Prevalence and subtypes of radiological cerebrovascular disease in late-onset isolated seizures and epilepsy

BACKGROUND

Late-onset epilepsy (LOE), onset over 60, is often attributed to cerebrovascular disease (CVD), and is associated with increased stroke risk. We investigated the radiological prevalence of CVD in LOE.

METHODS

We undertook a retrospective case-control study of patients with LOE and age and sex-matched controls, also matched for imaging modality. Radiological CVD was recorded, with radiological findings by an experienced consultant neuroradiologist usi a structured proforma.

RESULTS

105 cases and 105 controls were studied, comprising 61 (58.1%) males, mean (±SD) age (years) 72.7±7.48 (cases), 72.4±7.02 (controls). 9 cases had isolated seizures rather than LOE. Imaging modality (in cases and controls) was CT in 59 and MRI in 46. Radiological CVD was more prevalent amongst cases (65.7%) than controls (33.3%) (p<0.0001, Chi-square), odds ratio 3.83 (95% CI 2.16-6.79). Large vessel disease (LVD) (single or multiple cortical or subcortical infarcts>1.5 cm) was present in 23 (21.9%) cases and 2 (1.9%) (p<0.001) controls, with small vessel disease (SVD) (periventricular or subcortical white matter lesions (WMLs), including leukoaraiosis (LA)) present in 52 (49.5%) cases (LA in 4) and 34 (32.3%) controls (LA in 0) (p<0.05). When WMLs were rated using a semiquantitative visual rating scale, a trend towards greater severity was observed amongst cases compared to controls.

CONCLUSIONS

Radiological CVD is significantly more prevalent in patients with LOE than controls, including signs of both LVD and SVD. SVD also appears to be of greater severity. Further studies are needed in this area.

Plasticity of the superior and middle cerebellar peduncles in musicians revealed by quantitative analysis of volume and number of streamlines based on diffusion tensor tractography

This work was conducted to study the plasticity of superior (SCP) and middle (MCP) cerebellar peduncles in musicians. The cerebellum is well known to support several musically relevant motor, sensory and cognitive functions. Previous studies reported increased cerebellar volume and grey matter (GM) density in musicians. Here, we report on plasticity of white matter (WM) of the cerebellum. Our cohort included 10/10 gender and handedness-matched musicians and controls. Using diffusion tensor imaging, fibre tractography of SCP and MCP was performed. The fractional anisotropy (FA), number of streamlines and volume of streamlines of SCP/MCP were compared between groups. Automatic measurements of GM and WM volumes of the right/left cerebellar hemispheres were also compared. Musicians have significantly increased right SCP volume (p = 0.02) and number of streamlines (p = 0.001), right MCP volume (p = 0.004) and total WM volume of the right cerebellum (p = 0.003). There were no significant differences in right MCP number of streamlines, left SCP/MCP volume and number of streamlines, SCP/MCP FA values, GM volume of the right cerebellum and GM/WM volumes of the left cerebellum. We propose that increased volume and number of streamlines of the right cerebellar peduncles represent use-dependent structural adaptation to increased sensorimotor and cognitive functional demands on the musician's cerebellum.

Reproducibility of functional MRI localization within the human somatosensory cortex

PURPOSE

To evaluate the effect of fMRI localization approaches and region size on the reproducibility of digit localization in the human somatosensory cortex.

MATERIALS AND METHODS

Vibrotactile stimulation was applied to digits 2 and 4 producing cortical activation sites relating to each digit. Thirteen subjects were scanned twice on separate occasions in a 3 Tesla scanner using a voxel size of 2 mm. Regions of activity were thresholded to different sizes varying from 50 to 1000 voxels. Three measures of position were acquired from these regions: center of gravity (COG), center co-ordinate and peak voxel. To account for registration errors, Euclidean distance between the two digits was computed. Reproducibility was determined in terms of the 95% confidence interval for individual position in X, Y, and Z and also the distance between the two digit locations.

RESULTS

Region size of 200 most significant voxels was shown to have the best reproducibility. Center co-ordinate proved to be the most precise form of localizing activity with a 95% CI of 2.1 mm, 2.6 mm, and 3.1 mm in the X, Y, and Z axes. Euclidean distance between the center co-ordinates of the two digit activation sites was shown to be a reliable means of overcoming registration errors with a 95% CI of 1.7 mm.

CONCLUSION

This study shows a high level of reproducibility for fMRI localization in the somatosensory system.

