Higher b-values improve the correlation between diffusion MRI and the cortical microarchitecture.

PURPOSE: In diffusion MRI (dMRI), it remains unclear to know how much increase of b-value is conveying additional biological meaning. We tested the correlations between cortical microarchitecture and diffusion metrics computed from standard (1000 s/mm2), high (3000 s/mm2), to very high (5000 s/mm2) b-value dMRI. METHODS: Healthy volunteers were scanned with a dMRI pulse sequence that was first optimized together with a T1-WI and T2-WI. Averaged cortical surface map of estimated myelin (T1-WI/T2-WI) was compared with surface maps of mean diffusivity (MD) computed from each b-value (MD1000, MD3000, and MD5000) and to surface map of mean kurtosis (MK computed from the 0-, 1000-, to 3000-s/mm2 shells) in 360 cortical parcels using Spearman correlations, multiple linear regressions, and Akaike information criteria (AIC). RESULTS: Surface map from MD1000 showed variations not related to myelin but the MD3000 and MD5000 maps inversely mirrored estimated myelin map; lower MD values being observed in more myelinated cortical areas. MK mirrored myelinated cortical areas. Quantitatively, Spearman correlations between myelin and MD became more and more negative as long as b-values increased while the correlation was positive between myelin and MK. Multiple regression models confirmed negative associations between myelin and MD that were significantly better from MD1000 to MD3000 and MD5000 (R2 = 0.33, p < 0.001; R2 = 0.43, p < 0.001; and R2 = 0.50, p < 0.001) and positive association between myelin and MK (R2 = 0.53, p < 0.001). Comparisons of the 3 statistical models showed the best performances with MK and MD5000 (AICMK < AICMD5000 < AICMD3000 < AICMD1000). CONCLUSION: Higher b-values are more closely related to subtle cellular variations of the cortical microarchitecture.

OFSEP, a nationwide cohort of people with multiple sclerosis: Consensus minimal MRI protocol.

Multiple sclerosis (MS) is most generally considered as a severe disease with high physical and mental risks of disability. Since the end of the 1990s, several high cost long-term disease-modifying treatments provided some clinical efficiency. However, patient's follow-up was needed for the detection and the assessment of their side-effects. The "Observatoire français de la sclérose en plaques" (OFSEP) project aims to improve the clinical, biological and imaging systematic longitudinal follow-up of patients. It should increase the quality, efficiency and safety of patients' care, with a unique opportunity of large scale, about 41,000 patients followed in 62 French centers using the European Database for Multiple Sclerosis (EDMUS) software. OFSEP is divided into three working groups (clinical, biological and imaging). The imaging working group defines standards for routine MRI follow-up in the whole cohort and contains three subgroups: acquisition, workflow, and data processing. A common and feasible brain and spinal cord acquisition protocol has been defined by the acquisition group, and accepted by the OFSEP steering and scientific committees. This protocol can be implemented in all French MRI centers. The major MRI manufacturers have agreed to provide the dedicated collection of sequences as an "OFSEP box" with every software upgrade or new MRI machine. The new OFSEP protocol will provide a unique opportunity to study a population-based collection of data from people with MS.

Direct and inverse pumping in flows with homogeneous and non-homogeneous swirl.

The conditions in which meridional recirculations appear in swirling flows above a fixed wall are analysed. In the classical Bodewädt problem, where the swirl tends towards an asymptotic value away from the wall, the well-known "tea-cup effect" drives a flow away from the plate at the centre of the vortex. Simple dimensional arguments applied to a single vortex show that if the intensity of the swirl decreases away from the wall, the sense of the recirculation can be inverted, and that the associated flow rate scales with the swirl gradient. If the flow is quasi-2D, the classical tea-cup effect takes place. This basic theory is confirmed by numerical simulations of a square array of steady, electrically driven vortices. Experiments in the turbulent regimes of the same configuration reveal that these mechanisms are active in the average flow and in its fluctuating part. These mechanisms provide an explanation for previously observed phenomena in electrolyte flows. They also put forward a possible mechanism for the generation of helicity in flows close to two-dimensionality, which plays a key role in the transition between 2D and 3D turbulence.

