Using 3D spatial correlations to improve the noise robustness of multi component analysis of 3D multi echo quantitative T2 relaxometry data.

PURPOSE: We present a computationally feasible and iterative multi-voxel spatially regularized algorithm for myelin water fraction (MWF) reconstruction. This method utilizes 3D spatial correlations present in anatomical/pathological tissues and underlying B1+-inhomogeneity or flip angle inhomogeneity to enhance the noise robustness of the reconstruction while intrinsically accounting for stimulated echo contributions using T2-distribution data alone. METHODS: Simulated data and in vivo data acquired using 3D non-selective multi-echo spin echo (3DNS-MESE) were used to compare the reconstruction quality of the proposed approach against those of the popular algorithm (the method by Prasloski et al.) and our previously proposed 2D multi-slice spatial regularization spatial regularization approach. We also investigated whether the inter-sequence correlations and agreements improved as a result of the proposed approach. MWF-quantifications from two sequences, 3DNS-MESE vs 3DNS-gradient and spin echo (3DNS-GRASE), were compared for both reconstruction approaches to assess correlations and agreements between inter-sequence MWF-value pairs. MWF values from whole-brain data of six volunteers and two multiple sclerosis patients are being reported as well. RESULTS: In comparison with competing approaches such as Prasloski's method or our previously proposed 2D multi-slice spatial regularization method, the proposed method showed better agreements with simulated truths using regression analyses and Bland-Altman analyses. For 3DNS-MESE data, MWF-maps reconstructed using the proposed algorithm provided better depictions of white matter structures in subcortical areas adjoining gray matter which agreed more closely with corresponding contrasts on T2-weighted images than MWF-maps reconstructed with the method by Prasloski et al. We also achieved a higher level of correlations and agreements between inter-sequence (3DNS-MESE vs 3DNS-GRASE) MWF-value pairs. CONCLUSION: The proposed algorithm provides more noise-robust fits to T2-decay data and improves MWF-quantifications in white matter structures especially in the sub-cortical white matter and major white matter tract regions.

Can resistance training impact MRI outcomes in relapsing-remitting multiple sclerosis?

BACKGROUND: Multiple sclerosis (MS) is characterised by accelerated brain atrophy, which relates to disease progression. Previous research shows that progressive resistance training (PRT) can counteract brain atrophy in other populations. OBJECTIVE: To evaluate the effects of PRT by magnetic resonance imaging (MRI) and clinical measures of disease progression in people with MS. METHODS: This study was a 24-week randomised controlled cross-over trial, including a Training ( n = 18, 24 weeks of PRT followed by self-guided physical activity) and Waitlist group ( n = 17, 24 weeks of habitual lifestyle followed by PRT). Assessments included disability measures and MRI (lesion load, global brain volume, percentage brain volume change (PBVC) and cortical thickness). RESULTS: While the MS Functional Composite score improved, Expanded Disability Status Scale, lesion load and global brain volumes did not differ between groups. PBVC tended to differ between groups and higher absolute cortical thickness values were observed in 19 of 74 investigated cortical regions after PRT. Observed changes were confirmed and reproduced when comparing relative cortical thickness changes between groups for four areas: anterior cingulate gyrus, temporal pole, orbital sulcus and inferior temporal sulcus. CONCLUSION: PRT seem to induce an increase in cortical thickness, indicating that PRT have a neuroprotective or even neuroregenerative effect in relapsing-remitting MS.

Subtypes of primary angiitis of the CNS identified by MRI patterns reflect the size of affected vessels.

