Search PubMed⌕ Search

Biomedical subjects

P Scheltens

Publications and source records attributed to P Scheltens.

At least 109 records · Page 6Linked to original sources
PubMed1998

Patterns of lesion development in multiple sclerosis: longitudinal observations with T1-weighted spin-echo and magnetization transfer MR.

PURPOSE: We evaluated the appearance of enhancing multiple sclerosis (MS) lesions on unenhanced T1-weighted MR images and the natural course of enhancing MS lesions on serial unenhanced T1-weighted and magnetization transfer (MT) MR images. METHODS: One hundred twenty-six enhancing lesions were followed up monthly for 6 to 12 months to determine their signal intensity on unenhanced T1-weighted and MT MR images. At the time of initial enhancement, the size of the lesion and the contrast ratio of enhancement were calculated for each enhancing lesion. During follow-up, the contrast ratio on the corresponding unenhanced T1-weighted image was measured, and an MT ratio (MTR) was calculated. RESULTS: Twenty-five enhancing lesions (20%) appeared isointense and 101 lesions (80%) appeared hypointense relative to normal-appearing white matter on unenhanced T1-weighted images. During 6 months of follow-up, four MR patterns of active lesions were detected: initially isointense lesions remained isointense (15%); initially isointense lesions became hypointense (5%, most of which reenhanced); initially hypointense lesions became isointense (44%); and initially hypointense lesions remained hypointense (36%). MTR was significantly lower for hypointense lesions as compared with isointense lesions at the time of initial enhancement. For lesions that changed from hypointense to isointense, MTR increased significantly during 6 months of follow-up. Multiple regression analysis showed that strongly decreased MTR at the time of initial enhancement and enhancement duration of more than one scan were predictive of a hypointense appearance on unenhanced T1-weighted images at 6 months' follow-up. Ring enhancement was found to be the only (weak) predictor of persistently hypointense signal intensity. CONCLUSION: Most enhancing lesions appear slightly to significantly hypointense on unenhanced T1-weighted images. Although most hypointensities are reversible, only those lesions that fail to recover on unenhanced T1-weighted and MT images may have considerable irreversible structural changes.

Adolescent↗
PubMed1997

Visual association encoding activates the medial temporal lobe: a functional magnetic resonance imaging study.

The involvement of structures in the medial temporal lobe during the encoding of visual associations was studied with functional magnetic resonance imaging. In 11 out of 12 normal healthy volunteers this task resulted in activation in posterior portions of the parahippocampal region, close to the collateral sulcus. In seven subjects activation was encountered in the hippocampal formation. The visual association task as adapted for this study may provide a sensitive measure to study anterograde amnesia prevalent in Alzheimer's disease. Therefore, the present paradigm enables the study of individual changes in learning and memory capacities over time.

Adult↗
PubMed1997

rCBF SPECT in Parkinson's disease patients with mental dysfunction.

Functional imaging of the brain using SPECT provides information correlative to the alterations of regional blood flow. In this paper we review the literature pertaining to SPECT in Parkinson's disease with and without dementia and depression. Parkinson's disease itself is not associated with a consistent pattern of cerebral blood flow alterations in the basal ganglia, but reduced parietal blood flow is more often reported. The heterogeneity of blood flow changes possibly reflects the multifactorial pathophysiology of the disease. In demented Parkinson's disease patients frontal hypoperfusion is often found or bilateral temporoparietal deficits, probably indicative of concomitant Alzheimer's disease. The SPECT studies undertaken in depressed patients with and without Parkinson's disease show highly conflicting and inconsistent results, probably due to methodological and diagnostic flaws (especially the inclusion of demented Parkinson patients). Several lines of reasoning point to a prefrontal dysfunction and future SPECT studies are planned to study this region in non-demented Parkinson's disease patients with and without major depression.

Brain↗
PubMed1997

Comparison of four potential MR parameters for severe tissue destruction in multiple sclerosis lesions.

The purpose of this study was, first, to evaluate correlations between four potential magnetic resonance (MR) parameters for severe tissue destruction in multiple sclerosis (MS) lesions. Second, to evaluate the effect of incidental magnetization transfer (MT) effect on hypointense lesions in multislice T1 spin echo (SE) imaging. In 49 lesions, from 10 MS patients, MT ratio (MTR), T1 relaxation time, signal intensity (SI) on T1-weighted SE images normalized to normal-appearing white matter (NAWM), and SI normalized to cerebrospinal fluid (CSF) were measured. Differences in contrast of hypointense lesions were measured between single slice and multislice imaging. MTR correlated significantly (p < .001) with longitudinal relaxation rates (1/T1) (r = 0.84), SI normalized to NAWM (r = 0.78), and SI normalized to CSF (r = 0.75). The degree of reduction in contrast, caused by multislice imaging, correlated significantly with MTR of lesions (r = 0.60, p < .001), leading to reduction of hypointense lesion load (p < .01). We conclude that all four MR markers for severe tissue destruction are highly correlated when applied to selected hypointense lesions on T1-weighted SE images. Due to "incidental" off-resonance excitation, contrast and hypointense lesion load will be reduced in multislice T1-weighted SE images.

