To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Recently, there has been increasing research and development in the field of ultrasound contrast agents because of new technologies which produce agents that are non-toxic and that persist in the circulation for the duration of a diagnostic examination. Particularly in the field of cerebrovascular ultrasound, these advances have led to a number of new applications. In patients with high-grade carotid artery stenosis, for example, contrast agents have been shown to be effective in improving diagnostic confidence. In transcranial Doppler examinations, their use can increase the technical success rate, reduce examination time, and enable colour Doppler flow imaging and pulsed Doppler systems to detect a greater number of intracranial vessels. Recent studies have documented the value of contrast imaging in characterizing intracranial aneurysms and arteriovenous malformations. New developments in ultrasound technology that exploit the oscillating properties of microbubbles may provide unique opportunities for non-invasive assessment of brain perfusion. To better understand how stabilized microbubbles produce contrast, and how ultrasound propagating parameters affect the performance of these agents, this chapter presents the physical basis of the interaction between the impinging ultrasound wave and the contrast agent. It summarizes current state-of-the-art applications for evaluation of cerebrovascular disease and describes new imaging techniques such as harmonic, pulse inversion, stimulated acoustic emission, and intermittent modes with an emphasis on their potential applications in neurosonology.
Ultrasound contrast agents
Commercially available contrast agents consist of microbubbles with average diameters from 3 μm to 6 μm in concentrations typically of the order of 108 microbubbles/millilitre.
Ultrasound provides a unique diagnostic perspective in cerebrovascular disorders, with extremely high temporal resolution and excellent spatial display of extracranial arteries, brain structures and cerebral vessels. This comprehensive text covers the fundamentals of ultrasound physics, new technology, and clinical applications in all ages. It provides a firm grounding in hemodynamics and describes computational models for study of the cerebral circulation. Extracranial applications in assessing the carotid and vertebral arteries are discussed in detail, as are intracranial Doppler applications in stroke, subarachnoid hemorrhage, arteriovenous malformations, interventional and surgical procedures, and the detection and monitoring of cerebral microembolism. These and other topics, both clinical and technical, are presented by leading authorities in the field, with extensive illustrations, and tables are included for the standardized classification of cerebrovascular diseases based on international consensus conferences. For clinicians and clinical neuroscientists this is the definitive reference text in cerebrovascular ultrasound.
Ultrasound, an imaging technique that is safe, reliable, and relatively inexpensive, has played an increasingly important role in evaluation of cerebrovascular diseases over the last decade. This modality provides morphological and functional information on arterial walls at sites prone to atherosclerosis and allows surveillance of quantitative measurements of disease progress. Ultrasound has assumed a key position in recent epidemiological studies and is being used increasingly for assessment of the efficacy of atherosclerosis prevention trials. New developments in ultrasound equipment and novel methods for three- and four-dimensional sonography have broadened the scope of imaging arterial walls, providing both enhanced information on disease progression as well as new insights into pathomechanisms of plaque embolization. The role of transcranial Doppler microembolism detection has been expanded and improved methods for distinguishing between artefact and microembolism have been introduced. Recent highlights in cerebrovascular ultrasound research include imaging methods for characterization of intracranial aneurysms, use of echocontrast agents for improved evaluation of acute stroke patients and harmonic imaging for depiction of brain perfusion. New functional transcranial Doppler applications that are complementary to position emission tomography and functional magnetic resonance imaging studies are evolving for evaluation of functional recovery after stroke, investigation of perfusion asymmetries during complex spatial tasks, and elucidation of temporal patterns of regional neuronal activity. Exciting new developments are under way to introduce low-frequency ultrasound as a therapeutic adjunct in acute thrombolysis, thus greatly expanding the role of cerebrovascular ultrasound in stroke care.
Although three-dimensional ultrasound has only recently been applied for investigation of cerebrovascular disease, conceptual and technical developments of a multidimensional approach to ultrasonographic visualization and volumetry have occurred over more than two decades. The earliest report of three-dimensional imaging with ultra sound appeared in 1956 and described a technique for stereoscopic observation of body structures (Howry et al., 1956). Several years later a 3D ultrasonographic system for display of the human orbit was reported (Baum & Greenwood, 1961). This technique obtained serial parallel ultrasound images and then created a three-dimensional display by stacking sequential photographic plates of the images. Later, Dekker and coworkers described 3D ultrasound imaging of the heart with a mechanical tracking device to register images for volume reconstruction (Dekker et al., 1974). Although rapid developments in ultrasound scanning equipment, computer hardware and software have occurred since then, the basic requirements for producing three-dimensional ultrasonographic reconstructions have not changed; adequate two-dimensional images, known spatial relationship and orientation of each 2D image to a common external reference point, and techniques for volume reconstruction and visualization. This chapter will review the various approaches to meeting these requirements for three-dimensional ultrasound and then discuss current and emerging cerebrovascular applications of this technology.
Ultrasound data acquisition
A key determinant in the quality of any three-dimensional ultrasound application is the ultrasound equipment delivering the images. During the last decade we have witnessed signficant improvement in ultrasonographic image quality, due to new advances in transducer design and to rapid developments in computer hardware allowing realtime implementation of complex pre- and postprocessing algorithms.
Although atherosclerotic cerebrovascular disease may remain asymptomatic for decades, its first manifestation as stroke can be severe, even deadly. Prevention of atherosclerotic disease or of its progression has, therefore, become an important goal in medicine. For the study of the prevention of atherosclerosis, it is necessary to assess not only the presence but also the severity of the disease in asymptomatic subjects. This requires an ethically acceptable technique that is safe, reliable, and relatively inexpensive. Most important, the method should provide morphological information of arterial walls at sites prone to atherosclerosis and allow surveillance of quantitative measurements of disease progress. These requirements for assessment of early cerebrovascular disease are met by high-resolution B-mode imaging of intima-media thickness (IMT) in the carotid arteries. This non-invasive technique has played a central role in many recent epidemiological studies and is being used increasingly for assessment of the efficacy of atherosclerosis prevention trials.
This chapter will summarize relevant pathophysiologic mechanisms leading to intima-media thickening, the nature of the ultrasonographic equivalent of IMT and methods for measurement of intima-media thickness. It will also outline sources of measurement variability, and hopefully provide a basis for interpretation of clinical studies using IMT as endpoints. It will then summarize current data on normal distribution values for IMT in the carotid arteries and on risk factors associated with increased IMT. This approach will serve as a framework for dealing with relevant questions on the value of IMT measurements and for elucidation of future goals in IMT research.