Sylvie Grand

Diffusion MRI: Pitfalls, literature review and future directions of research in mild traumatic brain injury

Mild traumatic brain injury (mTBI) is a leading cause of disability in adults, many of whom report a distressing combination of physical, emotional and cognitive symptoms, collectively known as post-concussion syndrome, that persist after the injury. Significant developments in magnetic resonance diffusion imaging, involving voxel-based quantitative analysis through the measurement of fractional anisotropy or mean diffusivity, have enhanced our knowledge on the different stages of mTBI pathophysiology. Other diffusion imaging-derived techniques, including diffusion kurtosis imaging with multi-shell diffusion and high-order tractography models, have recently demonstrated their usefulness in mTBI. Our review starts by briefly outlining the physical basis of diffusion tensor imaging including the pitfalls for use in brain trauma, before discussing findings from diagnostic trials testing its usefulness in assessing brain structural changes in patients with mTBI. Use of different post-processing techniques for the diffusion imaging data, identified the corpus callosum as the most frequently injured structure in mTBI, particularly at sub-acute and chronic stages, and a crucial location for evaluating functional outcome. However, structural changes appear too subtle for identification using traditional diffusion biomarkers, thus disallowing expansion of these techniques into clinical practice. In this regard, more advanced diffusion techniques are promising in the assessment of this complex disease.

Reduced CMRO2 and cerebrovascular reserve in patients with severe intracranial arterial stenosis: A combined multiparametric qBOLD oxygenation and BOLD fMRI study

Multiparametric quantitative blood oxygenation level dependent (mqBOLD) magnetic resonance Imaging (MRI) approach allows mapping tissular oxygen saturation (StO2) and cerebral metabolic rate of oxygen (CMRO2). To identify hemodynamic alteration related to severe intracranial arterial stenosis (SIAS), functional MRI of cerebrovascular reserve (CVR BOLD fMRI) to hypercapnia has been proposed. Diffusion imaging suggests chronic low grade ischemia in patients with impaired CVR. The aim of the present study was to evaluate how oxygen parameters (StO2 and CMRO2), assessed with mqBOLD approach, correlate with CVR in patients (nu2009=u200912) with SIAS and without arterial occlusion. The perfusion (dynamic susceptibility contrast), oxygenation, and CVR were compared. The MRI protocol conducted at 3T lasted approximately 1 h. Regions of interest measures on maps were delineated on segmented gray matter (GM) of middle cerebral artery territories. We have shown that decreased CVR is spatially associated with decreased CMRO2 in GM of patients with SIAS. Further, the degree of ipsilateral CVR reduction was well‐correlated with the amplitude of the CMRO2 deficit. The altered CMRO2 suggests the presence of a moderate ischemia explained by both a decrease in perfusion and in CVR. CVR and mqBOLD method may be helpful in the selection of patients with SIAS to advocate for medical therapy or percutaneous transluminal angioplasty‐stenting. Hum Brain Mapp 36:695–706, 2015.

Post traumatic deafness: a pictorial review of CT and MRI findings

AbstractHearing loss is a common functional disorder after trauma, and radiologists should be aware of the ossicular, labyrinthine or brain lesions that may be responsible. After a trauma, use of a systematic approach to explore the main functional components of auditory pathways is essential. Conductive hearing loss is caused by the disruption of the conductive chain, which may be due to ossicular luxation or fracture. This pictorial review firstly describes the normal 2-D and 3-D anatomy of the ossicular chain, including the incudo-malleolar and incudo-stapedial joints. The role of 3-D CT in the post-traumatic evaluation of injury to the temporal bone is then evaluated. In the case of sensorineural hearing loss, CT can detect pneumolabyrinth and signs of perilymphatic fistulae but fails to detect subtle lesions within the inner ear, such as labyrinthine haemorrhage or localized brain axonal damage along central auditory pathways. The role that MRI with 3-D-FLAIR acquisition plays in the detection of inner ear haemorrhage and post-traumatic lesions of the brain parenchyma that may lead to auditory agnosia is also discussed.Key Points• The most common middle ear injuries are incudo-malleolar and incudo-stapedial joint luxation.n • In patients with SNHL, CT can detect pneumolabyrinth or perilymphatic fistulan • 3-D-FLAIR MRI appears the best sequence to highlight labyrinthine haemorrhagen • Axonal damage and brain hematoma may lead to deafness

