Multiband Echo Planar Imaging Research Articles

Magnetic resonance imaging of a stream of bubbles injected into liquid suspensions

Magnetic resonance imaging (MRI) is a powerful tool for characterizing opaque multiphase flows non-invasively. However, MRI has often (i) had low temporal resolution and thus not captured transient dynamics, (ii) only provided 2D slice images of 3D flows and (iii) been limited to flows in narrow (∼30 mm) tubes with significant wall effects. Here, we apply multi-band echo planar imaging (MB-EPI) with a custom-built radiofrequency coil in a full-body MRI scanner to provide fully 3D images of the dynamics of a stream of bubbles rising through a dense suspension with 151 ms resolution in a 178 mm diameter system. Image processing demonstrates that bubble rise and coalescence dynamics vary significantly with (a) initial spacing between bubbles and (b) particle volume fraction. The ability to image bubble dynamics in dense suspensions as well as in full 3D provides future opportunities to characterize complex, non-axisymmetric, multiphase flows.

Connectivity Profile of Middle Inferior Parietal Cortex Confirms the Hypothesis About Modulating Cortical Areas

According to the correlated transmitter-receptor based structure of the inferior parietal cortex (IPC), this brain area is divided into three clusters, namely, the caudal, the middle and the rostral. Nevertheless, in associating different cognitive functions to the IPC, previous studies considered this part of the cortex as a whole and thus inconsistent results have been reported. Using multiband echo planar imaging (EPI), we investigated the connectivity profile of the middle IPC while forty-five participants performed a task requiring cognitive control. The middle IPC demonstrated functional associations which do not have similarities to a contributing part in the frontoparietal network, in processing cognitive control. At the same time, this cortical area showed negative functional connectivity with both the precuneus cortex, which is resting- state related, and brain areas related to general cognitive functions. That is, the functions of the middle IPC are not accommodated by the traditional categorization of different brain areas i.e. resting state-related or task-related networks and this advanced our hypothesis about modulating cortical areas. Such brain areas are characterized by their negative functional connectivity with parts of the cortex involved in task performance, proportional to the difficulty of the task; yet, their functional associations are inconsistent with the resting state-related cortical areas.

Integrated intravoxel incoherent motion tensor and diffusion tensor brain MRI in a single fast acquisition.

The acquisition of intravoxel incoherent motion (IVIM) data and diffusion tensor imaging (DTI) data from the brain can be integrated into a single measurement, which offers the possibility to determine orientation-dependent (tensorial) perfusion parameters in addition to established IVIM and DTI parameters. The purpose of this study was to evaluate the feasibility of such a protocol with a clinically feasible scan time below 6 min and to use a model-selection approach to find a set of DTI and IVIM tensor parameters that most adequately describes the acquired data. Diffusion-weighted images of the brain were acquired at 3 T in 20 elderly participants with cerebral small vessel disease using a multiband echoplanar imaging sequence with 15 b-values between 0 and 1000 s/mm2 and six non-collinear diffusion gradient directions for each b-value. Seven different IVIM-diffusion models with 4 to 14 parameters were implemented, which modeled diffusion and pseudo-diffusion as scalar or tensor quantities. The models were compared with respect to their fitting performance based on the goodness of fit (sum of squared fit residuals, chi2 ) and their Akaike weights (calculated from the corrected Akaike information criterion). Lowest chi2 values were found using the model with the largest number of model parameters. However, significantly highest Akaike weights indicating the most appropriate models for the acquired data were found with a nine-parameter IVIM-DTI model (with isotropic perfusion modeling) in normal-appearing white matter (NAWM), and with an 11-parameter model (IVIM-DTI with additional pseudo-diffusion anisotropy) in white matter with hyperintensities (WMH) and in gray matter (GM). The latter model allowed for the additional calculation of the fractional anisotropy of the pseudo-diffusion tensor (with a median value of 0.45 in NAWM, 0.23 in WMH, and 0.36 in GM), which is not accessible with the usually performed IVIM acquisitions based on three orthogonal diffusion-gradient directions.

