F. Di Salle

The aerobic brain: Lactate decrease at the onset of neural activity

The metabolic events of neuronal energetics during functional activity are still partially unexplained. In particular, lactate (and not glucose) was recently proposed as the main substrate for neurons during activity. By means of proton magnetic resonance spectroscopy, lactate was reported to increase during the first minutes of prolonged stimulation, but the studies reported thus far suffered from low temporal resolution. In the present study we used a time-resolved proton magnetic resonance spectroscopy strategy in order to analyse the evolution of lactate during the early seconds following a brief visual stimulation (event-related design). A significant decrease in lactate concentration was observed 5 s after the stimulation, while a recovering of the baseline was observed at 12 s.

Sudden re-opening of collapsed transverse sinuses and longstanding clinical remission after a single lumbar puncture in a case of idiopathic intracranial hypertension. Pathogenetic implications

The aetiopathogenetic role of sinus venous obstructions carried by most idiopathic intracranial hypertension (IIH) patients is controversial. We report the case of a young woman diagnosed with IIH with papilloedema and narrowing of transverse sinuses, in which lowering of intracranial pressure by a single 20 ml cerebrospinal fluid (CSF) resulted in a strong dimensional increase of the transverse sinuses. Changes were followed by clinical remission and normalisation of optical nerve calibre, maintained after a 2-month follow-up. Our findings indicate that, although secondary to CSF hypertension, venous sinuses compression may have an important role in hypertensive status maintenance. Pathogenetic implications of venous sinus compression by hypertensive CSF in IIH are discussed.

Exploring brain function with magnetic resonance imaging.

Since its invention in the early 1990s, functional magnetic resonance imaging (fMRI) has rapidly assumed a leading role among the techniques used to localize brain activity. The spatial and temporal resolution provided by state-of-the-art MR technology and its non-invasive character, which allows multiple studies of the same subject, are some of the main advantages of fMRI over the other functional neuroimaging modalities that are based on changes in blood flow and cortical metabolism. This paper describes the basic principles and methodology of fMRI and some aspects of its application to functional activation studies. Attention is focused on the physiology of the blood oxygenation level-dependent (BOLD) contrast mechanism and on the acquisition of functional time-series with echo planar imaging (EPI). We also provide an introduction to the current strategies for the correction of signal artefacts and other image processing techniques. In order to convey an idea of the numerous applications of fMRI, we will review some of the recent results in the fields of cognitive and sensorimotor psychology and physiology.

Subcortical motor plasticity in patients with sporadic ALS : An fMRI study

OBJECTIVE To address the potential contribution of subcortical brain regions in the functional reorganization of the motor system in patients with sporadic ALS (sALS) and to investigate whether functional changes in brain activity are different in sALS patients with predominant upper motor neuron (UMN) or lower motor neuron (LMN) dysfunction. METHODS We studied 16 patients with sALS and 13 healthy controls, using BOLD-fMRI, while they performed a simple visually paced motor task. Seven patients had definite clinical UMN signs while nine patients had prevalent clinical and electrophysiological LMN involvement. fMRI data were analyzed with Brain Voyager QX. RESULTS Task-related functional changes were identified in motor cortical regions in both patients and healthy controls. Direct group comparisons revealed relatively decreased BOLD fMRI responses in left sensorimotor cortex, lateral premotor area, supplementary motor area and right posterior parietal cortex (p < 0.05 corrected) and relatively increased responses in the left anterior putamen (p < 0.001 uncorrected) in sALS patients. Additional analyses between the two patients subgroups demonstrated significant BOLD fMRI response differences in the anterior cingulate cortex and right caudate nucleus (p < 0.001 uncorrected) with more robust activation of these areas in patients with greater UMN burden. Importantly, there were no significant differences in performance of the motor task between sALS patients and controls as well as between sALS patient subgroups. CONCLUSIONS Our data demonstrate a different BOLD fMRI pattern between our sALS patients and healthy controls even during simple motor behavior. Furthermore, patients with sALS and greater UMN involvement show a different reorganization of the motor system compared to sALS patients with greater LMN dysfunction.

