Model-based iterative reconstruction for direct imaging with point spread function encoded echo planar MRI.

BACKGROUND: Echo planar imaging (EPI) is a fast measurement technique commonly used in magnetic resonance imaging (MRI), but is highly sensitive to measurement non-idealities in reconstruction. Point spread function (PSF)-encoded EPI is a multi-shot strategy which alleviates distortion, but acquisition of encodings suitable for direct distortion-free imaging prolongs scan time. In this work, a model-based iterative reconstruction (MBIR) framework is introduced for direct imaging with PSF-EPI to improve image quality and acceleration potential. METHODS: An MBIR platform was developed for accelerated PSF-EPI. The reconstruction utilizes a subspace representation, is regularized to promote local low-rankedness (LLR), and uses variable splitting for efficient iteration. Comparisons were made against standard reconstructions from prospectively accelerated PSF-EPI data and with retrospective subsampling. Exploring aggressive partial Fourier acceleration of the PSF-encoding dimension, additional comparisons were made against an extension of Homodyne to direct PSF-EPI in numerical experiments. A neuroradiologists' assessment was completed comparing images reconstructed with MBIR from retrospectively truncated data directly against images obtained with standard reconstructions from non-truncated datasets. RESULTS: Image quality results were consistently superior for MBIR relative to standard and Homodyne reconstructions. As the MBIR signal model and reconstruction allow for arbitrary sampling of the PSF space, random sampling of the PSF-encoding dimension was also demonstrated, with quantitative assessments indicating best performance achieved through nonuniform PSF sampling combined with partial Fourier. With retrospective subsampling, MBIR reconstructs high-quality images from sub-minute scan datasets. MBIR was shown to be superior in a neuroradiologists' assessment with respect to three of five performance criteria, with equivalence for the remaining two. CONCLUSIONS: A novel image reconstruction framework is introduced for direct imaging with PSF-EPI, enabling arbitrary PSF space sampling and reconstruction of diagnostic-quality images from highly accelerated PSF-encoded EPI data.

Detection and Mitigation of Neurovascular Uncoupling in Brain Gliomas.

Functional magnetic resonance imaging (fMRI) with blood oxygen level-dependent (BOLD) technique is useful for preoperative mapping of brain functional networks in tumor patients, providing reliable in vivo detection of eloquent cortex to help reduce the risk of postsurgical morbidity. BOLD task-based fMRI (tb-fMRI) is the most often used noninvasive method that can reliably map cortical networks, including those associated with sensorimotor, language, and visual functions. BOLD resting-state fMRI (rs-fMRI) is emerging as a promising ancillary tool for visualization of diverse functional networks. Although fMRI is a powerful tool that can be used as an adjunct for brain tumor surgery planning, it has some constraints that should be taken into consideration for proper clinical interpretation. BOLD fMRI interpretation may be limited by neurovascular uncoupling (NVU) induced by brain tumors. Cerebrovascular reactivity (CVR) mapping obtained using breath-hold methods is an effective method for evaluating NVU potential.

Improved Resting-State Functional MRI Using Multi-Echo Echo-Planar Imaging on a Compact 3T MRI Scanner with High-Performance Gradients.

In blood-oxygen-level-dependent (BOLD)-based resting-state functional (RS-fMRI) studies, usage of multi-echo echo-planar-imaging (ME-EPI) is limited due to unacceptable late echo times when high spatial resolution is used. Equipped with high-performance gradients, the compact 3T MRI system (C3T) enables a three-echo whole-brain ME-EPI protocol with smaller than 2.5 mm isotropic voxel and shorter than 1 s repetition time, as required in landmark fMRI studies. The performance of the ME-EPI was comprehensively evaluated with signal variance reduction and region-of-interest-, seed- and independent-component-analysis-based functional connectivity analyses and compared with a counterpart of single-echo EPI with the shortest TR possible. Through the multi-echo combination, the thermal noise level is reduced. Functional connectivity, as well as signal intensity, are recovered in the medial orbital sulcus and anterior transverse collateral sulcus in ME-EPI. It is demonstrated that ME-EPI provides superior sensitivity and accuracy for detecting functional connectivity and/or brain networks in comparison with single-echo EPI. In conclusion, the high-performance gradient enabled high-spatial-temporal resolution ME-EPI would be the method of choice for RS-fMRI study on the C3T.