OBJECTIVE: To describe patterns of diagnostic findings, and identify subgroups of primary angiitis of the central nervous system (PACNS). METHODS: We retrospectively analysed 31 patients with PACNS. Cases were selected by predetermined diagnostic criteria and stratified into biopsy-proven and imaging-based PACNS. We compared clinical characteristics, cerebrospinal fluid (CSF) findings and imaging results including high-resolution vessel wall MRI between groups. RESULTS: There were 31 cases of PACNS (mean age 45.6 years, 58.1% female), of whom 17 (55%) were biopsy-proven, 14 (45%) were based on imaging findings. Patients with a positive biopsy had fewer infarcts (29.4% vs 85.7%, p=0.003), were more likely to have meningeal and parenchymal contrast enhancement (76.5% vs 28.6%, p=0.012), were less likely to have abnormal MR angiography (11.8% vs 100%, p<0.001) and did not show vessel wall enhancement at the time of diagnosis (0% vs 76.9%, p<0.001). In contrast, patients with imaging-based diagnosis showed more frequently multiple infarcts and vessel abnormalities, with vessel wall enhancement in most of the cases. Clinical characteristics and CSF analysis did not reveal marked differences between groups. INTERPRETATION: Multi-parametric MRI distinguishes two subtypes of PACNS that most likely differ concerning the affected vessel size. Biopsy-proven PACNS primarily involves smaller vessels beyond the resolution of vascular imaging, while imaging-based PACNS affects predominantly medium-sized vessels leading to false-negative biopsy results. Using distinct MRI patterns may be helpful for selecting patients for appropriate invasive diagnostic modalities.

Noise robust spatially regularized myelin water fraction mapping with the intrinsic B1-error correction based on the linearized version of the extended phase graph model.

PURPOSE: To improve the quantification accuracy of transverse relaxometry by accounting for B1 -error, after minimizing slice profile imperfections. MATERIALS AND METHODS: The slice profile of refocusing pulses was optimized by setting refocusing slice thicknesses three times that of the excitation pulse. The first step of data processing combined the L-curve approach with the linearized version of the extended phase graph model to jointly estimate the temporal regularization constant map and the flip angle error (FAE)-map. The second step improved the noise robustness of the reconstruction by imposing a spatial smoothness constraint on T2 -distributions. The proposed method (spatial-regularization-with-FAE-correction) was evaluated against methods without FAE-correction (conventional-regularization-without-FAE-correction, spatial-regularization-without-FAE-correction) and conventional-regularization-with-FAE-correction using relevant statistics (simulated data: mean square myelin reconstruction error [MSMRE] and averaged-symmetric-Kullbeck-Leibler score [SKL] between returned distributions and ground truths; experimental data: median of mean square error [MMSE] of fitting across entire data-set and coefficient of variation [COV] in white-matter [WM] regions of interest [ROIs]). RESULTS: In simulation, our method resulted in reduced MSMRE (at signal-to-noise ratio [SNR] = 200: MSMRESpatial-regularization-without-FAEC = 0.057; MSMRESpatial-regularization-with-FAEC = 0.0107) and reduced SKL scores (at SNR = 200: SKLSpatial-regularization-without-FAEC = 0.061; SKLSpatial-regularization-with-FAEC = 0.0143). In human volunteers, our method yielded a reduced MSE of fitting (MMSESpatial-regularization-without-FAEC = (2.26 ± 0.60) × 10(-3) ; MMSESpatial-regularization-with-FAEC = (1.57 ± 0.44) × 10(-4) )and also resulted in reduced COV (COVSpatial-regularization-without-FAEC = 0.08-0.19; COVSpatial-regularization-with-FAEC = 0.09-0.12). In a water-phantom, a good correlation between the absolute value of measured B1 -map and FAE-map was found (regression analysis: slope = 1.04; R(2) = 0.66). CONCLUSION: The proposed method resulted in more accurate and noise robust myelin water fraction maps with improved depiction of subcortical WM structures.

Visual and region of interest-based inter-rater agreement in the assessment of the diffusion-weighted imaging- fluid-attenuated inversion recovery mismatch.

BACKGROUND AND PURPOSE: WAKE-UP is a randomized, placebo-controlled MRI-based trial of thrombolysis in wake-up stroke using the mismatch between a lesion's visibility in diffusion-weighted imaging and fluid-attenuated inversion recovery (FLAIR) sequences as its main imaging inclusion criterion. Visual judgment of lesion conspicuity on FLAIR is however methodically limited by moderate inter-rater agreement. We therefore sought to improve rating homogeneity by incorporating quantitative signal intensity measurements. METHODS: One hundred forty-three data sets of patients with acute ischemic stroke were visually rated by 8 raters with respect to WAKE-UP study inclusion and exclusion criteria, and inter-rater agreement was calculated. A subanalysis was performed on 45 cases to determine a threshold value of relative signal intensity (rSI) between the ischemic lesion and contralateral healthy tissue which best corresponded to a visually established verdict of FLAIR positivity. The usefulness of this threshold in improving inter-rater agreement was evaluated in an additional sample of 50 patients. RESULTS: Inter-rater agreement for inclusion into the WAKE-UP trial was 73% with a free-marginal κ of 0.46. A threshold of rSI which best correlated with the visual rating of lesions as FLAIR positive was 1.20. The addition of rSI measurements to visual evaluation did not change the inter-rater agreement. CONCLUSIONS: Introducing a semiquantitative measure for FLAIR rSI did not improve the agreement between individual raters. However, enhancing visual assessment with rSI measurements can provide reassurance to local investigators in cases of uncertainty.

