References of "Lemaire, Christian"
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See detailFrontal and posterior cingulate metabolic impairment in the behavioural variant of frontotemporal dementia with impaired autonoetic consciousness
Bastin, Christine ULg; Feyers, Dorothée ULg; Souchay, Céline et al

in Human Brain Mapping (2012), 33

Although memory dysfunction is not a prominent feature of the behavioural variant of frontotemporal dementia (bv-FTD), there is evidence of specific deficits of episodic memory in these patients. They ... [more ▼]

Although memory dysfunction is not a prominent feature of the behavioural variant of frontotemporal dementia (bv-FTD), there is evidence of specific deficits of episodic memory in these patients. They also have problems monitoring their memory performance. The objective of the present study was to explore the ability to consciously retrieve own encoding of the context of events (autonoetic consciousness) and the ability to monitor memory performance using feeling-of-knowing (FOK) in bv-FTD. Analyses of the patients’ cerebral metabolism (FDG-PET) allowed an examination of whether impaired episodic memory in bv-FTD is associated with the frontal dysfunction characteristic of the pathology or a dysfunction of memory-specific regions pertaining to Papez’s circuit. Data were obtained from 8 bv-FTD patients and 26 healthy controls. Autonoetic consciousness was evaluated by Remember responses during the recognition memory phase of the FOK experiment. As a group, bv-FTD patients demonstrated a decline in autonoetic consciousness and FOK accuracy at the chance level. While memory monitoring was impaired in most (7) patients, 4 bv-FTD participants had individual impairment of autonoetic consciousness. They specifically showed reduced metabolism in the anterior medial prefrontal cortex, the left dorsolateral prefrontal cortex (near the superior frontal sulcus), parietal regions and the posterior cingulate cortex. These findings were tentatively interpreted by considering the role of the metabolically impaired brain regions in self-referential processes, suggesting that the bv-FTD patients’ problem consciously retrieving episodic memories may stem at least partly from deficient access to and maintenance/use of information about the self. [less ▲]

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See detailUse of a beta microprobe system to measure arterial input function in PET via an arteriovenous shunt in rats
Warnock, Geoffrey ULg; Bahri, Mohamed Ali ULg; Goblet, David ULg et al

in European Journal of Nuclear Medicine and Molecular Imaging Research (2011), 1

Kinetic modeling of physiological function using imaging techniques requires the accurate measurement of the time-activity curve of the tracer in plasma, known as the arterial input function (IF). The ... [more ▼]

Kinetic modeling of physiological function using imaging techniques requires the accurate measurement of the time-activity curve of the tracer in plasma, known as the arterial input function (IF). The measurement of IF can be achieved through manual blood sampling, the use of small counting systems such as beta microprobes, or by derivation from PET images. Previous studies using beta microprobe systems to continuously measure IF have suffered from high background counts. In the present study, a light-insensitive beta microprobe with a temporal resolution of up to 1 s was used in combination with a pump-driven femoral arteriovenous shunt to measure IF in rats. The shunt apparatus was designed such that the placement of the beta microprobe was highly reproducible. The probe-derived IF was compared to that obtained from manual sampling at 5-s intervals and IF derived from a left ventricle VOI in a dynamic PET image of the heart. Probe-derived IFs were very well matched to that obtained by "gold standard" manual blood sampling, but with an increased temporal resolution of up to 1 s. The area under the curve (AUC) ratio between probe- and manually derived IFs was 1.07 ± 0.05 with a coefficient of variation of 0.04. However, image-derived IFs were significantly underestimated compared to the manually sampled IFs, with an AUC ratio of 0.76 ± 0.24 with a coefficient of variation of 0.32. IF derived from the beta microprobe accurately represented the IF as measured by blood sampling, was reproducible, and was more accurate than an image-derived technique. The use of the shunt removed problems of tissue-background activity, and the use of a light-tight probe with minimal gamma sensitivity refined the system. The probe/shunt apparatus can be used in both microprobe and PET studies. [less ▲]

