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Background Spatial resolution, soft-tissue contrast, and dose-efficient capabilities of photon-counting CT (PCCT) potentially allow a better quality and diagnostic confidence of coronary CT angiography (CCTA) in comparison to conventional CT. Purpose To compare the quality of CCTA scans obtained with a clinical prototype PCCT system and an energy-integrating detector (EID) dual-layer CT (DLCT) system. Materials and Methods In this prospective board-approved study with informed consent, participants with coronary artery disease underwent retrospective electrocardiographically gated CCTA with both systems after injection of 65-75 mL of 400 mg/mL iodinated contrast agent at 5 mL/sec. A prior phantom task-based quality assessment of the detectability index of coronary lesions was performed. Ultra-high-resolution parameters were used for PCCT (1024 matrix, 0.25-mm section thickness) and EID DLCT (512 matrix, 0.67-mm section thickness). Three cardiac radiologists independently performed a blinded analysis using a five-point quality score (1 = insufficient, 5 = excellent) for overall image quality, diagnostic confidence, and diagnostic quality of calcifications, stents, and noncalcified plaques. A logistic regression model, adjusted for radiologists, was used to evaluate the proportion of improvement in scores with the best method. Results Fourteen consecutive participants (12 men; mean age, 61 years ± 17) were enrolled. Scores of overall quality and diagnostic confidence were higher with PCCT images with a median of 5 (interquartile range [IQR], 2) and 5 (IQR, 1) versus 4 (IQR, 1) and 4 (IQR, 3) with EID DLCT images, using a mean tube current of 255 mAs ± 0 versus 349 mAs ± 111 for EID DLCT images (

Objectives To evaluate the quality of virtual monochromatic images (VMIs) from spectral photon-counting CT (SPCCT) and two energy-integrating detector dual-energy CT (EID-DECT) scanners from the same manufacturer, for the coronary lumen. Methods A 21-cm section of the Mercury v4.0 phantom was scanned using a cardiac CT protocol. VMIs from 40 to 90 keV were reconstructed using high-resolution (HR) parameters for EID-DECT and SPCCT (CB and HRB kernels at 0.67 mm slice thickness, respectively). Ultra-high-resolution (UHR) parameters were used in addition to SPCCT (detailed-2 kernel, 0.43 mm slice thickness). Noise-power-spectrum (NPS), task-based transfer function (TTF), and detectability index (d′) were computed for 2-mm-diameter lumen detection. In consensus, two radiologists analyzed the quality of the images from 8 patients who underwent coronary CTA on both CT systems. Results For all keV images, fpeak, f50, and d′ were higher with SPCCT. The fpeak and f50 were higher with UHR-SPCCT with greater noise and lower d′ compared to those of the HR-SPCCT images. Noise magnitude was constant for all energy levels (keV) with both systems, and lower with HR images, and d′ decreased as keV decreased. Subjective analysis showed greater lumen sharpness and overall quality for HR and UHR-SPCCT images using all keV, with a greater difference at low keV compared to HR-EID-DECT images. Conclusion HR and UHR-SPCCT images gave greater detectability of the coronary lumen for 40 to 90 keV VMIs compared to two EID-DECT systems, with benefits of higher lumen sharpness and overall quality. Key Points • Compared with 2 dual-energy CT systems, spectral photon-counting CT (SPCCT) improved spatial resolution, noise texture, noise magnitude, and detectability of the coronary lumen. • Use of ultra-high-resolution parameters with SPCCT improved spatial resolution and noise texture and provided high detectability of the coronary lumen, despite an increase in noise magnitude. • In eight patients, radiologists found greater overall image quality with SPCCT for all virtual monochromatic images with a greater difference at low keV, compared with dual-energy CT systems.

