Endovascular treatment of unruptured intracranial aneurysms: Rate of thromboembolic events depicted by diffusion-weighted imaging in relation to different techniques.

BACKGROUND: The rate of thromboembolic events (TEEs) associated with endovascular treatment (EVT) of intracranial aneurysms is not reported uniformly in the literature due to the various ways that are used to evaluate them. Analysis of Thromboembolic Complications after Endovascular Treatment of Unruptured Intracranial Aneurysms study (ACET) is a prospective, multicenter study, which analyzes the rate of TEEs using diffusion-weighted imaging (DWI) magnetic resonance imaging (MRI) in patients treated for unruptured aneurysms with different endovascular techniques. METHODS: Patients were prospectively included in six French centers. Postoperative DWI-MRI was performed within 72 hours post-procedure and independently evaluated. Univariate and multivariate analyses were conducted to determine factors associated with the occurrence of DWI lesions. RESULTS: Of the 233 included patients (54.5±11.2 years, 162 women, (69.5%)), 226 were effectively treated by EVT (coiling: 90 patients, 39.8%; balloon-assisted coiling (BAC): 62, 27.4%; stent-assisted coiling (SAC): 10, 4.4%; flow diversion (FD): 21, 9.3%; intrasaccular flow disruption (ISFD): 43, 19.0%) and had a postoperative MRI showing DWI lesions in 133 patients (58.8%). Univariate and multivariate analyses show the rate of patients with DWI lesions to be significantly higher with BAC (75.8%, P=0.001), SAC (90.0%, P=0.02), and FD (95.2%, P=0.001) compared with coiling alone (41.1%). CONCLUSIONS: The rate of DWI lesions after EVT of unruptured aneurysms is primarily influenced by the EVT technique used. Techniques using transient (BAC) or permanent (SAC and FD) device placement in the parent artery are associated with a higher rate of DWI lesions. TRIAL REGISTRATION NUMBER: ACET: Unique identifier: NCT02862756.

Longitudinal radiological follow-up of individual level non-ischemic cerebral enhancing lesions following endovascular aneurysm treatment.

BACKGROUND: Non-ischemic cerebral enhancing (NICE) lesions following aneurysm endovascular therapy are exceptionally rare, with unknown longitudinal evolution. OBJECTIVE: To evaluate the radiological behavior of individual NICE lesions over time. METHODS: Patients included in a retrospective national multicentric inception cohort were analyzed. NICE lesions were defined, using MRI, as delayed onset punctate, nodular, or annular foci enhancements with peri-lesion edema, distributed in the vascular territory of the aneurysm treatment, with no other confounding disease. Lesion burden and the longitudinal behavior of individual lesions were assessed. RESULTS: Twenty-two patients were included, with a median initial lesion burden of 36 (IQR 17-54) on the first MRI scan. Of the 22 patients with at least one follow-up MRI scan, 16 (73%) had new lesions occurring mainly within the first 200 weeks after the date of the procedure. The median number of new lesions per MRI was 6 (IQR 2-16). Among the same 22 patients, 7 (32%) had recurrent lesions. The median persistent enhancement of a NICE lesion was 13 weeks (IQR 6-30). No factor was predictive of early regression of enhancement activity with lesion regression kinetics mainly being patient-dependent. CONCLUSIONS: The behavior of individual NICE lesions was found to be highly variable with an overall patient-dependent regression velocity.

Rehearsals using patient-specific 3D-printed aneurysm models for simulation of endovascular embolization of complex intracranial aneurysms: 3D SIM study.

