Time-resolved assessment of collateral flow using 4D CT angiography in large-vessel occlusion stroke.

OBJECTIVES: In acute stroke patients with large vessel occlusion, collateral blood flow affects tissue fate and patient outcome. The visibility of collaterals on computed tomography angiography (CTA) strongly depends on the acquisition phase, but the optimal time point for collateral imaging is unknown. METHODS: We analysed collaterals in a time-resolved fashion using four-dimensional (4D) CTA in 82 endovascularly treated stroke patients, aiming to determine which acquisition phase best depicts collaterals and predicts outcome. Early, peak and late phases as well as temporally fused maximum intensity projections (tMIP) were graded using a semiquantitative regional leptomeningeal collateral score, compared with conventional single-phase CTA and correlated with functional outcome. RESULTS: The total extent of collateral flow was best visualised on tMIP. Collateral scores were significantly lower on early and peak phase as well as on single-phase CTA. Collateral grade was associated with favourable functional outcome and the strength of this relationship increased from earlier to later phases, with collaterals on tMIP showing the strongest correlation with outcome. CONCLUSIONS: Temporally fused tMIP images provide the best depiction of collateral flow. Our findings suggest that the total extent of collateral flow, rather than the velocity of collateral filling, best predicts clinical outcome. KEY POINTS: • Collateral flow visibility on CTA strongly depends on the acquisition phase • tMIP offers the best visualisation of the extent of collaterals • Outcome prediction may be better with tMIP than with earlier phases.• Total extent of collaterals seems more important than their filling speed • If triggered too early, CTA may underestimate collateral flow.

Antegrade flow across incomplete vessel occlusions can be distinguished from retrograde collateral flow using 4-dimensional computed tomographic angiography.

BACKGROUND AND PURPOSE: In acute stroke patients with intracranial vessel occlusion, angiographic demonstration of antegrade contrast opacification distal to the occlusion site (termed the "clot outline sign") has been associated with higher rates of vessel recanalization. We sought to determine whether antegrade flow can be demonstrated on time-resolved 4-dimensional computed tomographic angiography (4-dimensional CTA), whether it can be distinguished from retrograde collateral flow, and if it can be used to predict early recanalization. METHODS: Fifty-seven acute stroke patients with intracranial anterior circulation vessel occlusion were retrospectively identified. All patients had received a multimodal computed tomography examination including thin-section 4-dimensional CTA and subsequent digital subtraction angiography as part of an endovascular procedure. Pretreatment 4-dimensional CTA and single-phase CTA were assessed for presence of antegrade contrast opacification distal to the occlusion site. Digital subtraction angiograms were reviewed for preintervention Thrombolysis in Cerebral Infarction grade, presence of the clot outline sign, as well as postintervention Thrombolysis in Cerebral Infarction grade. RESULTS: On 4-dimensional CTA, evidence of antegrade flow was present in 11 of 57 cases (19.3%). Compared with angiography, 4-dimensional CTA predicted antegrade flow with 100% sensitivity and 97.9% specificity. Single-phase CTA offered 40% sensitivity and 87.2% specificity. Early recanalization occurred in 3 patients (6.5%) after intravenous thrombolysis (n=46); all demonstrated antegrade flow on 4-dimensional CTA. CONCLUSIONS: Using 4-dimensional CTA, it is possible to noninvasively distinguish antegrade flow across a cerebral artery occlusion from retrograde collateral flow. Presence of antegrade flow on 4-dimensional CTA is associated with an increased chance of early vessel recanalization.

Diagnostic performance of whole brain volume perfusion CT in intra-axial brain tumors: preoperative classification accuracy and histopathologic correlation.