Enhanced clinical task-based fMRI metrics through locally low-rank denoising of complex-valued data.

OBJECTIVE: This study investigates a locally low-rank (LLR) denoising algorithm applied to source images from a clinical task-based functional MRI (fMRI) exam before post-processing for improving statistical confidence of task-based activation maps. METHODS: Task-based motor and language fMRI was obtained in eleven healthy volunteers under an IRB approved protocol. LLR denoising was then applied to raw complex-valued image data before fMRI processing. Activation maps generated from conventional non-denoised (control) data were compared with maps derived from LLR-denoised image data. Four board-certified neuroradiologists completed consensus assessment of activation maps; region-specific and aggregate motor and language consensus thresholds were then compared with nonparametric statistical tests. Additional evaluation included retrospective truncation of exam data without and with LLR denoising; a ROI-based analysis tracked t-statistics and temporal SNR (tSNR) as scan durations decreased. A test-retest assessment was performed; retest data were matched with initial test data and compared for one subject. RESULTS: fMRI activation maps generated from LLR-denoised data predominantly exhibited statistically significant (p = 4.88×10-4 to p = 0.042; one p = 0.062) increases in consensus t-statistic thresholds for motor and language activation maps. Following data truncation, LLR data showed task-specific increases in t-statistics and tSNR respectively exceeding 20 and 50% compared to control. LLR denoising enabled truncation of exam durations while preserving cluster volumes at fixed thresholds. Test-retest showed variable activation with LLR data thresholded higher in matching initial test data. CONCLUSION: LLR denoising affords robust increases in t-statistics on fMRI activation maps compared to routine processing, and offers potential for reduced scan duration while preserving map quality.

Clinical 7-T MRI for neuroradiology: strengths, weaknesses, and ongoing challenges.

Since the relatively recent regulatory approval for clinical use in both Europe and North America, 7-Tesla (T) MRI has been adopted for clinical practice at our institution. Based on this experience, this article reviews the unique features of 7-T MRI neuroimaging and addresses the challenges of establishing a 7-T MRI clinical practice. The underlying fundamental physics principals of high-field strength MRI are briefly reviewed. Scanner installation, safety considerations, and artifact mitigation techniques are discussed. Seven-tesla MRI case examples of neurologic diseases including epilepsy, vascular abnormalities, and tumor imaging are presented to illustrate specific applications of 7-T MRI. The advantages of 7-T MRI in conjunction with advanced neuroimaging techniques such as functional MRI are presented. Seven-tesla MRI produces more detailed information and, in some cases, results in specific diagnoses where previous 3-T studies were insufficient. Still, persistent technical issues for 7-T scanning present ongoing challenges for radiologists.

Higher temporal resolution multiband fMRI provides improved presurgical language maps.

