Wilson Altmeyer

Functional Neuroimaging: Fundamental Principles and Clinical Applications

SUMMARY Functional imaging modalities, such as functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI), are rapidly changing the scope and practice of neuroradiology. While these modalities have long been used in research, they are increasingly being used in clinical practice to enable reliable identification of eloquent cortex and white matter tracts in order to guide treatment planning and to serve as a diagnostic supplement when traditional imaging fails. An understanding of the scientific principles underlying fMRI and DTI is necessary in current radiological practice. fMRI relies on a compensatory hemodynamic response seen in cortical activation and the intrinsic discrepant magnetic properties of deoxy- and oxyhemoglobin. Neuronal activity can be indirectly visualized based on a hemodynamic response, termed neurovascular coupling. fMRI demonstrates utility in identifying areas of cortical activation (i.e., task-based activation) and in discerning areas of neuronal connectivity when used during the resting state, termed resting state fMRI. While fMRI is limited to visualization of gray matter, DTI permits visualization of white matter tracts through diffusion restriction along different axes. We will discuss the physical, statistical and physiological principles underlying these functional imaging modalities and explore new promising clinical applications.

Use of Magnetic Resonance in the Evaluation of Cranial Trauma

MR imaging is an extremely useful tool in the evaluation of traumatic brain injury in the emergency department. Although CT still plays the dominant role in urgent patient triage, MR imagings impact on traumatic brain injury imaging continues to expand. MR imaging has shown superiority to CT for certain traumatic processes, such as diffuse axonal injury, cerebral contusion, and infarction. Magnetic resonance angiography and magnetic resonance venography allow emergent vascular imaging for patients that should avoid ionizing radiation or intravenous contrast.

Methylene blue modulates functional connectivity in the human brain

Methylene blue USP (MB) is a FDA-grandfathered drug used in clinics to treat methemoglobinemia, carbon monoxide poisoning and cyanide poisoning that has been shown to increase fMRI evoked blood oxygenation level dependent (BOLD) response in rodents. Low dose MB also has memory enhancing effect in rodents and humans. However, the neural correlates of the effects of MB in the human brain are unknown. We tested the hypothesis that a single low oral dose of MB modulates the functional connectivity of neural networks in healthy adults. Task-based and task-free fMRI were performed before and one hour after MB or placebo administration utilizing a randomized, double-blinded, placebo-controlled design. MB administration was associated with a reduction in cerebral blood flow in a task-related network during a visuomotor task, and with stronger resting-state functional connectivity in multiple regions linking perception and memory functions. These findings demonstrate for the first time that low-dose MB can modulate task-related and resting-state neural networks in the human brain. These neuroimaging findings support further investigations in healthy and disease populations.

Demystifying orbital emergencies: A pictorial review

Imaging of the orbit plays an important role in the workup of orbital emergencies. Orbital imaging is particularly useful in the emergency department, where clinical history and physical examination may be limited or delayed until the exclusion or treatment of more life-threatening conditions. Cross-sectional orbital imaging with multidetector computed tomography (CT) and magnetic resonance (MR) imaging is commonly performed in addition to ultrasonography. In an emergent setting, CT is the preferred modality when evaluating for intraorbital foreign bodies, fractures, or calcifications within a mass lesion. MR imaging is typically the modality of choice for orbital pathologic conditions, owing to its superior ability to delineate the orbital soft tissues and visual pathways. CT and MR imaging together may supplement clinical evaluation by helping establish an accurate diagnosis, providing an objective assessment of disease extent and progression, and assisting in pretreatment planning. Orbital emergencies have a spectrum of cross-sectional imaging findings in four major categories: infection, trauma, vascular disease, and inflammation. Use of a systematic approach to these entities will assist the radiologist with identifying immediate threats to vision and thereby facilitate prompt clinical management. Familiarity with the clinical presentations also improves the radiologists diagnostic confidence and role in guiding patient care. This article reviews imaging protocols, relevant orbital anatomy, the role of CT and MR imaging, and key imaging findings of orbital emergencies that the radiologist must know.

Venous Thrombosis: Causes and Imaging Appearance.

Cerebral venous sinus thrombosis is an elusive diagnosis with profound potential neurologic consequences. Although there are numerous reported predisposing conditions, by far the most common is a prothrombotic hypercoagulable state. Recent advances in MRI and computed tomography have improved diagnostic accuracy for this increasingly recognized disorder. Familiarity with imaging techniques and potential pitfalls is essential for accurate diagnosis and management of these patients.

