Dexamethasone and enhancing solitary cerebral mass lesions: alterations in perfusion and blood-tumor barrier kinetics shown by magnetic resonance imaging

OBJECTIVE

Glucocorticoid analogues are often administered to patients with intracranial space-occupying lesions. Clinical response can be dramatic, but the neurophysiological response is not well documented. This study sought to investigate the blood-lesion barrier, blood-brain barrier, and cerebral perfusion characteristics of patients who have undergone such therapy using magnetic resonance imaging.

METHODS

Seventeen patients with intracranial mass-enhancing lesions underwent magnetic resonance imaging before and after 3 days of high-dose dexamethasone therapy. Assessments of blood-lesion barrier and blood-brain barrier integrity were based on a dynamic T1-weighted exogenous contrast technique that yielded the normalized maximal change in contrast uptake (T1-uptake). Perfusion was assessed using a dynamic T2*-weighted exogenous contrast technique to yield relative regional cerebral blood volume and first-moment mean transit time. Comparisons were made in T1-uptake, regional cerebral blood volume, and first-moment mean transit time of both enhancing lesion and contralateral normal-appearing white matter (CNAWM) obtained before and after dexamethasone.

RESULTS

Significant reduction in T1-uptake was observed (19% decrease, P < 0.005) within enhancing pathological tissue, whereas no significant alteration was detected in CNAWM. Regional cerebral blood volume was significantly reduced in both enhancing tissue (28% decrease, P < 0.005) and in CNAWM (20% decrease, P < 0.001). Bolus first-moment mean transit time significantly increased (2.0 s prolongation, P < 0.05) in CNAWM, whereas there was no significant change (1.4 s prolongation, P > 0.05) within enhancing tissue.

CONCLUSION

Glucocorticoid-analogue therapy not only affects the permeability of the blood-lesion barrier and lesion blood volume but also affects blood flow within normal-appearing contralateral parenchyma. There is a need for controls in steroid therapy in magnetic resonance imaging studies, which involve assessments of cerebrovascular function.

Short echo-time proton magnetic resonance spectroscopy in regions of severe HIV-related diffuse white matter abnormality on MRI

The purpose of this study was to determine whether short echo-time proton magnetic resonance spectroscopy (H-MRS) could detect mobile lipid resonances attributable to myelin breakdown products in the deep cerebral white matter of patients with AIDS who have severe diffuse/patchy white matter hyperintensity on T2-weighted magnetic resonance imaging (MRI). Seven patients with AIDS and clinical HIV-associated dementia complex (HADC) and 12 male controls were studied at 1.5T using a single 8 ml voxel, gradient localised, stimulated echo acquisition mode (STEAM) spectroscopy sequence. Spectra were acquired at an echo time of 20 ms with a repetition time of 5000 ms. No spectroscopic peaks were identified at 0.9 ppm and 1.3 ppm (corresponding to lipid resonances) in 6 of the 7 patients with AIDS or in any of the controls. Lipid resonances were identified in 1 patient who had been taking anti-retroviral therapy for 8 weeks. Follow up MRI/H-MRS, performed after a further 14 weeks of anti-retroviral therapy, showed partial resolution of white matter hyperintensity and lipid resonances were not detectable. These data suggest that mobile lipids are only rarely detected by H-MRS in patients with HADC and abnormalities on MRI and that their presence may be transitory.

Idiopathic generalised epilepsy: a pilot study of memory and neuronal dysfunction in the temporal lobes, assessed by magnetic resonance spectroscopy

BACKGROUND

The memory deficits in patients with temporal lobe epilepsy (TLE) are associated with epileptogenic lesions of the temporal lobes, especially hippocampal sclerosis. Memory deficits have been extensively studied in TLE, but the presence of pre-existing temporal lobe abnormality has confounded studies on the relationship between memory dysfunction and seizure activity. Idiopathic generalised epilepsy (IGE) is characterised by primary generalised seizures and is found to occur in the absence of any macroscopic brain abnormalities. IGE is therefore ideal for investigations on the effects of seizure activity on memory and cognition.

AIM AND METHODS

Magnetic resonance spectroscopy (MRS) and neuropsychological testing were used to investigate the relationship between epileptic seizures, memory performance and neuronal dysfunction in the temporal lobes of a group of patients with IGE. 30 patients and 15 healthy controls participated in the study.

