization. This study compares the water and lipid induced GVD effects, important constituents in plaque, on the axial resolution. The point-spread function (PSF) was measured when a target mirror was immersed in either water or lipid. A Fourier transform was performed on the PSF data. No significant GVD was observed in oil up to 15 mm thickness. Water depths greater than 6 mm significantly broadened the PSF. This indicates that the distortion of the spectrum can be attributed to the GVD in water. These results suggest that when imaging through tissue (such as when performing intravascular imaging in vivo) one may be able to distinguish different tissue types for diagnostic purposes.

Optical coherence tomographic elastography technique for measuring deformation and strain of atherosclerotic tissues

OBJECTIVES

To evaluate optical coherence tomographic elastography as a method for assessing the elastic properties of atherosclerotic plaque and the parameters that influence interpretation.

METHODS

Phantoms and aorta were examined in vitro to quantify speckle modulation and measure the displacement and strain maps. A correlation method was used as a speckle tracking technique for measuring axial and lateral displacement vectors and calculation of strain maps. The influence of correlation kernel size on accuracy of the method was evaluated.

RESULTS

In terms of a percentage error between calculated and measured displacements, the best results for phantoms were obtained with a 41 x 41 kernel (1.88% error). For both phantom and aorta images, it was found that, with the increasing size of cross correlation kernel, the axial and lateral displacement maps are less noisy and the displacement vectors are more clearly defined. However, the large kernels tend to average out the differences in displacements of small particles in phantoms and decrease the ability of speckle tracking to make microstructural assessments. Therefore, it is important to select kernel size carefully, based on the image features.

CONCLUSIONS

Optical tomographic elastography can be used to assess the microstructural properties of atherosclerotic tissue at micrometre scale resolution, but preselected analysis criteria must be understood in a critical interpretation of the results.

Distal Shower Embolization During Directional Coronary Atherectomy and Stenting for Diffuse Stenosis of Right Coronary Artery-Current Limitations of Intravascular Ultrasonography for Evaluating Fragile Plaque-

A 74 year-old male with old anterior and inferior myocardial infarctions was treated with staged percutaneous coronary intervention. A chronic total occlusion of the middle segment of the left anterior descending branch was successfully stented during the first stage, and during the second stage, preprocedural intravascular ultrasonography (IVUS) revealed that the proximal segment of the right coronary artery was diffusely stenosed by mixed plaque. Directional coronary atherectomy under IVUS guidance was performed, but coronary slow flow appeared during the procedure. After successfully bailing out with intracoronary nicorandil, percutaneous thrombectomy and manual blood pumping, 2 coronary stents were implanted to fully cover the lesion. Quite contrary to expectation, the no-reflow phenomenon appeared just after post-dilatation and a repeat of the same maneuver could not completely recover coronary flow. Plaque fragility could not be predicted from the IVUS examination.

From vulnerable plaque to vulnerable patient: a call for new definitions and risk assessment strategies: Part I

Atherosclerotic cardiovascular disease results in >19 million deaths annually, and coronary heart disease accounts for the majority of this toll. Despite major advances in treatment of coronary heart disease patients, a large number of victims of the disease who are apparently healthy die suddenly without prior symptoms. Available screening and diagnostic methods are insufficient to identify the victims before the event occurs. The recognition of the role of the vulnerable plaque has opened new avenues of opportunity in the field of cardiovascular medicine. This consensus document concludes the following. (1) Rupture-prone plaques are not the only vulnerable plaques. All types of atherosclerotic plaques with high likelihood of thrombotic complications and rapid progression should be considered as vulnerable plaques. We propose a classification for clinical as well as pathological evaluation of vulnerable plaques. (2) Vulnerable plaques are not the only culprit factors for the development of acute coronary syndromes, myocardial infarction, and sudden cardiac death. Vulnerable blood (prone to thrombosis) and vulnerable myocardium (prone to fatal arrhythmia) play an important role in the outcome. Therefore, the term "vulnerable patient" may be more appropriate and is proposed now for the identification of subjects with high likelihood of developing cardiac events in the near future. (3) A quantitative method for cumulative risk assessment of vulnerable patients needs to be developed that may include variables based on plaque, blood, and myocardial vulnerability. In Part I of this consensus document, we cover the new definition of vulnerable plaque and its relationship with vulnerable patients. Part II of this consensus document focuses on vulnerable blood and vulnerable myocardium and provide an outline of overall risk assessment of vulnerable patients. Parts I and II are meant to provide a general consensus and overviews the new field of vulnerable patient. Recently developed assays (eg, C-reactive protein), imaging techniques (eg, CT and MRI), noninvasive electrophysiological tests (for vulnerable myocardium), and emerging catheters (to localize and characterize vulnerable plaque) in combination with future genomic and proteomic techniques will guide us in the search for vulnerable patients. It will also lead to the development and deployment of new therapies and ultimately to reduce the incidence of acute coronary syndromes and sudden cardiac death. We encourage healthcare policy makers to promote translational research for screening and treatment of vulnerable patients.

