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Intravascular ultrasound (IVUS) is a catheter-based coronary imaging technique. It utilises the emission & subsequent detection of reflected high frequency (30-60 MHz) sound waves to create high resolution, cross-sectional images of the coronary artery. IVUS has been the cornerstone of intracoronary imaging for more than two decades. When compared to the invasive coronary angiogram which studies only the silhouette of the contrast-filled artery lumen, IVUS also crucially images the vessel wall. Because of this capability, IVUS has greatly facilitated understanding of the coronary atherosclerosis process. Such insights from IVUS reveal how commonly and extensively plain angiography underestimates the true extent of coronary plaque, the characteristics of plaques prone to rupture and cause acute coronary syndromes (lipid rich, thin cap atheroma), and a realisation of the widespread occurrence of vessel remodelling in response to atherosclerosis. Similarly, IVUS has historically provided salutary mechanistic insights that have guided many of the incremental advances in the techniques of percutaneous coronary intervention (PCI). Examples include mechanisms of in-stent restenosis, and the importance of high-pressure post-dilatation of stents to ensure adequate stent apposition and thereby reduce the occurrence of stent thrombosis. IVUS also greatly facilitates the choice of correct diameter and length of stent to implant. Overall, a compelling body of evidence indicates that use of intravascular ultrasound in PCI helps to achieve optimal technical results and to mitigate the risk of adverse cardiac events. In this review, the role of intravascular ultrasound as an adjunct to PCI in complex coronary lesions is explored. The complex coronary situations discussed are the left main stem, ostial stenoses, bifurcation stenoses, thrombotic lesions, the chronically occluded coronary artery, and calcified coronary artery disease. By thorough review of the available evidence, we e

Intravascular ultrasound (IVUS) is a catheter-based coronary imaging technique. It utilises the emission & subsequent detection of reflected high frequency (30-60 MHz) sound waves to create high resolution, cross-sectional images of the coronary artery. IVUS has been the cornerstone of intracoronary imaging for more than two decades. When compared to the invasive coronary angiogram which studies only the silhouette of the contrast-filled artery lumen, IVUS also crucially images the vessel wall. Because of this capability, IVUS has greatly facilitated understanding of the coronary atherosclerosis process. Such insights from IVUS reveal how commonly and extensively plain angiography underestimates the true extent of coronary plaque, the characteristics of plaques prone to rupture and cause acute coronary syndromes (lipid rich, thin cap atheroma), and a realisation of the widespread occurrence of vessel remodelling in response to atherosclerosis. Similarly, IVUS has historically provided salutary mechanistic insights that have guided many of the incremental advances in the techniques of percutaneous coronary intervention (PCI). Examples include mechanisms of in-stent restenosis, and the importance of high-pressure post-dilatation of stents to ensure adequate stent apposition and thereby reduce the occurrence of stent thrombosis. IVUS also greatly facilitates the choice of correct diameter and length of stent to implant. Overall, a compelling body of evidence indicates that use of intravascular ultrasound in PCI helps to achieve optimal technical results and to mitigate the risk of adverse cardiac events. In this review, the role of intravascular ultrasound as an adjunct to PCI in complex coronary lesions is explored. The complex coronary situations discussed are the left main stem, ostial stenoses, bifurcation stenoses, thrombotic lesions, the chronically occluded coronary artery, and calcified coronary artery disease. By thorough review of the available evidence, we e

