First human case of tick-borne encephalitis virus infection acquired in the Netherlands, July 2016.

In July 2016, the first autochthonous case of tick-borne encephalitis was diagnosed in the Netherlands, five days after a report that tick-borne encephalitis virus (TBEV) had been found in Dutch ticks. A person in their 60s without recent travel history suffered from neurological symptoms after a tick bite. TBEV serology was positive and the tick was positive in TBEV qRT-PCR. TBEV infection should be considered in patients with compatible symptoms in the Netherlands.

Image-derived input functions for PET brain studies.

PURPOSE: To assess the robustness of a previously introduced method to obtain accurate image-derived input functions (IDIF) for three other tracers. METHODS: Dynamic PET and online blood data of five repeat [(11)C]PIB (Pittsburgh Compound-B) ([(11)C]PIB), six repeat (R)-[(11)C]verapamil, and ten single (R)-[(11)C]PK11195 studies were used. IDIFs were extracted from partial volume corrected scans using the four hottest pixels per plane method. Results obtained with IDIFs were compared with those using standard online measured arterial input functions (BSIF). IDIFs were used both with and without calibration based on manual blood samples. RESULTS: For (R)-[(11)C]verapamil, accurate IDIFs were obtained using noncalibrated IDIFs (slope 0.96+/-0.17; R (2) 0.92+/-0.07). However, calibration was necessary to obtain IDIFs comparable to the BSIF for both [(11)C]PIB (slope 1.04+/-0.05; R (2) 1.00+/-0.01) and (R)-[(11)C]PK11195 (slope 0.96+/-0.05; R (2) 0.99+/-0.01). The need for calibration may be explained by the sticking property of both tracers, indicating that BSIF may be affected by sticking and therefore may be unreliable. CONCLUSION: The present study shows that a previously proposed method to extract IDIFs is suitable for analysing [(11)C]PIB, (R)-[(11)C]verapamil and (R)-[(11)C]PK11195 studies, thereby obviating the need for online arterial sampling.

Impact of wavelet based denoising of [11C](R)-PK11195 time activity curves on accuracy and precision of kinetic analysis.

The purpose of the present study was to investigate the use of various wavelets based techniques for denoising of [11C](R)-PK11195 time activity curves (TACs) in order to improve accuracy and precision of PET kinetic parameters, such as volume of distribution (V(T)) and distribution volume ratio with reference region (DVR). Simulated and clinical TACs were filtered using two different categories of wavelet filters: (1) wave shrinking thresholds using a constant or a newly developed time varying threshold and (2) "statistical" filters, which filter extreme wavelet coefficients using a set of "calibration" TACs. PET pharmacokinetic parameters were estimated using linear models (plasma Logan and reference Logan analyses). For simulated noisy TACs, optimized wavelet based filters improved the residual sum of squared errors with the original noise free TACs. Furthermore, both clinical results and simulations were in agreement. Plasma Logan V(T) values increased after filtering, but no differences were seen in reference Logan DVR values. This increase in plasma Logan V(T) suggests a reduction of noise induced bias by wavelet based denoising, as was seen in the simulations. Wavelet denoising of TACs for [11C](R)-PK11195 PET studies is therefore useful when parametric Logan based V(T) is the parameter of interest.

Serum amyloid p component as a biomarker in mild cognitive impairment and Alzheimer's disease.