Influence of stroke infarct location on functional outcome measured by the modified rankin scale.

BACKGROUND AND PURPOSE: In the early days after ischemic stroke, information on structural brain damage from MRI supports prognosis of functional outcome. It is rated widely by the modified Rankin Scale that correlates only moderately with lesion volume. We therefore aimed to elucidate the influence of lesion location from early MRI (days 2-3) on functional outcome after 1 month using voxel-based lesion symptom mapping. METHODS: We analyzed clinical and MRI data of patients from a prospective European multicenter stroke imaging study (I-KNOW). Lesions were delineated on fluid-attenuated inversion recovery images on days 2 to 3 after stroke onset. We generated statistic maps of lesion contribution related to clinical outcome (modified Rankin Scale) after 1 month using voxel-based lesion symptom mapping. RESULTS: Lesion maps of 101 patients with middle cerebral artery infarctions were included for analysis (right-sided stroke, 47%). Mean age was 67 years, median admission National Institutes of Health Stroke Scale was 11. Mean infarct volumes were comparable between both sides (left, 37.5 mL; right, 43.7 mL). Voxel-based lesion symptom mapping revealed areas with high influence on higher modified Rankin Scale in regions involving the corona radiata, internal capsule, and insula. In addition, asymmetrically distributed impact patterns were found involving the right inferior temporal gyrus and left superior temporal gyrus. CONCLUSIONS: In this group of patients with stroke, characteristic lesion patterns in areas of motor control and areas involved in lateralized brain functions on early MRI were found to influence functional outcome. Our data provide a novel map of the impact of lesion localization on functional stroke outcome as measured by the modified Rankin Scale.

Elevated T2-values in MRI of stroke patients shortly after symptom onset do not predict irreversible tissue infarction.

Distinct from signal alterations in diffusion-weighted images, T(2)-values are also dependent on tissue water content and known to increase with time from symptom onset in acute ischaemic stroke. The purpose of this study was to evaluate whether there is a detectable increase of T(2)-values in different regions in acute ischaemic stroke in the acute and subacute situation and to study the effect of recanalization on the evaluation of T(2)-values in the subacute phase. In addition, we sought to evaluate whether this increase in T(2)-values is reversible. For this purpose, 22 patients with acute ischaemic stroke in the territory of the middle cerebral artery underwent magnetic resonance imaging including diffusion-weighted imaging, perfusion-weighted imaging, fluid-attenuated inversion recovery to determine final infarct size, time-of-flight-angiography (acute and on day 1 or 2) and a triple echo-T(2)-sequence (calculation of T(2) maps) within 6 h after symptom onset. Images were co-registered and regions of diffusion restriction and prolonged time-to-peak as well as surviving tissue (surviving tissue = time-to-peak - final infarct size) and lesion growth (lesion growth = final infarct size-diffusion restriction) were defined and superimposed onto the quantitative T(2) map. In addition, patients were dichotomized according to recanalization information. Mean quantitative T(2)-values were derived for each patient within each region of interest. Mean T(2)-values for patients with recanalization (n = 15) in surviving tissue region of interest were 115.8 ± 7.2 ms (mean ± SD) and in the lesion growth region of interest 114.6 ± 7.0 ms. T(2)-values for patients without recanalization (n = 7) were 117.7 ± 11.4 ms in surviving tissue region of interest and 117.3 ± 12.1 ms in lesion growth region of interest. There was no significant difference between T(2)-values measured in lesion growth and surviving tissue region of interest for patients with or without recanalization. Even though it has been shown that T(2)-values increase with time from symptom onset within the infarct core, increased T(2)-values in areas of perfusion impairment do not identify irreversible damaged brain tissue and high T(2)-values are even found in tissue that is not part of the final infarct lesion and can therefore normalize. In conclusion, this study suggests that T(2)-values are not a valid imaging biomarker in acute stroke to predict tissue outcome.

