Using EGFR amplification to stratify recurrent glioblastoma treated with immune checkpoint inhibitors.

PURPOSE: While immune checkpoint inhibitors (ICI) have had success with various malignancies, their efficacy in brain cancer is still unclear. Retrospective and prospective studies using PD-1 inhibitors for recurrent glioblastoma (GBM) have not established survival benefit. This study evaluated if ICI may be effective for select patients with recurrent GBM. METHODS: This was a single-center retrospective study of adult patients diagnosed with first recurrence GBM and received pembrolizumab or nivolumab with or without concurrent bevacizumab. Archival tissue was used for immunohistochemistry (IHC) and targeted DNA next-generation sequencing (NGS) analysis. RESULTS: Median overall survival (mOS) from initial diagnosis was 24.5 months (range 10-42). mOS from onset of ICI was 10 months (range 1-31) with 75% surviving > 6 months and 46% > 12 months. Additional IHC analysis on tumors from eight patients demonstrated a trend of longer survival after ICI for those with elevated PD-L1 expression. NGS of samples from 15 patients identified EGFR amplification at initial diagnosis and at any time point to be associated with worse survival after ICI (HR 12.2, 95% CI 1.37-108, p = 0.025 and HR 3.92, 95% CI 1.03-14.9, p = 0.045, respectively). This significance was corroborated with previously tested EGFR amplification via in situ hybridization. CONCLUSION: ICI did not extend overall survival for recurrent GBM. However, molecular sequencing identified EGFR amplification as associated with worse survival. Prospective studies can validate if EGFR amplification is a biomarker of ICI resistance and determine if its use can stratify responders from non-responders.

Arterial Spin Labeling: Techniques, Clinical Applications, and Interpretation.

Arterial spin labeling (ASL) is an emerging noninvasive MRI technique for assessing cerebral perfusion. An important advantage of ASL perfusion is the lack of a requirement for an exogenous tracer. ASL uses magnetically labeled water protons from arterial blood as an endogenous diffusible tracer. For this reason, ASL is an attractive perfusion imaging modality for children and for patients with contraindications or adverse reactions to gadolinium, patients with renal failure, and those who need repeated follow-up imaging. Another advantage of ASL is the possibility of quantifying cerebral blood flow, which provides an opportunity for comparative analysis among multiple longitudinal studies, unlike other MR perfusion techniques, which are semiquantitative and yield relative perfusion parameters. Advances in MRI technology and pulse sequence design have translated ASL beyond the research arena to successful clinical implementation. However, ASL is still underused in routine clinical practice. Some disadvantages of ASL include a lower signal-to-noise ratio and a longer acquisition time than those with dynamic susceptibility contrast-enhanced MRI. Additional factors limiting the use of ASL include variations in existing techniques and pulse sequence design, the complexity of implementation and postprocessing, insufficient experience with and/or knowledge of the potential clinical applications, and the absence of interpretation guidelines. The authors review the technical and physiologic basis of ASL perfusion, as well as artifacts, pitfalls, and its current clinical applications. A practical approach for interpreting ASL findings is also suggested.

Primary Extranodal NK/T-Cell Lymphoma Presenting as Neurolymphomatosis Involving Multiple Cranial Nerves: A Case Report.

Neurolymphomatosis (NL) is a rare condition caused by the lymphomatous or leukemic infiltration of nerves and manifests as neuropathy. Most often, NL is associated with B-lineage non-Hodgkin lymphoma (NHL) and only infrequently occurs in conjunction with T- or NK-lineage NHL. Extranodal NK/T-cell lymphoma (ENKTL)-associated NL is exceedingly unusual, with only 9 cases described in the English language literature, in addition to our case. Diagnosis of NL is challenging, as the entity can mimic neuropathies of more common etiologies, and an adequate biopsy may be difficult to obtain. Timely diagnosis demands a high index of suspicion, especially for patients without a history of hematologic malignancy. We expand upon a unique case of NL exclusively involving cranial nerves and cauda equina nerve roots, as the initial manifestation of ENKTL, and contextualize our findings within the framework of previously reported NK/T-lineage NL cases.

CT Perfusion collateral index in assessment of collaterals in acute ischemic stroke with delayed presentation: Comparison to single phase CTA.

