CERMEP-IDB-MRXFDG: a database of 37 normal adult human brain [18F]FDG PET, T1 and FLAIR MRI, and CT images available for research

We present a database of cerebral PET FDG and anatomical MRI for 37 normal adult human subjects (CERMEP-IDB-MRXFDG). Thirty-nine participants underwent static [18F]FDG PET/CT and MRI, resulting in [18F]FDG PET, T1 MPRAGE MRI, FLAIR MRI, and CT images. Two participants were excluded after visual quality control. We describe the acquisition parameters, the image processing pipeline and provide participants' individual demographics (mean age 38 ± 11.5 years, range 23-65, 20 women). Volumetric analysis of the 37 T1 MRIs showed results in line with the literature. A leave-one-out assessment of the 37 FDG images using Statistical Parametric Mapping (SPM) yielded a low number of false positives after exclusion of artefacts. The database is stored in three different formats, following the BIDS common specification: (1) DICOM (data not processed), (2) NIFTI (multimodal images coregistered to PET subject space), (3) NIFTI normalized (images normalized to MNI space). Bona fide researchers can request access to the database via a short form.

Variation in the sacroiliac joint in Felidae

Felidae species show a great diversity in their diet, foraging and hunting strategies, from small to large prey. Whether they belong to solitary or group hunters, the behavior of cats to subdue resisting small or large prey presents crucial differences. It is assumed that pack hunting reduces the per capita risk of each individual. We hypothesize that the sacroiliac articulation plays a key role in stabilizing the predator while subduing and killing prey. Using CT-scan from 59 felid coxal bones, we calculated the angle between both iliac articular surfaces. Correlation of this inter-iliac angle with body size was calculated and ecological stressors were evaluated on inter-iliac angle. Body size significantly influences inter-iliac angle with small cats having a wider angle than big cats. Arboreal species have a significantly larger angle compared to cursorial felids with the smallest value, and to scansorial and terrestrial species with intermediate angles. Felids hunting large prey have a smaller angle than felids hunting small and mixed prey. Within the Panthera lineage, pack hunters (lions) have a larger angle than all other species using solitary hunting strategy. According to the inter-iliac angle, two main groups of felids are determined: (i) predators with an angle of around 40° include small cats (i.e., Felis silvestris, Leopardus wiedii, Leptailurus serval, Lynx Canadensis, L. rufus; median = 43.45°), the only pack-hunting species (i.e., Panthera leo; median = 37.90°), and arboreal cats (i.e., L. wiedii, Neofelis nebulosa; median = 49.05°), (ii) predators with an angle of around 30° include solitary-hunting big cats (i.e., Acinonyx jubatus, P. onca, P. pardus, P. tigris, P. uncia; median = 31.80°). We suggest different pressures of selection to interpret these results. The tightening of the iliac wings around the sacrum probably enhances big cats’ ability for high speed and large prey control. In contrast, pack hunting in lions reduced the selective pressure for large prey.

Cortical inflammation and brain signs of high-risk atherosclerosis in a non-human primate model

Atherosclerosis is a chronic systemic inflammatory disease, inducing cardiovascular and cerebrovascular acute events. A role of neuroinflammation is suspected, but not yet investigated in the gyrencephalic brain and the related activity at blood−brain interfaces is unknown. A non-human primate model of advanced atherosclerosis was first established using longitudinal blood samples, multimodal imaging and gene analysis in aged animals. Non-human primate carotid lesions were compared with human carotid endarterectomy samples. During the whole-body imaging session, imaging of neuroinflammation and choroid plexus function was performed. Advanced plaques were present in multiple sites, premature deaths occurred and downstream lesions (myocardial fibrosis, lacunar stroke) were present in this model. Vascular lesions were similar to in humans: high plaque activity on PET and MRI imaging and systemic inflammation (high plasma C-reactive protein levels: 42 ± 14 µg/ml). We also found the same gene association (metabolic, inflammatory and anti-inflammatory markers) as in patients with similar histological features. Metabolic imaging localized abnormal brain glucose metabolism in the frontal cortex. It corresponded to cortical neuro-inflammation (PET imaging) that correlated with C-reactive protein level. Multimodal imaging also revealed pronounced choroid plexus function impairment in aging atherosclerotic non-human primates. In conclusion, multimodal whole-body inflammation exploration at the vascular level and blood−brain interfaces identified high-risk aging atherosclerosis. These results open the way for systemic and central inflammation targeting in atherosclerosis in the new era of immunotherapy.

[18F]F13640, a 5-HT1A Receptor Radiopharmaceutical Sensitive to Brain Serotonin Fluctuations

Introduction

Serotonin is involved in a variety of physiological functions and brain disorders. In this context, efforts have been made to investigate the in vivo fluctuations of this neurotransmitter using positron emission tomography (PET) imaging paradigms. Since serotonin is a full agonist, it binds preferentially to G-protein coupled receptors. In contrast, antagonist PET ligands additionally interact with uncoupled receptors. This could explain the lack of sensitivity to serotonin fluctuations of current 5-HT_1A radiopharmaceuticals which are mainly antagonists and suggests that agonist radiotracers would be more appropriate to measure changes in neurotransmitter release. The present study evaluated the sensitivity to endogenous serotonin release of a recently developed, selective 5-HT_1A receptor PET radiopharmaceutical, the agonist [¹⁸F]F13640 (a.k.a. befiradol or NLX-112).

Materials and Methods

Four cats each underwent three PET scans with [¹⁸F]F13640, i.e., a control PET scan of 90 min, a PET scan preceded 30 min before by an intravenous injection 1 mg/kg of d-fenfluramine, a serotonin releaser (blocking challenge), and a PET scan comprising the intravenous injection of 1 mg/kg of d-fenfluramine 30 min after the radiotracer injection (displacement challenge). Data were analyzed with regions of interest and voxel-based approaches. A lp-ntPET model approach was implemented to determine the dynamic of serotonin release during the challenge study.

Results

D-fenfluramine pretreatment elicited a massive inhibition of [¹⁸F]F13640 labeling in regions known to express 5-HT_1A receptors, e.g., raphe nuclei, hippocampus, thalamus, anterior cingulate cortex, caudate putamen, occipital, frontal and parietal cortices, and gray matter of cerebellum. Administration of d-fenfluramine during PET acquisition indicates changes in occupancy from 10% (thalamus) to 31% (gray matter of cerebellum) even though the dissociation rate of [¹⁸F]F13640 over the 90 min acquisition time was modest. The lp-ntPET simulation succeeded in differentiating the control and challenge conditions.

Conclusion

The present findings demonstrate that labeling of 5-HT_1A receptors with [¹⁸F]F13640 is sensitive to serotonin concentration fluctuations in vivo. Although the data underline the need to perform longer PET scan to ensure accurate measure of displacement, they support clinical development of [¹⁸F]F13640 as a tool to explore experimental paradigms involving physiological or pathological (neurological or neuropsychiatric pathologies) fluctuations of extracellular serotonin.

Iliac auricular surface morphofunctional study in felidae

Felids show remarkable phenotypic similarities and are conservative in behavioral and ecological traits. In contrast, they display a large range in body mass from around 1kg to more than 300kg. Body size and locomotory specializations correlate to skull, limb and vertebral skeleton morphology. With an increase in body mass, felids prey selection switches from small to large, from using a rapid skull or spine lethal bite for small prey, to sustained suffocating bite for large prey. Dietary specialization correlates to skull and front limbs morphology but no correlation was found on the spine or on the hind limb. The morphology of the sacroiliac junction in relation to ecological factors remained to be described. We are presenting a study of the overall shape of the iliac auricular surface with qualitative and quantitative analyses of its morphology. Our results demonstrate that body mass, prey selection, and bite type, crucially influence the auricular surface, where no significant effect of locomotor specialization was found. The outline of the surface is significantly more elevated dorso-caudally and the joint surface shows an irregular W-shape topography in big cats whereas the surface in small cats is smoother with a C-shape topography and less of an elevated ridge. Biomechanically, we suggest that a complex auricular surface increases joint stiffness and provides more support in heavier cats, an advantage for subduing big prey successfully during a sustained bite.

