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Resume Objectifs Nous avons compare les images de tomographie par emission de positons au [18]-Fluorodesoxyglucose reconstruites selon deux methodes : « attenuation-weighted ordered subset expectation maximization » (AW-OSEM) et « detector response » (AW-OSEM DR) pour la delimitation des volumes cibles en radiotherapie des cancers des voies aero-digestives superieures (VADS). Dans cette etude preliminaire, nous avons etudie, d’une part, la resolution spatiale du systeme Biograph™ 6 et, d’autre part, les volumes cibles de radiotherapie « Gross Tumor Volume » (GTV), « Clinical Target Volume » (CTV) et « Planning Target Volume » (PTV) obtenus avec chacune de ces deux methodes de reconstruction. Materiel et methodes La resolution spatiale a ete mesuree sur un objet test contenant 4 sources ponctuelles radioactives. Par ailleurs, les volumes cibles de radiotherapie ont ete definis avec le logiciel Eclipse™ a partir des images du scanner injecte (TDM IV) et de la TEP/TDM (TEP AW-OSEM et TEP AW-OSEM DR). Resultats La resolution spatiale a ete amelioree avec l’algorithme de reconstruction AW-OSEM DR compare aux images obtenues avec la reconstruction AW-OSEM (de 7,5 mm a 5,4 mm pour la plus forte reduction). Les GTV issus de la reconstruction avec AW-OSEM DR par seuillage semi-automatique a 42 et 50 % de la « maximun standard uptake value » (respectivement, de 1,2 et 0,7 cm 3 ) etaient inferieurs a ceux obtenus avec AW-OSEM (respectivement, de 3,6 et 2,2 cm 3 ). Ils etaient egalement inferieurs a celui realise avec la TDM IV (5,5 cm 3 ). Il en etait de meme pour les CTV et les PTV. Conclusion Cette etude montre que l’algorithme de reconstruction AW-OSEM DR permet de moins degrader la resolution spatiale qu’avec AW-OSEM utilise en routine clinique. Dans le cadre de la definition des volumes cibles de radiotherapie, AW-OSEM DR peut permettre de diminuer les GTV, CTV et PTV et donc le risque d’effets secondaires associes aux organes a risque.

In thoracic PET/computed tomography (CT) imaging, uptake foci usually appear smeared because of postreconstruction smoothing and respiratory motion.The aim of the present study was to assess the respective contributions of the reconstruction process and respiratory motion on PET/CT images.Thirty-one pulmonary lesions were studied. Free-breathing PET/CT acquisitions were followed by a 10-min respiratory-gated PET/CT acquisition. Four different reconstructions were performed by combining two different tomographic operators (TOs) (i.e. the geometric clinical system matrix or a system matrix including the detector response) and taking account (or not) of respiratory motion using a previously developed 'CT-based' technique. For each reconstruction method, lesion segmentation was performed with an adaptive threshold. Next, we computed the volume differences between each reconstruction. Finally, we applied a multiple linear model to compute the relative contributions of TO-based and CT-based respiratory compensation to lesion volume.The three groups, combining the reconstruction methods and the respiratory compensation (or not), differed significantly in terms of the volume differences. For all lesions, the full linear model yielded a regression coefficient R of 76.10%. The partial R values were 65.58 and 10.52% for the detector response operator and the CT-based method, respectively. For lesions in the upper/middle lobes, blurring was mainly because of TO (partial R=78.53%), whereas, for lower lobe lesions, smearing was mainly because of respiratory motion (partial R=56.76%).Our results showed that image reconstruction, by TO accuracy, was the main explanatory factor for lesion smearing when considering the chest as a whole. Respiration had a major impact on the lower lobes.

International audience; The diagnostic accuracy of hexamethylpropyleneamine oxime (HMPAo) single-photon emission computed tomography (SPECT) in Alzheimer disease (AD) remains undetermined in a real-life clinical population. The objective was to determine the HMPAo SPECT hypoperfusion pattern in cognitively impaired patients with positive CSF AD biomarker and to evaluate its diagnostic accuracy. This study included 120 patients referred to a university memory clinic assessed using HMPAo SPECT, MRI, and CSF biomarkers. Three biomarker signatures suggestive of AD were analyzed (1, A ss 1-42; 2, A ss 1-42+t-tau and/or p-tau; 3, A ss 1-42/p-tau). The clinical diagnoses were possible AD (n=29) or other causes of cognitive impairment (n=91). All CSF AD signatures were significantly (1, P=0.004; 2, P=0.017; 3, P=0.024) associated with the difference between inferior parietal perfusion and lateral dorsal frontal cortex perfusion. The hypoperfusion pattern discriminated between patients with positive CSF AD biomarkers and those with other cognitive impairments with a sensitivity of 67% to 71% and a specificity of 63% to 65% and a greatest negative predictive value (NPV) of 90%. Inferior parietal cortex hypoperfusion was the most sensitive and specific feature in AD patients diagnosed using clinical and CSF biomarker criteria. This hypoperfusion pattern was associated with an NPV of 90% and therefore discriminated sharply between AD and other cognitive disorders.

PET/CT acquisitions are affected by physiological motion, which lowers the quantization accuracy. Respiratory-gated PET/CT methods require a long acquisition time, which may not be compatible with the clinical schedule. The objective of the present study was to assess the quantization accuracy of short-duration, respiratory-gated PET acquisitions and processing with the "CT-based" methodology developed in our laboratory.Quantization accuracy was first assessed in a phantom study. A standard ("Ungated") PET/CT acquisition was followed by a 10-minute list-mode acquisition with simultaneous respiratory signal recording and a short breath-hold CT scan (BH-CT). These acquisitions were repeated 10 times. For the CT-based images, we reconstructed (i) 10 full-duration (FD-CT-based) volumes that took account of all events recorded in the position defined by BH-CT and (ii) 10 short-duration (SD-CT-based) volumes based on only 30 seconds of selected events. Using these volumes, we performed a bias-variance analysis to assess the effects of respiration-motion reduction and the counting statistics on the quantization accuracy. We also applied Ungated, FD- and SD-CT-based methods to 16 patients (21 pulmonary lesions) and measured the maximum standardized uptake (SUVmax) values.The bias values were 71%, 40% and 44% for Ungated, FD- and SD-CT-based images, respectively. In the clinical study, there was a statistically significant difference in SUVmax between Ungated images and both the CT-Based images (p 0.02) but not between the FD-CT-Based and SD-CT-Based images (p = 0.42).Our findings demonstrated that the additional acquisition time required by the CT-based method can be reduced without altering quantitative accuracy.