BACKGROUND & PURPOSE: Perfusion collateral index (PCI) has been recently defined as a promising measure of collateral status. We sought to compare collateral status assessed via CT-PCI in comparison to single-phase CTA and their relationship to outcome measures including final infarction volume, final recanalization status and functional outcome in ELVO patients. METHODS: ELVO patients with anterior circulation large vessel occlusion who had baseline CTA and CT perfusion and underwent endovascular treatment were included. Collateral status was assessed on CTA. PCI from CT perfusion was calculated in each patient and an optimal threshold to separate good vs insufficient collaterals was identified using DSA as reference. The collateral status determined by CTA and PCI were assessed against 3 measured outcomes: 1) final infarction volume; 2) final recanalization status defined by TICI scores; 3) functional outcome measured by 90-day mRS. RESULTS: A total of 53 patients met inclusion criteria. Excellent recanalization defined by TICI ≥2C was achieved in 36 (68%) patients and 23 patients (43%) had good functional outcome (mRS ≤2). While having good collaterals on both CTA and CTP-PCI was associated with significantly (p<0.05) smaller final infarction volume, only good collaterals status determined by CTP-PCI was associated with achieving excellent recanalization (p = 0.001) and good functional outcome (p = 0.003). CONCLUSION: CTP-based PCI outperforms CTA collateral scores in determination of excellent recanalization and good functional outcome and may be a promising imaging marker of collateral status in patients with delayed presentation of AIS.

Postoperative outcomes following glioblastoma resection using a robot-assisted digital surgical exoscope: a case series.

INTRODUCTION: Maximal extent of resection (EOR) of glioblastoma (GBM) is associated with greater progression free survival (PFS) and improved patient outcomes. Recently, a novel surgical system has been developed that includes a 2D, robotically-controlled exoscope and brain tractography display. The purpose of this study was to assess outcomes in a series of patients with GBM undergoing resections using this surgical exoscope. METHODS: A retrospective review was conducted for robotic exoscope assisted GBM resections between 2017 and 2019. EOR was computed from volumetric analyses of pre- and post-operative MRIs. Demographics, pathology/MGMT status, imaging, treatment, and outcomes data were collected. The relationship between these perioperative variables and discharge disposition as well as progression-free survival (PFS) was explored. RESULTS: A total of 26 patients with GBM (median age = 57 years) met inclusion criteria, comprising a total of 28 cases. Of these, 22 (79%) tumors were in eloquent regions, most commonly in the frontal lobe (14 cases, 50%). The median pre- and post-operative volumes were 24.0 cc and 1.3 cc, respectively. The median extent of resection for the cohort was 94.8%, with 86% achieving 6-month PFS. The most common neurological complication was a motor deficit followed by sensory loss, while 8 patients (29%) were symptom-free. CONCLUSIONS: The robotic exoscope is safe and effective for patients undergoing GBM surgery, with a majority achieving large-volume resections. These patients experienced complication profiles similar to those undergoing treatment with the traditional microscope. Further studies are needed to assess direct comparisons between exoscope and microscope-assisted GBM resection.

MRI Radiomic Features to Predict IDH1 Mutation Status in Gliomas: A Machine Learning Approach using Gradient Tree Boosting.

Patients with gliomas, isocitrate dehydrogenase 1 (IDH1) mutation status have been studied as a prognostic indicator. Recent advances in machine learning (ML) have demonstrated promise in utilizing radiomic features to study disease processes in the brain. We investigate whether ML analysis of multiparametric radiomic features from preoperative Magnetic Resonance Imaging (MRI) can predict IDH1 mutation status in patients with glioma. This retrospective study included patients with glioma with known IDH1 status and preoperative MRI. Radiomic features were extracted from Fluid-Attenuated Inversion Recovery (FLAIR) and Diffused Weighted Imaging (DWI). The dataset was split into training, validation, and testing sets by stratified sampling. Synthetic Minority Oversampling Technique (SMOTE) was applied to the training sets. eXtreme Gradient Boosting (XGBoost) classifiers were trained, and the hyperparameters were tuned. Receiver operating characteristic curve (ROC), accuracy, and f1-scores were collected. A total of 100 patients (age: 55 ± 15, M/F 60/40); with IDH1 mutant (n = 22) and IDH1 wildtype (n = 78) were included. The best performance was seen with a DWI-trained XGBoost model, which achieved ROC with Area Under the Curve (AUC) of 0.97, accuracy of 0.90, and f1-score of 0.75 on the test set. The FLAIR-trained XGBoost model achieved ROC with AUC of 0.95, accuracy of 0.90, f1-score of 0.75 on the test set. A model that was trained on combined FLAIR-DWI radiomic features did not provide incremental accuracy. The results show that a XGBoost classifier using multiparametric radiomic features derived from preoperative MRI can predict IDH1 mutation status with > 90% accuracy.

