Frank De Belder

Magnetic Resonance Imaging of the Brain

Magnetic resonance imaging (MRI) examinations of the brain can be performed with several coil types, depending on the design of the MRI unit and the information required. Traditionally, MRI examinations of the brain are performed with quadrature (i.e., circularly polarized) head coils. These volume coils are closely shaped around the head of the patient and usually present a so-called “bird-cage” configuration. Many coils are split in half, for easier patient access and positioning. Recently, phased-array head coils have become the standard of practice for state-of-the-art high-resolution MRI of the brain. Phased-array head coils contain multiple small coil elements, which are arranged in an integrated design which surrounds the head (e.g., 8-, 12- or even 32-channel head coils). Data from the individual coils are integrated by special software to compensate for the nonuniform distribution of the signal-to-noise ratio (SNR) between the peripheral and central parts of the brain. The major advantage of a multichannel, phased-array head coil is that it allows the application of parallel acquisition techniques (PAT), which can be used to speed up MRI. The concept is to reduce the number of phase-encoding steps by switching a field gradient for each phase-encoding step. Skipping, for example, every second phase-encoding line accelerates the acquisition speed by a factor of two. This is called the acceleration or PAT factor. The trade-off for this increased imaging speed is a decrease in SNR. Image reconstruction with PAT techniques is more complicated, and several algorithms have been described, depending on whether image reconstruction takes place before (SMASH, GRAPPA (generalized autocalibrating partially parallel acquisition)) or after (SENSE) Fourier transform of the image data.

Prefrontal GABA concentration changes in women-Influence of menstrual cycle phase, hormonal contraceptive use, and correlation with premenstrual symptoms.

Prefrontal regions are involved in processing emotional stimuli and are a topic of interest in clinical and neurological research. Although sex steroids are potent neuromodulators, the influence of menstrual cycle phase and hormonal contraceptive use is rarely taken into account in neuroimaging studies. Our purpose was to evaluate changes in gamma-aminobutyric acid (GABA) in women, as measured by magnetic resonance spectroscopy (MRS), with phases of the menstrual cycle and use of hormonal contraceptives, and to assess correlations with premenstrual symptoms.Three MRI sessions per cycle were obtained in the natural cycle group, and two sessions in the hormonal contraceptives group. In addition to an anatomical scan, single voxel MRS in the prefrontal area was performed. After quality control, 10 women with natural cycle and 21 women taking hormonal contraceptives were included for analysis. Peripheral blood samples were obtained to determine endogenous hormone concentrations. Subjects were asked to complete a daily rating of severity of problems questionnaire, to quantify premenstrual symptoms. In the natural cycle group, we found a significant increase in prefrontal GABA concentration at the time of ovulation. Conversely, in the hormonal contraceptives group, no differences were found between the pill phase and pill-free phase. GABA concentrations did not significantly correlate with endogenous hormone levels, nor with premenstrual symptoms. Our results indicate that spectroscopically measured GABA concentrations are higher during ovulation in women with a natural menstrual cycle. We suggest that neuroimaging studies should take into account this variability.

Diffusion tensor imaging provides an insight into the microstructure of meningiomas, high-grade gliomas, and peritumoral edema.

Objective Fractional anisotropy (FA) is a measure for the degree of microstructural organization. Several studies have used FA values to assess microstructural organization of brain tumors and peritumoral edema. The purpose of our study was to validate FA and apparent diffusion constant (ADC) values in the diagnosis of meningiomas versus high-grade glial tumors, with the focus on the ability of diffusion tensor imaging (DTI) to reveal tumor ultrastructure. Our hypothesis was that FA and ADC values significantly differ between high-grade gliomas and meningiomas, and in the peritumoral edema. Methods Diffusion tensor imaging values were obtained from 20 patients with meningiomas (21 tumors) and 15 patients with high-grade gliomas. Regions of interest were outlined in FA and ADC maps for solid-enhancing tumor tissue and peritumoral edema. Fractional anisotropy and ADC values were normalized by comparison to normal-appearing white matter (NAWM) in the contralateral hemisphere. Differences between meningiomas and high-grade gliomas were statistically analyzed. Results Meningiomas showed a significantly higher FA tumor/FA NAWM ratio (P = 0.0001) and lower ADC tumor/ADC NAWM ratio (P = 0.0008) compared to high-grade gliomas. On average, meningiomas also showed higher FA values in peritumoral edema than high-grade gliomas (P = 0.016). Apparent diffusion constant values of peritumoral edema for the 2 tumor groups did not differ significantly (P = 0.5). Conclusions Diffusion tensor imaging can be used to reveal microstructural differences between meningiomas and high-grade gliomas and may contribute toward predicting the histopathology of intracranial tumors. We advocate that diffusion tensor imaging should be included in the standard imaging protocol for patients with intracranial tumors.

