Susceptibility weighted imaging: a new tool in magnetic resonance imaging of stroke

Generative T2*-weighted images as a substitute for true T2*-weighted images on brain MRI in patients with acute stroke

PURPOSE

The purpose of this study was to validate a deep learning algorithm that generates T2*-weighted images from diffusion-weighted (DW) images and to compare its performance with that of true T2*-weighted images for hemorrhage detection on MRI in patients with acute stroke.

MATERIALS AND METHODS

This single-center, retrospective study included DW- and T2*-weighted images obtained less than 48 hours after symptom onset in consecutive patients admitted for acute stroke. Datasets were divided into training (60 %), validation (20 %), and test (20 %) sets, with stratification by stroke type (hemorrhagic/ischemic). A generative adversarial network was trained to produce generative T2*-weighted images using DW images. Concordance between true T2*-weighted images and generative T2*-weighted images for hemorrhage detection was independently graded by two readers into three categories (parenchymal hematoma, hemorrhagic infarct or no hemorrhage), and discordances were resolved by consensus reading. Sensitivity, specificity and accuracy of generative T2*-weighted images were estimated using true T2*-weighted images as the standard of reference.

RESULTS

A total of 1491 MRI sets from 939 patients (487 women, 452 men) with a median age of 71 years (first quartile, 57; third quartile, 81; range: 21-101) were included. In the test set (n = 300), there were no differences between true T2*-weighted images and generative T2*-weighted images for intraobserver reproducibility (κ = 0.97 [95 % CI: 0.95-0.99] vs. 0.95 [95 % CI: 0.92-0.97]; P = 0.27) and interobserver reproducibility (κ = 0.93 [95 % CI: 0.90-0.97] vs. 0.92 [95 % CI: 0.88-0.96]; P = 0.64). After consensus reading, concordance between true T2*-weighted images and generative T2*-weighted images was excellent (κ = 0.92; 95 % CI: 0.91-0.96). Generative T2*-weighted images achieved 90 % sensitivity (73/81; 95 % CI: 81-96), 97 % specificity (213/219; 95 % CI: 94-99) and 95 % accuracy (286/300; 95 % CI: 92-97) for the diagnosis of any cerebral hemorrhage (hemorrhagic infarct or parenchymal hemorrhage).

CONCLUSION

Generative T2*-weighted images and true T2*-weighted images have non-different diagnostic performances for hemorrhage detection in patients with acute stroke and may be used to shorten MRI protocols.

Small volume blood-brain barrier opening in macaques with a 1 MHz ultrasound phased array

The use of focused ultrasound to open the blood-brain barrier (BBB) has the potential to deliver drugs to specific regions of the brain. The size of the BBB opening and ability to localize the opening determines the spatial extent and is a limiting factor in many applications of BBB opening where targeting a small brain region is desired. Here we evaluate the performance of a system designed for small opening volumes and highlight the unique challenges associated with pushing the spatial precision of this technique. To achieve small volume openings in cortical regions of the macaque brain, we tested a custom 1 MHz array transducer integrated into a magnetic resonance image-guided focused ultrasound system. Using real-time cavitation monitoring, we demonstrated twelve instances of single sonication, small volume BBB opening with average volumes of 59 ± 37 mm3 and 184 ± 2 mm3 in cortical and subcortical targets, respectively. We found high correlation between subject-specific acoustic simulations and observed openings when incorporating grey matter segmentation (R2 = 0.8577), and the threshold for BBB opening based on simulations was 0.53 MPa. Analysis of MRI-based safety assessment and cavitation signals indicate a safe pressure range for 1 MHz BBB opening and suggest that our system can be used to deliver drugs and gene therapy to small brain regions.

FLAIR vascular hyperintensity combined with asymmetrical prominent veins in acute anterior circulation ischemic stroke: prediction of collateral circulation and clinical outcome

BACKGROUND

To investigate the value of fluid-attenuated inversion recovery vascular hyperintensity (FVH) within asymmetrical prominent veins sign (APVS) on susceptibility-weighted imaging predicting collateral circulation and prognosis in patients with acute anterior circulation ischemic stroke.

METHOD

Patients with severe stenosis or occlusion of ICA or MCA M1, who underwent MRI within 72 h from stroke onset were reviewed. The Alberta Stroke Program Early CT Score was used to evaluate the volume of infarction on DWI, the degree of FVH and APVS. Spearman correlation analysis was used to evaluate the correlation between FVH and APVS. All patients were divided into the good prognosis group and the poor prognosis group according to the score of the modified ranking scale (mRS) 90 days after the stroke. Logistic regression analysis was used to explore the relationship between FVH and APVS and functional prognosis, while receiver operating characteristic (ROC) curves were plotted to assess the value of FVH and APVS in predicting prognosis.

RESULTS

Spearman correlation analysis revealed moderate positive correlations between FVH and APVS (r = 0.586, P < 0.001). The poor prognosis group had a higher rate of a history of atrial fibrillation, a larger cerebral infarction volume, a higher NIHSS score at admission, and a higher FVH and APVS score compared with the good prognosis group (all P < 0.05). A further logistic regression indicated that the NIHSS score, cerebral infarction volume, FVH and APVS were independent risk factors for a poor functional prognosis. In terms of FVH, APVS, alone and their combination for the diagnosis of poor prognosis, the sensitivity, specificity, area under the ROC curve (AUC), and 95% confidence interval (CI) were 86.8%, 83.3%, 0.899 (95% CI 0.830-0.968); 60.5%, 93.7%, 0.818 (95% CI 0.723-0.912); 86.8%, 89.6%, 0.921 (95% CI 0.860-0.981), respectively.

CONCLUSION

The presence of FVH and APVS can provide a comprehensive assessment of collateral circulation from the perspective of veins and arteries, and the correlation between the two is positively correlated. Both of them were independent risk factors for poor prognosis, their combination is complementary and can improve the predictive value.

Epidemiology of Motoric Cognitive Risk Syndrome in the Kerala Einstein Study: Protocol for a Prospective Cohort Study

BACKGROUND

The southern India state of Kerala has among the highest proportion of older adults in its population in the country. An increase in chronic age-related diseases such as dementia is expected in the older Kerala population. Identifying older individuals early in the course of cognitive decline offers the best hope of introducing preventive measures early and planning management. However, the epidemiology and pathogenesis of predementia syndromes at the early stages of cognitive decline in older adults are not well established in India.

OBJECTIVE

The Kerala Einstein Study (KES) is a community-based cohort study that was established in 2008 and is based in the Kozhikode district in Kerala state. KES aims to establish risk factors and brain substrates of motoric cognitive risk syndrome (MCR), a predementia syndrome characterized by the presence of slow gait and subjective cognitive concerns in individuals without dementia or disability. This protocol describes the study design and procedures for this KES project.

