Use of ABC/2 method for rapidly estimating the target mismatch on computed tomography perfusion imaging in patients with acute ischemic stroke

Background Target mismatch (ischemic core, mismatch volume and mismatch ratio) in patients with acute ischemic stroke (AIS) highly relies on the automated perfusion analysis software. Purpose To evaluate the feasibility and accuracy of using the ABC/2 method to rapidly estimate the target mismatch on computed tomography perfusion (CTP) imaging in patients with AIS, using RAPID results as a reference. Material and Methods In total, 243 patients with anterior circulation AIS who underwent CTP imaging were retrospectively reviewed. Target mismatch associated perfusion parameters were derived from RAPID results and calculated using the ABC/2 method. Paired t-test was used to assess the difference of volumetric parameters between the two methods. The ability of using the ABC/2 method to predict the important cutoff volumetric metrics was also evaluated. Result There was no significant difference in the volumes of ischemic core ( P = 0.068), ischemic area ( P = 0.209), and mismatch volume ( P = 0.518) between ABC/2 and RAPID. Using RAPID results as reference, the ABC/2 method showed high accuracy for predicting perfusion parameters (70 mL and 90 mL: sensitivity=98.5% and 98.5%, specificity=100% and 100%, positive predictive value [PPV]=100% and 100%, negative predictive value [NPV]=93.8% and 92.9%; 10 mL and 15mL: sensitivity=99.6% and 99.5%, specificity=55.6% and 50.0%, PPV=96.6% and 94.8%, NPV=90.9% and 92.3%; 1.2 and 1.8: sensitivity=99.6% and 94.8%, specificity=75.0% and 96.9%, PPV=98.7% and 99.5%, NPV=90.0% and 73.8%). Conclusion The ABC/2 method may be a feasible alternative to RAPID for estimation of target mismatch parameters on CTP in patients with AIS.

Diagnostic Performance of Computed Tomography Angiography and Computed Tomography Perfusion Tissue Time‐to‐Maximum in Vasospasm Following Aneurysmal Subarachnoid Hemorrhage

Background Vasospasm is a treatable cause of deterioration following aneurysmal subarachnoid hemorrhage. Cerebral computed tomography perfusion mean transit times have been proposed as a predictor of vasospasm but suffer from well‐known technical limitations. We evaluated fully automated, thresholded time‐to‐maxima of the tissue residue function ( T max ) for determination of vasospasm following aneurysmal subarachnoid hemorrhage. Methods and Results Retrospective analysis of 540 arterial segments from 36 encounters in 31 consecutive patients with aneurysmal subarachnoid hemorrhage undergoing computed tomography angiography (CTA), computed tomography perfusion, and digital subtraction angiography (DSA) within 24 hours. T max at 4, 6, 8, and 10 s was generated using RAPID (iSchemaView Inc., Menlo Park, CA). Dual‐reader CTA and computed tomography perfusion interpretations were compared for patients with and without vasospasm on DSA (DSA+ and DSA−). Logistic regression models were developed using CTA and T max as input predictors and DSA vasospasm as outcome in adjusted and unadjusted models. Imaging studies from all 31 subjects (mean age 47.3±11.1, 77% female, 65% with single aneurysm with mean size of 6.0±2.9 mm) were included. Vasospasm was identified in 42 segments on DSA and 59 segments on CTA, with significant associations across individual vessel segments ( P <0.001). In adjusted analyses, DSA vasospasm was associated with CTA (odds ratio [OR], 2.43; 95% CI, 0.94–6.32; P =0.068) as well as territory‐specific T max >6 seconds delays (OR, 3.57; 95% CI, 1.36–9.35; P =0.009). Sensitivity/specificity for DSA vasospasm was 31%/91% for CTA, 26%/89% for T max >6 seconds, and 12%/99% for CTA+ T max >6 seconds. Conclusions CTA and T max offer high specificity for presence of vasospasm; their utility, even in combination, as screening tests is, however, limited by poor sensitivity.