International audience; Stroke is a devastating disease. Endovascular mechanical thrombectomy is dramatically changing the management of acute ischemic stroke, raising new challenges regarding brain outcome and opening up new avenues for brain protection. In this context, relevant experiment models are required for testing new therapies and addressing important questions about infarct progression despite successful recanalization, reversibility of ischemic lesions, blood-brain barrier disruption and reperfusion damage. Here, we developed a minimally invasive non-human primate model of cerebral ischemia (Macaca fascicularis) based on an endovascular transient occlusion and recanalization of the middle cerebral artery (MCA). We evaluated per-occlusion and post-recanalization impairment on PET-MRI, in addition to acute and chronic neuro-functional assessment. Voxel-based analyses between per-occlusion PET-MRI and day-7 MRI showed two different patterns of lesion evolution: "symptomatic salvaged tissue" (SST) and "asymptomatic infarcted tissue" (AIT). Extended SST was present in all cases. AIT, remote from the area at risk, represented 45% of the final lesion. This model also expresses both worsening of fine motor skills and dysexecutive behavior over the chronic post-stroke period, a result in agreement with cortical-subcortical lesions. We thus fully characterized an original translational model of ischemia-reperfusion damage after stroke, with consistent ischemia time, and thrombus retrieval for effective recanalization.

The aim of this study is to compare the image quality of in vivo coronary stents between an energy integrating detectors dual-layer computed tomography (EID-DLCT) and a clinical prototype of spectral photon counting computed tomography (SPCCT).In January to June 2021, consecutive patients with coronary stents were prospectively enrolled to undergo a coronary computed tomography (CT) with an EID-DLCT (IQon, Philips) and an SPCCT (Philips). The study was approved by the local ethical committee and patients signed an informed consent. A retrospectively electrocardiogram-gated acquisition was performed with optimized matching parameters on the 2 scanners (EID-DLCT: collimation, 64 × 0.625 mm; kVp, 120, automatic exposure control with target current at 255 mAs; rotation time, 0.27 seconds; SPCCT: collimation, 64 × 0.275 mm; kVp, 120; mAs, 255; rotation time, 0.33 seconds). The injection protocol was the same on both scanners: 65 to 75 mL of Iomeron (Bracco) at 5 mL/s. Images were reconstructed with slice thickness of 0.67 mm, 512 matrix, XCB (Xres cardiac standard) and XCD (Xres cardiac detailed) kernel, iDose 3 for EID-DLCT and 0.25-mm slice thickness, 1024 matrix, Detailed 2 and Sharp kernel, and iDose 6 for SPCCT. Two experienced observers measured the proximal and distal external and internal diameters of the stents to quantify blooming artifacts. Regions of interest were drawn in the lumen of the stent and of the upstream coronary artery. The difference (Δ S-C) between the respective attenuation values was calculated as a quantification of stent-induced artifacts on intrastent image quality. For subjective image quality, 3 experienced observers graded with a 4-point scale the image quality of different parameters: coronary wall before the stent, stent lumen, stent structure, calcifications surrounding the stent, and beam-hardening artifacts.Eight patients (age, 68 years [interquartile range, 8]; all men; body mass index, 26.2 kg/m2 [interquartile range, 4.2]) with 16 stents were scanned. Five stents were not evaluable owing to motion artifacts on the SPCCT. Of the remaining, all were drug eluting stents, of which 6 were platinum-chromium, 3 were cobalt-platinum-iridium, and 1 was stainless steel. For 1 stent, no information could be retrieved. Radiation dose was lower with the SPCCT (fixed CT dose index of 25.7 mGy for SPCCT vs median CT dose index of 35.7 [IQ = 13.6] mGy; P = 0.02). For 1 stent, the internal diameter was not assessable on EID-DLCT. External diameters were smaller and internal diameters were larger with SPCCT (all P0.05). Consequently, blooming artifacts were reduced on SPCCT (P0.05). Whereas Hounsfield unit values within the coronary arteries on the 2 scanners were similar, the Δ S-C was lower for SPCCT-Sharp as compared with EID-DLCT-XCD and SPCCT-Detailed 2 (P0.05). The SPCCT received higher subjective scores than EID-DLCT for stent lumen, stent structure, surrounding calcifications and beam-hardening for both Detailed 2 and Sharp (all P ≤ 0.05). The SPCCT-Sharp was judged better for stent structure and beam-hardening assessment as compared with SPCCT-Detailed 2.Spectral photon counting CT demonstrated improved objective and subjective image quality as compared with EID-DLCT for the evaluation of coronary stents even with a reduced radiation dose.

