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

Abstract

Background and PurposeThe 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.Materials and MethodsImages 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.ResultsThe 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).ConclusionOur 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.

Volume variation may be a relevant metric in the study of aneurysm pulsatility: a study using ECG-gated 4D-CTA (PULSAN)

“…In our sample, the mean variation of the volume was 10.9% (95% CI 4% to 17%), but caution must be taken considering the variety in size of the aneurysms. Previous studies such as that by Illies et al 17 also investigated aneurysm volumetric changes during the cardiac cycle and concluded that volume changes remained unsettled considering the lack of a pulsation-like volume curve during the cardiac cycle and the lack of a gold standard with which to compare. They used a half-reconstruction mode (using half of the projections during the acquisition), which is known for inducing noise, consequently complicating the aneurysmal segmentation process 24.…”

“…All phases were reconstructed with a slice thickness of 0.5 mm and a 0.5 mm interval, 0.3×0.3 mm in-plane resolution, with a convolution filter (FC 43) designed for vascular imaging and hybrid iterative reconstruction performed with AIDR3D (Adaptive Iterative Dose Reduction 3D). The AIDR3D algorithm is based on iterative reconstruction, allowing dose and noise reductions 17 18. The pre-contrast volume was used to remove all the bony structures in the 20 arterial phases using subtraction techniques (figure 1).…”

“…Very few studies have reported a quantitative evaluation of intracranial aneurysmal motion during the cardiac cycle. Previous studies have raised concern that observed volume changes can be induced by noise rather than true pulsation 16 17…”

“…4D-CTA acquisition allows the measurement of various two-dimensional and three-dimensional metrics during the cardiac cycle. Considering potential technical limitations in spatial and temporal resolution, this study focused on the maximal changes of these metrics over the cardiac cycle rather than their dynamics 16 17. Our goal is to identify which metrics vary the most during the cardiac cycle and which ones have the best reproducibility during one and multiple cardiac cycles.…”

Analysis of the influence of imaging-related uncertainties on cerebral aneurysm deformation quantification using a no-deformation physical flow phantom

“…Window/level settings are usually operator-specifically chosen. The resulting images and segmented structures are then used to calculate changes in volume over time or the like 16 – 18 . Such methods are, however, observer-dependent (in the case of a manual selection of thresholds).…”