Time resolved MRA can be critical for the proper identification of flow patterns (Fig. 4) within vascular lesions. Flow within various aortic pathologies is often faster than can be seen using slower high spatial resolution 3D CE MRA. Aneurysms and dissection, for example, often have important information revealed by watching their temporal filling patterns. The origin of the renal arteries, for example, may be misidentified as originating from the false lumen on conventional high spatial resolution 3D CE MRA. In these cases, time resolved imaging could often provide more conclusive information by revealing the actual filling pattern of the renal arteries either early from the true lumen or late via the false channel.
Although endovascular stent grafts are typically characterized by CTA, to meet investigational requirements for many multi-center clinical trials, some may be well visualized by MRA. However, make no mistake-not all stent grafts can be seen well on MR because of their associated T2* susceptibility artifacts. Certain stent grafts composed of novel materials such as nitinol produce less susceptibility artifacts that both extraluminal and intralu-minal areas of the stent graft can typically be evaluated by MRA and MRI. However, most stainless steel stent grafts produce significant signal loss and non-diagnostic images in the immediate vicinity of the stent graft. Other stents composed of elements and compounds such as nickel, and titanium are to a variable extent visualized on MR. Sub-second angiography may be a valuable tool in delineating collateral pathways (such as to lumbar arteries) of type 2 leaks . To this end, sub-second 3D MRA may even reveal direction of flow ("entry versus leak site") within these endoleaks helping to decide the best means of correction if necessary.
Was this article helpful?
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.