International audience; In neuropharmacology, the recent concept of 'biased agonism' denotes the capacity of certain agonists to target-specific intracellular pathways of a given receptor in specific brain areas. In the context of serotonin pharmacotherapy, 5-HT1A receptor-biased agonists could be of great interest in several neuropsychiatric disorders. The aim of this study was to determine whether biased agonists could be differentiated in terms of regional targeting by use of simultaneous functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) brain imaging. We compared two 5-HT1A-biased agonists, NLX-112 and NLX-101, injected at three different doses in anaesthetised cats (n = 4). PET imaging was acquired for 90 min after bolus administration followed by constant infusion of the 5-HT1A radiotracer, [18F]MPPF. Drug occupancy was evaluated after injection at 50 min and BOLD fMRI was simultaneously acquired to evaluate subsequent brain activation patterns. 5-HT1A receptor occupancy was found to be dose-dependent for both agonists, but differed in magnitude and spatial distribution at equal doses with distinct BOLD patterns. Functional connectivity, as measured by BOLD signal temporal correlations between regions, was also differently modified by NLX-112 or NLX-101. Voxel-based correlation analyses between PET and fMRI suggested that NLX-112 stimulates both 5-HT1A autoreceptors and post-synaptic receptors, whereas NLX-101 preferentially stimulates post-synaptic cortical receptors. In cingulate cortex, the agonists induced opposite BOLD signal changes in response to receptor occupancy. These data constitute the first simultaneous exploration of 5-HT1A occupancy and its consequences in terms of brain activation, and demonstrates differential signalling by two 5-HT1A-biased agonists. Combined PET/fMRI represents a powerful tool in neuropharmacology, and opens new ways to address the concept of biased agonism by translational approaches.

OBJECTIVE Chronic kidney disease is associated with higher morbidity and mortality in patients with diabetes. A low-protein diet is recommended to slow diabetic nephropathy progression because each protein load leads to renal hemodynamic variations. The aim of our study was to evaluate whether the advanced glycation end products (AGE) content of a protein load is responsible for the protein-induced renal hemodynamic variations in humans. RESEARCH DESIGN AND METHODS Ten healthy subjects were assigned to a high-protein (1 g/kg) low-AGE (3,000 kU AGE) versus high-AGE (30,000 kU AGE) meal. Renal perfusion, oxygen consumption, and oxygen content were measured before and 120 min after each meal. RESULTS Renal perfusion (3.2 ± 0.5 vs. 3.8 ± 0.4 mL/min/g; P = 0.0002) and oxygen consumption (0.3 ± 0.04 vs. 0.4 ± 0.08 min−1; P = 0.005) increased significantly after the high-AGE meal compared with the low-AGE meal. CONCLUSIONS Our results suggest that the AGE content of a protein load is responsible for renal hemodynamic modifications. Therefore, prevention of diabetic nephropathy progression could aim predominantly at reducing food AGE content.

Resume L’imagerie fonctionnelle de la perfusion permet d’en etudier les proprietes, telles que la vasoreactivite aux gaz circulants, l’autoregulation et le couplage neurovasculaire. En aval d’une stenose arterielle, cette imagerie peut estimer la reserve vasculaire et le risque d’ischemie pour adapter la strategie therapeutique. Cette methode montre les troubles hemodynamiques chez les patients atteints d’une maladie d’Alzheimer ou porteurs de malformations arterio-veineuses revelees par une epilepsie. L’IRM fonctionnelle de la vasoreactivite permet egalement de mieux interpreter l’IRM fonctionnelle d’activation en pratique et en recherche clinique.