BACKGROUND: In neurovascular treatment planning, endovascular devices to manage complex intracranial aneurysms requiring intervention are often selected based on conventional measurements and interventional neuroradiologist experience. A recently developed technology allows a patient-specific 3D-printed model to mimic the navigation experience. The goal of this study was to assess the effect of pre-procedure 3D simulation on procedural and clinical outcomes for wide-neck aneurysm embolization. MATERIALS & METHODS: In this unblinded, non-randomized, prospective, multicenter study conducted from November 18 through December 20, patients with complex intracranial aneurysms (neck > 4 mm or ratio < 21) were treated by WEB or flow diverter stents (FDS). The primary endpoint was concordance between simulation and procedure, 3D-printed model accuracy as well as embolization outcomes including complications, procedure times, and radiation dose were also assessed. Secondary endpoint was to compare versus a retrospective WEB cohort. RESULTS: Twenty-one patients were treated, 76% of cases by WEB and 24% by FDS. Concordance between post-simulation and real procedure efficiency was 0.85 [0.69 - 1.00] for size device selection and 0.93 [0.79 - 1.00] for wall-apposition/aneurysm neck closure. Geometrical accuracy of the 3D-printed model showed a mean absolute shift of 0.11 mm. Two complications without major clinical impact were reported with a post-operative mRS similar to pre-procedure mRS for all patients. CONCLUSIONS: Rehearsal using accurate 3D-printed patient-specific aneurysm models enabled optimization of embolization strategy, resulting in reduced procedure duration and cumulative fluoroscopy time which translated to reduced radiation exposure compared to procedures performed without simulation.

CLinical Assessment of WEB device in Ruptured aneurYSms (CLARYS): 12-month angiographic results of a multicenter study.

BACKGROUND: The CLinical Assessment of WEB device in Ruptured aneurYSms (CLARYS) study has shown that the endovascular treatment of ruptured bifurcation aneurysms with the Woven EndoBridge (WEB) is safe and effective and provides protection against rebleeding at 1 month and 1 year. The 12-month angiographic follow-up is an important endpoint of the study. METHODS: The CLARYS study is a prospective multicenter study conducted in 13 European centers. The study enrolled 60 patients with 60 ruptured aneurysms of the anterior and posterior circulation. The study was conducted with an independent assessment of safety outcomes and imaging. RESULTS: Sixty patients with 60 ruptured bifurcation aneurysms to be treated with the WEB were included. Fifty-three aneurysms (88.3%) had a broad base with a dome to neck ratio <2 (mean 1.6). Of these, 46 patients were evaluated by an independent core laboratory with follow-up imaging performed at 12 months or before eventual retreatment. At 1 year, 19/46 aneurysms (41.3%) were completely occluded (Raymond-Roy grade I), 21/46 (45.7%) had a residual neck and 6/46 (13.0%) had residual aneurysm filling. Adequate occlusion was reported in 40/46 (87%) aneurysms. Six patients underwent target aneurysm retreatment. CONCLUSIONS: The CLARYS study has previously shown that the use of the WEB in the endovascular treatment of ruptured bifurcation aneurysms provides effective protection against rebleeding with a good safety profile. The angiographic occlusion rates at 1 year reported here are comparable to those already seen in previous multicenter studies which primarily included unruptured aneurysms.

CLinical Assessment of WEB device in Ruptured aneurYSms (CLARYS): results of 1-month and 1-year assessment of rebleeding protection and clinical safety in a multicenter study.

BACKGROUND: The primary goal of the CLARYS study is to assess the protection against rebleeding when treating ruptured bifurcation aneurysms with the Woven EndoBridge (WEB) device. METHODS: The CLARYS study is a prospective, multicenter study conducted in 13 European centers. Patients with ruptured bifurcation aneurysms were consecutively included between February 2016 and September 2017. The primary endpoint was defined as the rebleeding rate of the target aneurysm treated with the WEB within 30 days postprocedure. Secondary endpoints included periprocedural and postprocedural adverse events, total procedure and fluoroscopy times, and modified Rankin Scale score at 1 month and 1 year. RESULTS: Sixty patients with 60 ruptured bifurcation aneurysms to be treated with the WEB were included. A WEB device was successfully implanted in 93.3%. The rebleeding rate at 1 month and 1 year was 0%. The mean fluoroscopy time was 27.0 min. Twenty-three periprocedural complications were observed in 18 patients and resolved without sequelae in 16 patients. Two of these complications were attributed to the procedure and/or the use of the WEB, leading to a procedure/device-related intraoperative complication rate of 3.3%. Overall mortality at 1 month and 1 year was 1.7% and 3.8%, respectively and overall morbidity at 1 month and 1 year was 15% and 9.6%, respectively. WEB-related 1-month and 1-year morbidity and mortality was 0%. CONCLUSIONS: The interim results of CLARYS show that the endovascular treatment of ruptured bifurcation aneurysms with the WEB is safe and effective and, in particular, provides effective protection against rebleeding. It may induce profound change in the endovascular management of ruptured bifurcation aneurysms.

