Biomedical subjects

E Achten

Publications and source records attributed to E Achten.

At least 19 recordsLinked to original sources

PubMed2005

Microglial imaging with positron emission tomography and atrophy measurements with magnetic resonance imaging in multiple sclerosis: a correlative study.

OBJECTIVE: The objectives of the present study were to assess brain atrophy in multiple sclerosis (MS) patients during different disease stages and to investigate by PET and [11C]PK11195, a marker of microglial activation, the relationship between inflammation, atrophy and clinically relevant measures. METHODS: Eight healthy subjects and 22 MS patients were included. Semiquantitative [11C]PK11195 uptake values, with normalization on cortical grey matter, were measured for magnetic resonance imaging T2- and T1-lesions and normal appearing white matter (NAWM). As atrophy index we used the ratio of the amount of white and grey matter divided by the ventricular size, using an optimized a priori based segmentation algorithm (SPM99). RESULTS: Atrophy was significantly greater in MS patients compared to age-matched controls. A significant correlation was found between brain atrophy and both disease duration and disability, as measured with the Expanded Disability Status Scale. For NAWM, [11C]PK11195 uptake increased with the amount of atrophy, while T2-lesional [11C]PK11195 uptake values decreased according to increasing brain atrophy. CONCLUSIONS: The present study suggests that brain atrophy, correlating with disease duration and disability, is directly related to NAWM and T2-lesional inflammation as measured by microglial activation.

Adult↗

PubMed2005

Comparison between 1 T MRI and non-MRI based volumetry in inoculated tumours in mice.

Tumour volume is an important therapeutic endpoint for mouse tumour models in the evaluation of new chemotherapeutic drugs and in pre-clinical evaluation of new radioimmunotherapy pharmaceuticals. In this study, two 1 T MRI-based methods both using T1-T2 hybrid weighting, a manual method (determination of the area per slice) and a semi-automated method (using thresholding), are compared with two classical methods, the abovementioned calliper method and volumetry by water displacement after dissection of the tumour. Interoperator and intraoperator differences for both MRI-based methods were good (no differences p<0.05 using a repeated measures analysis of variance (ANOVA) test). Correlation between the different methods was excellent. No significant differences were obtained (p<0.05), except for the semi-automated method, because it automatically excludes necrotic regions from the tumour. Therefore, we conclude that both manual and semi-automated tumour volumetry in subcutaneous tumour bearing athymic mice by low-field MRI are accurate and reliable methods. The semi-automated method is especially useful for larger tumour volumes, since it accounts for necrotic areas within the tumour.

Animals↗

PubMed2004

MRI language dominance assessment in epilepsy patients at 1.0 T: region of interest analysis and comparison with intracarotid amytal testing.

The primary goal of this study was to test the reliability of presurgical language lateralization in epilepsy patients with functional magnetic resonance imaging (fMRI) with a 1.0-T MR scanner using a simple word generation paradigm and conventional equipment. In addition, hemispherical fMRI language lateralization analysis and region of interest (ROI) analysis in the frontal and temporo-parietal regions were compared with the intracarotid amytal test (IAT). Twenty epilepsy patients under presurgical evaluation were prospectively examined by both fMRI and IAT. The fMRI experiment consisted of a word chain task (WCT) using the conventional headphone set and a sparse sequence. In 17 of the 20 patients, data were available for comparison between the two procedures. Fifteen of these 17 patients were categorized as left hemispheric dominant, and 2 patients demonstrated bilateral language representation by both fMRI and IAT. The highest reliability for lateralization was obtained using frontal ROI analysis. Hemispherical analysis was less powerful and reliable in all cases but one, while temporo-parietal ROI analysis was unreliable as a stand-alone analysis when compared with IAT. The effect of statistical threshold on language lateralization prompted for the use of t-value-dependent lateralization index plots. This study illustrates that fMRI-determined language lateralization can be performed reliably in a clinical MR setting operating at a low field strength of 1 T without expensive stimulus presentation systems.