Practical challenges of continuous real-time functional magnetic resonance imaging neurofeedback with multiband accelerated echo-planar imaging and short repetition times.

Continuous real-time functional magnetic resonance imaging (fMRI) neurofeedback is gaining increasing scientific attention in clinical neuroscience and may benefit from the short repetition times of modern multiband echoplanar imaging sequences. However, minimizing feedback delay can result in technical challenges. Here, we report a technical problem we experienced during continuous fMRI neurofeedback with multiband echoplanar imaging and short repetition times. We identify the possible origins of this problem, describe our current interim solution and provide openly available workflows and code to other researchers in case they wish to use a similar approach.

Investigation of Acupuncture-specific BOLD Signal Changes Using Multiband Acquisition and Deconvolution Analysis.

PurposeWe investigated the temporal dynamics of blood oxygen level-dependent (BOLD) signal responses during various stimuli, including real acupuncture, sham acupuncture, and palm scrubbing. For this purpose, deconvolution analysis was used to perform measurements using multi-band (MB) echo-planar imaging (EPI), which can improve time resolution, and to analyze brain responses without an expected reference function.MethodsWe devided 26 healthy right-handed adults into a group of 13 who received real acupuncture stimulation with manual manipulation and the other group of 13 who received sham acupuncture and palm scrubbing tactical stimulations. Data analysis was performed with a combination of analysis packages.ResultsWe found stimulus-specific impulse responses of the BOLD signal in various brain regions. During real acupuncture, activated areas were observed in the secondary somatosensory cortex (SII) and insula during stimulation and in the anterior cingulate cortex (ACC), supplementary motor area (SMA), and thalamus after the stimulation. During sham acupuncture, activated areas were observed in the SII, insula, and thalamus during simulation. During the scrubbing condition, activated areas were observed in the contralateral primary somatosensory cortex (SI), SII, insula, and thalamus during stimulation. In particular, during the real acupuncture condition, significantly delayed and long-sustained increased signals were observed in several brain regions, in contrast to the signals induced with sham acupuncture and palm scrubbing.CoclusionWe speculated that the delayed and long-sustained signal increases were caused by peripheral nociceptors, flare responses, and time-consuming processing in the central nervous system. We used deconvolution analysis with MB EPI and tent functions to identify the delayed increase in the BOLD signal in the area related to pain perception specifically observed in real acupuncture stimulation. We propose that the specific BOLD signal change observed in this study will lead to the elucidation of the mechanism underlying the therapeutic effect of acupuncture stimulation.

Evaluating High Spatial Resolution Diffusion Kurtosis Imaging at 3T: Reproducibility and Quality of Fit.

Diffusion kurtosis imaging (DKI) quantifies the non-Gaussian diffusion of water within tissue microstructure. However, it has increased fitting parameters and requires higher b-values. Evaluation of DKI reproducibility is important for clinical purposes. To assess the reproducibility in whole-brain high-resolution DKI at varying b-values. Retrospective. In all, 44 individuals from the test-retest Human Connectome Project (HCP) database and 12 3D-printed phantoms. Diffusion-weighted multiband echo-planar imaging sequence at 3T and 9.4T. magnetization-prepared rapid acquisition gradient echo at 3T for in vivo structural data only. From HCP data with b-values = 1000, 2000, 3000 s/mm2 (dataset A), two additional datasets with b-values = 1000, 3000 s/mm2 (dataset B) and b-values = 1000, 2000 s/mm2 (dataset C) were extracted. Estimated DKI metrics from each dataset were used for evaluating reproducibility and fitting quality in white matter (WM) and gray matter (GM) based on whole-brain and regions of interest (ROIs). DKI reproducibility was assessed using the within-subject coefficient of variation (CoV), fitting residuals to evaluate DKI fitting accuracy and Pearson's correlation to investigate the presence of systematic biases. Repeated measures analysis of variance was used for statistical comparison. Datasets A and B exhibited lower DKI CoVs (<20%) compared to C (<50%) in both WM and GM ROIs (all P < 0.05). This effect varies between DKI and DTI parameters (P < 0.005). Whole-brain fitting residuals were consistent across datasets (P > 0.05), but lower residuals in dataset B were detected for the WM ROIs (P < 0.001). A similar trend was observed for the phantom data CoVs (<7.5%) at varying fiber orientations for datasets A and B. Finally, dataset C was characterized by higher residuals across the different fiber crossings (P < 0.05). The study demonstrates that high reproducibility can still be achieved within a reasonable scan time, specifically dataset B, supporting the potential of DKI for aiding clinical tools in detecting microstructural changes.

