Standard CTs with contrast also include timing issues and recons/reformats. Only in CTA, however, is 3-D rendering a required element. This corresponds to the definitions that CMS has applied to the CPT codes. CTA imaging may be performed as a single arterial phase, biphasic study (noncontrast and arterial or arterial and delayed phases), or as a triphasic study (noncontrast, arterial, and delayed phases). To reduce the cumulative lifetime radiation dose of patients undergoing CTA surveillance, several authors have proposed eliminating either AAA: Interventional Planning & Follow-Up the arterial phase [37] or delayed phase [38,39], although one author has suggested eliminating noncontrast scans from all surveillance examinations with the exception of an initial 1-month follow-up [40]. Several studies have reported significant dose reduction using dual-energy CT with acquisition of delayed-phase images only [41,42]. Accompanying software allows for the isolation of iodine from a selected region and enables reconstruction of virtual noncontrast images. A colored overlay can be applied to voxels containing iodine, rendering detection of contrast material within the aneurysm sac external to the stent-graft more visible [41]. Dual-phase dual-energy CT can potentially reduce the radiation dose by 19.5% when compared to a standard triphasic CT examination [34]. Additional dose reduction techniques include the use of automatic exposure control and iterative reconstruction algorithms [34]. Determining the optimal dose-efficient CT technique is a work in progress that will continue to evolve with increased experience and technological advancement. Aortography Aortography is an invasive imaging modality that can accurately assess aortic side branch patency, knowledge of which is crucial for deployment of conventional and fenestrated endografts with or without bridging stents.
Abdominal Aortic Aneurysm or Dissection Interventional Planning and Follow up. Standard CTs with contrast also include timing issues and recons/reformats. Only in CTA, however, is 3-D rendering a required element. This corresponds to the definitions that CMS has applied to the CPT codes. CTA imaging may be performed as a single arterial phase, biphasic study (noncontrast and arterial or arterial and delayed phases), or as a triphasic study (noncontrast, arterial, and delayed phases). To reduce the cumulative lifetime radiation dose of patients undergoing CTA surveillance, several authors have proposed eliminating either AAA: Interventional Planning & Follow-Up the arterial phase [37] or delayed phase [38,39], although one author has suggested eliminating noncontrast scans from all surveillance examinations with the exception of an initial 1-month follow-up [40]. Several studies have reported significant dose reduction using dual-energy CT with acquisition of delayed-phase images only [41,42]. Accompanying software allows for the isolation of iodine from a selected region and enables reconstruction of virtual noncontrast images. A colored overlay can be applied to voxels containing iodine, rendering detection of contrast material within the aneurysm sac external to the stent-graft more visible [41]. Dual-phase dual-energy CT can potentially reduce the radiation dose by 19.5% when compared to a standard triphasic CT examination [34]. Additional dose reduction techniques include the use of automatic exposure control and iterative reconstruction algorithms [34]. Determining the optimal dose-efficient CT technique is a work in progress that will continue to evolve with increased experience and technological advancement. Aortography Aortography is an invasive imaging modality that can accurately assess aortic side branch patency, knowledge of which is crucial for deployment of conventional and fenestrated endografts with or without bridging stents.