Optical coherence tomography

BACKGROUND

Optical coherence tomography (OCT) is a light-based imaging modality that can be used in biological systems to study tissues in vivo with near-histologic, ultrahigh resolution. The rationale for intravascular application of OCT is its potential for in vivo visualisation of the coronary artery microstructure.

METHODS AND RESULTS

The principle is analogous to pulse-echo ultrasound imaging; however, light is used rather than sound to create the image. Low-coherent near-infrared light is emitted by a superluminescent diode and reflected by the microstructures within biological tissues. The echo time delay of reflected light waves is converted into a two-dimensional spatial image. The intensity of the reflected light waves is translated into an intensity map. Experimental studies confirmed the ability of intravascular OCT for plaque characterisation and accurate assessment of vascular structures that are close to the luminal surface. Preliminary clinical experience proved in vivo feasibility of intravascular OCT. A variety of atherosclerotic plaque structures including thin cap fibroatheromas can be visualized in vivo.

CONCLUSIONS

Intravascular OCT allows for accurate assessment of vessel structures close to the luminal side. Clinical application is feasible. To date, however, the clinical relevance of OCT findings in coronary arteries is unclear and further validation of OCT imaging is mandatory.

Simultaneous optical coherence tomography imaging and beta particle detection

A prototype hybrid catheter device designed for imaging and detection of vascular diseases is introduced. The prototype device integrates a high-resolution optical coherent tomography probe and a high-sensitivity beta detector into a single unit. With this prototype device we demonstrate the feasibility of simultaneous optical coherence tomography imaging and detection of beta particles.

Initial experience and safety in the treatment of chronic total coronary occlusions with a new optical coherent reflectometry-guided radiofrequency ablation guidewire

The Safe-Cross wire system, which has optical coherence reflectometry technology for navigating and radiofrequency energy provided at its tip for crossing chronic total occlusions (CTOs), provides a promising means to treat hard, organized CTOs. Using this system, we report on a 60% success rate in patients who had long-standing coronary CTOs that had > or =1 failed attempt using conventional percutaneous coronary intervention.

Integration of vascular biology and magnetic resonance imaging in the understanding of atherothrombosis and acute coronary syndromes

The interaction between the vulnerable atherosclerotic plaque prone to disruption and thrombus formation is the cornerstone of acute coronary syndrome (ACS). Although distinct from one another, the atherosclerotic and thrombotic processes appear to be interdependent, hence the term atherothrombosis. Inflammation is a crucial common pathophysiological mechanism. Overall, the association of plaque vulnerability and ACS has been well documented. Given the multifactorial origin of atherothrombosis the best preventive approach should be aggressive management of all the risk factors. New interventions should be directed toward decreasing vulnerability of the lesions thereby decreasing the risk of ACS.

Effect of dextran-induced changes in refractive index and aggregation on optical properties of whole blood

The purpose of the present study is to investigate systematically the mechanisms of alterations in the optical properties of whole blood immersed in the biocompatible agent dextran, and to define the optimal concentration of dextrans required for blood optical clearing in order to enhance the capability of light penetration depth for optical imaging applications. In the experiments, dextrans with different molecular weights and various concentrations were employed and investigated by the use of the optical coherence tomography technique. Changes in light attenuation, refractive index and aggregation properties of blood immersed in dextrans were studied. It was concluded from the results that the mechanisms for blood optical clearing are characteristic of the types of dextrans employed, their concentrations and the application stages. Among the substances applied, Dx500 at a concentration at 0.5 g dl(-1) gives the best result in improving light penetration depth through the blood. The increase of light transmission at the beginning of the addition of dextrans is mainly attributed to refractive index matching between the scattering centres and the ground matter. Thereafter, the transmission change is probably due to a dextran-induced aggregation-disaggregation effect. Overall, light scattering in the blood could be effectively reduced by the application of dextrans. It represents a promising approach to increasing the imaging depth for in vivo optical imaging of biological tissue, for example optical coherence tomography.