RESULTS

Patients with IGE were found to perform worse than controls on tests of speed of information processing, general cognitive performance and a range of memory tests, including face recognition, word recognition, verbal recall and complex figure recall. The performance of the patient group on the visual recognition and verbal recall sections of the Doors and People Test was found to correlate with MRS ratios of N-acetyl aspartate:choline and N-acetyl aspartate:creatine in the temporal lobes.

CONCLUSION

This result supports the hypothesis that memory deficits in epilepsy may be due to neuronal dysfunction secondary to epileptic activity itself in the absence of any macroscopic lesions in the temporal lobes.

Influence of Human Serum Albumin on Longitudinal and Transverse Relaxation Rates (R1 and R2) of Magnetic Resonance Contrast Agents

OBJECTIVES

Exogenous magnetic resonance (MR) contrast media (CM) are used to improve detection and delineation of physiological and pathologic structures. Temporary binding between CM and proteins such as human serum albumin (HSA) may alter the relaxation-enhancing properties of specific contrast agents. In this study, the presence and strength of HSA interaction with different CM was investigated.

MATERIAL AND METHODS

Three contrast agents were chosen: Gd-DTPA, Gd-BT-DO3A, and Gd-BOPTA, each of which is known to have a different protein interaction. Samples were prepared using 7 different HSA concentrations, all at a constant CM concentration of 0.5 mmol/L. The relaxation rates, R1 and R2, of each sample were measured at 1.5 T. Virtual docking studies were performed to estimate the number of high affinity-binding sites of Gd-BOPTA and the surface of the HSA dimer.

RESULTS

Gd-BOPTA caused the greatest increase in R1 and R2, which followed an exponential dependency with increasing HSA concentration. Between the range of 0 and 7 g/dL of HSA, Gd-DTPA and Gd-BT-DO3A showed a relative change in both relaxation rates of approximately 13% and 22% for R1 and 26% and 30% for R2, respectively. In contrast, Gd-BOPTA demonstrated a relative increase of approximately 108% and 363% for R1 and R2, respectively. Changes of HSA concentration within physiological range (3.5-5.5 g/dL) resulted in an increase of R1 and R2 of approximately 40% when using Gd-BOPTA. The docking study revealed that approximately 10 small hydrophobic pockets exist on the HSA surface where the aromatic tail of Gd-BOPTA can fit in and a stronger noncovalent binding can occur compared with Gd-DTPA and Gd-BT-DO3A.

CONCLUSION

Relaxation rates of Gd-BOPTA showed a strong dependency on HSA. In contrast, Gd-DTPA and Gd-BT-DO3A demonstrated little or no relevant dependency. On the basis of these results, the influence of serum protein concentration should be considered in both research studies and in clinical use.

MR imaging of recent non-traumatic intracranial hemorrhage: early experience at 3 T

Magnetic resonance imaging (MRI) using 3.0 T scanners in the clinical environment is in its infancy and is only available at a limited number of sites worldwide. There is great interest amongst radiologists about the perceived benefits of clinical imaging at 3.0 T; however, it remains to be seen whether the theoretical advantages will bring real gains. MRI in patients with non-traumatic intracranial hemorrhage (ICH) is difficult, yet, these patients benefit from non-invasive angiography. Conventional catheter angiography (CCA) remains the reference standard for excluding/confirming the presence of intracranial vascular abnormalities, but MR angiography at 3.0 T may offer opportunities for significant changes in patient management. We present our experiences of using 3.0 T MR angiography in 27 patients with acute or early subacute ICH.

Effects of creatine supplementation on cerebral white matter in competitive sportsmen

OBJECTIVES

To determine the neurobiochemical sequelae of oral creatine monohydrate supplementation in active athletes.

DESIGN/PARTICIPANTS

Eighteen sportsmen underwent single-voxel proton magnetic resonance spectroscopy of the deep frontal cerebral white matter before and after 5 days of oral ingestion: 12 of 18 swallowed 4 x 5 g creatine monohydrate per day, and the remaining swallowed a placebo.

MAIN OUTCOME MEASUREMENTS

Creatine, choline, and N-acetyl spectral resonances were evaluated at both long (135 ms) and short (20 ms) echo times.