Noninvasive quantification of macrophagic lung recruitment during experimental ventilation-induced lung injury

Macrophagic lung infiltration is pivotal in the development of lung biotrauma because of ventilation-induced lung injury (VILI). We assessed the performance of [¹¹C](R)-PK11195, a positron emission tomography (PET) radiotracer binding the translocator protein, to quantify macrophage lung recruitment during experimental VILI. Pigs (n = 6) were mechanically ventilated under general anesthesia, using protective ventilation settings (baseline). Experimental VILI was performed by titrating tidal volume to reach a transpulmonary end-inspiratory pressure (∆P_L) of 35-40 cmH₂O. We acquired PET/computed tomography (CT) lung images at baseline and after 4 h of VILI. Lung macrophages were quantified in vivo by the standardized uptake value (SUV) of [¹¹C](R)-PK11195 measured in PET on the whole lung and in six lung regions and ex vivo on lung pathology at the end of experiment. Lung mechanics were extracted from CT images to assess their association with the PET signal. ∆P_L increased from 9 ± 1 cmH₂O under protective ventilation, to 36 ± 6 cmH₂O during experimental VILI. Compared with baseline, whole-lung [¹¹C](R)-PK11195 SUV significantly increased from 1.8 ± 0.5 to 2.9 ± 0.5 after experimental VILI. Regional [¹¹C](R)-PK11195 SUV was positively associated with the magnitude of macrophage recruitment in pathology (P = 0.03). Compared with baseline, whole-lung CT-derived dynamic strain and tidal hyperinflation increased significantly after experimental VILI, from 0.6 ± 0 to 2.0 ± 0.4, and 1 ± 1 to 43 ± 19%, respectively. On multivariate analysis, both were significantly associated with regional [¹¹C](R)-PK11195 SUV. [¹¹C](R)-PK11195 lung uptake (a proxy of lung inflammation) was increased by experimental VILI and was associated with the magnitude of dynamic strain and tidal hyperinflation.NEW & NOTEWORTHY We assessed the performance of [¹¹C](R)-PK11195, a translocator protein-specific positron emission tomography (PET) radiotracer, to quantify macrophage lung recruitment during experimental ventilation-induced lung injury (VILI). In this proof-of-concept study, we showed that the in vivo quantification of [¹¹C](R)-PK11195 lung uptake in PET reflected the magnitude of macrophage lung recruitment after VILI. Furthermore, increased [¹¹C](R)-PK11195 lung uptake was associated with harmful levels of dynamic strain and tidal hyperinflation applied to the lungs.

Neural substrates of levodopa-responsive gait disorders and freezing in advanced Parkinson's disease: a kinesthetic imagery approach

Gait disturbances, including freezing of gait, are frequent and disabling symptoms of Parkinson's disease. They often respond poorly to dopaminergic treatments. Although recent studies have shed some light on their neural correlates, their modulation by dopaminergic treatment remains quite unknown. Specifically, the influence of levodopa on the networks involved in motor imagery (MI) of parkinsonian gait has not been directly studied, comparing the off and on medication states in the same patients. We therefore conducted an [H2 (15) 0] Positron emission tomography study in eight advanced parkinsonian patients (mean disease duration: 12.3 ± 3.8 years) presenting with levodopa-responsive gait disorders and FoG, and eight age-matched healthy subjects. All participants performed three tasks (MI of gait, visual imagery and a control task). Patients were tested off, after an overnight withdrawal of all antiparkinsonian treatment, and on medication, during consecutive mornings. The order of conditions was counterbalanced between subjects and sessions. Results showed that imagined gait elicited activations within motor and frontal associative areas, thalamus, basal ganglia and cerebellum in controls. Off medication, patients mainly activated premotor-parietal and pontomesencephalic regions. Levodopa increased activation in motor regions, putamen, thalamus, and cerebellum, and reduced premotor-parietal and brainstem involvement. Areas activated when patients are off medication may represent compensatory mechanisms. The recruitment of these accessory circuits has also been reported for upper-limb movements in Parkinson's disease, suggesting a partly overlapping pathophysiology between imagined levodopa-responsive gait disorders and appendicular signs. Our results also highlight a possible cerebellar contribution in the pathophysiology of parkinsonian gait disorders through kinesthetic imagery.

Reliability of the nitrogen washin-washout technique to assess end-expiratory lung volume at variable PEEP and tidal volumes

Background

End-expiratory lung volume measurement by the nitrogen washin-washout technique (EELV_WI-WO) may help titrating positive end-expiratory pressure (PEEP) during acute respiratory distress syndrome (ARDS). Validation of this technique has been previously performed using computed tomography (EELV_CT), but at mild PEEP levels, and relatively low fraction of inspired oxygen (FiO₂), which may have insufficiently challenged the validity of this technique. The aims of this study were (1) to evaluate the reliability of EELV_WI-WO measurements at different PEEP and V_T during experimental ARDS and (2) to evaluate trending ability of EELV_WI-WO to detect EELV changes over time.

Methods

ARDS was induced in 14 piglets by saline lavage. Optimal PEEP was selected during a decremental PEEP trial, based on best compliance, best EELV_WI-WO, or a PEEP-FiO₂ table. Eight V_T (4 to 20 mL · kg^-1) were finally applied at optimal PEEP. EELV_WI-WO and EELV_CT were determined after ARDS onset, at variable PEEP and V_T.

Results

EELV_WI-WO underestimated EELV_CT with a non-constant linear bias, as it decreased with increasing EELV. Limits of agreement for bias were ±398 mL. Bias between methods was greater at high PEEP, and further increased when high PEEP was combined with low V_T. Concordance rate of EELV changes between consecutive measurements was fair (79%). Diagnostic accuracy was good for detection of absolute EELV changes above 200 mL (AUC = 0.79).

Conclusions

The reliability of the WI-WO technique is critically dependent on ventilatory settings, but sufficient to accurately detect EELV change greater than 200 mL.

Electronic supplementary material

The online version of this article (doi:10.1186/2197-425X-2-10) contains supplementary material, which is available to authorized users.

Noninvasive quantitative assessment of pulmonary blood flow with 18F-FDG PET

Pulmonary blood flow (PBF) is a critical determinant of oxygenation during acute lung injury (ALI). PET/CT with (18)F-FDG allows the assessment of both lung aeration and neutrophil inflammation as well as an estimation of the regional fraction of blood (FB) if compartmental modeling is used to quantify (18)F-FDG pulmonary uptake. The aim of this study was to validate the use of FB to assess PBF, with PET and compartmental modeling of (15)O-H2O kinetics as a reference method, in both control animals and animals with ALI. For the purpose of studying a wide range of PBF values, supine and prone positions and various positive end-expiratory pressures (PEEPs) and tidal volumes (V(T)s) were selected.

