Computer-Assisted Three-Dimensional Morphology Evaluation of Intracranial Aneurysms

Abstract

Objective: Precise morphologic evaluation is important for intracranial aneurysm (IA) management. At present, clinicians manually measure the IA size and neck diameter on 2-dimensional (2D) digital subtraction angiographic (DSA) images and categorize the IA shape as regular or irregular on 3-dimensional (3D)-DSA images, which could result in inconsistency and bias. We investigated whether a computer-assisted 3D analytical approach could improve IA morphology assessment.

Methods: Five neurointerventionists evaluated the size, neck diameter, and shape of 39 IAs using current and computer-assisted 3D approaches. In the computer-assisted 3D approach, the size, neck diameter, and undulation index (UI, a shape irregularity metric) were extracted using semiautomated reconstruction of aneurysm geometry using 3D-DSA, followed by IA neck identification and computerized geometry assessment.

Results: The size and neck diameter measured using the manual 2D approach were smaller than computer-assisted 3D measurements by 2.01 mm (P < 0.001) and 1.85 mm (P < 0.001), respectively. Applying the definitions of small IAs (<7 mm) and narrow-necked IAs (<4 mm) from the reported data, interrater variation in manual 2D measurements resulted in inconsistent classification of the size of 14 IAs and the necks of 19 IAs. Visual inspection resulted in an inconsistent shape classification for 23 IAs among the raters. Greater consistency was achieved using the computer-assisted 3D approach for size (intraclass correlation coefficient [ICC], 1.00), neck measurements (ICC, 0.96), and shape quantification (UI; ICC, 0.94).

Conclusions: Computer-assisted 3D morphology analysis can improve accuracy and consistency in measurements compared with manual 2D measurements. It can also more reliably quantify shape irregularity using the UI. Future application of computer-assisted analysis tools could help clinicians standardize morphology evaluations, leading to more consistent IA evaluations.

Keywords: Aneurysm shape; Computer-assisted 3-dimensional; Intracranial aneurysm; Morphology; Size measurement.

Figure 1:

Computer-assisted three-dimensional (3D) morphology workflow. The workflow includes: A) importing 3D images, to import 3D Digital Imaging and Communications in Medicine (DICOM) images of the intracranial aneurysm (IA); B) segmentation, to generate a 3D geometry of the intracranial aneurysm (IA); C) pre-processing, to isolate the region of interest and remove small vessel branches; D) morphologic analysis, to analyze the IA geometry and extract morphologic parameters.

Figure 2:

Comparison of current clinical practice and computer-assisted 3D approaches for IA morphology evaluation. A) manual measurements of an internal carotid artery (ICA) aneurysm obtained from two-dimensional digital subtraction angiography (2D-DSA) and visual inspection of IA shape on 3D-DSA. B) Computer-assisted 3D size and neck measurements and quantification of shape of the same aneurysm using the undulation index (UI).

Figure 3:

Scattergrams of size (A) and neck diameter (B) measured using manual 2D and computer-assisted 3D approaches. Each data point represents the average of measurements taken by five raters. A line connects data points for the same IA. The dashed lines represent the 7mm IA size threshold for small to larger classification (A) and the 4mm IA neck diameter threshold for narrow- and wide-necked classifications (B).

Figure 4:

Scattergrams of manual 2D and computer-assisted 3D measurements of the sizes of 39 IAs. The dashed line represents the generally accepted 7mm IA size threshold for small to large classification.

Figure 5:

Scattergrams of manual 2D and computer-assisted 3D measurements of neck diameter of 39 IAs. The dashed line represents the accepted 4mm threshold for narrow- and wide-necked classification. The cross-signs (×) in A indicate that the aneurysm neck was not detectable in 4 of the 2D images; only 3D computer-assisted measurements are reported for those cases.

Figure 6:

Comparison of the UI between “regular” and “irregular” shaped IAs. Aneurysms classified “regular” and “irregular” by all the raters are identified by white circles and black triangles, respectively. Gray squares indicate shapes that were not agreed upon.