Adult↗
PubMed1997

Comparison of MRI criteria at first presentation to predict conversion to clinically definite multiple sclerosis.

We compared MRI criteria used to predict conversion of suspected multiple sclerosis to clinically definite multiple sclerosis. Seventy-four patients with clinically isolated neurological symptoms suggestive of multiple sclerosis were studied with MRI. Logistic regression analysis was used to remove redundant information, and a diagnostic model was built after each MRI parameter was dichotomized according to maximum accuracy using receiver operating characteristic analysis. Clinically definite multiple sclerosis developed in 33 patients (prevalence 45%). The optimum cut-off point (number of lesions) was one for most MRI criteria (including gadolinium-enhancement and juxta-cortical lesions), but three for periventricular lesions, and nine for the total number of T2-lesions. Only gadolinium-enhancement and juxta-cortical lesions provided independent information. A final model which, in addition, included infratentorial and periventricular lesions, had an accuracy of 80%, and having more abnormal criteria, predicted conversion to clinically definite multiple sclerosis strongly. The model performed better than the criteria of Paty et al. (Neurology 1988; 38: 180-5) and of Fazekas et al. (Neurology 1988; 38: 1822-5). We concluded that a four-parameter dichotomized MRI model including gadolinium-enhancement, juxtacortical, infratentorial and periventricular lesions best predicts conversion to clinically definite multiple sclerosis.

False Negative Reactions↗
PubMed1997

The diagnostic value of magnetic resonance imaging and technetium 99m-HMPAO single-photon-emission computed tomography for the diagnosis of Alzheimer disease in a community-dwelling elderly population.

The objective of this study was to assess the diagnostic value for Alzheimer disease (AD) of single-photon-emission computed tomography (SPECT) and magnetic resonance imaging (MRI), separately and in combination. The study was part of a two-stage population-based study of mental functioning among noninstitutionalized 65-to 85-year-olds living in Amsterdam, The Netherlands. Participants (n = 51) were randomly selected within strata of cognitive function to obtain a sample of AD patients (n = 10) and clinically normal subjects (n = 41), of whom 22 displayed some cognitive impairment and fulfilled criteria for "minimal dementia" according to the Cambridge Examination for Mental Disorders of the Elderly. Coronal T1-weighted MRI was used to visualize the medial temporal lobe. Medial temporal lobe atrophy (MTA) was assessed qualitatively on a 0-4 scale. Regional cerebral blood flow on SPECT was assessed with the use of technetium 99m-HMPAO in three manually drawn regions of interest (frontal, parietal, and temporoparietal). Ratios were calculated by using the cerebellum as the reference area. MTA differed significantly between AD patients and clinically normal subjects (p = 0.0009), with sensitivity for AD of 70% and a specificity of 76%. None of the three SPECT ratios differed between normal and AD subjects. The temporoparietal/cerebellar ratio had a sensitivity of 30% and a specificity of 71% as a cutoff of 0.76. When both tests were positive the combined sensitivity was low (20%), but the false-positive rate was also very low (5%). A negative result on MRI or any SPECT ratio yielded a high specificity (93%-98%) but also a high false-negative rate (60-80%). Adding SPECT to MRI seems useful only if a diagnosis of AD is suspected clinically and confirmation is needed. When the clinical probability that AD is absent is high, normal results on either MRI or SPECT may confirm this notion. Given the fact that structural imaging should be performed in a clinical workup for dementia, using MRI only would be the most cost-effective approach.

Aged↗
PubMed1997

Emerging treatments in dementia.

Dementia is one of the most common organic mental syndromes, usually caused by Alzheimer's disease (AD) or vascular dementia (VD) or both. Regarding AD we review the state or the art of the cholinergic approach and discuss some future options regarding preventive and nonsymptomatic strategies. Therapy for VD will consist mainly in influencing and preventing cerebrovascular pathology, because operational criteria for the diagnosis have only recently been proposed and are being discussed widely. One of the crucial problems here lies in the distinction between VD and AD and the recognition that the two disorders may be coexistent more often than assumed; the role of white matter changes seems to be particularly important. The same goes for the recognition that AD ist not a single entity. The question of heterogeneity may be solved when different therapeutic strategies are found for different subtypes. The focus of future plans should be on preventive strategies combined with an early diagnosis.

