Resting-state functional connectivity correlates of anxiety co-morbidity in major depressive disorder

Major depressive disorder (MDD) is frequently co-morbid with anxiety disorders. The co-morbid state has poorer functional outcomes and greater resistance to first line treatments, highlighting the need for novel treatment targets. This systematic review examined differences in resting-state brain connectivity associated with anxiety comorbidity in young- and middle-aged adults with MDD, with the aim of identifying novel targets for neuromodulation treatments, as these treatments are thought to work partly by altering dysfunctional connectivity pathways. Twenty-one studies met inclusion criteria, including a total of 1292 people with MDD. Only two studies included people with MDD and formally diagnosed co-morbid anxiety disorders; the remainder included people with MDD with dimensional anxiety measurement. The quality of most studies was judged as fair. Results were heterogeneous, partly due to a focus on a small set of connectivity relationships within individual studies. There was evidence for dysconnectivity between the amygdala and other brain networks in co-morbid anxiety, and an indication that abnormalities of default mode network connectivity may play an underappreciated role in this condition.

Accumulation of Brain Hypointense Foci on Susceptibility-Weighted Imaging in Childhood Ataxia Telangiectasia

BACKGROUND AND PURPOSE

SWI hypointense cerebral lesions have been reported in adults with the inherited cerebellar neurodegenerative disorder ataxia telangiectasia. This study aims to establish the prevalence, age-dependency, and spatial distribution of these lesions in children and young people with ataxia telangiectasia.

MATERIALS AND METHODS

Participants with classic ataxia telangiectasia and matched controls underwent SWI acquisition at 3T at 1 or 2 time points. SWI hypointense lesions were manually labeled according to the Microbleed Anatomical Rating Scale. Differences in prevalence of lesion number between groups with ataxia telangiectasia and without ataxia telangiectasia were tested with the Fisher exact test, and differences in age between participants with ataxia telangiectasia with and without lesions were tested using independent samples Mann-Whitney U test. The relationship between age and lesion number was modeled as an exponential function.

RESULTS

Analyzable SWI datasets from 17 participants with ataxia telangiectasia (with median age at first scan of 12.4 years; range, 4.6-20.2 years; 8 [47%] were female) and 22 matched healthy controls showed prevalence of SWI hypointense lesions in 41% of participants with ataxia telangiectasia and 0% in controls (P = .001, Fisher exact test). Lesions were exclusively supratentorial and predominantly lobar. Participants with ataxia telangiectasia with SWI hypointense lesions were older than those without (median age 5.2 years versus 9.3 years, U = 10.5, P = .014). An exponential curve described the relationship between age and lesion number (R ² = 0.67).

CONCLUSIONS

SWI hypointense lesions are common in children and young people with ataxia telangiectasia, accumulating from 12 years of age onward. In contrast to cerebellar-dominant neurodegeneration in ataxia telangiectasia, SWI hypointense lesions were exclusively supratentorial. Further investigation is needed to establish the clinical relevance of these imaging-detected lesions.

Are Linear Measurements of the Nucleus Basalis of Meynert Suitable as a Diagnostic Biomarker in Mild Cognitive Impairment and Alzheimer Disease?

BACKGROUND AND PURPOSE

Cell loss within the nucleus basalis of Meynert is an early event in Alzheimer disease. The thickness of the nucleus basalis of Meynert (NBM) can be measured on structural MR imaging. We investigated NBM thickness in relation to cognitive state and biochemical markers.

MATERIALS AND METHODS

Mean bilateral nucleus basalis of Meynert thickness was measured on coronal T1-weighted MR imaging scans from the Alzheimer's Disease Neuroimaging Initiative dataset. Three hundred and fifteen scans (80 controls, 79 cases of early mild cognitive impairment, 77 cases of late mild cognitive impairment and 79 cases of Alzheimer disease) were assessed. Alzheimer's Disease Assessment Scale-Cognitive scores, CSF tau, and amyloid quantification were extracted. Group differences in NBM thickness, their correlates and measurement reliability were assessed.

RESULTS

Mean NBM thickness ± SD progressively declined from 2.9 ± 0.3, 2.5 ± 0.3, and 2.3 ± 0.3 to 1.8 ± 0.4 mm in healthy controls, patients with early mild cognitive impairment, late mild cognitive impairment and Alzheimer disease respectively (P < .001). NBM thickness was negatively correlated with Alzheimer's Disease Assessment Scale-Cognitive scores (r = -0.53, P < .001) and weakly positively correlated with CSF amyloid (r = 0.250, P < .001) respectively. No association with CSF tau was found. NBM thickness showed excellent diagnostic accuracy to differentiate Alzheimer disease (area under the curve, 0.986) and late mild cognitive impairment from controls (area under the curve, 0.936) with excellent sensitivity, but lower specificity 66.7%. Intra- and interrater reliability for measurements was 0.66 and 0.47 (P < .001).

CONCLUSIONS

There is progressive NBM thinning across the aging-dementia spectrum, which correlates with cognitive decline and CSF markers of amyloid-β pathology. We show high diagnostic accuracy but limited reliability, representing an area for future improvement. NBM thickness is a promising, readily available MR imaging biomarker of Alzheimer disease warranting diagnostic-accuracy testing in clinical practice.

Coordinate based meta-analysis of networks in neuroimaging studies

Meta-analysis of summary results from published neuroimaging studies independently testing a common hypothesis is performed using coordinate based meta-analysis (CBMA), which tests for consistent activation (in the case of functional MRI studies) of the same anatomical regions. Using just the reported coordinates it is also possible to meta-analyse coactivated regions to reveal a network-like structure of coordinate clusters (network nodes) distributed at the coactivated locations and a measure of the coactivation strength (network edges), which is determined by the presence/absence of reported activation. Here a new coordinate-based method to estimate a network of coactivations is detailed, which utilises the Z score accompanying each reported. Coordinate based meta-analysis of networks (CBMAN) assumes that if the activation pattern reported by independent studies is truly consistent, then the relative magnitude of these Z scores might also be consistent. It is hypothesised that this is detectable as Z score covariance between coactivated regions provided the within study variances are small. Advantages of using the Z scores instead of coordinates to measure coactivation strength are that censoring by the significance thresholds can be considered, and that using a continuous measure rather than a dichotomous one can increase statistical power. CBMAN uses maximum likelihood estimation to fit multivariate normal distributions to the standardised Z scores, and the covariances are considered as edges of a network of coactivated clusters (nodes). Here it is validated by numerical simulation and demonstrated on real data used previously to demonstrate CBMA. Software to perform CBMAN is freely available.

Large-scale network dysfunction in vascular cognitive disorder supports connectional diaschisis in advanced arteriosclerosis

BACKGROUND AND PURPOSE

The interrelation of cognitive performance, cerebrovascular damage and brain functional connectivity (FC) in advanced arteriosclerosis remains unclear. Our aim was to investigate the associations between FC, white matter damage and cognitive impairment in carotid artery disease.