Increased gray matter volume of left pars opercularis in male orchestral musicians correlate positively with years of musical performance

PURPOSE

To compare manual volumetry of gray matter (GM) / white matter (WM) of Broca's area subparts: pars opercularis (POP) and pars triangularis (PTR) in both hemispheres between musicians and nonmusician, as it has been shown that these regions are crucial for musical abilities. A previous voxel-based morphometric (VBM) study conducted in our laboratory reported increased GM density in Broca's area of left hemisphere in male orchestral musicians. Functional segregation of POP/PTR justified separate volumetric analysis of these parts.

MATERIALS AND METHODS

We used the same cohort for the VBM study. Manual morphometry (stereology) was used to compare volumes between 26/26 right-handed orchestral musicians/nonmusicians.

RESULTS

As expected, musicians showed significantly increased GM volume in the Broca's area, specifically in the left POP. No significant results were detected in right POP, left/right PTR GM volumes, and WM volumes for all regions. Results were positively correlated with years of musical performance (r = 0.7, P = 0.0001).

CONCLUSION

This result corroborates the VBM study and is in line with the hypothesis of critical involvement of POP in hearing-action integration being an integral component of frontoparietotemporal mirror neuron network. We hypothesize that increased size of musicians' left POP represent use-dependent structural adaptation in response to intensive audiomotor skill acquisition.

Regional corpus callosum morphometry: effect of field strength and pulse sequence

PURPOSE

To investigate whether scanning at different field strengths and pulse sequences would influence reproducibility of corpus callosum (CC) morphometric measurements as variations in scanning parameters may result in differences in contrast properties between resulting images that are independent of the underlying tissue but rather reflect the physics of the imaging process.

MATERIALS AND METHODS

Ten subjects were scanned twice at 3T using magnetization-prepared rapid gradient-echo imaging (MPRAGE) and modified driven equilibrium Fourier transform (MDEFT) sequences and once at 1.5T using MPRAGE. Cross-sectional area measurements of four callosal regions were performed on midsagittal magnetic resonance imaging (MRI) sections.

RESULTS

Repeated measures analysis of variance with four regions as dependent variables and three scanning protocols (1.5T MPRAGE, 3T MPRAGE and 3T MDEFT) as independent variables revealed no significant region by protocol interaction: F(6,54) = 0.69, P = 0.52. Reliability measures for (3T MPRAGE/3T MDEFT) and (1.5T MPRAGE/3T MPRAGE; 1.5T MPRAGE/3T MDEFT) comparisons were high, ranging between 0.90 and 0.97.

CONCLUSION

Based on our results, combining and comparing CC morphometric data obtained at different field strengths and/or with different pulse sequences appears possible.

Depressive disorders: focally altered cerebral perfusion measured with arterial spin-labeling MR imaging

PURPOSE

To assess focal cerebral perfusion in patients with refractory depressive disorder (RDD), patients with nonrefractory depressive disorder (NDD), and healthy control subjects by using arterial spin-labeling (ASL) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

This study was approved by the local ethical committee, and written informed consent was obtained from all participants. Twenty-four patients with RDD, 37 patients with NDD, and 42 healthy control subjects were included. From February 2006 to July 2007, all participants were imaged with a 3-T MR system. ASL and echo-planar images were subtracted and averaged to give perfusion-weighted images. Voxel-based analysis was performed. Region-of-interest analysis was applied to the bilateral hippocampi, thalami, and lentiform nuclei.

RESULTS

Patients with NDD showed reduced perfusion in the left prefrontal cortex versus control subjects and increased perfusion mainly in the limbic-striatal areas (P < .05). In contrast, patients with RDD had decreased perfusion predominantly in the bilateral frontal and bilateral thalamic regions (P < .05). Compared with patients with RDD, patients with NDD showed higher perfusion mainly in the limbic-striatal areas (P < .05). In region-of-interest analysis, the NDD group showed higher regional cerebral blood flow than both RDD and control groups in the left hippocampus (P = .045), right hippocampus (P = .001), and right lentiform nucleus (P = .049).

CONCLUSION

This study revealed alterations of regional perfusion in the brains of patients with RDD that differed from those in patients with NDD. These results are consistent with the concept that RDD is associated with decreased activity of the bilateral prefrontal areas; and NDD, with decreased activity of left frontal areas in conjunction with overactivity of the bilateral limbic system.