Chronic obstructive pulmonary disease (COPD) is characterized by low vital capacity and tidal volume, which translate into smaller respiratory motions. We sought to demonstrate the limited respiratory motion in COPD by comparing respiratory-gated and free-breathing positron emission tomography (PET) images of lung nodules ("CT-based" and "Ungated" images) in patients with and without COPD.We studied 74 lung lesions (37 malignant) in 60 patients (23 patients with COPD; 37 without). An Ungated PET examination was followed by a CT-based acquisition. Maximum standard uptake value (SUVmax) for each lesion on PET images was measured. On CT images, we checked for the presence of emphysema and pleural adhesions or indentations associated with the nodules. Lastly, we used univariate and then multivariate analyses to determine the lung function parameters possibly affecting respiratory motion in patients with and without COPD.The mean "CT-based" vs. "Ungated" difference in SUVmax was 0.3 and 0.6 for patients with and without COPD, respectively. Statistical analysis revealed that lesion site, hyperinflation and pleural indentation were independently associated with a difference in SUVmax.PET lung lesion images in patients with COPD are barely influenced by respiratory motion. Thoracic hyperinflation in patients with COPD was found to be independently associated with an effect of respiratory motion on PET images. Moreover, pleural indentation limits the respiratory motion of lung nodules, regardless of the presence or absence of COPD.

Resume Problematique Les mouvements respiratoires en tomographie par emission de positons/tomodensitometrie (TEP/TDM) peuvent etre source d’erreurs dans les images TEP, mais egalement dans les images TDM. Cela induit des erreurs de correspondance entre les images anatomiques et fonctionnelles et donc des biais pour la correction d’attenuation conduisant a des standardized uptake values (SUV) erronees. Cet article a pour but de presenter les methodes de synchronisation respiratoire applicables en clinique ainsi que les evolutions a venir. Compensation des mouvements respiratoires La plupart des appareils actuels sont equipes d’un systeme de synchronisation respiratoire des acquisitions TEP. Cependant, les logiciels proposes par les constructeurs ne sont pas satisfaisants, notamment de par le fait que plusieurs images TEP, correspondant a differentes positions des tissus durant le cycle respiratoire, sont generees avec la meme carte d’attenuation. Certaines equipes ont propose des alternatives assurant une image TEP correspondant parfaitement a son image TDM associee. Ces dernieres methodes sont utilisables en routine et ont deja montre, dans differents essais cliniques, leur interet. Toutefois, les methodes de compensation necessitent un allongement du temps d’examen TEP par la realisation d’une acquisition supplementaire. Correction des mouvements respiratoires La nouvelle tendance cherche a developper des methodes de correction des mouvements en integrant directement l’information de deplacement de tissus soit dans les donnees (acquisition), soit dans l’algorithme de reconstruction. Ces methodes ont l’interet d’utiliser la totalite des donnees acquises pour la reconstruction de l’image, reduisant de ce fait la duree de l’examen synchronise. Neanmoins, ces methodes ne sont pas encore transferables en cliniques. En effet, la determination des deformations des tissus pose encore des problemes, de meme que la correction d’attenuation.

Choroid plexuses (CPs) are structures involved in CSF production and cerebral regulation and present atypical glucose metabolism. In addition, CPs impairment may be related to Alzheimer disease (AD). In the present study, we present the first results pointing out glucose metabolism in the CP with dynamic fluorodeoxyglucose positron emission tomography (dynamic 18 F-FDG-PET). We studied 47 elderly adults who were classified into three classes: healthy subjects (HS), amnestic mild cognitive impairment (aMCI) and AD. All participants have undergone dynamic 18 F-FDG-PET for 45 min. Acquisitions were divided into 34 frames to extract tissue time–activity curves (TTACs) in various structures including CSF and CPs. Results showed a decreased CPs 18 F-FDG metabolism in AD compared with aMCI and HS. Conversely, dynamic uptake was higher in CSF for AD compared with the other groups. ROC analysis showed that CPs TTACs are a promising tool as it yielded sensitivity of 85.7% and a specificity of 83.3%. Our study showed a disturbance of glucose exchange at the blood–CSF barrier level which is in favour of a key-role of the CPs in AD.

International audience; The aim of this study was to examine the relationship between cerebrospinal fluid (CSF) levels of biomarkers for Alzheimer's disease (AD) (A beta(1-42), t-tau, and p-tau) and (18)Fluorodeoxyglucose positron emission tomography (FDG-PET) hypometabolism in subjects from the Alzheimer's Disease Neuroimaging Initiative, and specifically to determine which index of neurodegeneration was most frequently affected. The secondary objective was to determine the most frequently hypometabolic region in patients with a CSF AD signature (abnormal A beta(1-42) and abnormal p-tau). We included the 372 subjects (85 normal subjects, 212 patients with mild cognitive impairment, and 75 patients with AD) with a CSF biomarker dosage (A beta(1-42), t-tau, and p-tau) and brain FDG-PET. The relationship between FDG-PET metabolism (in five regions of interest (ROI) known to be damaged in AD) and CSF t-tau and p-tau levels was studied as a function of CSF A beta(1-42) status. FDG-PET hypometabolism and CSF t-tau and p-tau levels were correlated only in patients with an abnormal CSF A beta(1-42) level (t-tau: R-2 = 0.044, p = 0.001; p-tau: R-2 = 0.02, p = 0.03). In the latter patients, CSF p-tau was the most frequently (p = 0.0001) abnormal neurodegeneration marker (p-tau: 92.8%; FDG-PET: 56.5%; CSF t-tau: 59.1%). Within the five ROI of FDG PET, the angular gyrus metabolism (R-2 = 0.149; p = 0.0001) was selected as the most tightly associated with CSF AD signature. The relation between CSF markers of neurodegeneration (p-tau and t-tau) and brain hypometabolism (in FDG-PET) is conditioned by presence of amyloid abnormality. This finding supports the current physiopathological model of AD. P-tau is the most frequently impaired biomarker. Using FDG PET angular gyrus hypometabolism is the most sensitive to CSF-biomarker-defined AD.

In 18F-fluorodeoxyglucose PET/CT, respiratory motion induces bias in image interpretations (i.e. organ misregistration or lesion omission/underestimation).The present study applied our custom gating method (referred to as 'CT-based gated PET' and that has already been validated by our research group) to PET imaging of the liver and compared its per lesion sensitivity with that of standard clinical (i.e. ungated) PET.A total of 13 patients scheduled for liver surgery were referred to our department for PET/CT imaging. Each patient underwent both ungated and CT-based gated PET imaging protocols. Two independent, blinded observers interpreted the two sets of PET images and reached a consensus when necessary. Image interpretations were combined with histological analysis and/or intraoperative ultrasound examination to compute each method's per lesion sensitivity and true positive fraction. Analyses were also performed by considering lesions according to their size (longest axis over 10 mm or over 15 mm).Forty-eight lesions were confirmed by pathology reports. When considering all the uptakes, the ungated and the CT-based gated PET methods had sensitivities of 54.2 and 64.6% (P=0.025) and true positive fractions of 83.9 and 86.1%, respectively. When considering uptakes greater than 10 mm in size, ungated and CT-based gated PET had sensitivities of 74.3 and 88.6% (P=0.025), respectively. For lesions greater than 15 mm in size, the corresponding sensitivities were 85.2 and 100% (P=0.046).CT-based gated PET yielded a higher lesion-based sensitivity than routine, ungated PET did. Hence, this method improves the detection of intrahepatic colorectal metastases--especially for lesions that are close in size to the detection limit of the PET gantry.

