Parallel imaging in the form of multiband radiofrequency excitation, together with reduced k-space coverage in the phase-encode direction, was applied to human gradient echo functional MRI at 7 T for increased volumetric coverage and concurrent high spatial and temporal resolution. Echo planar imaging with simultaneous acquisition of four coronal slices separated by 44mm and simultaneous 4-fold phase-encoding undersampling, resulting in 16-fold acceleration and up to 16-fold maximal aliasing, was investigated. Task/stimulus-induced signal changes and temporal signal behavior under basal conditions were comparable for multiband and standard single-band excitation and longer pulse repetition times. Robust, whole-brain functional mapping at 7 T, with 2 x 2 x 2mm(3) (pulse repetition time 1.25 sec) and 1 x 1 x 2mm(3) (pulse repetition time 1.5 sec) resolutions, covering fields of view of 256 x 256 x 176 mm(3) and 192 x 172 x 176 mm(3), respectively, was demonstrated with current gradient performance.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/mrm.22361

Multiband Multislice GE-EPI at 7 Tesla, With 16-Fold Acceleration Using Partial Parallel Imaging With Application to High Spatial and Temporal Whole-Brain FMRI

Simultaneous multislice Echo Planar Imaging (EPI) acquisition using parallel imaging can decrease the acquisition time for diffusion imaging and allow full-brain, high-resolution functional MRI (fMRI) acquisitions at a reduced repetition time (TR) However, the unaliasing of simultaneously acquired, closely spaced slices can be difficult, leading to a high g-factor penalty We introduce a method to create interslice image shifts in the phase encoding direction to increase the distance between aliasing pixels The shift between the slices is induced using sign- and amplitude-modulated slice-select gradient blips simultaneous with the EPI phase encoding blips This achieves the desired shifts but avoids an undesired "tilted voxel" blurring artifact associated with previous methods We validate the method in 3× slice-accelerated spin-echo and gradient-echo EPI at 3 T and 7 T using 32-channel radio frequency (RF) coil brain arrays The Monte-Carlo simulated average g-factor penalty of the 3-fold slice-accelerated acquisition with interslice shifts is <1% at 3 T (compared with 32% without slice shift) Combining 3× slice acceleration with 2× inplane acceleration, the g-factor penalty becomes 19% at 3 T and 10% at 7 T (compared with 41% and 23% without slice shift) We demonstrate the potential of the method for accelerating diffusion imaging by comparing the fiber orientation uncertainty, where the 3-fold faster acquisition showed no noticeable degradation

https://onlinelibrary.wiley.com/doi/pdf/10.1002/mrm.23097

Blipped-controlled aliasing in parallel imaging for simultaneous multislice echo planar imaging with reduced g-factor penalty.

At macroscopic scales, the human connectome comprises anatomically distinct brain areas, the structural pathways connecting them and their functional interactions. Annotation of phenotypic associations with variation in the connectome and cataloging of neurophenotypes promise to transform our understanding of the human brain. In this Review, we provide a survey of magnetic resonance imaging–based measurements of functional and structural connectivity. We highlight emerging areas of development and inquiry and emphasize the importance of integrating structural and functional perspectives on brain architecture.

Imaging human connectomes at the macroscale

Fast magnetic resonance imaging slice acquisition techniques such as single shot fast spin echo are routinely used in the presence of uncontrollable motion These techniques are widely used for fetal magnetic resonance imaging (MRI) and MRI of moving subjects and organs Although high-quality slices are frequently acquired by these techniques, inter-slice motion leads to severe motion artifacts that are apparent in out-of-plane views Slice sequential acquisitions do not enable 3-D volume representation In this study, we have developed a novel technique based on a slice acquisition model, which enables the reconstruction of a volumetric image from multiple-scan slice acquisitions The super-resolution volume reconstruction is formulated as an inverse problem of finding the underlying structure generating the acquired slices We have developed a robust M-estimation solution which minimizes a robust error norm function between the model-generated slices and the acquired slices The accuracy and robustness of this novel technique has been quantitatively assessed through simulations with digital brain phantom images as well as high-resolution newborn images We also report here successful application of our new technique for the reconstruction of volumetric fetal brain MRI from clinically acquired data

Robust Super-Resolution Volume Reconstruction From Slice Acquisitions: Application to Fetal Brain MRI

Spectral imaging technology, which records simultaneously spectral and spatial information about an object, was initially developed for remote sensing and has since been successfully applied to other areas of research. Although relatively new to the field of conservation, this non-invasive method of investigation has already provided promising results in the analysis of paintings and written documents, the characterization of materials and digital documentation. This article reviews the published literature relating to the application of multispectral and hyperspectral imaging for the study and conservation of works of art and presents some new perspectives offered by this innovative and fast-developing technology.