BACKGROUND: Serum amyloid P component (SAP), present in amyloid-beta (Abeta) plaques in Alzheimer's disease (AD), may protect Abeta deposits against proteolysis, thereby promoting plaque formation. The aim was to investigate if SAP levels in cerebrospinal fluid (CSF) and serum can be used to discriminate controls, AD and mild cognitive impairment (MCI) patients, and to identify incipient AD among MCI patients. METHODS: SAP levels in CSF and serum were determined in 30 controls, 67 MCI and 144 AD patients. At follow-up, 39 MCI patients had progressed to dementia, while 25 had remained stable (mean follow-up time: 2.6 +/- 1.0 and 2.1 +/- 0.8 years). RESULTS: Cross-sectionally no differences were found in SAP levels in CSF and serum between the groups. MCI patients that had progressed to dementia at follow-up had lower CSF SAP levels (13 microgram/l, range 3.3-199.3 microgram/l) than MCI nonprogressors (20.2 microgram/l, range 7.0-127.7 microgram/l; p < 0.05) [corrected]. A low CSF SAP level was associated with a 2-fold increased risk of progression to AD (hazard ratio = 2.2; 95% confidence interval = 0.9-5.4). CONCLUSION: Our data suggest that measurement of CSF SAP levels can aid in the identification of incipient AD among MCI patients.

Evaluation of methods for generating parametric (R-[11C]PK11195 binding images.

Activated microglia can be visualised using (R)-[(11)C]PK11195 (1-[2-chlorophenyl]-N-methyl-N-[1-methyl-propyl]-3-isoquinoline carboxamide) and positron emission tomography (PET). In previous studies, various methods have been used to quantify (R)-[(11)C]PK11195 binding. The purpose of this study was to determine which parametric method would be best suited for quantifying (R)-[(11)C]PK11195 binding at the voxel level. Dynamic (R)-[(11)C]PK11195 scans with arterial blood sampling were performed in 20 healthy and 9 Alzheimer's disease subjects. Parametric images of both volume of distribution (V(d)) and binding potential (BP) were obtained using Logan graphical analysis with plasma input. In addition, BP images were generated using two versions of the basis function implementation of the simplified reference tissue model, two versions of Ichise linearisations, and Logan graphical analysis with reference tissue input. Results of the parametric methods were compared with results of full compartmental analysis using nonlinear regression. Simulations were performed to assess accuracy and precision of each method. It was concluded that Logan graphical analysis with arterial input function is an accurate method for generating parametric images of V(d). Basis function methods, one of the Ichise linearisations and Logan graphical analysis with reference tissue input provided reasonably accurate and precise estimates of BP. In pathological conditions with reduced flow rates or large variations in blood volume, the basis function method is preferred because it produces less bias and is more precise.

Evaluation of reference regions for (R)-[(11)C]PK11195 studies in Alzheimer's disease and mild cognitive impairment.

Inflammation in Alzheimer's disease (AD) may be assessed using (R)-[(11)C]PK11195 and positron emission tomography. Data can be analyzed using the simplified reference tissue model, provided a suitable reference region is available. This study evaluates various reference regions for analyzing (R)-[(11)C]PK11195 scans in patients with mild cognitive impairment (MCI) and probable AD. Healthy subjects (n=10, 30+/-10 years and n=10, 70+/-6 years) and patients with MCI (n=10, 74+/-6 years) and probable AD (n=9, 71+/-6 years) were included. Subjects underwent a dynamic three-dimensional (R)-[(11)C]PK11195 scan including arterial sampling. Gray matter, white matter, total cerebellum and cerebrum, and cluster analysis were evaluated as reference regions. Both plasma input binding potentials of these reference regions (BP(PLASMA)) and corresponding reference region input binding potentials of a target region (BP(SRTM)) were evaluated. Simulations were performed to assess cluster analysis performance at 5% to 15% coefficient of variation noise levels. Reasonable correlations for BP(PLASMA) (R(2)=0.52 to 0.94) and BP(SRTM) (R(2)=0.59 to 0.76) were observed between results using anatomic regions and cluster analysis. For cerebellum white matter, cerebrum white matter, and total cerebrum a considerable number of unrealistic BP(SRTM) values were observed. Cluster analysis did not extract a valid reference region in 10% of the scans. Simulations showed that potentially cluster analysis suffers from negative bias in BP(PLASMA). Most anatomic regions outperformed cluster analysis in terms of absence of both scan rejection and bias. Total cerebellum is the optimal reference region in this patient category.

Evaluation of reference tissue models for the analysis of [11C](R)-PK11195 studies.