Comparison of Two Automated Computed Tomography Perfusion Applications to Predict the Final Infarct Volume After Thrombolysis in Cerebral Infarction 3 Recanalization

Background and Purpose: Several automated computed tomography perfusion software applications have been developed to provide support in the definition of ischemic core and penumbra in acute ischemic stroke. However, the degree of interchangeability between software packages is not yet clear. Our study aimed to evaluate 2 commonly used automated perfusion software applications (Syngo.via and RAPID) for the indication of ischemic core with respect to the follow-up infarct volume (FIV) after successful recanalization and with consideration of the clinical impact. Methods: Retrospectively, 154 patients with large vessel occlusion of the middle cerebral artery or the internal carotid artery, who underwent endovascular therapy with a consequent Thrombolysis in Cerebral Infarction 3 result within 2 hours after computed tomography perfusion, were included. Computed tomography perfusion core volumes were assessed with both software applications with different thresholds for relative cerebral blood flow (rCBF). The results were compared with the FIV on computed tomography within 24 to 36 hours after recanalization. Bland-Altman was applied to display the levels of agreement and to evaluate systematic differences. Results: Highest correlation between ischemic core volume and FIV without significant differences was found at a threshold of rCBF<38% for the RAPID software ( r =0.89, P <0.001) and rCBF<25% for the Syngo software ( r =0.87, P <0.001). Bland-Altman analysis revealed best agreement in these settings. In the vendor default settings (rCBF<30% for RAPID and rCBF<20% for Syngo) correlation between ischemic core volume and FIV was also high (RAPID: r =0.88, Syngo: r =0.86, P <0.001), but mean differences were significant ( P <0.001). The risk of critical overestimation of the FIV was higher with rCBF<38% (RAPID) and rCBF<25% (Syngo) than in the default settings. Conclusions: By adjusting the rCBF thresholds, comparable results with reliable information on the FIV after complete recanalization can be obtained both with the RAPID and Syngo software. Keeping the software specific default settings means being more inclusive in patient selection, but forgo the highest possible accuracy in the estimation of the FIV.

Thrombectomy With and Without Computed Tomography Perfusion Imaging in the Early Time Window: A Pooled Analysis of Patient-Level Data

Background and Purpose: The optimal imaging paradigm for endovascular thrombectomy (EVT) patient selection in early time window (0–6 hours) treated acute ischemic stroke patients remains uncertain. We aimed to compare post-EVT outcomes between patients who underwent prerandomization basic (noncontrast computed tomography [CT], CT angiography only) versus additional advanced imaging (computed tomography perfusion [CTP] imaging) and to determine the association of performance of prerandomization CTP imaging with clinical outcomes. Methods: The HERMES collaboration (Highly Effective Reperfusion Evaluated in Multiple Endovascular Stroke Trials) pooled patient-level data from randomized controlled trials comparing EVT with usual care for acute ischemic stroke due to anterior circulation large vessel occlusion. Good functional outcome, defined as modified Rankin Scale score 0 to 2 at 90 days, was compared between randomized patients with and without CTP baseline imaging. Univariable and multivariable binary logistic regression analysis was performed to determine the association of baseline CTP imaging and good functional outcome. Results: We analyzed 1348 patients 610 (45.3%) of whom underwent CTP prerandomization. The benefit of EVT compared with best medical management was maintained irrespective of the baseline imaging paradigm (90-day modified Rankin Scale score 0–2 in EVT versus control patients: with CTP: 46.0% (137/298) versus 28.9% (88/305), without CTP: 44.1% (162/367) versus 27.3% (100/366). Performance of CTP baseline imaging compared with baseline noncontrast CT and CT angiography only yielded similar rates of good outcome (odds ratio, 1.05 [95% CI, 0.82–1.33], adjusted odds ratio, 1.04, [95% CI, 0.80–1.35]). Conclusions: Rates of good functional outcome were similar among patients in whom CTP was or was not performed, and EVT treatment effect in the 0- to 6-hour time window was similar in patients with and without baseline CTP imaging.