High-resolution susceptibility-weighted imaging at 3 T with a 32-channel head coil: technique and clinical applications.

OBJECTIVE The purpose of this article is to illustrate the utility of susceptibility-weighted imaging (SWI) as an adjunct to routine MRI of the brain in neurologic disorders. CONCLUSION SWI is a 3D spoiled gradient-echo sequence that combines phase and magnitude information to provide a high sensitivity for the detection of blood degradation products, calcifications, and iron deposits.

Diffusion Kurtosis Imaging: A Possible MRI Biomarker for AD Diagnosis?

Abstract The purpose of this explorative study was to investigate whether diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) parameter changes are reliable measures of white matter integrity changes in Alzheimer’s disease (AD) patients using a whole brain voxel-based analysis (VBA). Therefore, age- and gender-matched patients with mild cognitive impairment (MCI) due to AD (n = 18), dementia due to AD (n = 19), and age-matched cognitively healthy controls (n = 14) were prospectively included. The magnetic resonance imaging protocol included routine structural brain imaging and DKI. Datasets were transformed to a population-specific atlas space. Groups were compared using VBA. Differences in diffusion and mean kurtosis measures between MCI and AD patients and controls were shown, and were mainly found in the splenium of the corpus callosum and the corona radiata. Hence, DTI and DKI parameter changes are suggestive of white matter changes in AD.

Brain stones revisited—between a rock and a hard place

Objectives and methodsLarge intracranial calcifications are occasionally encountered in routine computed tomography (CT) scans of the brain. These calcifications, also known as “brain stones”, can be classified according to location and aetiology. Combining imaging findings with relevant clinical history and physical examination can help narrow down the differential diagnosis and may allow confident diagnosis in certain situations.ResultsThis article provides a pictorial review illustrating various clinical entities resulting in brain stones.DiscussionBased on location, brain stones can be classified as extra- or intra-axial. Extra-axial brain stones comprise tumours and exaggerated physiological calcifications. Intra-axial brain stones can further be classified according to aetiology, namely neoplastic, vascular, infectious, congenital and endocrine/metabolic. Imaging findings combined with essential clinical information can help in narrowing the differential diagnosis, determining disease state and evaluating effect of therapy.Teaching Points• Based on location, brain stones can be either extra- or intra-axial.• Extra-axial brain stones comprise tumours and exaggerated physiological calcifications.• Intra-axial aetiologies include neoplastic, vascular, infectious, congenital and endocrine/metabolic.• CT scan is the mainstay in identifying and characterising brain stones.• Certain MRI sequences (gradient echo T2* and susceptibility-weighted imaging) are considered adjunctive.

Overview of the Complications and Sequelae in Spinal Infections

Spondylitis or infection of the spine is a spectrum of diseases involving the bone, disks, and/or ligaments. Because of a significant increase in the immunocompromised patient population, spinal infections are a growing and changing group of conditions, making the diagnosis based on imaging more challenging. Most cases of spinal infections are pyogenic and occur after hematogeneous spread of an infection located elsewhere in the body. A prompt diagnosis remains crucial and MR imaging remains the cornerstone in the diagnosis. This article provides a pictorial overview of the complications and sequelae in spinal infections in general. Discussed are postoperative infections, extraspinal spread of infection, fractures and malformations, and neurologic complications.