Background Respiratory motion is known to deteriorate positron emission tomography (PET) images and may lead to potential diagnostic errors when a standardized uptake value (SUV) cut-off threshold is used to discriminate between benign and malignant lesions. Purpose To evaluate and compare ungated and respiratory-gated 18F-fluorodeoxyglucose PET/computed tomography (CT) methods for the characterization of pulmonary nodules. Material and Methods The list-mode acquisition during respiratory-gated PET was combined with a short breath-hold CT scan to form the CT-based images. We studied 48 lesions in 43 patients. PET images were analyzed in terms of the maximum SUV (SUVmax) and the lesion location. Results Using receiver-operating characteristic (ROC) curves, the optimal SUV cut-off thresholds for the ungated and CT-based methods were calculated to be 2.0 and 2.2, respectively. The corresponding sensitivity values were 83% and 92%, respectively, with a specificity of 67% for both methods. The two methods gave equivalent performance levels for the upper and middle lobes (sensitivity 93%, specificity 62%). They differed for the lower lobes, where the CT-based method outperformed the ungated method (sensitivity values of 90% and 70%, respectively, and a specificity of 73% with both methods) – especially for lesions smaller than 15 mm. Conclusion The CT-based method increased sensitivity and did not diminish specificity, compared with the ungated method. It was more efficient than the ungated method for imaging the lower lobes and smallest lesions, which are most affected by respiratory motion.

It is now clear that cerebrospinal fluid [CSF, produced by the choroid plexi (CP)] plays a fundamental role in brain pathophysiology and neurodegenerative processes. However, the CP's functional activity has only been studied in vitro. This article presents a new approach for studying the CP and the CSF with 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET). Ten elderly, non-neurological patients underwent a 45-min, dynamic FDG-PET acquisition with scheduled 34 time frames. Our method provided successive images representing the FDG uptake dynamics, with calculation of three parameters of an exponential fitting function for the 34 frames and every voxel in the brain volume. Regions of interest in the CSF and CP were manually selected on the reconstructed map, and mean raw FDG uptake curves were reconstructed. We have monitored the kinetics of FDG uptake by the CP and the CSF during PET acquisition. The FDG kinetics in the CP differs markedly from those seen in the CSF and all other brain tissues. In our study population, the CP's final uptake intensity was significantly greater than that of the CSF. This work is an initial step toward using PET to evaluate CP functions in vivo.

Resume Les mouvements respiratoires, au cours d’un examen de tomographie par emission de positons (TEP) au 18 F-Fluoro-Desoxyglucose ( 18 F-FDG) associee a la tomodensitometrie (TDM), sont a l’origine de biais dans les interpretations. Ces mouvements peuvent induire une non-correspondance des organes entre les deux modalites, conduisant a une correction de l’auto-attenuation erronee et donc a une maximum standardized uptake value (SUV max ) biaisee. Nous presentons ici les resultats cliniques d’une etude qui vise a etudier les apports d’une methode de synchronisation respiratoire originale (CT-based) sur la detectabilite des lesions hepatiques. Quarante-neuf patients devant subir une chirurgie hepatique ont ainsi beneficie en preoperatoire d’une TEP/TDM standard et du protocole CT-based. Les lesions hepatiques retrouvees en TEP, par deux operateurs, ont ete confrontees a l’anatomopathologie. Les sensibilites pour l’operateur 1, calculees pour les methodes standard et CT-based, etaient de 60 et 64 %, respectivement. Pour l’operateur 2, elles etaient de 58,7 et 72 %. CT-based a montre une augmentation significative ( p max sont significativement plus elevees avec la methode CT-based ( p 18 F-FDG.

BACKGROUND ¹⁸F-fluorodeoxyglucose positron emission tomography has proven relevance in oncological diagnosis, staging and follow-up. The standardized uptake value (SUV) is one of the most widely used semi-quantitative criteria in PET imaging. However, factors such as noise and image resolution affect the measurement of the SUV. We reported earlier that a device-dedicated projector [attenuation-weighted ordered-subsets expectation maximization detector response (AW-OSEM DR), based on point-source measurements] introduces less noise than a geometrical model (AW-OSEM). OBJECTIVE The aim of this study was to investigate the AW-OSEM DR method's impact on SUV measurements under clinical conditions. METHODS We first performed a bias analysis to assess the accuracy of the quantitation for the two reconstruction methods as a function of target size and the number of iterations, with 14 acquisitions of the NEMA IEC/2001 phantom. We then used each method to calculate the maximum and average SUVs, respectively for 32 lesions. RESULTS For all spheres and all iterations, the bias was significantly lower with AW-OSEM DR than with AW-OSEM (P=0.012). Moreover, a paired Student's t-test showed significant intermethod differences for maximum SUV and average SUV (both P

Purpose: To directly compare and study the variability of parameters related to hepatic blood flow measurements using 3 T phase-contrast magnetic resonance imaging (PC-MRI) and Doppler ultrasound (US). Materials and Methods: Nine healthy subjects were studied. Blood velocities and flow rate measurements were performed in the portal vein and the proper hepatic artery. MR studies were performed using a 3 T imager. Gradient-echo fast phase contrast sequences were used with both cardiac and respiratory gating. MR and Doppler flow parameters were extracted and compared. Two methods of calculation were used for Doppler flow rate analysis. Results: Compared to Doppler US, PC-MRI largely underestimated hepatic flow data with lower variability and higher reproducibility. This reproducibility was more pronounced in the portal vein than in the proper hepatic artery associated with poorer velocity correlations. Total hepatic flow values were 1239 ± 223 mL/min and 1595 ± 521 mL/min for PC-MRI and Doppler US, respectively. Conclusion: Free-breathing PC-MRI can provide reliable noninvasive measurement of hepatic flow parameters compared to Doppler US. The MR technique could help to improve Doppler flow calculations, thereby allowing standardization of protocols, particularly for applications in disease. J. Magn. Reson. Imaging 2010;31:579–588. © 2010 Wiley-Liss, Inc.

Background/Aims To measure total hepatic blood flow including portal and proper hepatic artery flows as well as the temporal evolution of the vessel's section during a cardiac cycle. Methods Twenty healthy subjects, with a mean age of 26 years, were explored. Magnetic resonance imaging blood flow measurements were carried out in the portal vein and the proper hepatic artery. MR studies were performed using a 1.5T imager (General Electric Medical Systems). Gradient-echo 2D Fast Cine Phase Contrast sequences were used with both cardiac and respiratory gatings. Data analysis was performed using a semi-automatic software built in our laboratory. Results The total hepatic flow rate measured was 1.35±0.18L/min or 19.7±4.6mL/(minkg). The proper hepatic artery provided 19.1% of the total hepatic blood flow entering the liver. Those measurements were in agreement with earlier studies using direct measurements. Mean and maximum velocities were also assessed and a discrepancy between our values and the literature's Doppler data was found. Measurements of the portal vein area have shown a mean variation, defined as a "pulsatility" index of 18% over a cardiac cycle. Conclusions We report here proper hepatic artery blood flow rate measurements using MRI . Associated with portal flow measurements, we have shown the feasibility of total hepatic flowmetry using a non-invasive and harmless technique.