Adolescent↗

PubMed2004

Validation and application of polymer gel dosimetry for the dose verification of an intensity-modulated arc therapy (IMAT) treatment.

Polymer gel dosimetry was used to assess an intensity-modulated arc therapy (IMAT) treatment for whole abdominopelvic radiotherapy. Prior to the actual dosimetry experiment, a uniformity study on an unirradiated anthropomorphic phantom was carried out. A correction was performed to minimize deviations in the R2 maps due to radiofrequency non-uniformities. In addition, compensation strategies were implemented to limit R2 deviations caused by temperature drift during scanning. Inter- and intra-slice R2 deviations in the phantom were thereby significantly reduced. This was verified in an investigative study where the same phantom was irradiated with two rectangular superimposed beams: structural deviations between gel measurements and computational results remained below 3% outside high dose gradient regions; the spatial shift in those regions was within 2.5 mm. When comparing gel measurements with computational results for the IMAT treatment, dose deviations were noted in the liver and right kidney, but the dose-volume constraints were met. Root-mean-square differences between both dose distributions were within 5% with spatial deviations not more than 2.5 mm. Dose fluctuations due to gantry angle discretization in the dose computation algorithm were particularly noticeable in the low-dose region.

Algorithms↗

PubMed2004

Does egocentric mental rotation elicit sex differences?

Mental rotation tests traditionally show a male performance advantage. Some neuroimaging studies have reported sex-specific cortical activation patterns during mental rotation. However, these experiments used abstract stimuli and some studies did not systematically exclude performance as a confounding variable. The mental rotation of hands and hand-related objects, compared to abstract objects, is known to evoke an egocentric motor strategy. In this study, we used fMRI to explore potential gender-specific cortical activation patterns for the mental rotation of hands and tools in a sample with an adequate and equal performance for men and women. We found a common neural substrate for men and women comprising superior parietal lobe, dorsolateral premotor cortex, and extrastriate occipital areas, compatible with an egocentric motor strategy for the mental rotation of hands and tools. Sex differences were modest and limited to the mental rotation of hands. Women recruited more left ventral premotor cortex, which could imply that women rely more on imitation or use more perceptual comparisons. Men, on the other hand, drafted more the lingual gyrus, possibly referring to more extensive semantic or early visual processing. We conclude that men and women use a very similar motor strategy during egocentric mental rotation with a potential gender-specific accent.

Adult↗

PubMed2003

Usefulness of language and memory testing during intracarotid amobarbital testing: observations from an fMRI study.

BACKGROUND: Several procedures for testing language lateralization and memory function exist during the intracarotid amobarbital test (IAT). The use of functional magnetic resonance imaging (fMRI) gives the opportunity to assess the validity of some of these procedures, or at least to inspect the neuronal correlates. A comprehensive fMRI protocol was tested, aimed at addressing aspects of lateralization of language, as well as testing memory in relation to activation of mesiotemporal regions. Here we report observations with possible consequences for the current IAT procedures. MATERIALS AND METHODS: The protocol consisted of three language tasks (overt naming, semantic decision and silent word generation) and two memory tasks (encoding and retrieving visual scenes). The paradigms used a block-related procedure in nine right-handed normal volunteers. During the procedure dynamic weighted full brain images were acquired which are sensitive to the blood oxygenation activation effect. RESULTS: Encoding showed symmetrical bilateral activation in the mesiotemporal regions, specifically the hippocampus, parahippocampal gyrus and fusiform gyrus. With a retrieval task activation of the mesiotemporal areas was restricted to the posterior hippocampal area. Overt object naming showed results, similar to encoding tasks with bilateral activation of hippocampal areas. Silent word generation showed much stronger ability to lateralize than the other two language-related tasks and especially object naming. CONCLUSION: Activation revealed by fMRI activation shows that IAT procedures, using active semantic language processing or comprehensive procedures with multiple language tasks have the highest guarantee for individual activation lateralization. Simple object naming does not guarantee a lateralized language fMRI activation pattern. Of the different memory procedures during IAT, the procedures (Interview and the Montreal) demanding encoding processing will be related to larger areas of bilateral hippocampal activation than procedures (Seattle) exclusively requiring retrieval. Moreover, tasks using recognition of previously presented language items (naming objects) are equally effective for assessing hippocampal activation compared with presenting separate memory items.

