Fast acquisition times are particularly valuable in patients with known TAAA or dissection with new symptoms, given the high acuity of these conditions in the event of disease extension or worsening. The precise and reproducible measurements of the aorta with CTA are valuable for monitoring aortic growth and interval changes [33,34]. Electrocardiographically (ECG)-gated or triggered CTA is an additional option that can be used to evaluate the ascending aorta in patients with concern for conversion of a dissection into a type A dissection or for aneurysmal enlargement of the ascending aorta. With ECG gating, artifact from aortic pulsation is reduced and maximum interobserver variability of 1.2 mm in the ascending aorta has been reported, emphasizing the reproducibility of CTA [31,34]. Acquisition of thin axial slices with subsequent 3-D reconstruction along with homogenous luminal opacification allows for precise measurements and assessment of aortic anatomy, using postprocessing software for vessel analysis. Along with low interobserver variability, this allows for an excellent ability to detect changes in the aortic diameter or extent of dissection [31,33,34]. Furthermore, CTA can readily detect complications including thoracoabdominal aneurysm rupture or dissection extension causing malperfusion of the supra-aortic branch vessels, mesenteric arteries, renal arteries, lower extremities, or coronary arteries [31,35]. CTA has also been used in certain situations to predict enlargement of saccular aneurysms using flow dynamics [36]. Compared with CTA of the chest and abdomen, imaging of the pelvis carries the benefit of evaluation of the iliofemoral vessels to evaluate the extent of dissection or aneurysmal dilatation and suitability for possible endovascular intervention.
Thoracoabdominal Aneurysm or Dissection Treatment Planning and Follow Up. Fast acquisition times are particularly valuable in patients with known TAAA or dissection with new symptoms, given the high acuity of these conditions in the event of disease extension or worsening. The precise and reproducible measurements of the aorta with CTA are valuable for monitoring aortic growth and interval changes [33,34]. Electrocardiographically (ECG)-gated or triggered CTA is an additional option that can be used to evaluate the ascending aorta in patients with concern for conversion of a dissection into a type A dissection or for aneurysmal enlargement of the ascending aorta. With ECG gating, artifact from aortic pulsation is reduced and maximum interobserver variability of 1.2 mm in the ascending aorta has been reported, emphasizing the reproducibility of CTA [31,34]. Acquisition of thin axial slices with subsequent 3-D reconstruction along with homogenous luminal opacification allows for precise measurements and assessment of aortic anatomy, using postprocessing software for vessel analysis. Along with low interobserver variability, this allows for an excellent ability to detect changes in the aortic diameter or extent of dissection [31,33,34]. Furthermore, CTA can readily detect complications including thoracoabdominal aneurysm rupture or dissection extension causing malperfusion of the supra-aortic branch vessels, mesenteric arteries, renal arteries, lower extremities, or coronary arteries [31,35]. CTA has also been used in certain situations to predict enlargement of saccular aneurysms using flow dynamics [36]. Compared with CTA of the chest and abdomen, imaging of the pelvis carries the benefit of evaluation of the iliofemoral vessels to evaluate the extent of dissection or aneurysmal dilatation and suitability for possible endovascular intervention.