Respiratory motion correction in positron emission tomography (PET) seeks to incorporate motion information into an image reconstruction algorithm by using the full counting statistics of an acquisition to generate a single, motion-free volume. Here, we present a motion-incorporated ordered subsets expectation maximization (MOSEM) reconstruction based on a device-dedicated tomographic projector in which each matrix element is calculated directly from the voxels' Cartesian coordinates alone. The motion is corrected by updating this projector as a function of the respiratory level. The performance of the reconstruction method was investigated with three datasets: two simulations of a transaxially or axially moving lesion on a patient acquisition and a third acquisition of a moving sphere. After the 16th sub-iteration, the normalized mean square error (NMSE, with a motionless acquisition as reference) was 0.20 for the non-corrected (ungated) image and 0.01 for the MOSEM image with transaxial motion simulation. Likewise, NMSE was 0.30 for the ungated image and 0.03 for MOSEM image with axial motion simulation. For the phantom, ungated reconstruction yielded an error of 0.78, whereas MOSEM yielded 0.43. The error reduction resulted from enhancement and reduced spreading of the moving uptake. Our results show that MOSEM reconstruction yields motion-corrected images which are similar to motionless reference images.

In whole-body positron emission tomography (PET) imaging, the detection of small uptake foci (i.e., around two or three times the tomograph's spatial resolution) is a critical issue. Indeed, spatial resolution is altered by postreconstruction smoothing operations used to reduce the noise introduced by (among other things) an inaccurate system matrix. The authors previously proposed a device-dedicated projector, easily applicable on a clinical gantry, based on point-source measurements, which introduces less noise than a geometrical model. In the present study, they took advantage of the lower noise levels by reducing the postfilter and then quantified the approach's impact on image quality. This study was performed on an IEC Body Phantom Set filled with 18F (sphere-to-background activity ratio: 4:1). The same 3 min acquisition was reconstructed with either (i) a clinical system based on a geometrical tomographic operator (OSEM_CL) or (ii) an OSEM algorithm using the suggested system matrix (OSEM_DR). In order to compare the resulting images, they set the 3D Gaussian postfilter (3DGPF) for OSEM_DR so as to obtain similar background signal-to-noise ratio (SNR) to that of OSEM_CL with a Gaussian postfilter full width at half maximum of 5 mm (as recommended for whole-body imaging on a Biograph6). They then assessed the contrast-to-noise ratio (CNR) and quantitation [contrast recovery (CR)] for the phantom's four smallest spheres (with internal diameters of 10, 13, 17, and 22 mm). Evaluation of 3DGPFs ranging from 2.2 to 2.6 mm showed that a value of 2.4 mm in OSEM_DR gave the closest background SNR to that of OSEM_CL with a 3DGPF of 5 mm. For all studied targets, the CNR was higher with OSEM_DR than with OSEM_CL. For the 10 and 13 mm spheres, OSEM_DR increased the size of the CNR peaks by 37% and 20%, relative to OSEM_CL. The OSEM_DR technique yielded higher CR values than OSEM_CL did. For the 10, 13, 17, and 22 mm spheres, the CR values at eight iterations were 0.5, 0.6, 1.1, and 1.0 for OSEM_DR and 0.3, 0.4, 0.9, and 0.8 for OSEM_CL. They evaluated a practical method for determining a device-dedicated system matrix based on point-source acquisitions. This tomographic operator is more realistic than geometrical system matrix and introduces less noise into PET images during statistical reconstruction; it thus reduces the extent of postfiltering operations required. Thus, spatial resolution is better maintained with OSEM_DR than with clinical reconstruction. They showed that this method improves the contrast-to-noise ratio and quantification of uptake foci (especially those that are at the system's limit of detection) and, in a clinical context, could allow better detection and earlier diagnosis.

The prevalence of neurodegenerative diseases is growing in western countries and PET imaging is increasingly frequently used for clinical and research purposes. However, few PET cameras are dedicated to cerebral imaging. The Biograph 6 (Biograph6) (Siemens Medical Solutions) is a PET/CT dedicated to high throughput whole body studies. Its performance for cerebral imaging has not yet been assessed. The aims of this study were to compare the quantification and detectability of the Biograph for cerebral imaging with those of a well-validated PET camera, the ECAT EXACT HR+ (HR+) (Siemens Medical Solutions). A phantom measuring 19 cm long and 20 cm in diameter was filled with a 18F-fluorodeoxyglucose (18F-FDG) solution. Two 5.7 and 20 ml spheres filled with water (cold-spots), three 0.25 ml spheres (sphere-to-background: 3, 6, and 12), one 1.14 ml sphere (sphere-to-background: 3), and one 11.27 ml sphere (sphere-to-background: 2) filled with a radioactive solution were inserted into the phantom. The activity concentration was chosen so that the count rates for the phantom measurements matched those of typical brain studies on both cameras. Images were reconstructed using FORE and OSEM algorithms. The reconstruction parameters were adjusted to obtain a similar signal-to-noise ratio in images acquired with the two cameras. The contrast recovery (CR) coefficients were similar on the two scanners for the 5.7 and 20 ml spheres (cold spheres) and the 1.14 and 11.27 ml spheres (hot spheres). For the 0.25 ml spheres, the CR values were 35% higher for the sphere-to-background ratio of 12 and 39% higher for the sphere-to-background ratio of 6 on the Biograph6 for the 3 min scan. The variability of measurements was lower on the Biograph6 than on the HR+. The detectability for the smallest spheres on the Biograph6 was close to that on the HR+. The Biograph has similar performances as the HR+ reference tomograph for the detection and quantification of small hot spots and cold spots.

Resume Objet Determiner le mecanisme de survenue d’une hydrocephalie aigue (HCA) au decours de l’hemorragie subarachnoidienne (HSA), a travers une analyse du flux de liquide cerebrospinal (LCS) dans l’aqueduc du mesencephale par IRM de contraste de phase (IRM–CP). Methode Une etude prospective par IRM–CP chez 33 patients presentant une HSA, a ete effectuee a la phase aigue ( Resultats Chez 27 des 33 patients, parmi lesquels 11 presentaient une HCA, l’analyse du flux de LCS a ete possible. Ces 11 patients presentaient tous une modification du SV dans l’aqueduc. Trois patients presentaient un SV nul caracterisant une HCA non communicante par obstruction de l’aqueduc. Huit patients presentaient un SV augmente caracterisant une HCA communicante par conservation de l’ecoulement du LCS dans l’aqueduc. Tous les patients avec un SV normal n’ont pas developpe d’HCA. L’hemorragie intraventriculaire etait correlee a la survenue d’une HCA, de type communicant (aqueduc non obstrue) dans 70 % des cas. Conclusion L’HSA peut entrainer des modifications hydrodynamiques dans l’aqueduc du mesencephale. l’HCA aigue est de type communicant dans la majorite des cas, meme quand il existe une hemorragie intraventriculaire.