Multivoxel fMRI analysis of color tuning in human primary visual cortex

We use multivoxel pattern analysis (MVPA) to study the spatial clustering of color-selective neurons in the human brain. Our main objective was to investigate whether MVPA reveals the spatial arrangements of color-selective neurons in human primary visual cortex (V1). We measured the distributed fMRI activation patterns for different color stimuli (Experiment 1: cardinal colors (to which the LGN is known to be tuned), Experiment 2: perceptual hues) in V1. Our two main findings were that (i) cone-opponent cardinal color modulations produce highly reproducible patterns of activity in V1, but these were not unique to each color. This suggests that V1 neurons with tuning characteristics similar to those found in LGN are not spatially clustered. (ii) Unique activation patterns for perceptual hues in V1 support current evidence for a spatially clustered hue map. We believe that our work is the first to show evidence of spatial clustering of neurons with similar color preferences in human V1.

TIPIT: a randomised controlled trial of thyroxine in preterm infants under 28 weeks gestation: magnetic resonance imaging and magnetic resonance angiography protocol

Background

Infants born at extreme prematurity are at high risk of developmental disability. A major risk factor for disability is having a low level of thyroid hormone described as hypothyroxinaemia, which is recognised to be a frequent phenomenon in these infants. Derangements of critical thyroid function during the sensitive window in prematurity when early development occurs, may have a range of long term effects for brain development. Further research in preterm infants using neuroimaging techniques will increase our understanding of the specificity of the effects of hypothyroxinaemia on the developing foetal brain. This is an explanatory double blinded randomised controlled trial which is aimed to assess the effect of thyroid hormone supplementation on brain size, key brain structures, extent of myelination, white matter integrity and vessel morphology, somatic growth and the hypothalamic-pituitary-adrenal axis.

Methods

The study is a multi-centred double blinded randomised controlled trial of thyroid hormone supplementation in babies born below 28 weeks' gestation. All infants will receive either levothyroxine or placebo until 32 weeks corrected gestational age. The primary outcomes will be width of the sub-arachnoid space measured using cranial ultrasound and head circumference at 36 weeks corrected gestational age. The secondary outcomes will be thyroid hormone concentrations, the hypothalamic pituitary axis status and auxological data between birth and expected date of delivery; thyroid gland volume, brain size, volumes of key brain structures, extent of myelination and brain vessel morphology at expected date of delivery and markers of morbidity which include duration of mechanical ventilation and/or oxygen requirement and chronic lung disease.

Trial registration

Current Controlled Trials ISRCTN89493983

Inability to directly detect magnetic field changes associated with neuronal activity

The ability to directly detect neuronal magnetic fields by MRI would help investigators achieve the "holy grail" of neuroimaging, namely both high spatial and temporal resolution. Both positive and negative findings have been reported in the literature, with no clear consensus as to the feasibility of direct detection. The aim of this study was to replicate one of the most promising published in vivo results. A second aim was to investigate the use of steady-state visual evoked potentials (ssVEPs), which give a large evoked response and offer a well-controlled approach because the frequency of the neuronal response can be dictated by the experimenter. For both studies we used a general linear model (GLM) that included regressors for both the expected blood oxygen level-dependent (BOLD) signal and the magnetic source (MS) signal. The results showed no activity that could be attributed to the neuromagnetic signals in either study, and no frequency component corresponding to the frequency of the ssVEPs. This study demonstrates that for the particular stimuli and hardware used, the sensitivity of the magnitude MRI signal to detect evoked neuronal currents is too low to be of practical use.

Quantification of cerebral perfusion using arterial spin labeling: two-compartment models

One of the advantages of arterial spin labeling (ASL) techniques over other techniques for measuring cerebral perfusion is that with ASL it is possible to achieve accurate quantification. This is particularly useful in the field of functional imaging, where accurate measurements of perfusion change can help untangle the complex physiological changes that occur following neuronal activation. However, the linearity of the perfusion estimate over a wide range of perfusion values may be more important than absolute values. For several years, single-compartment models have dominated the literature, and it has been assumed that the labeled water diffuses freely throughout the tissue voxel. However, recent work, as summarized in this review, has shown that this assumption is inaccurate and leads to an overestimation of perfusion at low perfusion rates, and an underestimation at high rates. The inclusion of restricted permeability of the capillary wall to water in a two-compartment model offers improved quantification.

