Digital Subtraction Arteriography

The impact of conventional arteriography upon management has been apparent for decades. Newer imaging techniques have not replaced conventional angiography in part because of the increasing use of transcatheter therapies. High spatial and contrast resolution even in severely calcified vasculature is an additional reason that conventional angiography has not been replaced.

Transstenotic pressure measurements with and without pharmacologic stress are useful for assessing the physiologic significance of observed lesions. A peak systolic pressure gradient of more than 10 mm Hg or a 5 mm Hg mean gradient is considered hemodynamically significant. A 10 to 15 mm Hg gradient after intraarterial administration of a vasodilator is also clinically significant.

Arterial access is usually achieved through a femoral approach, although catheter introductions through brachial or radial arteries are alternative routes. Arterial thrombosis, free hemorrhage or local hematoma, and distal embolization remain inherent risks of conventional angiography, occurring in up to 1% of studies. In general, these risks are minimized with careful, meticulous image-guided access techniques using ultrasound and fluoroscopy. Smaller sheath size and prompt sheath removal reduce vascular access complications.

Patients with borderline kidney function no longer pose as much of a challenge to conventional angiography because carbon dioxide DSA and catheter manometry provide the necessary image and physiologic data to guide therapy (Figure 1). Carbon dioxide can be safely used for all aortoiliac imaging and therapy, as well as for completion images when iodinated contrast use must be minimized. Carbon dioxide use is contraindicated for imaging the central nervous system.

Limitations of two-dimensional DSA have led to the development of three-dimensional (3-D) DSA and 3-D digital angiography techniques. 3-D digital angiography uses unsubtracted rotational images generated by rotating the angiography unit around the patient. This characterizes vessels and adjacent structures with the inherent advantage of lower radiation exposure without the misregistration artifacts that occur with DSA. The evolving technology of cone beam CT allows volumetric data to be acquired from a single rotation of the x-ray source and flat-panel detector in tandem around the stationary patient. These data are then reconstructed to provide images of quality that approach those achieved with CTA.

Advantages of DSA include excellent resolution and the ability for immediate therapeutic intervention. Disadvantages of DSA include risk of arterial injury and significant radiation exposure.

Computed Tomography Angiography

CTA was developed in the early 1990s following the introduction of spiral (or helical) CT scanning. CTA for vascular diagnosis has become the favored imaging modality for evaluating aortoiliac occlusive disease (Figures 2 to 6).

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