Ghost infarct core following endovascular reperfusion: A risk for computed tomography perfusion misguided selection in stroke

Background Computed tomography perfusion (CTP) has been increasingly used for patient selection in mechanical thrombectomy for stroke. However, previous studies suggested that CTP might overestimate the infarct size. The term ghost infarct core (GIC) has been used to describe an overestimation of the final infarct volumes by pre-treatment CTP of >10 ml. Aim We sought to study the frequency and predictors of GIC. Methods A prospectively collected mechanical thrombectomy database at a comprehensive stroke center between September 2010 and August 2020 was reviewed. Patients were included if they had a successful reperfusion (mTICI2b-3), a pre-procedure CTP, and final infarct volume measured on follow-up magnetic resonance imaging. Uni- and multivariable analyses were performed to identify predictors of GIC. Results Among 923 eligible patients (median [IQR] age, 64 [55–75] years; NIHSS, 16 [11–21]; onset to reperfusion time, 436.5 [286–744.5] min), GIC was identified in 77 (8.3%) of the overall patients and in 14% (47/335) of those reperfused within 6 h of symptom onset. The median overestimation volume was 23.2 [16.4–38.3] mL. GIC was associated with higher NIHSS score, larger areas of infarct core and tissue at risk on CTP, unfavorable collateral scores, and shorter times from onset to image acquisition and to reperfusion as compared to non-GIC. Patients with GIC had smaller median final infarct volumes (10.7 vs. 27.1 ml, p < 0.001), higher chances of functional independence (76.2% vs. 55.5%, adjusted odds ratio (aOR) 3.829, 95% CI [1.505–9.737], p = 0.005), lower disability (one-point-mRS improvement, aOR 1.761, 95% CI [1.044–2.981], p = 0.03), and lower mortality (6.3% vs. 15%, aOR 0.119, 95% CI [0.014–0.984], p = 0.048) at 90 days. On multivariable analysis, time from onset to reperfusion ≤6 h (OR 3.184, 95% CI [1.743–5.815], p < 0.001), poor collaterals (OR 2.688, 95% CI [1.466–4.931], p = 0.001), and higher NIHSS score (OR 1.060, 95% CI [1.010–1.113], p = 0.018) were independent predictors of GIC. Conclusion GIC is a relatively common entity, particularly in patients with poor collateral status, higher baseline NIHSS score, and early presentation, and is associated with more favorable outcomes. Patients should not be excluded from reperfusion therapies on the sole basis of CTP findings, especially in the early window.

Changes in computed tomography perfusion parameters and maximum contrast enhancement in patients having hydrocephalus with a ventriculoperitoneal shunt: a pilot study

Background Acute hydrocephalus may decrease cerebral perfusion by increasing intracranial pressure. Computed tomography perfusion (CTP) has become a significant adjunct in evaluating regional and global cerebral blood flow (CBF). Purpose To investigate the changes in cerebral perfusion parameters and maximum contrast enhancement (MCE) in patients with hydrocephalus with ventriculoperitoneal shunt (VPS). Material and Methods We performed brain CTP in 45 patients, including those with subarachnoid hemorrhage (SAH)-induced hydrocephalus with VPS (n = 14, G1), hydrocephalus (not related to SAH) with VPS (n = 11, G2), SAH-induced hydrocephalus without VPS (n = 10, G3), and hydrocephalus (not related to SAH) without VPS (n = 10, G4). We measured the cerebral perfusion in the frontal white matter (FWM), centrum semiovale, basal ganglia (BG), and eight cortical lesions of interest and compared the differences in CTP parameters among the groups. Results Between the four groups, cerebral blood volume and MCE in the left FWM and CBF in the right FWM increased significantly in G1 and G2 who underwent VP shunt compared to G3 and G4, whereas perfusion significantly reduced in G3 and G4 who did not undergo VP shunt compared to G1 and G2. MCE in the left BG significantly increased in G2 and decreased in G3 and G4. SAH-induced hydrocephalus showed a lower perfusion than hydrocephalus (not related to SAH) in FWM. Conclusions Perfusion changes in patients with hydrocephalus after VP shunt were seen in the FWM and BG, which appears to be the result of the hydrocephalus reducing brain perfusion in the deep part of the brain. We concluded that SAH slows brain perfusion recovery.