Quantifying the spatial resolution of the gradient echo and spin echo BOLD response at 3 Tesla

The blood oxygen level dependent (BOLD) response, as measured with fMRI, offers good spatial resolution compared to other non-invasive neuroimaging methods. The use of a spin echo technique rather than the conventional gradient echo technique may further improve the resolution by refocusing static dephasing effects around the larger vessels, so sensitizing the signal to the microvasculature. In this work the width of the point spread function (PSF) of the BOLD response at a field strength of 3 Tesla is compared for these two approaches. A double echo EPI pulse sequence with simultaneous collection of gradient echo and spin echo signal allows a direct comparison of the techniques. Rotating multiple-wedge stimuli of different spatial frequencies are used to estimate the width of the BOLD response. Waves of activation are created on the surface of the visual cortex, which begin to overlap as the wedge separation decreases. The modulation of the BOLD response decreases with increasing spatial frequency in a manner dependent on its width. The spin echo response shows a 13% reduction in the width of the PSF, but at a cost of at least 3-fold reduction in contrast to noise ratio.

Localizing human visual gamma-band activity in frequency, time and space

Neuronal gamma-band (30-100 Hz) synchronization subserves fundamental functions in neuronal processing. However, different experimental approaches differ widely in their success in finding gamma-band activity. We aimed at linking animal and human studies of gamma-band activity and at preparing optimized methods for an in-depth investigation of the mechanisms and functions of gamma-band activity and gamma-band coherence in humans. In the first step described here, we maximized the signal-to-noise ratio with which we can observe visually induced gamma-band activity in human magnetoencephalographic recordings. We used a stimulus and task design that evoked strong gamma-band activity in animals and combined it with multi-taper methods for spectral analysis and adaptive spatial filtering for source analysis. With this approach, we found human visual gamma-band activity very reliably across subjects and across multiple recording sessions of a given subject. While increases in gamma-band activity are typically accompanied by decreases in alpha- and beta-band activity, the gamma-band enhancement was often the spectral component with the highest signal-to-noise ratio. Furthermore, some subjects demonstrated two clearly separate visually induced gamma bands, one around 40 Hz and another between 70 and 80 Hz. Gamma-band activity was sustained for the entire stimulation period, which was up to 3 s. The sources of gamma-band activity were in the calcarine sulcus in all subjects. The results localize human visual gamma-band activity in frequency, time and space and the described methods allow its further investigation with great sensitivity.

Combining EEG and fMRI to investigate the post-movement beta rebound

The relationship between synchronous neuronal activity as measured with EEG and the blood oxygenation level dependent (BOLD) signal as measured during fMRI is not clear. This work investigates the relationship by combining EEG and fMRI measures of the strong increase in beta frequency power following movement, the so-called post-movement beta rebound (PMBR). The time course of the PMBR, as measured by EEG, was included as a regressor in the fMRI analysis, allowing identification of a region of associated BOLD signal increase in the sensorimotor cortex, with the most significant region in the post-central sulcus. The increase in the BOLD signal suggests that the number of active neurons and/or their synaptic rate is increased during the PMBR. The duration of the BOLD response curve in the PMBR region is significantly longer than in the activated motor region, and is well fitted by a model including both motor and PMBR regressors. An intersubject correlation between the BOLD signal amplitude associated with the PMBR regressor and the PMBR strength as measured with EEG provides further evidence that this region is a source of the PMBR. There is a strong intra-subject correlation between the BOLD signal amplitude in the sensorimotor cortex during movement and the PMBR strength as measured by EEG, suggesting either that the motor activity itself, or somatosensory inputs associated with the motor activity, influence the PMBR. This work provides further evidence for a BOLD signal change associated with changes in neuronal synchrony, so opening up the possibility of studying other event-related oscillatory changes using fMRI.

Abnormalities of cerebral perfusion in multiple sclerosis

BACKGROUND

Measuring perfusion provides a potential indication of metabolic activity in brain tissue. Studies in multiple sclerosis (MS) have identified areas of decreased perfusion in grey matter (GM) and white matter (WM), but the pattern in clinical subgroups is unclear.

OBJECTIVES

This study investigated perfusion changes in differing MS clinical subgroups on or off beta-interferon therapy using a non-invasive MRI technique (continuous arterial spin labelling) to investigate whether different clinical MS subtypes displayed perfusion changes and whether this could give a further insight into the pathological mechanisms involved.