Non-ischemic cerebral enhancing lesions after intracranial aneurysm endovascular repair: a retrospective French national registry.

BACKGROUND: Non-ischemic cerebral enhancing (NICE) lesions are exceptionally rare following aneurysm endovascular therapy (EVT). OBJECTIVE: To investigate the presenting features and longitudinal follow-up of patients with NICE lesions following aneurysm EVT. METHODS: Patients included in a retrospective national multicentre inception cohort were analysed. NICE lesions were defined, using MRI, as delayed onset punctate, nodular or annular foci enhancements with peri-lesion edema, distributed in the vascular territory of the aneurysm EVT, with no other confounding disease. RESULTS: From a pool of 58 815 aneurysm endovascular treatment procedures during the study sampling period (2006-2019), 21/37 centres identified 31 patients with 32 aneurysms of the anterior circulation who developed NICE lesions (mean age 45±10 years). Mean delay to diagnosis was 5±9 months, with onset occurring a month or less after the index EVT procedure in 10 out of 31 patients (32%). NICE lesions were symptomatic at time of onset in 23 of 31 patients (74%). After a mean follow-up of 25±26 months, 25 patients (81%) were asymptomatic or minimally symptomatic without disability (modified Rankin Scale (mRS) score 0-1) at last follow-up while 4 (13%) presented with mild disability (mRS score 2). Clinical follow-up data were unavailable for two patients. Follow-up MRI (available in 27 patients; mean time interval after onset of 22±22 months) demonstrated persistent enhancement in 71% of cases. CONCLUSIONS: The clinical spectrum of NICE lesions following aneurysm EVT therapy spans a wide range of neurological symptoms. Clinical course is most commonly benign, although persistent long-term enhancement is frequent.

Combined use of contact aspiration and the stent retriever technique versus stent retriever alone for recanalization in acute cerebral infarction: the randomized ASTER 2 study protocol.

RATIONALE: Mechanical thrombectomy (MT) using a stent retriever (SR) device is currently the recommended treatment in ischemic stroke due to anterior circulation large vessel occlusion. Combining contact aspiration (CA) with SR is a promising new treatment, although it was not found to be superior to SR alone as first-line treatment for achieving successful reperfusion. AIM: To determine whether endovascular treatment combining first-line use of CA and SR is more efficient than SR alone. METHODS: The ASTER 2 clinical trial is a prospective, randomized, multicenter, open-label trial with a blinded endpoint. We included patients admitted with suspected anterior circulation ischemic stroke secondary to large vessel occlusion <8 hours from symptom onset. They were randomly allocated in a 1:1 ratio to one of two treatment groups (combined CA and SR or SR alone). In the case of failure of the assigned technique after three attempts, other adjunctive techniques were applied. STUDY OUTCOME: The primary outcome is the rate of successful/complete reperfusion (modified Thrombolysis In Cerebral Infarction (mTICI) score 2c/3) after the entire endovascular procedure. Secondary outcomes include reperfusion rates after the assigned first-line intervention alone and at the end of the procedure, procedural times, change in NIH Stroke Scale score at 24 hours, intracerebral hemorrhage at 24 hours, procedure-related serious adverse events, the modified Rankin Scale score, and all-cause mortality at 90 days and 1 year. The cost effectiveness of the two procedures will also be analyzed. DISCUSSION: This is the first head-to-head randomized trial to directly compare the efficacy of the combined use of CA and SR versus SR alone. This prospective trial aims to demonstrate the synergistic effects of CA and SR devices in first-line endovascular treatment.