Resume Les mouvements respiratoires induisent un etalement des zones hyperfixantes des structures mobiles dans les images de tomographie par emission de positons (TEP). Dans le cas ou les images TEP sont corrigees en autoattenuation a partir des images de la tomodensitometrie (TDM), ces mouvements peuvent egalement alterer la quantification des images TEP. Nous presentons les resultats cliniques d’une methode CT-based de traitement des acquisitions TEP synchronisees sur la respiration qui vise a ameliorer la quantification et la colocalisation TEP-TDM des lesions, notamment grâce a une acquisition TDM supplementaire en apnee. Le protocole CT-based consiste en une acquisition TEP mode liste de 10 minutes, synchronisee sur la respiration. Elle est suivie d’une acquisition TDM en apnee. Durant ces deux etapes, le signal respiratoire est enregistre en continu. Onze lesions pulmonaires ont ete incluses dans cette etude. Les patients ont beneficie d’un protocole standard TEP/TDM (en respiration libre) et du protocole CT-based. Les performances respectives des methodes standard et CT-based ont ete evaluees en comparant la distance entre les centroides d’une lesion dans les volumes TEP et TDM. Les variations de la SUVMAX (Standardized Uptake Value) et du volume des lesions ont egalement ete etudiees. La methode CT-based montre une diminution significative (p = 0,049) des distances des centroides (en moyenne 49 %), une augmentation de la SUVMAX (en moyenne 39 %) et une diminution significative (p = 0,026) du volume des lesions (en moyenne 43 %). La methode CT-based ameliore la colocalisation entre les images des lesions pulmonaires en TEP et TDM apportant ainsi une correction d’autoattenuation et une mesure de SUV probablement plus justes.

BACKGROUND AND PURPOSE: Patients with aqueductal stenosis (AS) present with various clinical and radiologic features. Conventional MR imaging provides useful information in AS but depends on a subjective evaluation by the neuroradiologist. The purpose of this study was to evaluate the support of the phase-contrast MR imaging (PC-MR imaging) technique (sensitive to CSF flows) for the diagnosis of AS. MATERIALS AND METHODS: We retrospectively considered 17 patients who underwent PC-MR imaging to explore hydrocephalus, with the absence of CSF flow at the aqueductal level. We analyzed their clinical and morphologic MR imaging data. RESULTS: None of the usually reported direct or indirect signs of aqueductal obstruction were seen in 7 patients in whom the clinical suggestion of AS was confirmed by PC-MR imaging results. Seven patients in this population had a third ventriculostomy, and 5 of them were among those in whom conventional MR imaging failed to reveal signs of aqueductal obstruction. All of these 7 patients had a positive postsurgical outcomes. The analysis of CSF and vascular dynamic data in this population was compared with an aged-matched population, and these data were found similar except for the fourth ventricular CSF flush flow latency. CONCLUSIONS: PC-MR imaging supports the diagnosis of CSF flow blockage at the aqueductal level in a reliable, reproducible, and rapid way, which aids in the diagnosis of AS in patients with clinical and/or radiologic suggestion of obstructive hydrocephalus. We, therefore, suggest using this technique in the current evaluation of hydrocephalus.

Resume Objectifs Nous cherchons a valider en imagerie par resonance magnetique fonctionnelle (IRMf), a partir d’une methode d’analyse spectrale du signal et d’une tâche visuomotrice, un modele de connectivite fonctionnelle compose de trois regions motrices : l’aire motrice pre-supplementaire (pre-AMS), l’AMS propre (AMS-propre) et le cortex moteur primaire (M1). Materiels et methodes Le paradigme que nous avons experimente chez des sujets jeunes ( n = 5) correspond a une tâche de preparation d’un mouvement moteur. Nous avons procede, dans une premiere etape, a une estimation dans le domaine frequentiel des coefficients de coherence et des valeurs de dephasage des signaux IRMf pour ces trois regions motrices. Dans une seconde etape, les coefficients de coherence estimes ont ete integres dans un modele de connectivite fonctionnelle. Deux coefficients d’interaction ont ete calcules, l’un entre les regions M1 et pre-AMS, l’autre entre les regions M1 et AMS-propre. Resultats et conclusion Nos resultats montrent une activite hemodynamique nettement plus precoce dans la region prefrontale pre-AMS au cours de la periode preparatoire de la tâche. De meme, une interaction plus importante retrouvee entre les regions M1 et pre-AMS corrobore l’hypothese du role predominant joue par ces deux regions dans le cas d’une tâche de preparation d’un mouvement moteur. Ainsi, cette etude a permis de mettre en evidence une dissociation fonctionnelle entre les deux sous-regions de l’AMS.

Our knowledge of cerebrospinal fluid (CSF) hydrodynamics has been considerably improved with the recent introduction of phase-contrast magnetic resonance imaging (phase-contrast MRI), which can provide CSF and blood flow measurements throughout the cardiac cycle. Key temporal and amplitude parameters can be calculated at different sites to elucidate the role played by the various CSF compartments during vascular brain expansion. Most of the models reported in the literature do not take into account CSF oscillation during the cardiac cycle and its kinetic energy impact on the brain. We propose a new lumped-parameter compartmental model of CSF and blood flows in healthy subjects during the cardiac cycle. The system was divided into five submodels representing arterial blood, venous blood, ventricular CSF, cranial subarachnoid space, and spinal subarachnoid space. These submodels are connected by resistances and compliances. The model developed was used to reproduce certain functional characteristics observed in seven healthy volunteers, such as the distribution (amplitude and phase shift) of arterial, venous, and CSF flows. The results show a good agreement between measured and simulated intracranial CSF and blood flows.

Resume L’imagerie par resonance magnetique en contraste de phase (IRMCP) est la seule technique non invasive pour l’etude des oscillations du liquide cerebrospinal (LCS). Elle permet la mesure des flux du LCS et du sang au cours du cycle cardiaque. Pour l’etude de l’hydro-hemodynamique cerebrale, des modeles ont ete developpes, mais la majorite d’entre eux ne prend pas en compte les oscillations du LCS. L’objectif de ce travail etait d’etablir les valeurs de reference des debits cerebraux et de proposer un nouveau modele de simulation. Materiel et methodes Les flux du LCS et du sang ont ete mesures par IRMCP sur 19 sujets temoins. Les images de flux ont ete analysees sur un logiciel dedie pour reconstruire les courbes de flux sur un cycle cardiaque. Un modele electrique a ete realise. Les entrees du modele correspondaient aux mesures par IRMCP des flux arteriels et veineux, et les sorties aux simulations des flux du LCS. Ces flux simules ont ete compares aux flux mesures par IRMPC pour la validation du modele. Resultats Les parametres clefs des flux de LCS et du sang ont ete obtenus, par exemple le debit arteriel cerebral moyen (688 ± 115 mL/min), le volume oscillatoire de LCS ventriculaire (0,05 ± 0,02 mL/cycle cardiaque) et le volume oscillatoire du LCS des espaces sous-arachnoidiens (0,55 ± 0,15 mL/cycle cardiaque). Il existe un bon accord entre les courbes du LCS simulees et mesurees. Conclusion Ce travail a decrit les principales valeurs caracterisant la dynamique cerebrale d’une population temoin. Cela permet de mieux comprendre les mecanismes de regulation des volumes intracrâniens pendant le cycle cardiaque. Nos resultats sont maintenant utilises en pratique clinique et le modele propose est valide pour l’etude de l’hydro-hemodynamique cerebrale.