Infarction of 'non-core-non-penumbral' tissue after stroke: multivariate modelling of clinical impact.

There is considerable intersubject variability in early neurological course after anterior circulation stroke, yet the pathophysiology underlying this variability is not fully understood. Here, we hypothesize that, although not predicted by current pathophysiological models, infarction of 'non-core-non-penumbral' (i.e. clinically silent) brain tissue may nevertheless occur, and negatively influence clinical course over and above the established positive impact of penumbral salvage. In order to test this hypothesis, non-core-non-penumbral tissue was identified in two independent prospectively recruited cohorts, using computed tomography perfusion, and magnetic resonance perfusion- and diffusion-weighted imaging, respectively. Follow-up structural magnetic resonance imaging was obtained about 1 month later in all patients to map the final infarct. The volumes of both the acutely silent but eventually infarcted tissue, and the eventually non-infarcted penumbra, were determined by performing voxel-wise analysis of the acute and follow-up image sets, using previously validated perfusion thresholds. Early neurological course was expressed as change in National Institutes of Health Stroke Scale scores between the acute and 1-month assessments, relative to the acute score. The relationship between the acutely silent but eventually infarcted tissue volume and early neurological course was tested using a multivariate regression model that included the volume of non-infarcted penumbra. Thirty-four and 58 patients were recruited in the computed tomography perfusion and magnetic resonance perfusion cohorts, respectively (mean onset-to-imaging time: 136 and 156 min; 27 and 42 patients received intravenous thrombolysis, respectively). Infarction of acutely silent tissue was identified in most patients in both cohorts. Although its volume (median 0.2 and 2 ml, respectively) was much smaller than that of salvaged penumbra (59.3 and 93 ml, respectively), it was substantial in ∼10% of patients. As expected, salvaged penumbra strongly positively influenced early neurological course. Even after correcting for the latter effect in the multivariate model, infarction of acutely silent tissue independently negatively influenced early neurological course in both cohorts (P=0.018 and 0.031, respectively). This is the first systematic study to document infarction of acutely silent tissue after anterior circulation stroke, and to show that it affects a sizeable fraction of patients and has the predicted negative impact on clinical course. These findings were replicated in two independent cohorts, regardless of the perfusion imaging modality used. Preventing infarction of the tissue not initially at risk should have direct clinical benefit.

Signal intensity in T2' magnetic resonance imaging is related to brain glioma grade.

OBJECTIVES: T2' values reflect the presence of deoxyhaemoglobin related to high local oxygen extraction. We assessed the feasibility of T2' imaging to display regions with high metabolic activity in brain gliomas. METHODS: MRI was performed in 25 patients (12 female; median age 46 years; range 2-69) with brain gliomas with additional T2 and T2* sequences. T2' maps were derived from T2 and T2*. Dynamic susceptibility weighted contrast (DSC) perfusion was performed in 12/25 patients. Images were visually assessed by two readers and five ROIs were evaluated for each patient. Pearson correlation, Mann-Whitney and Kruskal-Wallis tests were applied for statistical analysis. RESULTS: Three patients were not further evaluated because of artefacts. Mean values of high-grade (III-IV) gliomas showed significantly lower T2' values than low-grade (II) gliomas (p < 0.001). An inverse relationship was observed between rCBV and sqr (T2') (r = -0.463, p < 0.001). No correlation was observed between T2' and rCBV for grade II tumours (r = 0.038; p = 0.875). CONCLUSIONS: High-grade tumours revealed lower T2' values, presumably because of higher oxygen consumption in proliferating tissue. Our results indicate that T2' imaging can be used as an alternative to DSC perfusion in the detection of subtle deviations in tumour metabolism.

Macromolecule content influences proton diffusibility in gliomas.