Multispectral and hyperspectral imaging technologies in conservation: current research and potential applications

Classical techniques for solving linear inverse problems have been presented. Our aim was to show how these classical techniques are applied in current state-of-the-art imaging systems. Moreover, we have provided a classification of the techniques into four families: FT-based, direct reconstruction, indirect reconstruction, and interpolation. We hope that this classification will guide the curious reader into a discipline with a rich bibliography and sometimes sophisticated mathematics. In this survey, we skipped complicated methods to solve inverse problems. Through our examples, we have tried to emphasize the large variety of applications of linear inverse problems in imaging. Two main examples have been examined more deeply in this survey. We hope they have helped the reader to understand the application of the general techniques in two interesting contexts: multispectral imaging and magnetic resonance imaging.

Linear inverse problems in imaging

The CRISATEL multispectral acquisition system is dedicated to the digital archiving of fine art paintings. It is composed of a dynamic lighting system and of a high resolution camera equipped with a CCD linear array, 13 interference filters and several built-in electronically controlled mechanisms. A custom calibration procedure has been designed and implemented. It allows us to select the parameters to be used for the raw image acquisition and to collect experimental data, which will be used in the post processing stage to correct the obtained multispectral images. Various techniques have been tested and compared in order to reconstruct the spectral reflectance curve of the painting surface imaged in each pixel. Realistic color rendering under any illuminant can then be obtained from this spectral reconstruction. The results obtained with the CRISATEL acquisition system and the associated multispectral image processing are shown on two art painting examples.

Calibration and spectral reconstruction for CRISATEL : An art painting multispectral acquisition system

data. Materials and Methods: An improved EVI sequence was associated with parallel acquisition and field of view reduction in order to acquire a large brain volume in 200 msec. Temporal stability and functional sensitivity were increased through optimization of all imaging parameters and Tikhonov regularization of parallel reconstruction. Two human volunteers were scanned with parallel EVI in a 1.5T whole-body MR system, while submitted to a slow eventrelated auditory paradigm. Results: Thanks to parallel acquisition, the EVI volumes display a low level of geometric distortions and signal losses. After removal of low-frequency drifts and physiological artifacts, activations were detected in the temporal lobes of both volunteers and voxelwise hemodynamic response functions (HRF) could be computed. On these HRF different habituation behaviors in response to sentence repetition could be identified. Conclusion: This work demonstrates the feasibility of high temporal resolution 3D fMRI with parallel EVI. Combined with advanced estimation tools, this acquisition method should prove useful to measure neural activity timing differences or study the nonlinearities and nonstationarities of the BOLD response.

/pdf/high-temporal-resolution-functional-mri-using-parallel-echo-4nm5pwz07v.pdf

High temporal resolution functional MRI using parallel echo volumar imaging

A fully automatic method for the reconstruction of spectral reflectance curves by using mixture density networks

A description of multispectral image capture is presented from a signal processing point of view. Indeed, this article is based on an equation that models the multispectral acquisition of images. The main components of this equation are described. They correspond to the lighting conditions, the filters, the sensor sensitivity, and associated noise sources. Moreover, the optimization problems involved in the design of multispectral cameras, their calibration, and the processing of the obtained data are introduced within the same mathematical framework.

Alejandro Ribes

Papers

Linear inverse problems in imaging

Calibration and spectral reconstruction for CRISATEL : An art painting multispectral acquisition system

High temporal resolution functional MRI using parallel echo volumar imaging

A fully automatic method for the reconstruction of spectral reflectance curves by using mixture density networks

Studying That Smile