PURPOSE: We investigated the hypothesis that increasing fMRI temporal resolution using a multiband (MB) gradient echo-echo planar imaging (GRE-EPI) pulse sequence provides fMRI language maps of higher statistical quality than those acquired with a traditional GRE-EPI sequence. METHODS: This prospective study enrolled 29 consecutive patients receiving language fMRI prior to a potential brain resection for tumor, AVM, or epilepsy. A 4-min rhyming task was performed at 3.0 Tesla with a traditional GRE-EPI pulse sequence (TR = 2000, TE = 30, matrix = 64/100%, slice = 4/0, FOV = 24, slices = 30, time points = 120) and an additional MB GRE-EPI pulse sequence with an acceleration factor of 6 (TR = 333, TE = 30, matrix 64/100%, slice = 4/0, FOV = 24, time points = 720). Spatially filtered t statistical maps were generated. Volumes of interest (VOIs) were drawn around activations at Broca's, dorsolateral prefrontal cortex, Wernicke's, and the visual word form areas. The t value maxima were measured for the overall brain and each of the VOIs. A paired t test was performed for the corresponding traditional and MB GRE-EPI measurements. RESULTS: The mean age of subjects was 42.6 years old (18-75). Sixty-two percent were male. The average overall brain t statistic maxima for the MB pulse sequence (t = 15.4) was higher than for the traditional pulse sequence (t = 9.3, p = < .0001). This also held true for Broca's area (p < 0.0001), Wernicke's area (p < .0001), dorsolateral prefrontal cortex (p < .0001), and the visual word form area (p < .0001). CONCLUSION: A MB GRE-EPI fMRI pulse sequence employing high temporal resolution provides clinical fMRI language maps of greater statistical significance than those obtained with a traditional GRE-EPI sequence.

SMART syndrome: retrospective review of a rare delayed complication of radiation.

BACKGROUND: SMART (stroke-like migraine attacks after radiation therapy) is a rare, delayed complication of brain radiation. In this study, we wanted to review the spectrum of symptoms, neuroradiological findings, autoimmune status, and outcomes in SMART syndrome patients. METHODS: We conducted a retrospective cohort study of all consecutive adult patients (≥18 years) diagnosed with SMART syndrome at Mayo Clinic, Rochester between January 1995 and December 2018. RESULTS: We identified 25 unique patients with SMART syndrome and a total of 31 episodes and 15 (60%) patients were male. The median age at onset was 46 (interquartile range [IQR] 43-55) years and the median latency of onset after the initial radiation was 21.6 (IQR 14.4-28.2) years. Magnetic resonance imaging (MRI) showed gyral edema and enhancement in all cases with the temporal (25, 80.6%) and parietal (23, 74.2%) lobes being the most commonly affected. The median follow-up of the patients in our cohort was 10 (IQR 6-32) weeks. On univariate analysis, factors associated with an increased risk of recurrent SMART episodes were female gender (odds ratio [OR] 8.1, 95% confidence interval [95% CI] 1.1-52.6, p = 0.019) and absence of electrographic seizure discharges during initial symptoms (OR 7.4, 95% CI 1.1-45.9, p = 0.032). We could not identify an autoimmune etiology. Longer duration of symptoms (>10 weeks) correlated with an older age (p = 0.049), temporal lobe involvement (p < 0.001), and diffusion restriction (p = 0.043). CONCLUSIONS: SMART is a syndrome with characteristic imaging findings and clinical features. Incomplete recovery by 10 weeks occurred in one-third of individuals and was associated with older age, temporal lobe involvement, and restricted diffusion on MRI.

Current concepts of cross-sectional and functional anatomy of the cerebellum: a pictorial review and atlas.

Recognition of key concepts of structural and functional anatomy of the cerebellum can facilitate image interpretation and clinical correlation. Recently, the human brain mapping literature has increased our understanding of cerebellar anatomy, function, connectivity with the cerebrum, and significance of lesions involving specific areas.Both the common names and numerically based Schmahmann classifications of cerebellar lobules are illustrated. Anatomic patterns, or signs, of key fissures and white matter branching are introduced to facilitate easy recognition of the major anatomic features. Color-coded overlays of cross-sectional imaging are provided for reference of more complex detail. Examples of exquisite detail of structural and functional cerebellar anatomy at 7 T MRI are also depicted.The functions of the cerebellum are manifold with the majority of areas involved with non-motor association function. Key concepts of lesion-symptom mapping which correlates lesion location to clinical manifestation are introduced, emphasizing that lesions in most areas of the cerebellum are associated with predominantly non-motor deficits. Clinical correlation is reinforced with examples of intrinsic pathologic derangement of cerebellar anatomy and altered functional connectivity due to pathology of the cerebral hemisphere. The purpose of this pictorial review is to illustrate basic concepts of these topics in a cross-sectional imaging-based format that can be easily understood and applied by radiologists.

