CT perfusion stroke lesion threshold calibration between deconvolution algorithms

Abstract

Objective: CTP is an important diagnostic tool in managing patients with acute ischemic stroke, but challenges persist in the reliability of stroke lesion volumes determined with different software. We investigated a systematic method to calibrate CTP lesion thresholds between deconvolution algorithms using a digital perfusion phantom. Approach: The accuracy of one model-independent and two model-based deconvolution algorithms in estimating ground truth cerebral blood flow (CBF) and Tmax in the phantom was quantified. Reference thresholds for ischemic core and penumbra were model-independent CBF<30% and Tmax>6 s, respectively, which is the current clinical standard. The equivalent model-based CBF and Tmax thresholds were determined by comparing linear regressions of phantom ground truth and deconvolution-estimated perfusion between algorithms. Calibrated thresholds were then validated in 63 patients with large vessel stroke by comparing admission CTP ischemic core and <3-hour diffusion-weighted imaging (DWI) lesion volume by Bland-Altman analysis. Agreement in target mismatch (core < 70 ml, penumbra ≥ 15 ml, mismatch ratio ≥ 1.8) determined by the three methods was assessed by Cohen's kappa (κ) and concordance. Main Results: The calibrated thresholds were CBF<15% and Tmax>6 s for both model-based methods. DWI minus CTP lesion mean volume differences (95% limits of agreement) were +16.2 (-30.9 to 63.3) ml, +10.9 (-32.9 to 54.7) ml, and +13.8 (-48.1 to 75.7) ml for model-independent and the two calibrated model-based approaches, respectively. Agreement in mismatch profiles with the two model-based deconvolution methods versus model-independent assessment was κ = 0.87 (95% confidence interval [CI]: 0.72 to 1.00) and κ = 0.86 (95% CI: 0.70 to 1.00), and both achieved 95% concordance. Significance: We reported a systematic method of calibrating perfusion thresholds between deconvolution algorithms based on their quantitative accuracy. This may harmonize ischemic lesion volumes determined by different CTP software.

Multiphase CT angiography perfusion maps for predicting target mismatch and ischemic lesion volumes

“…Reader studies evaluating the potential benefit of mCTA-P maps in detecting ischemia and occlusions will be the subject of a future study. The optimal ischemic core threshold for our software was CBF < 15% for CTP 14 and CBF < 25% for mCTA-P ("Supplemental Materials") and not CBF < 30% as with RAPID CTP (RapidAI, Menlo Park, CA) used in clinical trials. Optimal stroke lesion thresholds vary by CTP software 14,37,38 and appropriate thresholds must accordingly be applied.…”

“…The optimal ischemic core threshold for our software was CBF < 15% for CTP 14 and CBF < 25% for mCTA-P ("Supplemental Materials") and not CBF < 30% as with RAPID CTP (RapidAI, Menlo Park, CA) used in clinical trials. Optimal stroke lesion thresholds vary by CTP software 14,37,38 and appropriate thresholds must accordingly be applied. We also found that stroke lesion thresholds for mCTA-P was different to those of CTP due to the 4-image protocol ("Supplemental Materials"), which used substantially fewer images compared to a standard CTP protocol.…”

“…Parametric maps of cerebral blood flow (CBF) and Tmax were generated by deconvolving the arterial TDC from each brain tissue TDC using a least-squares fitting algorithm. Lesion determination was limited to the ipsilateral brain hemisphere and hypoperfused tissue, which was defined as ipsilateral brain with Tmax > 4 s. The optimal ischemic core and penumbra thresholds for this software were CBF < 15% relative to the mean CBF in the contralateral brain hemisphere and Tmax > 6 s, respectively 14 . For dCTP and mCTA-P, the optimal ischemic core and penumbral thresholds were CBF < 25% and Tmax > 5 s, respectively, as determined by an independent threshold calibration experiment 14 ("Supplemental Materials").…”

“…Lesion determination was limited to the ipsilateral brain hemisphere and hypoperfused tissue, which was defined as ipsilateral brain with Tmax > 4 s. The optimal ischemic core and penumbra thresholds for this software were CBF < 15% relative to the mean CBF in the contralateral brain hemisphere and Tmax > 6 s, respectively 14 . For dCTP and mCTA-P, the optimal ischemic core and penumbral thresholds were CBF < 25% and Tmax > 5 s, respectively, as determined by an independent threshold calibration experiment 14 ("Supplemental Materials"). The disparity between CTP and mCTA-P lesion thresholds was due to the different CBF and Tmax estimations as a result of calculating perfusion maps with only four images (sparse sampling and shorter total scan duration compared to standard CTP; "Supplemental Materials").…”