METHODS

KES is proposing to enroll a sample of 1000 adults ≥60 years old from urban and rural areas in the Kozhikode district of Kerala state: 200 recruited in the previous phase of KES and 800 new participants to be recruited in this project. MCR is the cognitive phenotype of primary interest. The associations between previously established risk factors for dementia as well as novel risk factors (apathy and traumatic brain injury) and MCR will be examined in KES. Risk factor profiles for MCR will be compared between urban and rural residents as well as with individuals who meet the criteria for mild cognitive impairment (MCI). Cognitive and physical function, medical history and medications, sociodemographic characteristics, lifestyle patterns, and activities of daily living will be evaluated. Participants will also undergo magnetic resonance imaging and electrocardiogram investigations. Longitudinal follow-up is planned in a subset of participants as a prelude to future longitudinal studies.

RESULTS

KES (2R01AG039330-07) was funded by the US National Institutes of Health in September 2019 and received approval from the Indian Medical Council of Research to start the study in June 2021. We had recruited 433 new participants from urban and rural sites in Kozhikode as of May 2023: 41.1% (178/433) women, 67.7% (293/433) rural residents, and 13.4% (58/433) MCR cases. Enrollment is actively ongoing at all the KES recruitment sites.

CONCLUSIONS

KES will provide new insights into risk factors and brain substrates associated with MCR in India and will help guide future development of regionally specific preventive interventions for dementia.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/49933.

Susceptibility-weighted imaging at high-performance 0.5T magnetic resonance imaging system: Protocol considerations and experimental results

The high-performance low-field magnetic resonance imaging (MRI) system, equipped with modern hardware and contemporary imaging capabilities, has garnered interest within the MRI community in recent years. It has also been proven to have unique advantages over high-field MRI in both physical and cost aspects. However, for susceptibility weighted imaging (SWI), the low signal-to-noise ratio and the long echo time inherent at low field hinder the SWI from being applied to clinical applications. This work optimized the imaging protocol to select suitable parameters such as the values of time of echo (TE), repetition time (TR), and the flip angle (FA) of the RF pulse according to the signal simulations for low-field SWI. To improve the signal-to-noise ratio (SNR) performance, averaging multi-echo magnitude images and BM4D phase denoising were proposed. A comparison of the SWI in 0.5T and 1.5T was carried out, demonstrating the capability to identify magnetic susceptibility differences between variable tissues, especially, the blood veins. This would open the possibility to extend SWI applications in the high-performance low field MRI.

Quantitative susceptibility mapping as an imaging biomarker for Alzheimer’s disease: The expectations and limitations

Alzheimer’s disease (AD) is the most common type of dementia and a distressing diagnosis for individuals and caregivers. Researchers and clinical trials have mainly focused on β-amyloid plaques, which are hypothesized to be one of the most important factors for neurodegeneration in AD. Meanwhile, recent clinicopathological and radiological studies have shown closer associations of tau pathology rather than β-amyloid pathology with the onset and progression of Alzheimer’s symptoms. Toward a biological definition of biomarker-based research framework for AD, the 2018 National Institute on Aging–Alzheimer’s Association working group has updated the ATN classification system for stratifying disease status in accordance with relevant pathological biomarker profiles, such as cerebral β-amyloid deposition, hyperphosphorylated tau, and neurodegeneration. In addition, altered iron metabolism has been considered to interact with abnormal proteins related to AD pathology thorough generating oxidative stress, as some prior histochemical and histopathological studies supported this iron-mediated pathomechanism. Quantitative susceptibility mapping (QSM) has recently become more popular as a non-invasive magnetic resonance technique to quantify local tissue susceptibility with high spatial resolution, which is sensitive to the presence of iron. The association of cerebral susceptibility values with other pathological biomarkers for AD has been investigated using various QSM techniques; however, direct evidence of these associations remains elusive. In this review, we first briefly describe the principles of QSM. Second, we focus on a large variety of QSM applications, ranging from common applications, such as cerebral iron deposition, to more recent applications, such as the assessment of impaired myelination, quantification of venous oxygen saturation, and measurement of blood– brain barrier function in clinical settings for AD. Third, we mention the relationships among QSM, established biomarkers, and cognitive performance in AD. Finally, we discuss the role of QSM as an imaging biomarker as well as the expectations and limitations of clinically useful diagnostic and therapeutic implications for AD.

Multiple hypointense veins on susceptibility weighted imaging as a promising biomarker of impaired cerebral hemodynamics in chronic steno-occlusive disease: a multiparametric MRI study

PURPOSE

Patients with steno-occlusive arterial disease may develop cerebral hypoperfusion with possible neurologic sequelae. The aim of the study is to verify the possible role of SWI, as a marker of cerebral hypoperfusion, in the identification of patient subgroups with significant chronic occlusions/stenoses at risk of critical cerebral hypoperfusion.

METHODS

We retrospectively identified 37 asymptomatic patients with chronic intra-extracranial occlusion/stenosis of the anterior circulation from a prospective brain MRI register between 2016 and 2020. All patients underwent 3 Tesla MRI. The imaging protocol included the following: SWI, 3D-FLAIR, DWI sequences, and 3D-TOF MRA. SWI findings were graded for the presence of asymmetric intracranial cortical veins (grades 1 to 4). The presence of collateralization was assessed with concomitant multiphase-CTA. FLAIR was evaluated for the presence of distal hyperintense vessels (DHVs), a described marker of flow impairment, and possible collateralization. Cerebral blood flow and arterial transit artifacts (ATAs) were evaluated at pCASL in 29 patients.

RESULTS

SWI showed multiple hypointense vessels (MHVs) in 22/37 patients in the cerebral hemisphere ipsilateral to vessel occlusion/stenosis. SWI-MHV grade 1 was found in 15 patients (40.5%), grade 2 in 18 patients (48.7%), and grade 3 in 3 patients (8.1%); in one patient, SWI was graded as 4 (2.7%). A significant relationship was found among MHV, DHV, collaterals, ATAs, and hypoperfused areas on pCASL and with patients' previous neurological symptoms.

CONCLUSION

SWI-MVH correlates with chronic cerebral flow impairment and is related to hypoperfusion and collateralization. It may help identify a subgroup of patients benefitting from revascularization.

A Magnetic Resonance-Relaxometry-Based Technique to Identify Blood Products in Brain Parenchyma: An Experimental Study on a Rabbit Model

Magnetic resonance relaxometry is a quantitative technique that estimates T1/T2 tissue relaxation times. This has been proven to increase MRI diagnostic accuracy of brain disorders in human medicine. However, literature in the veterinary field is scarce. In this work, a T1 and T2-based relaxometry approach has been developed. The aim is to investigate its performance in characterizing subtle brain lesions obtained with autologous blood injections in rabbits. This study was performed with a low-field scanner, typically present in veterinary clinics. The approach consisted of a semi-automatic hierarchical classification of different regions, selected from a T2 map. The classification was driven according to the relaxometry properties extracted from a set of regions selected by the radiologist to compare the suspected lesion with the healthy parenchyma. Histopathological analyses were performed to estimate the performance of the proposed classifier through receiver operating characteristic curve analyses. The classifier resulted in moderate accuracy in terms of lesion characterization.

High-Resolution Vessel Wall MR Imaging in Diagnosis and Length Measurement of Cerebral Arterial Thrombosis: A Feasibility Study

BACKGROUND

Detecting and measuring intraluminal thrombus has prognostic and therapeutic implications for stroke patients.

