Brain atrophy in cerebral small vessel diseases: Extent, consequences, technical limitations and perspectives: The HARNESS initiative

Brain atrophy is increasingly evaluated in cerebral small vessel diseases. We aim at systematically reviewing the available data regarding its extent, correlates and cognitive consequences. Given that in this context, brain atrophy measures might be biased, the first part of the review focuses on technical aspects. Thereafter, data from the literature are analyzed in light of these potential limitations, to better understand the relationships between brain atrophy and other MRI markers of cerebral small vessel diseases. In the last part, we review the links between brain atrophy and cognitive alterations in patients with cerebral small vessel diseases.

Harmonizing brain magnetic resonance imaging methods for vascular contributions to neurodegeneration

INTRODUCTION

Many consequences of cerebrovascular disease are identifiable by magnetic resonance imaging (MRI), but variation in methods limits multicenter studies and pooling of data. The European Union Joint Program on Neurodegenerative Diseases (EU JPND) funded the HARmoNizing Brain Imaging MEthodS for VaScular Contributions to Neurodegeneration (HARNESS) initiative, with a focus on cerebral small vessel disease.

METHODS

Surveys, teleconferences, and an in-person workshop were used to identify gaps in knowledge and to develop tools for harmonizing imaging and analysis.

RESULTS

A framework for neuroimaging biomarker development was developed based on validating repeatability and reproducibility, biological principles, and feasibility of implementation. The status of current MRI biomarkers was reviewed. A website was created at www.harness-neuroimaging.org with acquisition protocols, a software database, rating scales and case report forms, and a deidentified MRI repository.

CONCLUSIONS

The HARNESS initiative provides resources to reduce variability in measurement in MRI studies of cerebral small vessel disease.

Alteration of the Cortex Shape as a Proxy of White Matter Swelling in Severe Cerebral Small Vessel Disease

CADASIL is a monogenic small vessel disease characterized by the accumulation of brain tissue lesions of microvascular origin leading to strokes and cognitive deficits. Both cortical and parenchymal alterations have been described using various MRI markers. However, relationships between cortical and subcortical alterations remain largely unexplored. While brain atrophy is a preponderant feature in cerebral small vessel disease, recent results in CADASIL suggest slightly larger brain volumes and increased white matter water content at early stages of the disease by comparison to controls. We hypothesized in this study that increased water content in gyral white matter balances expected brain atrophy. Direct white matter volume computation is challenging in these patients given widespread subcortical alterations. Instead, our approach was that a gyral white matter swelling would translate into a modification of the shape of cortical gyri. Our goal was then to assess the relationship between subcortical lesions and possible alteration of the cortex shape. More specifically, aims of this work were to assess 1) morphometric differences of the cortex shape between CADASIL patients and controls 2) the relationship between the cortex shape and the volume of white matter hyperintensities (WMH), a reflect of white matter alterations. Twenty-one patients at the early stage of the disease and 28 age- and sex-matched controls were included. Cortical surfaces were reconstructed from 3D-T1-weighted images. Folding power assessed from spectral analysis of gyrification and cortical morphometry using curvedness and shape index were computed as proxies of the cortex shape. Influence of segmentation errors were evaluated through the simulation of WMH in controls. As a result, patients had larger folding power and curvedness compared to controls. They also presented lower shape indices both related to sulci and gyri. In patients, the volume of WMH was associated with decreased gyral shape index. These results suggest that the cortex shape of CADASIL patients is different compared to controls and that the enlargement of gyri is related to the extent of white matter alterations. The study of the cortex shape might be another way to evaluate subcortical swelling or atrophy in various neurological disorders.