Atherosclerotic disease and its thrombotic complications remain the leading causes of mortality and morbidity in Western society. In Australia, cardiovascular disease is responsible for one in every 2.4 (41%) deaths and is the leading single cause of mortality. The crucial final common process for the conversion of a non-occlusive, often clinically silent, atherosclerotic lesion to a potentially fatal condition is plaque disruption. The mortality associated with atherosclerotic disease relates to the acute coronary syndromes, including acute myocardial infarction, unstable angina pectoris and sudden cardiac death. There is substantial clinical, experimental and post-mortem evidence demonstrating the role acute thrombosis upon a disrupted atherosclerotic plaque plays in the onset of acute coronary syndromes. Atherosclerotic plaque composition, rather than the stenotic severity, appears to be central in determining risk of both plaque rupture and subsequent thrombogenicity. In particular, a large lipid core and a thin fibrous cap render an atherosclerotic lesion susceptible or vulnerable to these complications. We are currently limited in our ability to accurately identify patients at risk for an acute coronary event. The armamentarium of diagnostic investigations, both non-invasive and invasive, currently clinically available is only able to provide us with data related to the stenotic severity of a coronary artery. The non-invasive testing includes stress-induced (exercise or pharmacological) ischaemic changes in electrical repolarisation, wall motion or myocardial radioactive-tracer uptake. The invasive test of coronary angiography, although the current 'gold standard' for the detection of coronary atherosclerotic disease, provides us with no data about the composition of the atherosclerotic lesion. However, the vast majority of acute coronary events involve a non-critically stenosed atherosclerotic lesion, and thus with currently available means of identification

Atherosclerotic disease and its thrombotic complications remain the leading causes of mortality and morbidity in Western society. In Australia, cardiovascular disease is responsible for one in every 2.4 (41%) deaths and is the leading single cause of mortality. The crucial final common process for the conversion of a non-occlusive, often clinically silent, atherosclerotic lesion to a potentially fatal condition is plaque disruption. The mortality associated with atherosclerotic disease relates to the acute coronary syndromes, including acute myocardial infarction, unstable angina pectoris and sudden cardiac death. There is substantial clinical, experimental and post-mortem evidence demonstrating the role acute thrombosis upon a disrupted atherosclerotic plaque plays in the onset of acute coronary syndromes. Atherosclerotic plaque composition, rather than the stenotic severity, appears to be central in determining risk of both plaque rupture and subsequent thrombogenicity. In particular, a large lipid core and a thin fibrous cap render an atherosclerotic lesion susceptible or vulnerable to these complications. We are currently limited in our ability to accurately identify patients at risk for an acute coronary event. The armamentarium of diagnostic investigations, both non-invasive and invasive, currently clinically available is only able to provide us with data related to the stenotic severity of a coronary artery. The non-invasive testing includes stress-induced (exercise or pharmacological) ischaemic changes in electrical repolarisation, wall motion or myocardial radioactive-tracer uptake. The invasive test of coronary angiography, although the current 'gold standard' for the detection of coronary atherosclerotic disease, provides us with no data about the composition of the atherosclerotic lesion. However, the vast majority of acute coronary events involve a non-critically stenosed atherosclerotic lesion, and thus with currently available means of identification

Rupture of vulnerable plaques is the main cause of acute coronary syndrome and myocardial infarction. Identification of vulnerable plaques is therefore essential to enable the development of treatment modalities to stabilize such plaques. Several diagnostic methods are currently tested to detect vulnerable plaques. Angiography has a low discriminatory power to identify the vulnerable plaque, but does provide information about the entire coronary tree and serves as guide for invasive imaging techniques and therapy. Angioscopy offers a direct visualization of the plaque surface and intra- luminal structures like thrombi and tears. However, angioscopy is difficult to perform, invasive and only the proximal part of the vessels can be investigated. IVUS (intravascular ultrasound) provides some insight into the composition of plaques. The detection of vulnerable plaques is mainly based on series of case reports with a lack of prospectivity and follow-up. Palpography, an IVUS derived technique, reveals information, which is not recognizable in IVUS. It can differentiate between deformable and non-deformable tissue, which enables the technique to detect vulnerable plaques with a positive predictive value. The clinical value of palpography is currently under investigation. Thermography assesses the temperature heterogeneity as an indicator of the metabolic state of the plaque. A coincidence of temperature rise and localization of vulnerable plaque was suggested. OCT (optical coherence tomography) can provide images with ultrahigh resolution utililizing the back-reflection of near-infrared light from optical interfaces in tissue. Drawbacks are the low penetration depth into tissue and the absorbance of light by blood. Raman spectroscopy can provide quantification about the molecular composition of the plaque. Long acquisition time, the low penetration depth and light absorbance by blood limit the performance of the technique. Another light emitting technique is NIR (near infr