OBJECTIVES: Different compositions of the extra cellular matrix with changing concentrations of more or less hydrophilic components like proteins may have a major influence on the diffusion phenomena found in gliomas. METHODS: 24 patients (14 male / 10 female) with histologically confirmed non necrotic glioma underwent preoperative MRI, including magnetisation transfer (MTR), triple echo T2 weighted (T2W) and diffusion weighted (DWI) sequences. Apparent diffusion coefficient (ADC), quantitative T2 and MTR maps were calculated and regions of interest (ROIs) were placed in the tumour centre (TU) and in the contralateral hemisphere (NWM). Informed consent was obtained. The study was approved by the local ethic comity. RESULTS: Mean values evaluated in the NWM / TU were (± standard deviation); ADC: 0.78 (±0.08) × 10-3 mm2/s / 1.32 (±0.27) × 10-3 mm2/s, T2: 101.66 (±12.00) ms / 252.11 (±104.53) ms, MTR: 0.52 (±0.01) / 0.40 (±0.04). The mean value of each parameter correlated highly significant with the others (p < 0.01). CONCLUSION: Our results suggest that macromolecules binding protons in their vicinity are a major determinant of proton diffusivity in brain tumours in addition to other factors such as mechanical barriers like membranes or the size of the extra-cellular space.

Negative fluid-attenuated inversion recovery imaging identifies acute ischemic stroke at 3 hours or less.

OBJECTIVE: To evaluate the use of fluid-attenuated inversion recovery (FLAIR) imaging as surrogate marker of lesion age within the first 6 hours of ischemic stroke. METHODS: e analyzed FLAIR and diffusion-weighted imaging (DWI) sequences performed within 6 hours of symptom onset in 120 consecutive patients with ischemic stroke with known symptom onset. The visibility of acute ischemic lesions on FLAIR images was judged in two steps (on FLAIR alone and with knowledge of DWI) and compared with DWI. RESULTS: egative FLAIR in the case of positive DWI allocated ischemic lesions to a time window 3 hours or less with a high specificity (0.93) and a high positive predictive value (0.94), whereas sensitivity (0.48) and negative predictive value (0.43) were low. Lesion visibility on FLAIR images alone (35.6%) and with knowledge of DWI (62.5%) was lower than on DWI (97.1%). The sensitivity of FLAIR increased with increasing time from symptom onset from 27.0/50.0%

Abciximab is a safe rescue therapy in thromboembolic events complicating cerebral aneurysm coil embolization: single center experience in 42 cases and review of the literature.

BACKGROUND AND PURPOSE: The purpose of this study was to estimate the safety and efficacy of abciximab treatment in combination with prophylactic heparin, acetylsalicylic acid (ASA), and clopidogrel application in cases of thrombus formation complicating endovascular coil embolization in cerebral aneurysms. METHODS: Thromboembolic incidents during endovascular management of 515 consecutive cerebral aneurysms were observed in 48 cases (9.3%). Eight incidents were observed during embolization of incidental aneurysms (8/174; 4.6%, 95% CI: 2.0 to 8.9%). All patients underwent anticoagulation with heparin and platelet-inhibition with ASA during treatment procedure. In addition, clopidogrel orally was applied 3 days preoperatively in patients with incidental aneurysms. In case of thrombus formation, glycoprotein IIb-IIIa inhibitor abciximab was given in 42 cases. No coagulation-effective rescue treatment was conducted in 5 cases. One patient was treated with r-tPA. End points were infarction on follow-up cranial CT and the rate of intracranial hemorrhages. RESULTS: No infarcts on follow-up CT were observed after treatment with abciximab in 29/42 patients (69.0%, 95% CI: 52.9 to 82.4%). No coagulant rescue therapy was applied in 5 patients because of a small nonocclusive thrombus or good collateral blood supply, showing consecutive infarction on follow-up CT in 3 cases as did the 1 patient treated with r-tPA. No periprocedural bleedings or rebleedings were observed in any case. CONCLUSIONS: Abciximab was safe as rescue treatment in cases of thrombus formation during endovascular aneurysm coiling. In our study the use of Abciximab, in combination with prophylactic anticoagulation and antiaggregation, does not lead to additional intracranial hemorrhages or any extracranial bleeding complications.

Quantitative t2 values predict time from symptom onset in acute stroke patients.