METHODS

Seventy-one participants with a recent cerebrovascular event and with written informed consent underwent resting-state functional magnetic resonance imaging and the Addenbrooke's Cognitive Examination - Revised (ACE-R). Network and inter-hemispheric FC metrics were compared between cognitively normal and impaired subjects, and interrelated with cognition. In order to explore the nature of FC changes, their associations with microstructural damage of related white matter tracts and cognitive performance were investigated, followed by mediation analysis.

RESULTS

Participants with global cognitive impairment showed reduced FC compared to the cognitively intact subjects within the central executive network (CEN), and between hemispheres. Patients with executive dysfunction had decreased CEN FC whilst patients with memory loss demonstrated low FC in both the CEN and the default mode network (DMN). Global performance correlated with connectivity metrics of the CEN hub with DMN nodes, and between hemispheres. Cingulum mean diffusivity (MD) was negatively correlated with ACE-R and CEN-DMN FC. The cingulum MD-cognition association was partially mediated by CEN-DMN FC.

CONCLUSIONS

Long-range functional disconnection of the CEN with DMN nodes is the main feature of cognitive impairment in elderly subjects with symptomatic carotid artery disease. Our findings provide further support for the connectional diaschisis concept of vascular cognitive disorder, and highlight a mediation role of functional disconnection to explain associations between microstructural white matter tract damage and cognitive impairment.

Baseline effective connectivity predicts response to repetitive transcranial magnetic stimulation in patients with treatment-resistant depression

Repetitive transcranial magnetic stimulation (rTMS) has become a popular treatment option for treatment-resistant depression (TRD). However, suboptimal response rates highlight the need for improved efficacy through optimisation of treatment protocol and patient selection. We investigate whether the limbic salience network and its connectivity with prefrontal stimulation sites predict immediate and longer-term responsiveness to rTMS. Twenty-seven patients with TRD were randomly allocated to receive 16 sessions of either conventional rTMS or intermittent theta-burst (iTBS) over 4 weeks; delivered using connectivity profiling and neuronavigation to target person-specific dorsolateral prefrontal cortex (DLPFC). At baseline and 3-month follow-up, patients underwent clinical assessment and scanning session, and 1-month clinical follow-up. Resting-state fMRI data were entered into seed-based functional and effective connectivity analyses between right anterior insula (rAI) and DLPFC target, and independent components analysis to extract resting-state networks. Cerebral blood flow (CBF) was also assessed in the rAI. All brain measures were compared between baseline and follow-up, and related to treatment response at 1- and 3-months. Baseline fronto-insular effective connectivity and salience network connectivity were significantly positively correlated, while baseline rAI CBF was negatively correlated, with early (1-month) response to rTMS treatment but not sustained response (3-months), suggesting persistence of therapeutic response is not associated with baseline features. Connectivity or CBF measures did not change between the two time points. We demonstrate that fronto-insular and salience-network interactions can predict early response to rTMS in TRD, suggesting that these network nodes may be key regions toward developing rTMS response biomarkers.

Measuring Cerebral and Cerebellar Glutathione in Children Using 1H MEGA-PRESS MRS

BACKGROUND AND PURPOSE

Glutathione is an important antioxidant in the human brain and therefore of interest in neurodegenerative disorders. The purpose of this study was to investigate the feasibility of measuring glutathione in healthy nonsedated children by using the ¹H Mescher-Garwood point-resolved spectroscopy (MEGA-PRESS) sequence at 3T and to compare glutathione levels between the medial parietal gray matter and the cerebellum.

MATERIALS AND METHODS

Glutathione was measured using MEGA-PRESS MRS (TR = 1.8 seconds, TE = 131 ms) in the parietal gray matter (35 × 25 × 20 mm³) of 6 healthy children (10.0 ± 2.4 years of age; range, 7-14 years; 3 males) and in the cerebellum of 11 healthy children (12.0 ± 2.7 years of age; range, 7-16 years; 6 males). A postprocessing pipeline was developed to account for frequency and phase variations in the edited ON and nonedited OFF spectra. Metabolites were quantified with LCModel and reported both as ratios and water-scaled values. Glutathione was quantified in the ON-OFF spectra, whereas total NAA, total Cho, total Cr, mIns, Glx, and taurine were quantified in the OFF spectra.

RESULTS

We found significantly higher glutathione, total Cho, total Cr, mIns, and taurine in the cerebellum (P < .01). Glx and total NAA were significantly higher in the parietal gray matter (P < .01). There was no significant difference in glutathione/total Cr (P = .93) between parietal gray matter and cerebellum.

CONCLUSIONS

We demonstrated that glutathione measurement in nonsedated children is feasible. We found significantly higher glutathione in the cerebellum compared with the parietal gray matter. Metabolite differences between the parietal gray matter and cerebellum agree with published MRS data in adults.

Manganese-enhanced magnetic resonance imaging depicts brain activity in models of acute and chronic pain: A new window to study experimental spontaneous pain?

Application of functional imaging techniques to animal models is vital to understand pain mechanisms, but is often confounded by the need to limit movement artefacts with anaesthesia, and a focus on evoked responses rather than clinically relevant spontaneous pain and related hyperalgesia. The aim of the present study was to investigate the potential of manganese-enhanced magnetic resonance imaging (MEMRI) to measure neural responses during on-going pain that underpins hyperalgesia in pre-clinical models of nociception. As a proof of concept that MEMRI is sensitive to the neural activity of spontaneous, intermittent behaviour, we studied a separate positive control group undergoing a voluntary running wheel experiment. In the pain models, pain behaviour (weight bearing asymmetry and hindpaw withdrawal thresholds (PWTs)) was measured at baseline and following either intra-articular injection of nerve growth factor (NGF, 10µg/50µl; acute pain model, n=4 rats per group), or the chondrocyte toxin monosodium iodoacetate (MIA, 1mg/50µl; chronic model, n=8 rats per group), or control injection. Separate groups of rats underwent a voluntary wheel running protocol (n=8 rats per group). Rats were administered with paramagnetic ion Mn²⁺ as soluble MnCl₂ over seven days (subcutaneous osmotic pump) to allow cumulative activity-dependent neural accumulation in the models of pain, or over a period of running. T1-weighted MR imaging at 7T was performed under isoflurane anaesthesia using a receive-only rat head coil in combination with a 72mm volume coil for excitation. The pain models resulted in weight bearing asymmetry (NGF: 20.0 ± 5.2%, MIA: 15 ± 3%), and a reduction in PWT in the MIA model (8.3 ± 1.5g) on the final day of assessment before undergoing MR imaging. Voxel-wise and region-based analysis of MEMRI data did not identify group differences in T1 signal. However, MnCl₂ accumulation in the VTA, right Ce amygdala, and left cingulate was negatively correlated with pain responses (greater differences in weight bearing), similarly MnCl₂ accumulation was reduced in the VTA in line with hyperalgesia (lower PWTs), which suggests reduced regional activation as a result of the intensity and duration of pain experienced during the 7 days of MnCl₂ exposure. Motor cortex T1-weighted signal increase was associated with the distance ran in the wheel running study, while no between group difference was seen. Our data suggest that on-going pain related signal changes identified using MEMRI offers a new window to study the neural underpinnings of spontaneous pain in rats.