Glioblastoma as differential diagnosis of autoimmune encephalitis

ObjectiveTo identify the clinical and radiological features that should raise suspicion for the autoimmune encephalitis (AE)-like presentation of glioblastoma.MethodsThis is an observational, retrospective case series of patients referred to the French National Reference Center on Paraneoplastic Neurological Diseases for suspected AE (possible, probable or definite, using the 2016 criteria) who later received a final diagnosis of glioblastoma according to 2016 WHO criteria. An extensive literature search was also conducted for similar existing cases.ResultsBetween 2014 and 2016, 306 patients were referred to our center for suspected AE. Six of these patients (2%) later developed pathologically confirmed glioblastoma. Thirteen patients (9 male) were included for analysis (6 from the present series and 7 from the literature); median age was 63. Initially, a diagnosis of AE was clinically suspected based on: working memory deficits (77%), seizures (62%) (including status epilepticus in 23%), and psychiatric symptoms (46%). Initial brain MRI was not in favor of a typical glioblastoma pattern and showed bilateral (54%) or unilateral selective limbic involvement. Five patients exhibited initial slight contrast enhancement. A clear inflammatory CSF was present in five patients and three from the literature showed autoantibody positivity (NMDAR, VGKC, GluRepsilon2). Median delay between suspicions of AE to GBM diagnosis was 3xa0months (range 1.5–24) and one patient from the literature was diagnosed post-mortem.ConclusionsAn alternative diagnosis of glioblastoma should be considered in patients presenting initially as AE, especially in patients who do not fulfill the criteria for definite AE and in those with a poor clinical evolution despite initial improvement.

The relationship between post-traumatic ossicular injuries and conductive hearing loss: A 3D-CT study

PURPOSEnAfter a trauma, the conductive ossicular chain may be disrupted by ossicular luxation or fracture. Recent developments in 3D-CT allow a better understanding of ossicular injuries. In this retrospective study, we compared patients with post-traumatic conductive hearing loss (CHL) with those referred without CHL to evaluate the relationship between ossicular injuries and CHL. We also assessed the added value of 3D reconstructions on 2D-CT scan to detect ossicular lesions in patients surgically managed.nnnMETHODSnThe CT scans were performed using a 40-section spiral CT scanner in 49 patients with post-traumatic CHL (n=29) and without CHL (n=20). Three radiologists performed independent blind evaluations of 2D-CT and 3D reconstructions to detect ossicular chain injury. We used the t-test to explore differences regarding the number of subjects with ossicular injury in the two groups. We also estimated the diagnostic accuracy and the inter-rater agreement of the 3D-CT reconstructions associated to 2D-CT scan.nnnRESULTSnWe identified ossicular abnormality in 14 patients out of 29 and in one patient out of 20 in the CHL and non-CHL groups respectively. There was a significant difference regarding the number of subjects with ossicular lesions between the two groups (P≤0.01). The diagnostic sensitivity of 3D-CT reconstructions associated with 2D-CT ranged from 66% to 100% and the inter-reader agreement ranged from 0.85 to 1, depending of the type of lesion.nnnCONCLUSIONnThe relationship between ossicular lesion and the presence of CHL tightly correlated. 3D-CT reconstructions of the temporal bone are useful to assess patients in a post-traumatic context.