[(11)C](R)-PK11195 is a marker of activated microglia, which can be used to measure inflammation in neurologic disorders. The purpose of the present study was to define the optimal reference tissue model based on a comparison with a validated plasma input model and using clinical studies and Monte Carlo simulations. Accuracy and reproducibility of reference tissue models were evaluated using Monte Carlo simulations. The effects of noise and variation in specific binding, nonspecific binding and blood volume were evaluated. Dynamic positron emission tomography scans were performed on 13 subjects, and radioactivity in arterial blood was monitored online. In addition, blood samples were taken to generate a metabolite corrected plasma input function. Both a (validated) two-tissue reversible compartment model with K(1)/k(2) fixed to whole cortex and various reference tissue models were fitted to the data. Finally, a simplified reference tissue model (SRTM) corrected for nonspecific binding using plasma input data (SRTM(pl_corr)) was investigated. Correlations between reference tissue models (including SRTM(pl_corr)) and the plasma input model were calculated. Monte Carlo simulations indicated that low-specific binding results in decreased accuracy and reproducibility. In this respect, the SRTM and SRTM(pl_corr) performed relatively well. Varying blood volume had no effect on performance. In the clinical evaluation, SRTM(pl_corr) and SRTM had the highest correlations with the plasma input model (R(2)=0.82 and 0.78, respectively). SRTM(pl_corr) is optimal when an arterial plasma input curve is available. Simplified reference tissue model is the best alternative when no plasma input is available.

Development of a tracer kinetic plasma input model for (R)-[11C]PK11195 brain studies.

(R)-[(11)C]PK11195 ([1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl]-3-isoquinoline carboxamide) is a ligand for the peripheral benzodiazepine receptor, which, in the brain, is mainly expressed on activated microglia. Using both clinical studies and Monte Carlo simulations, the aim of this study was to determine which tracer kinetic plasma input model best describes (R)-[(11)C]PK11195 kinetics. Dynamic positron emission tomography (PET) scans were performed on 13 subjects while radioactivity in arterial blood was monitored online. Discrete blood samples were taken to generate a metabolite corrected plasma input function. One-tissue, two-tissue irreversible, and two-tissue reversible compartment models, with and without fixing K(1)/k(2) ratio, k(4) or blood volume to whole cortex values, were fitted to the data. The effects of fixing parameters to incorrect values were investigated by varying them over a physiologic range and determining accuracy and reproducibility of binding potential and volume of distribution using Monte Carlo simulations. Clinical data showed that a two-tissue reversible compartment model was optimal for analyzing (R)-[(11)C]PK11195 PET brain studies. Simulations showed that fixing the K(1)/k(2) ratio of this model provided the optimal trade-off between accuracy and reproducibility. It was concluded that a two-tissue reversible compartment model with K(1)/k(2) fixed to whole cortex value is optimal for analyzing (R)-[(11)C]PK11195 PET brain studies.

[Idiopathic intracranial hypertension and obesity]. / Idiopathische intracraniële hypertensie bij obesitas.

BACKGROUND: Idiopathic intracranial hypertension (IIH) is a neurological syndrome characterized by elevated intracranial pressure in the absence of intracerebral abnormalities or hydrocephalus. CASE DESCRIPTION: A 17-year-old girl gained more than 25 kg in weight during treatment with risperidone and subsequently developed headache, diplopia and loss of vision due to IIH. After insertion of a ventriculoperitoneal drain and discontinuation of risperidone she lost weight and her symptoms improved. Her visual functions recovered almost fully during follow-up. CONCLUSION: Patients with IIH are mainly overweight young women who present with raised intracranial pressure evidenced by headache, nausea, vomiting and vision disturbances. Prescribed medication-induced weight gain may lead to IIH. Treatment of IIH should be focused on the prevention of severe and irreversible loss of vision.

Microglial activation in Alzheimer's disease: an (R)-[¹¹C]PK11195 positron emission tomography study.