Adult↗

PubMed2003

PET visualization of microglia in multiple sclerosis patients using [11C]PK11195.

Activated microglia are involved in the immune response of multiple sclerosis (MS). The peripheral benzodiazepine receptor (PBR) is expressed on microglia and up-regulated after neuronal injury. [11C]PK11195 is a positron emission tomography (PET) radioligand for the PBR. The objective of the present study was to investigate [11C]PK11195 imaging in MS patients and its additional value over magnetic resonance imaging (MRI) concerning the immuno-pathophysiological process. Seven healthy and 22 MS subjects were included. Semiquantitative [11C]PK11195 uptake values were assessed with normalization on cortical grey matter. Uptake in Gadolinium-lesions was significantly increased compared with normal white matter. Uptake in T2-lesions was generally decreased, suggesting a PBR down-regulation. However, uptake values increased whenever a clinical or MR-relapse was present, suggestive for a dynamic process with a transient PBR up-regulation. During disease progression, an increase of normal-appearing white matter (NAWM) uptake was found, propagating NAWM as the possible real burden of disease. In conclusion, [11C]PK11195 and PET are able to demonstrate inflammatory processes with microglial involvement in MS.

Adult↗

PubMed2003

A pure sensorimotor stroke due to cervical vertebral artery occlusion.

We reviewed the case history of a 45 year-old women, who presented a pure right sensorimotor stroke, due to a left paramedial medullary infarct as result of a left cervical vertebral artery occlusion. The unusual location of the infarct could be explained by the combination of an anatomical variant of the left branch of the anterior spinal artery and the presence of a deep cervical artery, issued from the costo-cervical trunck. This collateral circulation allowed that the lateral and upper medulla was not infarcted.

Angiography↗

PubMed2002

Developing a comprehensive presurgical functional MRI protocol for patients with intractable temporal lobe epilepsy: a pilot study.

Our aim was to put together and test a comprehensive functional MRI (fMRI) protocol which could compete with the intracarotid amytal (IAT) or Wada test for the localisation of language and memory function in patients with intractable temporal lobe epilepsy. The protocol was designed to be performed in under 1 h on a standard 1.5 tesla imager. We used five paradigms to test nine healthy right-handed subjects: complex scene-encoding, picture-naming, reading, word-generation and semantic-decision tasks. The combination of these tasks generated two activation maps related to memory in the mesial temporal lobes, and three language-related maps of activation in a major part of the known language network. The functional maps from the encoding and naming tasks showed typical and symmetrical posterior mesial temporal lobe activation related to memory in all subjects. Only four of nine subjects also showed symmetrical anterior hippocampal activation. Language lateralisation was best with the word generation and reading paradigms and proved possible in all subjects. The reading paradigm enables localisation of language function in the left anterior temporal pole and middle temporal gyrus, areas typically resected during epilepsy surgery. The combined results of this comprehensive f MRI protocol are adequate for a comparative study with the IAT in patients with epilepsy being assessed for surgery.

Adult↗

PubMed2001

T1 relaxation times for viability evaluation of the engrafted and the native liver in a rat model of heterotopic auxiliary liver transplantation: a pilot study.