METHODS

Pigs were randomized into 3 groups in which ALI was induced by HCl inhalation: pigs studied in the supine position with a low PEEP (5 ± 3 [mean ± SD] cm of H2O; n = 9) or a high PEEP (12 ± 1 cm of H2O; n = 8) and pigs studied in the prone position with a low PEEP (6 ± 3 cm of H2O; n = 9). Also included were a control group that did not have ALI (n = 6) and 2 additional groups (n = 6 each) that had a high V(T) to maintain a transpulmonary pressure of greater than or equal to 35 cm of H2O and that either received HCl inhalation or did not receive HCl inhalation. PBF and FB were measured with PET and compartmental modeling of (15)O-H2O and (18)F-FDG kinetics in 10 lung regions along the anterior-to-posterior lung dimension, and both were expressed in each region as a fraction of their values in the whole lung.

RESULTS

PBF and FB were strongly correlated (R(2) = 0.9), with a slope of the regression line close to unity and a negligible intercept. The mean difference between PBF and FB was 0, and the 95% limits of agreement were -0.035 to 0.035. This good agreement between methods was obtained in both normal and injured lungs and under a wide range of V(T), PEEP, and regional PBF values (7-71 mL/kg, 0-15 cm of H2O, and 24-603 mL·min(-1)·100 mL of lung(-1), respectively).

CONCLUSION

FB assessed with (18)F-FDG is a good surrogate for PBF in both normal animals and animals with ALI. PET/CT has the potential to be used to study ventilation, perfusion, and lung inflammation with a single tracer.

A multi-atlas based method for automated anatomical Macaca fascicularis brain MRI segmentation and PET kinetic extraction

MRI templates and digital atlases are needed for automated and reproducible quantitative analysis of non-human primate PET studies. Segmenting brain images via multiple atlases outperforms single-atlas labelling in humans. We present a set of atlases manually delineated on brain MRI scans of the monkey Macaca fascicularis. We use this multi-atlas dataset to evaluate two automated methods in terms of accuracy, robustness and reliability in segmenting brain structures on MRI and extracting regional PET measures.

METHODS

Twelve individual Macaca fascicularis high-resolution 3DT1 MR images were acquired. Four individual atlases were created by manually drawing 42 anatomical structures, including cortical and sub-cortical structures, white matter regions, and ventricles. To create the MRI template, we first chose one MRI to define a reference space, and then performed a two-step iterative procedure: affine registration of individual MRIs to the reference MRI, followed by averaging of the twelve resampled MRIs. Automated segmentation in native space was obtained in two ways: 1) Maximum probability atlases were created by decision fusion of two to four individual atlases in the reference space, and transformation back into the individual native space (MAXPROB)(.) 2) One to four individual atlases were registered directly to the individual native space, and combined by decision fusion (PROPAG). Accuracy was evaluated by computing the Dice similarity index and the volume difference. The robustness and reproducibility of PET regional measurements obtained via automated segmentation was evaluated on four co-registered MRI/PET datasets, which included test-retest data.

RESULTS

Dice indices were always over 0.7 and reached maximal values of 0.9 for PROPAG with all four individual atlases. There was no significant mean volume bias. The standard deviation of the bias decreased significantly when increasing the number of individual atlases. MAXPROB performed better when increasing the number of atlases used. When all four atlases were used for the MAXPROB creation, the accuracy of morphometric segmentation approached that of the PROPAG method. PET measures extracted either via automatic methods or via the manually defined regions were strongly correlated, with no significant regional differences between methods. Intra-class correlation coefficients for test-retest data were over 0.87.

CONCLUSIONS

Compared to single atlas extractions, multi-atlas methods improve the accuracy of region definition. They also perform comparably to manually defined regions for PET quantification. Multiple atlases of Macaca fascicularis brains are now available and allow reproducible and simplified analyses.

5-HT1A gene promoter polymorphism and [18F]MPPF binding potential in healthy subjects: a PET study

Background

Previous Positron Emission Tomography (PET) studies of 5-HT_1A receptors have shown an influence of several genetic factors, including the triallelic serotonin transporter gene-linked polymorphic region on the binding potential (BP_ND) of these receptors. The aim of our study was to investigate the relationship between a 5-HT_1A promoter polymorphism and the binding potential of another selective 5-HT_1A receptor antagonist, [¹⁸F]MPPF, in healthy subjects.

Methods

Thirty-five volunteers, including 23 women, underwent an [¹⁸F]MPPF scan and were genotyped for both the C(-1019)G 5-HT_1A promoter polymorphism and the triallelic serotonin transporter gene-linked polymorphic region. We used a simplified reference tissue model to generate parametric images of BP_ND. Whole brain Statistical Parametric Mapping and raphe nuclei region of interest analyses were performed to look for an association of [¹⁸F]MPPF BP_ND with the C(-1019)G 5-HT_1A promoter polymorphism.

Results

Among the 35 subjects, 5-HT_1A promoter genotypes occurred with the following frequencies: three G/G, twenty-one G/C, and eleven C/C. No difference of [¹⁸F]MPPF BP_ND between groups was observed, except for two women who were homozygote carriers for the G allele and showed greater binding potential compared to other age-matched women over the frontal and temporal neocortex. However, the biological relevance of this result remains uncertain due to the very small number of subjects with a G/G genotype. These findings were not modified by excluding individuals carrying the S/S genotype of the serotonin transporter gene-linked polymorphic region.

Conclusions

We failed to observe an association between the C(-1019)G 5-HT_1A promoter polymorphism and [¹⁸F]MPPF binding in healthy subjects. However our data suggest that the small number of women homozygote for the G allele might have greater [¹⁸F]MPPF BP_ND relative to other individuals. This finding should be confirmed in a larger sample.

Electrical impedance tomography compared to positron emission tomography for the measurement of regional lung ventilation: an experimental study

Introduction

Electrical impedance tomography (EIT), which can assess regional lung ventilation at the bedside, has never been compared with positron-emission tomography (PET), a gold-standard to quantify regional ventilation. This experiment systematically compared both techniques in injured and non-injured lungs.

Methods

The study was performed in six mechanically ventilated female piglets. In normal lungs, tidal volume (V_T) was randomly changed to 6, 8, 10 and 15 ml/kg on zero end-expiratory pressure (ZEEP), then, at V_T 10 ml/kg, positive end-expiratory pressure (PEEP) was randomly changed to 5, 10 and 15 cmH₂O. Afterwards, acute lung injury (ALI) was subsequently created in three animals by injecting 3 ml/kg hydrochloric acid into the trachea. Then at PEEP 5 cmH₂O, V_T was randomly changed to 8 and 12 ml/kg and PEEP of 10 and 15 cmH₂O applied at V_T 10 ml/kg. EIT and PET examinations were performed simultaneously. EIT ventilation (V_TEIT) and lung volume (V_L) were measured in the anterior and posterior area of each lung. On the same regions of interest, ventilation (V_PET) and aerated lung volume (VA_atten) were determined with PET.

Results

On ZEEP, V_TEIT and V_PET significantly correlated for global (V_TEIT = VPET - 2E-13, R² = 0.95, P < 0.001) and regional (V_TEIT = 0.81V_PET+7.65, R² = 0.63, P < 0.001) ventilation over both conditions. For ALI condition, corresponding R² were 0.91 and 0.73 (P < 0.01). Bias was = 0 and limits of agreement were -37.42 and +37.42 ml/min for global ventilation over both conditions. These values were 0.04 and -29.01 and +29.08 ml/min, respectively, for regional ventilation. Significant correlations were also found between V_L and VA_atten for global (V_L = VA_atten+1E-12, R² = 0.93, P < 0.0001) and regional (V_L = 0.99VA_atten+0.92, R² = 0.65, P < 0.001) volume. For ALI condition, corresponding R² were 0.94 (P < 0.001) and 0.54 (P < 0.05). Bias was = 0 and limits of agreement ranged -38.16 and +38.16 ml for global ventilation over both conditions. These values were -0.24 and -31.96 to +31.48 ml, respectively, for regional ventilation.