The different faces of central nervous system metastases

Cerebral metastases are the commonest central nervous system tumors. The MR assessment should include T1-weighted images with and without enhancement and T2/FLAIR images. They usually appear as multiple lesions with nodular or annular enhancement and are surrounded by edema. They are hypervascularized and have no restriction of their diffusion coefficient in their necrotic area and contain lipids on 1H spectroscopy. Metastases can be distinguished from primary tumors by the lack of malignant cell infiltration around the tumor. Stereotactic radiotherapy may temporarily increase tumor volume, although this is not of adverse oncological value. Less commonly, spinal disease may be asymptomatic and should be examined by MR.

Diagnostic value of 3DFLAIR in clinical practice for the detection of infratentorial lesions in multiple sclerosis in regard to dual echo T2 sequences

BACKGROUND AND PURPOSEnThe aim of this prospective study is to investigate and evaluate in clinical practice the diagnostic impact of 3DFLAIR in regards to 2DT2/PD in terms of infratentorial lesions detection in multiple sclerosis (MS).nnnMATERIAL AND METHODSn164 MS patients from the OFSEP database were reviewed retrospectively. MR examinations were performed on 1.5T or 3T systems from four different centers. Infratentorial lesions were counted and allocated to different regions of the posterior fossa by three raters independently (junior resident, resident with an expertise in neuroradiology, and senior neuro-radiologist) on the 3DFLAIR and 2DT2/PD. Both sequences do not have the same spatial resolution but reflect what is recommended by most of the consensus and done in clinical practice.nnnRESULTSnWith an overall number of 528 for Rater-1 and 798 for Rater-2 infratentorial lesions, 3DFLAIR had a significantly higher number of lesions detected than 2DT2/PD (303 for Rater-1 and 370 for Rater-2). The prevalence of trigeminal lesions detected by using 3DFLAIR was also significantly higher than 2DT2/PD. ROC analysis showed 3DFLAIR to be more specific and sensitive than 2DT2/PD. An overall difference between all three Raters has been observed. The more the Rater is experienced the more lesions he detects.nnnCONCLUSIONnAlong with the radiologist ability to detect lesions based on his level of experience, the OFSEP optimized 3DFLAIR can significantly improve infratentorial lesion detection in MS compared to 2DT2/PD. This is important in MS follow-up that takes into account new lesions number to adapt patients treatment.

Retinal tractography: Influence of diffusion acquisition, ocular laterality and ocular dominance in healthy subjects

PURPOSEnExploration of the human retina has never been described with MRI tractography, supposedly because of ocular movement-related artifacts and imaging distortions with EPI diffusion acquisition. In this work, we used track-weighting imaging to assess retinal fascicles. Diffusion acquisition parameters influence was studied and the relationship between variability and ocular laterality and ocular dominance was explored.nnnMATERIALS AND METHODSnTwenty healthy subjects underwent MRI, with retinal tractography calculated with the constrained spherical deconvolution model. A DWI protocol with b value of 1000 s/mm2 and 60 diffusion weighting directions was structured in 4 scans of 15 directions, and b=0 s/mm2 value repeated at each scan to ease motion estimation and correction. At post-processing, we merged subsets of 15 directions according to varied combinations. We generated whole-brain tractography with 10 million streamlines based on 30, 45 and 60 diffusion weighting directions. Ocular dominance was determined using a hole-in-a-card test.nnnRESULTSnRetinal nerve fiber layer appeared to have a heterogeneous distribution, with a fascicle-like display on tractography. Diffusion acquisition required at least 45 directions to display retinal fascicles. There was no significant difference on the number of fascicles displayed between 45 and 60 direction acquisitions, whereas there were significantly more fascicles using 60 and 45 directions than with 30 directions (P≤0.001). Regarding ocular dominance (OD), we observed there were more superior fascicles on the right OD group than on the left one (P≤0.05), whereas there were more inferior fascicles on the left OD group (P≤0.05).nnnCONCLUSIONnAlthough the distribution of reconstructed retinal fascicles depends on the number of diffusion weighting directions used, assessment of ocular laterality and dominance-related variability seems possible.