RESULTS

A mixed-design factorial ANOVA demonstrated no interaction over time in any of the measures (P at least 0.081).

CONCLUSIONS

The results suggest that, for the given dosage regimen, ingested creatine augmentation does not alter the magnetic resonance visible creatine pool in the deep frontal cerebral white matter of young active sportsmen.

Neural activity in speech-sensitive auditory cortex during silence

That auditory hallucinations are voices heard in the absence of external stimuli implies the existence of endogenous neural activity within the auditory cortex responsible for their perception. Further, auditory hallucinations occur across a range of healthy and disease states that include reduced arousal, hypnosis, drug intoxication, delirium, and psychosis. This suggests that, even in health, the auditory cortex has a propensity to spontaneously "activate" during silence. Here we report the findings of a functional MRI study, designed to examine baseline activity in speech-sensitive auditory regions. During silence, we show that functionally defined speech-sensitive auditory cortex is characterized by intermittent episodes of significantly increased activity in a large proportion (in some cases >30%) of its volume. Bilateral increases in activity are associated with foci of spontaneous activation in the left primary and association auditory cortices and anterior cingulate cortex. We suggest that, within auditory regions, endogenous activity is modulated by anterior cingulate cortex, resulting in spontaneous activation during silence. Hence, an aspect of the brain's "default mode" resembles a (preprepared) substrate for the development of auditory hallucinations. These observations may help explain why such hallucinations are ubiquitous.

The effects of dehydration on brain volume -- preliminary results

In adults the cranium is a rigid bony vault of fixed size and therefore the intra-cranial volume is a constant which equals the sum of the volume of the brain, the intra-cranial volume of CSF and the intra-cranial volume of blood. There can be marked changes in the volumes of these three intra-cranial compartments which may influence susceptibility to brain damage after head injury. This is the first study to investigate the relationship between dehydration and changes in the volume of the brain and the cerebral ventricles. Six healthy control subjects underwent magnetic resonance imaging of the brain before and after a period of exercise in an environmental chamber. The subjects lost between 2.1 % and 2.6 % of their body mass due to water loss through sweating. We found a correlation between the degree of dehydration and the change in ventricular volume (r=0.932, p=0.007). The changes in ventricular volume caused by dehydration were much larger than those seen in day-to-day fluctuations in a normally hydrated healthy control subject.

Structural brain correlates of unconstrained motor activity in people with schizophrenia

Avolition affects quality of life in chronic schizophrenia. We investigated the relationship between unconstrained motor activity and the volume of key executive brain regions in 16 male patients with schizophrenia. Wristworn actigraphy monitors were used to record motor activity over a 20 h period. Structural magnetic resonance imaging brain scans were parcellated and individual volumes for anterior cingulate cortex and dorsolateral prefrontal cortex extracted. Patients'total activity was positively correlated with volume of left anterior cingulate cortex. These data suggest that the volume of specific executive structures may affect (quantifiable) motor behaviours, having further implications for models of the 'will' and avolition.

Quantifiable change in functional brain response to empathic and forgivability judgments with resolution of posttraumatic stress disorder

Previous functional neuroimaging studies of posttraumatic stress disorder (PTSD) have mainly focused on symptom-provocation paradigms in combat-related PTSD. We sought to elucidate the effect of non-combat-related PTSD on the physiology of social cognition. Thirteen patients with PTSD underwent functional magnetic resonance imaging (fMRI) while they engaged in tasks that (i) involve speculation on another's intention, (ii) invoke empathy and (iii) involve making judgments of the forgivability of others' actions; each versus 'baseline' social reasoning judgments. A post-therapy fMRI scan followed a course of modified cognitive behavioural therapy. Post-therapy, we found increased activation in brain regions predicted on the basis of foregoing work in healthy subjects. These included significant left middle temporal gyrus activation in post-therapy response to empathy judgments and posterior cingulate gyrus activation in post-therapy response to forgivability judgments. The specific regions of the human brain activated by empathy and forgivability judgments changed with symptom resolution in PTSD. Time and therapy are likely contributory factors that lead to a degree of 'normalisation' of the neural response to these social cognition tasks.

First-line investigation of acute intracerebral hemorrhage using dynamic magnetic resonance angiography

PURPOSE

To report the initial experience of magnetic resonance (MR) digital subtraction angiography (MR-DSA) in the dynamic assessment of the cerebral circulation in acute non-traumatic intracerebral hemorrhage (ICH).