Guidance of aortic ablation using optical coherence tomography

PURPOSE

There is a significant need for an imaging modality that is capable of providing guidance for intravascular procedures, as current technologies suffer from significant limitations. In particular, laser ablation of in-stent restenosis, revascularization of chronic total occlusions, and pulmonary vein ablation could benefit from guidance. Optical coherence tomography (OCT), a recently introduced technology, is similar to ultrasound except that it measures the back-reflection of infrared light instead of sound. This study examines the ability of OCT to guide vascular laser ablation.

METHODS

Aorta samples underwent laser ablation using an argon laser at varying power outputs and were monitored with OCT collecting images at 4 frames. Samples were compared to the corresponding histopathology.

RESULTS

Arterial layers could be differentiated in the images sequences. This allowed correlation of changes in the OCT image with power and duration in addition to histopathology.

CONCLUSIONS

OCT provides real-time guidance of arterial ablation. At 4 frames, OCT was successfully able to show the microstructural changes in the vessel wall during laser ablation. Since current ablation procedures often injure surrounding tissue, the ability to minimize collateral damage to the adjoining tissue represents a useful advantage of this system. This study suggests a possible role for OCT in the guidance of intravascular procedures.

The vulnerable plaque and acute coronary syndromes

The interaction between the vulnerable atherosclerotic plaque and thrombus formation, a process referred to as atherothrombosis, is the cornerstone of acute coronary syndromes. Advances in noninvasive imaging have helped to identify novel approaches to plaque stabilization, with the potential to prevent plaque rupture, including lifestyle modification and dietary adjustments, as well as pharmacologic interventions such as statins. Following an acute coronary event, strategies combining mechanical and pharmacologic therapies provide considerable advances in prevention of subsequent cardiac events. Pharmacologic strategies to prevent and treat thrombotic complications related to acute coronary syndromes have been developed to dissolve preformed thrombi and to inhibit thrombogenesis. These regimens focus on inhibiting thrombin, preventing thrombi generation, blocking the initiation of coagulation, inhibiting platelet activation, and increasing fibrinolysis.

Characterizing arterial plaque with optical coherence tomography

Many imaging technologies have been pivotal in the reduction of mortality associated with coronary artery disease over the last 50 years. However, there are several areas where coronary disease could benefit from high-resolution imaging. Recently, optical coherence tomography (OCT) has been introduced for micron scale intravascular imaging. OCT is analogous to ultrasonography, measuring the intensity of back-reflected infrared light rather than sound. First, its resolution, at 4 to 20 microm, is higher than that of any currently available imaging technology. Second, acquisition rates are near video speed. Third, unlike ultrasonography, OCT catheters consist of simple fiber optics and contain no transducers within their frame. This makes imaging catheters both inexpensive and small, the current smallest cross-sectional diameter being 0.014 inches. Fourth, OCT systems are compact and portable. Finally, it can be combined with a range of spectroscopic techniques. This article reviews the application of OCT to intracoronary imaging.

Atherothrombotic plaques and the need for imaging

The assessment of atherothrombotic plaques by imaging techniques is essential for the in vivo identification of vulnerable plaques. Several invasive and noninvasive imaging techniques are available to assess atherothrombotic disease. The use of some of the available imaging modalities for the study of regression and progression of atherothrombosis are described in more detail in the subsequent articles.

Use of a blood substitute to determine instantaneous murine right ventricular thickening with optical coherence tomography

BACKGROUND

A satisfactory imaging technique to determine regional wall thickening of the murine myocardium is not available. Although cardiovascular imaging with light offers a novel solution, application is problematic because scattering by erythrocytes causes significant optical attenuation.

METHODS AND RESULTS

Optical coherence tomography (OCT) is a technique for detailed resolution imaging of highly scattering biological tissues. To reduce the high level of blood scattering, a method was devised whereby murine blood was replaced with a hemoglobin-based blood substitute. The scattering and absorption properties of in vitro preparations of whole blood and dilutions of blood with a blood substitute were determined with a spectrophotometer and an inverse-adding doubling algorithm. OCT imaging of the same dilutions demonstrated a significant reduction in scattering at a hematocrit <5%. A fiber-optic OCT imaging system was used to image the murine right midventricular free wall before and after isovolumic replacement with blood substitute. Strong light attenuation prevented full thickness imaging before replacement, whereas visualization of the full ventricular thickness was possible after replacement. Baseline and imaging hematocrits were 52.4+/-3.8% and 3.7+/-1.2%, respectively. End-systolic and end-diastolic thickness values were 0.458+/-0.051 mm and 0.352+/-0.047 mm. Percent thickening fraction was 30.8+/- 7.5%.

CONCLUSION

Optical imaging of the intact beating murine right ventricle was substantially improved by isovolumic blood replacement with a hemoglobin-based blood substitute. Although the current study has been directed toward imaging the murine heart, a blood substitute may be applied to various optical diagnostic and therapeutic techniques under investigation in cardiovascular medicine.