Clinical correlates of longitudinal MRI changes in CADASIL

Previous studies showed that various types of cerebral lesions, as assessed on MRI, largely contribute to the clinical severity of CADASIL. However, the clinical impact of longitudinal changes of classical markers of small vessel disease on conventional MRI has been only poorly investigated. One hundred sixty NOTCH3 mutation carriers (mean age ± SD, 49.8 ± 10.9 years) were followed over three years. Validated methods were used to determine the percent brain volume change (PBVC), number of incident lacunes, change of volume of white matter hyperintensities and change of number of cerebral microbleeds. Multivariable logistic regression analyses were performed to assess the independent association between changes of these MRI markers and incident clinical events. Mixed-effect multiple linear regression analyses were used to assess their association with changes of clinical scales. Over a mean period of 3.1 ± 0.2 years, incident lacunes are found independently associated with incident stroke and change of Trail Making Test Part B. PBVC is independently associated with all incident events and clinical scale changes except the modified Rankin Scale at three years. Our results suggest that, on conventional MRI, PBVC and the number of incident lacunes are the most sensitive and independent correlates of clinical worsening over three years in CADASIL.

Different types of white matter hyperintensities in CADASIL: Insights from 7-Tesla MRI

In Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL), by contrast to sporadic cerebral small vessel disease related to age and hypertension, white matter hyperintensities (WMH) are frequently observed in the white matter of anterior temporal poles, external capsules, and superior frontal regions. Whether these WMH (specific WMH) differ from those observed in other white matter areas (nonspecific WMH) remains unknown. Twenty patients were scanned to compare specific and nonspecific WMH using high-resolution images and analyses of relaxation times (T1_R: longitudinal relaxation time and T2*_R: effective transversal relaxation time). Specific WMH were characterized by significantly longer T1_R and T2*_R (T1_R: 2309 ± 120 ms versus 2145 ± 138 ms; T2*_R: 40 ± 5 ms versus 35 ± 5 ms, p < 0.001). These results were not explained by the presence of dilated perivascular spaces found in the close vicinity of specific WMH. They were not either explained by the normal regional variability of T1_R and T2*_R in the white matter nor by systematic imaging artifacts as shown by the study of 17 age- and sex-matched healthy controls. Our results suggest large differences in water content between specific and nonspecific WMH in CADASIL, supporting that mechanisms underlying WMH may differ according to their location.

Why Are Only Some Subcortical Ischemic Lesions on Diffusion Magnetic Resonance Imaging Associated With Stroke Symptoms in Small Vessel Disease?

Background and Purpose- In cerebral small vessel diseases, small subcortical ischemic lesions (SSIL) on diffusion imaging are responsible for stroke manifestations but can also be occasionally observed in the absence of overt neurological symptoms. We aimed to determine, in a large cohort of young patients with CADASIL (Cerebral Autosomal-Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy), a severe monogenic condition leading to SSIL in young patients, the characteristics of SSIL and of surrounding cerebral tissue associated with the presence of stroke symptoms. Methods- Among a cohort of 323 genetically confirmed CADASIL patients who were systematically evaluated every 18 months clinically and with magnetic resonance imaging, we studied all visible SSIL and documented ischemic stroke events with available magnetic resonance imaging data. We used mixed-effect logistic regression models to determine whether the presence of stroke symptoms was associated with age, sex, the volume of SSIL, their location with respect to preexisting white matter hyperintensities and with the load of the different magnetic resonance imaging markers of small vessel disease. Results- We identified 73 SSIL (30 with stroke symptoms and 43 without) in 55 patients. In multivariable models, stroke symptoms were more frequent in male patients (estimate=1.94; SE=0.82; P=0.03) and less frequent when SSIL appeared in contact to preexisting white matter hyperintensities (estimate=-2.12; SE=0.83; P=0.01). Within pyramidal tracts, stroke symptoms were more frequent in patients with extensive white matter hyperintensities (estimate=3.8×10^-5; SE=9.3×10^-6; P<10^-4). Conclusions- Altogether, our results suggest that when SSIL occur, the presence of stroke symptoms may depend on sex and alterations of the surrounding brain tissue rather than on the characteristics of the SSIL itself.

Different Types of White Matter Hyperintensities in CADASIL

Objective: In CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy), white matter hyperintensities (WMH) are considered to result from hypoperfusion. We hypothesized that in fact the burden of WMH results from the combination of several regional populations of WMH with different mechanisms and clinical consequences.