Mesiotemporal atrophy and hippocampal diffusivity distinguish amnestic from non-amnestic vascular cognitive impairment

Background and purpose

The role of clinical factors, cerebral infarcts and hippocampal damage in vascular cognitive impairment (VCI) subtypes remains unclear.

Methods

Non‐demented patients with carotid stenosis and recent transient ischemic attack/stroke had cognitive assessment and brain magnetic resonance imaging (MRI). Amnestic VCI was defined as memory impairment; non‐amnestic VCI was any other subdomain impairment. Associations of MRI metrics [log‐transformed total ischemic lesion load (log TILL), mesiotemporal atrophy (MTA) score, hippocampal mean diffusivity (hipMD)] with cognitive performance were assessed.

Results

A hundred and eight patients, 47 with amnestic VCI and 21 with non‐amnestic VCI, were assessed. A higher MTA (odds ratio 12.89, P = 0.001) and left hipMD (odds ratio 4.43, P = 0.003) contributed to amnestic VCI versus normal. Age‐adjusted fluency correlated with log TILL (P = 0.002). Age‐adjusted memory was associated with left hipMD (P = 0.001), MTA (P < 0.001) but not log TILL (P = 0.14). Left hipMD, MTA and smoking showed classification potential between amnestic VCI versus normal (area 0.859, P < 0.001).

Conclusions

Neuroimaging assists stratification in amnestic VCI characterized by hippocampal changes and in non‐amnestic VCI by higher ischemic burden. MTA and hippocampal diffusivity show diagnostic biomarker potential.

Coordinate based random effect size meta-analysis of neuroimaging studies

Low power in neuroimaging studies can make them difficult to interpret, and Coordinate based meta-analysis (CBMA) may go some way to mitigating this issue. CBMA has been used in many analyses to detect where published functional MRI or voxel-based morphometry studies testing similar hypotheses report significant summary results (coordinates) consistently. Only the reported coordinates and possibly t statistics are analysed, and statistical significance of clusters is determined by coordinate density. Here a method of performing coordinate based random effect size meta-analysis and meta-regression is introduced. The algorithm (ClusterZ) analyses both coordinates and reported t statistic or Z score, standardised by the number of subjects. Statistical significance is determined not by coordinate density, but by a random effects meta-analyses of reported effects performed cluster-wise using standard statistical methods and taking account of censoring inherent in the published summary results. Type 1 error control is achieved using the false cluster discovery rate (FCDR), which is based on the false discovery rate. This controls both the family wise error rate under the null hypothesis that coordinates are randomly drawn from a standard stereotaxic space, and the proportion of significant clusters that are expected under the null. Such control is necessary to avoid propagating and even amplifying the very issues motivating the meta-analysis in the first place. ClusterZ is demonstrated on both numerically simulated data and on real data from reports of grey matter loss in multiple sclerosis (MS) and syndromes suggestive of MS, and of painful stimulus in healthy controls. The software implementation is available to download and use freely.

Motor associations of iron accumulation in deep grey matter nuclei in Parkinson's disease: a cross-sectional study of iron-related magnetic resonance imaging susceptibility

BACKGROUND AND PURPOSE

To determine whether iron deposition in deep brain nuclei assessed using high-pass filtered phase imaging plays a role in motor disease severity in Parkinson's disease (PD).

METHODS

Seventy patients with mild to moderate PD and 20 age- and gender-matched healthy volunteers (HVs) underwent susceptibility-weighted imaging on a 3 T magnetic resonance imaging scanner. Phase shifts (radians) in deep brain nuclei were derived from high-pass filtered phase images and compared between groups. Analysis of clinical laterality and correlations with motor severity (Unified Parkinson's Disease Rating Scale, Part III, UPDRS-III) were performed. Phase shifts (in radians) were compared between HVs and three PD subgroups divided according to UPDRS-III scores using analysis of covariance, adjusting for age and regional area.

RESULTS

Parkinson's disease patients had significantly (P < 0.001) higher radians than HVs bilaterally in the putamen, globus pallidus and substantia nigra (SN). The SN contralateral to the most affected side showed higher radians (P < 0.001) compared to the less affected side. SN radians positively correlated with UPDRS-III and bradykinesia-rigidity subscores, but not with tremor subscores. ancova followed by post hoc Bonferroni-adjusted pairwise comparisons revealed that SN radians were significantly greater in the PD subgroup with higher UPDRS-III scores compared to both lowest UPDRS-III PD and HV groups (P < 0.001).

CONCLUSIONS

Increased nigral iron accumulation in PD appears to be stratified according to disease motor severity and correlates with symptoms related to dopaminergic neurodegeneration. This semi-quantitative in vivo iron assessment could prove useful for objectively monitoring PD progression, especially in clinical trials concerning iron chelation therapies.

Impaired Cerebrovascular Reactivity Predicts Recurrent Symptoms in Patients with Carotid Artery Occlusion: A Hypercapnia BOLD fMRI Study

BACKGROUND AND PURPOSE

A key factor in predicting recurrent ischemic episodes in patients with carotid artery occlusion is the presence of hemodynamic impairment. There is, however, no consensus on how to best assess this risk in terms of imaging modalities or thresholds used. Here we investigated whether a predefined threshold of hemispheric asymmetry in hypercapnia fMRI predicts recurrent symptoms in patients with carotid artery occlusion.

MATERIALS AND METHODS

We studied 23 patients (2 women) with a mean age of 67.5 ± 9 years. Patients were assessed for recurrent ischemic events until lost to follow-up, study end, death, or recurrent ischemic event. Hypercapnia fMRI was used to assess the cerebrovascular reserve and quantify the percentage signal change in GM in the MCA territory and the hemispheric asymmetry index. Kaplan-Meier survival analysis and log-rank tests were performed to assess differences between patients with normal or abnormal hemispheric indices.

RESULTS

The median follow-up was 20 months. During this period, 8 patients experienced recurrent events, and 15 did not. The percentage signal change in GM in the MCA territory was significantly decreased in those patients with recurrent events compared with those without (2.39 ± 0.22 versus 2.70 ± 0.42, P = .032). The normal hemispheric index predicted event-free survival during follow-up (median, 20 months) for both the combined outcome (recurrent events and/or death, log-rank, P = .034) and recurrent retinal or ipsilateral ischemic events only (log-rank, P = .012).