T2*-based MR imaging of hyperglycemia-induced hemichorea-hemiballism

INTRODUCTION Hyperglycemia can induce hemichorea-hemiballism, especially in elderly type II diabetics. CT and MRI findings include hyperdensity and T1-shortening in the contralateral lentiform nucleus, respectively. This study explores the associated imaging findings on T2*-based sequences. METHODS Six patients with clinically documented hyperglycemia-induced hemichorea-hemiballism who had undergone MR imaging with a T2*-based sequence (T2* gradient echo or susceptibility-weighted imaging) were included in this retrospective case series. RESULTS All six patients demonstrated T1-shortening contralateral to their hemichorea-hemiballism. T2*-based sequences demonstrated unilateral hypointense signal within the striatum in four patients. One patient had mild bilateral striatal hyperintensities, while another did not show significant signal changes. CONCLUSION It is important for the radiologist to be aware of the signal changes that can be seen on T2*-based sequences in hyperglycemia-induced hemochorea-hemiballism.

Basion–Cartilaginous Dens Interval: An Imaging Parameter for Craniovertebral Junction Assessment in Children

BACKGROUND AND PURPOSE: Widening of the basion-dens interval is an important sign of cranioverterbral junction injury. The current literature on basion-dens interval in children is sparse and based on bony measurements with variable values. Our goal was to establish the normal values of a recently described new imaging parameter, the basion–cartilaginous dens interval in children. MATERIALS AND METHODS: Three hundred healthy pediatric patients (0–10 years of age) were selected retrospectively. These patients were divided into 3 different groups: A (0–3 years), B (3–6 years), and C (6–10 years). The basion–cartilaginous dens interval was calculated on the sagittal MPR image of cervical spine CT in a soft-tissue window. The mean, SD, and the upper limit of normal (mean +2 SDs) of the 3 groups were calculated, and statistical tests were used to check for significant differences of the basion–cartilaginous dens interval among these 3 groups. RESULTS: The upper limits of the basion–cartilaginous dens interval for the 3 groups were 5.34 mm in group A, 5.64 mm in group B, and 7.24 mm in group C. There were statistically significant differences in the basion–cartilaginous dens interval values among the 3 groups. There was no statistically significant difference in basion–cartilaginous dens interval values between groups A and B; however, values in group C were significantly different from those in both A and B. There was no statistically significant difference in the basion–cartilaginous dens interval values between males and females. CONCLUSIONS: The basion–cartilaginous dens interval is a novel imaging parameter to assess cranioverterbral junction integrity in children, which includes the nonossified cartilage in the measurement.

Posterior fossa giant tumefactive perivascular spaces: 8-year follow-up in an adolescent.

Background: Cystic masses in the posterior fossa are ominous appearing lesions with broad differential diagnosis. Giant tumefactive perivascular spaces (GTPS) are rarely occurring pathological findings in the posterior fossa with unclear etiology and ill-defined long-term prognosis. Case Description: We present a case of a 15-year-old male diagnosed with posterior fossa GTPS. The patient remained asymptomatic during the 8-year follow-up after diagnosis with the serial magnetic resonance imaging (MRI) showing no change in the size and morphology of the lesion. Conclusion: This case supports prior literature on supratentorial GTPS suggesting that the natural history of GTPS is mostly benign. Identification of GTPS in the posterior fossa could prevent the patient from unnecessary surgery or other aggressive treatment modalities.

Stroke-like migraine attacks after radiation therapy syndrome: Case report and review of the literature:

A 26-year-old female presented with vision loss accompanied by migraine-like headaches. A contrast-enhanced magnetic resonance imaging of the brain was performed which revealed findings suggestive of stroke-like migraine attacks after radiation therapy (SMART) syndrome. SMART syndrome is a delayed complication of brain radiation characterized by neurologic symptoms including migraine-like headaches, seizures, and hemispheric impairment. The purpose of this article is to make the readers aware of this rare complication of brain irradiation. Appropriate diagnosis of SMART syndrome is essential to avoid invasive tests.

Imaging Spectrum of Facial Nerve Lesions

The facial nerve is affected by a wide variety of pathologies, including congenital, traumatic, inflammatory, and neoplastic conditions. Imaging plays a vital role in the diagnosis of these pathologies. The facial nerve has a complex anatomy and course. A strong grasp of normal facial nerve anatomy is essential for the radiologist to maintain a high level of diagnostic sensitivity. This article details the normal imaging anatomy of the facial nerve and the imaging features of common facial nerve pathologies.