METHODS

Sixty patients (21 relapsing remitting, 14 secondary progressive, 12 primary progressive, 13 benign) and 34 healthy controls were compared. Statistical parametric mapping (SPM '99) was used to investigate regional variations in perfusion in both GM and WM. Global WM perfusion was derived by segmenting WM from images using T(1) relaxation times.

RESULTS

Regions of lower perfusion in predominantly GM were observed in the primary and secondary progressive cohorts, particularly in the thalamus. Increased WM perfusion was seen in relapsing remitting and secondary progressive cohorts.

CONCLUSIONS

Low GM perfusion could reflect decreased metabolism secondary to neuronal and axonal loss or dysfunction with a predilection for progressive forms of MS. Increased WM perfusion may indicate increased metabolic activity possibly due to increased cellularity and inflammation. Improved methodology and longitudinal studies may enable further investigation of regional and temporal changes, and their relationship with physical and cognitive impairment.

Normal cerebral perfusion measurements using arterial spin labeling: reproducibility, stability, and age and gender effects

Before meaningful conclusions can be drawn from clinical measures of cerebral blood perfusion, the precision of the measurement must be determined and set in the context of inter- and intrasubject sources of variability. This work establishes the reproducibility of perfusion measurements using the noninvasive MRI technique of continuous arterial spin labeling (CASL). Perfusion was measured in 34 healthy normal subjects. Intersubject variability was assessed, and age and gender contributions were estimated. Intersubject variation was found to be large, with up to 100% perfusion difference for subjects of the same age and gender. Repeated measurements in one subject showed that perfusion remains remarkably stable in the short term when compared with intersubject variation and the large capacity for perfusion change in the brain. A significant decrease in the ratio of gray-matter to white-matter perfusion was found with increasing age (0.79% per year (P < 0.0005)). This appears to be due mainly to a reduction in gray-matter perfusion, which was found to decrease by 0.45% per year (P = 0.04). Regional analysis suggested that the gray-matter age-related changes were predominantly localized in the frontal cortex. Whole-brain perfusion was 13% higher (P = 0.02) in females compared to males.

Reduced BOLD response to periodic visual stimulation

The blood oxygenation level-dependent (BOLD) response to entrained neuronal firing in the human visual cortex and lateral geniculate nuclei was investigated. Periodic checkerboard flashes at a range of frequencies (4-20 Hz) were used to drive the visual cortex neurons into entrained oscillatory firing. This is compared to a checkerboard flashing aperiodically, with the same average number of flashes per unit time. A magnetoencephalography (MEG) measurement was made to confirm that the periodic paradigm elicited entrainment. We found that for frequencies of 10 and 15 Hz, the periodic stimulus gave a smaller BOLD response than for the aperiodic stimulus. Detailed investigation at 15 Hz showed that the aperiodic stimulus gave a similar BOLD increase regardless of the magnitude of jitter (+/-17 ms compared to +/-33 ms), indicating that flashes need to be precise to at least 17 ms to maintain entrainment. This is also evidence that for aperiodic stimuli, the amplitude of the BOLD response ordinarily reflects the total number of flashes per unit time, irrespective of the precise spacing between them, suggesting that entrainment is the main cause of the BOLD reduction in the periodic condition. The results indicate that, during entrainment, there is a reduction in the neuronal metabolic demand. We suggest that because of the selective frequency band of this effect, it could be connected to synchronised reverberations around an internal feedback loop.

Improved accuracy of human cerebral blood perfusion measurements using arterial spin labeling: accounting for capillary water permeability

A two-compartment exchange model for perfusion quantification using arterial spin labeling (ASL) is presented, which corrects for the assumption that the capillary wall has infinite permeability to water. The model incorporates an extravascular and a blood compartment with the permeability surface area product (PS) of the capillary wall characterizing the passage of water between the compartments. The new model predicts that labeled spins spend longer in the blood compartment before exchange. This makes an accurate blood T(1) measurement crucial for perfusion quantification; conversely, the tissue T(1) measurement is less important and may be unnecessary for pulsed ASL experiments. The model gives up to 62% reduction in perfusion estimate for human imaging at 1.5T compared to the single compartment model. For typical human perfusion rates at 1.5T it can be assumed that the venous outflow signal is negligible. This simplifies the solution, introducing only one more parameter than the single compartment model, PS/v(bw), where v(bw) is the fractional blood water volume per unit volume of tissue. The simplified model produces an improved fit to continuous ASL data collected at varying delay time. The fitting yields reasonable values for perfusion and PS/v(bw).