Functional evaluation of intracranial atherosclerotic stenosis by pressure ratio measurements

Abstract

Background: Fractional flow reserve is widely used for the functional evaluation of coronary artery stenosis. Some studies have similarly used the translesional pressure ratio measurements for the functional evaluation of intracranial atherosclerotic stenosis. In this paper, we aimed to investigate the relationship between pressure ratio and cerebral tissue perfusion by MR perfusion imaging and provided a non-invasive method for evaluating the functional significance of intracranial atherosclerotic stenosis.

Methods: A total of 18 consecutive patients with intracranial atherosclerotic stenosis patients including 19 stenotic vessels were recruited. The pressure was measured using a pressure guidewire, the pressure ratio before and after the endovascular intervention was calculated and compared with the severity of diameter stenosis and perfusion-derived MR (the time to maximum tissure residue function (Tmax)). Moreover, the DSA-derived pressure ratio was computed using a novel computational fluid dynamics-based model, termed CFD-PR, and was compared with the actual pressure ratio to assess its diagnostic accuracy.

Results: The pressure ratio increased after percutaneous transluminal angioplasty or stenting, while the correlation between pressure ratio and diameter stenosis was not significant. The pressure ratio was negatively correlated with Tmax (r = -0.73, P < 0.01), and a 95% confidence interval for the cutoff value of pressure ratio = 0.67 (95% confidence interval: 0.58-0.76) was suggested. There was a good correlation (mean = 0.02, Spearman's correlation coefficient r = 0.908, P < 0.001) and agreement (limits of agreement: -0.157 to 0.196, P = 0.954) between CFD-PR and the actual pressure ratio.

Conclusions: This exploratory study indicates the pressure ratio may correlate with the perfusion status. The pressure ratio can be calculated through a non-invasive method using a computational fluid dynamics-based method.

Keywords: CFD, computational fluid dynamics; Cerebral ischemia; Computational fluid dynamics; DSA, digital subtraction angiography; FFR, fractional flow reserve; Fractional flow reserve; ICAS, intracranional flow reserve; Intracranial atherosclerotic stenosis; PCI, percutaneous coronary intervention; PR, pressure ratio; PTA, the percutaneous transluminal angioplasty; Pressure ratio; Tmax, the time to maximum tissue residue function.

Fig. 1

3D model reconstruction based on 3D angiography of intracranial arterial stenosis. A) DSA image of an intracranial arterial stenosis. B) Segmented 3D intracranial arterial stenosis. C) Vascular meshing. D) Distribution of pressure ratio (PR) results obtained by computational fluid dynamics analysis.

Fig. 2

Clinical application of PR in intracranial arterial stenosis. A) Scatterplot showing the value of PR increased from 0.53 ± 0.17 preprocedually to 0.79 ± 0.11 after PTA, and 0.84 ± 0.06 after stenting (P < 0.01). B) Scatterplot showing the relationship between PR and diameter stenosis (r = −0.15, P = 0.55). C) Scatterplot showing PR was significantly negatively correlated with Tmax (r = −0.73, P < 0.01). When Tmax＞6 s was selected as the intentional indication in our study, we got the cut-off PR value of 0.67 (95% CI: 0.58–0.76).

Fig. 3

Good correlation and agreement between CFD-PR and actual PR. A) Correlation between CFD-PR measurement and AccuFFRicas (r = 0.96, p < 0.0001). B) Agreement between CFD-PR measurement and AccuFFRicas values (limits of agreement: -0.151 to 0.149, P = 0.954).