Biomedical subjects

I D Wilkinson

Publications and source records attributed to I D Wilkinson.

At least 19 recordsLinked to original sources

PubMed2007

Proton spectroscopy and imaging at 3T in ataxia-telangiectasia.

BACKGROUND AND PURPOSE: Ataxia-telangiectasia (A-T) is an autosomal recessive disorder with characteristic neurodegeneration of the cerebellum. We used MR spectroscopy to test the hypothesis that cerebellar metabolism in A-T patients would be abnormal relative to healthy controls. METHODS: Twelve adults with A-T and 12 healthy control subjects underwent MR imaging and long-echo time (1)H-MR spectroscopy at 3T. Voxels were acquired in the region of the dentate nucleus of the cerebellum and in parietooccipital white matter, and ratios for N-acetylaspartate (NAA), choline (Cho), and creatine (Cr) were calculated. RESULTS: All of the A-T patients showed marked cerebellar atrophy of the vermis and hemispheres. Two patients showed multiple small foci of hypointensity on T2*-weighted images throughout their brain suggestive of capillary telangiectasia. A further 2 patients had single low-signal-intensity foci. One patient had a tumor, thought to be meningioma radiologically, that was not suspected clinically. No group differences were found in the cerebral spectra, but analysis of the cerebellum revealed significantly lower NAA/Cho and higher Cho/Cr ratios in the A-T patients compared with the controls. There was no difference between groups for the NAA/Cr ratio. CONCLUSION: The findings suggest increased Cho signal intensity in the cerebellum of adult A-T patients. If this finding is shown through the course of the disease, it may assist in the differentiation of early A-T from other forms of ataxia and provide a marker for monitoring treatment efficacy.

Adult↗

PubMed2006

Stereotactic radiosurgery for brain arteriovenous malformations: quantitative MR assessment of nidal response at 1 year and angiographic factors predicting early obliteration.

INTRODUCTION: We investigated the role of magnetic resonance angiography (MRA) in the early follow-up of patients after stereotactic radiosurgery (STRS) for cerebral arteriovenous malformations (AVMs) and determined the influence of individual morphological factors of AVMs in early response to treatment. METHODS: A group of 40 patients (41 AVMs) consented to a dedicated 1.5-T MR protocol 12 months after receiving STRS for a brain AVM. In addition to standard spin echo sequences, 3-D contrast-enhanced sliding interleaved Ky MRA (CE-SLINKY) and dynamic time-resolved subtraction angiography (MR-DSA) were performed. Nidal volumes were calculated using CE-SLINKY data in patients with a persisting arteriovenous shunt. Planning angiographic data was investigated in all 40 patients. The following AVM factors were used in the statistical analysis to determine their role in nidus obliteration: (1) maximum linear dimension, (2) nidal volume, (3) AVM location (4) nidal morphology, (5) venous drainage, (6) "high-flow angiographic change", (7) prior embolization, and (8) dose reduction. RESULTS: Complete nidal obliteration was found in 9 patients, 26 showed greater than 50% nidal reduction and 6 had less than 50%. Two AVM factors, venous drainage and AVM location, were found to significantly correlate with rate of obliteration. CONCLUSION: We successfully demonstrated the use of MRA to quantitatively assess the response of AVMs to STRS. Two AVM factors, venous drainage and AVM location were found to correlate with rate of obliteration prior to the application of the Bonferroni correction, but if this more rigorous statistical test was applied then none of the factors was found to be significant.

Adolescent↗

PubMed2006

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.

Adult↗

PubMed2006

Misrepresentation of surface rendering of pediatric brain malformations performed following spatial normalization.

PURPOSE: To evaluate the effects of spatial normalization on volume rendering in cases of pediatric brain malformation. MATERIAL AND METHODS: Three-dimensional (3D) T1-weighted volume datasets were acquired in three children, one with pachygyria, one with a Dandy-Walker malformation associated with polymicrogyria, and one with dysgenesis of the corpus callosum. On the non-normalized datasets, the skull margins were cropped and the remainder stripped with the brain extraction technique (BET). The data were also normalized into standard anatomic reference space using pediatric templates prior to the BET script. The surface constructions obtained by both techniques were then compared for geometric distortions. RESULTS: Normalization of 3D datasets resulted in significant distortions in the shape of the brain, with increased anterior-posterior dimensions and narrower transverse diameter in all three cases. In two cases, there were alterations in the appearance of the gyri and sulci, leading to a potential misinterpretation of the volume-rendered surface when the gyri and sulci were in fact normal. CONCLUSION: In pediatric brain, particularly those with congenital brain anomalies, normalization as a post-processing step should be avoided as this may lead to misrepresentation of brain morphometry.

Diagnostic Errors↗

PubMed2006

Sequential dynamic gadolinium magnetic resonance perfusion-weighted imaging: effects on transit time and cerebral blood volume measurements.