Methods: To identify regional WMH populations, we used a 4-step approach. First, we used an unsupervised principal component algorithm to determine, without a priori knowledge, the main sources of variation of the global spatial pattern of WMH. Thereafter, to determine whether these sources are likely to include relevant information regarding regional populations of WMH, we tested their relationships with: (1) MRI markers of the disease; (2) the clinical severity assessed by the Mattis Dementia Rating scale (MDRS) (cognitive outcome) and the modified Rankin's score (disability outcome). Finally, through careful interpretation of all the results, we tried to identify different regional populations of WMH.

Results: The unsupervised principal component algorithm identified 3 main sources of variation of the global spatial pattern of WMH, which showed significant and sometime inverse relationships with MRI markers and clinical scores. The models predicting clinical severity based on these sources outperformed those evaluating WMH by their volume (MDRS, coefficient of determination of 39.0 vs. 35.3%, p = 0.01; modified Rankin's score, 43.7 vs. 38.1%, p = 0.001). By carefully interpreting the visual aspect of these sources as well as their relationships with MRI markers and clinical severity, we found strong arguments supporting the existence of different regional populations of WMH. For instance, in multivariate analyses, larger extents of WMH in anterior temporal poles and superior frontal gyri were associated with better outcomes, while larger extents of WMH in pyramidal tracts were associated with worse outcomes, which could not be explained if WMH in these different areas shared the same mechanisms.

Conclusion: The results of the present study support the hypothesis that the whole extent of WMH results from a combination of different regional populations of WMH, some of which are associated, for yet undetermined reasons, with milder forms of the disease.

Cerebral Microbleeds and the Risk of Incident Ischemic Stroke in CADASIL (Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy)

BACKGROUND AND PURPOSE

Cerebral microbleeds are associated with an increased risk of intracerebral hemorrhage. Recent data suggest that microbleeds may also predict the risk of incident ischemic stroke. However, these results were observed in elderly individuals undertaking various medications and for whom causes of microbleeds and ischemic stroke may differ. We aimed to test the relationship between the presence of microbleeds and incident stroke in CADASIL (Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy)-a severe monogenic small vessel disease known to be responsible for both highly prevalent microbleeds and a high incidence of ischemic stroke in young patients.

METHODS

We assessed microbleeds on baseline MRI in all 378 patients from the Paris-Munich cohort study. Incident ischemic strokes were recorded during 54 months. Survival analyses were used to test the relationship between microbleeds and incident ischemic stroke.

RESULTS

Three hundred sixty-nine patients (mean age, 51.4±11.4 years) were followed-up during a median time of 39 months (interquartile range, 19 months). The risk of incident ischemic stroke was higher in patients with microbleeds than in patients without (35.8% versus 19.6%, hazard ratio, 1.87; 95% confidence interval, 1.16-3.01; P=0.009). These results persisted after adjustment for history of ischemic stroke, age, sex, vascular risk factors, and antiplatelet agents use (hazard ratio, 1.89; 95% confidence interval, 1.10-3.26; P=0.02).

CONCLUSIONS

The presence of microbleeds is an independent risk marker of incident ischemic stroke in CADASIL, emphasizing the need to carefully interpret MRI data.

Focal Macroscopic Cortical Lesions in Cerebral Autosomal-Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy

Background and Purpose—

Cortical microinfarcts and secondary cortical degeneration have been demonstrated in cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a severe monogenic cerebral small vessel disease. The aim of this study was to determine whether focal macroscopic cortical lesions can be detected using a specific in vivo magnetic resonance imaging approach.

Methods—

Three-dimensional T1 magnetic resonance imaging scans were obtained in 28 nondemented nondisabled CADASIL patients and 29 age- and sex-matched controls. The cortical mantle of patients and controls were extracted using Brainvisa by an experienced user and then evaluated during a dedicated reading session by a second reader after removing the white matter to stay blind to the clinical status. Thereafter, confirmed focal macroscopic cortical lesions were characterized using all available imaging data, including 7-T magnetic resonance imaging in some patients.

Results—

Three focal macroscopic cortical lesions were confirmed in 3 of 28 patients (11%) but none in controls. All lesions were observed in the close vicinity of severe signal changes in the underlying white matter.