CONCLUSIONS

The hemispheric asymmetry index derived from hypercapnia fMRI showed hemodynamic impairment in more than half of the studied patients with carotid occlusion, and those patients showed a higher risk of recurrent ischemic symptoms.

Magnetic resonance diffusion metrics indexing high focal cellularity and sharp transition at the tumour boundary predict poor outcome in glioblastoma multiforme

AIM

To investigate the prognostic power of intra-tumoural and gradient magnetic resonance imaging (MRI) diffusion metrics in patients with glioblastoma multiforme (GBM).

MATERIALS AND METHODS

Forty-six consecutive patients with histologically confirmed GBM who had undergone preoperative diffusion tensor imaging at 3 T were included. Mean diffusivity (MD) and MD gradient maps were computed. Regions of interest were analysed to determine the minimum MD within the enhancing tumour (minMD). MD gradients were calculated along the enhancing tumour boundary and subjected to histogram analysis. Overall survival (OS) and time to progression (TTP) were derived and survival analysis was undertaken.

RESULTS

There were 31 deaths and 37 patients progressed during the study period. Multivariate survival analysis, controlling for treatment and gender, showed that minMD values<6.1×10(-4) mm(2)/s predicted shorter OS (hazard ratio [HR]=2.82, 1.25-6.34; p=0.012) and TTP (HR=5.43, 1.96-15.05; p=0.001). Higher MD gradient values of the tumour boundary predicted shorter survival: MD gradient values >4.7×10(-5) mm(2)/s (10(th) centile) had a significantly shorter OS with a HR of 0.43 (0.19-0.96; p=0.04). Similarly, a value above 1.4×10(-4) mm(2)/s (75(th) centile) was a significant predictor for shorter OS (HR=0.39, 0.17-0.89; p=0.03).

CONCLUSIONS

Lower minMD and higher MD gradient values for the 10(th) and 75(th) percentile of the tumour boundary demonstrated prognostic value in preoperative GBM. This suggests that MRI diffusion metrics indicative of higher focal cellularity and steeper transition from high cellular tumour edge to low cellular oedema define more aggressive glioblastoma subtypes with a poorer prognosis.

MR imaging-detected carotid plaque hemorrhage is stable for 2 years and a marker for stenosis progression

BACKGROUND AND PURPOSE

MR imaging-detected carotid plaque hemorrhage is associated with an increased risk of recurrent ischemic cerebrovascular events and could be an indicator of disease progression; however, there are limited data regarding the dynamics of the MR imaging-detected carotid plaque hemorrhage signal. We assessed the temporal change of this signal and its impact on carotid disease progression.

MATERIALS AND METHODS

Thirty-seven symptomatic patients with 54 carotid stenoses of >30% on sonography underwent serial MR imaging during 24 months. A signal-intensity ratio of >1.5 between the carotid plaque and adjacent muscle was defined as plaque hemorrhage, and a change in signal-intensity ratio of >0.31 between time points was considered significant. Sixteen patients underwent ≥2 carotid sonography scans to determine the peak systolic velocities and degree of stenosis with time.

RESULTS

Of the 54 carotids, 28 had the presence of hyperintense signal on an MR imaging sequence (PH+) and 26 had the absence of hyperintense signal on an MR imaging sequence (PH-) at baseline. The signal-intensity ratio was stable in 33/54 carotid plaques, but 39% showed a change. Plaque hemorrhage classification did not change in 87% of carotid plaques, but 4 became PH+, and 3, PH-. As a group, PH+ carotids did not change significantly in signal-intensity ratio (P = .585), whereas PH- showed an increased signal-intensity ratio at 24.5 months (P = .02). In PH+ plaques, peak systolic velocities significantly increased by 22 ± 39.8 cm/s from baseline to last follow-up sonography (Z = 2.427, P = .013).

CONCLUSIONS

During 2 years, MR imaging-detected carotid plaque hemorrhage status remained stable in most (87%) cases with 4 (7%) incident plaque hemorrhages. PH+ plaques were associated with increased flow velocity during the follow-up period.

Metrics and textural features of MRI diffusion to improve classification of pediatric posterior fossa tumors

BACKGROUND AND PURPOSE

Qualitative radiologic MR imaging review affords limited differentiation among types of pediatric posterior fossa brain tumors and cannot detect histologic or molecular subtypes, which could help to stratify treatment. This study aimed to improve current posterior fossa discrimination of histologic tumor type by using support vector machine classifiers on quantitative MR imaging features.

MATERIALS AND METHODS

This retrospective study included preoperative MRI in 40 children with posterior fossa tumors (17 medulloblastomas, 16 pilocytic astrocytomas, and 7 ependymomas). Shape, histogram, and textural features were computed from contrast-enhanced T2WI and T1WI and diffusivity (ADC) maps. Combinations of features were used to train tumor-type-specific classifiers for medulloblastoma, pilocytic astrocytoma, and ependymoma types in separation and as a joint posterior fossa classifier. A tumor-subtype classifier was also produced for classic medulloblastoma. The performance of different classifiers was assessed and compared by using randomly selected subsets of training and test data.

RESULTS

ADC histogram features (25th and 75th percentiles and skewness) yielded the best classification of tumor type (on average >95.8% of medulloblastomas, >96.9% of pilocytic astrocytomas, and >94.3% of ependymomas by using 8 training samples). The resulting joint posterior fossa classifier correctly assigned >91.4% of the posterior fossa tumors. For subtype classification, 89.4% of classic medulloblastomas were correctly classified on the basis of ADC texture features extracted from the Gray-Level Co-Occurence Matrix.

CONCLUSIONS

Support vector machine-based classifiers using ADC histogram features yielded very good discrimination among pediatric posterior fossa tumor types, and ADC textural features show promise for further subtype discrimination. These findings suggest an added diagnostic value of quantitative feature analysis of diffusion MR imaging in pediatric neuro-oncology.

Precision of cerebrovascular reactivity assessment with use of different quantification methods for hypercapnia functional MR imaging

BACKGROUND AND PURPOSE

Tools for noninvasive mapping of hemodynamic function including cerebrovascular reactivity are emerging and may become clinically useful to predict tissue at hemodynamic risk. One such technique assesses blood oxygen level-dependent (BOLD) MR imaging contrast in response to hypercapnia, but the reliability of its quantification is uncertain. The aim of this study was to prospectively investigate the intersubject and interhemispheric variability and short-term reproducibility of hypercapnia functional MR imaging (fMRI) in healthy volunteers and to assess the effects of different methods of quantification and normalization.

MATERIALS AND METHODS

Sixteen healthy volunteers, (7 women and 9 men) underwent hypercapnia fMRI with a clinical 1.5T scanner; 8 underwent scanning twice. We determined BOLD amplitude changes using a visually defined block design or automated regression to end-tidal (ET) carbon dioxide (CO2). Absolute percent signal intensity changes (PSC) were extracted for whole-brain, gray matter, and middle cerebral artery territory, and also normalized to ETCO2 change. Intersubject and intrasubject (between hemispheres and sessions) coefficients of variation (COV) were derived. We assessed the effects of different quantification methods on reproducibility indices using the t test and U tests.