Semicircular Canal Fibrosis as a Biomarker for Lateral Semicircular Canal Function Loss

Background and purpose Radiological abnormalities at the level of the semicircular canals are frequently observed without known correlation to a pathologic condition or function. They include narrowing or sclerosis on computed tomography (CT) and narrowing or signal loss on T2-weighted magnetic resonance imaging (MRI). Our hypothesis was that these radiological abnormalities at the level of the semicircular canals reflect an aspecific but advanced stage of vestibular decay. Materials and methods Retrospective study in 35 consecutive patients with bilateral profound deafness eligible for cochlear implantation. Electronystagmography, CT, and MRI were performed as part of evaluation for cochlear implant candidacy. Results In our population, 31.4% had a bilateral lateral semicircular canal function loss, while 11.4% had a unilateral lateral semicircular canal function loss. CT-scan abnormalities did not correlate to lateral semicircular canal function loss at a statistically significant level. However, abnormalities observed on MRI correlated significantly with ipsilateral lateral semicircular canal function loss. This statistically significant difference was present not only if abnormalities were observed in at least one of the semicircular canals but also if we studied the posterior, superior, and lateral semicircular canals separately. Conclusion Semicircular canal abnormalities on T2-weighted MRI (including narrowing and/or signal loss in one or more semicircular canals) are correlated to lateral semicircular canal function loss.

Resting state functional MRI as a possible biomarker for Alzheimer’s disease: An innovative approach for robust extraction of the default mode network

P4-248 RESTING STATE FUNCTIONAL MRI AS A POSSIBLE BIOMARKER FOR ALZHEIMER’S DISEASE: AN INNOVATIVE APPROACH FOR ROBUST EXTRACTION OF THE DEFAULT MODE NETWORK Hanne Struyfs, Dirk Smeets, Vasilis Terzopoulos, Sylvie Slaets, Laura Wuyts, Benjamin Peters, Frank De Belder, Paul M. Parizel, Wim Van Hecke, Sebastiaan Engelborghs, Reference Center for Biological Markers of Dementia (BIODEM), Laboratory of Neurochemistry and Behavior, Institute Born-Bunge, University of Antwerp, Antwerp, Belgium; icoMetrix, Leuven, Belgium; icoMetrix, Leuven, Belgium; University of Antwerp, Antwerp, Belgium; Antwerp University Hospital & University of Antwerp, Antwerp, Belgium; Department of Neurology and Memory Clinic, Hospital Network Antwerp, Middelheim and Hoge Beuken, Antwerp, Belgium; Institute Born-Bunge, University of Antwerp, Antwerp, Belgium; Hospital Network Antwerp (ZNA), Antwerp, Belgium. Contact e-mail: hanne.struyfs@uantwerpen.be

Rapid Ventricular Pacing for Neurovascular Surgery: A Study on Cardiac and Cerebral Effects

BACKGROUND AND OBJECTIVE Intraoperative rupture of a cerebral aneurysm during neurosurgery can be a devastating event that increases perioperative morbidity and mortality. Rapid ventricular pacing (RVP) is a technique to obtain flow arrest for short periods of time during dissection or rupture of the aneurysm. The objective of this study was to evaluate the neurological and cardiac effects of repetitive periods of RVP during cerebrovascular surgery. METHODS Data from patients who underwent repetitive RVP during craniotomy for cerebrovascular disorders were retrospectively analyzed from a single-center medical records database (Cegeka Medical Health Care Systems). We compared preoperative and postoperative troponin levels (cTnI) to assess cardiac ischemia. Preoperative and postoperative magnetic resonance imaging (MRI) results were screened for RVP-induced infarcts by evaluating diffusion restriction in the hemisphere contralateral to the operated side and the fossa posterior. RESULTS A total of 37 patients were analyzed. An immediate decrease of systolic arterial blood pressure (<60 mm Hg) was achieved after initiation of RVP. Postoperative MRI did not reveal areas of diffusion restriction. RVP tended to be a predictor of postoperative cTnI increase. Preoperative and postoperative cTnI levels were higher in patients with a subarachnoid hemorrhage compared to patients without one. After 24 hours cTnI jevels normalized to preoperative values. CONCLUSIONS Systolic arterial blood pressure decreased after RVP but normalized immediately when pacing stopped. MRI of the brain did not show RVP-related ischemia and the limited cTnI level increase normalized to preoperative values. Therefore, RVP during short periods of time seems to be a safe blood pressure-lowering technique for the brain and heart.