3D Image Fusion to Localise Intercostal Arteries During TEVAR.

PURPOSE: Preservation of intercostal arteries during thoracic aortic procedures reduces the risk of post-operative paraparesis. The origins of the intercostal arteries are visible on pre-operative computed tomography angiography (CTA), but rarely on intra-operative angiography. The purpose of this report is to suggest an image fusion technique for intra-operative localisation of the intercostal arteries during thoracic endovascular repair (TEVAR). TECHNIQUE: The ostia of the intercostal arteries are identified and manually marked with rings on the pre-operative CTA. The optimal distal landing site in the descending aorta is determined and marked, allowing enough length for an adequate seal and attachment without covering more intercostal arteries than necessary. After 3D/3D fusion of the pre-operative CTA with an intra-operative cone-beam CT (CBCT), the markings are overlaid on the live fluoroscopy screen for guidance. The accuracy of the overlay is confirmed with digital subtraction angiography (DSA) and the overlay is adjusted when needed. Stent graft deployment is guided by the markings. The initial experience of this technique in seven patients is presented. RESULTS: 3D image fusion was feasible in all cases. Follow-up CTA after 1 month revealed that all intercostal arteries planned for preservation, were patent. None of the patients developed signs of spinal cord ischaemia. CONCLUSION: 3D image fusion can be used to localise the intercostal arteries during TEVAR. This may preserve some intercostal arteries and reduce the risk of post-operative spinal cord ischaemia.

Predisposing Factors for Re-interventions with Additional Iliac Stent Grafts After Endovascular Aortic Repair.

BACKGROUND: Endoleaks of type Ib and III are relatively common causes of re-intervention after EVAR. The aim was to determine underlying causes and identify anatomical factors associated with these re-interventions. METHODS: A total of 444 patients with standard bifurcated stent grafts were included in a retrospective observational study. Patients requiring additional iliac stent grafts (n = 24) were compared to those who did not (n = 420). Pre- and post-operative CT examinations were reviewed in patients with additional iliac stents. Reasons for re-interventions were defined as migration (>5 mm at the distal end or at interconnections), progression of disease (iliac artery diameter exceeding graft diameter), inadequate distal seal length at primary repair, or a combination of these factors. RESULTS: Twenty-four patients received 31 additional grafts in 30 limbs after a median 46 months (range 2-92 months). Five re-interventions (21%) were due to rupture. Re-intervened limbs had a larger iliac artery diameter 18 mm (25th and 75th percentile 20-25) versus 15 mm (13-18 mm), p < .001. The degree of iliac limb oversizing at primary EVAR was lower in re-intervened patients (11% (8-18%) versus 18% (12-26%), p = .003). In re-intervened patients, iliac attachment zones were shorter in treated limbs than in untreated 23 mm (11-34) versus 34 mm (25-44), p < .001). Sixteen of 31 re-interventions (51%) were caused by migration (10 at the distal landing site, 6 at interconnections), nine of 31 (29%) by disease progression, and nine of 31 (29%) had inadequate initial stent graft placement. Three of 31 re-interventions (10%) were done as proactive procedures. CONCLUSIONS: Additional iliac stent grafting occurred late after primary repair; a considerable number were caused by rupture. A low degree of oversizing, migration at the distal landing site, separation of stent graft interconnections, disease progression at the distal landing site, and inadequate initial stent graft placement may all contribute. Patients with large iliac dimensions and short attachment zones may need a larger degree of oversizing and more vigorous surveillance.

Orthogonal Rings, Fiducial Markers, and Overlay Accuracy When Image Fusion is Used for EVAR Guidance.

OBJECTIVE: Evaluation of orthogonal rings, fiducial markers, and overlay accuracy when image fusion is used for endovascular aortic repair (EVAR). METHODS: This was a prospective single centre study. In 19 patients undergoing standard EVAR, 3D image fusion was used for intra-operative guidance. Renal arteries and targeted stent graft positions were marked with rings orthogonal to the respective centre lines from pre-operative computed tomography (CT). Radiopaque reference objects attached to the back of the patient were used as fiducial markers to detect patient movement intra-operatively. Automatic 3D-3D registration of the pre-operative CT with an intra-operative cone beam computed tomography (CBCT) as well as 3D-3D registration after manual alignment of nearby vertebrae were evaluated. Registration was defined as being sufficient for EVAR guidance if the deviation of the origin of the lower renal artery was less than 3 mm. For final overlay registration, the renal arteries were manually aligned using aortic calcification and vessel outlines. The accuracy of the overlay before stent graft deployment was evaluated using digital subtraction angiography (DSA) as direct comparison. RESULTS: Fiducial markers helped in detecting misalignment caused by patient movement during the procedure. Use of automatic intensity based registration alone was insufficient for EVAR guidance. Manual registration based on vertebrae L1-L2 was sufficient in 7/19 patients (37%). Using the final adjusted registration as overlay, the median alignment error of the lower renal artery marking at pre-deployment DSA was 2 mm (0-5) sideways and 2 mm (0-9) longitudinally, mostly in a caudal direction. CONCLUSION: 3D image fusion can facilitate intra-operative guidance during EVAR. Orthogonal rings and fiducial markers are useful for visualization and overlay correction. However, the accuracy of the overlaid 3D image is not always ideal and further technical development is needed.