Conclusions—

Focal macroscopic cortical lesions can be detected using specific magnetic resonance imaging approaches in CADASIL patients long before the end stage of the disorder. The underlying mechanisms and precise clinical consequences of these cortical changes still need to be determined.

Predictors and Clinical Impact of Incident Lacunes in Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy

Background and Purpose—

Previous studies in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy showed that accumulation of lacunes strongly relate to clinical severity. However, the potential predictors of incident lacunes and their clinical consequences over a short time frame have not been investigated. This study aimed to determine the predictors and clinical impact of such lesions in a large cohort of patients.

Methods—

Two hundred and six NOTCH3 mutation carriers (mean age, 49.5±10.6 years) were followed up over 3 years. Incident lacunes were identified using difference imaging from 3-dimensional T1 images. Clinical events and change in different clinical scores such as the Mattis Dementia Rating Scale, Modified Rankin Scale, Barthel index, and time to complete part A and part B of Trail Making Test were recorded. Associations were analyzed with multivariable logistic regression analysis and ANCOVA.

Results—

Over a mean period of 3.4±0.7 years, incident lacunes occurred in 51 of 206 patients. Both the number of lacunes ( P <0.0001) and systolic blood pressure at baseline ( P <0.01) were independent predictors of incident lacunes during follow-up. The results were still significant after excluding patients with systolic blood pressure >140 mm Hg. Incident lacunes were also associated with incident stroke and with change in time to complete Trail Making Test part B, initiation/perseveration subscale of the Mattis Dementia Rating Scale and Barthel Index over the study period.

Conclusions—

Systolic blood pressure and the number of prevalent lacunes are independent predictors of incident lacunes in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. These lesions mainly impact executive performances and functional independence over 3 years.

Prediction of 3-year clinical course in CADASIL

OBJECTIVE

To obtain simple models predicting disease evolution at 3 years for a given patient with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL).

METHODS

Based on data obtained in a prospective study of 236 patients, we built and validated models predicting, at the individual level, 3-year changes in Mini-Mental State Examination (MMSE), Mattis Dementia Rating Scale (MDRS), Trail Making Test version B (TMTB), and modified Rankin Scale (mRS). These models were based on different sets of predictors obtained at baseline, including either clinical data (epidemiologic data and cardiovascular risk factors) or clinical data and quantitative MRI markers (volume of lacunes [LL_V], volume of white matter hyperintensities, normalized brain volume [BPF], number of microbleeds). The Bayesian information criterion (BIC) and the coefficient of determination (R²) were used to determine models with the highest predictive ability and the lowest numbers of predictors.

RESULTS

We obtained validated models with a demonstrated ability to predict, for a given patient, 3-year changes in MMSE, MDRS, TMTB, and mRS (R² on independent samples: 0.22, 0.12, 0.09, and 0.17, respectively). In all cases, the best models according to R² and BIC values included only the baseline values of the outcome, of BPF, and of LL_V. Inclusion of other potential predictors always led to a loss of generalizability.

CONCLUSIONS

The prediction of 3-year changes in MMSE, MDRS, TMTB, and mRS for a given patient with CADASIL can be obtained using simple models relying only on the initial values of the considered score, BPF, and LL_V.

Reproducibility and variability of quantitative magnetic resonance imaging markers in cerebral small vessel disease

Brain imaging is essential for the diagnosis and characterization of cerebral small vessel disease. Several magnetic resonance imaging markers have therefore emerged, providing new information on the diagnosis, progression, and mechanisms of small vessel disease. Yet, the reproducibility of these small vessel disease markers has received little attention despite being widely used in cross-sectional and longitudinal studies. This review focuses on the main small vessel disease-related markers on magnetic resonance imaging including: white matter hyperintensities, lacunes, dilated perivascular spaces, microbleeds, and brain volume. The aim is to summarize, for each marker, what is currently known about: (1) its reproducibility in studies with a scan-rescan procedure either in single or multicenter settings; (2) the acquisition-related sources of variability; and, (3) the techniques used to minimize this variability. Based on the results, we discuss technical and other challenges that need to be overcome in order for these markers to be reliably used as outcome measures in future clinical trials. We also highlight the key points that need to be considered when designing multicenter magnetic resonance imaging studies of small vessel disease.