Following a heterotopic auxiliary liver transplantation, commonly used measurements are either invasive or non-indicative of individual viability of the coexisting engrafted and native livers. Magnetic resonance imaging (MRI) was therefore tested for its potential to monitor the post-transplant hepatic viability in a rat model. Thirteen Wistar rats were systematically evaluated with MRI and serum biochemical liver parameters. Post-transplant complications and the causes of animal death were identified by autopsy and histo-pathological examinations. The data of the healthy survivors were compared with those of the rats that developed complications. On MRI, the hepatic complications could be depicted in the individual livers. A specific pattern of signal evolution was found in the livers of the healthy survivors: the mean T1 relaxation times of the engrafted livers increased immediately after transplantation (476 +/- 64 ms, mean +/- standard deviation, pre-operative; 730 +/- 48 ms, week 1) and then declined steadily to a 3 month value of 489 +/- 246 ms, while, following a transient first rise (476 +/- 64 ms, pre-operative; 589 +/- 28 ms, week 1), the mean T1 value of the native livers increased again 4 weeks after surgery and reached a 3 month value of 859 +/- 43 ms. However, in the rats with various complications, the mean T1 relaxation times of the engrafted livers continued to increase throughout the first post-operative month (760 +/- 48 ms, week 1; 922 +/- 76 ms, week 4), while that of the native liver only varied mildly (546 +/- 25 ms, week 1; 473 +/- 25 ms, week 4). After the first post-transplant week, the healthy engrafted livers could already be distinguished from those with complications by a significant decrease in T1 relaxation times. These data suggest that, besides demonstrating major complications, MRI may allow one to monitor the viability of each liver by analysing the relative signal intensity and T1 relaxation times after a heterotopic auxiliary liver transplantation.

Alanine Transaminase↗

PubMed2001

99mTc-ECD brain perfusion SPET: variability, asymmetry and effects of age and gender in healthy adults.

Reliable and high-resolution reference data for regional cerebral blood flow measured with single-photon emission tomography (SPET) are necessary for optimal clinical and research use. Therefore, a large dataset of normal technetium-99m labelled ethylene cysteine dimer (ECD) perfusion SPET in carefully screened healthy volunteers with an age range spanning six decades was created, with correction for non-uniform attenuation and scatter and based on an anatomically standardised analysis. Eighty-nine healthy volunteers, stratified for gender (46 females, 43 males; age 20-81 years), were included. Twelve volunteers underwent repeated 99mTc-ECD SPET after 2.5+/-2.3 weeks. An automated whole-brain volume of interest analysis with MANOVA as well as voxelwise analysis using SPM99 was conducted. Average intersubject variability was 4.8% while intrasubject reproducibility was 3.0%. An age-related decline in tracer uptake was found in the anterior cingulate gyrus, bilateral basal ganglia, left prefrontal, left lateral frontal and left superior temporal and insular cortex (all P=0.001-0.02). There was an overall increase in right/left asymmetry with age, which was most pronounced in the frontal and temporal neocortex. The most significant correlations between AI and age decade were found in the prefrontal (R=0.35, P=0.001) and superior temporal neocortex (R=0.43, P<0.001). Women had significantly higher uptake in the right parietal cortex (P<0.001), while men showed higher uptake in the cerebellum and the left anterior temporal and orbitofrontal cortex (all P<0.01). This normative dataset allows age- and gender-specific patient and group assessment of 99mTc-ECD perfusion SPET under a wide variety of clinical circumstances in relation to normal variations and highlights the importance of both age- and gender-specific normal datasets for optimal analysis sensitivity.

Adult↗

PubMed2001

MR spectroscopy detection of lactate and lipid signals in the brains of healthy elderly people.

Magnetic resonance spectroscopy was used to assess the presence of brain lactate and lipid signals, frequently associated with the presence of pathology, in healthy persons of 60-90 years old (n = 540). Lactate and lipid signals were observed in, respectively, 25 and 6% of women, and 18 and 2% of men. Upon adjustment for age, and for MRI-detected cerebral atrophy and white matter lesions, the gender differences in lactate and lipid remained the same (p = 0.05 and p = 0.03, respectively). Brain lactate and lipid signals appear to be intrinsic to aging. However, the presence of these metabolites in very focal areas only, rather than in any distributed fashion within the brain (the latter generally the case with cerebral atrophy and white matter lesions), strongly suggests the existence of asymptomatic focal pathology not shown on MRI.

Aged↗

PubMed2001

Relationship between periventricular or deep white matter lesions and arterial elasticity indices in very old people.