RESULTS

The mean change in ETCO2 was 7.8 +/- 3.3 mm Hg. Averaged BOLD increases varied from 2.54% to 2.92%. Short-term reproducibility was good for absolute PSC (4.8% to 10%) but poor for normalized PSC (range, 24% to 27% COV). Intersubject reproducibility varied between 11% and 23% for absolute PSC and, again, was poorer for normalized data (32% to 39%). Interhemispheric reproducibility of absolute PSC was excellent ranging between 1.24 and 2.16% COV.

CONCLUSIONS

In conclusion, quantification of cerebrovascular reactivity with use of hypercapnia fMRI was found to have good between-session and very good interhemispheric reproducibility. The technique holds promise as a diagnostic tool, especially for sensitive detection of unilateral disease.

Effects of social isolation rearing on the limbic brain: a combined behavioral and magnetic resonance imaging volumetry study in rats

Rearing rats in social isolation from weaning induces robust behavioral and neurobiological alterations resembling some of the core symptoms of schizophrenia, such as reduction in prepulse inhibition of acoustic startle (PPI) and locomotor hyperactivity in a novel arena. The aim of this study was to investigate whether social isolation rearing induces volumetric remodeling of the limbic system, and to probe for anatomical structure-behavioral interrelations. Isolation- (n=8) and group-reared (n=8) rats were examined by magnetic resonance (MR) volumetry using high-resolution T2-weighted imaging at 7 T. Volumes of medial prefrontal cortex (mPFC), anterior cingulate cortex (ACC), retrosplenial cortex (RSC) and hippocampal formation were compared between groups and with behavioral measures, i.e. PPI and locomotor activity in a novel arena. Isolation rearing induced locomotor hyperactivity and impaired PPI compared with group-housed rats. The right mPFC was significantly reduced (5.4%) in isolation-reared compared with group-reared rats, with a similar trend on the left side (5.2%). mPFC volumes changes were unrelated to behavioral abnormalities. No significant volume changes were observed in ACC, RSC or hippocampal formation. Hippocampal volumes were associated with the magnitude of PPI response in control but not in isolation-reared rats. Rearing rats in social isolation induced remodeling of the limbic brain with selective prefrontal cortex volume loss. In addition, a dissociation of the interrelation between hippocampal volume and PPI was noted in the isolation-reared rats. Taken together, limbic morphometry is sensitive to the effects of social isolation rearing but did not reveal direct brain-behavior interrelations, calling for more detailed circuitry analysis.

Disconnection as a mechanism for cognitive dysfunction in multiple sclerosis

Disconnection of cognitively important processing regions by injury to the interconnecting white matter provides a potential mechanism for cognitive dysfunction in multiple sclerosis. The contribution of tract-specific white matter injury to dysfunction in different cognitive domains in patients with multiple sclerosis has not previously been studied. We apply tract-based spatial statistics (TBSS) to diffusion tensor imaging (DTI) in a cohort of multiple sclerosis patients to identify loci where reduced white matter tract fractional anisotropy (FA) predicts impaired performance in cognitive testing. Thirty-seven multiple sclerosis patients in remission (median age 43.5 years; Expanded Disability Status Scale range 1.5-6.5; 35 relapsing remitting, two secondary-progressive) underwent 3 T MRI including high-resolution DTI. Multiple sclerosis patients underwent formal testing of performance in multiple cognitive domains. Normalized cognitive scores were used for voxel-wise statistical analysis using TBSS, while treating age as a covariate of no interest. Permutation-based inference on cluster size (t > 2, P <0.05 corrected) was used to correct for multiple comparisons. Statistical mapping revealed differential patterns of FA reduction for tests of sustained attention, working memory and processing speed, visual working memory and verbal learning and recall. FA was not associated with frontal lobe function or visuospatial perception. Cognitively relevant tract localizations only partially overlapped with areas of high FLAIR lesion probability, confirming the contribution of normal-appearing white matter abnormality to cognitive dysfunction. Of note, tract localizations showing significant associations with cognitive impairment were found to interconnect cortical regions thought to be involved in processing in these cognitive domains, or involve possible compensatory processing pathways. This suggests that TBSS reveals functionally relevant tract injury underlying cognitive dysfunction in patients with multiple sclerosis.

Diffusion-weighted magnetic resonance imaging of treatment-associated changes in recurrent and residual medulloblastoma: preliminary observations in three children

PURPOSE

To emphasize a possible role of magnetic resonance (MR) diffusion-weighted imaging (DWI) for lesion conspicuity and detection of treatment effects in children with medulloblastoma.

MATERIAL AND METHODS

Three children with medulloblastoma (two residual and one recurrent) were examined repetitively by MR diffusion-weighted imaging. Regional assessment of the apparent diffusion coefficient (ADC) was done for tumorous lesions and periventricular white matter appearing normal on standard MR images.

RESULTS

All lesions were clearly visible on DWI. In the case of recurrent tumor, on one scan, DWI showed lesions that were not seen on contrast-enhanced MRI. Increase (41%) of ADC was seen in one lesion, which subsequently responded completely to treatment over 27 months' follow-up. Intermediate increases (23-26%) of ADC were found with partial therapy response in three lesions. In contrast, a decrease (-11%) of ADC in two lesions was seen with tumor progression.

CONCLUSION

These observations may suggest a role for DWI in early detection of metastatic disease and treatment monitoring of medulloblastoma, warranting a formal study.

Deep gray matter and fatigue in MS: a T1 relaxation time study

Fatigue in multiple sclerosis (MS) occurs commonly, sometimes as the earliest symptom. Some MS patients consider fatigue to be their most troublesome complaint, and it has been shown to be an independent predictor of impaired quality of life. Several reports have demonstrated that subcortical gray matter pathology is related to fatigue. We hypothesized that MRI detectable changes in the deep gray matter of MS patients may correlate with fatigue severity. Our objective was: to assess the relationship between fatigue severity and detectable changes on magnetic resonance imaging (MRI), quantified using the mean T1 relaxation time (T1), in deep gray matter structures in relapsing remitting multiple sclerosis (RRMS). Using region of interest analysis, T1 values were measured for the thalamus, putamen and caudate nucleus in 52 RRMS patients and 19 healthy volunteers. Fatigue was assessed using the Fatigue Severity Scale.