Patient and aneurysm factors associated with aneurysm rupture in the population of the ARETA study.

BACKGROUND AND PURPOSE: Identifying patients with intracranial aneurysms (IA) who have a high risk of rupture is critical to determine optimal management. ARETA (Analysis of Recanalization after Endovascular Treatment of intracranial Aneurysm) is a prospective, multicenter study, dedicated to evaluating endovascular treatment of IA. We aimed to identify factors associated with ruptured status, using this very large series of patients with ruptured and unruptured aneurysms. METHODS: Several analyses were conducted in the ARETA population: univariate and multivariate analyses in the whole population of patients and aneurysms to determine patient and aneurysm factors associated with aneurysm rupture, as well as a matched pair analysis (based on aneurysm size) conducted in the subgroup of patients with only one aneurysm to analyze the patient and aneurysm factors simultaneously. RESULTS: From December 2013 to May 2015, 1289 patients with 1761 aneurysms were included in ARETA. The multivariate analysis identified four patient factors: elevated blood pressure (EBP), no familial history, single IA, and active smoking, and four aneurysm factors: size≥5mm, narrow neck, irregular shape, and ACA/Acom location, associated with rupture status. In the matched pair analysis, five risk factors of rupture were identified: no familial history of aneurysm, narrow neck, active smoking, ACA/Acom location, and irregular shape. CONCLUSIONS: The most important patient factors associated with IA rupture are smoking and EBP. Given that size is a well-identified aneurysm factor, narrow neck also seems to be associated with aneurysm rupture. Further studies are needed to confirm this factor and determine underlying mechanisms. Clinical Trial Registration-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01942512.

Patch-based super-resolution of arterial spin labeling magnetic resonance images.

Arterial spin labeling is a magnetic resonance perfusion imaging technique that, while providing results comparable to methods currently considered as more standard concerning the quantification of the cerebral blood flow, is subject to limitations related to its low signal-to-noise ratio and low resolution. In this work, we investigate the relevance of using a non-local patch-based super-resolution method driven by a high resolution structural image to increase the level of details in arterial spin labeling images. This method is evaluated by comparison with other image dimension increasing techniques on a simulated dataset, on images of healthy subjects and on images of subjects scanned for brain tumors, who had a dynamic susceptibility contrast acquisition. The influence of an increase of ASL images resolution on partial volume effects is also investigated in this work.

Is bridging therapy still required in stroke due to carotid artery terminus occlusions?

INTRODUCTION: Studies comparing endovascular stroke treatment using mechanical thrombectomy (MT) with or without prior IV tissue plasminogen activator (tPa) have included only 30% of internal carotid artery terminus occlusions (ICA-O), a known predictor of recanalization failure with IV tPa. OBJECTIVE: To carry out a retrospective multicenter analysis of prospectively collected data of consecutive patients to investigate the impact of intravenous thrombolysis on ICA-O by comparing patients treated with MT alone or bridging therapy (BT). MATERIAL AND METHODS: Patients with ICA-O treated with MT alone or BT were retrospectively examined and compared. Demographic data, vascular risk factors, treatment modalities, complications, technical and clinical outcomes were recorded. A propensity score (PS) analysis was used to compare modified Rankin Scale (mRS) score at 3 months and intracerebral hemorrhage (ICH) between groups. RESULTS: 141 consecutive patients (60% BT/40% MT) were included between January 2014 and June 2016. Baseline characteristics did not differ between the groups. There was no significant difference in the rate of Thrombolysis in Cerebral Infarction 2b/3, distal emboli, and median number of passes between the groups. There was a significant difference between BT and MT groups in the median time between imaging and groin puncture (median 97 min vs 75, p=0.007), the rate of ICH (44% vs 27%, p=0.05), but not for symptomatic ICH (18% vs 13%, p=0.49). With PS, there was a trend towards a higher rate of ICH (OR=2.3, 95% CI 0.9 to 5.9, p=0.09) in the BT group compared with the MT alone group, with no difference in mRS score ≤2 at 3 months (OR=1.6, 95% CI 0.7 to 3.7, p=0.29). CONCLUSION: There was no significant difference in clinical outcomes between patients receiving bridging therapy versus direct thrombectomy. Bridging therapy delayed time to groin puncture and increased ICH rate.