Reaction Time is a Marker of Early Cognitive and Behavioral Alterations in Pure Cerebral Small Vessel Disease

BACKGROUND

The assessment of early and subtle cognitive and behavioral effects of cerebral small vessel disease (SVD) requires specific and long-lasting evaluations performed by experienced neuropsychologists. Simpler tools would be helpful for daily clinical practice.

OBJECTIVE

To determine whether a simple reaction time task that lasts 5 minutes and can be performed without external supervision on any tablet or laptop can be used as a proxy of early cognitive and behavioral alterations in CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy), a monogenic form of pure SVD related to NOTCH3 mutations.

METHODS

Twenty-two genetically confirmed patients with CADASIL having preserved global cognitive abilities and without disability (MMSE >24 and modified Rankin's scale ≤1) were compared to 29 age-and-gender matched controls to determine group differences according to: 1) conventional neuropsychological and behavioral testing; 2) a computerized battery evaluating reaction time, processing speed, and executive functions. In a second step, correlations between reaction time and cognitive and behavioral alterations detected using both conventional and computerized testing were tested in patients.

RESULTS

Reaction time was significantly higher in patients than in controls (mean in patients: 283 ms - in controls: 254 ms, p = 0.03). In patients, reaction time was significantly associated with conventional and chronometric tests of executive functions, working memory, and apathy.

CONCLUSION

Reaction time obtained using a very simple task may serve as a proxy of early cognitive and behavioral alterations in SVD and could be easily used in daily clinical practice.

Alterations of the cerebral cortex in sporadic small vessel disease: A systematic review of in vivo MRI data

Cerebral small vessel diseases of the brain are a major determinant of cognitive impairment in the elderly. In small vessel diseases, the most easily identifiable lesions, both at post-mortem evaluation and magnetic resonance imaging, lie in subcortical areas. However, recent results obtained post-mortem, particularly in severe cases, have highlighted the burden of cortex lesions such as microinfarcts and diffuse neuronal loss. The recent development of image post-processing methods allows now assessing in vivo multiple aspects of the cerebral cortex. This systematic review aimed to analyze in vivo magnetic resonance imaging studies evaluating cortex alterations at different stages of small vessel diseases. Studies assessing the relationships between small vessel disease magnetic resonance imaging markers obtained at the subcortical level and cortex estimates were reviewed both in community-dwelling elderly and in patients with symptomatic small vessel diseases. Thereafter, studies analyzing cortex estimates in small vessel disease patients compared with healthy subjects were evaluated. The results support that important cortex alterations develop along the course of small vessel diseases independently of concomitant neurodegenerative processes. Easy detection and quantification of cortex changes in small vessel diseases as well as understanding their underlying mechanisms are challenging tasks for better understanding cognitive decline in small vessel diseases.

Are Developmental Trajectories of Cortical Folding Comparable Between Cross-sectional Datasets of Fetuses and Preterm Newborns?

Magnetic resonance imaging has proved to be suitable and efficient for in vivo investigation of the early process of brain gyrification in fetuses and preterm newborns but the question remains as to whether cortical-related measurements derived from both cases are comparable or not. Indeed, the developmental folding trajectories drawn up from both populations have not been compared so far, neither from cross-sectional nor from longitudinal datasets. The present study aimed to compare features of cortical folding between healthy fetuses and early imaged preterm newborns on a cross-sectional basis, over a developmental period critical for the folding process (21-36 weeks of gestational age [GA]). A particular attention was carried out to reduce the methodological biases between the 2 populations. To provide an accurate group comparison, several global parameters characterizing the cortical morphometry were derived. In both groups, those metrics provided good proxies for the dramatic brain growth and cortical folding over this developmental period. Except for the cortical volume and the rate of sulci appearance, they depicted different trajectories in both groups suggesting that the transition from into ex utero has a visible impact on cortical morphology that is at least dependent on the GA at birth in preterm newborns.