Évaluation de l'oxygénation tissulaire et du métabolisme de l'oxygène de tumeurs cérébrales en Imagerie par Résonance Magnétique

Objectif La mesure de l’oxygenation des tissus in vivo presente un grand interet dans la pathologie tumorale, compte tenu du pronostic defavorable et des possibles implications therapeutiques de l’hypoxie tumorale. Le but de l’etude etait d’appliquer a differents types de tumeurs cerebrales un protocole de mesure de la saturation tissulaire en oxygene (StO 2 ) et de la consommation d’oxygene (CMRO 2 ) par imagerie par resonance magnetique (IRM) en utilisant l’effet blood oxygen level dependent (BOLD). Methode Dans cette etude prospective monocentrique, 40xa0patients ont ete inclus, atteints de tumeurs cerebrales primitives ou secondaires. Chacun a beneficie d’une ou plusieurs IRM, associant des sequences morphologiques, de perfusion et de mesure de l’oxygenation. Le critere de jugement principal etait l’analyse des valeurs de StO 2 xa0et de CMRO 2 xa0dans differents types tumoraux, les objectifs secondaires etaient d’analyser la zone peritumorale et les variations avant et apres traitement par radiotherapie. Resultats Par rapport au cerveau sain, la StO 2 xa0etait augmentee dans les bourgeons tumoraux des glioblastomes et des meningiomes. La CMRO 2 xa0etait plus basse dans toutes les tumeurs que dans le cerveau sain. On distinguait deux zones perilesionnelles dans le cas des tumeurs gliales de haut grade, l’une d’elle a potentiel evolutif probable. Les valeurs tendaient a se normaliser apres radiotherapie. Conclusion Cette etude montrait la faisabilite du protocole, reproductible, avec des resultats prometteurs, coherents avec la litterature et ouvrant la voie a des essais futurs incluant un plus grand nombre de patients, axes sur l’etude de la region perilesionnelle et sur l’evolution avant et apres traitement par radiotherapie.

Technical Note: Clinical translation of the Rapid-Steady-State-T1 MRI method for direct cerebral blood volume quantification.

PURPOSEnIn preclinical studies, the Rapid-Steady-State-T1 (RSST1) MRI method has advantages over conventional MRI methods for blood volume fraction (BVf) mapping, since after contrast agent administration, the BVf is directly quantifiable from the signal amplitude corresponding to the vascular equilibrium magnetization. This study focuses on its clinical implementation and feasibility.nnnMETHODSnFollowing sequence implementation on clinical Philips Achieva scanners, the RSST1-method is assessed at 1.5 and 3 T in the follow-up examination of neurooncological patients receiving 0.1-0.2 mmol/kg Gd-DOTA to determine the threshold dose needed for cerebral BVf quantification. Confounding effects on BVf quantification such as transendothelial water exchange, transverse relaxation, and contrast agent extravasation are evaluated.nnnRESULTSnFor a dose≥0.13 mmol/kg at 1.5 T and ≥0.16 mmol/kg at 3 T, the RSST1-signal time course in macrovessels and brain tissue with Gd-DOTA impermeable vasculature reaches a steady state at maximum amplitude for about 8 s. In macrovessels, a BVf of 100% was obtained validating cerebral microvascular BVf quantification (3.5%-4.5% in gray matter and 1.5%-2.0% in white matter). In tumor tissue, a continuously increasing signal is detected, necessitating signal modeling for tumor BVf calculation.nnnCONCLUSIONSnUsing approved doses of Gd-DOTA, the steady state RSST1-signal in brain tissue is reached during the first pass and corresponds to the BVf. The first-pass duration is sufficient to allow accurate BVf quantification. The RSST1-method is appropriate for serial clinical studies since it allows fast and straightforward BVf quantification without arterial input function determination. This quantitative MRI method is particularly useful to assess the efficacy of antiangiogenic agents.