Parasympathetic arousal-related cortical activity is associated with attention during cognitive task performance

Parasympathetic arousal is associated with states of heightened attention and well-being. Arousal may affect widespread cortical and subcortical systems across the brain, however, little is known about its influence on cognitive task processing and performance. In the current study, healthy adult participants (n ​= ​20) underwent multi-band echo-planar imaging (TR ​= ​0.72 ​s) with simultaneous pulse oximetry recordings during performance of the Multi Source Interference Task (MSIT), the Oddball Task (OBT), and during rest. Processing speed on both tasks was robustly related to heart rate (HR). Participants with slower HR responded faster on both the MSIT (33% variance explained) and the OBT (25% variance explained). Within all participants, trial-to-trial fluctuations in processing speed were robustly related to the heartbeat-stimulus interval, a metric that is dependent both on the concurrent HR and the stimulus timing with respect to the heartbeat. Models examining the cardiac-BOLD response revealed that a distributed set of regions showed arousal-related activity that was distinct for different task conditions. Across these cortical regions, activity increased with slower HR. Arousal-related activity was distinct from task-evoked activity and it was robust to the inclusion of additional physiological nuisance regressors into the models. For the MSIT, such arousal-related activity occurred across visual and dorsal attention network regions. For the OBT, this activity occurred within fronto-parietal regions. For rest, arousal-related activity also occurred, but was confined to visual regions. The pulvinar nucleus of the thalamus showed arousal-related activity during all three task conditions. Widespread cortical activity, associated with increased parasympathetic arousal, may be propagated by thalamic circuits and contributes to improved attention. This activity is distinct from task-evoked activity, but affects cognitive performance and therefore should be incorporated into neurobiological models of cognition and clinical disorders.

Whole brain 7T-fMRI during pelvic floor muscle contraction in male subjects.

AimThe primary aim of this study is to demonstrate that 7‐tesla functional magnetic resonance imaging (7T‐fMRI) can visualize the neural representations of the male pelvic floor in the whole brain of a single subject.MethodsIn total, 17 healthy male volunteers (age 20‐47) were scanned in a 7T‐MRI scanner (Philips Achieva). The scanning protocol consisted of two functional runs using a multiband echo planar imaging sequence and a T1‐weighted scan. The subjects executed two motor tasks, one involving consecutive pelvic floor muscle contractions (PFMC) and a control task with tongue movements.ResultsIn single subjects, results of both tasks were visualized in the cortex, putamen, thalamus, and the cerebellum. Activation was seen during PFMC in the superomedial and inferolateral primary motor cortex (M1), supplementary motor area (SMA), insula, midcingulate gyrus (MCG), putamen, thalamus, and in the anterior and posterior lobes of the cerebellum. During tongue movement, activation was seen in the inferolateral M1, SMA, MCG, putamen, thalamus, and anterior and posterior lobes of the cerebellum. Tongue activation was found in the proximity of, but not overlapping with, the PFMC activation. Connectivity analysis demonstrated differences in neural networks involved in PFMC and tongue movement.ConclusionThis study demonstrated that 7T‐fMRI can be used to visualize brain areas involved in pelvic floor control in the whole brain of single subjects and defined the specific brain areas involved in PFMC. Distinct differences between brain mechanisms controlling the pelvic floor and tongue movements were demonstrated using connectivity analysis.