PURPOSE

To investigate the feasibility of 3D isotropic high-resolution T1w-CUBE imaging to detect and measure intraluminal thrombus in stroke patients.

STUDY TYPE

Retrospective.

SUBJECTS

A total of 93 patients with acute (N = 39) and subacute (N = 54) stroke.

FIELD STRENGTH/SEQUENCE

A 3.0 T/spin-echo echo-planar diffusion-weighted imaging (DWI), high-resolution T1w-CUBE imaging and 3D flow compensated gradient-echo susceptibility-weighted imaging (SWI).

ASSESSMENT

Data assessment was performed by three neuroradiologists with 11, 13, and 20 years of clinical experience. The accuracy of T1W-CUBE and SWI in diagnosing thrombosis was compared by using digital subtraction angiography (DSA) as the reference. For thrombus length measurement, the image quality of proximal and distal thrombus of T1w-CUBE images was first evaluated with a 4-point rating system. Then, the proximal and distal positions to lesions were determined on T1w-CUBE images and compared with those from DSA acquired during endovascular reperfusion therapy. If comparable both locations were found between CUBE and DSA, CUBE imaging can thus be considered for accurate measurement of thrombus length.

STATISTICAL TESTS

Fleiss' Kappa; the area under the receiver operating characteristic (ROC) curve (AUC); Pearson's chi-squared test with Yates' continuity correction.

RESULTS

Moderate-to-good interobserver agreements were validated with all Kappa coefficients higher than 0.40 in thrombus diagnosis and measurement. CUBE imaging showed higher clinical efficacy than SWI (AUC: 0.966 vs. 0.850) in thrombus diagnosis. Additionally, high quality of CUBE imaging was confirmed with 3 or 4 points rated by all three observers. Compared to intraoperative DSA, T1w CUBE showed consistent proximal and distal positions of thrombi in 16 of the 18 patients, validating the accuracy of T1w-CUBE in measuring thrombus length.

DATA CONCLUSION

T1w-CUBE imaging has potential to facilitate diagnosis and measurement of intraluminal thrombus.

EVIDENCE LEVEL

4 TECHNICAL EFFICACY: Stage 2.

Clinical Implications of Prominent Cortical Vessels on Susceptibility-Weighted Imaging in Acute Ischemic Stroke Patients Treated with Recanalization Therapy

Prominent cortical vessels on susceptibility-weighted imaging (PCV–SWI) correlate with poor leptomeningeal collaterals. However, little is known about PCV–SWI in recanalization therapy-treated patients with anterior circulation large vessel occlusions (LVO). We investigated PCV–SWI-based assessment of leptomeningeal collaterals and outcome predictions in 100 such patients in an observational study. We assessed PCV–SWI using the Alberta Stroke Program Early CT Score and evaluated leptomeningeal collaterals on multiphase CT angiography (mCTA). Predictive abilities were analyzed using multivariable logistic regression and area of receiver operating curves (AUCs). The extent of PCV–SWI correlated with leptomeningeal collaterals on mCTA (Spearman test, r = 0.77; p < 0.001); their presence was associated with worse functional outcomes and a lower successful recanalization rate (adjusted odds ratios = 0.24 and 0.23, 95% CIs = 0.08–0.65 and 0.08–0.65, respectively). The presence of PCV–SWI predicted outcomes better than good collaterals on mCTA did (C-statistic = 0.84 vs. 0.80; 3-month modified Rankin Scale (mRS) 0–2 = 0.75 vs. 0.67 for successful recanalization). Comparison of AUCs showed that they had similar abilities for predicting outcomes (p = 0.68 for 3-month mRS 0–2; p = 0.23 for successful recanalization). These results suggest that PCV–SWI is a useful feature for assessing leptomeningeal collaterals in acute ischemic stroke patients with anterior circulation LVO and predicting outcomes after recanalization therapy.

Improved susceptibility weighted imaging at ultra-high field using bipolar multi-echo acquisition and optimized image processing: CLEAR-SWI

Purpose

Susceptibility Weighted Imaging (SWI) has become established in the clinical investigation of stroke, microbleeds, tumor vascularization, calcification and iron deposition, but suffers from a number of shortcomings and artefacts. The goal of this study was to reduce the sensitivity of SWI to strong B₁ and B₀ inhomogeneities at ultra-high field to generate homogeneous images with increased contrast and free of common artefacts. All steps in SWI processing have been addressed −coil combination, phase unwrapping, image combination over echoes, phase filtering and homogeneity correction −and applied to an efficient bipolar multi-echo acquisition to substantially improve the quality of SWI.

Principal results

Our findings regarding the optimal individual processing steps lead us to propose a Contrast-weighted, Laplace-unwrapped, bipolar multi-Echo, ASPIRE-combined, homogeneous, improved Resolution SWI, or CLEAR-SWI. CLEAR-SWI was compared to two other multi-echo SWI methods and standard, single-echo SWI with the same acquisition time at 7 T in 10 healthy volunteers and with single-echo SWI in 13 patients with brain tumors. CLEAR-SWI had improved contrast-to-noise and homogeneity, reduced signal dropout and was not compromised by the artefacts which affected standard SWI in 10 out of 13 cases close to tumors (as assessed by expert raters), as well as generating T2* maps and phase images which can be used for Quantitative Susceptibility Mapping. In a comparison with other multi-echo SWI methods, CLEAR-SWI had the fewest artefacts, highest SNR and generally higher contrast-to-noise.

Major conclusions

CLEAR-SWI eliminates the artefacts common in standard, single-echo SWI, reduces signal dropouts and improves image homogeneity and contrast-to-noise. Applied clinically, in a study of brain tumor patients, CLEAR-SWI was free of the artefacts which affected standard, single-echo SWI.

Susceptibility-diffusion mismatch correlated with leptomeningeal collateralization in large vessel occlusion stroke

Objective

To investigate the relationship between asymmetric prominent hypointense vessels (prominent vessel sign, PVS) on susceptibility-weighted imaging (SWI) and leptomeningeal collateralization in patients with acute ischemic stroke due to large vessel occlusion.

Methods

We retrospectively enrolled patients with M1 segment occlusion of the middle cerebral artery who underwent emergency magnetic resonance imaging and digital subtraction angiography within 24 hours from stroke onset. The extent of PVS on SWI was assessed using the Alberta Stroke Program Early CT Score (ASPECTS). Leptomeningeal collateralization on digital subtraction angiography images was assessed using the American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology (ASITN/SIR) scale. Spearman’s rank correlation test was performed to explore the correlation of ASITN/SIR scores with SWI-ASPECTS and SWI-diffusion-weighted imaging (DWI) mismatch scores.

Results

Thirty-five patients were enrolled. There was no significant correlation between SWI-ASPECTS and ASITN/SIR scores. However, SWI-DWI mismatch scores were positively correlated with ASITN/SIR scores.

Conclusion

The range of PVS on SWI did not closely reflect the collateral status, while the range of SWI-DWI mismatch was significantly correlated with the leptomeningeal collateralization. In patients with acute anterior circulation stroke due to large vessel occlusion, larger SWI-DWI mismatch was associated with better leptomeningeal collaterals.