Resume Description et objectifs de l’etude Les oscillations de liquide cerebro-spinal (LCS) sont synchronisees avec le flux sanguin cerebral et sont impliquees dans le controle de la variation de la pression intracrânienne. Le but de cette etude est d’explorer les alterations possibles de la dynamique des flux de LCS lors des hemorragies meningees (HM). Methodes Onze patients avec HM confirmee au scanner cerebral ont beneficie d’une IRM qui comprenait des sequences morphologiques et des sequences dynamiques de flux pour la quantification des flux de LCS et des flux arteriels. Les oscillations de LCS etaient enregistrees au niveau de l’aqueduc du mesencephale et des espaces sous-arachnoidiens en C2-C3 (ESA), ou une sequence vasculaire etait egalement realisee afin de quantifier les flux arteriels. Les resultats obtenus etaient compares a ceux de 44 sujets temoins, et une difference de plus de deux deviations standards permettait de definir un flux de LCS hypo- ou hyperdynamique. La dilatation du systeme ventriculaire etait appreciee par deux radiologues et un neurochirurgien. Resultats Un patient a ete exclu pour defaut de mesure. L’etude du LCS ventriculaire montre que seulement 4 patients presentaient un flux normal, 1 patient un flux hypodynamique et 5 patients des flux hyperdynamiques. En ce qui concerne le LCS extra-ventriculaire, 5 patients presentaient un flux normal et 5 patients un flux hyperdynamique. Les 2 patients qui ont developpe une dilatation ventriculaire avaient tous les deux des flux ventriculaires hyperdynamiques avec un flux de LCS cervical normal. Conclusion Nous avons montre qu’il existe des alterations de la dynamique des flux de LCS lors des HM, ce qui laisse supposer que le saignement entraine une augmentation du volume intracrânien et une reduction de la compliance cerebrale avec une augmentation de la pression intracrânienne. L’augmentation des oscillations intra-ventriculaires pourrait favoriser la dilatation ventriculaire.

Aim To assess the extent to which bone marrow scintigraphy (BMS) makes the interpretation of leucocyte scintigraphy (LS) easier and improves its diagnostic value. Methods Seventy-three 111In LSs, 99mTc hydroxymethylene diphosphonate bone scintigraphies (BSs) and 99mTc sulfur colloid BMSs were performed in 60 patients with suspected infection related to a hip prosthesis or knee prosthesis, either in situ (+group, n = 43) or after removal for septic loosening (-group, n = 30). Bacteriological samples were obtained from all patients. LS was interpreted together with BS (LS-BS) or with BMS (LS-BMS) by three independent readers. Results The concordance among readers, estimated by the kappa test, was average with LS-BS (kappa/kappam coefficients = 0.58, 0.58 and 0.46, respectively, for the three pairs of readers) and excellent with LS-BMS (kappa/kappam coefficients = 1.00 for the three pairs of readers). With LS-BS, 64/219 interpretations were equivocal whereas only one was equivocal with LS-BMS. Sensitivity, specificity and accuracy of LS-BMS were, respectively, 80%, 94% and 91% in the +group, and 33%, 100% and 93% in the -group. Conclusion We conclude that (1) the interpretation of the results for LS-BMS is very easy, in contrast to LS-BS; (2) the diagnostic value of LS-BMS for detecting infected joint prostheses is good; and (3) additional data are needed to assess the accuracy of LS-BMS when the prosthesis has been removed.

Rationale and Objectives: Using magnetic resonance imaging (MRI), we investigated cerebral blood and cerebrospinal fluid (CSF) flows in patients with communicating hydrocephalus (CH) and in healthy volunteers to determine the contribution of CSF flow to brain pressure regulation in CH patients. Methods: Cine phase-contrast MRI data from 16 healthy volunteers and 12 patients with CH characterized by hyperdynamic aqueductal CSF flow were analyzed using in-house image-processing software that automatically measured flow curves. Amplitude and temporal CSF and blood flow parameters were compared in the 2 groups. Results: Jugular peak flow occurred significantly earlier (P 0.01) in the CH patients than in the healthy volunteers. Cervical CSF oscillations were not significantly different between the 2 groups. Conclusion: Venous vessel compression and/or changes in intracranial subarachnoid CSF flow produce an increase in ventricular CSF flush that compensates for vascular brain expansion in patients with CH.

Background The objective of this study is to investigate the feasibility and the additional interest of a parametric imaging (PI) method to monitor the early tumour metabolic response in a prospective series of oesophageal cancer patients who underwent positron emission tomography with fluoro-2-deoxy-d-glucose (FDG-PET/CT) before and during curative-intent chemo-radiotherapy. Methods Fifty-seven patients with squamous cell carcinoma (SCC) of the oesophagus prospectively underwent FDG-PET/CT before chemo-radiotherapy (CRT) (PET1) and at 21 ± 3 days after the beginning of CRT (PET2). The outcome was assessed at 3 months and 1 year after the completion of CRT (clinical examination, CT scan or FDG-PET/CT, biopsy). For each patient, PET1 and PET2 were registered using CT images. The 2 PET image sets were subtracted, so the voxels with significant changes in FDG uptake were identified. A model-based analysis of this graph was used to identify the tumour voxels in which significant changes occurred between the two scans and yielded indices characterising these changes (green and red clusters). Quantitative parameters were compared with clinical outcome at 3 months and at 1 year. Results The baseline tumour FDG uptake decreased significantly at PET2 (p