Imaging-based Selection for Endovascular Treatment in Stroke.

Treatment of acute ischemic stroke (AIS) has evolved significantly in the past few years. Endovascular treatment (EVT) is now proved to be efficacious up to 24 hours from onset in properly selected patients. The recently updated 2018 American Heart Association-American Stroke Association guidelines reflect the important role of imaging in triage and patient selection for EVT of AIS. Pretreatment imaging in patients with acute stroke should (a) allow assessment for intracranial hemorrhage and demonstrate (b) the extent of early ischemic changes, (c) the presence of large arterial occlusion, and (d) in some cases potential salvageable tissue before the decision to proceed with EVT. The authors review how multimodality imaging can be used for EVT selection in the context of the recent guidelines. They highlight the importance of having streamlined imaging workflows that are integrated with clinical decision making to maximize treatment efficiency. Knowledge of the various imaging criteria including perfusion imaging used for EVT selection is highlighted. The authors discuss variable imaging paradigms used for selection of patients in the early and late windows (who present before vs after 6 hours from onset of symptoms), as reflected in the latest guidelines and in relation to their level of evidence. Finally, they focus on challenges in the subgroups of patients who were excluded from recent EVT trials and with limited evidence to prove the efficacy of EVT, such as patients with low NIHSS (National Institutes of Health Stroke Scale) score, distal occlusion, or large ischemic core. ©RSNA, 2019 See discussion on this article by Leslie-Mazwi.

Utility of preoperative meningioma consistency measurement with magnetic resonance elastography (MRE): a review.

Meningioma consistency is a critical factor that influences preoperative planning for surgical resection. Recent studies have investigated the utility of preoperative magnetic resonance elastography (MRE) in predicting meningioma consistency. However, it is unclear whether existing methods are optimal for application to clinical practice. The results and conclusions of these studies are limited by their imaging acquisition methods, such as the use of a single MRE frequency and the use of shear modulus as the final measurement variable, rather than its storage and loss modulus components. In addition, existing studies do not account for the effects of cranial anatomy, which have been shown to significantly distort the MRE signal. Given the interaction of meningiomas with these anatomic structures and the lack of supporting evidence with more accurate imaging parameters, MRE may not yet be reliable for use in clinical practice.

Estimation of Ischemic Core Volume Using Computed Tomographic Perfusion.

Background and Purpose- Estimation of infarction based on computed tomographic perfusion (CTP) has been challenging, mainly because of noise associated with CTP data. The Bayesian method is a robust probabilistic method that minimizes effects of oscillation, tracer delay, and noise during residue function estimation compared with other deconvolution methods. This study compares CTP-estimated ischemic core volume calculated by the Bayesian method and by the commonly used block-circulant singular value deconvolution technique. Methods- Patients were included if they had (1) anterior circulation ischemic stroke, (2) baseline CTP, (3) successful recanalization defined by thrombolysis in cerebral infarction ≥IIb, and (4) minimum infarction volume of >5 mL on follow-up magnetic resonance imaging (MRI). CTP data were processed with circulant singular value deconvolution and Bayesian methods. Two established CTP methods for estimation of ischemic core volume were applied: cerebral blood flow (CBF) method (relative CBF, <30% within the region of delay >2 seconds) and cerebral blood volume method (<2 mL per 100 g within the region of relative mean transit time >145%). Final infarct volume was determined on MRI (fluid-attenuated inversion recovery images). CTP and MRI-derived ischemic core volumes were compared by univariate and Bland-Altman analysis. Results- Among 35 patients included, the mean/median (mL) difference for CTP-estimated ischemic core volume against MRI was -4/-7 for Bayesian CBF ( P=0.770), 20/12 for Bayesian cerebral blood volume ( P=0.041), 21/10 for circulant singular value deconvolution CBF ( P=0.006), and 35/18 for circulant singular value deconvolution cerebral blood volume ( P<0.001). Among all methods, Bayesian CBF provided the narrowest limits of agreement (-28 to 19 mL) in comparison with MRI. Conclusions- Despite existing variabilities between CTP postprocessing methods, Bayesian postprocessing increases accuracy and limits variability in CTP estimation of ischemic core.