Cerebrovascular disease, in particular intracranial atherosclerotic stenosis and cerebral aneurysm, is a common cause of stroke, which is the third leading cause of death in many places including Hong Kong. Understanding the geometric char-acteristics of those lesions is an essential part of diagnosis and endovascular treat-ment planning. In the clinical environment, quantitation of the lesions is often conducted on 2-D digital subtraction angiography (DSA). The quantitation may suffer from the foreshortening effect due to inappropriate X-ray projection angle selection and the non-linear magnification caused by the perspective projection. The technological advances in 3-D medical imaging open up new opportunities for the elucidation of the lesion characteristics. This motivates us to develop three novel algorithms for the segmentation of vessels and vascular lesions in 3-D angiography. The first and the second algorithms are low-level segmentation algorithms aiming at producing angiographic segmentation for the third algorithm to per-form high-level segmentation of the atherosclerotic plaque volume and aneurysm body from the diseased portion of the arteries. Such an approach enables later in-teractive or automatic quantitative analyses on the pathological structures. In an in vivo study with nearly twenty angiograms, the results show that our method can help increase the measurement repeatability of the clinical parameters by more than ten times. Therefore, we believe that the works presented can help elucidate the lesion characteristics for diagnosis of the cerebrovascular diseases and endovascular treatment planning. Lastly, the direction of future studies is discussed in this dissertation.

Cerebrovascular disease, in particular intracranial atherosclerotic stenosis and cerebral aneurysm, is a common cause of stroke, which is the third leading cause of death in many places including Hong Kong. Understanding the geometric char-acteristics of those lesions is an essential part of diagnosis and endovascular treat-ment planning. In the clinical environment, quantitation of the lesions is often conducted on 2-D digital subtraction angiography (DSA). The quantitation may suffer from the foreshortening effect due to inappropriate X-ray projection angle selection and the non-linear magnification caused by the perspective projection. The technological advances in 3-D medical imaging open up new opportunities for the elucidation of the lesion characteristics. This motivates us to develop three novel algorithms for the segmentation of vessels and vascular lesions in 3-D angiography. The first and the second algorithms are low-level segmentation algorithms aiming at producing angiographic segmentation for the third algorithm to per-form high-level segmentation of the atherosclerotic plaque volume and aneurysm body from the diseased portion of the arteries. Such an approach enables later in-teractive or automatic quantitative analyses on the pathological structures. In an in vivo study with nearly twenty angiograms, the results show that our method can help increase the measurement repeatability of the clinical parameters by more than ten times. Therefore, we believe that the works presented can help elucidate the lesion characteristics for diagnosis of the cerebrovascular diseases and endovascular treatment planning. Lastly, the direction of future studies is discussed in this dissertation.

Cerebrovascular disease, in particular intracranial atherosclerotic stenosis and cerebral aneurysm, is a common cause of stroke, which is the third leading cause of death in many places including Hong Kong. Understanding the geometric char-acteristics of those lesions is an essential part of diagnosis and endovascular treat-ment planning. In the clinical environment, quantitation of the lesions is often conducted on 2-D digital subtraction angiography (DSA). The quantitation may suffer from the foreshortening effect due to inappropriate X-ray projection angle selection and the non-linear magnification caused by the perspective projection. The technological advances in 3-D medical imaging open up new opportunities for the elucidation of the lesion characteristics. This motivates us to develop three novel algorithms for the segmentation of vessels and vascular lesions in 3-D angiography. The first and the second algorithms are low-level segmentation algorithms aiming at producing angiographic segmentation for the third algorithm to per-form high-level segmentation of the atherosclerotic plaque volume and aneurysm body from the diseased portion of the arteries. Such an approach enables later in-teractive or automatic quantitative analyses on the pathological structures. In an in vivo study with nearly twenty angiograms, the results show that our method can help increase the measurement repeatability of the clinical parameters by more than ten times. Therefore, we believe that the works presented can help elucidate the lesion characteristics for diagnosis of the cerebrovascular diseases and endovascular treatment planning. Lastly, the direction of future studies is discussed in this dissertation.