Mechanical thrombectomy with the ERIC retrieval device: initial experience.

OBJECTIVE: To report our experience with the Embolus Retriever with Interlinked Cage (ERIC) stentriever for use in mechanical endovascular thrombectomy (MET). METHODS: Thirty-four consecutive patients with acute stroke (21 men and 13 women; median age 66 years) determined appropriate for MET were treated with ERIC and prospectively included over a 6-month period at three different centers. The ERIC device differs from typical stentrievers in that it is designed with a series of interlinked adjustable nitinol cages that allow for fast thrombus capture, integration, and withdrawal. The evaluated endpoints were successful revascularization (Thrombolysis in Cerebral Infarction (TICI) 2b-3) and good clinical outcomes at 3 months (modified Rankin Scale (mRS) 0-2). RESULTS: Locations of the occlusions included the middle cerebral artery (13 patients), terminal carotid artery (11 patients), basilar artery (1 patient), and tandem occlusions (9 patients). IV thrombolysis was performed in 20/34 (58.8%) patients. Median times from symptom onset to recanalization and from puncture to recanalization were 325.5 min (180-557) and 78.5 min (14-183), respectively. Used as the first-line device, ERIC achieved a successful recanalization in 20/24 (83.3%) patients. Successful recanalization was associated with lower National Institutes of Health Stroke Scale scores at 24 h (8±6.5 vs 21.5±2.1; p=0.008) and lower mRS at 3 months (2.7±2.1 vs 5.3±1.1; p=0.04). Three procedural complications and four asymptomatic hemorrhages were recorded. Good clinical outcomes at 3 months were seen in 15/31 (48.4%) patients. CONCLUSIONS: The ERIC device is an innovative stentriever allowing fast, effective, and safe MET.

Diagnostic Value of Fractal Analysis for the Differentiation of Brain Tumors Using 3-Tesla Magnetic Resonance Susceptibility-Weighted Imaging.

BACKGROUND: Susceptibility-weighted imaging (SWI) of brain tumors provides information about neoplastic vasculature and intratumoral micro- and macrobleedings. Low- and high-grade gliomas can be distinguished by SWI due to their different vascular characteristics. Fractal analysis allows for quantification of these radiological differences by a computer-based morphological assessment of SWI patterns. OBJECTIVE: To show the feasibility of SWI analysis on 3-T magnetic resonance imaging to distinguish different kinds of brain tumors. METHODS: Seventy-eight patients affected by brain tumors of different histopathology (low- and high-grade gliomas, metastases, meningiomas, lymphomas) were included. All patients underwent preoperative 3-T magnetic resonance imaging including SWI, on which the lesions were contoured. The images underwent automated computation, extracting 2 quantitative parameters: the volume fraction of SWI signals within the tumors (signal ratio) and the morphological self-similar features (fractal dimension [FD]). The results were then correlated with each histopathological type of tumor. RESULTS: Signal ratio and FD were able to differentiate low-grade gliomas from grade III and IV gliomas, metastases, and meningiomas (P < .05). FD was statistically different between lymphomas and high-grade gliomas (P < .05). A receiver-operating characteristic analysis showed that the optimal cutoff value for differentiating low- from high-grade gliomas was 1.75 for FD (sensitivity, 81%; specificity, 89%) and 0.03 for signal ratio (sensitivity, 80%; specificity, 86%). CONCLUSION: FD of SWI on 3-T magnetic resonance imaging is a novel image biomarker for glioma grading and brain tumor characterization. Computational models offer promising results that may improve diagnosis and open perspectives in the radiological assessment of brain tumors. ABBREVIATIONS: FD, fractal dimensionSR, signal ratioSWI, susceptibility-weighted imaging.