Resting-State Functional Connectivity Magnetic Resonance Imaging and Outcome After Acute Stroke.

Background and Purpose- Physiological effects of stroke are best assessed over entire brain networks rather than just focally at the site of structural damage. Resting-state functional magnetic resonance imaging can map functional-anatomic networks by analyzing spontaneously correlated low-frequency activity fluctuations across the brain, but its potential usefulness in predicting functional outcome after acute stroke remains unknown. We assessed the ability of resting-state functional magnetic resonance imaging to predict functional outcome after acute stroke. Methods- We scanned 37 consecutive reperfused stroke patients (age, 69±14 years; 14 females; 3-day National Institutes of Health Stroke Scale score, 6±5) on day 3 after symptom onset. After imaging preprocessing, we used a whole-brain mask to calculate the correlation coefficient matrices for every paired region using the Harvard-Oxford probabilistic atlas. To evaluate functional outcome, we applied the modified Rankin Scale at 90 days. We used region of interest analyses to explore the functional connectivity between regions and graph-computation analysis to detect differences in functional connectivity between patients with good functional outcome (modified Rankin Scale score ≤2) and those with poor outcome (modified Rankin Scale score >2). Results- Patients with good outcome had greater functional connectivity than patients with poor outcome. Although 3-day National Institutes of Health Stroke Scale score was the most accurate independent predictor of 90-day modified Rankin Scale (84.2%), adding functional connectivity increased accuracy to 94.7%. Preserved bilateral interhemispheric connectivity between the anterior inferior temporal gyrus and superior frontal gyrus and decreased connectivity between the caudate and anterior inferior temporal gyrus in the left hemisphere had the greatest impact in favoring good prognosis. Conclusions- These data suggest that information about functional connectivity from resting-state functional magnetic resonance imaging may help predict 90-day stroke outcome.

Multiparametric MRI for Differentiation of Radiation Necrosis From Recurrent Tumor in Patients With Treated Glioblastoma.

OBJECTIVE: Differentiation of radiation necrosis (RN) from recurrent tumor (RT) in treated patients with glioblastoma remains a diagnostic challenge. The purpose of this study is to evaluate the diagnostic performance of multiparametric MRI in distinguishing RN from RT in patients with glioblastoma, with the use of a combination of MR perfusion and diffusion parameters. MATERIALS AND METHODS: Patients with glioblastoma who had a new enhancing mass develop after completing standard treatment were retrospectively evaluated. Apparent diffusion coefficient (ADC), volume transfer constant (Ktrans), and relative cerebral blood volume (rCBV) values were calculated from the MR images on which the enhancing lesions first appeared. Repeated measure of analysis, logistic regression, and ROC analysis were performed. RESULTS: Of a total of 70 patients evaluated, 46 (34 with RT and 12 with RN) met our inclusion criteria. Patients with RT had significantly higher mean rCBV (p < 0.001) and Ktrans (p = 0.006) values and lower ADC values (p = 0.004), compared with patients with RN. The overall diagnostic accuracy was 85.8% for rCBV, 75.5% for Ktrans, and 71.3% for ADC values. The logistic regression model showed a significant contribution of rCBV (p = 0.024) and Ktrans (p = 0.040) as independent imaging classifiers for differentiation of RT from RN. Combined use of rCBV and Ktrans at threshold values of 2.2 and 0.08 min-1, respectively, improved the overall diagnostic accuracy to 92.8%. CONCLUSION: In patients with treated glioblastoma, rCBV outperforms ADC and Ktrans as a single imaging classifier to predict recurrent tumor versus radiation necrosis; however, the combination of rCBV and Ktrans may be used to improve overall diagnostic accuracy.