BACKGROUND AND PURPOSE: We hypothesize that in comparison to diffusion-weighted imaging, quantitative T2 values (qT2) are more directly related to water uptake in ischemic tissue, depending on time from symptom onset. We measured the increase of qT2 in the infarct core to quantify the correlation between time from symptom onset and change in qT2. METHODS: Thirty-six patients with acute ischemic stroke in the territory of the proximal middle cerebral artery underwent MRI including diffusion-weighted imaging, fluid-attenuated inversion recovery, and a triple-echo T2 sequence (calculation of T2 maps) within 6 hours after symptom onset. Regions of decreased apparent diffusion coefficient <550 x 10(-9) mm(2)/sec were defined and superimposed onto the corresponding T2 map and the unaffected side in the horizontally flipped maps. Differences of T2/apparent diffusion coefficient values between affected and unaffected side were calculated (differences of T2/differences of apparent diffusion coefficient). Fluid-attenuated inversion recovery images were rated for lesion visibility. RESULTS: Differences of T2 showed a significant correlation with time from symptom onset (R=0.580; P<0.001). T2 values measured in patients with visible fluid-attenuated inversion recovery lesions were significantly higher than in those without visible hyperintensity (P<0.001). The accuracy of qT2 to predict a time from symptom onset <3 hours was 0.794, whereas the corresponding accuracy for visual assessment of fluid-attenuated inversion recovery images was 0.676. CONCLUSIONS: T2 values demonstrated a strong correlation with time from onset, suggesting different pathophysiologic mechanisms than diffusion restriction. Whereas fluid-attenuated inversion recovery only provides binary information on lesion visibility, T2 values correlate well with time from symptom onset, and are free from operator bias, increasing reproducibility to determine time from symptom onset.

Technical considerations of multi-parametric tissue outcome prediction methods in acute ischemic stroke patients.

Decisions regarding acute stroke treatment rely heavily on imaging, but interpretation can be difficult for physicians. Machine learning methods can assist clinicians by providing tissue outcome predictions for different treatment approaches based on acute multi-parametric imaging. To produce such clinically viable machine learning models, factors such as classifier choice, data normalization, and data balancing must be considered. This study gives comprehensive consideration to these factors by comparing the agreement of voxel-based tissue outcome predictions using acute imaging and clinical parameters with manual lesion segmentations derived from follow-up imaging. This study considers random decision forest, generalized linear model, and k-nearest-neighbor machine learning classifiers in conjunction with three data normalization approaches (non-normalized, relative to contralateral hemisphere, and relative to contralateral VOI), and two data balancing strategies (full dataset and stratified subsampling). These classifier settings were evaluated based on 90 MRI datasets from acute ischemic stroke patients. Distinction was made between patients recanalized using intraarterial and intravenous methods, as well as those without successful recanalization. For primary quantitative comparison, the Dice metric was computed for each voxel-based tissue outcome prediction and its corresponding follow-up lesion segmentation. It was found that the random forest classifier outperformed the generalized linear model and the k-nearest-neighbor classifier, that normalization did not improve the Dice score of the lesion outcome predictions, and that the models generated lesion outcome predictions with higher Dice scores when trained with balanced datasets. No significant difference was found between the treatment groups (intraarterial vs intravenous) regarding the Dice score of the tissue outcome predictions.

Neuroradiologic Characteristics of Primary Angiitis of the Central Nervous System According to the Affected Vessel Size.

INTRODUCTION: Magnetic resonance imaging (MRI) has an important impact in diagnosing primary angiitis of the central nervous system (PACNS). However, neuroradiologic findings may vary immensely, making an easy and definite diagnosis challenging. METHODS: In this retrospective, single center study, we analyzed neuroradiologic findings of patients with PACNS diagnosed at our hospital between 2009 and 2014. Furthermore, we classified patients according to the affected vessel size and compared imaging characteristics between the subgroups. RESULTS: Thirty-three patients were included (mean age 43 [±15.3] years, 17 females) in this study. Patients with positive angiographic findings were classified as either medium or large vessel PACNS and presented more ischemic lesions (p < 0.001) and vessel wall enhancement (p = 0.017) compared to patients with small vessel PACNS. No significant differences were detected for the distribution of contrast-enhancing lesions (parenchymal or leptomeningeal), hemorrhages, or lesions with mass effect. Twenty-five patients underwent brain biopsy. Patients with medium or large vessel PACNS were less likely to have positive biopsy results. DISCUSSION: It is essential to differentiate between small and medium/large vessel PACNS since results in MRI, digital subtraction angiography and brain biopsy may differ immensely. Since image quality of MR scanners improves gradually and brain biopsy may often be nonspecific or negative, our results emphasize the importance of MRI/MRA in the diagnosis process of PACNS.