Cerebral blood flow modulation by transcutaneous cranial electrical stimulation with Limoge's current.

OBJECTIVES: Transcutaneous cranial electrical stimulation (TCES) delivers a high-frequency (166 kHz) pulsed biphasic balanced current with a pulse repetition frequency of 100 Hz with 40% duty cycle through a negative electrode and two positive electrodes over the skull. TCES has a proven ability to potentiate anesthesia and analgesia, although the physiological mechanisms of this effect remain unclear. We hypothesized that the mechanism is a modulation of CBF in the central endogenous opioid system. This study aimed at determining the effects of TCES on CBF to elucidate its physiological mechanism. METHODS: Thirty-six healthy volunteers were randomly assigned to active or placebo TCES, and all assessments were double blind. TCES was performed using the Anesthelec™ device. In the stimulated group, an active cable was used, and in the control group (sham), the cable was inactive. CBF was measured by XeCT™ before and after two hours of TCES. RESULTS: Globally, CBF was unchanged by TCES. However, locally, TCES induced a significant CBF decrease in the brainstem and thalamus, which are structures involved in pain and anxiety (TCES and control CBF decrease were 18.5 and 11.9 mL/100g brain tissue/min, respectively). CONCLUSION: TCES can modulate local CBF but it has no effect on overall CBF. [Clinical Trials. gov number: NCT00273663].

Validation of a Denoising Method Using Deep Learning-Based Reconstruction to Quantify Multiple Sclerosis Lesion Load on Fast FLAIR Imaging.

BACKGROUND AND PURPOSE: Accurate quantification of WM lesion load is essential for the care of patients with multiple sclerosis. We tested whether the combination of accelerated 3D-FLAIR and denoising using deep learning-based reconstruction could provide a relevant strategy while shortening the imaging examination. MATERIALS AND METHODS: Twenty-eight patients with multiple sclerosis were prospectively examined using 4 implementations of 3D-FLAIR with decreasing scan times (4 minutes 54 seconds, 2 minutes 35 seconds, 1 minute 40 seconds, and 1 minute 15 seconds). Each FLAIR sequence was reconstructed without and with denoising using deep learning-based reconstruction, resulting in 8 FLAIR sequences per patient. Image quality was assessed with the Likert scale, apparent SNR, and contrast-to-noise ratio. Manual and automatic lesion segmentations, performed randomly and blindly, were quantitatively evaluated against ground truth using the absolute volume difference, true-positive rate, positive predictive value, Dice similarity coefficient, Hausdorff distance, and F1 score based on the lesion count. The Wilcoxon signed-rank test and 2-way ANOVA were performed. RESULTS: Both image-quality evaluation and the various metrics showed deterioration when the FLAIR scan time was accelerated. However, denoising using deep learning-based reconstruction significantly improved subjective image quality and quantitative performance metrics, particularly for manual segmentation. Overall, denoising using deep learning-based reconstruction helped to recover contours closer to those from the criterion standard and to capture individual lesions otherwise overlooked. The Dice similarity coefficient was equivalent between the 2-minutes-35-seconds-long FLAIR with denoising using deep learning-based reconstruction and the 4-minutes-54-seconds-long reference FLAIR sequence. CONCLUSIONS: Denoising using deep learning-based reconstruction helps to recognize multiple sclerosis lesions buried in the noise of accelerated FLAIR acquisitions, a possibly useful strategy to efficiently shorten the scan time in clinical practice.

[Diffusion-weighted MR imaging of the spine and cord]. / Imagerie de diffusion: moelle et rachis.

Due to its excellent sensitivity, MR imaging is invaluable for the evaluation of lesions of the cord and spine. Several studies dedicated to diffusion-weighted MR evaluation of the cord and spine have been published. While diffusion-weighted MR imaging of the brain is routinely performed, it is seldom performed when imaging the spine due to serious limitations. While anatomical limitations may not be changed, the voxel size, phase-encoding direction, mode of k-space filling, and acceleration factor are all parameters that can be optimized in order to routinely obtain diffusion-weighted imaging of the spine on 1.5T and 3T scanners.