OBJECTIVE: To examine the relationship between the presence of cerebral white matter lesions and large and small artery elasticity indices in a population of healthy, very old subjects. METHODS: We studied 24 subjects (14 women, 10 men) with a mean age of 84+/-5 years, who were free from overt neurological, cardiovascular or psychiatric illness. We measured blood pressure and heart rate in supine and standing positions. Elasticity indices of the large arteries (C1) and small arteries (C2) were derived from radial artery pulse waves. Each subject had multi-slice spin-echo cerebral magnetic resonance imaging. The severity of white matter lesions was graded as 0, 1 or 2. RESULTS: Cerebral white matter lesions on magnetic resonance imaging were common in very old apparently healthy subjects: grade 0 (n=4, C1=2.68+/-1.80 ml/mmHg and C2=0.045+/-0.017 ml/mmHg), grade 1 (n=7, C1=2.13+/-0.36 ml/mmHg and C2=0.040+/-0.016 ml/mmHg) and grade 2 (n=13, C1=1.12+/-0.36 ml/mmHg and C2=0.018+/-0.003 ml/mmHg). There was no significant association between elasticity indices and blood pressure. CONCLUSION: In very old, apparently healthy subjects, both large and small artery elasticity indices were inversely related to the severity of cerebral white matter lesions on magnetic resonance imaging.

Aged↗

PubMed2001

Human brain chemical shift imaging at age 60 to 90: analysis of the causes of the observed sex differences in brain metabolites.

RATIONALE AND OBJECTIVES: To assess whether differences in cerebral atrophy and white matter lesions or in the presence of lactate and lipid signals can explain the observed differences in brain choline, creatine, and N-acetylaspartate levels between healthy elderly women and men. METHODS: In addition to standard magnetic resonance imaging of the brain, an 8 x 8 x 2-cm3 supraventricular transverse brain volume parallel to the canthomeatal line was examined by magnetic resonance spectroscopy (automated 1H chemical shift imaging) in 540 healthy elderly persons. RESULTS: At P = 0.01, 0.001, and 0.0001, choline differed between women and men in 14, 9, and 5 of 36 voxels, respectively. On correction for cerebral atrophy (more frequent in men than in women), white matter lesions (more frequent in women), and lactate and lipid (more frequent in women), the differences in choline were reduced to 13, 6, and 3. Sex differences for creatine and N-acetylaspartate were similar but less numerous after correction. CONCLUSIONS: Elderly women and men in the general population show differences in the levels of creatine, N-acetylaspartate, and especially choline in portions of the brain. The sex-related differences in brain metabolite levels cannot be explained by differences in cerebral atrophy or other aging-related phenomena (white matter lesions, lactate, lipid).

Aged↗

PubMed2001

57Co SPECT, 99mTc-ECD SPECT, MRI and neuropsychological testing in senile dementia of the Alzheimer type.

Inflammatory mechanisms contribute to the pathophysiology of senile dementia of the Alzheimer type (sDAT). Previous studies have shown that 57Co single photon emission computed tomography (SPECT) is able to visualize inflammatory lesions, probably by means of the final common pathway of Ca2+ homeostasis disturbance in both neuronal degeneration and inflammation. The aims of this study were: (1) to detect 57Co SPECT changes in sDAT patients; (2) to correlate these findings with those of conventional neuroimaging techniques and neuropsychological testing (NPT); and (3) to compare 57Co SPECT findings in sDAT patients with those in other types of dementia. Six patients suffering from probable sDAT were included and compared with four patients suffering from other types of dementia. All patients had a magnetic resonance imaging (MRI) scan, NPT, 57Co and 99mTc-ethyl cysteinate dimer (ECD) SPECT scan. Perfusion SPECT images were semiquantitatively evaluated by comparison with an age-matched normal database, while 57Co SPECT scans were assessed qualitatively. MRI and 99mTc-ECD SPECT scans yielded conclusive results with regard to the exclusion of other pathologies and the confirmation of the diagnosis. Using visual analysis, 57Co SPECT scans were unable to show any regional raised uptake, irrespective of the disorder, depth or extent of the perfusion defects, presence of atrophy on MRI or the results of NPT.

