Prospective head motion correction using FID-guided on-demand image navigators

PURPOSE: We suggest a motion correction concept that employs free-induction-decay (FID) navigator signals to continuously monitor motion and to guide the acquisition of image navigators for prospective motion correction following motion detection. METHODS: Motion causes out-of-range signal changes in FID time series that, and in this approach, initiate the acquisition of an image navigator. Co-registration of the image navigator to a reference provides rigid-body-motion parameters to facilitate prospective motion correction. Both FID and image navigator are integrated into a prototype magnetization-prepared rapid gradient-echo (MPRAGE) sequence. The performance of the method is investigated using image quality metrics and the consistency of brain volume measurements. RESULTS: Ten healthy subjects were scanned (a) while performing head movements (nodding, shaking, and moving in z-direction) and (b) to assess the co-registration performance. Mean absolute errors of 0.27 +/- 0.38 mm and 0.19 +/- 0.24 degrees for translation and rotation parameters were measured. Image quality was qualitatively improved after correction. Significant improvements were observed in automated image quality measures and for most quantitative brain volume computations after correction. CONCLUSION: The presented method provides high sensitivity to detect head motion while minimizing the time invested in acquiring navigator images. Limits of this implementation arise from temporal resolution to detect motion, false-positive alarms, and registration accuracy

Surface-based characteristics of the cerebellar cortex visualized with ultra-high field MRI

Although having a relatively homogeneous cytoarchitectonic organization, the cerebellar cortex is a heterogeneous region characterized by different amounts of myelin, iron and protein expression profiles. In this study, we used quantitative T1 and T2* mapping at ultra-high field (7T) MRI to investigate the tissue characteristics of the cerebellar gray matter surface and its layers. Detailed subject-specific surfaces were generated at three different cortical depths and averaged across subjects to create averaged T1 and T2* maps on the cerebellar surface. T1 surfaces showed an alternation of lower and higher T1 values when going from the median to the lateral part of the cerebellar hemispheres. In addition, longer T1 values were observed in the more superficial gray matter layers. T2* maps showed a similar longitudinal pattern, but no change related to the cortical depths. These patterns are possibly due to variations in the level of myelination, iron and zebrin protein expression

MP2RAGE provides new clinically-compatible correlates of mild cognitive deficits in relapsing-remitting multiple sclerosis

Despite that cognitive impairment is a known early feature present in multiple sclerosis (MS) patients, the biological substrate of cognitive deficits in MS remains elusive. In this study, we assessed whether T1 relaxometry, as obtained in clinically acceptable scan times by the recent Magnetization Prepared 2 Rapid Acquisition Gradient Echoes (MP2RAGE) sequence, may help identifying the structural correlate of cognitive deficits in relapsing-remitting MS patients (RRMS). Twenty-nine healthy controls (HC) and forty-nine RRMS patients underwent high-resolution 3T magnetic resonance imaging to obtain optimal cortical lesion (CL) and white matter lesion (WML) count/volume and T1 relaxation times. T1 z scores were then obtained between T1 relaxation times in lesion and the corresponding HC tissue. Patient cognitive performance was tested using the Brief Repeatable Battery of Neuro-psychological Tests. Multivariate analysis was applied to assess the contribution of MRI variables (T1 z scores, lesion count/volume) to cognition in patients and Bonferroni correction was applied for multiple comparison. T1 z scores were higher in WML (p<0.001) and CL-I (p<0.01) than in the corresponding normal-appearing tissue in patients, indicating relative microstructural loss. (1) T1 z scores in CL-I (p=0.01) and the number of CL-II (p=0.04) were predictors of long-term memory; (2) T1 z scores in CL-I (β=0.3; p=0.03) were independent determinants of long-term memory storage, and (3) lesion volume did not significantly influenced cognitive performances in patients. Our study supports evidence that T1 relaxometry from MP2RAGE provides information about microstructural properties in CL and WML and improves correlation with cognition in RRMS patients, compared to conventional measures of disease burden

L'Hydroptère: A story of a dream

In 2009, l’Hydroptère broke the symbolic barrier of 50 knots and became the world fastest sailing boat over both 500 meters and 1 nautical mile. This major achievement relied on the high skills of the sailing team but also on technical advances of the boat, resulting from long years of studies and development. This achievement is also an open window to a new goal: flying around the world. In the present article, we present this long and incredible story, highlighting the different steps, the technology involved, and the background of that project.

Language impairment associated with arachnoid cysts : recovery after surgical treatment.

