The advantages for using MRA as a noninvasive method for evaluating the extracranial carotid and vertebral vasculature are obvious. MRA is safer, faster and cheaper than traditional x-ray angiogra-phy, and avoids the complications inherent to invasive catheterization. Nowhere in the body is this more important than in evaluation of the supra-aortic vessels. Catheterization of the carotid and vertebral arteries can lead to cerebral complications, resulting in major neurologic disability or even death. Over the past fifteen years, a number of different MRA approaches have been explored for imaging the extracranial carotid and vertebral arteries. These include 3D time-of-flight (TOF), 3D phase contrast and 2D TOF imaging. Each has its advantages and disadvantages as will be discussed in the subsequent passages. Recently, arterial-phase bolus contrast enhanced MRA has rapidly evolved to the point where it is now the preferred method for cervical vascular evaluation. However, even this method has its limitations, resulting in its frequent combination with one or more of the above-mentioned techniques.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.