Intravascular Ultrasound

Intravascular ultrasound (IVUS) is a cardiovascular imaging technology using a specially designed catheter with a miniaturized ultrasound probe for the assessment of vascular anatomy with detailed visualization of arterial layers. Over the past two decades, this technology has developed into an indispensable tool for research and clinical practice in cardiovascular medicine, offering the opportunity to gather diagnostic information about the process of atherosclerosis in vivo, and to directly observe the effects of various interventions on the plaque and arterial wall. This book aims to give a comprehensive overview of this rapidly evolving technique from basic principles and instrumentation to research and clinical applications with future perspectives

Reconstruction of coronary arteries from X-ray angiography: A review.

Despite continuous progress in X-ray angiography systems, X-ray coronary angiography is fundamentally limited by its 2D representation of moving coronary arterial trees, which can negatively impact assessment of coronary artery disease and guidance of percutaneous coronary intervention. To provide clinicians with 3D/3D+time information of coronary arteries, methods computing reconstructions of coronary arteries from X-ray angiography are required. Because of several aspects (e.g. cardiac and respiratory motion, type of X-ray system), reconstruction from X-ray coronary angiography has led to vast amount of research and it still remains as a challenging and dynamic research area. In this paper, we review the state-of-the-art approaches on reconstruction of high-contrast coronary arteries from X-ray angiography. We mainly focus on the theoretical features in model-based (modelling) and tomographic reconstruction of coronary arteries, and discuss the evaluation strategies. We also discuss the potential role of reconstructions in clinical decision making and interventional guidance, and highlight areas for future research

Intravascular ultrasound: a technique in evolution: methodological considerations

As the title of the thesis suggests, intravascular ultrasound has been, and continues to be, an imaging technique that is in active evolution. Image quality has improved dramatically from the crude, low resolution 'black and white' images of the first generation of intravascular ultrasound scanners and transducers are now small enough to image most arteries before intervention. Although intravascular ultrasound is increasingly seen as the most informative method of assessing the coronary arteries, there are outstanding problems that must be addressed and overcome before its full potential can be achieved.The aim of this thesis is to examine a number of these methodological shortcomings of intravascular ultrasound so that appropriate solutions can be found.After a general overview, provided in Chapter 1, the reproducibility of intravascular ultrasound quantitation is assessed in Chapter 2. For reasons elaborated above, ultrasound is seen as the best technique to study the acute and long term outcome of coronary interventions and the effect of plaque modifying agents. Without detailed data concerning its reproducibility, such studies are uninterpretable.Chapter 3 deals with the impact of catheter malfunction on the geometric integrity of intravascular ultrasound images. At present, the mechanical ultrasound devices are the most widely used systems. All mechanical systems are potentially subject to the problem of non -uniform rotation of the transducer, and to date its impact has been poorly characterised.The difficulty encountered in discriminating unstable coronary lesions is examined in Chapter 4. There is a widely held view that acute coronary lesions cannot be discriminated using intravascular ultrasound. Specific echographic markers are described that are found in the majority of unstable lesions. Close scrutiny of grey scale images allows identification of acute lesions and may allow discrimination of thrombus from underlying atheromatous plaque.In the last two chapters, methodological issues relating to the clinical application of intravascular ultrasound in guiding coronary stenting are explored. In chapter 5, the findings of an observational study confirm the potential of intravascular ultrasound to provide additional information in cases in which favourable angiographic appearances have been achieved. However, the choice of one particular 'expansion index' over another is seen to impact significantly on the proportion of lesions that are judged to be successful. Before ultrasound guidance based on the attainment of specific quantitative expansion criteria be advocated as a widely applied technique, the reproducibility of reference segment measurements must be known. This issue is studied in chapter 6.Separate studies are described in each of the data chapters. A similar layout is employed in each, consisting of the study aims, methods, findings, discussion and conclusion. At the risk of introducing a degree of repetition in the methods sections of each chapter, the ultrasound examination and image interpretation protocol are elaborated in each case, as important differences exist between the studies

Magnetic resonance coronary vessel wall imaging with highly efficient respiratory motion correction

There is a need for a noninvasive imaging technique for use in longitudinal studies of sub-clinical coronary artery disease. Magnetic resonance (MR) can be used to selectively and non-invasively image the coronary wall without the use of ionising radiation. However, high-resolution 3D studies are often time consuming and unreliable, as data acquisition is generally gated to a small window of diaphragm positions around end-expiration which results in inherently poor and variable respiratory efficiency. This thesis describes the development and application of a novel technique (beat-to-beat respiratory motion correction (B2B-RMC)) for correcting respiratory motion in 3D spiral MR coronary imaging. This technique uses motion of the epicardial fat surrounding the artery as a surrogate for the motion of the artery itself and enables retrospective motion correction with respiratory efficiency close to 100%. This thesis first describes an assessment of the performance of B2B-RMC using a purpose built respiratory motion phantom with realistic coronary artery test objects. Subsequently, MR coronary angiography studies in healthy volunteers show that the respiratory efficiency of B2B-RMC far exceeds that of conventional navigator gating, yet the respiratory motion correction is equally effective. The performance and reproducibility of 3D spiral imaging with B2B-RMC for assessment of the coronary artery vessel wall is subsequently compared to that of commonly used 2D navigator gated techniques. The results demonstrate the high performance, reproducibility and reliability of 3D spiral imaging with B2B-RMC when data acquisition is gated to alternate cardiac cycles. Using this technique, a further in-vivo study demonstrates thickening of the coronary vessel wall with age in healthy subjects and these results are shown to be consistent with outward remodelling of the vessel wall. Finally, the performance of B2B-RMC in a variety of coronary vessel wall applications, including in a small cohort of patients with confirmed coronary artery disease, is presented

REAL-TIME 4D ULTRASOUND RECONSTRUCTION FOR IMAGE-GUIDED INTRACARDIAC INTERVENTIONS

Image-guided therapy addresses the lack of direct vision associated with minimally- invasive interventions performed on the beating heart, but requires effective intraoperative imaging. Gated 4D ultrasound reconstruction using a tracked 2D probe generates a time-series of 3D images representing the beating heart over the cardiac cycle. These images have a relatively high spatial resolution and wide field of view, and ultrasound is easily integrated into the intraoperative environment. This thesis presents a real-time 4D ultrasound reconstruction system incorporated within an augmented reality environment for surgical guidance, whose incremental visualization reduces common acquisition errors. The resulting 4D ultrasound datasets are intended for visualization or registration to preoperative images. A human factors experiment demonstrates the advantages of real-time ultrasound reconstruction, and accuracy assessments performed both with a dynamic phantom and intraoperatively reveal RMS localization errors of 2.5-2.7 mm, and 0.8 mm, respectively. Finally, clinical applicability is demonstrated by both porcine and patient imaging