RESULTS

The median T1 in the thalamus and the putamen were significantly higher in the patient cohort than in the healthy controls; the median T1 in the caudate was also higher in the MS patients but did not reach statistical significance. There was a significant correlation between fatigue severity and the T1 of the thalamus (rho = 0.418; p = 0.014). Furthermore, the median T1 in the thalamus was significantly higher in patients with fatigue compared with those without (p = 0.018). Our results provide further evidence for the role of subcortical gray matter structures in the pathogenesis of multiple sclerosis (MS)-related fatigue. This study also demonstrates that T1 relaxation time measurement is a suitable technique for detecting abnormalities of the deep gray matter in RRMS and presents further support of gray matter involvement in MS.

Brain activation and hypothalamic functional connectivity during human non-rapid eye movement sleep: an EEG/fMRI study

Regional differences in sleep EEG dynamics indicate that sleep-related brain activity involves local brain processes with sleep stage specific activity patterns of neuronal populations. Macroscopically, it is not fully understood which cerebral brain regions are involved in the successive discontinuation of wakefulness. We simultaneously used EEG and functional MRI on 9 subjects (6 female: mean = 24.1 years, 3 male: mean = 26.0 years) and analyzed local blood oxygenation level dependent signal changes linked to the transition from wakefulness to different non-rapid eye movement (NREM) sleep stages (according to Rechtschaffen and Kales) of the first sleep cycles after 36 h of total sleep deprivation. Several brain regions throughout the cortex, the limbic lobe, the thalamus, the caudate nucleus, as well as midbrain structures, such as the mammillary body/hypothalamus, showed reduced activity during NREM sleep across all sleep stages. Additionally, we found deactivation patterns specific to NREM sleep stages compared with wakefulness suggesting that a synchronized sleeping state can be established only if these regions interact in a well-balanced way. Sleep stage 2, which is usually linked to the loss of self-conscious awareness, is associated with signal decreases comprising thalamic and hypothalamic regions, the cingulate cortex, the right insula and adjacent regions of the temporal lobe, the inferior parietal lobule and the inferior/middle frontal gyri. The hypothalamic region known to be of particular importance in the regulation of the sleep-wake cycle shows specific temporally correlated network activity with the cortex while the system is in the sleeping state, but not during wakefulness. We describe a specific pattern of decreased brain activity during sleep and suggest that this pattern must be synchronized for establishing and maintaining sleep.

1H-MRS alterations in the cerebellum of patients with familial hemiplegic migraine type 1

BACKGROUND

About 20% of patients with familial hemiplegic migraine (FHM) develop progressive cerebellar signs. Genetic studies have established an association with mutations in the CACNA1A gene. However, the mechanisms underlying cerebellar involvement are largely unknown.

OBJECTIVE

To use proton MR spectroscopy (1H-MRS) to investigate metabolic alterations in the cerebellum as well as cortical regions known to be involved in the propagation of migraine aura.

METHODS

Fifteen CACNA1A mutation carriers from three FHM families and 17 healthy control subjects were studied. Eleven patients had clinical signs of cerebellar involvement. LCModel fits were used to estimate absolute concentrations of N-acetyl aspartate (NAA), myo-inositol (mI), glutamate (Glu), choline-containing compounds, total creatine, and lactate in the superior cerebellar vermis (SCV), parietal cortex, and occipital cortex. To control for atrophy effects, automated image segmentation was performed using SPM99. The brain parenchyma fraction (BPF) was determined for all three regions.

RESULTS

Compared with controls, the brain parenchyma fraction (BPF), NAA, and Glu were significantly reduced and mI was significantly elevated in the SCV of patients with FHM. In contrast, no metabolite alterations were found in supratentorial regions. BPF and NAA in the SCV significantly correlated with cerebellar scores, in particular, gait ataxia.

CONCLUSIONS

The findings suggest that there is a regionally distinct neuronal impairment in the superior cerebellar vermis that exceeds macroscopic tissue loss. Correlations with clinical scores emphasize the functional relevance of localized atrophy (brain parenchyma fraction) and N-acetyl aspartate levels. These measures may be useful to monitor disease progression. The observed reduction in glutamate may in part reflect impaired glutamatergic neurotransmission.

Cerebral white matter hyperintense lesions are associated with unstable carotid plaques

OBJECTIVES

The aim of this study was to determine whether unstable carotid plaques, a known risk factor for cerebral emboli, are associated with cerebral white matter lesions.

METHODS

Seventy-one symptomatic patients undergoing magnetic resonance imaging prior to carotid endarterectomy for high grade carotid stenosis were included in this study. The number and volume of white matter hyperintense lesions (WMHL) on fluid attenuated inversion recovery brain scans were compared according to the morphology of carotid plaque based upon the American Heart Association (AHA) histological classification.

RESULTS

Of the 57 patients who had good quality brain scans and non-fragmented carotid plaques, 15 plaques were defined as stable (type V) and 42 as unstable (type VI). After adjustment for the major risk factors affecting WMHL, unstable carotid plaques were found to be associated with more WMHL in the ipsilateral cerebral hemisphere than stable plaques (transformed means 2.50+/-1.2 vs. 1.53+/-1.1, p=0.016), however, there was only a trend towards larger WMHL volumes (p=0.079).

CONCLUSIONS

The observed association between unstable carotid plaques and the number of white matter lesions suggest that thromboembolic plaque activity may contribute to the development of leukoaraiosis, in particular smaller individual lesions. Larger studies are warranted to confirm this finding and explore the potential clinical impact for selecting candidates for carotid endarterectomy.

Corticosteroid status influences the volume of the rat cingulate cortex - a magnetic resonance imaging study

Imbalances in the corticosteroid milieu result in reductions in hippocampal volume in humans and experimental rodents. The functional correlates of these changes include deficits in cognitive performance and regulation of the hypothalamic-pituitary-adrenal axis. Since other limbic structures which are intricately connected with the hippocampal formation, also play an important role in behavioural and neuroendocrine functions, we here used magnetic resonance imaging (MRI) to analyse how two of these areas, the anterior cingulate and retrosplenial cortex, respond to chronic alterations of adrenocortical status: hypocortisolism (induced by adrenalectomy, ADX), normocortisolism (ADX with low-dose corticosterone replacement), and hypercortisolism (ADX with high-dose dexamethasone supplementation). Hypercortisolism was associated with a significant reduction in the volume (absolute and normalized) of the left anterior cingulate gyrus as measured by MRI and confirmed using classical histological methods; a similar trend was observed in the right anterior cingulate region. In contrast, hypercortisolism did not influence the volume of the adjacent retrosplenial cortex. The volumes of the anterior cingulate gyrus and retrosplenial cortex were unaffected by the absence of adrenocortical hormones. These findings are the first to suggest that corticosteroid influences on the structure of the limbic system extend beyond the hippocampal formation, i.e., to fronto-limbic areas also.