Ultrafast fMRI of the rodent brain using simultaneous multi-slice EPI

Increasing spatial and temporal resolutions of functional MRI (fMRI) measurement has been shown to benefit the study of neural dynamics and functional interaction. However, acceleration of rodent brain fMRI using parallel and simultaneous multi-slice imaging techniques is hampered by the lack of high-density phased-array coils for the small brain. To overcome this limitation, we adapted phase-offset multiplanar and blipped-controlled aliasing echo planar imaging (EPI) to enable simultaneous multi-slice fMRI of the mouse brain using a single loop coil on a 9.4T scanner. Four slice bands of 0.3 × 0.3 × 0.5 mm3 resolution can be simultaneously acquired to cover the whole brain at a temporal resolution of 300 ms or the whole cerebrum in 150 ms. Instead of losing signal-to-noise ratio (SNR), both spatial and temporal SNR can be increased due to the increased k-space sampling compared to a standard single-band EPI. Task fMRI using a visual stimulation shows close to 80% increase of z-score and 4 times increase of activated area in the visual cortex using the multiband EPI due to the highly increased temporal samples. Resting-state fMRI shows reliable detection of bilateral connectivity by both single-band and multiband EPI, but no significant difference was found. Without the need of a dedicated hardware, we have demonstrated a practical method that can enable unparallelly fast whole-brain fMRI for preclinical studies. This technique can be used to increase sensitivity, distinguish transient response or acquire high spatiotemporal resolution fMRI.

Safety and EEG data quality of concurrent high-density EEG and high-speed fMRI at 3 Tesla.

PurposeConcurrent EEG and fMRI is increasingly used to characterize the spatial-temporal dynamics of brain activity. However, most studies to date have been limited to conventional echo-planar imaging (EPI). There is considerable interest in integrating recently developed high-speed fMRI methods with high-density EEG to increase temporal resolution and sensitivity for task-based and resting state fMRI, and for detecting interictal spikes in epilepsy. In the present study using concurrent high-density EEG and recently developed high-speed fMRI methods, we investigate safety of radiofrequency (RF) related heating, the effect of EEG on cortical signal-to-noise ratio (SNR) in fMRI, and assess EEG data quality.Materials and methodsThe study compared EPI, multi-echo EPI, multi-band EPI and multi-slab echo-volumar imaging pulse sequences, using clinical 3 Tesla MR scanners from two different vendors that were equipped with 64- and 256-channel MR-compatible EEG systems, respectively, and receive only array head coils. Data were collected in 11 healthy controls (3 males, age range 18–70 years) and 13 patients with epilepsy (8 males, age range 21–67 years). Three of the healthy controls were scanned with the 256-channel EEG system, the other subjects were scanned with the 64-channel EEG system. Scalp surface temperature, SNR in occipital cortex and head movement were measured with and without the EEG cap. The degree of artifacts and the ability to identify background activity was assessed by visual analysis by a trained expert in the 64 channel EEG data (7 healthy controls, 13 patients).ResultsRF induced heating at the surface of the EEG electrodes during a 30-minute scan period with stable temperature prior to scanning did not exceed 1.0° C with either EEG system and any of the pulse sequences used in this study. There was no significant decrease in cortical SNR due to the presence of the EEG cap (p > 0.05). No significant differences in the visually analyzed EEG data quality were found between EEG recorded during high-speed fMRI and during conventional EPI (p = 0.78). Residual ballistocardiographic artifacts resulted in 58% of EEG data being rated as poor quality.ConclusionThis study demonstrates that high-density EEG can be safely implemented in conjunction with high-speed fMRI and that high-speed fMRI does not adversely affect EEG data quality. However, the deterioration of the EEG quality due to residual ballistocardiographic artifacts remains a significant constraint for routine clinical applications of concurrent EEG-fMRI.

