Robust cerebrovascular blood velocity and flow rate estimation from 4D‐CTA

Abstract

Purpose Blood velocity and flow rate information may be helpful for a wide variety of applications, but it often requires separate acquisitions. The dynamic information combined with the high spatial resolution of four‐dimensional computed tomography angiography (4D‐CTA) offers the possibility to quantify blood flow simultaneous to vascular anatomy. Methods A 4D‐CTA clinical protocol with a novel dedicated postprocessing were validated in vitro in a patient‐specific model, and tested in a pilot study of six patients. Blood flow was assessed in both internal carotid (ICAs) and vertebral (VAs) arteries by analyzing spatial displacement of contrast agent in the form of time‐intensity curves (TICs). Unlike previous approaches, it does not require any a priori assumptions about TIC shape, but rather computes mean velocity and flow rates from the spatial displacement of the TICs along the automatically segmented vessels. Results In vitro experiments showed good agreement between 4D‐CTA and flowmeter measurements under steady and pulsatile flow conditions. In vivo measurements exhibited large interpatient variability of the TIC shapes, from which blood flow rates could nevertheless be successfully measured in all patients and investigated vessels. On average, measured flow rates were 3.2 ± 0.7 ml/s (in ICAs) and 1.3 ± 0.8 ml/s (in VAs) consistent with previous reference standards. Contrary to our novel approach, which considered the full TIC shape, application of previous time‐to‐peak analyses based on idealized TIC shapes showed limited reliability. Conclusions We demonstrate the high potential of 4D‐CTA for assessing blood velocity and flow rate in addition to anatomical evaluation. The wide variety of TIC shapes encountered in vivo highlights the importance of an adaptive TIC analysis as proposed in the present work.

4D-CT angiography versus 3D-rotational angiography as the imaging modality for computational fluid dynamics of cerebral aneurysms

“…As demonstrated in this study and by others, the length of proximal anatomy that is kept and where the parent artery is clipped can impact calculation of the inlet diameter and influence the flow rate depending on the estimation method used (ie, power laws) 21 28. 4D-CTA may remove this bias by providing accurate (in vitro validated) flow rate calculations 12…”

“…Also, although not statistically significant, there was a trend towards 4D-CTA models underestimating aneurysm sac volumes and overestimating aneurysm neck size, particularly for smaller aneurysms. One could speculate that the variance was due to differences in spatial resolution (4D-CTA 0.5 mm vs 3D-RA 0.15–0.35 mm); however, our group and others previously performed in vitro experiments using aneurysm models and showed that vessel diameters were consistent between both imaging modalities 10 12. Another possibility is that injection of the large contrast bolus by the automatic injector pump during the 3D-RA acquisition was causing an enlargement of the proximal ICA due to compliance of the vessels.…”

“…Because these inflow rates depended on inlet diameter, they might be different between the 4D-CTA and 3D-RA models for a given patient. The second set of 'matched' models were simulated using the same assumed waveform shape, but now scaled to the corresponding patient-specific cycle-averaged flow rate calculated from 4D-CTA blood velocity measurements 12. In other words, for each patient, the 'matched' 4D-CTA and 3D-RA models had the same inflow rates.…”

“…In an attempt to improve the current CFD workflow, we propose utilization of novel four-dimensional CT angiography (4D-CTA) imaging for aneurysm hemodynamic analysis. 4D-CTA is a time-resolved volumetric CT imaging sequence that produces angiographic images free from bone with good spatial resolution (0.5 mm 3 resolution), from which patient-specific cycle average flow rates can be reliably calculated 12. Although the image resolution is inferior to 3D-RA (the current gold standard for CFD; 0.15–0.35 mm 3 resolution), 4D-CTA is advantageous as it is non-invasive and provides accurate patient-specific flow rate information that 3D-RA does not.…”

Irregular Pulsation of Intracranial Aneurysm Detected by Four-Dimensional CT Angiography and Associated With Small Aneurysm Rupture: A Single-Center Prospective Analysis

“…Conventional morphological parameters, such as aneurysm irregularity, aneurysm location, and size ratio, are associated with aneurysm rupture (4,6); however, these parameters are confounding and controversial (8). Fourdimensional CT angiography (4D-CTA) can acquire timeresolved three-dimensional reconstructions to get geometric and hemodynamic information on and quantification of aneurysm volume changes during cardiac cycle (9)(10)(11). Recent studies have reported that irregular pulsation observed by 4D-CTA could be a novel imaging marker of aneurysm vulnerability (12)(13)(14).…”