Conclusions

Regional lung ventilation and volume were accurately measured with EIT in healthy and injured lungs and validated by simultaneous PET imaging.

Association between triallelic polymorphism of the serotonin transporter and [18F]MPPF binding potential at 5-HT1A receptors in healthy subjects

Previous [(11)C]WAY100-635 PET studies have demonstrated that the short (S) and long (L) alleles of the serotonin transporter gene-linked polymorphic region (5-HTTLPR) were associated with distinct patterns of 5-HT(1A) receptor distribution in human. However, these studies reported discordant findings and did not take into account the recent description of two functional variants of the L allele (L(A)/L(G)). To further explore this issue, we investigated the triallelic functional polymorphism of the 5-HTTLPR in 38 healthy volunteers who underwent a [(18)F]MPPF PET study of 5-HT1A receptors. We used a simplified reference tissue model to generate parametric images of [(18)F]MPPF binding potential (BP(ND)), and compared these data among the different genotypes using statistical parametric mapping and region of interest of the raphe nuclei. Homozygote carriers of the S allele demonstrated greater [(18)F]MPPF BP(ND) than carriers of the L(A) allele, but this association was only found in women. Differences in [(18)F]MPPF BP(ND) between women with and without L(A) allele were observed over large clusters encompassing the right and left temporal lobes, cingulate and perisylvian regions, as well as the right precuneus and frontal dorso-lateral cortex, and the left orbitofrontal cortex. In contrast, no difference was found between groups in the raphe nuclei. The greater [(18)F]MPPF BP(ND) observed in women homozygote carriers of the S allele could either reflect a greater 5-HT1A receptor density or a lower extracellular concentration of 5-HT. Our data suggest that any future PET studies of 5-HT1A receptors should incorporate the 5-HTTLPR polymorphism status of the population studied.

Cardiovascular risk factors in a sample of a rural Belgian population: the Bellux MONICA Study

A sample of 1949 subjects of the population of the Belgian province of Luxembourg was screened for levels of cardiovascular risk factors. Cigarette smoking was more prevalent among males (51%) than among females (17%). The relationship between smoking and socio-economic status was inverse in males (M) and direct in females (F). Blood pressure (BP) measurements showed definite high BP in 10% of this sample, and 60% of those with definite high BP were not taking any hypertensive drugs. The average total cholesterol value was 6.49 mmol/L in M and 6.45 mmol/L in F. F had lower values than M at a younger age, but higher values than M at an older age. The high-density lipoprotein cholesterol was higher in F (1.57 mmol/L) than in M (1.27 mmol/L). Diabetes was present in 4.2% of this sample. In nearly half of these participants, the disease had been discovered during the screening. Obesity was especially frequently among F in all three age groups. In conclusion, the main cardiovascular risk factors were found to be at a fairly high level in this population sample.

Effect of activated protein C on pulmonary blood flow and cytokine production in experimental acute lung injury

OBJECTIVE

In acute lung injury (ALI) activated protein C (APC) may reopen occluded lung vessels and minimize lung inflammation. We aimed at assessing the effect of APC on regional lung perfusion, aerated lung volume, cytokine production and oxygenation in experimental ALI.

DESIGN AND SETTING

Prospective, controlled study in an imaging facility.

PARTICIPANTS

Pigs tracheotomized and mechanically ventilated.

INTERVENTION

Pigs were randomly given intravenously APC (n = 8) or saline (n = 8). Thirty minutes later, ALI was induced by injecting oleic acid.

MEASUREMENTS AND RESULTS

Lung perfusion and aerated lung volume measured with positron emission tomography, plasma cytokines and arterial blood gas were determined just before ALI and 110 and 290 min thereafter. Lung cytokines were measured at the end of the experiment. PaO2 under F I O2 1 was significantly lower in the APC group before lung injury (473+/-129 vs. 578+/-54 mmHg) and 110 min (342+/-138 vs. 446+/-103 mmHg) and 290 min (303+/-171 vs. 547+/-54 mmHg) thereafter (p < 0.05). Lung perfusion nonsignificantly tended to redistribute towards dorsal lung regions with APC. Total aerated lung volume was not different between APC and control before ALI (10.0+/-1.5 vs. 11.0+/-2.5 ml/kg) (p > 0.05) or thereafter. Plasma IL-6 and IL-8 at 110 min were greater with APC (p < 0.05).

CONCLUSIONS

In contrast to studies using other models, pretreatment with APC was associated with worsening oxygenation in the present investigation. This might be due to ventilation-perfusion mismatch, with more perfusion to dependent nonaerated areas.

Test-retest reproducibility of 18F-MPPF PET in healthy humans: a reliability study

The aim of this study was to assess the reliability of 2'-methoxyphenyl-(N-2'-pyridinyl)-p-18F-fluoro-benzamidoethylpiperazine (18F-MPPF) PET binding parameter's quantification via a test-retest study over a long-term period.

METHODS

Ten healthy volunteers underwent 2 dynamic 18F-MPPF PET scans in an interval of 6 mo. As a methodologic control, 10 simulated datasets, including interindividual functional and anatomic variabilities, were also used to assess the measurement variations in the absence of intraindividual variability. Indices of tracer binding were computed using 2 different models: (a) the simplified reference tissue model (SRTM) and (b) the Logan graphical model. The SRTM allows computing the binding potential (BP) index and plasma-to-brain transport constants (R1, k2). The Logan model evaluates the distribution volume (DV). For both methods, cerebellum was taken as the reference region. From both models, binding indices were calculated with time-activity curves extracted from regions of interest, on one hand, and for each voxel to perform parametric images on the other hand.

RESULTS

Reliability indices--that is, bias, variability, and intraclass correlation (ICC)--indicated a good reproducibility: the BP percentage change in mean between test and retest is close to 1% in rich regions and 2% in poor regions. The typical error is around 7%. Mean ICC is over 0.70. The DV percentage change in the mean is +/-2.5%, with a typical error close to 6% and an ICC over 0.60.

CONCLUSION

Our results show a good reliability, with a reasonable level of intraindividual biologic variability that allows crossover studies with 18F-MPPF in which small percentage changes are expected between test and retest measurements, in group studies and for single subject assessment.

Functional anatomy of motor urgency

This PET H(2)(15)O study uses a reaching task to determine the neural basis of the unconscious motor speed up observed in the context of urgency in healthy subjects. Three conditions were considered: self-initiated (produce the fastest possible movement toward a large plate, when ready), externally-cued (same as self-initiated but in response to an acoustic cue) and temporally-pressing (same as externally-cued with the plate controlling an electromagnet that prevented a rolling ball from falling at the bottom of a tilted ramp). Results show that: (1) Urgent responses (Temporally-pressing versus Externally-cued) engage the left parasagittal and lateral cerebellar hemisphere and the sensorimotor cortex (SMC) bilaterally; (2) Externally-driven responses (Externally-cued versus Self-initiated) recruit executive areas within the contralateral SMC; (3) Volitional responses (Self-initiated versus Externally-cued) involve prefrontal cortical areas. These observations are discussed with respect to the idea that neuromuscular energy is set to a submaximal threshold in self-determined situations. In more challenging tasks, this threshold is raised and the first answer of the nervous system is to optimize the response of the lateral (i.e. crossed) corticospinal tract (contralateral SMC) and ipsilateral cerebellum. In a second step, the anterior (i.e. uncrossed) corticospinal tract (ipsilateral SMC) and the contralateral cerebellum are recruited. This recruitment is akin to the strategy observed during recovery in patients with brain lesions.