Interval Change in Diffusion and Perfusion MRI Parameters for the Assessment of Pseudoprogression in Cerebral Metastases Treated With Stereotactic Radiation.

OBJECTIVE: Apparent increases in the size of cerebral metastases after stereotactic radiosurgery (SRS) can be caused by pseudoprogression or true disease progression, which poses a diagnostic challenge at conventional MRI. The purpose of this study was to assess whether interval change in DWI and perfusion MRI parameters can differentiate pseudoprogression from progressive disease after treatment with SRS. MATERIALS AND METHODS: Patients with apparent growth of cerebral metastases after SRS treatment who underwent pre- and post-SRS DWI, dynamic susceptibility contrast (DSC)-MRI, and perfusion dynamic contrast-enhanced (DCE)-MRI were retrospectively evaluated. Final assignment of pseudoprogression or progressive disease was determined at 6-month follow-up imaging using the Response Assessment in Neuro-Oncology Brain Metastases criteria. Mean values of apparent diffusion coefficient (ADC), DCE-MRI-derived volume transfer constant (Ktrans), and DSC-MRI-derived relative cerebral blood volume (CBV) from pre- and post-SRS MRI scans were compared between groups using univariate and regression analysis. Fisher exact test was used to compare interval change of imaging biomarkers. RESULTS: Of 102 cerebral metastases evaluated, 32 lesions in 29 patients met our inclusion criteria. The mean duration of follow-up was 7.2 months (range, 6-14 months). Twenty-two lesions were determined as pseudoprogression, and 10 lesions were determined as progressive disease using the Response Assessment in Neuro-Oncology Brain Metastases criteria at 6-month follow-up MRI. The interval change pattern of our imaging parameters matched the expected patterns of treatment response for ADC (23/32 lesions; 72%; p = 0.055; odds ratio, 5.1), Ktrans (24/32 lesions; 75%; p = 0.006; odds ratio, 19.2), and relative CBV (27/32 lesions; 84%; p = 0.001; odds ratio, 25.3). CONCLUSION: Pseudoprogression can be distinguished from disease progression in cerebral metastases treated with SRS via an interval decrease in relative CBV and Ktrans values.

Multiparametric Magnetic Resonance Imaging for Prediction of Parenchymal Hemorrhage in Acute Ischemic Stroke After Reperfusion Therapy.

BACKGROUND AND PURPOSE: Patients with acute ischemic stroke are at increased risk of developing parenchymal hemorrhage (PH), particularly in the setting of reperfusion therapies. We have developed a predictive model to examine the risk of PH using combined magnetic resonance perfusion and diffusion parameters, including cerebral blood volume (CBV), apparent diffusion coefficient, and microvascular permeability (K2). METHODS: Voxel-based values of CBV, K2, and apparent diffusion coefficient from the ischemic core were obtained using pretreatment magnetic resonance imaging data from patients enrolled in the MR RESCUE clinical trial (Mechanical Retrieval and Recanalization of Stroke Clots Using Embolectomy). The associations between PH and extreme values of imaging parameters were assessed in univariate and multivariate analyses. Receiver-operating characteristic curve analysis was performed to determine the optimal parameter(s) and threshold for predicting PH. RESULTS: In 83 patients included in this analysis, 20 developed PH. Univariate analysis showed significantly lower 10th percentile CBV and 10th percentile apparent diffusion coefficient values and significantly higher 90th percentile K2 values within the infarction core of patients with PH. Using classification tree analysis, the 10th percentile CBV at threshold of 0.47 and 90th percentile K2 at threshold of 0.28 resulted in overall predictive accuracy of 88.7%, sensitivity of 90.0%, and specificity of 87.3%, which was superior to any individual or combination of other classifiers. CONCLUSIONS: Our results suggest that combined 10th percentile CBV and 90th percentile K2 is an independent predictor of PH in patients with acute ischemic stroke with diagnostic accuracy superior to individual classifiers alone. This approach may allow risk stratification for patients undergoing reperfusion therapies. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov. Unique identifier: NCT00389467.

MR phase imaging with bipolar acquisition.