Prominent hypointense vessel on susceptibility-weighted images accompanying hyperacute and acute large infarction

BACKGROUND

Multiple prominent hypointense vessels on susceptibility-weighted image (SWI) have been found in the ischemic territory of patients with acute ischemic stroke. SWI is suitable for venous imaging.

PURPOSE

To evaluate the conditions of prominent hypointense vessel (PHV) in hyperacute and acute cerebral infarctions using susceptibility-weighted image (SWI).

MATERIALS AND METHODS

Magnetic resonance images, including SWI, of 284 patients with acute infarction were evaluated. Based on lesion size, the infarction was classified as a small (< 3 cm) or a large (> 3 cm) infarction. Stage of infarction was classified as hyperacute (< 6 h) or acute (> 6 h, < 1 week) on the basis of the onset of stroke. The site of infarction was categorised as a deep grey matter or a mixed (cortical and/or deep grey matter) infarction. The venous structures were analysed qualitatively for the calibre difference between ipsilateral and contralateral hemispheres. We quantitatively analysed the relationship between the size of areas with PHV on SWI and the abnormalities on MR angiography, apparent diffusion coefficient value, and signal intensity on T2WI in the 271 patients.

RESULTS

PHV over the infarction site was observed in 54.1% (137/253) of the large infarctions, and 19.3% (6/31) of the small infarctions on SWI. PHV was demonstrated in 63.1% (118/187) of mixed infarctions and 25.8% (25/97) of deep grey matter infarctions, and 59.2% (58/98) in hyperacute and 45.7% (85/186) of acute infarctions. The presence of PHV was statistically significant in the size and region of cerebral infarction (p < 0.05), and was not significant in the stage of infarction (p = 0.137). Quantitative analysis revealed significant differences in the MRA abnormalities and ADC values in the PHV ( +) group (p < 0.05) and no significant difference in the T2WI SI ratio in the PHV ( +) group (p = 0.086), compared with PHV (-) group.

CONCLUSION

PHV on SWI was more prominent at the portions with the large and mixed infarctions. PHV was observed both in hyperacute and acute infarction.

Factors associated with prominent vessel sign on susceptibility-weighted imaging in acute ischemic stroke

The prominent vessel sign (PVS) on susceptibility-weighted imaging (SWI) is not displayed in all cases of acute ischemia. We aimed to investigate the factors associated with the presence of PVS in stroke patients. Consecutive ischemic stroke patients admitted within 24 h from symptom onset underwent emergency multimodal MRI at admission. Associated factors for the presence of PVS were analyzed using univariate analyses and multivariable logistic regression analyses. A total of 218 patients were enrolled. The occurrence rate of PVS was 55.5%. Univariate analyses showed significant differences between PVS-positive group and PVS-negative group in age, history of coronary heart disease, baseline NIHSS scores, total cholesterol, hemoglobin, anterior circulation infarct, large vessel occlusion, and cardioembolism. Multivariable logistic regression analyses revealed that the independent factors associated with PVS were anterior circulation infarct (odds ratio [OR] 13.7; 95% confidence interval [CI] 3.5–53.3), large vessel occlusion (OR 123.3; 95% CI 33.7–451.5), and cardioembolism (OR 5.6; 95% CI 2.1–15.3). Anterior circulation infarct, large vessel occlusion, and cardioembolism are independently associated with the presence of PVS on SWI.

Value of susceptibility-weighted imaging for the assessment of angle measurements reflecting hip morphology

Radiographs are the clinical first line imaging modality for evaluating hip morphology and pathology. MRI offers additional information and is the method of choice to evaluate soft tissue, bone marrow and preradiographic signs of osteoarthritis. Radiographs are used to measure the most morphometric parameters. The aim of this study was to compare susceptibility weighted MRI (SWMR) with radiographs to evaluate hip morphology. 40 Patients were examined with standard MR-sequences, coronal SWMR and radiographs in anteroposterior pelvic view. Coronal maximum intensity projection (MIP) images of both hips were automatically reconstructed on SWMR and T1weighted images. Sharp´s angle, Tönnis angle, lateral center–edge angle of Wiberg and caput-collum-diaphyseal angle were measured on coronal SWMR MIP-images, T1weighted MIP-images and radiographs. Measurements were compared by linear regression analysis and Bland-Altmann Plots, using radiographs as reference standard. Additionally, a ratio between the signal intensity of muscles and bone on SWMR and T1weighted MIP-images was calculated and compared between these two sequences. SWMR enables the reliable assessment of Sharp´s angle (SWMR: R² = 0.80; T1weighted: R² = 0.37), Tönnis angle (SWMR: R² = 0.86; T1weighted: not measurable), lateral center–edge angle of Wiberg (SWMR: R² = 0.88; T1weighted: R² = 0.40) and caput-collum-diaphyseal angle (SWMR: R² = 0.38; T1weighted: R² = 0.18) compared to radiographs with a higher accuracy than conventional MR imaging. The ratio between the intensity of muscles and bone was significant higher on SWMR (2.00 and 2.02) than on T1weighted MIP-images (1.6 and 1.42; p < 0.001).

Recognition of Brain Metastases Using Gadolinium-Enhanced SWI MRI: Proof-of-Concept Study

Background and purpose: SWI MRI, a T2^*-dominant MRI sequence with T1 shine-through effect, uses intrinsic structural susceptibility to create enhancement among brain structures. We evaluated whether gadolinium-enhanced SWI (SWI-Gd) improves brain metastasis detection in combination with other MRI sequences.

Materials and methods: MRI images of 24 patients (46 studies) were prospectively acquired using a 1.5-T scanner. T1-weighted, unenhanced SWI (SWI-U) and SWI-Gd were evaluated blindly to clinical features by two board-certified radiologists.

Results: SWI-Gd revealed more significant metastatic lesions than either T1-Gd or SWI-U (p = 0.0004 for either comparator sequence). Moreover, SWI-Gd revealed more lesions only for those patients with ≤5 lesions on T1-Gd (n = 30 studies from 16 patients; p = 0.046). Performing SWI-Gd added <5 min of scanning time with no further additional risk.

Conclusions: Our findings suggest that, when added to T1-Gd and other common sequences, SWI-Gd may improve the diagnostic yield of brain metastases with only a few extra minutes of scanning time and no further risk than that of a regular gadolinium-enhanced MRI.

T2*-Weighted MRI Detected Dilated Cerebral Veins in a Patient with Acute-Phase Cerebral Venous Sinus Thrombosis-A Case Report

We describe a 45-year-old man who presented with nausea, vomiting, and strong occipital headache on the right side. Although no abnormalities on neurological examination or computed tomography imaging were found on admission, peripheral blood cell counts showed polycythemia (hemoglobin 20.6 g/dL) and electrocardiography demonstrated atrial fibrillation. Therefore, anticoagulant treatment with heparin was started immediately. On the following day, the occipital headache continued. Brain T2*-weighted (T2*WI) magnetic resonance imaging (MRI) and, to a lesser extent, susceptibility-weighted imaging showed dilation of numerous cortical veins, suggesting the possibility of cerebral venous thrombosis (CVT). MR venography (MRV) showed a deficit of the right transverse sinus. Contrast-enhanced MRI revealed partial defects of the right transverse sinus, and led to the definite diagnosis of CVT, and the anticoagulation therapy was continued. On day 7 the headache disappeared, and MRV on day 16 showed the recanalization of the right transverse sinus. There were no complications subsequent to the CVT. On day 25, the patient was discharged with no after-effect. We speculate that the dilation of cortical veins on T2*WI is a helpful sign in detecting acute-phase CVT.