Alveolar recruitment assessed by positron emission tomography during experimental acute lung injury

OBJECTIVES

To compare changes in aerated lung volumes measured by positron emission tomography (PET) and inflation volume-pressure curve (V-P) of the respiratory system, and to evaluate the reliability of PET to assess alveolar recruitment.

DESIGN AND SETTING

Experimental study in six anesthetized and mechanically ventilated pigs in a PET facility in an experimental university laboratory.

INTERVENTIONS

Lung injury was induced by oleic acid. Animals were randomly studied in four conditions: PEEP 0cmH(2)O (ZEEP) in supine position (SP), PEEP 10cmH(2)O in SP, ZEEP in prone position (PP) and PEEP in PP, each applied for 30min.

MEASUREMENTS AND RESULTS

With PET aerated lung volume was obtained from pulmonary density analysis using transmission scan (VA(trans)) and from nitrogen-13 kinetics on emission scan (VA(em)). Changes in VA(trans) and VA(em) were computed as the difference in aerated volume between conditions. VA(trans) and VA(em) did not differ between SP and PP, on either ZEEP or PEEP, suggesting no modification in relaxation volume of the respiratory system induced by posture. Changes in VA(trans) or VA(em) were significantly correlated with changes in aerated volume assessed from superimposed V-P curves (R (2)=0.74 and 0.75, respectively). Alveolar recruitment assessed by PET was significantly correlated with both PaO(2) (R (2)=0.61) and PaCO(2) (R (2)=0.40) variations induced by PEEP.

CONCLUSIONS

PET is a new reliable tool of scientific interest to image lung volume and alveolar recruitment during acute lung injury.

A 18F-MPPF PET normative database of 5-HT1A receptor binding in men and women over aging

Neurotransmission imaging studies require normative data for the statistical assessment of neurophysiologic dysfunctions. 2'-Methoxyphenyl-(N-2'-pyridinyl)-p-18F-fluoro-benzamidoethylpiperazine (18F-MPPF) is a specific serotonin 5-HT1A antagonist PET tracer recently characterized, modeled, and used for clinical research to explore abnormalities in the serotoninergic system. Our study reports, to our knowledge, the first large normative imaging database of 18F-MPPF binding potential (BP) over aging, for both males and females.

METHODS

Fifty-three healthy volunteers (27 females, 26 males; age, 20-70 y) were selected to undergo structural MRI and single-injection 18F-MPPF multiframe dynamic PET. 18F-MPPF BP values were computed using a nonlinear modeling method with tissue reference. The statistical assessment of the effect of age and sex was performed both at the anatomic structure level, using regions of interest drawn manually on individual MR images, and at the voxel level, using normalized BP parametric images in different statistical parametric mapping designs.

RESULTS

A negative linear correlation between age and 18F-MPPF binding (3.6% decrease by decade) was found in females but not in males and involved most of the limbic and paralimbic regions; on the other hand, males in their 30s showed decreased binding in most cerebral regions.

CONCLUSION

A comparison of males and females revealed higher BP values independent of age in females in the right hemisphere and a different evolution of BP over aging. These results confirm the necessity of a database for further statistical analysis in individuals or groups with pathology.

Double dissociation in neural correlates of visual working memory: A PET study

Using positron emission tomography (PET), we investigated the organisation of spatial versus object-based visual working memory in 11 normal human subjects. The paradigm involved a conditional colour-response association task embedded within two visual working memory tasks. The subject had to remember a position (spatial) or shape (object-based) and then use this to recover the colour of the matching element for the conditional association. Activation of the nucleus accumbens and the anterior cingulate cortex was observed during the conditional associative task, indicating a possible role of these limbic structures in associative memory. When the 2 memory tasks were contrasted, we observed activation of 2 distinct cortical networks: (1) The spatial task activated a dorsal stream network distributed in the right hemisphere in the parieto-occipital cortex and the dorsal prefrontal cortex, and (2) The non spatial task activated a ventral stream network distributed in the left hemisphere in the temporo- occipital cortex, the ventral prefrontal cortex and the striatum. These results support the existence of a domain-specific dissociation with dorsal and ventral cortical systems involved respectively in spatial and non spatial working memory functions.

Quantitative assessment of regional alveolar ventilation and gas volume using 13N-N2 washout and PET

Measurement of alveolar volume (Va) and regional ventilation (a) is crucial to understanding the pathophysiology of acute lung injury and ventilator-induced lung injury. PET has previously been used as a noninvasive, quantitative method to assess a, but formal validation of this technique in experimental lung injury is lacking. This study aims to validate Va and a regional assessment with PET, using inhaled (13)N-N(2) in pigs.

METHODS

Two normal and 2 oleic acid-injured pigs were tracheotomized, mechanically ventilated, and studied in 5 different levels of ventilation by changing respiratory rate. In each experimental condition, lungs were washed-in and then washed-out with (13)N-N(2) through an open circuit in the ventilator. Using this method, multiframe images were acquired with a dedicated PET camera. Regions of interest (ROIs) were drawn on each lung. Regional time-activity curves during washout were generated for each ROI and fitted to a mono- and a bicompartmental model. Validation of this method was performed in 2 ways. First, regional values of predicted Va (Va(emission)) were compared with regional volume obtained independently from density analysis on a transmission scan (Va(trans)). Second, regional values of predicted a were summed in each animal during each experimental condition and compared with minute-ventilation values set on the ventilator.

RESULTS

The bicompartmental model best fitted the experimental values in normal (94.7% [62.2%-100.0%] (median [interquartile range]) of the ROIs) as well as in injured animals (90.7% [81.6%-97.4%] of the ROIs) (P = 0.49). Va(emission) significantly correlated with Va(trans) (R(2) = 0.89, P < 0.001) but exceeded Va(trans) by 10%. Finally, a strongly and positively correlated with minute-ventilation in both normal (R(2) = 0.96, P < 0.001) and injured (R(2) = 0.96, P < 0.001) animals.

CONCLUSION

Measurement of (13)N-N(2) washout using PET is accurate to assess regional alveolar volume and ventilation during experimental acute lung injury.

Seizure-related short-term plasticity of benzodiazepine receptors in partial epilepsy: a [11C]flumazenil-PET study

We have undertaken a test-re-test [11C]flumazenil (FMZ) PET study in 10 drug-resistant epileptic patients, including six with a mesiotemporal epilepsy (MTE), and 10 normal controls, in order to investigate seizure-related short-term plasticity of benzodiazepine (BZD) receptors. All subjects underwent two FMZ-PET scans at a 1 week interval. Patients benefited from a concurrent video-EEG monitoring which allowed determination of the duration of the interictal period (IP) preceding each PET. Test-re-test whole brain B'(max) variations, evaluated with a partial-saturation injection protocol, were similarly observed in patients and controls, suggesting a physiological modulation of BZD receptors. Five patients (50%), but no controls, also demonstrated clinically significant test-re-test FMZ-PET variations in the mesial temporal region. This was observed in all three patients with MTE and no hippocampal atrophy in whom only the PET study associated with the shortest IP correctly identified the epileptogenic zone. Statistical analysis revealed a significant effect of IP duration on BZD receptor B'(max) in MTE patients, suggesting that the shorter the IP, the lower the B'(max) in the epileptogenic hippocampus. FMZ-PET appears to be an interesting tool for investigating both normal and abnormal short-term modulations of the BZD receptor system, and should ideally be performed within a few days following a seizure in patients with MTE and a normal MRI.