Aged↗

PubMed2001

Prevalence of cerebral white matter lesions in elderly people: a population based magnetic resonance imaging study. The Rotterdam Scan Study.

OBJECTIVE: White matter lesions are often seen on MR scans of elderly non-demented and demented people. They are attributed to degenerative changes of small vessels and are implicated in the pathogenesis of cognitive decline and dementia. There is evidence that especially periventricular white matter lesions are related to cognitive decline, whereas subcortical white matter lesions may be related to late onset depression. The frequency distribution of subcortical and periventricular white matter lesions according to age and sex reported. METHODS: A total of 1077 subjects aged between 60-90 years were randomly sampled from the general population. All subjects underwent 1.5T MR scanning; white matter lesions were rated separately for the subcortical region and the periventricular region. RESULTS: Of all subjects 8% were completely free of subcortical white matter lesions, 20% had no periventricular white matter lesions, and 5% had no white matter lesions in either of these locations. The proportion with white matter lesions increased with age, similarly for men and women. Women tended to have more subcortical white matter lesions than men (total volume 1.45 ml v 1. 29 ml; p=0.33), mainly caused by marked differences in the frontal white matter lesion volume (0.89 ml v 0.70 ml; p=0.08). Periventricular white matter lesions were also more frequent among women than men (mean grade 2.5 v 2.3; p=0.07). Also severe degrees of subcortical white matter lesions were more common in women than in men (OR 1.1; 95% confidence interval (95% CI) 0.8-1.5) and periventricular white matter lesions (OR 1.2; 95% CI 0.9-1.7), albeit that none of these findings were statistically significant. CONCLUSIONS: The prevalence and the degree of cerebral white matter lesions increased with age. Women tended to have a higher degree of white matter lesions than men. This may underlie the finding of a higher incidence of dementia in women than in men, particularly at later age.

Aged↗

PubMed2000

Validation of MR-based polymer gel dosimetry as a preclinical three-dimensional verification tool in conformal radiotherapy.

The aim of this work was to investigate MR-based polymer gel dosimetry as a three-dimensional (3D) dosimetry technique in conformal radiotherapy. A cylindrical container filled with polymer gel was placed in a water-filled torso phantom to verify a treatment plan for the conformal irradiation of a mediastinal tumor located near the esophagus. Magnetic resonance spin-spin relaxation rate images were acquired and, after calibration, converted to absorbed dose distributions. The dose maps were compared with dose distributions measured using radiographic film. The average root-mean-square structural deviation, for the complete dose distribution, amounted to less than 3% between gel and film dose maps. It may be expected that MR gel dosimetry will become a valuable tool in the verification of 3D dose distributions. The influence of imaging artifacts arising from eddy currents, temperature drift during scanning, and B1 field inhomogeneity on the dose maps was taken into account and minimized.

Acrylamide↗

PubMed2000

An investigation of the chemical stability of a monomer/polymer gel dosimeter.

The aim of this work is to investigate the temporal stability of a polyacrylamide gelatin hydrogel used for 3D monomer/polymer gel dosimetry techniques involving different methods of analysis. Long-term instabilities for a similar gel have recently been reported, but differ markedly from those described in this work. Two kinds of long-term instabilities are described. One affects the slope of the dose-R2 plot and is related to post-irradiation polymerization of the comonomer/polymer aggregates. It is observed that post-irradiation polymerization only lasts 12 hours after irradiation. The other instability affects the intercept of the dose-R2 plot, lasts for up to 30 days and is related to the gelation process of gelatin. Further studies were performed on gelatin gels of varying compositions to obtain a better understanding of the molecular mechanism that causes the instability due to gelation. The studies included observations of the spin-spin and spin-lattice relaxation rates in combination with diffusion measurements and optical measurements. It is shown that the heating history during the manufacture of the gel affects the absolute R2 value of the gel but not its variation. The findings presented in this study may help in producing more stable and reproducible monomer/polymer gel dosimeters.

Dose-Response Relationship, Radiation↗