[Magnetic resonance imaging of central nervous system inflammation]. / Imagerie par résonance magnétique de l'inflammation du système nerveux central.

Magnetic resonance imaging (MRI) is widely used to explore central nervous system inflammatory disorders, especially multiple sclerosis (MS). Advanced MRI methods are bringing more sensitive and specific tools for each step of the inflammatory process. In this review, we discuss the different MRI approaches for inflammatory disorders exploration, especially MS. We give particular emphasize on sensibility and specificity of each MRI approach and we also discuss the current knowledge concerning biological and histopathological substratum that could explain MRI signal with each modality.

Pharmacological control of head motion during cerebral blood flow imaging with CT or MRI.

Uncontrolled head motion during CT/MRI cerebral blood flow (CBF) imaging has been estimated between 3 and 15% of the cases. We present a pharmacological approach which permitted us to maintain the incident at 0.06% with few side effects. The protocol involves the systematic use of general anesthesia (sevoflurane) in children below five years and those with mental retardation. In anxious, claustrophobic or agitated adults, mild sedation with propofol, midazolam or hydroxyzine was used with mild effects on CBF. We strongly recommend the availability of basic cardiorespiratory resuscitation equipment and a recovery room before any sedation or general anesthesia is undertaken.

[Postoperative analgesia with continuous intra-articular infusion of ropivacaine following trapeziectomy]. / Analgésie post-trapézectomie par diffusion intra-articulaire continue de ropivacaïne.

OBJECTIVES: A pilot study was implemented to evaluate the efficacy of patient controlled analgesia (PCA) with continuous intra-articular infusion of ropivacaine following trapeziectomy with ligament reconstruction and tendon interposition. METHODS: Twelve patients were prospectively included. A catheter was placed into the trapezium void and connected to a PCA pump set on a continuous intra-articular infusion rate of ropivacaine: 2mg/ml. Patients were allowed to deliver additional boluses when analgesia was incomplete. RESULTS: Pain was evaluated less than 3/10 (Numeric Scale Evaluation) by 92% of the patients during the first 48 h. No toxicity of the local anaesthetic nor catheter-related complication were reported. CONCLUSION: This preliminary study showed continuous basal and bolus infusion of ropivacaine through a single catheter placed into the trapezium void to provide an excellent postoperative pain control and to be related to a high patient's satisfaction level.

Validation of the Behavioural Observation Scale 3 for the evaluation of pain in adults.

BACKGROUND: Many behavioural scales are available to assess pain but none are suitable for a quick evaluation of non-sedated and non-geriatric adults. The Behavioural Observation Scale 3 (BOS-3) is short, composed of five items. This study examined its feasibility and diagnostic performances. METHODS: Adult patients were included from medical and surgical departments of the University Hospital of Bordeaux. In a cross-sectional study, BOS-3 was compared to Numerical Rate Scale (NRS) with communicating patients (CP) and Behavioural Scale for the Elderly Person (ECPA2) with non-communicating patients (NCP). Each time, BOS-3 and reference scale were performed by an internal caregiver and an external expert. RESULTS: We included 447 patients: 395 communicating and 52 non-communicating. All patients were assessed by the BOS-3 and the reference test. All BOS-3 were carried out in less than one minute with only four missing data. Its reproducibility (ICC = 0.77 [95% CI 0.73-0.81] with CP and 0.93 [95% CI 0.89-0.97] with NCP) and its internal consistency (Cronbach α = 0.67 with CP and 0.70 with NCP) were good. In non-communicating patients, ROC analysis set a threshold at 3 on 10. Sensitivity was 0.87 [95% CI 0.77-0.96], specificity 0.97 [95% CI 0.93-1.00], positive predictive value 0.93 [95% CI 0.86-0.99] and negative predictive value 0.95 [95% CI 0.89-1.00]. In communicating patients, sensitivity decreased to 0.34 [95% CI 0.28-0.38] but specificity reached 0.96 [95% CI 0.94-0.98] and positive predictive value 0.75 [95% CI 0.70-0.79]. CONCLUSIONS: BOS-3 had good metrological properties in non-communicating adults. With communicating patients, a positive BOS-3 could be an additional tool to confirm pain, when underestimated on the NRS. SIGNIFICANCE: This study describes the diagnostic performances of a behavioral pain assessment scale designed for non-geriatric and non-sedated adults. The results show its validity in non-communicating patients and suggest its usefulness as an ancillary tool in communicating patients in whom simple numerical scales are often insufficient.