An a contrario approach for the detection of patient-specific brain perfusion abnormalities with arterial spin labelling.

In this paper, we introduce a new locally multivariate procedure to quantitatively extract voxel-wise patterns of abnormal perfusion in individual patients. This a contrario approach uses a multivariate metric from the computer vision community that is suitable to detect abnormalities even in the presence of closeby hypo- and hyper-perfusions. This method takes into account local information without applying Gaussian smoothing to the data. Furthermore, to improve on the standard a contrario approach, which assumes white noise, we introduce an updated a contrario approach that takes into account the spatial coherency of the noise in the probability estimation. Validation is undertaken on a dataset of 25 patients diagnosed with brain tumours and 61 healthy volunteers. We show how the a contrario approach outperforms the massively univariate general linear model usually employed for this type of analysis.

Ultra-small superparamagnetic iron oxide enhancement is associated with higher loss of brain tissue structure in clinically isolated syndrome.

BACKGROUND: Macrophages are important components of inflammatory processes in multiple sclerosis, closely linked to axonal loss, and can now be observed in vivo using ultra-small superparamagnetic iron oxide (USPIO). In the present 1-year longitudinal study, we aimed to determine the prevalence and the impact on tissue injury of macrophage infiltration in patients after the first clinical event of multiple sclerosis. METHODS: Thirty-five patients, 32 years mean age, were imaged in a mean of 66 days after their first event using conventional magnetic resonance imaging, gadolinium (Gd) to probe blood-brain barrier integrity, USPIO to study macrophage infiltration and magnetization transfer ratio (MTR) to assess tissue structure integrity. Statistics were performed using two-group repeated-measures ANOVA. Any patient received treatment at baseline. RESULTS: At baseline, patients showed 17 USPIO-positive lesions reflecting infiltration of macrophages present from the onset. This infiltration was associated with local higher loss of tissue structure as emphasized by significant lower MTRnorm values (p<0.03) in USPIO(+)/Gd(+) lesions (n=16; MTRnormUSPIO(+)/Gd(+)=0.78 at baseline, MTRnormUSPIO(+)/Gd(+)=0.81 at M12) relative to USPIO(-)/Gd(+) lesions (n=67; MTRnormUSPIO(-)/Gd(+)=0.82 at baseline, MTRnormUSPIO(-)/Gd(+)=0.85 at M12). No interaction in MTR values was observed during the 12 months follow-up (lesion type × time). CONCLUSION: Infiltration of activated macrophages evidenced by USPIO enhancement, is present at the onset of multiple sclerosis and is associated with higher and persistent local loss of tissue structure. Macrophage infiltration affects more tissue structure while tissue recovery during the following year has a similar pattern for USPIO and Gd-enhanced lesions, leading to relative higher persistent local loss of tissue structure in lesions showing USPIO enhancement at baseline.

Dynamic contrast-enhanced MRI: Study of inter-software accuracy and reproducibility using simulated and clinical data.