We have previously proposed a novel magnetic resonance (MR) phase imaging framework (MAGPI) based on a three-echo sequence that demonstrated substantial gains in phase signal-to-noise ratio (SNR). We improve upon the performance of MAGPI by extending the formulation to handle (i) an alternating gradient polarity (bipolar) readout scheme and (ii) an arbitrary number of echoes. We formulate the phase-imaging problem using maximum-likelihood (ML) estimation. The acquisition uses an optimized multi-echo gradient echo (MEGE) sequence. The tissue-phase estimation algorithm is a voxel-per-voxel approach, which requires no reference scans, no phase unwrapping and no spatial denoising. Unlike other methods, our bipolar readout model is general and does not make simplifying assumptions about the even-odd echo phase errors. The results show that (a) our proposed bipolar MAGPI approach improves on the phase SNR gains achieved with monopolar MAGPI and (b) the phase SNR converges with the number of echoes more rapidly with bipolar MAGPI. Importantly, bipolar MAGPI enables phase imaging in severely SNR-constrained scenarios, where monopolar MAGPI is unable to find solutions. The substantial phase SNR gains achieved with our framework are used here to (a) accelerate acquisitions (full brain 0.89 mm in-plane resolution in 2 min 30 sec) and (b) enable high-contrast high-resolution phase imaging (310 µm in-plane resolution) at clinical field strengths. Copyright © 2016 John Wiley & Sons, Ltd.

Venous imaging-based biomarkers in acute ischaemic stroke.

Vascular neuroimaging plays a decisive role in selecting the best therapy in patients with acute ischaemic stroke. However, compared with the arterial system, the role of veins has not been thoroughly studied. In this review, we present the major venous imaging-based biomarkers in ischaemic stroke. First, the presence of hypodense veins in the monophasic CT angiography ipsilateral to the arterial occlusion. Second, the asymmetry of venous drainage in the pathological cerebral hemisphere on CT and MRI dynamic angiography. Finally, the presence of hypodense veins on T2* -based MRI. From the physiological point of view, the venous imaging-based biomarkers would detect the alteration of brain perfusion (flow), as well as the optimisation of extraction oxygen mechanisms (misery perfusion). Several studies have correlated the venous imaging-based biomarkers with grade of collateral circulation, the ischaemic penumbra and clinical functional outcome. Although venous imaging-based biomarkers still have to be validated, growing evidence highlights a potential complementary role in the acute stroke clinical decision-making process.

Diffusion tensor imaging as a prognostic biomarker for motor recovery and rehabilitation after stroke.

PURPOSE: Despite improved acute treatment and new tools to facilitate recovery, most patients have motor deficits after stroke, often causing disability. However, motor impairment varies considerably among patients, and recovery in the acute/subacute phase is difficult to predict using clinical measures alone, particularly in severely impaired patients. Accurate early prediction of recovery would help rationalize rehabilitation goals and improve the design of trials testing strategies to facilitate recovery. METHODS: We review the role of diffusion tensor imaging (DTI) in predicting motor recovery after stroke, in monitoring treatment response, and in evaluating white matter remodeling. We critically appraise DTI studies and discuss their limitations, and we explore directions for future study. RESULTS: Growing evidence suggests that combining clinical scores with information about corticospinal tract (CST) integrity can improve predictions about motor outcome. The extent of CST damage on DTI and/or the overlap between the CST and a lesion are key prognostic factor that determines motor performance and outcome. Three main strategies to quantify stroke-related CST damage have been proposed: (i) measuring FA distal to the stroke area, (ii) measuring the number of fibers that go through the stroke with tractography, and (iii) measuring the overlap between the stroke and a CST map derived from healthy age- and gender-matched controls. CONCLUSION: Recovery of motor function probably involves remodeling of the CST proper and/or a greater reliance on alternative motor tracts through spontaneous and treatment-induced plasticity. DTI-metrics represent promising clinical biomarkers to predict motor recovery and to monitor and predict the response to neurorehabilitative interventions.

MAGPI: A framework for maximum likelihood MR phase imaging using multiple receive coils.