Background and purpose: Intravascular angioplasty and stenting of intracranial arterial stenosis provided controversial results. Besides the expertise of the practitioners, the selection of the patients remains challenging. BOLD MRI of the cerebral vasoreactivity (BOLD MRI CVR) to hypercapnia provides reproducible maps of the entire brain of the vascular reserve, and could be helpful to assess the best therapeutic strategy. Case history: We report the case of a 63-year-old woman referred for a severe stenosis of the proximal portion of the left middle cerebral artery, revealed by a lenticulostriate and precentral infarction. Despite an aggressive medical treatment during 5 months, the occurrence of iterative transient ischemic attacks motivated intravascular stenting. Functional MRI of the vasoreactivity to hypercapnia using both Blood Oxygen Level Dependent (BOLD) and arterial spin labeling sequences showed normal basal perfusion and impaired vasoreactivity in the left middle cerebral artery territory. Three months after stenting, the BOLD MRI CVR showed vasoreactivity normalization. Since, the patient remains free of ischemic disorders one year after stenting. Conclusion: BOLD MRI of the CVR to hypercapnia may be helpful to optimize the treatment of patients with intracranial arterial stenosis, and could be performed in future therapeutic trials. Hum Brain Mapp 35:1320–1324, 2014. © 2013 Wiley Periodicals, Inc.

Objective. Hypoxic exposure in healthy subjects can induce acute mountain sickness including headache, lethargy, cerebral dysfunction and substantial cerebral structural alterations which, in worst case, can lead to potentially fatal high altitude cerebral edema. Within this context, the relationships between high altitude-induced cerebral edema, changes in cerebral perfusion, increased brain parenchyma volume, increased intracranial pressure and symptoms remain unclear. Methods. In 11 subjects before and after 6 days at 4,350 m, we performed multiparametric magnetic resonance investigations including anatomical, apparent diffusion coefficient and arterial spin labelling sequences. Results. After the altitude stay, while subjects were asymptomatic, white matter volume (+0.7±0.4%, p=0.005), diffusion (+1.7±1.4%, p=0.002) and cerebral blood flow (+28±38%; p=0.036) were significantly increased while cerebrospinal fluid volume was reduced (-1.4±1.1%, p=0.009). Optic nerve sheath diameter (used as an index of increased intracranial pressure) was unchanged from before (5.84±0.53 mm) to after (5.92±0.60 mm, p=0.390) altitude exposure. Correlations were observed between increases in white matter volume and diffusion (rho=0.81, p=0.016) and between changes in cerebrospinal fluid volume and changes in optic nerve sheath diameters (rho=-0.92, p=0.006) and symptoms during the altitude stay (rho=-0.67, p=0.031). Conclusions. These data demonstrate white matter alterations after several days at high altitude when subjects are asymptomatic that may represent the normal brain response to prolonged high altitude exposure.

Brain mapping of task-associated changes in metabolism with PET has been accomplished by subtracting scans acquired during two distinct static states. We have demonstrated that PET can provide truly dynamic information on cerebral energy metabolism using constant infusion of FDG and multiple stimuli in a single experiment. We demonstrate here that the functional PET (fPET-FDG) method accomplished simultaneously with fMRI, can enable the first direct comparisons in time, space and magnitude of hemodynamics and oxygen and glucose consumption. The imaging studies were performed on a 3T Tim-Trio MR scanner modified to support an MR-compatible BrainPET insert. Ten healthy subjects were included. The total PET acquisition and infusion time was 90 minutes. We did 3 blocks of right hand fingers tapping for 10 minutes at 30, 50 and 70 minutes after the beginning of the PET acquisition. ASL and BOLD imaging were acquired simultaneously during the motor paradigm. Changes in glucose utilization are easily observed as changes in the TAC slope of the PET data (FDG utilization rate) and in the derivative signal during motor stimuli in the activated voxels. PET and MRI (ASL, and BOLD) activations are largely colocalized but with very different statistical significance and temporal dynamic, especially in the ipsilateral side of the stimuli. This study demonstrated that motor activation can be measured dynamically during a single FDG PET scan. The complementary nature of fPET-FDG to fMRI capitalizes on the emerging technology of hybrid MR-PET scanners. fPET-FDG, combined with quantitative fMRI methods, allow us to simultaneously measure dynamic changes in glucose utilization and hemodynamic, addressing vital questions about neurovascular coupling.