Clinical and tissue response to intravenous thrombolysis in tandem internal carotid artery/middle cerebral artery occlusion: an MRI study.

BACKGROUND AND PURPOSE: The benefit of intravenous thrombolysis in tandem internal carotid artery (ICA)/middle cerebral artery (MCA) occlusion remains unclear. We studied clinical and imaging outcome of intravenous thrombolysis in MRI-selected patients with tandem ICA/MCA occlusion as compared to isolated MCA occlusion. METHODS: We analyzed data of MRI-selected acute ischemic stroke patients treated with intravenous tissue plasminogen activator within 6 hours. Initial perfusion and diffusion lesion volumes were calculated. Final infarct volume was assessed on follow-up imaging after 5 to 8 days. Recanalization/reperfusion was assessed after 24 hours using MRA. Favorable outcome was defined as a modified Rankin scale score of 0 to 1 after 90 days. RESULTS: Of 38 patients with proximal MCA occlusion, 14 (37%) had a tandem ICA/MCA occlusion. Median NIHSS on admission (15 vs 15), initial perfusion (246 vs 246 mL), and diffusion lesion volume (22 vs 21 mL), final infarct volume (30 vs 39 mL), and the proportion of patients with a favorable outcome after 3 months (50% vs 46%) were similar in tandem ICA/MCA occlusion versus isolated MCA occlusion. CONCLUSIONS: The presence of tissue at risk appears to play a key role for the likelihood of clinical recovery after intravenous tissue plasminogen activator treatment in acute stroke patients with tandem ICA/MCA occlusion. There appears to be no evidence to exclude patients with tandem ICA/MCA occlusion from intravenous thrombolysis.

T2' imaging predicts infarct growth beyond the acute diffusion-weighted imaging lesion in acute stroke.

PURPOSE: To show that measurement of the transverse relaxation time that characterizes signal loss caused by local susceptibilities (T2') is sensitive to an increased deoxyhemoglobin concentration in the brain, indicating tissue at risk for infarction. MATERIALS AND METHODS: The study was approved by the local institutional review board; patients or their guardians provided informed consent. Magnetic resonance (MR) imaging was performed within 6 hours of symptom onset and again 1-11 days thereafter in 100 consecutive stroke patients, all of whom received intravenous thrombolytic therapy (mean age, 67 years). The MR imaging protocol included diffusion- and perfusion-weighted imaging for determination of apparent diffusion coefficient (ADC) and time to peak (TTP), along with quantitative T2 and T2* imaging. T2' maps were calculated and visually compared with ADC and TTP lesions by two independent observers. RESULTS: A T2'>ADC mismatch was observed by reader 1 in 73 (73%) of 100 patients, and by reader 2 in 65 (65%) patients. Respective sensitivities of T2'>ADC and of TTP>ADC mismatches for later infarct growth were 0.87 and 0.98 for reader 1 and 0.78 and 0.98 for reader 2, with respective specificities of 0.42 and 0.04 for reader 1 and 0.46 and 0.04 for reader 2. The odds ratios for infarct growth in the presence of a T2'>ADC mismatch were 4.59 (reader 1 P = .002) and 3.10 (reader 2 P = .012), while the odds ratios for TTP>ADC mismatch were 2.22 (reader 1 P = .606) and 1.73 (reader 2 P > .999). CONCLUSION: The presence of a T2'>ADC mismatch is a more specific predictor of infarct growth than is TTP>ADC mismatch and hence may be of clinical value in patient selection for acute stroke therapies in the future.

T2 relaxation time correlates of face recognition deficits in temporal lobe epilepsy.