Effect of sensory stimulus on striatal dopamine release in humans and cats: a [11C]raclopride PET study

BACKGROUND

Sensory stimulation of the forelimb extremities constitutes a well-established experimental model that has consistently shown to activate dopamine (DA) neurotransmission in the mammals' forebrain.

OBJECTIVES

To visualize in vivo this modification of striatal DA release in healthy human volunteers using Positron Emission Tomography (PET) and [(11)C]raclopride. Experiments in humans were paralleled by experiments in anesthetized cats. Changes in endogenous DA release were assessed through its competition with [(11)C]raclopride binding (BP(raclo)), a radioligand probing DA D2-receptors.

RESULTS

In humans no significant difference of BP(raclo) in caudate (with sensory stimulation: 2.0 +/- 0.3 versus without sensory stimulation: 2.2 +/- 0.3; P = 0.3) or putamen (2.6 +/- 0.3 versus 2.6 +/- 0.2; P = 0.9) ipsilateral to the stimulus was disclosed as a result of sensory stimulation. Similarly, no change of BP(raclo) was observed contralaterally to the stimulation in the caudate nucleus (with sensory stimulation: 2.0 +/- 0.4 versus without sensory stimulation: 2.1 +/- 0.2; P = 0.5) and the putamen (2.5 +/- 0.4 versus 2.6 +/- 0.2; P = 0.4). In cats the same results were obtained in the ipsilateral to stimulation striatum (with sensory stimulation: 2.5 +/- 0.03 versus without sensory stimulation: 2.4 +/- 0.05; P = 0.7). No change was also observed contralaterally to the stimulation (2.4 +/- 0.04 versus 2.5 +/- 0.06; P = 0.6). The [(11)C]raclopride binding remained unchanged by sensory stimuli in both humans and cats.

CONCLUSION

This suggests that the DA release induced by sensory stimulus is mostly extrasynaptic whereas the synaptic DA release is probably small, which fits well with the absence of [(11)C]raclopride displacement. The mechanism of this extrasynaptic DA release could be related to a local action of glutamate on dopaminergic terminals via a thalamo-cortico-striatal loop. Present results also underline homology between cat and human responses to sensory stimuli and validate the use of cat brain to find physiological concepts in humans.

Globus pallidus internus stimulation in primary generalized dystonia: a H215O PET study

Globus pallidus internus (GPi) deep brain stimulation (DBS) increasingly shows promising efficacy in the treatment of severe primary generalized dystonia. Functional imaging studies have shown previously that dystonia could be related to abnormal cortical activation during voluntary movement. In the present study, the effects of GPi DBS on regional cerebral blood flow (rCBF) during a motor task were studied in patients with primary generalized dystonia. rCBF was measured using H215O and PET in eight control subjects and six patients with dystonia treated with bilateral GPi DBS. Subjects were scanned at rest and while performing joystick movements. Dystonic patients were tested in two conditions: 'OFF' (stimulator bilaterally switched off) and 'ON' (unilateral stimulation). In the 'OFF' condition, compared with rest, motor activation of the most dystonic hand was associated with overactivity in the contralateral dorsolateral prefrontal cortex, gyrus frontalis medialis, superior frontal gyrus (area 10), frontoorbital cortex and thalamus. In the 'ON' condition, GPi DBS contralaterally to the most dystonic hand induced a decrease of the overactivation in the same areas, as well as the putamen. According to the present study, generalized dystonia is associated with prefrontal overactivation which can be reversed by effective GPi DBS.

Statistical parametric mapping of 5-HT1A receptor binding in temporal lobe epilepsy with hippocampal ictal onset on intracranial EEG

Experimental data in animals show that 5-HT(1A) receptors are predominantly located in limbic areas and suggest that serotonin, via these receptors, mediates an antiepileptic and anticonvulsant effect. In this PET study, we used an antagonist of the 5-HT(1A) receptor, [(18)F]MPPF, to assess the extent of 5-HT(1A) receptor binding changes in a group of seven temporal lobe epilepsy (TLE) patients with hippocampal ictal onset demonstrated by intracerebral EEG recording. On the basis of MRI-measured hippocampal volumes (HV), patients were classified into "normal HV" or "hippocampal atrophy" (HA). Voxel-based analyses (SPM99) were performed to objectively assess the differences in [(18)F]MPPF binding potential (BP) between patients (taken as a group or as individuals) and a database of 48 controls subjects. In the full group of patients, a significant decreased BP was detected ipsilateral to the epileptogenic zone in the hippocampus, temporal pole, insula, and temporal neocortex. This result was confirmed in the subgroup of patients with HA. In patients with normal HV, the BP decrease was restricted to the temporal pole. TLE patients also demonstrated an increased BP in various regions contralateral to the epileptogenic zone. These data suggest that in TLE patients with hippocampal seizure onset, the decrease in 5-HT(1A) receptor binding partly reflects hippocampal neuronal loss, but is also observed in various regions involved in temporo-limbic epileptogenic networks that appeared normal on MRI. Further studies are warranted to evaluate the clinical usefulness of [(18)F]MPPF-PET as compared to other established PET tracers in drug resistant TLE.

5-HT1A receptor binding and intracerebral activity in temporal lobe epilepsy: an [18F]MPPF-PET study

The aim of our study was to assess abnormalities in 5-hydroxytryptamine-1A (5-HT1A) receptor density in patients suffering from refractory temporal lobe epilepsy (TLE). Experimental data in animals show that 5-HT1A receptors are predominantly located in limbic areas, and that serotonin, via these receptors, mediates an antiepileptic and anticonvulsant effect. In TLE patients, we quantified 5-HT1A receptor density in epileptogenic and non-epileptogenic areas, as defined by intracranial recordings with stereo-electroencephalography (SEEG). Nine TLE patients and 53 control subjects were studied by PET using a 5-HT1A receptor antagonist ([18F]MPPF). Anatomical regions of interest (ROIs) were drawn on patient and control MRIs co-registered with PET. PET data were quantified using a simplified model to assess binding potential (BP) values in each ROI, with cerebellum as reference. For each patient, a normalized percentage BP change was calculated as the relative variation of BP in each ROI compared with the corresponding ROI in control subjects. In patients, ROIs explored by SEEG were categorized according to their degree of epileptic activity (ictal onset, ictal spreading, interictal spikes, no epileptic activity) and according to their lesional aspect and volume (lesional with volume loss, lesional without volume loss, non-lesional). Compared with control values, the binding to 5-HT1A receptors in TLE patients was decreased in the epileptogenic temporal lobe. BP decrease was significantly greater in: (i) regions involved in the seizure onset than regions where only interictal paroxysms or no epileptic activity was recorded; and (ii) regions where the discharge propagated than regions where only interictal paroxysms or no epileptic activity was recorded. BP decrease was shown to be significantly influenced by the existence of a lesion on MRI. However, in the group of ROIs with normal quantitative and qualitative MRI aspect, BP decrease remained strongly correlated to the degree of epileptic activity. This study shows that in vivo availability of 5-HT1A receptors is decreased in epileptic patients compared with normal subjects. This decrease is highly correlated to the degree of epileptogenicity of cortical areas explored by intracerebral recordings, and does not reflect only pathological changes or neuronal loss in the epileptic focus.