Superficial Siderosis of the Central Nervous System: Neurotological Findings Related to Magnetic Resonance Imaging

OBJECTIVE

To compare the neurotological results of five patients suffering from progressive hearing loss and ataxia due to superficial siderosis (SS) with the magnetic resonance imaging (MRI) findings.

STUDY DESIGN

Retrospective case review.

SETTING

Primary and hospital care center.

PARTICIPANTS

Five adult patients with neurotological symptoms of SS underwent MRI with acquisition of our temporal bone protocol including 3D-constructive interference in steady state (3D-CISS) and susceptibility-weighted imaging (SWI). All patients underwent a complete neurotological examination, the results of which were compared with the imaging findings.

MAIN OUTCOME MEASURES

Cochleovestibular deficits were present in all five patients as determined by uni- or bilateral bithermal caloric testing and/or video head impulse tests. Sacculocollic reflex was present with increased P1 and N1 latencies on both sides in all patients. MRI revealed an extensive hypointense SWI signal outlining the surface of the brain and the VIIIth cranial nerve in all five patients. Desynchronization of the brainstem auditory evoked potentials (BAEP) and partial or complete absence of the visual suppression of vestibulo-ocular reflex during the pendular rotatory test was particularly consistent with the lesions of the cochleovestibular nerves as well as the cerebellar atrophy seen on MRI.

CONCLUSION

The MRI results with SWI were related to neurotological findings in patients suffering from sensorineural deafness with ataxia due to SS. Our findings support the integration of the SWI and 3D-CISS sequences into the MRI protocol for all patients referred for evaluation of the extent of SS.

Clinical application of susceptibility-weighted imaging in the evaluation of leptomeningeal collateralization

The feasibility of using susceptibility-weighted imaging (SWI) in a clinical setting was assessed for quantifying leptomeningeal collateralization.Eighteen patients with stroke and acute infarction underwent diffusion-weighted imaging, SWI, perfusion-weighted imaging, and magnetic resonance angiography within 3 days after symptom onset. Lesions were evaluated by the Alberta Stroke Program Early CT score (ASPECTS), based on mean transit time, SWI, and cerebral blood volume (CBV).For evaluating ischemic penumbra and leptomeningeal collateralization, the SWI-ASPECTS significantly correlated, respectively, with mean transit time and CBV-ASPECTS (Spearman test, r = 0.793 and 0.682; P < .001, both).The SWI may be useful to quantify leptomeningeal collateralization in patients with acute cerebral infarction.

Differentiation of Predominantly Osteoblastic and Osteolytic Spine Metastases by Using Susceptibility-weighted MRI

Purpose To evaluate the use of susceptibility-weighted MRI for the differentiation of predominantly osteoblastic and osteolytic spine metastases. Materials and Methods For this prospective study, 53 study participants (mean age, 54.5 years ± 14.3 [range, 22-88 years]; 27 men with a mean age of 55.3 years ± 12.7 [range, 22-72 years] and 26 women with a mean age of 53.8 years ± 15.7 [range, 23-88 years]) with clinically suspected spine metastases underwent imaging with standard MRI sequences, susceptibility-weighted MRI, and CT. Sensitivities and specificities of MRI sequences for the detection of predominantly osteoblastic and osteolytic metastases were determined by using CT as the reference standard. The metastases-to-vertebral body signal intensity ratio (MVR) was calculated to compare modalities. Phantom measurements were obtained to correlate bone densities between MRI sequences and CT. Results A total of 64 metastases (38 predominantly osteoblastic, 26 predominantly osteolytic) were detected. Susceptibility-weighted MRI achieved a sensitivity of 100% (38 of 38) and specificity of 96% (25 of 26) for predominantly osteoblastic metastases and a sensitivity of 96% (25 of 26) and specificity of 100% (38 of 38) for predominantly osteolytic metastases. Standard MRI sequences achieved a sensitivity of 89% (34 of 38) and specificity of 73% (19 of 26) for predominantly osteoblastic metastases and a sensitivity of 73% (19 of 26) and specificity of 92% (35 of 38) for predominantly osteolytic metastases. MVR measurements obtained with susceptibility-weighted MRI demonstrated a strong correlation with those obtained with CT (R² = 0.75), whereas those obtained with T1-weighted MRI, T2-weighted MRI, and turbo inversion-recovery magnitude MRI showed a weak to moderate correlation (R² = 0.00, R² = 0.35, and R² = 0.39, respectively). Susceptibility-weighted MRI showed a strong correlation with CT with regard to metastases size (R² = 0.91). In phantom measurements, susceptibility-weighted MRI enabled the reliable differentiation of different degrees of mineralization (R² = 0.92 compared with CT). Conclusion Susceptibility-weighted MRI enables the reliable differentiation between predominantly osteoblastic and osteolytic spine metastases with a higher accuracy than standard MRI sequences. © RSNA, 2018 Online supplemental material is available for this article. See also the editorial by Schweitzer in this issue.

Susceptibility-weighted Imaging in Thrombolytic Therapy of Acute Ischemic Stroke

Objective:

To provide a comprehensive and latest overview of susceptibility-weighted imaging (SWI) in the application of thrombolysis in acute ischemic stroke, and to update the decision-making effect and clinical value of SWI on identifying stroke patients suitable for thrombolytic therapy and possible benefits and risks followed.

Data Sources:

Literatures referred to this review were collected from PubMed, Medline, and EMBASE published till May 2017, using the search terms including susceptibility-weighted imaging, gradient-echo, T2*, thrombolysis, recombinant tissue plasminogen activator (rt-PA), thrombolytic therapy, and stroke.

Study Selection:

Papers in English or with available English abstracts were considered, with no limitation of study design. References were also identified from the bibliographies of identified articles and the authors’ files.

Results:

SWI is of guiding significance for thrombolytic therapy in stroke patients, it can predict the location and length of thrombus and ischemic penumbra. It is worthy of noting that susceptibility vessel sign (SVS) on SWI can be used to predict recanalization after thrombolytic therapy and whether it is better to implement endovascular thrombolectomy in combination or alone. SWI is sensitive in detecting cerebral microbleed (CMB), and CMB might not be a contraindication for thrombolytic therapy, yet CMBs in multiple foci could possibly be related to intracranial hemorrhage (ICH) after thrombolysis. SVS and CMB on SWI sequence are of instructive value in performing antiplatelet therapy after thrombolytic therapy. Cerebral venous change on SWI is related to lower recanalization rate and poor outcome after thrombolysis.

Conclusions:

It seems that SWI can be applied to guide individualized thrombolytic therapies and assist clinicians in making better decisions by weighing benefits and risks. However, there still exist controversies about the relationship between signs on SWI and thrombolytic therapy.