Angiographic images are routinely acquired for the medical diagnosis of arterial diseases. The digital images are in the form of three-dimensional (3D) volume, which consists of a stack of slices. Because of the lack of 3D information in those angiographic slices, radiologists generate maximum intensity project ion (MIP) images at different view angles to facilitate the diagnosis. This two-dimensional (2D) representation of the arterial morphology creates ambiguities in the assessment of position and size of arterial abnormalities. The motivation of this work stems from the clinical need for a 3D representation of the vascular structure. In this work, two new segmentation techniques are presented for extracting 3D vessels from angiographic images and can be used complementarily. The first technique extracts 3D vessels based on MIP images using a unified platform to segment different kinds of angiograms; the second technique refines an initial 3D vascular segmentation based on orientation tensor used to analyze the local structure of the arterial morphology. Initial segmentation is then refined on a probabilistic framework based on local structure descriptions. We take the maximum a posteriori (MAP)-Markov random field (MRF) approach to solve the segmentation problem. The benefits of our segmentation techniques are twofold: (1) different kinds of angiograms are segmented with a unified algorithm; and (2) only intrinsic information (local structure) from arterial morphology is used to extract 3D vessels. Experimental results on time-of-flight (TOF) magnetic resonance angiography (MRA), phase contrast (PC) MRA and 3D rotational angiography (RA) show that our algorithms outperform other methods in extracting vascular structures with low signal-to-noise ratios (SNR), e.g., small vessels and vessel edges.

Angiographic images are routinely acquired for the medical diagnosis of arterial diseases. The digital images are in the form of three-dimensional (3D) volume, which consists of a stack of slices. Because of the lack of 3D information in those angiographic slices, radiologists generate maximum intensity project ion (MIP) images at different view angles to facilitate the diagnosis. This two-dimensional (2D) representation of the arterial morphology creates ambiguities in the assessment of position and size of arterial abnormalities. The motivation of this work stems from the clinical need for a 3D representation of the vascular structure. In this work, two new segmentation techniques are presented for extracting 3D vessels from angiographic images and can be used complementarily. The first technique extracts 3D vessels based on MIP images using a unified platform to segment different kinds of angiograms; the second technique refines an initial 3D vascular segmentation based on orientation tensor used to analyze the local structure of the arterial morphology. Initial segmentation is then refined on a probabilistic framework based on local structure descriptions. We take the maximum a posteriori (MAP)-Markov random field (MRF) approach to solve the segmentation problem. The benefits of our segmentation techniques are twofold: (1) different kinds of angiograms are segmented with a unified algorithm; and (2) only intrinsic information (local structure) from arterial morphology is used to extract 3D vessels. Experimental results on time-of-flight (TOF) magnetic resonance angiography (MRA), phase contrast (PC) MRA and 3D rotational angiography (RA) show that our algorithms outperform other methods in extracting vascular structures with low signal-to-noise ratios (SNR), e.g., small vessels and vessel edges.

The development of atherectomy catheters and their use in clinical practice during percutaneous revascularization procedures permitted the analysis of the pathophysiology of obstructive coronary disease in vivo. The various clinical presentations of coronary disease are related to distinct morphological aspects of the culprit coronary stenosis as assessed by angiography, angioscopy or intravascular ultrasound imaging. Analysis of plaque fragments revealed the underlying histopathology. Restenotic lesions following various mechanical interventions have been studied in detail both in native coronary arteries and in bypass conduits. The biological reaction to implantation of endovascular stents involves inflammation around the stent wires as well as smooth muscle cell proliferation. Specific processes such as nitric oxide production or the activity of intramural proteases can be characterized and contribute to identify targets for future pharmacological therapy.