UNLABELLED: Inflammatory mechanisms, like microglial activation, could be involved in the pathogenesis of Alzheimer's disease (AD). (R)-[(11)C]PK11195 (1-(2-chlorophenyl)-N-methyl-N-1(1-methylpropyl)-3-isoquinolinecarboxamide), a positron emission tomography (PET) ligand, can be used to quantify microglial activation in vivo. The purpose of this study was to assess whether increased (R)-[(11)C]PK11195 binding is present in AD and mild cognitive impairment (MCI), currently also known as "prodromal AD." METHODS: Nineteen patients with probable AD, 10 patients with prodromal AD (MCI), and 21 healthy control subjects were analyzed. Parametric images of binding potential (BP(ND)) of (R)-[(11)C]PK11195 scans were generated using receptor parametric mapping (RPM) with supervised cluster analysis. Differences between subject groups were tested using mixed model analysis, and associations between BP(ND) and cognition were evaluated using Pearson correlation coefficients. RESULTS: Voxel-wise statistical parametric mapping (SPM) analysis showed small clusters of significantly increased (R)-[(11)C]PK11195 BP(ND) in occipital lobe in AD dementia patients compared with healthy control subjects. Regions of interest (ROI)-based analyses showed no differences, with large overlap between groups. There were no differences in (R)-[(11)C]PK11195 BP(ND) between clinically stable prodromal AD patients and those who progressed to dementia, and BP(ND) did not correlate with cognitive function. CONCLUSION: Microglial activation is a subtle phenomenon occurring in AD.

Optimization of supervised cluster analysis for extracting reference tissue input curves in (R)-[(11)C]PK11195 brain PET studies.

Performance of two supervised cluster analysis (SVCA) algorithms for extracting reference tissue curves was evaluated to improve quantification of dynamic (R)-[(11)C]PK11195 brain positron emission tomography (PET) studies. Reference tissues were extracted from images using both a manually defined cerebellum and SVCA algorithms based on either four (SVCA4) or six (SVCA6) kinetic classes. Data from controls, mild cognitive impairment patients, and patients with Alzheimer's disease were analyzed using various kinetic models including plasma input, the simplified reference tissue model (RPM) and RPM with vascular correction (RPMV(b)). In all subject groups, SVCA-based reference tissue curves showed lower blood volume fractions (V(b)) and volume of distributions than those based on cerebellum time-activity curve. Probably resulting from the presence of specific signal from the vessel walls that contains in normal condition a significant concentration of the 18 kDa translocation protein. Best contrast between subject groups was seen using SVCA4-based reference tissues as the result of a lower number of kinetic classes and the prior removal of extracerebral tissues. In addition, incorporation of V(b) in RPM improved both parametric images and binding potential contrast between groups. Incorporation of V(b) within RPM, together with SVCA4, appears to be the method of choice for analyzing cerebral (R)-[(11)C]PK11195 neurodegeneration studies.

Microglial activation in healthy aging.

Healthy brain aging is characterized by neuronal loss and decline of cognitive function. Neuronal loss is closely associated with microglial activation and postmortem studies have indeed suggested that activated microglia may be present in the aging brain. Microglial activation can be quantified in vivo using (R)-[(11)C]PK11195 and positron emission tomography. The purpose of this study was to measure specific binding of (R)-[(11)C]PK11195 in healthy subjects over a wide age range. Thirty-five healthy subjects (age range 19-79 years) were included. In all subjects 60-minute dynamic (R)-[(11)C]PK11195 scans were acquired. Specific binding of (R)-[(11)C]PK11195 was calculated using receptor parametric mapping in combination with supervised cluster analysis to extract the reference tissue input function. Increased binding of (R)-[(11)C]PK11195 with aging was found in frontal lobe, anterior and posterior cingulate cortex, medial inferior temporal lobe, insula, hippocampus, entorhinal cortex, thalamus, parietal and occipital lobes, and cerebellum. This indicates that activated microglia appear in several cortical and subcortical areas during healthy aging, suggesting widespread neuronal loss.