MATERIAL AND METHODS

Twelve patients with acute ICH were investigated within 6 days of the ictus using a dynamic contrast-enhanced 2-D MR angiogram that produces subtracted images with a temporal resolution of 1-2 frame/s. The MR-DSA examinations were assessed for evidence of an intracranial vascular abnormality and were compared with (i) the routine MR sequences, (ii) non-dynamic time-of-flight MR angiography, and (iii) catheter angiogram performed during the same admission.

RESULTS

All 12 MR-DSA examinations were considered to be technically satisfactory. MR-DSA detected an intracranial vascular abnormality in 7 patients (3 arteriovenous malformations, 2 aneurysms, 1 dural arteriovenous fistula, and 1 venous thrombosis). All abnormalities were confirmed by catheter angiography with the exception of one patient with venous sinus thrombosis found on MR imaging that did not undergo catheter angiography. All four arteriovenous shunts were detected by MR-DSA by virtue of early venous filling.

CONCLUSION

MR-DSA can be performed satisfactorily in the setting of acute ICH and provides an alternative method to catheter angiography for identifying shunting vascular abnormalities such as arteriovenous malformations and fistulae, as well as large aneurysms and venous occlusions. MR-DSA is a contrast-medium-based technique that does not suffer from the T1 shortening effects of acute hemorrhage that can obscure abnormalities on conventional flow-based non-dynamic techniques.

MR imaging of patients with localisation-related seizures: initial experience at 3.0T and relevance to the NICE guidelines

The purpose of this study is to describe our initial experience of imaging adults with localisation-related epilepsy using MR imaging at 3.0T. We discuss the findings in the context of the recently released NICE guidelines that provide detailed advice on imaging people with epilepsy in the UK. 120 consecutive people over the age of 16 years with localisation-related epilepsy were referred for clinical MR examinations from a regional neuroscience centre in England. None of the people had had MR examinations prior to the present study. High resolution MR imaging was performed taking advantage of the high field strength and high performance gradients of the system. Two experienced neuroradiologists reported on the examinations independently and the presence and type of pathology was recorded. There was complete agreement between the two reporters in all 120 cases. The overall frequency of abnormalities shown by MR was 31/120 (26%) and the commonest abnormality shown was mesial temporal sclerosis found in 10/120 (8%). Tumours were shown in 4/120, all of which appeared low grade as judged by imaging criteria. Epilepsy is the commonest neurological condition and demands a significant resource in order to provide good care for sufferers. Recent guidelines published in the UK have suggested that the majority of people with epilepsy should receive brain MR as part of their routine assessment. Our work shows that using the most sophisticated MR imaging in a highly selected population there is a modest pick-up rate of brain abnormalities. If a widespread epilepsy-imaging programme is started the detection rate is likely to be much lower. Although MR is acknowledged to be a reliable way of detecting pathology in people with epilepsy there is a dearth of information studying the health economics of imaging epilepsy in relation to patient management and outcomes.

Male and female voices activate distinct regions in the male brain

In schizophrenia, auditory verbal hallucinations (AVHs) are likely to be perceived as gender-specific. Given that functional neuro-imaging correlates of AVHs involve multiple brain regions principally including auditory cortex, it is likely that those brain regions responsible for attribution of gender to speech are invoked during AVHs. We used functional magnetic resonance imaging (fMRI) and a paradigm utilising 'gender-apparent' (unaltered) and 'gender-ambiguous' (pitch-scaled) male and female voice stimuli to test the hypothesis that male and female voices activate distinct brain areas during gender attribution. The perception of female voices, when compared with male voices, affected greater activation of the right anterior superior temporal gyrus, near the superior temporal sulcus. Similarly, male voice perception activated the mesio-parietal precuneus area. These different gender associations could not be explained by either simple pitch perception or behavioural response because the activations that we observed were conjointly activated by both 'gender-apparent' and 'gender-ambiguous' voices. The results of this study demonstrate that, in the male brain, the perception of male and female voices activates distinct brain regions.

Expanding the response space in chronic schizophrenia: the relevance of left prefrontal cortex

OBJECTIVE

This study probed the ability of people with chronic schizophrenia to control their behavior in time by requiring them to deliberately vary responses within the temporal domain (i.e., to avoid regular inter-response intervals).

