Pitfalls and Limitations

Despite the encouraging results of initial evaluations, whole-bodyMR angiography faces some relevant limitations regarding spatial resolution for the depiction of tight stenoses and small vesselsin the lower legs. This has resulted in some over- and undergrading of disease. Potential advantages associated with the acquisition of higher resolution data sets are offset by the development of venous overlap. Hence, delineation of small arteries, particularly those potentially needed for surgical grafting, remains challenging with whole-body MR angiography [15], as well as with most other bolus-chase techniques [27].

Various strategies have been employed to achieve high-resolution peripheral MR angiogra-phy images without venous overlap. The mere increase in spatial resolution is not sufficient, as was recently illustrated [28]. The quality of the highresolution images of the calf arteries was both quantitatively and qualitatively inferior in comparison withthat of the standard protocol with an interpolated matrix. In addition, the longer acquisition times translated into considerable venous contamination of the high-resolution image set in comparisonwith the standard whole-body MR angiography protocol, therebyfurther reducing diagnostic confidence. The need for imagingat the two distal stations with high resolution is reflected by the localization of the infrapopliteal trifurcation in whole-bodyMR angiography; this important vascular region is acquired either at the penultimate or the last station, depending on the size of the patient. High resolution with submillimeter isotropic voxel size for the last station in multistation MR angiographyhas been described with parallel imaging techniques (eg, sensitivity encoding) [29] and thus might be extended to the last two stations in whole-body MR angiography.

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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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