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See detailBrain energization in response to deep brain stimulation of subthalamic nuclei in Parkinson's disease.
Garraux, Gaëtan ULg; Bahri, Mohamed Ali ULg; Lemaire, Christian ULg et al

in Journal of Cerebral Blood Flow & Metabolism (2011)

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment in a subgroup of medically refractory patients with Parkinson's disease (PD). Here, we compared resting-state (18)F ... [more ▼]

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment in a subgroup of medically refractory patients with Parkinson's disease (PD). Here, we compared resting-state (18)F-fluorodeoxyglucose (FDG) positron emission tomography images in the stimulator off (DBS_OFF) and on (DBS_ON) conditions in eight PD patients in an unmedicated state, on average 2 years after bilateral electrode implantation. Global standardized uptake value (SUV) significantly increased by approximately 11% in response to STN-DBS. To avoid any bias in the voxel-based analysis comparing DBS_ON and DBS_OFF conditions, individual scan intensity was scaled to a region where FDG-SUV did not differ significantly between conditions. The resulting FDG-SUV ratio (FDG-SUVR) was found to increase in many regions in response to STN-DBS including the target area of surgery, caudate nuclei, primary sensorimotor, and associative cortices. Contrary to previous studies, we could not find any regional decrease in FDG-SUVR. These findings were indirectly supported by comparing the extent of areas with depressed FDG-SUVR in DBS_OFF and DBS_ON relatively to 10 normal controls. Altogether, these novel results support the prediction that the effect of STN-DBS on brain activity in PD is unidirectional and consists in an increase in many subcortical and cortical regions.Journal of Cerebral Blood Flow & Metabolism advance online publication, 6 April 2011; doi:10.1038/jcbfm.2011.41. [less ▲]

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See detail[18F]fallypride binding in the mouse brain: test-retest and effects of registration
Bahri, Mohamed Ali ULg; Geuzaine, Annabelle ULg; Warnock, Geoffrey ULg et al

Conference (2011, January 17)

The quantification of in vivo receptor kinetics with PET tracer experiments is an intricate and challenging problem especially for small animals such as rats and mice. A test-retest scan is usually set up ... [more ▼]

The quantification of in vivo receptor kinetics with PET tracer experiments is an intricate and challenging problem especially for small animals such as rats and mice. A test-retest scan is usually set up in order to confirm an observed experimental effect or to examine the reliability of the experiment design. Inadequate processing of the image data may also mask small effects. The purpose of this study was to investigate the effect of image registration on [18F]fallypride binding potentials calculated from PET mouse test-retest data. Sub-optimal registration affected the quantification of in vivo receptor kinetics with [18F]fallypride. The absence of anatomical information in the [18F]fallypride image and the lack of a homogeneous tracer distribution, even during the earlier minutes of the scan, lead to erroneous automatic registration. A FDG scan after each [18F]fallypride test could improve registration as FDG provides a more homogeneous brain image. Variability in the data could also result from stress induced by anaesthesia or the experimental environment. [less ▲]

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See detailThe cerebral metabolic correlates of episodic autobiographical memory in amnestic Mild Cognitive Impairment
Bastin, Christine ULg; Feyers, Dorothée ULg; Jedidi, Haroun ULg et al

in Proceedings of the 5th International Conference on Memory (2011)

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See detailSynthesis and hydrolytic stability of novel 3-[18F]fluoroethoxybis(1-methylethyl)silyl]propanaminebased prosthetic groups
collet, Charlotte; Lamandé-Langle, Sandrine; Balentova, Eva et al

Poster (2011)

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See detailNeural correlates of controlled memory processes in questionable Alzheimer’s disease
Bastin, Christine ULg; Kerrouche, Nacer; LEKEU, Françoise ULg et al

in Ashford, J. Wesson; Rosen, Allyson; Adamson, Maheen (Eds.) et al Advances in Alzheimer's Disease. Volume 2: Handbook of imaging the Alzheimer brain (2011)

Alzheimer’s disease (AD) is characterized by a progressive loss of controlled cognitive processes (processes requiring mental effort and attentional resources), and functional neuroimaging at early stages ... [more ▼]