METHODS

Thirteen schizophrenia patients performed single finger movements (at moments of their own choosing) in an event-related functional magnetic resonance imaging paradigm. Their performance was computed using the coefficient of variation of inter-response interval duration.

RESULTS

Task performance was positively correlated with activation of left lateral prefrontal cortex. Post hoc analyses revealed an inverse correlation between activation in this region and severity of attentional impairment.

CONCLUSION

These findings implicate left lateral prefrontal cortex in the modulation of the temporal response space in schizophrenia and imply greater attentional (executive) impairment among those who fail to modulate their behavior in time.

Cerebellar abnormalities on proton MR spectroscopy in gluten ataxia

Gluten sensitivity can manifest with ataxia. The metabolic status of the cerebellum was investigated in 15 patients with gluten ataxia and 10 controls using proton MR spectroscopy. Significant differences were present in mean N-acetyl aspartate levels at short echo time and N-acetyl aspartate/choline ratios at long echo time between the patient and control groups. These data support the hypothesis that cerebellar neuronal physiology differs between patients with gluten ataxia and healthy controls.

Modafinil modulates anterior cingulate function in chronic schizophrenia

BACKGROUND

Schizophrenia is associated with widespread cognitive deficits that have an impact on social function. Modafinil promotes wakefulness and is reported to enhance cognition.

AIMS

To study the acute effects of modafinil administration upon brain activity and cognitive performance in people with chronic schizophrenia.

METHOD

In a randomised double-blind placebo-controlled crossover design, 19 patients received either modafinil (100 mg) or placebo prior to undertaking a working memory task with functional magnetic resonance imaging.

RESULTS

Seventeen patients completed the study and another underwent acute relapse 4 days post-drug. Modafinil administration was associated with significantly greater activation in the anterior cingulate cortex during the working memory task. The anterior cingulate cortex signal correlated with cognitive performance, although only a subset of patients exhibited 'enhancement'.

CONCLUSIONS

Modafinil modulates anterior cingulate cortex function in chronic schizophrenia but its beneficial cognitive effects may be restricted to a subset of patients requiring further characterisation.

The nonspecific nature of proton spectroscopy in brain masses in children: a series of demyelinating lesions

MRI imaging has significantly improved the detection of brain lesions over the past few decades. It has high sensitivity to intracranial pathology but confident preoperative tissue diagnosis is relatively unusual. MR spectroscopy provides in-vivo biochemical information and has been used to improve the low specificity of tumour diagnosis. During the last decade there have been a number of reports making the case that proton spectroscopy can distinguish different grades of glial tumours and in some situations provide information on histological type. We report four children who presented with neurological symptoms and focal masses on MRI. MRS in each of them gave results consistent with textbook descriptions of malignancy, but in all four cases the abnormalities were subsequently shown to be due to demyelination. We reiterate that spectroscopic appearances are nonspecific and spectroscopic data should be evaluated in the light of concurrent imaging features and the clinical presentation.

Assessment of cerebral haemodynamics and vascular reserve in patients with symptomatic carotid artery occlusion: an integrated MR method

We describe an MR-based methodology designed to study cerebral haemodynamic compromise in patients with symptomatic carotid occlusions. We present the results of eight patients who underwent MR angiography of the cervical carotids and circle of Willis, MR imaging of the brain and dynamic gadolinium MR perfusion studies before and after the injection of the carbonic anhydrase inhibitor acetazolamide. All patients showed increased transit times in the symptomatic hemisphere at rest indicating reduced flow. The transit time asymmetries became more pronounced after acetazolamide in all patients because of failed vasodilatation on the affected side. There was an inverse correlation between the degree of increased transit time and the degree of collateralisation around the circle of Willis. We believe that demonstration of both macroscopic vascular anatomy and microvascular reserve is important when assessing patients with possible low-flow states and the described method is a robust means of obtaining that data.

Diffusion tensor imaging for the assessment of upper motor neuron integrity in ALS

BACKGROUND

High angular resolution diffusion tensor imaging (HARD) is an MRI technique that exploits the mobility of water molecules to yield maps of structural order and directionality of white matter tracts with greater precision than six-direction diffusion tensor imaging (DTI) schemes.

