Imaging Protocols

To image the subclavian and brachial arteries a moderately thick slab of 80-90 mm is required. Pre- and post-contrast images are obtained during breath-hold to avoid image blurring of the in-trathoracic portions of the vessels. When a conventional gadolinium contrast agent is used a bolus of 0.1-0.2 mmol/kg is typically injected at an injection rate of 2-3 mL/sec.Venous overlay can be avoided by injecting the contrast agent in the contralateral arm. Use of a body phased array coil results in higher signal-to-noise ratios.

MRA of the hand vessels is still a challenge due to the limited arterial/venous time window and the need for high spatial resolution imaging [6,7]. The head coil or, preferably, a dedicated surface coil should be used to obtain images with as high a spatial resolution as possible. The arterio-venous transit time in the hands is short (approximately 12 seconds) and differs between the two hands in almost all cases (mean difference 4.5 seconds) [8]. Imaging of the arteries in the hand requires accurate timing of the start of image acquisition, preferably using a sequence with elliptically reordered k-space sampling. Wentz et al developed a promising technique for CE MRA of the hand vessels using timed arterial compression (tac-MRA) [9]. In this method, a blood-pressure cuff is placed around the upper arm and inflated after the first pass of contrast agent in order to arrest the flow in the arm. This lengthens the arterial-venous time window enabling a lengthening of the examination times in order to acquire images with higher spatial resolution than those obtained using standard first pass CE MRA without compression. Radial, ulnar and arch arteries also appear sharper with tac-MRA than with standard CE MRA.

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Essentials of Human Physiology

Essentials of Human Physiology

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.

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