PURPOSE: Combining MR phase images from multiple receive coils is a challenging problem, complicated by ambiguities introduced by phase wrapping, noise, and the unknown phase-offset between the coils. Various techniques have been proposed to mitigate the effect of these ambiguities but most of the existing methods require additional reference scans and/or use ad hoc post-processing techniques that do not guarantee any optimality. THEORY AND METHODS: Here, the phase estimation problem is formulated rigorously using a maximum-likelihood (ML) approach. The proposed framework jointly designs the acquisition-processing chain: the optimized pulse sequence is a single multiecho gradient echo scan and the corresponding postprocessing algorithm is a voxel-per-voxel ML estimator of the underlying tissue phase. RESULTS: Our proposed framework (Maximum AmbiGuity distance for Phase Imaging, MAGPI) achieves substantial improvements in the phase estimate, resulting in phase signal-to-noise ratio (SNR) gains by up to an order of magnitude compared to existing methods. CONCLUSION: The advantages of MAGPI are: (1) ML-optimal combination of phase data from multiple receive coils, without a reference scan; (2) voxel-per-voxel ML-optimal estimation of the underlying tissue phase, without the need for phase unwrapping or image smoothing; and (3) robust dynamic estimation of channel-dependent phase-offsets.

Tissue-Negative Transient Ischemic Attack: Is There a Role for Perfusion MRI?

OBJECTIVE: Approximately 60% of patients with a clinical transient ischemic attack (TIA) do not have DWI evidence of cerebral ischemia. The purpose of this study was to assess the added diagnostic value of perfusion MRI in the evaluation of patients with TIA who have normal DWI findings. MATERIALS AND METHODS: The inclusion criteria for this retrospective study were clinical presentation of TIA at admission with a discharge diagnosis of TIA confirmed by a stroke neurologist, MRI including both DWI and perfusion-weighted imaging within 48 hours of symptom onset, and no DWI lesion. Cerebral blood flow (CBF) and time to maximum of the residue function (Tmax) maps were evaluated independently by two observers. Multivariate analysis was used to assess perfusion findings; clinical variables; age, blood pressure, clinical symptoms, diabetes (ABCD2) score; duration of TIA; and time between MRI and onset and resolution of symptoms. RESULTS: Fifty-two patients (33 women, 19 men; age range, 20-95 years) met the inclusion criteria. A regional perfusion abnormality was identified on either Tmax or CBF maps of 12 of 52 (23%) patients. Seven (58%) of the patients with perfusion abnormalities had hypoperfused lesions best detected on Tmax maps; the other five had hyperperfusion best detected on CBF maps. In 11 of 12 (92%) patients with abnormal perfusion MRI findings, the regional perfusion deficit correlated with the initial neurologic deficits. Multivariable analysis revealed no significant difference in demographics, ABCD2 scores, or presentation characteristics between patients with and those without perfusion abnormalities. CONCLUSION: Perfusion MRI that includes Tmax and CBF parametric maps adds diagnostic value by depicting regions with delayed perfusion or postischemic hyperperfusion in approximately one-fourth of TIA patients who have normal DWI findings.

Fractures of the posterolateral maxillary sinus: a masticator space blowout injury?

BACKGROUND AND PURPOSE: Segmental, depressed fractures of the posterolateral maxillary sinus may occur as a result of trauma to the masticator space, previously described in association with mandibular fractures. The authors hypothesize that the fracture is due to a transient increase in pressure in the masticator space (blow out) and therefore should be seen in association with other regional fractures. MATERIALS AND METHODS: Injuries of the masticator space were retrospectively identified by searching the imaging database from January 2014 to November 2014 for keywords that would identify regional trauma. The images were reviewed for segmental depressed fractures in the posterolateral aspect of the maxillary sinus accompanied by herniation of a variable amount of masticator space fat and/or muscle into the adjacent sinus. Three neuroradiologists reviewed the images and agreed by consensus on the presence or absence of a masticator space blowout fracture. RESULTS: Forty-three zygomaticomaxillary complex (ZMC) fractures, 89 mandibular fractures, and 49 isolated zygomatic arch fractures were identified. While all of the ZMC fractures had a maxillary component, 3 of 43 (7.0 %) additional fractures met our fracture definition. Five of 89 (5.6 %) of the mandibular fractures and 6 of 49 (12.2 %) zygomatic arch fractures had an associated posterolateral maxillary fracture. CONCLUSIONS: Segmental depressed fracture of the posterolateral maxillary sinus is relatively common, occurring in conjunction with other regional injuries. The authors hypothesize that it is due to a transient increase in pressure in the masticator space and is a separate entity from other fractures of the region that may occur concurrently.