Spatial independent component analysis of functional magnetic resonance imaging time-series: characterization of the cortical components

Abstract Spatial independent component analysis (sICA) can be applied to human brain functional magnetic resonance imaging (fMRI) data. Here, we address the problem of identifying the “meaningful” subset in the large set of components (ICs). While this problem ultimately requires interpretation, we propose kurtosis of the component histogram, spatial clustering of the components layout in the brain and one-lag autocorrelation of the time course as criteria useful in selecting components for more in-depth examination. Using our method of cortex-based sICA, we illustrate this selection approach by applying it to two fMRI data sets already well understood by us. The criteria in combination allow the selection of the task-related fMRI-ICs, independent of a priori information pertaining to the particular temporal structure of the experiment.

3.0-T functional brain imaging: a 5-year experience

The aim of this paper is to illustrate the technical, methodological and diagnostic features of functional imaging (comprising spectroscopy, diffusion, perfusion and cortical activation techniques) and its principal neuroradiological applications on the basis of the experience gained by the authors in the 5 years since the installation of a high-field magnetic resonance (MR) magnet. These MR techniques are particularly effective at 3.0 Tesla (T) owing to their high signal, resolution and sensitivity, reduced scanning times and overall improved diagnostic ability. In particular, the high-field strength enhances spectroscopic analysis due to a greater signal-to-noise ratio (SNR) and improved spectral, space and time resolution, resulting in the ability to obtain highresolution spectroscopic studies not only of the more common metabolites, but also – and especially – of those which, due to their smaller concentrations, are difficult to detect using 1.5-T systems. All of these advantages can be obtained with reduced acquisition times. In diffusion studies, the high-field strength results in greater SNR, because 3.0-T magnets enable increased spatial resolution, which enhances accuracy. They also allow exploration in greater detail of more complex phenomena (such as diffusion tensor and tractography), which are not clearly depicted on 1.5-T systems. The most common perfusion study (with intravenous injection of a contrast agent) benefits from the greater SNR and higher magnetic susceptibility by achieving dramatically improved signal changes, and thus greater reliability, using smaller doses of contrast agent. Functional MR imaging (fMRI) is without doubt the modality in which high-field strength has had the greatest impact. Images acquired with the blood-oxygen-level-dependent (BOLD) technique benefit from the greater SNR afforded by 3.0-T magnets and from their stronger magnetic susceptibility effects, providing higher signal and spatial resolution. This enhances reliability of the localisation of brain functions, making it possible to map additional areas, even in the millimetre and submillimetre scale. The data presented and results obtained to date show that 3.0-T morphofunctional imaging can become the standard for highresolution investigation of brain disease.

Issues concerning the construction of a metabolic model for neuronal activation

The metabolic events underlying neuronal activity still remain the object of intense debate, in spite of the considerable amount of information provided from different experimental techniques. Indeed, several attempts at linking the cellular metabolic phenomena with the macroscopic physiological changes have not yet attained foolproof conclusions. The difficulties in drawing definitive conclusions are due primarily to the heterogeneity of the experimental procedures used in different laboratories, and also given the impossibility of extrapolating the findings obtained under stationary conditions (prolonged stimulation) to dynamic and transient phenomena. Recently, lactate has received much attention, following its proposal by Pellerin and Magistretti (1994; Proc. Natl. Acad. Sci. USA 91:10625–10629), instead of glucose, as the main substrate for neurons during activity. Several challenging aspects suggest the return to a more conventional view of neuronal metabolism, in which neurons are able to metabolize ambient glucose directly as their major substrate, also during activation.

T2 relaxometry of brain in myotonic dystrophy.