A Resilient, Non-neuronal Source of the Spatiotemporal Lag Structure Detected by BOLD Signal-Based Blood Flow Tracking.

Recent evidence has suggested that blood oxygenation level-dependent (BOLD) signals convey information about brain circulation via low frequency oscillation of systemic origin (sLFO) that travels through the vascular structure (“lag mapping”). Prompted by its promising application in both physiology and pathology, we examined this signal component using multiple approaches. A total of 30 healthy volunteers were recruited to perform two reproducibility experiments at 3 Tesla using multiband echo planar imaging. The first experiment investigated the effect of denoising and the second was designed to study the effect of subject behavior on lag mapping. The lag map's intersession test-retest reproducibility and image contrast were both diminished by removal of either the neuronal or the non-neuronal (e.g., cardiac, respiratory) components by independent component analysis-based denoising, suggesting that the neurovascular coupling also comprises a part of the BOLD lag structure. The lag maps were, at the same time, robust against local perfusion increases due to visuomotor task and global changes in perfusion induced by breath-holding at the same level as the intrasession reliability. The lag structure was preserved after time-locked averaging to the visuomotor task and breath-holding events, while any preceding signal changes were canceled out for the visuomotor task, consistent with the passive effect of neurovascular coupling in the venous side of the vasculature. These findings support the current assumption that lag mapping primarily reflects vascular structure despite the presence of sLFO perturbation of neuronal or non-neuronal origin and, thus, emphasize the vascular origin of the lag map, encouraging application of BOLD-based blood flow tracking.

Accelerated Resting-State Functional Magnetic Resonance Imaging Using Multiband Echo-Planar Imaging with Controlled Aliasing

Accelerated Resting-State Functional Magnetic Resonance Imaging Using Multiband Echo-Planar Imaging with Controlled Aliasing

Multiband echo-shifted echo planar imaging.

To propose the technique multiband echo-shifted (MESH) echo planar imaging (EPI), which combines the principles of echo-shifted acquisition for two-dimensional multislice EPI, with both in-plane and multiband acceleration by means of partial parallel imaging techniques. MESH EPI is suitable for functional MRI (fMRI) in situations where there is sufficient time to insert an additional EPI readout in the dead time between slice selection and the standard EPI readout. In such situations, MESH EPI can further accelerate data acquisition compared with standard multiband techniques. The method is particularly well suited for low static magnetic field strengths and lower spatial resolutions. We compared MESH with multiband and standard EPI with temporal signal-to-noise ratio (tSNR) measurements and resting state fMRI data. Results obtained at 1.5 T from healthy subjects revealed that the additional gradient switching did not additionally affect time course SNR over and above the reduction inherent to multiband imaging. Functional results were qualitatively similar between methods. MESH was not affected by the tSNR reduction and echo shifting gradients. The MESH data were acquired at a factor 2 or 3 faster than corresponding multiband acquisitions for echo shift factors of 1 and 2, respectively. MESH can offer further acceleration of image acquisition for fMRI at no loss in sensitivity. Magn Reson Med 77:1981-1986, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

NIMG-24HIGH SPATIOTEMPORAL DYNAMIC SUSCEPTIBILITY CONTRAST (DSC) PERFUSION MRI USING MULTIBAND ECHOPLANAR IMAGING (MB-EPI)