The aim of this work was to study cerebral vasoreactivity to hypercapnia in Parkinson's disease (PD) before and after levodopa administration. The prospective study was conducted in 20 patients presenting with PD, using 3T blood oxygenation level-dependent (BOLD) functional MRI (fMRI) covering the whole brain. The hypercapnic stimulus was block-designed using carbogen inhalation, a gas mixture of 7% CO2 and 93% O2, before (OFF) and 60 minutes after administration of a suprathreshold (120%) therapeutic L-dopa dose (ON). Ten age-matched controls were enrolled for between-group comparisons. Analyses were conducted with a random effects model and corrected for multiple comparisons. No adverse reaction to the hypercapnic stimulus was reported. However, 10 patients and 2 controls were excluded because of incomplete protocol realization, inappropriate hypercapnic stimulus, or excessive movements, leaving 10 patients and 8 controls for further analyses. The hypercapnic stimulus increased whole-brain BOLD signal of 1.48% ± 0.06% (mean ± standard error) in controls, 1.59% ± 0.05% in patients OFF, and 1.62% ± 0.09% in patients ON. Regions of interest analyses showed a signal increase in gray matter of 2.60% ± 0.16% in controls, 2.89% ± 0.21% in patients OFF, and 2.87% ± 0.12% in patients ON. No global or regional significant difference was detected, when comparing patients OFF and ON L-dopa, or between patients and controls. Contrary to Alzheimer's disease, the vasoreactivity to hypercapnia was normal in PD before and after L-dopa administration, compared to controls. This negative result is an important finding, especially for neuroscientists using fMRI to investigate motricity and cognition, discarding a significant confounding effect.

Introduction Les regimes pauvres en proteines permettent de ralentir la progression de l’insuffisance renale chronique (IRC) en raison de l’hyperfiltration glomerulaire induite par chaque charge proteique. Cependant, les etudes ayant demontre les effets hemodynamiques renaux d’une charge proteique ont ete construites sur des charges en advanced glycation end products (AGEs), correspondant a des proteines modifiees (viande cuite, perfusion d’acides amines). Alors que le mecanisme exact de l’hyperfiltration glomerulaire induite par les proteines reste debattu, le but de notre etude etait de demontrer l’impact du contenu en AGE sur l’hyperfiltration glomerulaire induite par les proteines. Patients et methodes Dix sujets sains ont recu deux charges orales riches en proteines (1 g/kg) au cours de 2 journees differentes, l’une pauvre en AGE (3000 kU AGE) et l’autre riche en AGE (30 000 kU AGE), apres une randomisation pour determiner l’ordre de passage. Chaque intervention etait encadree par 2 sessions de TEP-IRM (pre et postprandiales [120 minutes apres le repas]) pour evaluer la perfusion renale par TEP a l’eau marquee [15O], le metabolisme oxydatif renal par TEP a l’acetate marque [11 C] et le contenu en oxygene par BOLD-IRM. Resultats La perfusion renale a augmente de maniere significative apres le repas riche en AGE (3,16 ± 0,55 vs. 3,80 ± 0,42 mL/min/g [p = 0,0002]) alors qu’il n’a pas ete observe de modification significative apres le repas pauvre en AGE (3,35 ± 0,65 vs. 3,38 ± 0,53 mL/min/g, p = 0,88). Le metabolisme oxydatif a augmente significativement apres la charge riche en AGE (0,3 ± 0,04 vs. 0,36 ± 0,08 min−1, p = 0,005) par rapport a la charge pauvre en AGE (0,30 ± 0,02 vs. 0,31 ± 0,06 min−1, p = 0,76). Nous n’avons pas observe de difference du contenu en oxygene entre les 2 charges pratiquees (donnees insuffisantes). Discussion Nos resultats sont en faveur d’un impact direct du contenu en AGE sur la perfusion et le metabolisme oxydatif renal. Ces resultats demontrent qu’au-dela de la quantite de proteines, la qualite des proteines de notre alimentation est determinante dans l’effet exerce par ces proteines sur la perfusion et le metabolisme oxydatif renal. Conclusion Cette etude suggere que la prevention de la progression de l’IRC doive donc se focaliser sur une reduction de l’apport alimentaire en AGE au-dela d’une reduction de l’apport proteique global.

