Description: The dynamics of accretionary convergent margins are severely influenced by intense deformation and fluid expulsion. To quantify the fluid pressure and fluid flow velocities in the Hellenic subduction system, we set up 2D hydrogeological numerical models following two seismic reflection lines across the Mediterranean Ridge. These profiles bracket the along-strike variation in wedge geometry: moderate compression and a 〉 4km-thick underthrust sequence in the west vs. enhanced compression and 〈 1km of downgoing sediment in the center. Input parameters were obtained from preexisting geophysical data, drill cores, and new geotechnical laboratory experiments. A permeability-porosity relationship was determined by a sensitivity analysis, indicating that porosity and intrinsic permeability are small. This hampers the expulsion of fluids and leads to the build-up of fluid overpressure in the deeper portion of the wedge and in the underthrust sediment. The loci of maximum fluid pressure are mainly controlled by the compactional fluid source, which generally decreases towards the backstop. However, pore pressure is still high at the decollement level at distances 〈 100km from the deformation front, either by the incorporation of low permeability evaporites or additional compaction of the wedge sediments in the two profiles. In the west, however, formation of a wide accretionary complex is facilitated by high pore pressure zones. When compared to other large accretionary complexes such as Nankai or Barbados, our results show broad similarities, but also that near-lithostatic pore pressures may be easier to maintain in the Hellenic Arc because of accentuated collision, some underthrust evaporates and a thicker underthrust sequence.

Description: Background and Purpose— Hyperintense vessels (HVs) have been observed in fluid-attenuated inversion recovery imaging of patients with acute ischemic stroke and been linked to slow flow in collateral arterial circulation. Given the potential importance of HV, we used a large, multicenter data set of patients with stroke to clarify which clinical and imaging factors play a role in HV. Methods— We analyzed data of 516 patients from the previously published PRE-FLAIR study ( PRE dictive value of FLAIR and DWI for the identification of acute ischemic stroke patients ≤3 and ≤4.5 hours of symptom onset—a multicenter study) study. Patients were studied by MRI within 12 hours of symptom onset. HV were defined as hyperintensities in fluid-attenuated inversion recovery corresponding to the typical course of a blood vessel that was not considered the proximal, occluded main artery ipsilateral to the diffusion restriction. Presence of HV was rated by 2 observers and related to clinical and imaging findings. Results— Presence of HV was identified in 240 of all 516 patients (47%). Patients with HV showed larger initial ischemic lesion volumes (median, 12.3 versus 4.9mL; P 〈0.001) and a more severe clinical impairment (median National Institutes of Health Stroke Scale 10.5 versus 6; P 〈0.001). In 198 patients with MR angiography, HVs were found in 80% of patients with vessel occlusion and in 17% without vessel occlusion. In a multivariable logistic regression model, vessel occlusion was associated with HV (OR, 21.7%; 95% CI, 9.6–49.9; P 〈0.001). HV detected vessel occlusion with a specificity of 0.86 (95% CI, 0.80–0.90) and sensitivity of 0.76 (95% CI, 0.69–0.83). Conclusions— HVs are a common finding associated with proximal arterial occlusions and more severe strokes. HVs predict arterial occlusion with high diagnostic accuracy.

Description: Background and Purpose— A significant amount of strokes are reported to be diffusion-weighted imaging (DWI) negative in acute imaging. We attempted to quantify the rate of false-negative high-resolution (hr) DWI and to identify a valid screening tool to guide follow-up MRI to diagnose infarction initially not visible on hrDWI. Methods— An a priori–defined post hoc analysis of a prospective 3T MRI cohort of acute cerebrovascular events imaged within 24 hours of ictus. Basic demographics, risk factors, National Institute of Health Stroke Scale, and imaging parameters were recorded. Results— Of 151 patients with negative acute hrDWI, 63 received follow-up scans depicting infarction in 7 cases (11.1%). Persistence of clinical symptoms as established by National Institute of Health Stroke Scale on the following day was strongly associated with infarction on follow-up MRI (odds ratios, 17.5; 95% confidence interval, 2.83–108.12). Negative predictive value of follow-up National Institute of Health Stroke Scale was 0.96. Conclusions— Infarcts are frequently invisible on initial hrDWI, but we may well trust in negative hrDWI in completely transient cerebrovascular events.

Description: Background and Purpose— The so-called smoking-thrombolysis paradox of an improved outcome after thrombolysis was first described in smokers with myocardial infarction. We investigated whether reperfusion rates and clinical outcome differ between smokers and nonsmokers with ischemic stroke after intravenous tissue plasminogen activator. Methods— Consecutive acute ischemic stroke patients, who had magnetic resonance imaging before and 1 day after thrombolysis, were included for analysis. All of the patients received intravenous tissue plasminogen activator within 4.5 hours. Reperfusion was defined as a 75% reduction in perfusion deficit (mean transit time 〉6 s) after thrombolysis compared with baseline. Magnetic resonance angiography was used to evaluate arterial stenosis and occlusion. Functional outcome was assessed 3 months after stroke using the modified Rankin Score. Results— Of 148 patients, 21.6% were smokers (n=32). Smokers were younger (median, 61 years [ SD , 9.4 years] versus 75 years [ SD , 11.6 years]; P 〈0.001), less often women (28% versus 51%; P =0.03), had lower baseline glucose levels (median, 6.2 mmol/L [interquartile range, 5.7–6.8 mmol/L] versus 6.7 mmol/L [interquartile range, 6.1–8.2 mmol/L]; P 〈0.01) and higher baseline perfusion deficits (median, 53 mL [interquartile range, 13–141 mL] versus 17 mL [interquartile range, 2–66 mL]; P =0.04). In a backward stepwise regression analysis including age, sex, hypertension, glucose, perfusion deficit, and smoking, smoking had an odds ratio of 4 (95% confidence interval, 1–16; P =0.03) for reperfusion and 6 (95% confidence interval, 1–30; P =0.05) for recanalization (regression analysis for recanalization also included localization of arterial occlusion). Smokers had a better outcome (modified Rankin Score=0–2) than nonsmokers (77% versus 55%; P =0.05). Conclusions— Smoking is independently associated with recanalization and reperfusion, indicating that thrombolytic therapy acts more effectively in smokers; because of small numbers, these results should be considered preliminary. Clinical Trial Registration— URL: http://clinicaltrials.gov . Unique Identifier: NCT00715533.

Description: Background and Purpose— We investigated whether hyperintensities with a diameter of at least 3, 3.5, and 4 cm and visible on at least 3 slices on diffusion-weighted imaging enables patient selection with an infarct volume of ≥15 mL. Methods— Consecutive acute stroke patients were screened for the AXIS2 trial and examined according to a standardized magnetic resonance imaging protocol in 65 sites. Diffusion-weighted lesion diameters were measured and compared with volumetric assessments. Results— Out of 238 patients, 86.2% (N=206) had infarct diameter of at least 3 cm. Volumetric assessments showed infarct volume of ≥15 mL in 157 patients. A cut-off value of 3 cm led to 96.8% sensitivity and 33.3% specificity for predicting lesion volume of ≥15 mL. Analogously, a 3.5 cm cut-off led to 96.8% sensitivity and 50.6% specificity and a 4 cm cut-off led to 91.7% sensitivity and 61.7% specificity. Conclusions— Lesion diameter measures may enable multicentric patient recruitment with a prespecified minimal infarct volume. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT00927836.