Lumbar spinal muscles and spinal canal study by MRI three-dimensional reconstruction in adult lumbar spinal stenosis.

BACKGROUND: Lumbar spinal stenosis is degenerative disc disease most common manifestation. If stenosis degree seems poorly related to symptom severity, lumbar muscles role is recognized. Many studies report imaging methods, to analyze muscle volumes and fat infiltration (FI), but remain limited due to the difficulty to represent entire muscle volume variability. Recently a 3D muscle reconstruction protocol (using the deformation of a parametric specific object method (DPSO) and three-point Dixon images) was reported. It offers the ability to evaluate, muscles volumes and muscle FI. PURPOSE: To describe, in a lumbar spinal stenosis population, muscle volumes, muscle FI and lumbar spinal canal volume with 3D MRI images reconstructions. MATERIALS AND METHODS: Ten adults presenting L4-L5 lumbar stenosis, were included. After specific MRI protocol, three-dimensional, muscle and spinal canal, reconstructions were performed. Muscle (psoas and paraspinal muscles) volumes and fat infiltration (FI), the spinal canal volume, age, and height were correlated one to each other with Spearman correlation factor. An ANOVA was performed to evaluate the intervertebral level influence (P≤0.05). RESULTS: Muscle volumes correlated with height (r=0.68 for psoas). Muscles FI correlated with age (r=0.66 for psoas) and lumbar spinal canal volume (r=0.91). Psoas and paraspinal volumes were maximum at L3-L4 level whereas FI increased from L1-L2 to L5-S1 level. DISCUSSION: These first results illustrate the importance to consider muscles entirely and report correlations between muscles FI, lumbar spinal canal volume and age; and between muscle volumes and patients height. Muscle degeneration seems more related to muscle FI than muscle volume. LEVEL OF EVIDENCE: 3.

MR imaging of relapsing multiple sclerosis patients using ultra-small-particle iron oxide and compared with gadolinium.

BACKGROUND AND PURPOSE: Inflammatory multiple sclerosis (MS) lesions are characterized by microglia activation and infiltration of T cells, B cells, and macrophages across the blood-brain barrier (BBB). In the experimental autoimmune encephalomyelitis (EAE) rat model of MS, previous MR imaging investigations with a new contrast agent ultra-small-particle iron oxide (USPIO) that accumulates in phagocytic cells revealed in vivo the presence of macrophage brain infiltration. The goal of this study was to characterize MS lesions with the use of this contrast agent. METHODS: A prospective MR imaging study of 10 patients with MS in acute relapses was achieved by using USPIO and gadolinium. RESULTS: Twenty-four hours after USPIO injection, 33 acute MS lesions in 9 patients showed USPIO uptake. Lesions were seen as high signal intensities on T1-weighted images and low signal intensities on T2-weighted images. Gadolinium enhancement was seen in 31 of these lesions in 7 patients. These 7 patients presented 24 gadolinium-enhanced lesions that did not enhance with USPIO. Two patients showed USPIO-enhanced lesions but no gadolinium-enhanced lesions. CONCLUSION: Taken together with earlier findings obtained in experimental models or in human stroke, the visualization of macrophage activity in vivo with USPIO characterize a distinct cellular and inflammatory event of the dynamic process of MS lesion formation. The macrophage activity information obtained with USPIO is distinct and complementary to the increased BBB permeability seen with gadolinium.

A longitudinal study of cognition in primary progressive multiple sclerosis.