Alzheimer Disease↗
PubMed1997

Qualitative assessment of cerebral atrophy on MRI: inter- and intra-observer reproducibility in dementia and normal aging.

To assess the reproducibility of a qualitative rating scale of cerebral atrophy on MRI in an aged population of demented and non-demented individuals, 4 raters independently judged cerebral atrophy (CA) in 13 regions on a 0-3 scale on 75 MRI scans, on two occasions. The level of agreement was expressed by kappa statistics as well as by analysis of variance for interexaminer reproducibility studies. The mean CA scores ranged from 13.3 to 21.2, indicating moderately high prevalence of cerebral atrophy in this sample. Complete agreement among observers was reached in 49.7% of the ratings during the first assessment and in 44.1% in the second assessment. The inter-observer agreement was poor in both sessions (mean overall kappas 0.34 and 0.24). The intra-observer agreement was moderate to good for all raters (mean overall kappa: 0.58). The average standard deviation of the differences between CA scores of the 4 raters was 5.12 in the first and 5.13 in the second session. The average standard deviation for the differences within raters was 2.4. We conclude that the assessment of cerebral atrophy using this rating scale on MRI in an aged population has a poor reproducibility among raters. However, it provides regional atrophy measurements and is quite reliable when performed by a single rater.

Aged↗
PubMed1997

Test-retest analysis with functional MR of the activated area in the human visual cortex.

PURPOSE: To investigate the intersubject and intrasubject variability of the activated area in the visual cortex with functional MR imaging. METHODS: Double-section gradient-echo MR images were acquired at 1.5 T in 28 healthy volunteers using the fast low-angle shot (FLASH) technique. Visual stimulation was obtained with light-emitting diode (LED) goggles. Eighteen volunteers were studied twice. The size of the activated areas in the visual cortex and the increase in signal were measured. A reproducibility ratio for size (R[size]) and for location (R[overlap]) was calculated on a scale of 0.0 to 1.0. RESULTS: Activation was seen in 89% of the subjects. The size of the activated area was widely variable among subjects: mean, 460 +/- 284 mm2; range, 0 to 1029 mm2 in the first study in all volunteers. Signal increases ranged from 3.2% to 10.9%, with a mean of 6.6 +/- 1.7%. The mean values of intrasubject variability testing were R(size) = 0.83 +/- 0.16 and R(overlap) = 0.31 +/- 0.11. CONCLUSION: Functional MR imaging with the FLASH technique is useful in identifying certain cortical areas that have quite variable locations among subjects. This study provides reference data for the intrasubject and intersubject variability of the activation pattern of the visual cortex.

Adult↗
PubMed1997

Protocols to demonstrate slowing of Alzheimer disease progression. Position paper from the International Working Group on Harmonization of Dementia Drug Guidelines. The Disease Progression Sub-Group.

Two suggested clinical trial designs for assessing progression of Alzheimer disease are the randomized withdrawal design and the randomized start design. The most promising of these, the randomized start design, has the potential to demonstrate a delay in progression, but there remain problematic design, ethical, and statistical issues to be solved before the protocol can be used in a clinical trial. The development of biological markers of the disease process using neuroimaging or other measures also may provide a robust method of measuring disease progression and demonstrating the biological effect of a drug on the disease process.

Aged↗
PubMed1996

The functional basis of ocular dominance: functional MRI (fMRI) findings.

Changes in cortical metabolism and cerebral perfusion may be recorded non-invasively with functional magnetic resonance imaging (fMRI). In pilot experiments, using fMRI with photic stimulation, we found differences between activated areas when the left or the right eye was stimulated separately. In this study we investigated whether this could be explained by ocular dominance. We studied 26 healthy volunteers (mean age 23.3 +/- 3.5 years). Ocular dominance was determined by means of the near-far alignment test. fMRI-measurements consisted of a double-slice gradient echo sequence. Slices were acquired placed parallel on either side of the calcarine fissure. Visual stimulation was done with goggles with two LED matrices (red light, 8 Hz); each in front of one eye. In each subject, the left and right eye were stimulated separately and together, in a randomly alternating order. Twenty-two subjects showed activation, of whom eight subjects had a dominant left eye and 14 a dominant right eye. In general the size of the activated area was bigger upon stimulation of the dominant eye. The difference with the area upon stimulation of the non-dominant eye was statistically significant in the right eye dominant group. These results indicate that the dominant eye actually activates a larger area of the primary visual cortex than the non-dominant eye. This provides for the first time a functional basis for the concept of ocular dominance.

Adult↗
PubMed1996

Circadian rest-activity rhythm disturbances in Alzheimer's disease.