PURPOSE: To test the reproducibility and accuracy of pharmacokinetic parameter measurements on five analysis software packages (SPs) for dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), using simulated and clinical data. MATERIALS AND METHODS: This retrospective study was Institutional Review Board-approved. Simulated tissues consisted of pixel clusters of calculated dynamic signal changes for combinations of Tofts model pharmacokinetic parameters (volume transfer constant [K(trans) ], extravascular extracellular volume fraction [ve ]), longitudinal relaxation time (T1 ). The clinical group comprised 27 patients treated for rectal cancer, with 36 3T DCE-MR scans performed between November 2012 and February 2014, including dual-flip-angle T1 mapping and a dynamic postcontrast T1 -weighted, 3D spoiled gradient-echo sequence. The clinical and simulated images were postprocessed with five SPs to measure K(trans) , ve , and the initial area under the gadolinium curve (iAUGC). Modified Bland-Altman analysis was conducted, intraclass correlation coefficients (ICCs) and within-subject coefficients of variation were calculated. RESULTS: Thirty-one examinations from 23 patients were of sufficient technical quality and postprocessed. Measurement errors were observed on the simulated data for all the pharmacokinetic parameters and SPs, with a bias ranging from -0.19 min(-1) to 0.09 min(-1) for K(trans) , -0.15 to 0.01 for ve , and -0.65 to 1.66 mmol.L(-1) .min for iAUGC. The ICC between SPs revealed moderate agreement for the simulated data (K(trans) : 0.50; ve : 0.67; iAUGC: 0.77) and very poor agreement for the clinical data (K(trans) : 0.10; ve : 0.16; iAUGC: 0.21). CONCLUSION: Significant errors were found in the calculated DCE-MRI pharmacokinetic parameters for the perfusion analysis SPs, resulting in poor inter-software reproducibility. J. Magn. Reson. Imaging 2016;43:1288-1300.

Robust estimation of the cerebral blood flow in arterial spin labelling.

The introduction of arterial spin labelling (ASL) techniques in magnetic resonance imaging (MRI) has made feasible a non-invasive measurement of the cerebral blood flow (CBF). However, to date, the low signal-to-noise ratio of ASL gives us no option but to repeat the acquisition to accumulate enough data in order to get a reliable signal. The perfusion signal is then usually extracted by averaging across the repetitions. But the sample mean is very sensitive to outliers. A single incorrect observation can therefore be the source of strong detrimental effects on the perfusion-weighted image estimated with the sample mean. We propose to estimate robust ASL CBF maps with M-estimators to overcome the deleterious effects of outliers. The behavior of this method is compared to z-score thresholding as recommended in Tan et al. (Journal of Magnetic Resonance Imaging 2009;29(5):1134-9.). Validation on simulated and real data is provided. Quantitative validation is undertaken by measuring the correlation with the most widespread technique to measure perfusion with MRI: dynamic susceptibility weighted contrast imaging.

Template-based approach for detecting motor task activation-related hyperperfusion in pulsed ASL data.

Arterial spin labeling (ASL) permits the noninvasive measurement of quantitative values of cerebral blood flow (CBF) and is thus well adapted to study inter- and intrasubject perfusion variations whether at rest or during an fMRI task. In this study, a template approach to detect brain activation as a CBF difference between resting and activated groups was compared with a standard generalized linear model (GLM) analysis. A basal perfusion template of PICORE-Q2TIPS ASL images acquired at 3T from a group of 25 healthy subjects (mean age 31.6 ± 8.3 years) was created. The second group of 12 healthy subjects (mean age 28.6 ± 2.7 years) performed a block-design motor task. The template was compared with the mean activated image of the second group both at the individual and at the group level to extract activation maps. The results obtained using a GLM analysis of the whole sequence was used as ground truth for comparison. The influences of spatial normalization using DARTEL registration and of correction of partial volume effects (PVE) in the construction of the template were assessed. Results showed that a basal perfusion template can detect activation-related hyperperfusion in motor areas. The true positive ratio was increased by 2.5% using PVE-correction and by 3.2% using PVE-correction with DARTEL registration. On average, the group comparison presented a 2.2% higher true positive ratio than the one-to-many comparison.

Highly accelerated dynamic contrast enhanced imaging.