Intravascular angioscopy has been hampered by its limitation in quantifying obtained images. To circumvent this problem, a lightwire was used, which projects a ring of light onto the endoluminal wall in front of the angioscope. This investigation was designed to quantify luminal dimensions of casts from stenotic human coronary arteries and to investigate the feasibility of performing volume reconstruction. Angioscopic video recordings were made during simultaneous motorized pullback (2 mm/s) of an angioscopic catheter and light-emitting fiber through 4 epoxy casts from human coronary arteries. Quantification of the images was performed using a computerized cross-sectional area measurement system. The coronary casts were divided into cross-sectional segments of 4 to 10 mm in thickness, with the true volume of each segment determined by means of a microdispenser. Because of vessel curvature and luminal narrowing, complete visualization of the ring of light at all 1-mm-distant locations was only possible in 19 of 40 segments. For these 19 segments, linear regression analysis showed a

OBJECTIVES: This study was undertaken to compare coronary angioscopy with angiography for the detection of intimal dissection and intracoronary thrombus. BACKGROUND. It has been demonstrated previously that coronary angioscopy provides more intravascular detail than cineangiography. Both imaging methods have to be compared directly to assess the additional diagnostic value of angioscopy. METHODS. The angiograms and videotapes of 52 patients who had undergone angioscopy were reviewed independently by two observers unaware of other findings. Classic angiographic definitions were used for dissection and thrombus. Angioscopic dissection was defined as visible cracks or fissures on the lumen surface or mobile protruding structures that are contiguous with the vessel wall. Angioscopic thrombus was defined as a red, white or mixed red and white intraluminal mass. RESULTS. Angiography and angioscopy were in agreement in 40.4% of cases in the absence of thrombus and in 11.5% in the presence of thrombus. No fewer than 25 (48.1%) angioscopically observed thrombi remained undetected at angiography. With angioscopy as the standard, although the specificity of angiography for thrombus was 100%, sensitivity was very low at 19%. Angioscopic dissection was present in 40 patients (76.9%) versus angiographic dissection in 15 patients (28.8%). With regard to dissection, there was no correlation between the two imaging methods (r phi = 0.15, p = 0.29). CONCLUSIONS. Coronary angiography underestimates the presence of intracoronary thrombus. Angioscopy and angiography are complementary techniques for detecting and grading intimal dissections.

We report on the use of intravascular ultrasound, coronary angioscopy and on-line quantitative angiography in an unstable patient soon after myocardial infarction. Combined intracoronary imaging made it possible to solve the therapeutic problem posed by an unusual angiographic appearance secondary to intracoronary thrombolysis during coronary recanalization. The pathological validation of the observations performed with angioscopy and intravascular ultrasound was made possible with the concomitant use of directional atherectomy.

The efficacy of radiofrequency (RF) angioplasty for recanalization of arterial thrombosis was assessed angioscopically in five dogs. A thrombus was induced by balloon injury of the left femoral artery. Within two hr, thrombi led to total occlusion of the artery in three dogs, subtotal occlusion in one, and about 70% obstruction in one. A metal-tipped catheter, with a tip size of 2.0mm×5.7mm, was advanced into the thrombus and RF at 13.56MHz was delivered repeatedly with gradually increased energies. The arterial lumina were recanalized or enlarged in all dogs. The thrombus surface had a shaggy appearance, and were dark (charring), or mixed dark and white in color. There were relatively large variations in the energies required; 140J in one, 200J in two and 250J in two. The present results suggest that trombotic arterial occlusion, such as acute occlusion complicating balloon angioplasty, can be treated with RF thermal angioplasty. Angioscopy provided detailed information about thrombus surfaces. The variations in required energies indicate the inability to control the thermal effect by energy settings alone. A more sophisticated method such as measurement of tip temperature will be able to overcome this difficulty.