The eye-of-the-tiger sign is not a reliable disease marker for Hallervorden-Spatz syndrome

Pantothenate kinase-associated neurodegeneration (PKAN), formerly Hallervorden-Spatz syndrome, is a rare autosomal recessive disorder characterized by extrapyramidal dysfunction as demonstrated by dystonia, rigidity, and choreoathetosis. Iron deposition in conjunction with destruction of the globus pallidus gives rise to the characteristic eye-of-the-tiger sign in MRI. It has been postulated that pantothenate kinase 2 mutations underlying all cases of classic Hallervorden-Spatz syndrome are always associated with the eye-of-the-tiger sign. Here, we report a patient with classic Hallervorden-Spatz syndrome and a homozygous pantothenate kinase 2 mutation in whom the initially present eye-of-the-tiger sign vanished during the course of the disease. Thus, the alleged one-to-one correlation between the eye-of-the-tiger sign and the presence of pantothenate kinase 2 mutation does not hold true over the course of the disease in PKAN.

Assessing DTI data quality using bootstrap analysis

Diffusion tensor imaging (DTI) is an established method for characterizing and quantifying ultrastructural brain tissue properties. However, DTI-derived variables are affected by various sources of signal uncertainty. The goal of this study was to establish an objective quality measure for DTI based on the nonparametric bootstrap methodology. The confidence intervals (CIs) of white matter (WM) fractional anisotropy (FA) and Clinear were determined by bootstrap analysis and submitted to histogram analysis. The effects of artificial noising and edge-preserving smoothing, as well as enhanced and reduced motion were studied in healthy volunteers. Gender and age effects on data quality as potential confounds in group comparison studies were analyzed. Additional noising showed a detrimental effect on the mean, peak position, and height of the respective CIs at 10% of the original background noise. Inverse changes reflected data improvement induced by edge-preserving smoothing. Motion-dependent impairment was also well depicted by bootstrap-derived parameters. Moreover, there was a significant gender effect, with females displaying less dispersion (attributable to elevated SNR). In conclusion, the bootstrap procedure is a useful tool for assessing DTI data quality. It is sensitive to both noise and motion effects, and may help to exclude confounding effects in group comparisons.

Involuntary vocalisations and a complex hyperkinetic movement disorder following left side thalamic haemorrhage

A variety of involuntary speech phenomena as for example palilalia have been described as consequences of neurological disorders. Palilalia is the involuntary repetition of syllabels, words and phrases in ongoing speech. We describe a 73 year old woman who suffered from a hypertensive thalamic haemorrhage. MRI revealed that the lesion was predominantly located within the pulvinar, extending to the lateroposterior thalamic nuclei and to the pretectal area with possible involvement of the medial geniculate body. Few months after the event she developed involuntary vocalisations with whole words and meaningless syllables being rapidly reiterated. In contrast to typical palilalia these vocalisations were not meaningfully related to the ongoing speech of the patient. In addition, the patient developed a complex hyperkinetic movement disorder with right-sided painful hemidystonia and bilateral clonic jerks and a right-sided postural tremor.

Neuronavigation and functional MRI for surgery in patients with lesion in eloquent brain areas

OBJECTIVE

Surgery in patients with lesions in eloquent areas is still a challenge for the neurosurgeon. The aim of surgical interventions should be the radical removal of the lesions with functional preservation. Functional brain imaging methods provide the preoperative demonstration of those brain areas and their relationship to pathologic structures.

MATERIAL

Twenty-seven patients with pathologic lesions in or near eloquent regions were investigated with functional magnetic resonance imaging (fMRI). Nineteen patients were neurologically intact preoperatively, and presented only with headache and/or seizure. Eight patients had a minor neurological deficit. Twenty-five patients underwent surgery. Preoperatively a computed tomography (CT) scan or a magnetic resonance imaging procedure with five skin fiducials was performed. The data were transferred to the neuronavigation workstation. The tumour was lined out in colours, and reconstruction in a triplanar format as well as three-dimensionally was implemented. The information from the fMRI concerning the functional areas was transferred into the images manually to account for EPI distortions. Fifteen patients were operated on using the combination fMRI/neuronavigation. Diagnoses included eleven gliomas, two meningeomas, one metastasis and one cavernoma.

RESULTS

In seven patients the tumour was removed completely, eight patients had residual tumour, demonstrated by early postoperative MRI. All patients with residual tumour had gliomas that involved functional areas. Postoperatively no patient had an additional neurological deficit.

CONCLUSION

Functional MRI provides important additional information in patients with lesions in eloquent brain areas. In combination with neuronavigation this is a very helpful technique for surgical interventions on these patients to reduce morbidity. Nonetheless, there are still open questions concerning accuracy of display of the functional areas and integration into a neuronavigation system.

Fiber tracking from DTI using linear state space models: detectability of the pyramidal tract

Diffusion tensor imaging (DTI) is an emerging and promising tool to provide information about the course of white matter fiber tracts in the human brain. Based on specific acquisition schemes, diffusion tensor data resemble local fiber orientations allowing for a reconstruction of the fiber bundles. Current techniques to calculate fascicles range from simple heuristic tracking solutions to Bayesian and differential equations approaches. Most methods are based only on local diffusion information, often resulting in bending or kinking fiber paths in voxels with reduced diffusion properties. In this article we present a new tracking approach based on linear state space models encompassing an inherent smoothness criterion to avoid too wiggly tracked fiber bundles. The new technique will be described formally and tested on simulated and real data. The performance tests are focused on the pyramidal tract, where we employed a test-retest study and a group comparison in healthy subjects. Anatomical course was confirmed in a patient with selective degeneration of the pyramidal tract. The potential of the presented technique for improved neurosurgical planning is demonstrated by visualization of a tumor-induced displacement of the motor pathways. The paper closes with a thorough discussion of perspectives and limitations of the new tracking approach.

Homozygosity (E140K) in SCO2 causes delayed infantile onset of cardiomyopathy and neuropathy

OBJECTIVE

To report three unrelated infants with a distinctive phenotype of Leigh-like syndrome, neurogenic muscular atrophy, and hypertrophic obstructive cardiomyopathy. The patients all had a homozygous missense mutation in SCO2.

BACKGROUND

SCO2 encodes a mitochondrial inner membrane protein, thought to function as a copper transporter to cytochrome c oxidase (COX), the terminal enzyme of the respiratory chain. Mutations in SCO2 have been described in patients with severe COX deficiency and early onset fatal infantile hypertrophic cardioencephalomyopathy. All patients so far reported are compound heterozygotes for a missense mutation (E140K) near the predicted CxxxC metal binding motif; however, recent functional studies of the homologous mutation in yeast failed to demonstrate an effect on respiration.

METHODS

Here we present clinical, biochemical, morphologic, functional, MRI, and MRS data in two infants, and a short report in an additional patient, all carrying a homozygous G1541A transition (E140K).

RESULTS

The disease onset and symptoms differed significantly from those in compound heterozygotes. MRI and muscle morphology demonstrated an age-dependent progression of disease with predominant involvement of white matter, late appearance of basal ganglia lesions, and neurogenic muscular atrophy in addition to the relatively late onset of hypertrophic cardiomyopathy. The copper uptake of cultured fibroblasts was significantly increased.

