The function of sleep in humans has been investigated using simultaneous electroencephalography (EEG) and functional magnetic resonance imaging recordings to provide accurate sleep scores with spatial precision. Recent studies have demonstrated that spontaneous brain oscillations and functional connectivity dissociate during nonrapid eye movement (NREM) sleep; this leads to spontaneous cognitive processes, such as memory consolidation and emotional modulation. However, variations in network connectivity across the sleep stages or between sleep/wake transitions require further elucidation. We observed changes in the connectivity of the sensorimotor and default-mode networks (DMN) mediated by midnight sleep among 18 healthy participants. The results indicated that (1) functional connectivity in both networks showed increasing dissociation as NREM sleep deepened, whereas hyperconnectivity occurred during rapid eye movement (REM) sleep; and (2) compared with connectivity before sleep, the DMN presented a comparable connectivity pattern immediately after awakening, whereas the connectivity of the sensorimotor network remained disrupted. These findings showed that connectivity patterns dissociate and reconnect coherently in both cortical networks during NREM and REM sleep, respectively. After the person awakened, the DMN connectivity was re-established before the sensorimotor reconnection. These dynamic sleep-related dissociations and reconnections between sleep/wake conditions might provide the key to understanding cognitive modulations in sleep. If so, connectivity changes might serve as an alternative indicator beyond the EEG signature to unveil the spontaneous processes that occur during sleep.

Tractography algorithms have been developed to reconstruct likely WM pathways in the brain from diffusion tensor imaging (DTI) data. In this study, an elegant and simple means for improving existing tractography algorithms is proposed by allowing tracts to propagate through diagonal trajectories between voxels, instead of only rectilinearly to their facewise neighbors. A series of tests (using both real and simulated data sets) are utilized to show several benefits of this new approach. First, the inclusion of diagonal tract propagation decreases the dependence of an algorithm on the arbitrary orientation of coordinate axes and therefore reduces numerical errors associated with that bias (which are also demonstrated here). Moreover, both quantitatively and qualitatively, including diagonals decreases overall noise sensitivity of results and leads to significantly greater efficiency in scanning protocols; that is, the obtained tracts converge much more quickly (i.e., in a smaller amount of scanning time) to those of data sets with high SNR and spatial resolution. Importantly, the inclusion of diagonal propagation adds essentially no appreciable time of calculation or computational costs to standard methods. This study focuses on the widely-used streamline tracking method, FACT (fiber assessment by continuous tracking), and the modified method is termed “FACTID” (FACT including diagonals).

Purpose: To reduce the scan time of high angular resolution diffusion imaging (HARDI) by using the hemispherical encoding scheme with the cross-term correction. Materials and Methods:Unidirectional and 45°crossing phantoms were built to evaluate the accuracy of the fiber orientation estimation when using a hemispherical encoding scheme with and without the cross-term correction. The q-ball imaging using the spherical harmonic basis was adopted for estimation of fiber orientation. By recalculating the diffusion gradient strengths, we make the actual b value in all directions equal to the expected b value for the correction of the cross-term. Results:The separation angles measured on the crossing phantom are 42.67°Ϯ 1.50°, 42.75°Ϯ 2.10°, and 42.93°Ϯ 2.78°for cross-term-free results, for the results from the hemispherical encoding scheme with and without the crossterm correction. The angular errors in mapping the unidirectional phantom are 1.87°-2.29°and 4.01°-4.92°for the results using the hemispherical encoding scheme with and without correcting for the cross-term at different b values. Conclusion:Using the hemispherical encoding scheme with the cross-term correction can potentially halve the scan time of HARDI and obtain accurate fiber orientation estimation simultaneously. This will be helpful in the clinical application of HARDI. THE DEVELOPMENT OF diffusion nuclear magnetic resonance (NMR) enables us to noninvasively retrieve microstructural information that can hardly be detected using conventional NMR methods (1,2). Diffusion tensor imaging (DTI) was later proposed to measure the fiber orientation by estimating threedimensional probability distribution using a Gaussian approximation (3). This opened the door to advances in white matter (WM) connectivity (4 -8). Even though DTI can well assess the integrity of axonal fibers and accurately define the fiber orientation within a voxel containing fibers with a coherent orientation, its drawback is that the fiber orientation estimate is ambiguous in voxels containing multiple orientation structures. This drawback was highlighted in human cerebral studies with the millimeter width of a typical magnetic resonance imaging (MRI) voxel (9,10). In order to address the inability of DTI to resolve intravoxel fiber crossings, several reconstruction methods based on the high angular resolution diffusion imaging (HARDI) sampling scheme (11-17) were proposed and assessed to resolve intravoxel fiber crossings via numerical phantoms and in vivo studies. However, long acquisition times due to the need to obtain a great deal of diffusion-weighted images (DWIs) in HARDI (Ϸ60 -400 DWIs) limit the possibility of routine HARDI and its clinical applications.In previous studies, shortening of the acquisition times of HARDI was achieved using an improved reconstruction method with a lower number of DWIs. Khachaturian et al (18) boosted a sampling efficiency gain of 274%-377% for q-ball imaging (QBI) by nonlinearly fusing the diffusion signal from separate low and high wavevector acquis...

In this report, we generated a ferritin and red fluorescent protein fusion reporter gene that enables the visualization of transgene expression in living animals by magnetic resonance imaging (MRI) and optical imaging. Ferritin heavy chain (FTH) or light chain (FTL) was linked to the N terminus of the monomeric DsRed red fluorescent protein to create FTH-DsRed and FTL-DsRed, MRI-fluorescence dual reporters. Transfection of these dual reporters into cells resulted in increased iron loading and strong red fluorescence in cells. Adenoviral vectors to express FTH-DsRed or FTL-DsRed fusion reporter in infected cells were created, but only the adenovirus expressing FTH-DsRed resulted in a high level of red fluorescence in cells. Delivery and expression of FTH-DsRed in the mouse brain using adenovirus was detected by MRI and fluorescence imaging, revealing a T2shortening effect and an increase of contrast in T2-weighted images at the sites co-localized with strong red fluorescence. While the details of the structure of ferritin-DsRed fusion reporter remains to be solved, this dual reporter is useful for visualizing dynamic processes such as the migration of reporter-transfected stem cells or metastasis of tumors using MRI with the added flexibility of combining optical tools such as fluorescence activated cell sorting and fluorescence microscopy.