White Matter Edema at the Early Stage of Cerebral Autosomal-Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy

Background and Purpose—

Recently, in a mouse model of cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy, a monogenic cerebral small vessel disease, intramyelinic edema was detected in the white matter (WM) early during the course of the disease. We hypothesized that if this mechanism holds true in patients, it would translate in larger WM volume. We aimed to measure WM volume in patients with cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy in comparison with age- and sex-matched controls, along with the ratio of cortical surface area to the volume of brain hemispheres as an indirect measure that should be reduced in patients.

Methods—

Twenty patients at the early stage of the disease (Mini Mental State Examination >24 and modified Rankin scale ≤1) and 27 age- and sex-matched controls had high-quality 3-Tesla 3DT1 MRI acquisitions. Volumes of brain hemispheres and of WM were determined. The ratio of cortical surface area to the volume of brain hemispheres was evaluated as a proxy of underlying WM volume.

Results—

Patients had larger volumes of WM than controls (patients: 479.4±71.7; controls: 463.9±44.2; P =0.03). They presented a lower cortical surface area and cortical volume leading to a lower ratio of cortical surface area to the volume of brain hemispheres (patients: 15.7±0.7; controls: 16.1±0.5; P =0.004). Volume of WM tended to be associated with that of WM hyperintensities ( P =0.06).

Conclusions—

Patients with cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy have larger WM volume than age- and sex-matched controls, a finding compatible with the hypothesis of intramyelinic edema as observed recently in mice.

In vivo high-resolution 7 Tesla MRI shows early and diffuse cortical alterations in CADASIL

Background and Purpose

Recent data suggest that early symptoms may be related to cortex alterations in CADASIL (Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy), a monogenic model of cerebral small vessel disease (SVD). The aim of this study was to investigate cortical alterations using both high-resolution T2* acquisitions obtained with 7 Tesla MRI and structural T1 images with 3 Tesla MRI in CADASIL patients with no or only mild symptomatology (modified Rankin’s scale ≤1 and Mini Mental State Examination (MMSE) ≥24).

Methods

Complete reconstructions of the cortex using 7 Tesla T2* acquisitions with 0.7 mm isotropic resolution were obtained in 11 patients (52.1±13.2 years, 36% male) and 24 controls (54.8±11.0 years, 42% male). Seven Tesla T2* within the cortex and cortical thickness and morphology obtained from 3 Tesla images were compared between CADASIL and control subjects using general linear models.

Results

MMSE, brain volume, cortical thickness and global sulcal morphology did not differ between groups. By contrast, T2* measured by 7 Tesla MRI was significantly increased in frontal, parietal, occipital and cingulate cortices in patients after correction for multiple testing. These changes were not related to white matter lesions, lacunes or microhemorrhages in patients having no brain atrophy compared to controls.

Conclusions

Seven Tesla MRI, by contrast to state of the art post-processing of 3 Tesla acquisitions, shows diffuse T2* alterations within the cortical mantle in CADASIL whose origin remains to be determined.

A study of cortical morphology in children with fetal alcohol spectrum disorders

Prenatal alcohol exposure is responsible for a broad range of brain structural malformations, which can be studied using magnetic resonance imaging (MRI). Advanced MRI methods have emerged to characterize brain abnormalities, but the teratogenic effects of alcohol on cortical morphology have received little attention to date. Twenty-four 9-year-old children with fetal alcohol spectrum disorders (9 with fetal alcohol syndrome, 15 heavy exposed nonsyndromal children) and 16 age-matched controls were studied to assess the effect of alcohol consumption during pregnancy on cortical morphology. An automated method was applied to 3D T1-weighted images to assess cortical gyrification using global and regional sulcal indices and two region-based morphological measurements, mean sulcal depth and fold opening. Increasing levels of alcohol exposure were related to reduced cortical folding complexity, even among children with normal brain size, indicating a reduction of buried cortical surface. Fold opening was the strongest anatomical correlate of prenatal alcohol intake, indicating a widening of sulci in all regions that were examined. These data identify cortical morphology as a suitable marker for further investigation of brain damage associated with prenatal alcohol exposure.