Although the study of cerebral vasoreactivity using fMRI is mainly conducted through the BOLD fMRI modality, owing to its relatively high signal-to-noise ratio (SNR), ASL fMRI provides a more interpretable measure of cerebral vasoreactivity than BOLD fMRI. Still, ASL suffers from a low SNR and is hampered by a large amount of physiological noise. The current contribution aims at improving the recovery of the vasoreactive component from the ASL signal. To this end, a Bayesian hierarchical model is proposed, enabling the recovery of perfusion levels as well as fitting their dynamics. On a single-subject ASL real data set involving perfusion changes induced by hypercapnia, the approach is compared with a classical GLM-based analysis. A better goodness-of-fit is achieved, especially in the transitions between baseline and hypercapnia periods. Also, perfusion levels are recovered with higher sensitivity and show a better contrast between gray- and white matter.

Background: There is increasing interest in using oxygen challenges during MRI to image metabolic dysfunction in acute ischemic stroke. Methods: Subjects enrolled in a prospective MRI study of patients imaged within 48 h of stroke onset underwent arterial spin labeling (ASL) MRI for 10-12 min, while receiving a transient normobaric oxygen (NBO) challenge, according to this protocol: (1) Room air (RA) for 2-5 min; (2) NBO at 10-12 L/min via nonrebreather mask for 4 min; (3) RA for 2-4 min. ASL data were motion corrected and used to calculate CBF. Changes of blood-oxygen level dependent (BOLD) and perfusion MRI signal intensities during NBO were calculated (along with Z-scores) using FEAT. Mean changes within the DWI lesion (Core), ipsilateral normal tissue (IPS) and contralesional hemisphere (CNL) were compared. Results: Patient characteristics (N=19) were age 62±13 years, median admission NIHSS 12 [IQR 3-12], time-to-MRI 33±13 h, median Core volume 31.2 [IQR 14.3-68] cc. 6 patients were imaged after tPA therapy. One subject’s CBF data were unusable due to artifacts. Both hyperemia (N=8) and hypoperfusion (N=12) were observed in areas in and around the DWI lesion. Baseline CBF in Core was significantly higher than in CNL (P=0.01) and IPS (P=0.03), indicative of hyperemia. No significant difference was found for perfusion change in response to NBO (mean Z-score < 1.1 for all regions). In contrast, strong positive and negative BOLD responses were found both ipsilaterally and contralaterally. Negative BOLD responses were significantly smaller (P Discussion: Our results confirm previous reports in both human and experimental stroke models of strong increases in BOLD signal in response to NBO challenges. In addition, we found negative BOLD responses both ipsilesionally and contralesionally, often in conjunction with hyperemia, perhaps suggesting a steal effect. Future research may further elucidate the complexities of oxygen metabolism in stroke, perhaps encouraging the development of novel therapies.

International audience; Although the study of cerebral vasoreactivity using fMRI is mainly conducted through the BOLD fMRI modality, owing to its relatively high signal-to-noise ratio (SNR), ASL fMRI provides a more interpretable measure of cerebral vasoreactivity than BOLD fMRI. Still, ASL suffers from a low SNR and is hampered by a large amount of physiological noise. The current contribution aims at improving the re- covery of the vasoreactive component from the ASL signal. To this end, a Bayesian hierarchical model is proposed, enabling the recovery of per- fusion levels as well as fitting their dynamics. On a single-subject ASL real data set involving perfusion changes induced by hypercapnia, the approach is compared with a classical GLM-based analysis. A better goodness-of-fit is achieved, especially in the transitions between baseline and hypercapnia periods. Also, perfusion levels are recovered with higher sensitivity and show a better contrast between gray- and white matter.