NIMG-24. HIGH SPATIOTEMPORAL DYNAMIC SUSCEPTIBILITY CONTRAST (DSC) PERFUSION MRI USING MULTIBAND ECHOPLANAR IMAGING (MB-EPI) Benjamin Ellingson, Kevin Leu, Whitney Pope, Albert Lai, Phioanh Nghiemphu, Linda Liau, and Timothy Cloughesy; University of California Los Angeles, Los Angeles, CA, USA BACKGROUND: Dynamic susceptibility contrast (DSC)-MRI is a commonlyusedperfusion imaging techniqueused toassessbrain tumorvascularity and angiogenesis by estimation of relative cerebral blood volume (rCBV). Despite widespread use, technical limitations lead to compromises in terms of resolution, slice coverage, and temporal resolution when acquiring dynamic data using the current single-shot echoplanar (EPI) imaging approach. In the current study we demonstrate the use of a new “multiband” (MB)-EPI sequence for multislice excitation, originally developed for fMRI as part of the Human Connectome Project, to obtain DSC perfusion MRI with whole brain coverage, higher spatial resolution, and twice the temporal resolution of current strategies. METHODS: DSC data collected using standard EPI were compared with DSC obtained using MB-EPI in 20 prospective GBM patients. Standard DSC-MRI were collected on conventional 1.5T or 3T MR scanners using a temporal resolution of 1250-1900ms, matrix size 1⁄4 96x96–128x128, and 5-20 slices with 5mm slice thickness. High spatiotemporalDSC-MRI datawere collectedona3TSiemensPrismawith temporal resolution of 600-750ms, matrix size 1⁄4 100x100–200x200, and 30-32 slices with 4mm slice thickness. Both DSC-MRI datasets were post-processed using standard leakage correction and deconvolution techniques to calculate rCBV and rCBF. RESULTS: Data collected using standard and MB-EPI showed similar dynamic contrast-to-noise, although MB-EPI showed more T1-weighting and leakage effects. RCBV maps obtained using both techniques provided similar information regarding the extent of hypervascularity within the tumor after leakage correction; however, rCBV maps calculated from MB-EPI data had more brain coverage and higher spatial resolution. Parametric maps of blood flow differed slightly due to higher temporal resolution MB-EPI data. CONCLUSION: High spatiotemporal DSC perfusion MRI is desirable and clinically feasible using MB-EPI. DSC using MB-EPI provides comparablequantitativedataand dataqualitywith betteraccuracyandspatial resolution. Neuro-Oncology 17:v153–v171, 2015. doi:10.1093/neuonc/nov225.24 Published by Oxford University Press on behalf of the Society for Neuro-Oncology 2015.

Evaluation of 2D multiband EPI imaging for high-resolution, whole-brain, task-based fMRI studies at 3T: Sensitivity and slice leakage artifacts

Functional magnetic resonance imaging (fMRI) studies that require high-resolution whole-brain coverage have long scan times that are primarily driven by the large number of thin slices acquired. Two-dimensional multiband echo-planar imaging (EPI) sequences accelerate the data acquisition along the slice direction and therefore represent an attractive approach to such studies by improving the temporal resolution without sacrificing spatial resolution. In this work, a 2D multiband EPI sequence was optimized for 1.5mm isotropic whole-brain acquisitions at 3T with 10 healthy volunteers imaged while performing simultaneous visual and motor tasks. The performance of the sequence was evaluated in terms of BOLD sensitivity and false-positive activation at multiband (MB) factors of 1, 2, 4, and 6, combined with in-plane GRAPPA acceleration of 2× (GRAPPA 2), and the two reconstruction approaches of Slice-GRAPPA and Split Slice-GRAPPA. Sensitivity results demonstrate significant gains in temporal signal-to-noise ratio (tSNR) and t-score statistics for MB 2, 4, and 6 compared to MB 1. The MB factor for optimal sensitivity varied depending on anatomical location and reconstruction method. When using Slice-GRAPPA reconstruction, evidence of false-positive activation due to signal leakage between simultaneously excited slices was seen in one instance, 35 instances, and 70 instances over the ten volunteers for the respective accelerations of MB 2×GRAPPA 2, MB 4×GRAPPA 2, and MB 6×GRAPPA 2. The use of Split Slice-GRAPPA reconstruction suppressed the prevalence of false positives significantly, to 1 instance, 5 instances, and 5 instances for the same respective acceleration factors. Imaging protocols using an acceleration factor of MB 2×GRAPPA 2 can be confidently used for high-resolution whole-brain imaging to improve BOLD sensitivity with very low probability for false-positive activation due to slice leakage. Imaging protocols using higher acceleration factors (MB 3 or MB 4×GRAPPA 2) can likely provide even greater gains in sensitivity but should be carefully optimized to minimize the possibility of false activations.