Introduction La maladie d’Alzheimer (MA) est caracterisee par un depot des plaques amyloides (reflete par la proteine cerebrospinale As1-42) suivi d’une degenerescence neurofibrillaire (DNF). Objectifs Determiner la relation entre les marqueurs de DNF (l’hypometabolisme cerebral en TEP FDG versus les proteines cerebrospinales t-tau ou p-tau) et quel en etait l’indice le plus frequemment atteint. Methodes Dans cette etude multicentrique (Canada et Etats-Unis), prospective furent selectionnees : 82 participants sains, 215 patients ayant des troubles neurocognitifs legers et 75 patients ayant une MA clinique. Ils eurent une ponction lombaire avec un dosage des marqueurs cerebrospinaux (As1-42, t-tau et p-tau) et une TEP-FDG cerebrale. La relation entre le metabolisme et TEP-FDG (de 5 regions d’interet typiquement atteintes dans la MA) et les proteines t-tau et p-tau fut etudiee en fonction du statut de la proteine As1-42. Resultats La correlation entre les proteines t-tau/p-tau et l’hypometabolisme cerebrale des 5 ROI en TEP FDG etait significative seulement chez les patients ayant une proteine As1-42 anormale (t-tau : R 2 = 0,044, p = 0,001 ; p-tau : R 2 = 0,02, p = 0,03). Chez ces patients ayant une As1-42 anormale, la proteine p-tau etait l’indice de DNF le plus frequemment atteint (metabolisme en TEP FDG : McNemar test ; p = 0,0001 ; proteine t-tau : McNemar test, p = 0,0001). Discussion La correlation entre les indices de DNF etait significative seulement en cas de depots amyloide, donc la DNF etait presente dans les ROI caracteristiques de la MA uniquement si le depots de plaque amyloides eut lieu, ce qui est conforme au model physiopathologique actuel : la DNF suit la pathologie amyloide. La proteine p-tau etait l’indice de DNF le plus frequemment atteint en desaccord avec les etudes avec une verification neuropathologique. Conclusion Les indices de DNF (proteines t-tau/p-tau et hypometabolisme cerebral en TEP-FDG) etaient correles seulement chez les patients ayant une As1-42 anormale. La proteine p-tau etait l’indice de DNF le plus frequemment atteint.

Positron emission tomography (PET) with ^1^8fluorodeoxyglucose (^1^8F-FDG) is increasingly used in neurology. The measurement of cerebral arterial inflow (QA) using ^1^8F-FDG complements the information provided by standard brain PET imaging. Here, injections were performed after the beginning of dynamic acquisitions and the time to arrival (t0) of activity in the gantry's field of view was computed. We performed a phantom study using a branched tube (internal diameter: 4mm) and a ^1^8F-FDG solution injected at 240mL/min. Data processing consisted of (i) reconstruction of the first 3s after t0, (ii) vascular signal enhancement and (iii) clustering. This method was then applied in four subjects. We measured the volumes of the tubes or vascular trees and calculated the corresponding flows. In the phantom, the flow was calculated to be 244.2mL/min. In each subject, our QA value was compared with that obtained by quantitative cine-phase contrast magnetic resonance imaging; the mean QA value of 581.4+/-217.5mL/min calculated with ^1^8F-FDG PET was consistent with the mean value of 593.3+/-205.8mL/min calculated with quantitative cine-phase contrast magnetic resonance imaging. Our ^1^8F-FDG PET method constitutes a novel, fully automatic means of measuring QA.

To assess prospectively the prognostic value of FDG PET/CT during curative-intent radiotherapy (RT) with or without concomitant chemotherapy in patients with non-small-cell lung cancer (NSCLC).Patients with histological proof of invasive localized NSCLC and evaluable tumour, and who were candidates for curative-intent radiochemotherapy (RCT) or RT were preincluded after providing written informed consent. Definitive inclusion was conditional upon significant FDG uptake before RT (PET₁). All included patients had a FDG PET/CT scan during RT (PET₂, mean dose 43 Gy) and were evaluated by FDG PET/CT at 3 months and 1 year after RT. The main endpoint was death (from whatever cause) or tumour progression at 1 year.Of 77 patients preincluded, 52 were evaluable. Among the evaluable patients, 77% received RT with induction chemotherapy and 73% RT with concomitant chemotherapy. At 1 year, 40 patients (77 %) had died or had tumour progression. No statistically significant association was found between stage (IIIB vs. other), histology (squamous cell carcinoma vs. other), induction or concomitant chemotherapy, and death/tumour progression at 1 year. The SUVmax in the PET2 scan was the single variable predictive of death or tumour progression at 1 year (odds ratio 1.97, 95% CI 1.25 - 3.09, p = 0.003) in multivariate analysis. The area under the receiver operating characteristic curve was 0.85 (95% CI 0.73 - 0.94, p 10(-4)). A SUVmax value of 5.3 in the PET₂ scan yielded a sensitivity of 70% and a specificity of 92% for predicting tumour progression or death at 1 year.This prospective multicentre study demonstrated the prognostic value in terms of disease-free survival of SUVmax assessed during the 5th week of curative-intent RT or RCT in NSCLC patients (NCT01261598; RTEP2 study).

FDG PET has been suggested to have predictive value in the prognosis of oesophageal carcinoma. However, the retrospective studies reported in the literature have shown discordant results. Additionally, only four studies have evaluated FDG PET during chemoradiotherapy (CRT) in patients with different histological lesions. The purpose of this study was to investigate the predictive value of FDG PET performed early during CRT (on day 21) in a population of patients with oesophageal squamous cell carcinoma.Included in this prospective study were 57 patients with a histological diagnosis of squamous cell carcinoma of the oesophagus. Of these 57 patients, 48 (84%) were evaluated (aged 63 ± 11 years; 44 men, 4 women). Each patient underwent FDG PET (4.5 MBq/kg) before CRT, according to the Herskovic protocol (t0; PET₁) and on day 21 ± 3 from the start of CRT (d21; PET₂). The response assessment included a clinical examination, CT scan or FDG PET and histological analysis 3 months and 1 year after PET₁. The patients were classified as showing a complete response (CR) or a noncomplete response. A quantitative analysis was carried out for PET₁ and PET₂ using the following parameters: SUVmax, SUVmean (with SUVmean40 as the 3-D volume at an SUVmax threshold of 40% and SUVmeanp as that defined by a physician), tumour volume (TV, with TV40 defined as the TV at 40% of SUVmax, and TVp as that defined by a physician); and the total lesion glycolysis (TLG, SUVmean × TV, with TLG₄₀ defined as the TLG at 40% of SUVmax, and TLGp as that defined by a physician). The differences in responses at 3 months and 1 year between PET₁ (t0) and PET₂ (d21) were assessed in terms of variations in SUV, TV and TLG using a repeated measures of variance (ANOVA).SUVmax, SUVmean and TLG decreased significantly between PET₁ (t0) and PET₂ (d21; p0.0001). The TV significantly decreased only when assessed as TVp (p = 0.02); TV₄₀ did not decrease significantly. With respect to the predictive value of PET₁, only TV40_1 and TVp_1 values, and therefore TLG40_1 and TLGp_1, but not the SUV values, were significantly lower in patients with CR at 3 months. SUVmax1, TVp_1 and TLGp_1 were significantly lower in patients with CR at 1 year. With respect to the predictive value of PET₂, only TV40_2 and TVp_2 values, and therefore TLG40_2 and TLGp_2, but not the SUV values, were significantly lower in patients with CR at 3 months. None of the PET₂ parameters had significant value in predicting patient outcome at 1 year. The changes in SUVmax, TV₄₀, TVp, TLG₄₀ and TLGp between PET₁ and PET₂ had no relationship to patient outcome at 3 months or 1 year.This prospective, multicentre study performed in a selected population of patients with oesophageal squamous cell cancer demonstrates that the parameters derived from baseline PET₁ are good predictors of response to CRT. Specifically, a high TV and TLG are associated with a poor response to CRT at 3 months and 1 year, and a high SUVmax is associated with a poor response to CRT at 1 year. FDG PET performed during CRT on day 21 appears to have less clinical relevance. However, patients with a large functional TV on day 21 of CRT have a poor clinical outcome (ClinicalTrials.gov NCT 00934505).