Feasibility of Four-Dimensional Similarity Filter For Radiation Dose Reduction in Dynamic Myocardial Computed Tomography Perfusion Imaging

Purpose: We aimed to evaluate the impact of four-dimensional noise reduction filtering using a similarity algorithm (4D-SF) on image noise during dynamic myocardial computed tomography perfusion (CTP) to simulate the reduction of radiation dose.Methods: A total of 43 patients who underwent dynamic myocardial CTP using 320-row CT were included in the study. The original images were reconstructed using iterative reconstruction (IR); three different CTP datasets with simulated noise, which corresponded to 25%, 50%, and 75% reduction of the original dose (= 300mA), were reconstructed using a combination of IR and 4D-SF. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed, and CT-derived myocardial blood flow (CT-MBF) was quantified. The results were compared between the original and simulated images with radiation dose reduction.Results: The original, 25%-, 50%-, and 75%-dose reduced images with 4D-SF showed an SNR of 8.3 (6.5–10.2), 16.5 (11.9–21.7), 15.6 (11.0–20.1), and 12.8 (8.8–18.1) and a CNR of 4.4 (3.2–5.8), 6.7 (4.6–10.3), 6.6 (4.3–10.1), and 5.5 (3.5–9.1), respectively. Compared to the original images, the 25%-, 50%-, and 75%-dose reduced-simulated images showed significant improvement in both SNR and CNR with 4D-SF. There was no significant difference in CT-MBF between the original and 25%- or 50%-dose reduced-simulated images with 4D-SF, however, there was a significant difference in CT-MBF between the original and 75%-dose reduced-simulated images.Conclusion: 4D-SF has the potential to reduce the radiation dose associated with dynamic myocardial CTP imaging by half, without impairing the robustness of MBF quantification.

Low Baseline Ischemic Water Uptake is Directly Related to Overestimation of CT Perfusion-Derived Ischemic Core Volume

Background Computed-tomography perfusion (CTP) is frequently used to screen acute ischemic stroke (AIS) patients for endovascular treatment (EVT), despite known problems with ischemic “core” overestimation. This potentially leads to the unfair exclusion of patients from EVT. We propose that net water uptake (NWU) can be used in addition to CTP to more accurately assess the extent and/or stage of tissue infarction. Methods Patients treated for AIS between 06/2015-07/2020 were retrospectively analyzed. Baseline CTP-derived core volume (pCore) and NWU were determined. Logistic regression tested the relationship between baseline clinical and imaging variables and core-overestimation (primary outcome). The secondary outcomes comprised 90-day functional independence (modified Rankin score) and lesion growth. Results 284 patients were included. Median NWU was 7.2% (IQR:2.6–12.8). ASPECTS (RR:1.28,95%CI:1.09-1.51), NWU (RR:0.94,95%CI:0.89-0.98), onset to recanalization (RR:1.00,95%CI:0.99-1.00) and imaging (RR:1.00,95%CI1.00-1.00) times, and pCore (RR:1.02,95%CI:1.01-1.02) were significantly associated with core overestimation. Core-overestimation was more likely to occur in patients with large pCores and low NWU at baseline. NWU was significantly correlated with lesion growth. Conclusion NWU can be used as a supplemental tool to CTP during admission imaging to more accurately assess the extent of ischemia, particularly relevant for patients with large CTP-defined cores who would otherwise be excluded from treatment.