OBJECTIVE

To assess whether HARD is more sensitive than conventional MRI or neurologic assessment in detecting the upper motor neuron (UMN) pathology of patients with ALS.

METHODS

Twenty-five patients with definite UMN clinical signs and 23 healthy volunteers underwent conventional MRI. HARD datasets were collected from a subset of these participants plus four patients with isolated lower motor neuron (LMN) signs. ALS symptom severity was assessed by a neurologist, the conventional MR images were reviewed by neuroradiologists, and the DTI maps were subject to quantitative region of interest analysis.

RESULTS

Motor cortex hypointensity on T2-weighted images and corona radiata hyperintensity on proton density-weighted images distinguished patients with UMN involvement from volunteers with 100% specificity, but only 20% sensitivity. Fractional anisotropy (FA) was reduced in the posterior limb of the internal capsule in patients with UMN involvement compared to volunteers. A FA threshold value with a sensitivity of 95% to detect patients with ALS (including those with isolated LMN signs) had a specificity of 71%.

CONCLUSIONS

High angular resolution diffusion tensor imaging may be more sensitive than conventional MRI or neurologic assessment to the upper motor neuron (UMN) pathology of ALS, but it lacks the specificity required of a diagnostic marker. Instead, it is potentially useful as a quantitative tool for monitoring the progression of UMN pathology.

Smaller hippocampal volume in patients with recent-onset posttraumatic stress disorder

BACKGROUND

Previous structural magnetic resonance (MR) research in patients with posttraumatic stress disorder (PTSD) has found smaller hippocampal volumes in patients compared with control subjects. These studies have mostly involved subjects who have had PTSD for a number of years, such as war veterans or adult survivors of childhood abuse. Patients with recent-onset PTSD have rarely been investigated. To our knowledge only one other study has investigated such a group. The aim of this study was to compare hippocampal volumes of patients with recent onset PTSD and nontrauma-exposed control subjects.

METHODS

Fifteen patients with PTSD, recruited from an accident and emergency department, were compared with 11, non-trauma-exposed, healthy control subjects. Patients underwent a structural MR scan soon after trauma (mean time = 158 +/- 41 days). Entire brain volumes, voxel size 1 x 1 x 1 mm, were acquired for each subject. Point counting and stereology were used to measure the hippocampal and amygdala volume of each subject.

RESULTS

Right-sided hippocampal volume was significantly smaller in PTSD patients than control subjects after controlling for effects of whole brain volume and age. Neither left nor total hippocampal volume were significantly smaller in the PTSD group after correction. Whole brain volume was also found to be significantly smaller in patients. There were no differences in amygdala or white matter volumes between patients and control subjects.

CONCLUSIONS

This result replicates previous findings of smaller hippocampal volumes in PTSD patients, but in an underinvestigated population, suggesting that either smaller hippocampal volume is a predisposing factor in the development of PTSD or that damage occurs within months of trauma, rather than a number of years. Either of these two hypotheses have significant implications for the treatment of PTSD. For instance, if it could be shown that screening for hippocampal volume may, in some cases, predict those likely to develop clinical PTSD.

Corroboration of in utero MRI using post-mortem MRI and autopsy in foetuses with CNS abnormalities

AIMS

To corroborate the findings of in utero magnetic resonance imaging (MRI) with autopsy and post-mortem MRI in cases of known or suspected central nervous system (CNS) abnormalities on ultrasound and to compare the diagnostic accuracy of ante-natal ultrasound and in utero MRI.

METHODS

Twelve pregnant women, whose foetuses had suspected central nervous system abnormalities underwent in utero MRI. The foetuses were imaged using MRi before autopsy. The data were used to evaluate the diagnostic accuracy of in utero MRI when compared with a reference standard of autopsy and post-mortem MRI in 10 cases and post-mortem MRI alone in two cases.

RESULTS

The diagnostic accuracy of antenatal ultrasound and in utero MRI in correctly characterizing brain and spine abnormalities were 42 and 100%, respectively.

CONCLUSION

In utero MRI provides a useful adjuvant to antenatal ultrasound when assessing CNS abnormalities by providing more accurate anatomical information. Post-mortem MRI assists the diagnosis of macroscopic structural abnormalities.