Scrambler therapy for chemotherapy neuropathy: a randomized phase II pilot trial.

INTRODUCTION: Chemotherapy-induced peripheral neuropathy (CIPN) is a prominent clinical problem, with limited effective therapies. Preliminary non-randomized clinical trial data support that Scrambler Therapy is helpful in this situation. METHODS: Patients were eligible if they had CIPN symptoms for at least 3 months and CIPN-related tingling or pain at least 4/10 in severity during the week prior to registration. They were randomized to receive Scrambler Therapy versus transcutaneous electrical nerve stimulation (TENS) for 2 weeks. Patient-reported outcomes (PROs) were utilized to measure efficacy and toxicity daily for 2 weeks during therapy and then weekly for 8 additional weeks. RESULTS: This study accrued 50 patients, 25 to each of the 2 study arms; 46 patients were evaluable. There were twice as many Scrambler-treated patients who had at least a 50% documented improvement during the 2 treatment weeks, from their baseline pain, tingling, and numbness scores, when compared with the TENS-treated patients (from 36 to 56% compared with 16-28% for each symptom). Global Impression of Change scores for "neuropathy symptoms," pain, and quality of life were similarly improved during the treatment weeks. Patients in the Scrambler group were more likely than those in the TENS group to recommend their treatment to other patients, during both the 2-week treatment period and the 8-week follow-up period (p < 0.0001). Minimal toxicity was observed. CONCLUSIONS: The results from this pilot trial were positive, supporting the conduct of further investigations regarding the use of Scrambler Therapy for treating CIPN.

Neuroanatomical Considerations in Preoperative Functional Brain Mapping.

Task-based functional magnetic resonance imaging (fMRI) for the presurgical assessment of eloquent cortex is increasingly relied upon by surgeons, neurologists, and radiologists. The utility of fMRI stems from the lack of correlation between topographic anatomy and functional anatomy. fMRI can noninvasively reveal the functional anatomy of a given individual thereby allowing the surgeon to choose the most appropriate surgical trajectory, attain the most complete resection, and offer the best chance of preserving function. This dissociation between function and topography is even more critical to understand when disease distorts normal anatomic relations and when chronic evolution of pathology leads to reorganization of cortical function as can be seen with seizures or slow growing tumors. fMRI can demonstrate the functional anatomy of language, motor, vision, and memory systems. Accurate interpretation not only requires knowledge of the expected patterns of activations in the regions of interest but also demands an understanding of the many adjacent "bystander" activations that represent participatory neural activity but not the eloquent region in question. In addition, fMRI interpretation requires an understanding of the limitations of this technique when expected activity is either missing or seemingly displaced in location.

Brain Changes in Responders vs. Non-Responders in Chronic Migraine: Markers of Disease Reversal.