This study explored structural correlates of immediate and delayed face recognition in 22 nonsurgical patients with nonlesional, unilateral mesial temporal lobe epilepsy (TLE, 10 left/12 right). We measured T2 relaxation time bilaterally in the hippocampus, the amygdala, and the fusiform gyrus. Apart from raised T2 values in the ipsilateral hippocampus, we found increased T2 values in the ipsilateral amygdala. Patients with right TLE exhibited impaired face recognition as a result of a decrease from immediate to delayed recognition. Higher T2 values in the right than left fusiform gyrus or hippocampus were related to worse immediate face recognition, but did not correlate with 24-hour face recognition. These preliminary results indicate that structural changes in the fusiform gyrus and hippocampus may influence immediate face recognition deficits, but have no linear influence on long-term face recognition in TLE. We suggest that long-term face recognition depends on a right hemispheric network encompassing structures outside the temporal lobe.

Computed Tomography-Based Imaging of Voxel-Wise Lesion Water Uptake in Ischemic Brain: Relationship Between Density and Direct Volumetry.

OBJECTIVES: Net water uptake per volume of brain tissue may be calculated by computed tomography (CT) density, and this imaging biomarker has recently been investigated as a predictor of lesion age in acute stroke. However, the hypothesis that measurements of CT density may be used to quantify net water uptake per volume of infarct lesion has not been validated by direct volumetric measurements so far. The purpose of this study was to (1) develop a theoretical relationship between CT density reduction and net water uptake per volume of ischemic lesions and (2) confirm this relationship by quantitative in vitro and in vivo CT image analysis using direct volumetric measurements. MATERIALS AND METHODS: We developed a theoretical rationale for a linear relationship between net water uptake per volume of ischemic lesions and CT attenuation. The derived relationship between water uptake and CT density was tested in vitro in a set of increasingly diluted iodine solutions with successive CT measurements. Furthermore, the consistency of this relationship was evaluated using human in vivo CT images in a retrospective multicentric cohort. In 50 edematous infarct lesions, net water uptake was determined by direct measurement of the volumetric difference between the ischemic and normal hemisphere and was correlated with net water uptake calculated by ischemic density measurements. RESULTS: With regard to in vitro data, water uptake by density measurement was equivalent to direct volumetric measurement (r = 0.99, P < 0.0001; mean ± SD difference, -0.29% ± 0.39%, not different from 0, P < 0.0001). In the study cohort, the mean ± SD uptake of water within infarct measured by volumetry was 44.7 ± 26.8 mL and the mean percent water uptake per lesion volume was 22.7% ± 7.4%. This was equivalent to percent water uptake obtained from density measurements: 21.4% ± 6.4%. The mean difference between percent water uptake by direct volumetry and percent water uptake by CT density was -1.79% ± 3.40%, which was not significantly different from 0 (P < 0.0001). CONCLUSIONS: Volume of water uptake in infarct lesions can be calculated quantitatively by relative CT density measurements. Voxel-wise imaging of water uptake depicts lesion pathophysiology and could serve as a quantitative imaging biomarker of acute infarct lesions.

The use of multiparametric quantitative magnetic resonance imaging for evaluating visually assigned lesion groups in patients with multiple sclerosis.

In multiple sclerosis (MS), inflammatory lesions present a broad spectrum of histopathologic processes. For a better discrimination, lesions are visually defined into different lesion groups according to their appearance on conventional magnetic resonance imaging (MRI). The aim of this study was to investigate the properties of different MS lesion groups using multiparametric quantitative MRI. 35 patients diagnosed with relapsing-remitting MS received 3 Tesla MRI including magnetization-prepared 2 rapid acquisition gradient echo, diffusion tensor imaging and magnetization transfer imaging. Lesion segmentation was performed for T2 lesions, black holes and contrast-enhancing lesions. A subtraction mask was created including only T2 lesions that did not correspond to a black hole or contrast-enhancing lesion. T1 relaxation time (T1-RT), magnetization transfer ratio (MTR), mean diffusivity (MD) and fractional anisotropy (FA) were determined for every lesion and in normal-appearing white matter. Only MD differed significantly between all lesion groups and NAWM (p < 0.05), while FA differed between all lesion groups but not NAWM. T1-RT and MTR were not useful imaging biomarkers to distinguish between lesion groups. A lack of sensitivity and specificity and unproportional alterations of quantitative MRI measures, due to heterogenous histopathologic processes within lesions, may be a possible explanation for missing discrimination. Thus, not only interpretation of visually defined MS lesion but also interpretation of quantitative MRI measures remains challenging and should be conducted carefully.