Alzheimer’s disease (AD) is characterized by a progressive loss of controlled cognitive processes (processes requiring mental effort and attentional resources), and functional neuroimaging at early stages of AD provides an opportunity to tease out the neural correlates of controlled processes. Controlled and automatic memory performance was assessed with the Process Dissociation Procedure in 50 patients diagnosed with questionable Alzheimer’s disease (QAD). The patients’ brain glucose metabolism was measured using FDG-PET. After a follow-up period of 36 months, 27 patients had converted to AD, while 23 remained stable. Both groups showed a similar decrease in controlled memory processes but preserved automatic processes at entry into the study, suggesting that impairment of controlled memory would not be specific for AD. Patients who subsequently converted to Alzheimer type dementia showed significantly decreased brain metabolism at baseline compared to stable QAD in associative cortices known to be involved in AD (the left precuneus, the right inferior parietal lobule and bilateral middle temporal cortex).Voxel-based cognitive and metabolic correlations showed that a decrease in controlled memory processes was preferentially correlated with lower activity in the dorsomedial prefrontal and posterior cingulate cortices in very early AD patients. The dorsomedial prefrontal cortex would play a role in controlled memory processes as they relate to reflective and monitoring processes, while the posterior cingulate cortex is involved in the controlled access to previously encoded episodes. In stable QAD patients, reduced controlled performance in verbal memory correlated with impaired activity in the left anterior hippocampal structure, which would alter the reactivation of associations created at encoding. [less ▲]

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See detailSynthesis and hydrolytic stability of novel 3-[18F]fluoroethoxybis(1-methylethyl)silyl]propanamine-based prosthetic groups
Balentova, Eva; Collet, Charlotte; Lamande-Langle, Sandrine et al

in Journal of Fluorine Chemistry (2011), 132(4), 250-257

Two new silicon-based prosthetic groups, derived from 3-[ethoxybis(1-methylethyl)silyl]propanamine, have been prepd. in good yields. These silicon groups bearing an acid or an azide group were coupled to ... [more ▼]

Two new silicon-based prosthetic groups, derived from 3-[ethoxybis(1-methylethyl)silyl]propanamine, have been prepd. in good yields. These silicon groups bearing an acid or an azide group were coupled to a model tripeptide (Leu-Gly- Gly) either through a classical amide bond formation or through "click chem." via the Huisgen cycloaddn. The radiolabeling with fluorine-18 by substitution of the ethoxy group at silicon has been carried out with success in 51-54% decay cor. radiochem. yields. Radiolabeled peptides were easily prepd. by direct 18F-fluorination of the silicon-bearing tripeptide or by coupling the peptide with a radiolabeled silicon-based prosthetic group. Their stabilities in physiol. medium were studied and proved poor. [less ▲]

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See detailGeneral Method for Labeling siRNA by Click Chemistry with Fluorine-18 for the Purpose of PET Imaging
Mercier, Frédéric; Paris, Jérôme ULg; Kaisin, Geoffroy ULg et al

in Bioconjugate Chemistry (2011), 22(1), 108-114

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See detailIN VIVO PET IMAGING OF THE EFFECT OF THE NMDA ANTAGONIST MEMANTINE ON GLUCOSE METABOLISM IN THE RODENT BRAIN
Warnock, Geoffrey ULg; Dedeurwaerdere, Stefanie; Bahri, Mohamed Ali ULg et al

Poster (2010, September)

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See detailTHE EFFECT OF BETA MICROPROBE IMPLANTATION ON THE BLOOD BRAIN BARRIER
Warnock, Geoffrey ULg; Dedeurwaardere, Stefanie; Bahri, Mohamed Ali ULg et al

Poster (2010, September)

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See detailIs posterior cerebral hypometabolism always predicitve of dementia in Parkinson's disease?
Deville, Benjamin ULg; Lemaire, Christian ULg; Degueldre, Christian ULg et al

Poster (2010, June 08)

In Parkinson's disease, altered activity in posterior associative cortices has often been associated with dementia. It remains to be determined if this pattern is a reliable marker of a progression toward ... [more ▼]

