Feasibility of Quantification of Intracranial Aneurysm Pulsation with 4D CTA with Manual and Computer-Aided Post-Processing

<div><p>Background and Purpose</p><p>The analysis of the pulsation of unruptured intracranial aneurysms might improve the assessment of their stability and risk of rupture. Pulsations can easily be concealed due to the small movements of the aneurysm wall, making post-processing highly demanding. We hypothesized that the quantification of aneurysm pulsation is technically feasible and can be improved by computer-aided post-processing.</p><p>Materials and Methods</p><p>Images of 14 cerebral aneurysms were acquired with an ECG-triggered 4D CTA. Aneurysms were post-processed manually and computer-aided on a 3D model. Volume curves and random noise-curves were compared with the arterial pulse wave and volume curves were compared between both post-processing modalities.</p><p>Results</p><p>The aneurysm volume curves showed higher similarity with the pulse wave than the random curves (Hausdorff-distances 0.12 vs 0.25, p<0.01). Both post-processing methods did not differ in intra- (r = 0.45 vs r = 0.54, p>0.05) and inter-observer (r = 0.45 vs r = 0.54, p>0.05) reliability. Time needed for segmentation was significantly reduced in the computer-aided group (3.9 ± 1.8 min vs 20.8 ± 7.8 min, p<0.01).</p><p>Conclusion</p><p>Our results show pulsatile changes in a subset of the studied aneurysms with the final prove of underlying volume changes remaining unsettled. Semi-automatic post-processing significantly reduces post-processing time but cannot yet replace manual segmentation.</p></div

Workflow on the 3D+t model: On axial images the vasculature is defined with a threshold (green).

<p>To reduce computation time for the 3D+t model, the volume for post-processing is reduced by placing a VOI over the aneurysm (A). The resulting 3D+t model can be rotated, translated and zoomed (B). Segmentation points are placed on the aneurysms neck (C) and the aneurysm (green) is separated from the parent vessel (red) and the volume and surface is calculated (D).</p

Aneurysm characteristics.

<p>Aneurysm characteristics.</p

Boxplots of Hausdorff distances between the volume curves and random curves and the pulse wave on the right and left-hand side (0.12 vs 0.25, p<0.01).

<p>Boxplots of Hausdorff distances between the volume curves and random curves and the pulse wave on the right and left-hand side (0.12 vs 0.25, p<0.01).</p

Results of the intraobserver (mean±LOA -0.02 ± 0.11 vs. 0.01 ± 0.11, upper row) and interobserver agreements (mean±LOA 0.007 ± 0.11 vs. -0.01 ± 0.12 lower row) for the 2D post-processing (right) and 3D+t post-processing (left).

<p>Results of the intraobserver (mean±LOA -0.02 ± 0.11 vs. 0.01 ± 0.11, upper row) and interobserver agreements (mean±LOA 0.007 ± 0.11 vs. -0.01 ± 0.12 lower row) for the 2D post-processing (right) and 3D+t post-processing (left).</p

Relative volume changes of all 14 aneurysms with manual segmentation.

<p>Aneurysms 1, 2, 5, and 8 show a pulsation-like profile. Plot number 15 shows the cumulative pulsation of all aneurysms.</p

Mixed model coefficients for correlation of perfusion parameters in NAWM with WM and atrophy measurements (all models adjusted for age, gender and time).

<p>Abbreviations: CBV = cerebral blood volume, CBF = cerebral blood flow, CI = confidence interval, T2-LV = T2 hyperintense lesion volume, T1-LV = T1 hypointense lesion volume, Gd-LV = contrast enhancing lesion volume, WMV = white matter volume, GMV = gray matter volume, EDSS = Expanded Disability Status Scale</p><p>Mixed model coefficients for correlation of perfusion parameters in NAWM with WM and atrophy measurements (all models adjusted for age, gender and time).</p

Temporal evolution of perfusion parameters in NAWM comparing high inflammatory with low inflammatory patients: a) CBV, b) CBF.

<p>Temporal evolution of perfusion parameters in NAWM comparing high inflammatory with low inflammatory patients: a) CBV, b) CBF.</p

Segmentation results of white matter CBV (a,b) and CBF (c,d) maps with excluded lesions (NAWM) in a single low inflammatory and high inflammatory patient.

<p>Exemplary regions of interest drawn in the left frontal white matter of each individual map show elevated mean CBV (9.61 ± 1.35 vs 7.22 ± 0.77 ml/100g) and CBF (46.47 ±6.93 vs. 39.42 ± 6.32 ml/100g/min) in high inflammatory patients.</p