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The in vivo binding characteristics of (18)F-GE-180 demonstrate a better signal to noise ratio than (11)C-R-PK11195 due to both a better signal in the lesion and lower nonspecific binding in healthy tissue. These results provide evidence that (18)F-GE-180 is a strong candidate to replace (11)C-R-PK11195.

Highlights► Risk factors for stroke include atherosclerosis, obesity, diabetes and hypertension. ► Stroke risk factors are associated with peripheral inflammation. ► Corpulent rats and atherogenic mice show increased inflammation in the brain. ► Pilot data show that patients at risk of stroke may also develop brain inflammation. ► Chronic peripheral inflammation can drive inflammatory changes in the brain.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS. Activated microglia/macrophages play a key role in the immunopathogenesis of MS and its corresponding animal models, experimental autoimmune encephalomyelitis (EAE). Microglia activation begins at early stages of the disease and is associated with elevated expression of the 18 kDa mitochondrial translocator protein (TSPO). Thus, positron emission tomography (PET) imaging of microglial activation using TSPO-specific radioligands could be valuable for monitoring disease-associated neuroinflammatory processes. EAE was induced in rats using a fragment of myelin basic protein, yielding acute clinical disease that reflects extensive spinal cord inflammation. Enhanced TSPO expression in spinal cords of EAE rats versus those of controls was confirmed by Western blot and immunohistochemistry. Biodistribution studies in control and EAE rats were performed using the TSPO radioligand

While the clinical presentation of posterior cortical atrophy is clearly distinct from typical Alzheimer's disease, neuropathological studies have suggested that most patients with posterior cortical atrophy have Alzheimer's disease with an atypical visual presentation. We analysed in vivo pathophysiological markers of Alzheimer's disease such as cerebrospinal fluid biomarkers and positron emission tomography imaging with ¹¹C-labelled Pittsburgh compound-B in posterior cortical atrophy to determine whether biochemical profile and fibrillar amyloid-β burden topography are associated with the clinical presentation. Nine patients with posterior cortical atrophy and nine with typical Alzheimer's disease individually matched for age, duration and severity of the disease and 10 cognitively normal age-matched controls were included. ¹¹C-labelled Pittsburgh compound-B images were analysed both using volumes of interest and on a voxel-wise basis using statistical parametric mapping, taking into account the individual regional cortical atrophy. Cerebrospinal fluid biomarkers did not differ between posterior cortical atrophy and patients with Alzheimer's disease. Compared with normal controls, both posterior cortical atrophy and Alzheimer's disease groups showed increased ¹¹C-labelled Pittsburgh compound-B uptake. No significant difference was found in regional or global ¹¹C-labelled Pittsburgh compound-B binding between posterior cortical atrophy and Alzheimer's disease groups with both volumes of interest and voxel-wise basis using statistical parametric mapping methods. Our findings demonstrate that cerebrospinal fluid biomarkers and positron emission tomography imaging with ¹¹C-labelled Pittsburgh compound-B may be useful in identifying an atypical visual form of Alzheimer's disease. The similar topography of fibrillar amyloid-β deposition between typical Alzheimer's disease and posterior cortical atrophy groups suggests that, although amyloid-β accumulation plays a critical role in the pathogenesis of Alzheimer's disease, other factors such as neurofibrillary tangles may contribute to the different clinical features observed in posterior cortical atrophy.

The aim of this study was to compare eight methods for the estimation of the image-derived input function (IDIF) in [ 18 F]-FDG positron emission tomography (PET) dynamic brain studies. The methods were tested on two digital phantoms and on four healthy volunteers. Image-derived input functions obtained with each method were compared with the reference input functions, that is, the activity in the carotid labels of the phantoms and arterial blood samples for the volunteers, in terms of visual inspection, areas under the curve, cerebral metabolic rates of glucose (CMRglc), and individual rate constants. Blood-sample-free methods provided less reliable results as compared with those obtained using the methods that require the use of blood samples. For some of the bloodsample-free methods, CMRglc estimations considerably improved when the IDIF was calibrated with a single blood sample. Only one of the methods tested in this study, and only in phantom studies, allowed a reliable calculation of the individual rate constants. For the estimation of CMRglc values using an IDIF in [ 18 F]-FDG PET brain studies, a reliable absolute blood-sample-free procedure is not available yet.

PurposeNeuroinflammation is involved in several brain disorders and can be monitored through expression of the translocator protein 18 kDa (TSPO) on activated microglia. In recent years, several new PET radioligands for TSPO have been evaluated in disease models. [18F]DPA-714 is a TSPO radiotracer with great promise; however results vary between different experimental models of neuroinflammation. To further examine the potential of [18F]DPA-714, it was compared directly to [11C]PK11195 in experimental cerebral ischaemia in rats.MethodsUnder anaesthesia, the middle cerebral artery of adult rats was occluded for 60 min using the filament model. Rats were allowed recovery for 5 to 7 days before one hour dynamic PET scans with [11C]PK11195 and/or [18F]DPA-714 under anaesthesia.ResultsUptake of [11C]PK11195 vs [18F]DPA-714 in the ischemic lesion was similar (core/contralateral ratio: 2.84±0.67 vs 2.28±0.34 respectively), but severity of the brain ischemia and hence ligand uptake in the lesion appeared to vary greatly between animals scanned with [11C]PK11195 or with [18F]DPA-714. To solve this issue of inter-individual variability, we performed a direct comparison of [11C]PK11195 and [18F]DPA-714 by scanning the same animals sequentially with both tracers within 24 h. In this direct comparison, the core/contralateral ratio (3.35±1.21 vs 4.66±2.50 for [11C]PK11195 vs [18F]DPA-714 respectively) showed a significantly better signal-to-noise ratio (1.6 (1.3–1.9, 95%CI) fold by linear regression) for [18F]DPA-714.ConclusionsIn a clinically relevant model of neuroinflammation, uptake for both radiotracers appeared to be similar at first, but a high variability was observed in our model. Therefore, to truly compare tracers in such models, we performed scans with both tracers in the same animals. By doing so, our result demonstrated that [18F]DPA-714 displayed a higher signal-to-noise ratio than [11C]PK11195. Our results suggest that, with the longer half-life of [18F] which facilitates distribution of the tracer across PET centre, [18F]DPA-714 is a good alternative for TSPO imaging.

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