Spatial and temporal dissociation in prefrontal cortex during action execution

It is widely accepted that dorsolateral prefrontal cortex (DLPFC) is activated at the time of action generation in humans. However, the previous functional neuroimaging studies that have supported this hypothesis temporally integrated brain dynamics and therefore could not demonstrate when DLPFC underwent activation relative to the emergence of voluntary behavior. Data that are time-locked to the instant of voluntary action execution do not reveal DLPFC activation at that moment. Rather, activated foci are seen at the frontal poles. We investigated this apparent conundrum through three differentially constrained experiments, utilizing functional magnetic resonance imaging to identify those prefrontal areas exhibiting functional change at the moment of spontaneous action execution. We observed profound functional dissociation between anterior and dorsolateral regions, compatible with their involvement at different points during the temporal evolution of action: bilaterally the frontal poles activated at the moment of execution, while simultaneously (and relative to a prior activation state) left DLPFC 'deactivated.'

Comparison of ultrasound and magnetic resonance imaging in 100 singleton pregnancies with suspected brain abnormalities

OBJECTIVE

To compare the diagnostic accuracy of the current reference standard-ultrasound with in utero magnetic resonance imaging, in a selected group of patients.

DESIGN

Prospective study.

SETTING

Five fetal maternal tertiary referral centres and an academic radiology unit.

SAMPLE

One hundred cases of fetuses with central nervous system abnormalities where there has been diagnostic difficulties on ultrasound. In 48 cases the women were less than 24 weeks of gestation and in 52 cases later in pregnancy.

METHODS

All women were imaged on a 1.5 T clinical system using a single shot fast spin echo technique. The results of antenatal ultrasound and in utero magnetic resonance were compared.

MAIN OUTCOME MEASURES

The definitive diagnosis was made either at autopsy or by postmortem magnetic resonance imaging, in cases that went to termination of pregnancy, or a combination of postnatal imaging and clinical follow up in the others.

RESULTS

In 52 of cases, ultrasound and magnetic resonance gave identical results and in a further 12, magnetic resonance provided extra information that was judged not to have had direct effects on management. In 35 of cases, magnetic resonance either changed the diagnosis (29) or gave extra information that could have altered management (6). In 11 of the 30 cases where magnetic resonance changed the diagnosis, the brain was described as normal on magnetic resonance.

CONCLUSIONS

In utero magnetic resonance imaging is a powerful tool in investigating fetal brain abnormalities. Our results suggest that in selected cases of brain abnormalities, detected by ultrasound, antenatal magnetic resonance may provide additional, clinically useful information that may alter management.

Analysis of diffusion tensor magnetic resonance imaging data using principal component analysis

An analysis method for diffusion tensor (DT) magnetic resonance imaging data is described, which, contrary to the standard method (multivariate fitting), does not require a specific functional model for diffusion-weighted (DW) signals. The method uses principal component analysis (PCA) under the assumption of a single fibre per pixel. PCA and the standard method were compared using simulations and human brain data. The two methods were equivalent in determining fibre orientation. PCA-derived fractional anisotropy and DT relative anisotropy had similar signal-to-noise ratio (SNR) and dependence on fibre shape. PCA-derived mean diffusivity had similar SNR to the respective DT scalar, and it depended on fibre anisotropy. Appropriate scaling of the PCA measures resulted in very good agreement between PCA and DT maps. In conclusion, the assumption of a specific functional model for DW signals is not necessary for characterization of anisotropic diffusion in a single fibre.

A method of generalized projections (MGP) ghost correction algorithm for interleaved EPI

Investigations into the method of generalized projections (MGP) as a ghost correction method for interleaved EPI are described. The technique is image-based and does not require additional reference scans. The algorithm was found to be more effective if a priori knowledge was incorporated to reduce the degrees of freedom, by modeling the ghosting as arising from a small number of phase offsets. In simulations with phase variation between consecutive shots for n-interleaved echo planar imaging (EPI), ghost reduction was achieved for n = 2 only. With no phase variation between shots, ghost reduction was obtained with n up to 16. Incorporating a relaxation parameter was found to improve convergence. Dependence of convergence on the region of support was also investigated. A fully automatic version of the method was developed, using results from the simulations. When tested on in vivo 2-, 16-, and 32-interleaved spin-echo EPI data, the method achieved deghosting and image restoration close to that obtained by both reference scan and odd/even filter correction, although some residual artifacts remained.