The aim of this study was to identify structural and functional brain changes that accompanied the transition from chronic (CM; ≥15 headache days/month) to episodic (EM; <15 headache days/month) migraine following prophylactic treatment with onabotulinumtoxinA (BoNT-A). Specifically, we examined whether CM patients responsive to prophylaxis (responders; n = 11), as evidenced by a reversal in disease status (defined by at least a 50% reduction in migraine frequency and <15 headache days/month), compared to CM patients whose migraine frequency remained unchanged (non-responders; n = 12), showed differences in cortical thickness using surface-based morphometry. We also investigated whether areas showing group differences in cortical thickness displayed altered resting-state functional connectivity (RS-FC) using seed-to-voxel analyses. Migraine characteristics measured across groups included disease duration, pain intensity and headache frequency. Patient reports of headache frequency over the 4 weeks prior to (pre-treatment) and following (post-treatment) prophylaxis were compared (post minus pre) and this measure served as the clinical endpoint that determined group assignment. All patients were scanned within 2 weeks of the post-treatment visit. Results revealed that responders showed significant cortical thickening in the right primary somatosensory cortex (SI) and anterior insula (aINS), and left superior temporal gyrus (STG) and pars opercularis (ParsOp) compared to non-responders. In addition, disease duration was negatively correlated with cortical thickness in fronto-parietal and temporo-occipital regions in responders but not non-responders, with the exception of the primary motor cortex (MI) that showed the opposite pattern; disease duration was positively associated with MI cortical thickness in responders versus non-responders. Our seed-based RS-FC analyses revealed anti-correlations between the SI seed and lateral occipital (LOC) and dorsomedial prefrontal cortices (DMPFC) in responders, whereas non-responders showed increased connectivity between the ParsOp seed and LOC. Overall, our findings revealed distinct morphometric and functional brain changes in CM patients that reverted to EM following prophylactic treatment compared to CM patients that showed no change in disease status. Elucidating the CNS changes involved in disease reversal may be critical to discovering interventions that prevent or slow the progression of CM. Such changes may aid in the evaluation of treatments as well as provide markers for disease "de-chronification".

Expanding the spectrum of subacute diencephalic angioencephalopathy.

We present a patient with subacute diencephalic angioencephalopathy (SDAE), a poorly understood syndrome of progressive confusion, disorientation, and dementia that rapidly deteriorates to severe encephalopathy and death. This is the seventh and most thoroughly investigated report of this exceedingly rare diagnosis to date, and we present the first evidence of a potential sentinel syndrome that may allow for earlier diagnosis and therapeutic intervention. We also review the relevant literature, and highlight new evidence that suggests that SDAE and the related disorder, subacute brainstem angioencephalopathy (SBAE), represent severe and terminal variants of posterior reversible encephalopathy syndrome (PRES). Taken together, we suggest a new understanding of SDAE/SBAE and PRES as a spectrum of hypertension-associated non-inflammatory vascular encephalopathies that are mediated by a loss of venous autoregulation, marked by cytotoxic edema, and that ultimately produce subacute-to-acute diencephalic, brainstem, and posterior fossa injuries with devastating neurologic consequences.

Temporal lobe anatomy: eight imaging signs to facilitate interpretation of MRI.

PURPOSE: The temporal lobe is anatomically and functionally complex. However, relatively few radiologic signs are described to facilitate recognition of temporal lobe sulci and gyri in clinical practice. We devised and tested 8 radiologic signs of temporal lobe anatomy. METHODS: Images from volumetric magnetization-prepared rapid gradient-echo imaging were analyzed of 100 temporal lobes from 26 female and 24 male patients. Patient age ranged from 1 to 79 years (mean 19 years; standard deviation 16 years). Standardized axial, coronal, and sagittal planes were evaluated and cross-referenced. Eight signs to delineate the superior temporal gyrus, Heschl gyrus (HG), parahippocampal gyrus, rhinal sulcus, collateral sulcus proper, or the occipitotemporal sulcus, or a combination, were evaluated in the sagittal or axial plane. Two neuroradiologists independently evaluated each sign; the sign was considered present only with positive reader agreement. RESULTS: All 8 signs were present in most patients. The most frequent signs were the posterior insular corner to identify HG in the axial plane (100 %), pointed STG to identify STG in the axial plane (98 %), and parahippocampal Y to identify the posterior parahippocampal gyrus in the sagittal plane (98 %). The frequencies were similar between the right and left cerebral hemispheres. CONCLUSIONS: Temporal lobe gyri and sulci can be reliably identified in multiple planes using anatomic signs.

Emergent, After Hours Magnetic Resonance Imaging of the Spine.