Effect of position, nitric oxide, and almitrine on lung perfusion in a porcine model of acute lung injury

In a porcine model of oleic acid-induced lung injury, the effects of inhaled nitric oxide (iNO) and intravenous almitrine bismesylate (ivALM), which enhances the hypoxic pulmonary vasoconstriction on the distribution of regional pulmonary blood flow (PBF), were assessed. After injection of 0.12 ml/kg oleic acid, 20 anesthetized and mechanically ventilated piglets [weight of 25 +/- 2.6 (SD) kg] were randomly divided into four groups: supine position, prone position, and 10 ppm iNO for 40 min followed by 4 microg x kg(-1) x min(-1) ivALM for 40 min in supine position and in prone position. PBF was measured with positron emission tomography and H(2)15O. The redistribution of PBF was studied on a pixel-by-pixel basis. Positron emission tomography scans were performed before and then 120, 160, and 200 min after injury. With prone position alone, although PBF remained prevalent in the dorsal regions it was significantly redistributed toward the ventral regions (P < 0.001). A ventral redistribution of PBF was also obtained with iNO regardless of the position (P = 0.043). Adjunction of ivALM had no further effect on PBF redistribution. PP and iNO have an additive effect on ventral redistribution of PBF.

Comparison of PET with radioactive microspheres to assess pulmonary blood flow

Microsphere technique is the reference for assessment of pulmonary blood flow (PBF) but is destructive; PET, however, can determine PBF noninvasively. Comparisons of these 2 methods are scanty. Our study aimed at comparing these 2 techniques using a mathematic model taking into account the right ventricle in determining the transit time of a tracer through lung tissue.

METHODS

Ten normal pigs were investigated at baseline, during dobutamine infusion, and during 10 cm H(2)O of positive end-expiratory pressure. Under each condition, PBF was successively measured with PET (PET-PBF) and radioactive microspheres (MS-PBF). For PET-PBF, 2 mCi (74 MBq) (15)O-labeled water were injected intravenously over 20 s and PET scanning was performed for 10 min. The input function was determined noninvasively from PET and invasively from mixed venous blood withdrawals. PET-PBF was computed using a mathematic model taking into account the right ventricle in determining the transit time of the tracer through lung tissue. For MS-PBF, 1 given isotope was injected under a given condition. PET-PBF and MS-PBF for 5 lung regions were compared.

RESULTS

PET-PBF significantly correlated with MS-PBF both over all experimental points (PET-PBF = 0.79. MS-PBF + 1,538; r = 0.79; P < 0.001) and in separate lung regions. Invasive and noninvasive input functions also correlated significantly (r = 0.90; P < 0.001). Simulations stressed the crucial role of the right ventricle to the transit time of tracer through lung tissue in the determination of PET-PBF.

CONCLUSION

PBF can accurately be assessed using PET and a mathematic model taking into account the right ventricle in determining the transit time of a tracer through lung tissue. Noninvasive determination of the input function of the right ventricle is accurate and can readily be used for clinical applications.

Modeling [18 F]MPPF positron emission tomography kinetics for the determination of 5-hydroxytryptamine(1A) receptor concentration with multiinjection

The selectivity of [18F]MPPF (fluorine-18-labeled 4-(2;-methoxyphenyl)-1-[2;-(N-2"-pirydynyl)-p-fluorobenzamido]ethylpiperazine) for serotonergic 5-hydroxytryptamine(1A) (5-HT1A) receptors has been established in animals and humans. The authors quantified the parameters of ligand-receptor exchanges using a double-injection protocol. After injection of a tracer and a coinjection dose of [18F]MPPF, dynamic positron emission tomography (PET) data were acquired during a 160-minute session in five healthy males. These PET and magnetic resonance imaging data were coregistered for anatomical identification. A three-compartment model was used to determine six parameters: Fv (vascular fraction), K1, k2 (plasma/free compartment exchange rate), koff, kon/Vr (association and dissociation rate), Bmax (receptor concentration), and to deduce Kd (apparent equilibrium dissociation rate). The model was fitted with regional PET kinetics and arterial input function corrected for metabolites. Analytical distribution volume and binding potential were compared with indices generated by Logan-Patlak graphical analysis. The 5HT1A specificity for MPPF was evidenced. A Bmax of 2.9 pmol/mL and a Kd of 2.8 nmol/L were found in hippocampal regions, Kd and distribution volume in the free compartment were regionally stable, and the Logan binding potential was linearly correlated to Bmax. This study confirms the value of MPPF in the investigation of normal and pathologic systems involving the limbic network and 5-HT1A receptors. Standard values can be used for the simulation of simplified protocols.

Brain processing of visual sexual stimuli in human males

Despite its critical sociobiological importance, the brain processing of visual sexual stimuli has not been characterized precisely in human beings. We used Positron Emission Tomography (PET) to investigate responses of regional cerebral blood flow (rCBF) in nine healthy males presented with visual sexual stimuli of graded intensity. Statistical Parametric Mapping was used to locate brain regions whose activation was associated with the presentation of the sexual stimuli and was correlated with markers of sexual arousal. The claustrum, a region whose function had been unclear, displayed one of the highest activations. Additionally, activations were recorded in paralimbic areas (anterior cingulate gyrus, orbito-frontal cortex), in the striatum (head of caudate nucleus, putamen), and in the posterior hypothalamus. By contrast, decreased rCBF was observed in several temporal areas. Based on these results, we propose a model of the brain processes mediating the cognitive, emotional, motivational, and autonomic components of human male sexual arousal.

Functional neuroanatomy of different olfactory judgments

Humans routinely make judgments about olfactory stimuli. However, few studies have examined the functional neuroanatomy underlying the cognitive operations involved in such judgments. In order to delineate this functional anatomy, we asked 12 normal subjects to perform different judgments about olfactory stimuli while regional cerebral blood flow (rCBF) was measured with PET. In separate conditions, subjects made judgments about the presence (odor detection), intensity, hedonicity, familiarity, or edibility of different odorants. An auditory task served as a control condition. All five olfactory tasks induced rCBF increases in the right orbitofrontal cortex (OFC), but right OFC activity was highest during familiarity judgments and lowest during the detection task. Left OFC activity increased significantly during hedonic and familiarity judgments, but not during other odor judgments. Left OFC activity was significantly higher during hedonicity judgments than during familiarity or other olfactory judgments. These data demonstrate that aspects of odor processing in the OFC are lateralized depending on the type of olfactory task. They support a model of parallel processing in the left and right OFC in which the relative level of activation depends on whether the judgment involves odor recognition or emotion. Primary visual areas also demonstrated a differential involvement in olfactory processing depending on the type of olfactory task: significant rCBF increases were observed in hedonic and edibility judgments, whereas no significant rCBF increases were found in the other three judgments. These data indicate that judgments of hedonicity and edibility engage circuits involved in visual processing, but detection, intensity, and familiarity judgments do not.

Brain processing of visual sexual stimuli in human males

Despite its critical sociobiological importance, the brain processing of visual sexual stimuli has not been characterized precisely in human beings. We used Positron Emission Tomography (PET) to investigate responses of regional cerebral blood flow (rCBF) in nine healthy males presented with visual sexual stimuli of graded intensity. Statistical Parametric Mapping was used to locate brain regions whose activation was associated with the presentation of the sexual stimuli and was correlated with markers of sexual arousal. The claustrum, a region whose function had been unclear, displayed one of the highest activations. Additionally, activations were recorded in paralimbic areas (anterior cingulate gyrus, orbito-frontal cortex), in the striatum (head of caudate nucleus, putamen), and in the posterior hypothalamus. By contrast, decreased rCBF was observed in several temporal areas. Based on these results, we propose a model of the brain processes mediating the cognitive, emotional, motivational, and autonomic components of human male sexual arousal.