Neuroradiologic Pearls for Neuro-oncology

PURPOSE OF REVIEW

This article reviews key principles in the identification of tumors of the central nervous system (CNS) using standard and advanced imaging modalities. This article highlights the pitfalls and pearls of the imaging evaluation of patients with cancer at time of diagnosis and during cancer therapy and discusses the challenges of the imaging evaluation of treatment-related toxicities.

RECENT FINDINGS

Treatment of CNS tumors with surgery, chemotherapy, or radiation alters the imaging appearance of the tumor and can be associated with a variety of treatment-related toxicities. The clinician must be familiar with how to assess response to treatment and how to differentiate tumor progression from treatment-related effects.

SUMMARY

Management and follow-up of neuro-oncology patients is optimized by a comprehensive radiologic approach to CNS tumors and recognition of the challenges in the assessment of response to treatments.

Decreased oxygen saturation levels in neonates with transposition of great arteries: Impact on appearance of cerebral veins in susceptibility-weighted imaging

Purpose of this study was to investigate a potential correlation between the pattern of cerebral veins (CV) on susceptibility-weighted imaging (SWI) and blood oxygen saturation, as well as preoperative brain injury, in neonates with transposition of the great arteries (TGA). Eleven neonates with TGA underwent MRI preoperatively, including SWI, T1- and T2-weighted scans. Images were retrospectively evaluated and appearance of CV was graded from 0 (normal appearance) to 3 (severe prominent appearance). White matter injuries (WMI) and strokes were analysed. Results were correlated with preductal arterial oxygen saturation. As findings one subject showed a normal CV appearance (grade 0) whereas 10 showed pathological prominent CV (grades 1–3); median 2. Mean oxygen saturation ranged between 67.5% and 89.0% (median 81.0%). CV grade and mean oxygen saturation correlated significantly (p = 0.011). WMI were absent in 5 cases, mild in 4, and moderate in 2 cases. We conclude, that SWI has the potential to be used to estimate the current hypoxic burden on brain tissue in TGA newborns by assessing the prominence of the CV.

Removal of Arterial Vessel Contributions in Susceptibility-Weighted Images for Quantification of Normalized Visible Venous Volume in Children with Sickle Cell Disease

Purpose

To evaluate a new postprocessing framework that eliminates arterial vessel signal contributions in the quantification of normalized visible venous volume (NVVV, a ratio between venous and brain volume) in susceptibility-weighted imaging (SWI) exams in patients with sickle cell disease (SCD).

Materials and Methods

We conducted a retrospective study and qualitatively reviewed for hypointense arterial vessel contamination in SWI exams from 21 children with SCD. We developed a postprocessing framework using magnetic resonance angiography in combination with SWI to provide a more accurate quantification of NVVV. NVVV was calculated before and after removing arterial vessel contributions to determine the error from hypointense arterial vessels in quantifying NVVV.

Results

Hypointense arterial vessel contamination was observed in 86% SWI exams and was successfully corrected by the proposed method. The contributions of hypointense arterial vessels in the original SWI were significant and accounted for approximately 33% of the NVVV [uncorrected NVVV = 0.012 ± 0.005 versus corrected NVVV = 0.008 ± 0.003 (mean ± SD), P < 0.01].

Conclusion

Hypointense arterial vessel contamination occurred in the majority of SWI exams and led to a sizeable overestimation of the visible venous volume. A prospective longitudinal study is needed to evaluate if quantitation of NVVV was improved and to assess the role of NVVV as a biomarker of SCD severity or stroke risk.

Physiological Laterality of Superficial Cerebral Veins on Susceptibility-Weighted Imaging

OBJECTIVE

The purpose of this study is to evaluate whether laterality of the superficial cerebral veins can be seen on susceptibility-weighted imaging (SWI) in patients with no intracranial lesions that affect venous visualization.

METHODS

We retrospectively evaluated 386 patients who underwent brain magnetic resonance imaging including SWI in our institute. Patients with a lesion with the potential to affect venous visualization on SWI were excluded. Two neuroradiologists visually evaluated the findings and scored the visualization of the superficial cerebral veins.

RESULTS

Of the 386 patients, 315 (81.6%) showed no obvious laterality on venous visualization, 64 (16.6%) showed left-side dominant laterality, and 7 (1.8%) showed right-side dominant laterality.

CONCLUSIONS

Left-side dominant physiological laterality exists in the visualization of the superficial cerebral veins on SWI. Therefore, when recognizing left-side dominant laterality of the superficial cerebral veins on SWI, the radiologist must also consider the possibility of physiological laterality.

Cerebral Microhemorrhage: A Frequent Magnetic Resonance Imaging Finding in Pediatric Patients after Cardiopulmonary Bypass

Objectives:

This study was undertaken to estimate the incidence and burden of cerebral microhemorrhage (CM) in patients with heart disease who underwent cardiopulmonary bypass (CPB), as detected on susceptibility-weighted imaging (SWI), a magnetic resonance (MR) sequence that is highly sensitive to hemorrhagic products.

Materials and Methods:

With Institutional Review Board waiver of consent, MR imaging (MRI) of a cohort of 86 consecutive pediatric patients with heart failure who underwent heart transplantation evaluation were retrospectively reviewed for CM. A nested case–control study was performed. The CPB group consisted of 23 pediatric patients with heart failure from various cardiac conditions who underwent CPB. The control group was comprised of 13 pediatric patients with similar cardiac conditions, but without CPB history. Ten patients in the CPB group were female (age: 5 days to 16 years at the time of the CPB and 6 days to 17 years at the time of the MRI). The time interval between the CPB and MRI ranged from 11 days to 4 years and 5 months. Six patients in the control group were female, age range of 2 days to 6 years old. The number of CM on SWI was counted by three radiologists (PK, EK and DK). The differences in number of CM between groups were tested for significance using Mann–Whitney U-test, α = 0.05. Using the univariate analysis of variance model, the differences in number of CM between groups were also tested with adjustment for age at MRI.

Results:

There are statistically significant differences in CM on SWI between the CPB group and control group with more CM were observed in the CPB group without and with adjustment for age at MRI (P < 0.001).

Conclusions:

Exposure of CPB is associated with increased prevalence and burden of CM among pediatric patients with heart failure.

Ipsilateral Prominent Thalamostriate Vein on Susceptibility-Weighted Imaging Predicts Poor Outcome after Intravenous Thrombolysis in Acute Ischemic Stroke

BACKGROUND AND PURPOSE

The impact of deep cerebral veins on neurologic outcome after intravenous thrombolysis in patients with acute ischemic stroke is unclear. We investigated the relationship between the appearance of deep cerebral veins on susceptibility-weighted imaging and neurologic outcome in patients who underwent thrombolysis.

MATERIALS AND METHODS

We retrospectively analyzed 109 consecutive patients with acute ischemic stroke who had pretreatment SWI and received intravenous thrombolysis within 6 hours. We calculated the signal difference ratio (defined as the relative difference in signal intensity between the ipsilateral and contralateral veins) of the thalamostriate vein, septal vein, and internal cerebral vein on pretreatment SWI.