International audience; Changes in cerebral perfusion and CO(2) cerebrovascular reactivity during and immediately after a sojourn at high altitude remain unclear but may be critical for acclimatization. The aim of the present study was to assess the effects of 6days at 4,350m on cerebral perfusion and cerebrovascular reactivity (CVR) to CO(2) by arterial spin labeling (ASL) magnetic resonance imaging at sea level and to compare it with transcranial Doppler (TCD) results at altitude. Eleven healthy male subjects, non-acclimatized to altitude, stayed for 6days at 4,350m (Observatoire Vallot, massif du Mont-Blanc). Prior to the stay and within 6h after returning to sea level, subjects were investigated using pseudo-continuous ASL at 3T during a block-design inhalation paradigm to measure basal cerebral blood flow (CBF) and CO(2) CVR. End-tidal CO(2) (PetCO(2)), respiratory rate, heart rate and oxygen saturation were recorded during the exam. Subjects were also examined using TCD prior to and on day 5 of the stay at altitude to measure blood velocity in the middle cerebral artery (MCAv) and CO(2) CVR. CO(2) CVR was expressed as percent change in ASL CBF or TCD MCAv per mmHg change in PetCO(2). PetCO(2) was significantly decreased during and after altitude. Significant increases in TCD MCAv compared to before altitude measurements were observed on day 5 at altitude (+20.5±15.5 %). Interestingly, ASL CBF remained increased in the MCA and anterior vascular territories (+22.0±24.1 % and 20.5±20.3 %, respectively) after altitude under normoxic conditions. TCD CVR tended to decrease on day 5 at 4,350m (-12.3±54.5 % in the MCA) while the ASL CVR was significantly decreased after altitude (-29.5±19.8 % in the MCA). No correlation was observed between cerebral hemodynamic changes and symptoms of acute mountain sickness at high altitude. In conclusion, prolonged exposure to high altitude significantly increases blood flow during the altitude stay and within 6h after returning to sea level. Decreased CO(2) CVR after prolonged altitude exposure was also observed using ASL. Changes in cerebral hemodynamics with altitude exposure probably involve other mechanisms than the vasodilatory effect of hypoxia only, since it persists under normoxia several hours following the descent.

Background and purpose: Intravascular angioplasty and stenting of intracranial arterial stenosis provided controversial results. Besides the expertise of the practitioners, the selection of the patients remains challenging. BOLD MRI of the cerebral vasoreactivity (BOLD MRI CVR) to hypercapnia provides reproducible maps of the entire brain of the vascular reserve, and could be helpful to assess the best therapeutic strategy. Case history: We report the case of a 63‐year‐old woman referred for a severe stenosis of the proximal portion of the left middle cerebral artery, revealed by a lenticulostriate and precentral infarction. Despite an aggressive medical treatment during 5 months, the occurrence of iterative transient ischemic attacks motivated intravascular stenting. Functional MRI of the vasoreactivity to hypercapnia using both Blood Oxygen Level Dependent (BOLD) and arterial spin labeling sequences showed normal basal perfusion and impaired vasoreactivity in the left middle cerebral artery territory. Three months after stenting, the BOLD MRI CVR showed vasoreactivity normalization. Since, the patient remains free of ischemic disorders one year after stenting. Conclusion: BOLD MRI of the CVR to hypercapnia may be helpful to optimize the treatment of patients with intracranial arterial stenosis, and could be performed in future therapeutic trials. Hum Brain Mapp 35:1320–1324, 2014. © 2013 Wiley Periodicals, Inc.