Inflammatory markers in AD and MCI patients with different biomarker profiles.

OBJECTIVE: The aim of this study was to demonstrate the involvement of the inflammatory proteins IL-6, ACT and CRP early in the pathology process of AD in patients with mild cognitive impairment (MCI) and AD. METHODS: IL-6, ACT, CRP, Abeta42, phospho-tau (p-tau) and total tau concentrations in serum and CSF of 145 patients with probable AD and 67 patients with MCI were measured by sandwich ELISA. MCI patients were characterized as high- respectively low-risk MCI according to their Abeta42/tau risk profile. RESULTS: CSF and serum CRP levels were significantly higher in MCI compared to AD patients after adjustment for age, ApoE epsilon4 genotype and cardiovascular diseases (p<0.01). This difference remained present in patients with a low-risk biomarker profile for AD after adjustment for abovementioned covariates. CSF IL-6 levels were also significantly higher in MCI patients with a low-risk CSF profile. CONCLUSIONS: These findings suggest that inflammatory processes might be involved in early stages of AD, even before Abeta and tau changes are present in CSF of MCI patients.

Microglia activation in recent-onset schizophrenia: a quantitative (R)-[11C]PK11195 positron emission tomography study.

BACKGROUND: Schizophrenia is a brain disease involving progressive loss of gray matter of unknown cause. Most likely, this loss reflects neuronal damage, which should, in turn, be accompanied by microglia activation. Microglia activation can be quantified in vivo using (R)-[(11)C]PK11195 and positron emission tomography (PET). The purpose of this study was to investigate whether microglia activation occurs in patients with recent-onset schizophrenia. METHODS: Ten patients with recent-onset schizophrenia and 10 age-matched healthy control subjects were included. A fully quantitative (R)-[(11)C]PK11195 PET scan was performed on all subjects, including arterial sampling to generate a metabolite-corrected input curve. RESULTS: Compared with control subjects, binding potential of (R)-[(11)C]PK11195 in total gray matter was increased in patients with schizophrenia. There were no differences in other PET parameters. CONCLUSIONS: Activated microglia are present in schizophrenia patients within the first 5 years of disease onset. This suggests that, in this period, neuronal injury is present and that neuronal damage may be involved in the loss of gray matter associated with this disease. Microglia may form a novel target for neuroprotective therapies in schizophrenia.

SPM analysis of parametric (R)-[11C]PK11195 binding images: plasma input versus reference tissue parametric methods.

(R)-[11C]PK11195 has been used for quantifying cerebral microglial activation in vivo. In previous studies, both plasma input and reference tissue methods have been used, usually in combination with a region of interest (ROI) approach. Definition of ROIs, however, can be labourious and prone to interobserver variation. In addition, results are only obtained for predefined areas and (unexpected) signals in undefined areas may be missed. On the other hand, standard pharmacokinetic models are too sensitive to noise to calculate (R)-[11C]PK11195 binding on a voxel-by-voxel basis. Linearised versions of both plasma input and reference tissue models have been described, and these are more suitable for parametric imaging. The purpose of this study was to compare the performance of these plasma input and reference tissue parametric methods on the outcome of statistical parametric mapping (SPM) analysis of (R)-[11C]PK11195 binding. Dynamic (R)-[11C]PK11195 PET scans with arterial blood sampling were performed in 7 younger and 11 elderly healthy subjects. Parametric images of volume of distribution (Vd) and binding potential (BP) were generated using linearised versions of plasma input (Logan) and reference tissue (Reference Parametric Mapping) models. Images were compared at the group level using SPM with a two-sample t-test per voxel, both with and without proportional scaling. Parametric BP images without scaling provided the most sensitive framework for determining differences in (R)-[11C]PK11195 binding between younger and elderly subjects. Vd images could only demonstrate differences in (R)-[11C]PK11195 binding when analysed with proportional scaling due to intersubject variation in K1/k2 (blood-brain barrier transport and non-specific binding).