Brain activity and perceived exertion during cycling exercise: an fMRI study

BACKGROUND/AIM

Currently, the equipment and techniques available to assess brain function during dynamic exercise are limited, which has restricted our knowledge of how the brain regulates exercise. This study assessed the brain areas activated during cycling by making use of a novel cycle ergometer, constructed to measure functional MRI (fMRI) brain images during dynamic exercise. Furthermore, we compared brain activation at different levels of ratings of perceived exertion (RPE) generated during the exercise.

METHODS

Seven healthy adults performed cycling exercise in a novel MRI compatible cycle ergometer while undergoing brain  fMRI. Participants completed a cycling block protocol comprising six trials of 2 min cycling with 16-s intervals between trials. Participants reported their RPE every minute through an audio link. The MRI cycling ergometer transferred the torque generated on the ergometer through a cardan system to a cycling ergometer positioned outside the MRI room. For data analysis, the effects of cycling as opposed to rest periods were examined after motion correction.

RESULTS

The multiparticipant analysis revealed in particular the activation of the cerebellar vermis and precentral and postcentral gyrus when periods of cycling versus rest were compared. Single participant analysis in four participants revealed that activation of the posterior cingulate gyrus and precuneus occurred in cycling blocks perceived as 'hard' compared with exercise blocks that were less demanding.

CONCLUSIONS

The present study offers a new approach to assess brain activation during dynamic cycling exercise, and suggests that specific brain areas could be involved in the sensations generating the rating of perceived exertion.

Functional magnetic resonance imaging study comparing rhythmic finger tapping in children and adults

This study compared brain activation during unpaced rhythmic finger tapping in 12-year-old children with that of adults. Subjects pressed a button at a pace initially indicated by a metronome (12 consecutive tones), and then continued for 16 seconds of unpaced tapping to provide an assessment of their ability to maintain a steady rhythm. These analyses focused on the superior vermis of the cerebellum, which is known to play a key role in timing. Twelve adults and 12 children performed this rhythmic finger tapping task in a 3 T scanner. Whole-brain analyses were performed in Brain Voyager, with a random-effects analysis of variance using a general linear model. A dedicated cerebellar atlas was used to localize cerebellar activations. As in adults, unpaced rhythmic finger tapping in children demonstrated activations in the primary motor cortex, premotor cortex, and cerebellum. However, overall activation was different, in that adults demonstrated much more deactivation in response to the task, particularly in the occipital and frontal cortices. The other main differences involved the additional recruitment of motor and premotor areas in children compared with adults, and increased activity in the vermal region of the cerebellum. These findings suggest that the timing component of the unpaced rhythmic finger tapping task is less efficient and automatic in children, who need to recruit the superior vermis more intensively to maintain the rhythm, although they performed somewhat more poorly than adults.

Signal decay due to susceptibility-induced intravoxel dephasing on multiple air-filled cylinders: MRI simulations and experiments

OBJECTIVE

Characterization of magnetic susceptibility artefacts with assessment of the gradient-echo signal decay function of echo time, pixel size, and object geometry in the case of air-filled cylinders embedded in water.

MATERIALS AND METHODS

Experiments were performed with a 0.2 T magnet on a network of small interacting air-filled cylinders along with Magnetic resonance imaging (MRI) simulations integrating intravoxel dephasing. Signal decay over echo time was assessed at different pixel sizes on real and simulated images. The effects of radius, distance between cylinders and main magnetic field were studied using simulation.

RESULTS

Signal loss was greater as echo time or pixel size increased. Voxel signal decay was not exponential but was weighted by sinus cardinalis functions integrating echo time, pixel size and field inhomogeneities which depended on main magnetic field strength and geometric configuration of the object. Simulation was able to model signal decay, even for a complex object constituted of several cylinders. The specific experimental signal modulation we observed was thus reproduced and explained by simulation.

CONCLUSION

The quantitative signal decay approach at 0.2 T can be used in characterization studies in the case of locally regular air/water interfaces as the signal depends on object size relative to pixel size and is relevant to the geometric configuration. Moreover, the good concordance between simulation and experiments should lead to further studies of magnetic susceptibility effects with other objects such as networks of spheres. MRI simulation is thus a potential tool for molecular and porous media imaging.