There are few longitudinal studies of cognition in patients with multiple sclerosis, and the results of these studies remain inconclusive. No serial neuropsychological data of an exclusively primary progressive series are available. Cross-sectional analyses have revealed significant correlations between cognition and magnetic resonance imaging (MRI) parameters in primary progressive multiple sclerosis (PPMS). This study investigated cognitive and MRI change in 99 PPMS patients from five European centres for 2 years. They were assessed at 12 month intervals using the Brief Repeatable Battery, a reasoning test, and a measure of depression. The MRI parameters of T1 hypointensity load, T2 lesion load, and partial brain volume were also calculated at each time point. There were no significant differences between the mean cognitive scores of the patients at year 0 and year 2. However, one-third of the patients demonstrated absolute cognitive decline on individual test scores. Results indicated that initial cognitive status on entry into the study was a good predictor of cognitive ability at 2 years. There was only a small number of significant correlations between changes in cognition and changes on MRI, notably T1 hypointensity load with the two attentional tasks (r = -0.266, P = 0.017; r = -0.303, P = 0.012). It is probable that multiple factors underlie this weak relation between the cognitive and MRI measures.

[ADEM: a rare and serious demyelinating disorder of adults]. / Presentation atypique d'adem: à propos de deux observations chez l'adulte.

Acute Disseminated Encephalomyelitis is a serious demyelinating disorder of childhood that typically occurs following vaccination or a viral prodrome. Some etiologies remain unrecognized, and multiple mechanisms of immune response may explain the pathophysiology of this syndrome. Based on a report of two adult cases presenting with neurologic deficit and ataxia, we report our experience with this syndrome that may affect adults without evident infectious disorder. Prompt treatment is important to avoid rapid progression.

Cervical Spinal Cord DTI Is Improved by Reduced FOV with Specific Balance between the Number of Diffusion Gradient Directions and Averages.

BACKGROUND AND PURPOSE: Reduced-FOV DTI is promising for exploring the cervical spinal cord, but the optimal set of parameters needs to be clarified. We hypothesized that the number of excitations should be favored over the number of diffusion gradient directions regarding the strong orientation of the cord in a single rostrocaudal axis. MATERIALS AND METHODS: Fifteen healthy individuals underwent cervical spinal cord MR imaging at 3T, including an anatomic 3D-Multi-Echo Recombined Gradient Echo, high-resolution full-FOV DTI with a NEX of 3 and 20 diffusion gradient directions and 5 sets of reduced-FOV DTIs differently balanced in terms of NEX/number of diffusion gradient directions: (NEX/number of diffusion gradient directions = 3/20, 5/16, 7/12, 9/9, and 12/6). Each DTI sequence lasted 4 minutes 30 seconds, an acceptable duration, to cover C1-C4 in the axial plane. Fractional anisotropy maps and tractograms were reconstructed. Qualitatively, 2 radiologists rated the DTI sets blinded to the sequence. Quantitatively, we compared distortions, SNR, variance of fractional anisotropy values, and numbers of detected fibers. RESULTS: Qualitatively, reduced-FOV DTI sequences with a NEX of ≥5 were significantly better rated than the full-FOV DTI and the reduced-FOV DTI with low NEX (N = 3) and a high number of diffusion gradient directions (D = 20). Quantitatively, the best trade-off was reached by the reduced-FOV DTI with a NEX of 9 and 9 diffusion gradient directions, which provided significantly fewer artifacts, higher SNR on trace at b = 750 s/mm2 and an increased number of fibers tracked while maintaining similar fractional anisotropy values and dispersion. CONCLUSIONS: Optimized reduced-FOV DTI improves spinal cord imaging. The best compromise was obtained with a NEX of 9 and 9 diffusion gradient directions, which emphasizes the need for increasing the NEX at the expense of the number of diffusion gradient directions for spinal cord DTI contrary to brain DTI.

Comparative overview of brain perfusion imaging techniques.

Numerous imaging techniques have been developed and applied to evaluate brain hemodynamics. Among these are: Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), Xenon-enhanced Computed Tomography (XeCT), Dynamic Perfusion-computed Tomography (PCT), Magnetic Resonance Imaging Dynamic Susceptibility Contrast (DSC), Arterial Spin-Labeling (ASL), and Doppler Ultrasound. These techniques give similar information about brain hemodynamics in the form of parameters such as cerebral blood flow (CBF) or volume (CBV). All of them are used to characterize the same types of pathological conditions. However, each technique has its own advantages and drawbacks. This article addresses the main imaging techniques dedicated to brain hemodynamics. It represents a comparative overview, established by consensus among specialists of the various techniques. For clinicians, this paper should offers a clearer picture of the pros and cons of currently available brain perfusion imaging techniques, and assist them in choosing the proper method in every specific clinical setting.

