Quantifying irregular pulsation of intracranial aneurysms using 4D-CTA

Abstract

Recent studies have suggested that irregular pulsation of intracranial aneurysm during the cardiac cycle may be potentially associated with aneurysm rupture risk. However, there is a lack of quantification method for irregular pulsations. This study aims to quantify irregular pulsations by the displacement and strain distribution of the intracranial aneurysm surface during the cardiac cycle using four-dimensional CT angiographic image data. Four-dimensional CT angiography was performed in 8 patients. The image data of a cardiac cycle was divided into approximately 20 phases, and irregular pulsations were detected in four intracranial aneurysms by visual observation, and then the displacement and strain of the intracranial aneurysm was quantified using coherent point drift and finite element method. The displacement and strain were compared between aneurysms with irregular and normal pulsations in two different ways (total and stepwise). The stepwise first principal strain was significantly higher in aneurysms with irregular than normal pulsations (0.20±0.01 vs 0.16±0.02, p=0.033). It was found that the irregular pulsations in intracranial aneurysms usually occur during the consecutive ascending or descending phase of volume changes during the cardiac cycle. In addition, no statistically significant difference was found in the aneurysm volume changes over the cardiac cycle between the two groups. Our method can successfully quantify the displacement and strain changes in the intracranial aneurysm during the cardiac cycle, which may be proven to be a useful tool to quantify intracranial aneurysm deformability and aid in aneurysm rupture risk assessment.

Keywords: 4D-CTA; Intracranial aneurysm; Irregular pulsation; Strain.

Fig. 1.

The two-point clouds, the fixed-point cloud (green) and the moving-point cloud (purple): (a) The two-point clouds before motion tracking and (b) The two-point clouds after motion tracking. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2.

Self-validation results for the relative spatial variation in displacement compared to Phase 1: (a) Phase 5 as reference; (b) Phase 9 as reference; (c) Phase 13 as reference; and (d) Phase 17 as reference.

Fig. 3.

The displacement results from compression stages 1 to 6: (a) Displacement field computed by OpenCorr; (b) Displacement field computed by CPD-FEM (coherent point drift finite element method) and (c) Comparison of displacement difference from OpenCorr and CPD-FEM results with error colour bar.

Fig. 4.

The intracranial aneurysms with irregular pulsation: (a) Patient 1, (b) Patient 2, (c) Patient 3, and (d) Patient 4.

Fig. 5.

The analysis results of patient-specific intracranial aneurysms with irregular pulsation, the original geometry (1st column) and black circles show the irregular pulsations region; space displacement (2nd column); space strain (3rd column); first principal strain (4th column); and Von Mises strain (5th column): (a) Patient 1; (b) Patient 2; (c) Patient 3 and (d) Patient 4.

Fig. 5.

The analysis results of patient-specific intracranial aneurysms with irregular pulsation, the original geometry (1st column) and black circles show the irregular pulsations region; space displacement (2nd column); space strain (3rd column); first principal strain (4th column); and Von Mises strain (5th column): (a) Patient 1; (b) Patient 2; (c) Patient 3 and (d) Patient 4.

Fig. 6.

(a) Volume variation during the cardiac cycle; (b) to (e) Volume change during the cardiac cycle of aneurysms with irregular pulsations and blue markers showing the presence of irregular pulsations. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)