Theoretical and experimental evaluation of multi-band EPI for high-resolution whole brain pCASL Imaging

Multi-band echo planar imaging (MB-EPI), a new approach to increase data acquisition efficiency and/or temporal resolution, has the potential to overcome critical limitations of standard acquisition strategies for obtaining high-resolution whole brain perfusion imaging using arterial spin labeling (ASL). However, the use of MB also introduces confounding effects, such as spatially varying amplified thermal noise and leakage contamination, which have not been evaluated to date as to their effect on cerebral blood flow (CBF) estimation. In this study, both the potential benefits and confounding effects of MB-EPI were systematically evaluated through both simulation and experimentally using a pseudo-continuous arterial spin labeling (pCASL) strategy. These studies revealed that the amplified noise, given by the geometry factor (g-factor), and the leakage contamination, assessed by the total leakage factor (TLF), have a minimal impact on CBF estimation. Furthermore, it is demonstrated that MB-EPI greatly benefits high-resolution whole brain pCASL studies in terms of improved spatial and temporal signal-to-noise ratio efficiencies, and increases compliance with the assumptions of the commonly used single blood compartment model, resulting in improved CBF estimates.

Reducing respiratory effect in motion correction for EPI images with sequential slice acquisition order

Motion correction is critical for data analysis of fMRI time series. Most motion correction algorithms treat the head as a rigid body. Respiration of the subject, however, can alter the static magnetic field in the head and result in motion-like slice shifts for echo planar imaging (EPI). The delay of acquisition between slices causes a phase difference in respiration so that the shifts vary with slice positions. To characterize the effect of respiration on motion correction, we acquired fast sampled fMRI data using multi-band EPI and then simulated different acquisition schemes. Our results indicated that respiration introduces additional noise after motion correction. The signal variation between volumes after motion correction increases when the effective TR increases from 675ms to 2025ms. This problem can be corrected if slices are acquired sequentially. For EPI with a sequential acquisition scheme, we propose to divide the image volumes into several segments so that slices within each segment are acquired close in time and then perform motion correction on these segments separately. We demonstrated that the temporal signal-to-noise ratio (TSNR) was increased when the motion correction was performed on the segments separately rather than on the whole image. This enhancement of TSNR was not evenly distributed across the segments and was not observed for interleaved acquisition. The level of increase was higher for superior slices. On superior slices the percentage of TSNR gain was comparable to that using image based retrospective correction for respiratory noise. Our results suggest that separate motion correction on segments is highly recommended for sequential acquisition schemes, at least for slices distal to the chest.

Investigating univariate temporal patterns for intrinsic connectivity networks based on complexity and low-frequency oscillation: A test–retest reliability study

