Abdominal Aortic Aneurysm:

Standard or Endoluminal Repair?

Patient History

Ambiguity regarding aneurysmal involvement of the bifurcation persisted despite shaded surface display rendering. Analysis of reformatted oblique planes through the volume of interest defined an insufficient distal neck for seating an endoluminal stent graft. The patient was treated by conventional surgical aneurysm replacement.

Mpeg Movies

Original Reconstructed Helical CT data set

The original trans axial, 79 slice, 2mm thick Toshiba Helical CT data set of a patient with an abominal aortic aneurysm reconstructed with a 1:1 pitch at 1mm increments. Isoview 370 was the contrast used. Note: this scan could have been improved by instucting the patient not to breath during the scan. To obtain a good volumetric scan, instructing the patient not to move and not to breath is extremely important.

Maximum Intensity Projection

Maximum Intensity Projections (MIPs) can be used to get a general feeling for the geometry of an aneurysm if contrast has been administered during the scan. Accurate depiction of the aneursym is dependent upon the the inner wall of the aneurysm being close to the outer wall. Aneurysms with extensive thrombus may not appear aneurysmal at all when analyzed by MIPs alone. Note also the bright spots in the iliac arteries shown nicely in the side MIP views; they are calcium deposits probably due to atherosclerosis.

Shaded Surface Display (SSD)

Shaded Surface Displays (SSDs) are often useful to surgeons to gain preoperative knowledge about the aneurysm and its relationship to other important structures. Accurate depiction is dependent upon the accurate segmentation of the outer wall of the aneurysm and associated vessels.

Oblique Images

First a coronal image through the aneurysm was obtained using oblique sections. Next an oblique through middle of the bifurcation into the iliac arteries along the local long axis of the aorta was generated. A movie was generated consisting of oblique images 0.468 mm apart perpendicular to the local long axis of the aorta. The oblique images were necessary to determine how long a segment of healthy vessel was present below the aneurysm but above the bifurcation. The oblique images showed the aorta distal to the aneurysm, before the bifurcation was less than 1 cm which was determined to be less than adequate for placement of a simple tube stent.

Tube Geometry Measurements

The outer wall measurement of the aneurysm was measured to be approximately 4.8 cm using Tube Geometry Analysis. The tube geometry module of VIDA automatically calculates the centerline of the tubular structure (aorta, airway, carotids, vocal tract, etc) and then calculates a set of oblique sections which are each perpendicular to the local airway centerline. A graphic display of the tube cross sectional area vs distance along the tube is generated, and when the user points to any portion of the graph, the associated oblique section is displayed along with the numberical values of interest which include area, A-P and Lateral diameters, maximum and minimum diameters. For tortuous aortic regions, this objective means of obtaining aneurysmal area is imperative for informed clinical decisions. (see our SPIE paper on this subject).