Optimising CT Perfusion (CTP) in Posterior circulation infarction (POCI): A comprehensive analysis of CTP postprocessing algorithms for POCI.

Background and purpose: CTP Software packages utilise various mathematical techniques to transform source data into clinically useful maps. These techniques have not been validated for Posterior circulation infarction (POCI). Studies of anterior circulation stroke have shown that algorithm differences significantly influence the accuracy and best tissue parameters and thresholds of output maps. We examined the influence of the processing algorithm on CTP accuracy and best tissue parameters and thresholds in acute POCI.

Materials and methods: Data were analysed from patients diagnosed with a POCI enrolled in the International-stroke-perfusionimaging-registry (INSPIRE). Fifty-eight-patients with baseline multimodal-CT with occlusion of a large posterior-circulation artery and follow up diffusion-weighted-MRI at 24-48 hours were included. CTP parametric maps were generated using five algorithms; Singular value deconvolution, Singular value deconvolution with delay and dispersion correction (SVDd), Partial-deconvolution, Stroke-stenosis and Maximum Slope models. Receiver operating curve (ROC) analysis and linear regression were used for voxel-based analysis and volume-based analysis respectively.

Results: Partial-deconvolution using the Mean Transit Time (MTT) parameter was the optimal technique for characterising ischaemic-penumbra (AUC=0.73 [0.64-0.81]) and infarct-core (AUC=0.70 [0.63-0.73]). The optimal MTT threshold was >165% and >180% for core and penumbra respectively. The optimal MTT threshold was >165% and >180% for core and penumbra respectively. By volume analysis; the SVDd and Maximum Slope (MS) using MTT were the best algorithms for estimation of penumbra and core respectively. Estimates of core volume were weak (all R²<0.02). Processing algorithm influenced model accuracy (AUC-range: 0.700.73 [core], 0.67-0.72 [penumbra]) and optimal tissue parameter and threshold. MTT was the most consistent optimal parameter across algorithms. The optimal MTT threshold varied from >120% to >200% for core and 155% to 195% for penumbra.

Conclusions: CTP has diagnostic utility in POCI. There were notable differences in optimal parameter and threshold by algorithm. Clinicians should be aware of the specific algorithm used in their CTP processing software and apply caution when comparing output maps between vendors.

Abbreviations: CTP = CT Perfusion; POCI = Posterior circulation infarction, ACS = Anterior circulation stroke, ROC = Reciever operating curve, AUC = Area under the curve, SVD = Singular value deconvolution, SVDd = Singular value deconvolution with delay and dispersion correction, MTT = Mean transit Time, TTP = Time to Peak, DT = Delay time, TMax = Time to maximum of the tissue resiude curve, CBV = Cerebral blood volume, CBF = Cerebral blood flow, AIF = Arterial input function, VOF = Venous output function, EVT = endovascular thrombectomy, mRS = modified rankin score, LKW = Last known well, MVD = mean volumetric difference.