Background and Purpose: Recent studies of the organization of the cerebral venous system in healthy subjects using phase contrast magnetic resonance imaging (PC-MRI) show its structural complexity and inter-individual variations. Our objective was to study the venous blood and CSF flows in cerebral venous thrombosis (CVT). Materials and Methods: PC-MRI sequences were added to brain MRI conventional protocol in 19 patients suspected of CVT, among whom 6 patients had CVT diagnosis confirmed by MR venography. Results were compared with 18 healthy age-matched volunteers (HV). Results: In patients without CVT (NoCVT) confirmed by venography, we found heterogeneous individual venous flows, and variable side dominance in paired veins and sinuses, comparable to those in healthy volunteers. In CVT patients, PC-MRI detected no venous flow in the veins and/or sinuses with thrombosis. Arterial flows were preserved. CSF aqueductal and cervical stroke volumes were increased in a patient with secondary cerebral infarction, and decreased in 4 patients with extended thrombosis in the superior sagittal and transverse sinuses. These results suggest the main role of the venous system in the regulation of the dynamic intracranial equilibrium. Conclusions: CVT produces highly individualized pattern of disturbance in venous blood drainage. Complementary to MRI venography, PC-MRI provides non-invasive data about venous blockage consequences on CSF flow disturbances.

To develop a method for segmenting cerebrospinal fluid (CSF) regions with complex, inhomogeneous pulsatile patterns in phase contrast magnetic resonance imaging (PC-MRI) sequences. Our approach used various temporal features of flow behavior as input attributes in an unsupervised k-means classification algorithm. CSF flow parameters for the cervical subarachnoid spaces and the pontine cistern were calculated in 26 healthy volunteers. Background and aliasing corrections were applied automatically. The algorithm's reproducibility was determined by calculating two parameters (area and stroke volume) while varying the initially selected seed point. The influence of background correction on these parameters was also assessed. The method was highly reproducible, with coefficients of variation of 3 and 4% for the cervical stroke volume and area, respectively. In an analysis of variance, background correction did not have a statistically significant effect on either the stroke volume (p = 0.32) or the CSF net mean flow (p = 0.69) at the C2C3 level. The method presented here enables rapid, reproducible, quantitative analysis of CSF flow in complex regions such as the C2C3 subarachnoid spaces and the pontine cistern. © 2011 Wiley Periodicals, Inc., Grant sponsor: Generalitat Valenciana; Grant number: CTBPRB/2004/342 FPI.

In whole-body positron emission tomography (PET) imaging, the detection of small uptake foci (i.e., around two or three times the tomograph's spatial resolution) is a critical issue. Indeed, spatial resolution is altered by postreconstruction smoothing operations used to reduce the noise introduced by (among other things) an inaccurate system matrix. The authors previously proposed a device-dedicated projector, easily applicable on a clinical gantry, based on point-source measurements, which introduces less noise than a geometrical model. In the present study, they took advantage of the lower noise levels by reducing the postfilter and then quantified the approach's impact on image quality. This study was performed on an IEC Body Phantom Set filled with 18F (sphere-to-background activity ratio: 4:1). The same 3 min acquisition was reconstructed with either (i) a clinical system based on a geometrical tomographic operator (OSEM_CL) or (ii) an OSEM algorithm using the suggested system matrix (OSEM_DR). In order to compare the resulting images, they set the 3D Gaussian postfilter (3DGPF) for OSEM_DR so as to obtain similar background signal-to-noise ratio (SNR) to that of OSEM_CL with a Gaussian postfilter full width at half maximum of 5 mm (as recommended for whole-body imaging on a Biograph6). They then assessed the contrast-to-noise ratio (CNR) and quantitation [contrast recovery (CR)] for the phantom's four smallest spheres (with internal diameters of 10, 13, 17, and 22 mm). Evaluation of 3DGPFs ranging from 2.2 to 2.6 mm showed that a value of 2.4 mm in OSEM_DR gave the closest background SNR to that of OSEM_CL with a 3DGPF of 5 mm. For all studied targets, the CNR was higher with OSEM_DR than with OSEM_CL. For the 10 and 13 mm spheres, OSEM_DR increased the size of the CNR peaks by 37% and 20%, relative to OSEM_CL. The OSEM_DR technique yielded higher CR values than OSEM_CL did. For the 10, 13, 17, and 22 mm spheres, the CR values at eight iterations were 0.5, 0.6, 1.1, and 1.0 for OSEM_DR and 0.3, 0.4, 0.9, and 0.8 for OSEM_CL. They evaluated a practical method for determining a device-dedicated system matrix based on point-source acquisitions. This tomographic operator is more realistic than geometrical system matrix and introduces less noise into PET images during statistical reconstruction; it thus reduces the extent of postfiltering operations required. Thus, spatial resolution is better maintained with OSEM_DR than with clinical reconstruction. They showed that this method improves the contrast-to-noise ratio and quantification of uptake foci (especially those that are at the system's limit of detection) and, in a clinical context, could allow better detection and earlier diagnosis.

Although crucial in regulating intracranial hydrodynamics, the cerebral venous system has been rarely studied because of its structural complexity and individual variations. The purpose of our study was to evaluate the organization of cerebral venous system in healthy adults. Phase-contrast magnetic resonance imaging (PC-MRI) was performed in 18 healthy volunteers, in the supine position. Venous, arterial, and cerebrospinal fluid (CSF) flows were calculated. We found heterogeneous individual venous flows and variable side dominance in paired veins and sinuses. In some participants, the accessory epidural drainage preponderated over the habitually dominant jugular outflow. The PC-MRI enabled measurements of venous flows in superior sagittal (SSS), SRS (straight), and TS (transverse) sinuses with excellent detection rates. Pulsatility index for both intracranial (SSS) and cervical (mainly jugular) levels showed a significant increase in pulsatile blood flow in jugular veins as compared with that in SSS. Mean cervical and cerebral arterial blood flows were 714 ± 124 and 649 ± 178 mL/min, respectively. Cerebrospinal fluid aqueductal and cervical stroke volumes were 41 ± 22 and 460 ± 149 μL, respectively. Our results emphasize the variability of venous drainage for side dominance and jugular/epidural organization. The pulsatility of venous outflow and the role it plays in the regulation of intracranial pressure require further investigation.