Image processing techniques for noise removal, enhancement and segmentation of cartilage OCT images

Osteoarthritis, whose hallmark is the progressive loss of joint cartilage, is a major cause of morbidity worldwide. Recently, optical coherence tomography (OCT) has demonstrated considerable promise for the assessment of articular cartilage. Among the most important parameters to be assessed is cartilage width. However, detection of the bone cartilage interface is critical for the assessment of cartilage width. At present, the quantitative evaluations of cartilage thickness are being done using manual tracing of cartilage-bone borders. Since data is being obtained near video rate with OCT, automated identification of the bone-cartilage interface is critical. In order to automate the process of boundary detection on OCT images, there is a need for developing new image processing techniques. In this paper we describe the image processing techniques for speckle removal, image enhancement and segmentation of cartilage OCT images. In particular, this paper focuses on rabbit cartilage since this is an important animal model for testing both chondroprotective agents and cartilage repair techniques. In this study, a variety of techniques were examined. Ultimately, by combining an adaptive filtering technique with edge detection (vertical gradient, Sobel edge detection), cartilage edges can be detected. The procedure requires several steps and can be automated. Once the cartilage edges are outlined, the cartilage thickness can be measured.

Dynamic optical coherence tomography in studies of optical clearing, sedimentation, and aggregation of immersed blood

The concept of refractive-index matching to enhance the optical penetration depth of whole blood is discussed on the basis of in vitro studies that used the technique of near-infrared optical coherence tomography. It was found that optical clearing of blood is defined not only by refractive-index matching but also by changes in the size of red blood cells and in their aggregation ability when chemicals are added. For example, in whole blood diluted to twice its volume by saline with the addition of 6.5% glycerol, the total attenuation coefficient was reduced from 4.2 to 2.0 mm(-1), and the optical penetration at 820 nm was correspondingly increased to 117%. For the other agents tested (glucose, dextrans, propylene glycol, and trazograph) the enhancement of penetration was 20-150.5%. In the blood sedimentation study, regular or irregular oscillations or jumps of the red-blood cell-plasma boundary were observed. The 1-min time period of regular oscillations correlated well with the kinetics of the aggregation process as described by the two subsequent stages of formation of linear and three-dimensional aggregates. The results also showed that optical clearing of blood by osmotic agents is potentially useful not only in blood sedimentation and aggregation studies but also in intravascular optical coherence tomography imaging techniques.

Optical coherence tomography of the biliary tree during ERCP

BACKGROUND

Optical coherence tomography (OCT) is a high-resolution imaging technique that produces cross-sectional images in vivo. This is a report of the first use of OCT to acquire images of the biliary tree during ERCP.

METHODS

A 2.6-mm diameter OCT catheter delivered through the accessory channel of a duodenoscope was used to acquire images of the intrahepatic and extrahepatic bile ducts in 5 patients. Histology-correlated OCT images of 5 cadaveric livers, each imaged at 3 sites, were used to guide interpretation of the in vivo images.

RESULTS

Biliary ductal epithelium and subepithelial structures, including peribiliary glands, vasculature, and hepatic parenchyma, were visualized in vivo. The papillary architecture of cholangiocarcinoma was identified by OCT. There were no OCT-related complications.

CONCLUSIONS

High-resolution OCT imaging of the biliary tree is feasible and may provide useful diagnostic information during ERCP.

New understanding of atherosclerosis (clinically and experimentally) with evolving MRI technology in vivo

Atherosclerosis and its thrombotic complications are the major cause of morbidity and mortality in industrialized countries. Despite advances in our understanding of the pathogenetic mechanisms and new treatment modalities, the absence of an adequate noninvasive method for early detection limits the prevention or treatment of patients with various degrees and localizations of atherothrombotic disease. High-resolution magnetic resonance (MR) has recently emerged as one of the most promising techniques for the noninvasive study of atherothrombotic disease. Most importantly, MR can be used to characterize plaque composition and monitor progression. Thus, MR opens new strategies, ranging from the screening of high-risk patients for early detection and treatment as well as the monitoring of target areas for pharmacological intervention.