RESULTS

Only the signal difference ratio of the thalamostriate vein was significantly associated with poor outcome (3-month modified Rankin Scale score > 2, P = .008). The optimal threshold was relative hypointensity of the ipsilateral vein of >4.8% (sensitivity of 53.7% and specificity of 80.9%). We defined a signal difference ratio of the thalamostriate vein of ≥5% as an ipsilateral prominent thalamostriate vein. Patients with an ipsilateral prominent thalamostriate vein were more likely to have poor outcome (OR = 3.66; 95% CI, 1.25-10.68; P = .02) and a lower rate of successful reperfusion (reperfusion rate of ≥70%; OR = 0.35; 95% CI, 0.13-0.92; P = .03), compared with those without an ipsilateral prominent thalamostriate vein. However, patients with an ipsilateral prominent thalamostriate vein were still less likely to experience poor outcome when reperfusion was achieved compared with when reperfusion did not occur (80.0% versus 44.4%, P = .04).

CONCLUSIONS

A pretreatment ipsilateral prominent thalamostriate vein was associated with reduced reperfusion after thrombolysis and poor outcome. More intensive reperfusion approaches may be required for patients with an ipsilateral prominent thalamostriate vein.

Susceptibility-weighted imaging: current status and future directions

Susceptibility-weighted imaging (SWI) is a method that uses the intrinsic nature of local magnetic fields to enhance image contrast in order to improve the visibility of various susceptibility sources and to facilitate diagnostic interpretation. It is also the precursor to the concept of the use of phase for quantitative susceptibility mapping (QSM). Nowadays, SWI has become a widely used clinical tool to image deoxyhemoglobin in veins, iron deposition in the brain, hemorrhages, microbleeds and calcification. In this article, we review the basics of SWI, including data acquisition, data reconstruction and post-processing. In particular, the source of cusp artifacts in phase images is investigated in detail and an improved multi-channel phase data combination algorithm is provided. In addition, we show a few clinical applications of SWI for the imaging of stroke, traumatic brain injury, carotid vessel wall, siderotic nodules in cirrhotic liver, prostate cancer, prostatic calcification, spinal cord injury and intervertebral disc degeneration. As the clinical applications of SWI continue to expand both in and outside the brain, the improvement of SWI in conjunction with QSM is an important future direction of this technology. Copyright © 2016 John Wiley & Sons, Ltd.

Susceptibility-based time-resolved whole-organ and regional tissue oximetry

The magnetism of hemoglobin - being paramagnetic in its deoxy and diamagnetic in its oxy state - offers unique opportunities to probe oxygen metabolism in blood and tissues. The magnetic susceptibility χ of blood scales linearly with blood oxygen saturation, which can be obtained by measuring the magnetic field ΔB of the intravascular MR signal relative to tissue. In contrast to χ, the induced field ΔB is non-local. Therefore, to obtain the intravascular susceptibility Δχ relative to adjoining tissue from the measured ΔB demands solution of an inverse problem. Fortunately, for ellipsoidal structures, to which a straight, cylindrically shaped blood vessel segment conforms, the solution is trivial. The article reviews the principle of MR susceptometry-based blood oximetry. It then discusses applications for quantification of whole-brain oxygen extraction - typically on the basis of a measurement in the superior sagittal sinus - and, in conjunction with total cerebral blood flow, the cerebral metabolic rate of oxygen (CMRO₂ ). By simultaneously measuring flow and venous oxygen saturation (SvO₂ ) a temporal resolution of a few seconds can be achieved, allowing the study of the response to non-steady-state challenges such as volitional apnea. Extensions to regional measurements in smaller cerebral veins are also possible, as well as voxelwise quantification of venous blood saturation in cerebral veins accomplished by quantitative susceptibility mapping (QSM) techniques. Applications of susceptometry-based oximetry to studies of metabolic and degenerative disorders of the brain are reviewed. Lastly, the technique is shown to be applicable to other organ systems such as the extremities using SvO₂ as a dynamic tracer to monitor the kinetics of the microvascular response to induced ischemia. Copyright © 2016 John Wiley & Sons, Ltd.

Evaluation of the role of susceptibility-weighted imaging in thrombolytic therapy for acute ischemic stroke

We inspected low-intensity venous signals and microbleeds in patients with acute ischemic stroke (AIS) using susceptibility-weighted imaging (SWI) before and after administration of within-thrombolytic-time-window thrombolytic therapies, and observed their prognosis and safety, in order to guide individualized thrombolytic therapies. Patients with AIS were divided into groups A or B according to the presence of symmetric or asymmetric veins on SWI, and were re-inspected by SWI after intravenous thrombolysis using recombinant tissue plasminogen activator (rt-PA). The National Institutes of Health stroke scale (NIHSS) score before treatment and at 1-h and 24-h posttreatment in the two groups were 11.9, 7.3, and 7.1 in group A, 12.4, 8.2, and 7.9 in group B, significant difference was detected between the two groups after treatment. The 90-day mortality rate was 0, and the incidences of cerebral microbleeds (CMBs) and symptomatic cerebral hemorrhage (SCH) were 17.6%, and 0% in group A, 25.6% and 0% in group B, respectively. The incidences of CMBs and SCH in group A were lower than those in group B, but the intergroup differences were not statistically significant (P>0.05). The 90-day neurological improvement rates in the two groups were 70.2% and 58.1%, respectively, and group A showed a significantly better prognosis than group B (P<0.05). Thus, low-intensity venous signals in SWI can be used to evaluate a low level of perfusion, post-thrombolytic prognosis, and bleeding indexes, and can therefore be used to guide individualized thrombolytic therapies.

Susceptibility-Based Neuroimaging: Standard Methods, Clinical Applications, and Future Directions

The evaluation of neuropathologies using MRI methods that leverage tissue susceptibility have become standard practice, especially to detect blood products or mineralization. Additionally, emerging MRI techniques have the ability to provide new information based on tissue susceptibility properties in a robust and quantitative manner. This paper discusses these advanced susceptibility imaging techniques and their clinical applications.

Prominent cortical and medullary veins on susceptibility-weighted images of acute ischaemic stroke

OBJECTIVE

To determine the clinical and imaging implications of prominent cortical and medullary veins on susceptibility-weighted images (SWI) of patients with acute stroke.

METHODS

Consecutive patients with acute ischaemic stroke who had SWI scan within 24 h of symptom onset or time last-seen-well were included. The SWI series were reviewed for the presence of prominent cortical and medullary veins and were graded independently by two neuroradiologists. The correlations between prominent vein grades with different imaging and clinical variables were determined.

RESULTS

Among 213 patients, prominent SWI cortical and medullary veins were identified in 35 (16.4%) patients and 20 (9.4%) patients, respectively. There was fair interobserver agreement (k = 0.314-0.338, p ≤ 0.001) for grading, and moderate agreement (k = 0.406-0.413, p ≤ 0.001) for the presence of prominent veins. Both prominent cortical and medullary veins were associated with the presence of arterial occlusion (rho = 0.232, p = 0.001; rho = 0.180, p = 0.008; respectively) and larger infarct volume (rho = 0.445, p < 0.001; rho = 0.167, p = 0.015; respectively). However, neither cortical nor medullary cortical veins were associated with the severity of symptoms at admission or clinical outcome. Prominent cortical veins were independent predictors of arterial occlusion (p = 0.018), whereas prominent medullary veins were more strongly associated with larger infarct volumes (p < 0.001).