[Long term clinical follow up of vertebral hemangiomas treated by percutaneous vertebroplasty]. / Evaluation clinique à long terme des patients traités par vertébroplastie pour des angiomes vertébraux.

PURPOSE: Long term clinical follow up of vertebral hemangiomas (VH) treated by percutaneous vertebroplasty. PATIENTS AND METHODS: A retrospective analysis of 19 patients treated fro 21 VH associated with chronic pain in 16 cases, using pecutaneous vertebrosplasty. One patient underwent both vertebroplasty and surgery. Long term follow up (mean 38.6 months; 16-83 months) consisted in the evaluation of residual or secondary pain, its impact on daily activities (using the Oswestry Low Back Pain scale) and the need for pain medication. RESULTS: Long term follow up found 56.2% of patients to be asymptomatic (9/16) and 31.2% (5/16) with occasional pain without much impact on daily activities and no need for chronic use of pain medication. The treatment was ineffective in 2 cases. Three patients treated for aggressive hemangiomas remained painless. There was no complication due to the treatment. No poor outcome was noted. CONCLUSION: Percutaneous vertebroplasty appears to be an effective technique in the treatment of VH with approximately 90% of satisfactory results in the short or long term period.

Chiasmatic cavernoma haemorrhage: To treat or not to treat? Concerning a clinical case.

We present the case of a 43-year-old man with acute visual loss due to an optic chiasm cavernoma. Our clinical and imaging findings quickly led us to this diagnosis. As a clinical improvement spontaneously occurred soon after the initial diagnosis, we decided not to perform any surgical treatment. The visual evolution was satisfactory and, to date after a 36-months follow-up, no clinical worsening has been reported. We present this clinical case regarding our approach, primarily a close follow-up, as well as a review of the literature.

MS lesions are better detected with 3D T1 gradient-echo than with 2D T1 spin-echo gadolinium-enhanced imaging at 3T.

BACKGROUND AND PURPOSE: In multiple sclerosis, gadolinium enhancement is used to classify lesions as active. Regarding the need for a standardized and accurate method for detection of multiple sclerosis activity, we compared 2D-spin-echo with 3D-gradient-echo T1WI for the detection of gadolinium-enhancing MS lesions. MATERIALS AND METHODS: Fifty-eight patients with MS were prospectively imaged at 3T by using both 2D-spin-echo and 3D-gradient recalled-echo T1WI in random order after the injection of gadolinium. Blinded and independent evaluation was performed by a junior and a senior reader to count gadolinium-enhancing lesions and to characterize their location, size, pattern of enhancement, and the relative contrast between enhancing lesions and the adjacent white matter. Finally, the SNR and relative contrast of gadolinium-enhancing lesions were computed for both sequences by using simulations. RESULTS: Significantly more gadolinium-enhancing lesions were reported on 3D-gradient recalled-echo than on 2D-spin-echo (n = 59 versus n = 30 for the junior reader, P = .021; n = 77 versus n = 61 for the senior reader, P = .017). The difference between the 2 readers was significant on 2D-spin-echo (P = .044), for which images were less reproducible (κ = 0.51) than for 3D-gradient recalled-echo (κ = 0.65). Further comparisons showed that there were statistically more small lesions (<5 mm) on 3D-gradient recalled-echo than on 2D-spin-echo (P = .04), while other features were similar. Theoretic results from simulations predicted SNR and lesion contrast for 3D-gradient recalled-echo to be better than for 2D-spin-echo for visualization of small enhancing lesions and were, therefore, consistent with clinical observations. CONCLUSIONS: At 3T, 3D-gradient recalled-echo provides a higher detection rate of gadolinium-enhancing lesions, especially those with smaller size, with a better reproducibility; this finding suggests using 3D-gradient recalled-echo to detect MS activity, with potential impact in initiation, monitoring, and optimization of therapy.