In Parkinson's disease, altered activity in posterior associative cortices has often been associated with dementia. It remains to be determined if this pattern is a reliable marker of a progression toward dementia in patients without demonstratable dementia. In this retrospective analysis, we used positron emission tomography to study resting-state cerebral fluodeoxyglucose uptake in 8 healthy controls and 8 Parkinson's disease patients who did not have evidence of dementia at the time of assessment. For those patients, clinical follow up was available and we know that they did not meet dementia criteria on average 10,37 years after assessment. The results show that patients had reduced fluodeoxyglucose uptake mostly localised in the right hemisphere and including precuneus, superior temporal, middle temporal and inferior parietal cortices. It also includes right insula. These cerebral activity predominating in posterior cortices is present in non-demened patients but is not always predictive of dementia within the 10,34 years. [less ▲]

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See detailControlled Memory Processes in Questionable Alzheimer's Disease: A View from Neuroimaging Research
Bastin, Christine ULg; Kerrouche N; Lekeu, Françoise ULg et al

in Journal of Alzheimer's Disease [=JAD] (2010), 20(2), 547-560

Alzheimer's disease (AD) is characterized by a progressive loss of controlled cognitive processes, and neuroimaging studies at early stages of AD provide an opportunity to tease out the neural correlates ... [more ▼]

Alzheimer's disease (AD) is characterized by a progressive loss of controlled cognitive processes, and neuroimaging studies at early stages of AD provide an opportunity to tease out the neural correlates of controlled processes. Accordingly, controlled and automatic memory performance was assessed with the Process Dissociation Procedure in 50 patients diagnosed with questionable Alzheimer's disease (QAD). The patients' brain glucose metabolism was measured using FDG-PET. After a follow-up period of 36 months, 27 patients had converted to AD, while 23 remained stable. Both groups showed a similar decrease in controlled memory processes but preserved automatic processes at entry into the study. Voxel-based cognitive and metabolic correlations showed that a decrease in controlled memory processes was preferentially correlated with lower activity in the dorsomedial prefrontal and posterior cingulate cortices in very early AD patients. In stable QAD patients, reduced controlled performance in verbal memory correlated with impaired activity in the left anterior hippocampal structure. The results demonstrated the central role of a medial frontal-posterior cingulate network for controlled processing of episodic memory in the early stages of AD. [less ▲]

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See detailClick chemistry : radiolabelling of oligonucleotides with fluorine- 18 for PET
Kaisin, Geoffroy ULg; Flagothier, Jessica ULg; Mercier, Frédéric ULg et al

Poster (2010, June)

Oligonucleotides (ONs), especially small interfering RNA (siRNA), are promising therapeutic agents, but their pharmacokinetics and biodistributions are widely unknown. Positron Emission Tomography (PET ... [more ▼]

Oligonucleotides (ONs), especially small interfering RNA (siRNA), are promising therapeutic agents, but their pharmacokinetics and biodistributions are widely unknown. Positron Emission Tomography (PET) using fluorine-18 is a suitable technique to image and quantify such biological processes. The challenge for the radiochemist is to introduce this short half-life isotope (t1/2(18F)=109.7 min) onto oligonucleotides or, more generally, biomolecules. The most common technique requires the coupling of a prosthetic group bearing the radiotracer with the biomolecule. Current methods for labeling ONs with fluorine-18 have sub-optimal yields and require a long synthesis time.1 Click chemistry, e.g. 1,3-dipolar Huisgen cycloaddition of azides to alkynes, could be an efficient way to increase yields and reduce synthesis time. Conjugations with ONs are usually performed at 3’-ends using a well-chosen linker in order to limit degradation by exonucleases and to avoid alteration of hybridization properties and siRNA gene silencing efficiency. This also allows the development of universal solid supports used for the solidphase synthesis of ONs. Here we report the synthesis of three alkyne-bearing linkers , the synthesis and radiosynthesis of the complementary azido-bearing prosthetic groups (1-(azidomethyl)-4-[18F]- fluorobenzene) and coupling with functionalized ONs. [less ▲]

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