CONCLUSION

There were small but significant correlations between cortical and medullary veins on SWI with arterial occlusion and large infarct volume in acute ischaemic stroke. Advances in knowledge: In consecutive patients with acute ischaemic stroke within anterior and posterior circulation territories, prominent cortical and medullary veins on SWI series are associated with imaging biomarkers of poor clinical outcome (i.e. large infarct volume and major arterial occlusion).

Evaluating the Role of Reduced Oxygen Saturation and Vascular Damage in Traumatic Brain Injury Using Magnetic Resonance Perfusion-Weighted Imaging and Susceptibility-Weighted Imaging and Mapping

The cerebral vasculature, along with neurons and axons, is vulnerable to biomechanical insult during traumatic brain injury (TBI). Trauma-induced vascular injury is still an underinvestigated area in TBI research. Cerebral blood flow and metabolism could be important future treatment targets in neural critical care. Magnetic resonance imaging offers a number of key methods to probe vascular injury and its relationship with traumatic hemorrhage, perfusion deficits, venous blood oxygen saturation changes, and resultant tissue damage. They make it possible to image the hemodynamics of the brain, monitor regional damage, and potentially show changes induced in the brain's function not only acutely but also longitudinally following treatment. These methods have recently been used to show that even mild TBI (mTBI) subjects can have vascular abnormalities, and thus they provide a major step forward in better diagnosing mTBI patients.

A Comparison Study of Single-Echo Susceptibility Weighted Imaging and Combined Multi-Echo Susceptibility Weighted Imaging in Visualizing Asymmetric Medullary Veins in Stroke Patients

Background

Asymmetric medullary veins (AMV) are frequently observed in stroke patients and single-echo susceptibility weighted imaging (SWI_s) is the main technique in detecting AMV. Our study aimed to investigate which echo time (TE) on single-echo susceptibility is the optimal echo for visualizing AMV and to compare the ability in detecting AMV in stroke patients between SWI_s and multi-echo susceptibility weighted imaging (SWI_c).

Materials and Methods

Twenty patients with middle cerebral artery stroke were included. SWI was acquired by using a multi-echo gradient-echo sequence with six echoes ranging from 5 ms to 35.240 ms. Three different echoes of SWI_s including SWI_s1 (TE = 23.144 ms), SWI_s2 (TE = 29.192 ms) and SWI_s3 (TE = 35.240 ms) were reconstructed. SWI_c was averaged using the three echoes of SWI_s. Image quality and venous contrast of medullary veins were compared between SWI_s and SWI_c using peak signal-to-noise ratio (PSNR), mean opinion score (MOS), contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR). The presence of AMV was evaluated in each SWI_{s (1–3)} and SWI_c.

Results

SWI_s2 had the highest PSNR, MOS and CNR and SWI_s1 had the highest SNR among three different echoes of SWI_s. No significant difference was found in SNR between SWI_s1 and SWI_s2. PSNR, MOS and CNR in SWI_c were significantly increased by 27.9%, 28.2% and 17.2% compared with SWI_s2 and SNR in SWI_c was significantly increased by 32.4% compared with SWI_s1. 55% of patients with AMV were detected in SWI_s2, SWI_s3 and SWI_c, while 50% AMV were found in SWI_s1.

Conclusions

SWI_s using TE around 29ms was optimal in visualizing AMV. SWI_c could improve image quality and venous contrast, but was equal to SWI_s using a relative long TE in evaluating AMV. These results provide the technique basis for further research of AMV in stroke.

Susceptibility-Diffusion Mismatch in Hyperacute Stroke: Correlation with Perfusion-Diffusion Mismatch and Clinical Outcome

BACKGROUND

A prominent vein (PV) on susceptibility-weighted imaging (SWI) was recently proposed to be a marker of the penumbra. We aimed to compare the utility of SWI and perfusion-weighted imaging (PWI) sequences for the evaluation of the penumbra in hyperacute middle cerebral artery (MCA) stroke, and to determine whether SWI-DWI mismatch is a neuroimaging marker of clinical outcome.

METHODS

A total of 149 consecutive patients with MCA stroke were prospectively enrolled. Magnetic resonance imaging (MRI) was performed within 6 hours of the onset of stroke. The ASPECTS values on diffusion-weighted imaging (DWI), PWI (delayed mean transit time), and SWI (visualization of PVs) were calculated by 2 independent raters. Correlation between PWI-ASPECTS and SWI-ASPECTS was calculated with the Pearson coefficient. Reliability of the PV rating system was calculated by an intraclass correlation coefficient (ICC). Favorable outcome was defined as a modified Rankin Scale score of 0-2 at 3 months for the 88 patients who received thrombolytic therapy.

RESULTS

The ASPECTS-SWI and ASPECTS-PWI scores showed a good correlation (Pearson coefficient of .69, P <.001). The reproducibility between the findings of the junior and the senior radiologists was excellent with an ICC of .89 (confidence interval of 95% (IC95): .85-.92, P <.001). However, neither SWI-DWI mismatch nor PWI-SWI mismatch was associated with clinical outcome.

CONCLUSION

SWI and PWI were complementary but not commutable for the assessment of the penumbra. Susceptibility-diffusion mismatch was not found in this study to have predictive value for stroke outcome.

Predicting Mortality in Patients With "Malignant" Middle Cerebral Artery Infarction Using Susceptibility-Weighted Magnetic Resonance Imaging: Preliminary Findings

To evaluate malignant middle cerebral artery (MCA) infarction (defined as space-occupying edema in more than 50% to 75% of the MCA territory) on magnetic resonance imaging (MRI) with susceptibility-weighted imaging (SWI) sequence and assess the usefulness of SWI findings, diffusion-weighted imaging (DWI) findings, and apparent diffusion coefficient (ADC) as predictors of clinical outcome.Data from 16 patients with large MCA infarction previously admitted to our institution between December 2009 and October 2012 were retrospectively collected and analyzed. Within 7 days after stroke onset, 1 neurologist and 1 neuroradiologist estimated the area of infarction on DWI/ADC and extent of prominent vessel sign (PVS) on SWI images using the Stroke Program Early MR Score (SPEMRS). The PVS on SWI was defined as a local prominence of hypointense vessels with either increased vessel number or diameter in the target area, when compared with the number or diameter of the contralateral MCA territory vessels.Six patients died and 10 survived. Although the DWI/ADC-SPEMRS and clinical profiles were similar between the nonsurvivor and survivor groups, SWI-SPEMRS was significantly lower in the nonsurvivor group (P < 0.001).The area of deoxygenation on SWI in patients with malignant MCA infarction can predict mortality. Lower SWI-SPEMRS is a potentially better predictor of poor outcome than lower DWI-SPEMRS. A larger prospective study is needed to clarify the role of SWI as a therapeutic guide in malignant MCA.