Brain processing of visual sexual stimuli in human males

Despite its critical sociobiological importance, the brain processing of visual sexual stimuli has not been characterized precisely in human beings. We used Positron Emission Tomography (PET) to investigate responses of regional cerebral blood flow (rCBF) in nine healthy males presented with visual sexual stimuli of graded intensity. Statistical Parametric Mapping was used to locate brain regions whose activation was associated with the presentation of the sexual stimuli and was correlated with markers of sexual arousal. The claustrum, a region whose function had been unclear, displayed one of the highest activations. Additionally, activations were recorded in paralimbic areas (anterior cingulate gyrus, orbito-frontal cortex), in the striatum (head of caudate nucleus, putamen), and in the posterior hypothalamus. By contrast, decreased rCBF was observed in several temporal areas. Based on these results, we propose a model of the brain processes mediating the cognitive, emotional, motivational, and autonomic components of human male sexual arousal.

Brain processing of visual sexual stimuli in human males

Despite its critical sociobiological importance, the brain processing of visual sexual stimuli has not been characterized precisely in human beings. We used Positron Emission Tomography (PET) to investigate responses of regional cerebral blood flow (rCBF) in nine healthy males presented with visual sexual stimuli of graded intensity. Statistical Parametric Mapping was used to locate brain regions whose activation was associated with the presentation of the sexual stimuli and was correlated with markers of sexual arousal. The claustrum, a region whose function had been unclear, displayed one of the highest activations. Additionally, activations were recorded in paralimbic areas (anterior cingulate gyrus, orbito-frontal cortex), in the striatum (head of caudate nucleus, putamen), and in the posterior hypothalamus. By contrast, decreased rCBF was observed in several temporal areas. Based on these results, we propose a model of the brain processes mediating the cognitive, emotional, motivational, and autonomic components of human male sexual arousal.

Emotional responses to pleasant and unpleasant olfactory, visual, and auditory stimuli: a positron emission tomography study

Neural correlates of responses to emotionally valenced olfactory, visual, and auditory stimuli were examined using positron emission tomography. Twelve volunteers were scanned using the water bolus method. For each sensory modality, regional cerebral blood flow (rCBF) during presentation of both pleasant and unpleasant stimuli was compared with that measured during presentation of neutral stimuli. During the emotionally valenced conditions, subjects performed forced-choice pleasant and unpleasant judgments. During the neutral conditions, subjects were asked to select at random one of a two key-press buttons. All stimulations were synchronized with inspiration, using an airflow olfactometer, to present the same number of stimuli for each sensory modality. A no-stimulation control condition was also performed in which no stimulus was presented. For all three sensory modalities, emotionally valenced stimuli led to increased rCBF in the orbitofrontal cortex, the temporal pole, and the superior frontal gyrus, in the left hemisphere. Emotionally valenced olfactory and visual but not auditory stimuli produced additional rCBF increases in the hypothalamus and the subcallosal gyrus. Only emotionally valenced olfactory stimuli induced bilateral rCBF increases in the amygdala. These findings suggest that pleasant and unpleasant emotional judgments recruit the same core network in the left hemisphere, regardless of the sensory modality. This core network is activated in addition to a number of circuits that are specific to individual sensory modalities. Finally, the data suggest a superior potency of emotionally valenced olfactory over visual and auditory stimuli in activating the amygdala.

Parietal and cingulate processes in central pain. A combined positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) study of an unusual case

Parietal, insular and anterior cingulate cortices are involved in the processing of noxious inputs and genesis of pain sensation. Parietal lesions may generate central pain by mechanisms generally assumed to involve the 'medial' pain system (i.e. medial thalamic nuclei and anterior cingulate cortex (ACC)). We report here PET and fMRI data in a patient who developed central pain and allodynia in her left side after a bifocal infarct involving both the right parietal cortex (SI and SII) and the right ACC (Brodmann areas 24 and 32), thus questioning the schematic representation of cortical pain processing. No rCBF increase was found in any part of the residual cingulate cortices, neither in the basal state (which included spontaneous pain and extended hypoperfusion around the infarct), nor during left allodynic pain. Thus, as previously observed in patients with lateral medullary infarct, neither spontaneous pain nor allodynia reproduce the cingulate activation observed after noxious pain in normal subjects. Conversely, both PET and fMRI data argue in favour of plastic changes in the 'lateral discriminative' pain system. Particularly, allodynia was associated with increased activity anteriorly to the infarct in the right insula/SII cortex. This response is likely to be responsible for the strange and very unpleasant allodynic sensation elicited on the left side by a non-noxious stimulation.

Electrical stimulation of motor cortex for pain control: a combined PET-scan and electrophysiological study

Although electrical stimulation of the precentral gyrus (MCS) is emerging as a promising technique for pain control, its mechanisms of action remain obscure, and its application largely empirical. Using positron emission tomography (PET) we studied regional changes in cerebral flood flow (rCBF) in 10 patients undergoing motor cortex stimulation for pain control, seven of whom also underwent somatosensory evoked potentials and nociceptive spinal reflex recordings. The most significant MCS-related increase in rCBF concerned the ventral-lateral thalamus, probably reflecting cortico-thalamic connections from motor areas. CBF increases were also observed in medial thalamus, anterior cingulate/orbitofrontal cortex, anterior insula and upper brainstem; conversely, no significant CBF changes appeared in motor areas beneath the stimulating electrode. Somatosensory evoked potentials from SI remained stable during MCS, and no rCBF changes were observed in somatosensory cortex during the procedure. Our results suggest that descending axons, rather than apical dendrites, are primarily activated by MCS, and highlight the thalamus as the key structure mediating functional MCS effects. A model of MCS action is proposed, whereby activation of thalamic nuclei directly connected with motor and premotor cortices would entail a cascade of synaptic events in pain-related structures receiving afferents from these nuclei, including the medial thalamus, anterior cingulate and upper brainstem. MCS could influence the affective-emotional component of chronic pain by way of cingulate/orbitofrontal activation, and lead to descending inhibition of pain impulses by activation of the brainstem, also suggested by attenuation of spinal flexion reflexes. In contrast, the hypothesis of somatosensory cortex activation by MCS could not be confirmed by our results.

Haemodynamic brain responses to acute pain in humans: sensory and attentional networks

Turning attention towards or away from a painful heat stimulus is known to modify both the subjective intensity of pain and the cortical evoked potentials to noxious stimuli. Using PET, we investigated in 12 volunteers whether pain-related regional cerebral blood flow (rCBF) changes were also modulated by attention. High (mean 46.6 degrees C) or low (mean 39 degrees C) intensity thermal stimuli were applied to the hand under three attentional conditions: (i) attention directed towards the stimuli, (ii) attention diverted from the stimuli, and (iii) no task. Only the insular/second somatosensory cortices were found to respond whatever the attentional context and might, therefore, subserve the sensory-discriminative dimension of pain (intensity coding). In parallel, other rCBF changes previously described as 'pain-related' appeared to depend essentially on the attentional context. Attention to the thermal stimulus involved a large network which was primarily right-sided, including prefrontal, posterior parietal, anterior cingulate cortices and thalamus. Anterior cingulate activity was not found to pertain to the intensity coding network but rather to the attentional neural activity triggered by pain. The attentional network disclosed in this study could be further subdivided into a non-specific arousal component, involving thalamic and upper brainstem regions, and a selective attention and orientating component including prefrontal, posterior parietal and cingulate cortices. A further effect observed in response to high intensity stimuli was a rCBF decrease within the somatosensory cortex ipsilateral to stimulation, which was considered to reflect contrast enhancing and/or anticipation processes. Attentional processes could possibly explain part of the variability observed in previous PET reports and should therefore be considered in further studies on pain in both normal subjects and patients with chronic pain.