Objective To evaluate the cerebral vasoreactivity using blood oxygenation level dependent functional MRI during carbogen inhalation with 7% CO 2 in Alzheimer's disease and amnestic mild cognitive impairment. Participants and methods Thirty nine subjects were included to be investigated using blood oxygenation level dependent (BOLD) functional MRI at 1.5 T during a block-design carbogen inhalation paradigm, with a high concentration face-mask under physiological monitoring. Basal cerebral perfusion was measured using pulsed arterial spin labeling. Image analyses were conducted using Matlab® and SPM5 with physiological regressors and corrected for partial volume effect. Results Among selected participants, 12 subjects were excluded because of incomplete protocol, leaving for analysis 27 subjects without significant microangiopathy diagnosed for Alzheimer's disease (n = 9), amnestic mild cognitive impairment (n = 7), and matched controls (n = 11). No adverse reaction related to the CO 2 challenge was reported. Carbogen inhalation induced a whole-brain signal increase, predominant in the gray matter. In patients, signal changes corrected for gray matter partial volume were decreased (0.36 ± 0.13% BOLD/mmHg in Alzheimer's disease, 0.36 ± 0.12 in patients with mild cognitive impairment, 0.62 ± 0.20 in controls). Cerebral vasoreactivity impairments were diffuse but seemed predominant in posterior areas. The basal hypoperfusion in Alzheimer's disease was not significantly different from patients with mild cognitive impairment and controls. Among clinical and biological parameters, no effect of apoE4 genotype was detected. Cerebral vasoreactivity values were correlated with cognitive performances and hippocampal volumes. Among age and hippocampal atrophy, mean CVR was the best predictor of the mini-mental status examination. Conclusion This BOLD functional MRI study on CO 2 challenge shows impaired cerebral vasoreactivity in patients with Alzheimer's disease and amnestic mild cognitive impairment at the individual level. These preliminary findings using a new MRI approach may help to better characterize patients with cognitive disorders in clinical practice and further investigate vaso-protective therapeutics.

Objectifs La maladie d’Alzheimer (MA) est une maladie neurodegenerative frequente associee a des troubles de la regulation de la perfusion cerebrale. Une evaluation par IRM de la vasoreactivite cerebrale a la modulation hypercapnique a ete developpee pour rechercher des variations regionales des proprietes fonctionnelles de la perfusion cerebrale chez les patients atteints et a risque de maladie d’Alzheimer. Patients et methodes Vingt et un sujets repartis en 3 groupes apparies pour l’age et le sexe (Maladie d’Alzheimer debutante (MA) (n=7), Troubles cognitifs legers amnesiques (TCL-a) (n=7), Temoins (n=7)) ont ete examines en IRM (1,5T) en mesurant le signal BOLD et la perfusion cerebrale par marquage de spins arteriels lors d’epreuves hypercapniques par inhalation alternee d’air et d’un melange gazeux enrichi en CO2. Surveillance de la pression expiratoire en CO2, de la saturation en O2 et des frequences respiratoire et cardiaque pendant l’examen par un appareillage dedie. Analyses des images avec SPM5 avec un regresseur hemodynamique dedie. Resultats Les examens se sont bien deroules sans effet secondaire pendant ni au decours des epreuves hypercapniques. Chez les sujets sains, la reponse BOLD induite par l’hypercapnie predomine dans la substance grise mais les artefacts de susceptibilite magnetique de la base du crâne ne permettent pas une analyse satisfaisante du cortex temporobasal et fronto-basal. Chez les patients TCL-a, la reponse BOLD etait normale ou augmentee de facon diffuse alors que chez les patients MA la reponse BOLD etait globalement diminuee en particulier dans les regions frontales. L’analyse de la perfusion par marquage de spins arteriels est en cours. Conclusion Ces resultats preliminaires montrent la faisabilite et la bonne tolerance de l’IRM de la vasoreactivite cerebrale a l’hypercapnie controlee. Ils confirment l’existence d’une alteration fonctionnelle de la perfusion cerebrale dans la MA alors que chez les sujets a risque des mecanismes compensatoires pourraient etre presents pour faire face a une hypoperfusion chronique. Ces elements devront etre confrontes a l’etude d’une population plus importante, a la mesure quantitative de la perfusion et aux resultats du genotypage de l’APOE4.