The use of mechanical devices as adjuncts to intracoronary stenting

A number of mechanical adjuncts to intracoronary stenting are now available to the interventional cardiologist. These devices have assisted in the development of a safer and more effective stenting practice. Intravascular ultrasound-guided stenting has been shown to reduce the rate of subacute thrombosis and subsequent restenosis. It allows a greater appreciation of lesion structure and severity so that an appropriate intervention strategy can be devised. Debulking techniques may allow the optimal deployment of stents so that restenosis is reduced; however, the results of large randomized studies are still awaited. The use of thrombectomy and distal embolization protection devices is emerging as a safer alternate to stenting alone in difficult patient subsets, such as those with thrombus-laden lesions and degenerated vein grafts. Doppler and pressure wires may be useful in determining optimal stent deployment and predict subsequent patient outcomes. An understanding of the indications and limitations of these devices is of increasing importance to the interventional cardiologist as the coming decade threatens to yield an impressive array of high-tech innovations.

Clinical imaging of the high-risk or vulnerable atherosclerotic plaque

The study of atherosclerotic disease during its natural history and after therapeutic intervention will enhance our understanding of disease progression and regression and aid in selecting appropriate treatments. Several invasive and noninvasive imaging techniques are available to assess atherosclerotic vessels. Most of the standard techniques identify luminal diameter, stenosis, wall thickness, and plaque volume; however, none can characterize plaque composition and therefore identify the high-risk plaques. We will present the different imaging modalities that have been used for the direct assessment of the carotid, aortic, and coronary atherosclerotic plaques. We will review in detail the use of high-resolution, multicontrast magnetic resonance for the noninvasive imaging of vulnerable plaques and the characterization of plaques in terms of their various components (ie, lipid, fibrous, calcium, or thrombus).

Index matching to improve optical coherence tomography imaging through blood

BACKGROUND

Most myocardial infarctions are caused by the rupture of small rather than large plaques in the arteries of the heart that are beyond the detection limit of current technologies.

METHODS AND RESULTS

Recently, optical coherence tomography (OCT) has demonstrated considerable potential as a method for high-resolution assessment of vulnerable plaque. However, intravascular OCT imaging is complicated by the need to remove blood from the imaging field because blood results in substantial signal attenuation. This work examines index matching as a method for increasing penetration. Index matching is based on the hypothesis that the predominant source of scattering in blood is the difference in refractive index between the cytoplasm of erythrocytes and serum. By increasing the refractive index of serum to a value near that of the cytoplasm, or index matching, scattering can be substantially reduced. The concept was tested with a system that pumped blood in vitro through transparent tubing. The test compounds, dextran and intravenous contrast agent, both led to significant improvements in penetration (69+/-12% and 45+/-4%). No significant effect was seen with the saline control. For dextran, the effect could not be attributed to reductions of red cell number or volume because changes in these parameters were not different from the control. In the case of intravenous contrast, a small but significant relative reduction in red cell volume was seen.

CONCLUSIONS

This study demonstrates the feasibility of index matching for improving OCT imaging through blood. Future studies are required to identify compounds for effective index matching in vivo.

New developments in the detection of vulnerable plaque

Failure of coronary angiography (luminography) in prediction of future acute coronary syndromes has cast a shadow of doubt over the value of this old gold-standard technique. The fact that angiographically invisible or nonsignificant lesions cause the majority of acute coronary syndromes has driven scientists to develop new diagnostic methods. In this article, we review the ongoing worldwide research on both invasive techniques (such as intravascular angioscopy and colorimetry, ultrasound, thermography, optical coherence tomography, near infrared spectroscopy, Raman spectroscopy, fluorescence emission spectroscopy, elastography, magnetic resonance imaging and spectroscopy, nuclear immunoscintigraphy, electrical impedance imaging, vascular tissue doppler, and shear stress imaging) and noninvasive techniques (such as MRI, contrast-enhanced MRI with and without immunolabeled agents, electron beam computed tomography, multi-slice spiral / helical computed tomography, and nuclear imaging, including positron emission tomography). Each of these techniques and their potential combination holds promise for characterization of plaques responsible for acute coronary syndromes, namely vulnerable plaque.

Evaluation of the adaptive speckle suppression filter for coronary optical coherence tomography imaging

During the last few years, optical coherence tomography (OCT) has demonstrated considerable promise as a method of high-resolution intravascular imaging. The goal of this study was to apply and to test the applicability of the rotating kernel transformation (RKT) technique to the speckle reduction and enhancement of OCT images. The technique is locally adaptive. It is based on sequential application of directional masks and selection of the maximum of all outputs. This method enhances the image features by emphasizing thin edges while suppressing a noisy background. Qualitatively, the RKT algorithm provides noticeable improvement over the original image. All processed images are smoother and have better-defined borders of media, intima, and plaque. The quantitative evaluation of RKT performance showed that in terms of average contrast-to-noise ratio, there is a significant improvement in image quality between original and enhanced images. The RKT image enhancement technique shows great promise in improving OCT images for superior boundary identification.