CONCLUSIONS

The clinical spectrum of SCO2 deficiency includes the delayed development of hypertrophic obstructive cardiomyopathy and severe neurogenic muscular atrophy. There is increased copper uptake in patients' fibroblasts indicating that the G1541A mutation effects cellular copper metabolism.

Blood pressure changes induced by arterial blood withdrawal influence bold signal in anesthesized rats at 7 Tesla: implications for pharmacologic mri

Functional magnetic resonance imaging (fMRI) using the blood oxygenation level-dependent (BOLD) contrast is now increasingly applied for measuring drug effects on brain activity. A possible confound in pharmacologic fMRI (phMRI) is that the BOLD signal may be sensitive to systemic cardiovascular or respiratory parameters, which can themselves be modulated by a drug. To assess whether abrupt changes in arterial blood pressure (BP) as may be observed in phMRI experiments influence the BOLD signal, a hemorrhage model was studied in anesthesized rats at 7 T using spin-echo EPI. BP and BOLD signal time courses were found to be significantly correlated (P < 0.01). This effect was detected under the three different anesthetic regimens employed (isoflurane, halothane, and propofol). The regional pattern of BP-BOLD correlations was heterogeneous and may reflect vascular density. In physiological terms, a BOLD decrease during a decrease in BP may result from an increase in mostly venous cerebral blood volume (CBV) as an autoregulatory response to maintain cerebral blood flow (CBF) during decreased perfusion pressure. The observed influence of BP on BOLD may complicate qualitative and quantitative description of drug effects.

Reduced NAA in the thalamus and altered membrane and glial metabolism in schizophrenic patients detected by 1H-MRS and tissue segmentation

Functional and structural abnormalities in the thalamus as well as a generalized phospholipid membrane disorder have been implicated in the pathogenesis of schizophrenic psychosis. To determine whether thalamic neuronal abnormalities and altered membrane-associated metabolites can be detected in schizophrenic patients, we used in vivo proton magnetic resonance spectroscopy (1H-MRS) in 32 acutely-ill, medicated schizophrenic patients and 17 age-matched controls. Thalamic and white matter metabolite concentrations (myo-inositol (mI), choline-containing compounds (Cho), total creatine (Cr) and N-acetylaspartate (NAA)) were estimated and corrected for atrophy (CSF) and gray and white matter contributions (GM, WM) by use of image-based voxel segmentation. Thalamic NAA was significantly reduced in schizophrenic patients, whereas Cho and mI were significantly increased in the parietal white matter. White matter Cr was significantly elevated in patients and correlated positively with the brief psychiatric rating scores (BPRS). Regional metabolite levels were inversely associated with GM and WM content reaching significance for mI and Cr in the thalamus and Cho and NAA in the white matter. Reduced NAA in the left thalamus of schizophrenic patients confirms and extends previous spectroscopic data and agrees well with histologic and imaging findings of reduced neuronal density and volume. Elevated Cho in line with 31P-MRS studies suggests increased myelin degradation thus further supporting a generalized membrane disorder in schizophrenic patients. In addition, we demonstrate the need to correct metabolite concentrations for regional tissue composition in studies employing patients with altered brain morphology.

Improved analysis of 1H-MR spectra in the presence of mobile lipids

Focal brain lesions can be associated with proton magnetic resonance spectra (1H-MRS)-detectable mobile lipids, reflecting severe tissue degradation and necrosis. However, advanced fitting procedures, such as the LCModel, fail to adequately fit spectra in the presence of lipid resonances. To overcome this, different approaches to generate lipid model spectra were compared using a phantom, real in vivo data, and simulated data. Twenty-six in vivo short-echo time (TE) 1H-MRS from 21 malignant gliomas, four infections, and one ischemia were analyzed to evaluate the performance of the modified LCModel fit. Adding simulated aliphatic resonances at 1.3 and 0.9 ppm improved the overall fitting quality remarkably and allowed good separation of lactate and alanine. Also, a better differentiation of glioblastomas and anaplastic gliomas was achieved. In conclusion, we propose a simple way to efficiently include lipid resonances in the LCModel, allowing a better fit of in vivo short-TE 1H-MRS, and demonstrate the diagnostic potential of quantitative assessment of mobile lipids in brain tumors.

Bayesian modeling of the hemodynamic response function in BOLD fMRI

In functional magnetic resonance imaging (fMRI), modeling the complex link between neuronal activity and its hemodynamic response via the neurovascular coupling requires an elaborate and sensitive response model. Methods based on physiologic assumptions as well as direct, descriptive models have been proposed. The focus of this study is placed on such a direct approach that allows for a robust pixelwise determination of hemodynamic characteristics, such as time to peak or the poststimulus undershoot. A Bayesian procedure is presented that can easily be adapted to different hemodynamic properties in question and can be estimated without numerical problems known from nonlinear optimization algorithms. The usefulness of the model is demonstrated by thorough analyzes of the poststimulus undershoot in visual and acoustic stimulation paradigms. Further, we show the capability of this approach to improve analysis of fMRI data in altered hemodynamic conditions.

Frequency dependence and gender effects in visual cortical regions involved in temporal frequency dependent pattern processing

Neural response to flickering stimuli has been shown to be frequency dependent in the primary visual cortex. Controversial gender differences in blood oxygen level dependent (BOLD) amplitude upon 6 and 8 Hz visual stimulation have been reported. In order to analyze frequency and gender effects in early visual processing we employed a passive graded task paradigm with a dartboard stimulus combining eight temporal frequencies from 0 to 22 Hz in one run. Activation maps were calculated within Statistical Parametric Mapping, and BOLD amplitudes were estimated for each frequency within the striate and extrastriate visual cortex. The BOLD amplitude was found to steadily rise up to 8 Hz in BA 17 and 18 with an activation plateau at higher frequencies. In addition, we observed a laterality effect in the striate cortex with higher BOLD contrasts in the right hemisphere in men and in women. BOLD response rises similarly in men and women up to 8 Hz but with lower amplitudes in women at 4, 8, and 12 Hz (30% lower). No frequency effect above 1 Hz was found in the extrastriate visual cortex. There was also a regional specific gender difference. Men activated more in the right lingual gyrus (BA 18) and the right cerebellum compared with women, whereas women showed more activation in the right inferior temporal gyrus (BA 17). The study indicates that frequency dependent processing at the cortical level is limited to the striate cortex and may be associated with a more global information processing (right hemisphere dominance), particularly in men. The finding of significantly lower BOLD amplitudes in women despite previously shown larger VEP (visual evoked potential) amplitudes might suggest gender differences in cerebral hemodynamics (baseline rCBV, rCBF, or neurovascular coupling). The regional distinction points at additional differences in psychological processing even when using a simple visual stimulus.