Supporting data from the literature, we observe that large arachnoid cysts may affect cognitive function. Neuropsychologic assessment plus magnetic resonance imaging allowed for documentation of associations between left temporal arachnoid cysts, language impairment, and other cognitive dysfunctions. Significant cognitive improvements were evident soon after cysto-peritoneal shunting. These observations reinforce the rationale for neuropsychologic assessments of patients with developmental delay and arachnoid cysts, and support the potential benefit of surgical decompression for arachnoid cysts associated with neurologic deficits, even if surgery is performed well after the occurrence of neurologic deficits

Ultrahigh field in vivo characterization of microstructural abnormalities in the orbitofrontal cortex and amygdala in autism

There are currently no biomarkers for autism spectrum disorder (ASD). This neurodevelopmental condition has previously been associated with histopathological findings, including increased neuronal packing density in the amygdala, abnormal laminar cytoarchitecture and increased average neuronal density in the prefrontal cortex. The present study examined whether new brain imaging technologies could reveal in vivo, in adults with ASD, the manifestation of previously described histopathological changes. Using quantitative mapping at ultrahigh field (7 Tesla), we show that we can observe microstructural alterations in the right lateral orbitofrontal cortex and the bilateral amygdala in adult individuals with ASD in vivo. These imaging alterations point to an abnormal laminar cytoarchitecture and to an increased neuronal density, similar to what has been previously described in post-mortem data in ASD. Our data demonstrate that it is possible to visualize, in vivo and at the individual level, alterations of cortical and subcortical microstructure in ASD. Future studies will be needed to extend these findings to a larger group of individuals and evaluate their association with symptomatology as well as their specificity among the different neurodevelopmental disorders

Neuroimaging of intraparenchymal lesions predicts outcome in shaken baby syndrome.

OBJECTIVE: Studies of long-term outcome on nonaccidental head injury (NAHI) in young children have shown severe neurodevelopmental sequelae in most cases. For improving the knowledge of outcome and for identifying prognostic factors, additional clinical and cerebral imaging data are needed. The aim of this study was to describe clinical and imaging features over time and to consider their value for predicting neurodevelopmental outcome. METHODS: A retrospective medical record review was conducted of 23 children with confirmed NAHI, for whom an extended follow-up of 2.5 to 13 years (mean: 6 years) was contemplated. Glasgow Coma Scale scores, severity of retinal hemorrhages, presence of skull fractures, cranial growth deceleration, and sequential neuroimaging data (computed tomography and/or magnetic resonance imaging) were compared with patterns of clinical evolution assessed by the Glasgow Outcome Scale. RESULTS: Clinical outcome showed that 14 (61%) children had severe disabilities, 8 (35%) had moderate disabilities, and 1 (4%) was normal. A low initial Glasgow Coma Scale score, severe retinal hemorrhages, presence of skull fracture, and cranial growth deceleration were significantly associated with poor developmental outcome. Eighteen of the 23 patients had abnormal magnetic resonance imaging scans. This examination disclosed atrophy when performed beyond 15 days of injury. Atrophy seemingly resulted from various brain lesions, namely, contusions, infarcts, and other lesions within the white matter. Presence of intraparenchymal brain lesions within the first 3 months was significantly associated with neurodevelopmental impairment. Severity of motor and cognitive dysfunctions was related to the extent of intraparenchymal lesions. CONCLUSIONS: Early clinical and radiologic findings in NAHI are of prognostic value for neurodevelopmental outcome

Quantitative brain relaxation atlases for personalized detection and characterization of brain pathology

Purpose To exploit the improved comparability and hardware independency of quantitative MRI, databases of MR physical parameters in healthy tissue are required, to which tissue properties of patients can be compared. In this work, normative values for longitudinal and transverse relaxation times in the brain were established and tested in single-subject comparisons for detection of abnormal relaxation times. Methods Relaxometry maps of the brain were acquired from 52 healthy volunteers. After spatially normalizing the volumes into a common space, T-1 and T-2 inter-subject variability within the healthy cohort was modeled voxel-wise. A method for a single-subject comparison against the atlases was developed by computing z-scores with respect to the established healthy norms. The comparison was applied to two multiple sclerosis and one clinically isolated syndrome cases for a proof of concept. Results The established atlases exhibit a low variation in white matter structures (median RMSE of models equal to 32 ms for T-1 and 4 ms for T-2), indicating that relaxation times are in a narrow range for normal tissues. The proposed method for single-subject comparison detected relaxation time deviations from healthy norms in the example patient data sets. Relaxation times were found to be increased in brain lesions (mean z-scores >5). Moreover, subtle and confluent differences (z-scores similar to 2-4) were observed in clinically plausible regions (between lesions, corpus callosum). Conclusions Brain T-1 and T-2 quantitative norms were derived voxel-wise with low variability in healthy tissue. Example patient deviation maps demonstrated good sensitivity of the atlases for detecting relaxation time alterations

Prospective motion correction with FID-triggered image navigators

In this work, we propose a method for prospective motion correction in MRI using a novel image navigator module, which is triggered by a free induction decay (FID) navigator. Only when motion occurs, the image navigator is run and new positional information is obtained through image registration. The image navigator was specifically designed to match the impact on the magnetization and the acoustic noise of the host sequence. This detection-correction scheme was implemented for an MP-RAGE sequence and 5 healthy volunteers were scanned at 3T while performing various head movements. The correction performance was demonstrated through automated brain segmentation and an image quality index whose results are sensitive to motion artifacts