PURPOSE: Dynamic contrast-enhanced imaging provides unique physiological information, notably the endothelial permeability (K(trans)), and may improve the diagnosis and management of multiple pathologies. Current acquisition methods provide limited spatial-temporal resolution and field-of-view, often preventing characterization of the entire pathology and precluding measurement of the arterial input function. We present a method for highly accelerated dynamic imaging and demonstrate its utility for dynamic contrast-enhanced modeling. METHODS: We propose a novel Poisson ellipsoid sampling scheme and enforce multiple spatial and temporal l1-norm constraints during image reconstruction. Retrospective and prospective analyses were performed to validate the approach. RESULTS: Retrospectively, no mean bias or diverging trend was observed as the acceleration rate was increased from 3× to 18×; less than 10% error was measured in K(trans) at any individual rates in this range. Prospectively accelerated images at a rate of 36× enabled full brain coverage with 0.94 × 0.94 × 1.9 mm(3) spatial and 4.1 s temporal resolutions. Images showed no visible degradation and provided accurate K(trans) values when compared to a clinical population. CONCLUSION: Highly accelerated dynamic MRI using compressed sensing and parallel imaging provides accurate permeability modeling and enables full brain, high resolution acquisitions.

Development of workflow task analysis during cerebral diagnostic angiographies: time-based comparison of junior and senior tasks.

OBJECTIVE: Assessing neuroradiologists' skills in the operating room (OR) is difficult and often subjective. This study used a workflow time-based task analysis approach while performing cerebral angiography. METHODS: Eight angiographies performed by a senior neuroradiologist and eight performed by a junior neuroradiologist were compared. Dedicated software with specific terminology was used to record the tasks. Procedures were subdivided into phases, each comprising multiple tasks. Each task was defined as a triplet, associating an action, an instrument and an anatomical structure. The duration of each task was the metric. Total duration of the procedure, task duration and the number of times a task was repeated were identified. The focus was on tasks using fluoroscopy and for moving the X-ray table/tube. RESULTS: The total duration of tasks to complete the entire procedure was longer for the junior operators than for the seniors (P=0.012). The mean duration per task during the navigation phase was 86s for the juniors and 43s for the seniors (P=0.002). The total and mean durations of tasks involving the use of fluoroscopy were also longer for the juniors (P=0.002 and P=0.033, respectively). For tasks involving the table/tube, the total and mean durations were again longer for the juniors (P=0.019 and P=0.082, respectively). CONCLUSION: This approach allows reliable skill assessment in the radiology OR and comparison of junior and senior competencies during cerebral diagnostic angiography. This new tool can improve the quality and safety of procedures, and facilitate the learning process for neuroradiologists.

Patient-specific detection of perfusion abnormalities combining within-subject and between-subject variances in Arterial Spin Labeling.

In this paper, patient-specific perfusion abnormalities in Arterial Spin Labeling (ASL) were identified by comparing a single patient to a group of healthy controls using a mixed-effect hierarchical General Linear Model (GLM). Two approaches are currently in use to solve hierarchical GLMs: (1) the homoscedastic approach assumes homogeneous variances across subjects and (2) the heteroscedastic approach is theoretically more efficient in the presence of heterogeneous variances but algorithmically more demanding. In practice, in functional magnetic resonance imaging studies, the superiority of the heteroscedastic approach is still under debate. Due to the low signal-to-noise ratio of ASL sequences, within-subject variances have a significant impact on the estimated perfusion maps and the heteroscedastic model might be better suited in this context. In this paper we studied how the homoscedastic and heteroscedastic approaches behave in terms of specificity and sensitivity in the detection of patient-specific ASL perfusion abnormalities. Validation was undertaken on a dataset of 25 patients diagnosed with brain tumors and 36 healthy volunteers. We showed evidence of heterogeneous within-subject variances in ASL and pointed out an increased false positive rate of the homoscedastic model. In the detection of patient-specific brain perfusion abnormalities with ASL, modeling heterogeneous variances increases the sensitivity at the same specificity level.