Previous studies showed circadian rhythm disturbances in patients with Alzheimer's disease. Rest-activity rhythm disturbances manifest themselves through a fragmentation of the rhythm, a weak coupling with Zeitgebers, and high levels of activity during the night. The aim of the present study was to investigate which factors contribute to the presence of these disturbances. Therefore, several rest-activity rhythm, constitutional, and environmental variables were assessed in a heterogeneous group of 34 patients with Alzheimer's disease, including presenile and senile patients living at home or in a nursing home, as well as in 11 healthy controls. Circadian rest-activity rhythm disturbances were most prominent in institutionalized patients. Regression analyses showed the involvement of the following variables. First stability of the rest-activity rhythm is associated with high levels of daytime activity and high levels of environmental light resulting from seasonal effects as well as from indoor illumination. Presenile onset contributed to instability of the rhythm. Second, fragmentation of periods of activity and rest is associated with low levels of daytime activity, and is most prominent in moderately severe dementia. Third, night-time activity level is higher during the times of the year when the days are getting shorter and lower when the days are growing longer. These findings indicate that rest-activity rhythm disturbances may improve by increasing environmental light and daytime activity, an assumption for which empirical evidence has recently been published.

Aged↗
PubMed1996

Inter- and intraobserver reproducibility of cerebral atrophy assessment on MRI scans with hemispheric infarcts.

Cerebral atrophy (CA) in stroke patients is associated with poststroke dementia and may reflect underlying neurodegenerative pathology. Therefore, regional CA may be valuable to study in patients who develop poststroke dementia. The aim of this study was to test the reproducibility of a qualitative rating scale of CA on MRI. MRI scans were performed in 50 consecutive patients (age range 19-81) admitted for an acute hemispheric ischemic stroke. CA was assessed on 2 occasions 24 h apart, on axial T2-weighted sequences by 4 independent observers. We evaluated CA in 13 regions on a 0-3 scale. The sum of the subscores was called the CA score (range: 0-39). The level of agreement was expressed by kappa statistics as well as by analysis of variance for interexaminer reproducibility studies. The mean CA scores ranged from 2.8 to 11.0, indicating the low prevalence of CA in this sample. Complete agreement was reached in 41.7% during the first assessment and in 44.1% in the second assessment. The interobserver agreement was moderate in the first session (mean overall kappa: 0.48) and substantial in the second (mean overall kappa: 0.67). The intraobserver agreement was good for all raters (mean kappa: 0.65). Standardized to the range of the scale, standard deviations of the differences between CA scores of the 4 raters in the 2 sessions were 11.1 and 11.2%; within raters it was 4.4%. We conclude that the assessment of CA using this rating scale is possible in stroke patients. It provides regional atrophy measurements and is reproducible when performed by 1 rater.

Adult↗
PubMed1995

Visual assessment of medial temporal lobe atrophy on magnetic resonance imaging: interobserver reliability.

We conducted an interobserver study to assess agreement on visual rating of medial temporal lobe atrophy on coronal T1-weighted MRI. A total of 100 studies of elderly individuals, using two different MRI techniques (spin echo and inversion recovery sequences), were analysed by four raters (three neurologists and one neuroradiologist) using a five-point rating scale. Complete agreement was found in 37% of the total sample. Interobserver agreement as expressed by kappa values was 0.44 (95% CI = 0.34-0.54) and 0.51 (95% CI = 0.41-0.61) for the two techniques. After dichotomizing medial temporal lobe atrophy into present or absent, a post hoc analysis revealed higher complete agreement (70%), with kappa values of 0.59 (95% CI = 0.51-0.67) and 0.62 (95% CI = 0.48-0.075), for the two techniques (all four raters). From this study we conclude that visual rating of medial temporal lobe atrophy on MRI in the coronal plane yields fair to good agreement among observers. We recommend this type of visual rating for use in clinical settings when a quick judgement on the presence of medial temporal lobe atrophy is needed.

Atrophy↗
PubMed1995

[Morphological imaging in the diagnosis of dementia. II. Vascular dementia].

Magnetic resonance imaging (MRI) and CT-scan are crucial for the diagnosis of cerebrovascular diseases. Multi-infarct dementias may be divided into (i) dementias due to multiple cortical infarcts and (ii) dementias due to multiple lacunar infarcts in the basal ganglia, thalamus and hemispheric white matter, usually associated with leukoaraiosis. A single infarct located in the thalamus or in the left angular gyrus may also induce dementia. Abnormalities of the cerebral white matter, so-called leukoaraiosis, are usually the consequence of a cerebrovascular disease and may be called Binswanger's disease in severe cases. However, leukoaraiosis is not specific of vascular dementia and may also be found in Alzheimer's disease and even in normal aging.

Brain↗