BACKGROUND AND PURPOSE: Requests for after-hours emergent spine MR imaging seem to be increasing. We sought to review the trend in after hours spine MRI utilization at our institution and to determine how these results impacted therapeutic intervention. METHODS: Following Institutional Review Board approval, reports from 179 after hours spinal MRI's performed over the past 13 years were obtained and the relevant electronic medical records were reviewed. RESULTS: Emergent after hours spine MRI utilization increased from 7 per year to 23 over 13 years. Fifty-eight percent (104/179) had significant findings. Twenty-nine percent (52/179) of all patients imaged underwent surgery to treat pathologies identified on MR. Surgery was performed in only 2% (4/179) of these patients within 3 hours and 6% (10/179) within 6 hours of MRI completion. Five percent (8/179) had findings that were treated with radiation therapy and in 78% of these it was performed within 6-12 hours. Of those in whom steroids or antibiotics were initiated, 41% and 50% were treated within 3 hours of MR scanning, respectively. DISCUSSION: Clinical use of emergent after hours spine MRI is steadily increasing at our institution. While MR imaging often discerned significant pathologies, performing these emergent studies rarely resulted in immediate surgical or radiotherapeutic intervention.

Vertebral body infarct and ventral cauda equina enhancement: two confirmatory findings of acute spinal cord infarct.

Two valuable confirmatory MRI findings of acute spinal cord infarct are highlighted and discussed: concomitant vertebral body infarct and ventral cauda equina nerve root enhancement.

Retrospective Analysis of Interobserver Spatial Variability in the Localization of Broca's and Wernicke's Areas Using Three Different fMRI Language Paradigms.

PURPOSE: To determine interobserver spatial variability in language area localization using three commonly employed language tasks. MATERIALS AND METHODS: With institutional review board approval, 125 fMRI time series from 50 different clinical language cases were retrospectively reviewed by three blinded readers who selected 3-dimensional points representing the perceived center of Wernicke's and Broca's areas using three language tasks (semantic decision, SD; sentence comprehension, SC; and silent word generation, WG). Point dispersion values were then calculated using the perimeter of the 3-dimensional triangle defined by the three readers' selections. RESULTS: After resolving interobserver laterality disagreements, there was no difference in spatial variability between the three tasks (P = .069). The SD task had the fewest interobserver laterality disagreements (P = .028) and the SC task had fewer failed localizations for Broca's area (P = .050) and Wernicke's area (P = .013). CONCLUSION: While there were no differences between interobserver spatial variability in language area localization between the three tasks, language task choice impacts the accuracy of fMRI language area identification because tasks vary in their rates of interobserver laterality disagreements and failed localizations. A combination of tasks including one with low laterality disagreements (eg, SD) and one with few failed localizations (eg, SC) may offer the best combination.

Failure of dabigatran and rivaroxaban to prevent thromboembolism in antiphospholipid syndrome: a case series of three patients.

Direct oral factor inhibitors (DOFIs) are an attractive alternative to vitamin K antagonists (VKA) for the treatment of patients with antiphospholipid syndrome (APS). In the absence of prospective, randomised trial data, reports of therapeutic failures in clinical practice alert clinicians to potential limitations of DOFI therapy for this indication. Data for all cases were collected from a centralised system that contains complete medical records of all patients treated and followed at Mayo Medical Center. We present here three consecutive APS patients who had had no thromboembolism recurrence on warfarin but were switched to DOFIs. The diagnosis of APS was established according to currently recommended criteria. The three cases were as follows: A woman with primary APS developed thrombotic endocarditis with symptomatic cerebral emboli after transition to dabigatran. A second woman with primary APS experienced ischemic arterial strokes and right transverse-sigmoid sinus thrombosis after conversion to rivaroxaban. A man with secondary APS suffered porto-mesenteric venous thrombosis after switching to rivaroxaban. None of these patients had failed warfarin prior to the transition to DOFIs. Based on these three cases, we advocate caution in using DOFIs for APS patients outside of a clinical trial setting, until further data becomes available.