BACKGROUND: To evaluate the preoperative diagnostic power and classification accuracy of perfusion parameters derived from whole brain volume perfusion CT (VPCT) in patients with cerebral tumors. METHODS: Sixty-three patients (31 male, 32 female; mean age 55.6 ± 13.9 years), with MRI findings suspected of cerebral lesions, underwent VPCT. Two readers independently evaluated VPCT data. Volumes of interest (VOIs) were marked circumscript around the tumor according to maximum intensity projection volumes, and then mapped automatically onto the cerebral blood volume (CBV), flow (CBF) and permeability Ktrans perfusion datasets. A second VOI was placed in the contra lateral cortex, as control. Correlations among perfusion values, tumor grade, cerebral hemisphere and VOIs were evaluated. Moreover, the diagnostic power of VPCT parameters, by means of positive and negative predictive value, was analyzed. RESULTS: Our cohort included 32 high-grade gliomas WHO III/IV, 18 low-grade I/II, 6 primary cerebral lymphomas, 4 metastases and 3 tumor-like lesions. Ktrans demonstrated the highest sensitivity, specificity and positive predictive value, with a cut-off point of 2.21 mL/100mL/min, for both the comparisons between high-grade versus low-grade and low-grade versus primary cerebral lymphomas. However, for the differentiation between high-grade and primary cerebral lymphomas, CBF and CBV proved to have 100% specificity and 100% positive predictive value, identifying preoperatively all the histopathologically proven high-grade gliomas. CONCLUSION: Volumetric perfusion data enable the hemodynamic assessment of the entire tumor extent and provide a method of preoperative differentiation among intra-axial cerebral tumors with promising diagnostic accuracy.

Angiographic reconstructions from whole-brain perfusion CT for the detection of large vessel occlusion in acute stroke.

BACKGROUND AND PURPOSE: Multimodal CT imaging consisting of nonenhanced CT, CT angiography (CTA), and whole-brain volume perfusion CT is increasingly used for acute stroke imaging. In these patients, presence of vessel occlusion is an important factor governing treatment decisions and possible endovascular therapy. The goal of this study was to assess the value and diagnostic accuracy of angiographic thin-slice volume perfusion CT reconstructions for the detection of intracranial large vessel occlusion in patients with stroke. METHODS: Fifty-eight patients with acute stroke received nonenhanced CT, CTA, and volume perfusion CT. All images were obtained on a 128-slice multidetector CT scanner. CT angiographic axial and coronal maximum-intensity projections of the head were reconstructed from conventional CTA and from the peak arterial scan of the volume perfusion CT data set (4-dimensional CTA). Images were assessed for the presence of intracranial vessel occlusion. The distribution of ischemic lesions was analyzed on perfusion parameter maps. RESULTS: On CTA, 30 patients (52%) had a total of 33 occluded intracranial artery segments. Twenty-eight occlusions were identified on 4-dimensional CTA, resulting in an 85% sensitivity with a positive predictive value of 97%. When combined with an analysis of the perfusion parameter maps, sensitivity of 4-dimensional CTA increased to 94% with a positive predictive value of 100%. CONCLUSIONS: In acute stroke, angiographic volume perfusion CT reconstructions may be a feasible option to detect intracranial arterial occlusion and evaluate patients for endovascular therapy. Sensitivity for detection of intracranial arterial occlusion can be increased by simultaneous assessment of perfusion parameter maps. Future studies should assess whether time-resolved 4-dimensional CTA may offer additional diagnostically relevant information compared with single-phase CTA.

Brain volume perfusion CT performed with 128-detector row CT system in patients with cerebral gliomas: a feasibility study.

OBJECTIVES: Validation of the feasibility and efficacy of volume perfusion computed tomography (VPCT) in the preoperative assessment of cerebral gliomas by applying a 128-slice CT covering the entire tumour. METHODS: Forty-six patients (25 men, 21 women; mean age 52.8 years) with cerebral gliomas were evaluated with VPCT. Two readers independently evaluated VPCT data, drawing volumes of interest (VOIs) around the tumour according to maximum intensity projection volumes, which were mapped automatically onto the cerebral blood volume (CBV), flow (CBF) and permeability (Ktrans) perfusion datasets. As control, a second VOI was placed in the contralateral healthy cortex. Correlation among perfusion parameters, tumour grade, hemisphere and VOIs was assessed. The diagnostic power of perfusion parameters was analysed by receiver operating characteristics curve analyses. RESULTS: VPCT was feasible in the assessment of the entire tumour extent. Mean values of Ktrans, CBV, CBF in high-grade gliomas were significantly higher compared with low-grade (p < 0.01). Ktrans demonstrated the highest diagnostic (97% sensitivity), positive (100%) and negative (94%) prognostic values. CONCLUSIONS: VPCT was feasible in all subjects. All areas of different perfusion characteristics are depicted and quantified in colour-coded 3D maps. The derived parameters correlate well with tumour histopathology, differentiating low- from high-grade gliomas.