PURPOSE: To evaluate if two gadolinium perfusion studies can be performed during the same table occupancy without degradation of the derived data in the second study. MATERIAL AND METHODS: Magnetic resonance (MR) perfusion studies of the whole brain were performed on 12 patients during the administration of two gadolinium boluses separated by 8 min. In six patients, gadolinium was given as two 20-ml administrations of standard 0.5 M chelate (Magnevist), whilst the other six patients received two 10-ml administrations of 1.0 M chelate (Gadovist). RESULTS: There were no significant differences in subjective quality between the time-intensity curves of the first and second perfusion studies using either the 0.5 M or 1.0 M gadolinium chelate. The objective measurements in quality of the time-intensity curves (maximum signal change and full width at half maximum) changed by less than 5% of the original values on the second perfusion study. The first-moment mean transit times did not change significantly on the sequential studies. The regional cerebral blood volume tended to increase on the second study (by 15% on average), but this did not reach statistical significance. CONCLUSION: The results from two sequential dynamic gadolinium-based perfusion studies can be compared in a meaningful manner using the technique described.

Aged↗

PubMed2005

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.

Acoustic Stimulation↗

PubMed2005

Brain arteriovenous malformations: measurement of nidal volume using a combination of static and dynamic magnetic resonance angiography techniques.

Arteriovenous malformations of the brain are complex vascular lesions that are an important cause of death and long-term disability. Currently, catheter angiography (CA) is the reference standard procedure for the diagnosis and follow-up of treated arteriovenous malformations (AVMs). This is an invasive procedure with potential risks. Magnetic resonance angiography (MRA) is commonly used in neurovascular imaging as a non-invasive alternative. Various MRA techniques have been used in the diagnosis and follow-up of AVMs but these have suffered from lack of temporal or spatial resolution. In this 60-patient study we describe the combination of two techniques: dynamic magnetic resonance digital subtraction angiography with a high temporal resolution, and a non-dynamic contrast-enhanced time-of-flight sequence with a high spatial resolution technique, in the assessment of AVM. The results showed an excellent correlation between MRA and CA measurement of both maximum linear dimension and AVM nidus volume.

Adult↗

PubMed2005

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.

Adolescent↗

PubMed2005

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.

Aged↗

PubMed2005

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.

Adult↗

PubMed2005

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.

Adult↗

PubMed2005

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.

Adult↗

PubMed2004

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.

Adult↗

PubMed2004

MR imaging and spectroscopy in Lhermitte-Duclos disease.

Lhermitte-Duclos disease is a rare abnormality occurring in the cerebellum with only 130 cases reported in the literature. There is debate as to whether this abnormality is a hamartoma, a malformation or a tumour. In this case report we discuss the spectroscopy findings from two patients presenting with this disease. The patients, one 40-year-old Caucasian woman with a 6-year history of headaches, unsteady gait and falls, deterioration in vision and another 28-year-old Caucasian man with a 1-year history of headaches and a previous history of a transient stroke, were found to have this lesion in the cerebellum. Proton spectroscopic data were obtained using a single-voxel PRESS technique (TE=135 ms, TR=1600 ms), from the region of the abnormality. The results were expressed as ratios under the three prominent resonances representing choline (Cho), creatine (Cr), and N-acetyl (NA) moieties. The metabolite ratios were compared to normative data. The two cases demonstrated reduced ratios in NA/Cho and NA/Cr in relation to the controls. The ratios of Cho/Cr appeared closer to the normal mean ratio. There were peaks attributable to lactate in both cases. The low NA/Cr and NA/Cho ratios could be due to the apparent lack of neuronal architecture and the presence of embryonic neural tissue, which does not express NA, indicating more favourably towards a 'benign' hamartoma rather than a tumour.

Adult↗

PubMed2004

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.

Adult↗

PubMed2004

Differential growth rates of the cerebellum and posterior fossa assessed by post mortem magnetic resonance imaging of the fetus: implications for the pathogenesis of the chiari 2 deformity.

PURPOSE: To evaluate post mortem magnetic resonance imaging of the fetus to provide data on the rate of growth of the cerebellum, bony posterior fossa, supratentorial bony compartment and cerebrum. MATERIAL AND METHODS: Twenty fetuses subsequently shown to have normal brain and spines on autopsy were studied using MRI post mortem. MRI from 20 normal pediatric brain examinations in children aged 6 years or younger were studied for comparison. Post mortem MRI was performed using a high-resolution fast spin echo technique providing T2 weighted images. The area of the cerebellar vermis, posterior fossa, supratentorial skull cavity and cerebral hemispheres was measured in the sagittal plane in all cases. These measurements were compared over the age ranges studied. RESULTS: We have shown that there are differences in the rate of growth and the apparent commencement of growth between the structures under study. The cerebellum appeared to start its significant growth at 16.5 weeks with a rate of 16 mm2/week throughout pregnancy, while the cerebral hemisphere appeared to commence significant growth at 13 weeks at a rate of 184 mm2/week throughout pregnancy. This is in contrast to the bony posterior fossa, whose growth paralleled the supratentorial bony compartment at all ages studied. CONCLUSION: We interpret our findings as showing relatively late commencement of cerebellar growth compared to the cerebral hemispheres, whereas the growth of the bony posterior fossa appears to be in advance and independent of cerebellar growth. Our results support the hypothesis that posterior fossa development depends on raised hydrostatic pressure in the CSF containing structures of the posterior fossa. When this mechanism fails, as in some cases of myelomeningocoele, a small posterior fossa is formed which characterizes the Chiari 2 malformation.

Arnold-Chiari Malformation↗

PubMed2004

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.

Algorithms↗

PubMed2004

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.

Brain↗