Developing new quantitative CT image markers to predict prognosis of acute ischemic stroke patients

Abstract

Background: Endovascular mechanical thrombectomy (EMT) is an effective method to treat acute ischemic stroke (AIS) patients due to large vessel occlusion (LVO). However, stratifying AIS patients who can and cannot benefit from EMT remains a clinical challenge.

Objective: To develop a new quantitative image marker computed from pre-intervention computed tomography perfusion (CTP) images and evaluate its feasibility to predict clinical outcome among AIS patients undergoing EMT after diagnosis of LVO.

Methods: A retrospective dataset of 31 AIS patients with pre-intervention CTP images is assembled. A computer-aided detection (CAD) scheme is developed to pre-process CTP images of different scanning series for each study case, perform image segmentation, quantify contrast-enhanced blood volumes in bilateral cerebral hemispheres, and compute features related to asymmetrical cerebral blood flow patterns based on the cumulative cerebral blood flow curves of two hemispheres. Next, image markers based on a single optimal feature and machine learning (ML) models fused with multi-features are developed and tested to classify AIS cases into two classes of good and poor prognosis based on the Modified Rankin Scale. Performance of image markers is evaluated using the area under the ROC curve (AUC) and accuracy computed from the confusion matrix.

Results: The ML model using the neuroimaging features computed from the slopes of the subtracted cumulative blood flow curves between two cerebral hemispheres yields classification performance of AUC = 0.878±0.077 with an overall accuracy of 90.3%.

Conclusions: This study demonstrates feasibility of developing a new quantitative imaging method and marker to predict AIS patients' prognosis in the hyperacute stage, which can help clinicians optimally treat and manage AIS patients.

Keywords: Acute ischemic stroke (AIS); computer-aided detection and diagnosis (CAD); prediction of AIS prognosis; quantitative image markers.

Figure 1.

Distribution of patients based on the Modified Rankin Scale (mRS). (a) Separated by individual mRS, (b) Separated by mRS into two classes: [‘class-0’: 0–3]; [‘class-1’: 4–6].

Figure 2.

A sample illustration of the proposed dice-similarity based approach identifying the parameters (scan-type and number of unique brain indices).

Figure 3.

Picture of the implemented interactive graphical user interface (GUI) of the CAD scheme, which includes two image windows showing the original CT image slice (left) and the segmented brain area (right), and multiple operating functionalities and parameter assignment boxes on both left and right column.

Figure 4.

A sample illustration of sectoring cumulative volume of blood line plot into three equal phases and computing corresponding intermediate slopes for left and right hemisphere.

Figure 5.

A detailed flow diagram of each step of the proposed CAD scheme.

Figure 6.

From top-left to bottom-right: A sample brain index over CTP acquisition time depicting the variation in blood flow between the left and right hemisphere.

Figure 7.

Illustration of proposed segmentation scheme using image markers and consecutive mapping technique for a sample brain series.

Figure 8.

Comparison between two cumulative blood flow curves in left and right hemispheres of the brain, where case (a) is classified to ‘class-0’ and case (b) is classified to ‘class-1’ of mRS.

Figure 9.

Comparison of various ROC curves generated using 5 models to classify between two mRS classes.