Abstract We investigated the nature and extent of brain involvement in myotonic dystrophy (DM), examining possible T2 relaxation abnormalities in the brain of 20 patients with adult-onset DM and 20 sex- and age-matched normal controls. Brain MRI was performed at 0.5 T, and T2 values were calculated from signal intensity in two echoes. Regions of interest included: frontal, parietal, temporal, occipital and callosal (rostral and splenial) normal-appearing white matter; frontal, occipital, insular and hippocampal cortex; caudate nucleus, putamen, globus pallidus and thalamus. All white-matter and occipital and right frontal cortex regions showed a significantly longer T2 in the patients. Multiple regression analysis, including grey- and white-matter T2 as dependent variables, plus age at onset and at imaging, disease duration, muscular disability, brain atrophy and CTG trinucleotide repeats as independent variables, revealed that only white-matter T2 elongation and disease duration correlated positively. White-matter involvement in DM is more extensive than previously reported by MRI and neuropathological studies and seems to be progressive in the course of disease.

Brain Changes in Kallmann Syndrome

BACKGROUND AND PURPOSE: Kallmann syndrome is a rare inherited disorder due to defective intrauterine migration of olfactory axons and gonadotropin-releasing hormone neurons, leading to rhinencephalon hypoplasia and hypogonadotropic hypogonadism. Concomitant brain developmental abnormalities have been described. Our aim was to investigate Kallmann syndrome–related brain changes with conventional and novel quantitative MR imaging analyses. MATERIALS AND METHODS: Forty-five male patients with Kallmann syndrome (mean age, 30.7 years; range, 9–55 years) and 23 age-matched male controls underwent brain MR imaging. The MR imaging study protocol included 3D-T1, FLAIR, and diffusion tensor imaging (32 noncollinear gradient-encoding directions; b-value = 800 s/mm2). Voxel-based morphometry, sulcation, curvature, and cortical thickness analyses and tract-based spatial statistics were performed by using Statistical Parametric Mapping 8, FreeSurfer, and the fMRI of the Brain Software Library. RESULTS: Corpus callosum partial agenesis, multiple sclerosis–like white matter abnormalities, and acoustic schwannoma were found in 1 patient each. The total amount of gray and white matter volume and tract-based spatial statistics measures (fractional anisotropy and mean, radial, and axial diffusivity) did not differ between patients with Kallmann syndrome and controls. By specific analyses, patients with Kallmann syndrome presented with symmetric clusters of gray matter volume increase and decrease and white matter volume decrease close to the olfactory sulci; reduced sulcal depth of the olfactory sulci and deeper medial orbital-frontal sulci; lesser curvature of the olfactory sulcus and sharper curvature close to the medial orbital-frontal sulcus; and increased cortical thickness within the olfactory sulcus. CONCLUSIONS: This large MR imaging study on male patients with Kallmann syndrome featured significant morphologic and structural brain changes, likely driven by olfactory bulb hypo-/aplasia, selectively involving the basal forebrain cortex.

Risonanza Magnetica 3.0 Tesla

Dall’avvento della Risonanza Magnetica (RM) le apparecchiature con intensità di campo magnetico di 1.5 Tesla (T) sono state sempre considerate il “gold standard” per lo studio dei vari distretti corporei. Fino a qualche tempo fa parlare di sistemi RM a più alto campo significava riferirsi a sistemi dedicati solo ed esclusivamente alla ricerca e non certo per l’uso clinico. In realtà recentemente sono stati messi in commercio sistemi RM a più alto campo (3.0 T) da utilizzare non solo per la ricerca, ma anche e soprattutto per far fronte a nuove e più sofisticate applicazioni cliniche con conseguenti importanti benefici soprattutto in campo neuroradiologico. Da oltre 1 anno il servizio di Neuroradiologia del nostro Istituto Scientifico è stato dotato di un’apparecchiatura RM 3.0 T con gradienti di alta potenza (50 mT/m). Lo scopo del lavoro è quello di illustrare le principali applicazioni cliniche di interesse neuroradiologico che tale apparecchiatura è in grado di eseguire mettendo in risalto i vantaggi e i limiti rispetto a sistemi RM 1.5 T.