Intrinsic connectivity networks (ICNs) are composed of spatial components and time courses. The spatial components of ICNs were discovered with moderate-to-high reliability. So far as we know, few studies focused on the reliability of the temporal patterns for ICNs based their individual time courses. The goals of this study were twofold: to investigate the test–retest reliability of temporal patterns for ICNs, and to analyze these informative univariate metrics. Additionally, a correlation analysis was performed to enhance interpretability. Our study included three datasets: (a) short- and long-term scans, (b) multi-band echo-planar imaging (mEPI), and (c) eyes open or closed. Using dual regression, we obtained the time courses of ICNs for each subject. To produce temporal patterns for ICNs, we applied two categories of univariate metrics: network-wise complexity and network-wise low-frequency oscillation. Furthermore, we validated the test–retest reliability for each metric. The network-wise temporal patterns for most ICNs (especially for default mode network, DMN) exhibited moderate-to-high reliability and reproducibility under different scan conditions. Network-wise complexity for DMN exhibited fair reliability (ICC<0.5) based on eyes-closed sessions. Specially, our results supported that mEPI could be a useful method with high reliability and reproducibility. In addition, these temporal patterns were with physiological meanings, and certain temporal patterns were correlated to the node strength of the corresponding ICN. Overall, network-wise temporal patterns of ICNs were reliable and informative and could be complementary to spatial patterns of ICNs for further study.

Evaluation of slice accelerations using multiband echo planar imaging at 3 T

We evaluate residual aliasing among simultaneously excited and acquired slices in slice accelerated multiband (MB) echo planar imaging (EPI). No in-plane accelerations were used in order to maximize and evaluate achievable slice acceleration factors at 3T. We propose a novel leakage (L-) factor to quantify the effects of signal leakage between simultaneously acquired slices. With a standard 32-channel receiver coil at 3T, we demonstrate that slice acceleration factors of up to eight (MB=8) with blipped controlled aliasing in parallel imaging (CAIPI), in the absence of in-plane accelerations, can be used routinely with acceptable image quality and integrity for whole brain imaging. Spectral analyses of single-shot fMRI time series demonstrate that temporal fluctuations due to both neuronal and physiological sources were distinguishable and comparable up to slice-acceleration factors of nine (MB=9). The increased temporal efficiency could be employed to achieve, within a given acquisition period, higher spatial resolution, increased fMRI statistical power, multiple TEs, faster sampling of temporal events in a resting state fMRI time series, increased sampling of q-space in diffusion imaging, or more quiet time during a scan.

Non-linear and non-stationary resting state functional connectivity examined using fast (sub-second) functional MRI.

Event Abstract Back to Event Non-linear and non-stationary resting state functional connectivity examined using fast (sub-second) functional MRI. Bryan Paton1, 2, 3, 4*, Parnesh Raniga1, 5 and Gary Egan1, 2 1 Monash University, Monash Biomedical Imaging, Australia 2 Monash University, School of Psychology & Psychiatry, Australia 3 Monash University, Philosophy & Cognition Lab, SOPHIS, Australia 4 Monash University, tLab, Australia 5 The Australian e-Health Research Centre-BioMedIA, CSIRO Preventative Health National Research Flagship ICTC, Australia Background: Functional connectivity (FC) analyses of functional MRI resting state data has revealed a robust set of spatial networks of intrinsic neural activity. Echo planar imaging (EPI), the primary sequence for acquiring fMRI data, has a limited whole brain imaging temporal resolution of 2-3 seconds that limits the investigation of network dynamics. Recent fast EPI sequences that decrease the minimum EPI scanning time to less than one second include the MREG and Multiband EPI sequences. Accelerated whole brain fMRI, up to ten times the temporal resolution of standard EPI, permits dynamic network analyses not previously possible. Our aim was to examine non-linear and non-stationary resting state functional connectivity using fast EPI methods and compare them to typical unaccelerated EPI data. Method: Whole brain fMRI resting state data using was collected (TR: 650 ms, TE: 30 ms, Flip Angle: 30°, 44 slices, 64 x 64 matrix, 3mm isotropic voxels, Multiband acceleration: x4) from healthy controls using the Human Connectome Project Multiband EPI sequence. We compared a number of correlational measures including cross-correlation, Kullback–Leibler divergence and sample-entropy based statistics with and without windowing. Graph theoretical network measures were derived from the resulting FC matrices. Results: Contrary to typical resting state analyses, FC derived from Multiband EPI sequences shows changes in state and configuration over both short (less than 20 s) and long (greater than 60 s) time scales. The results highlight that the assumptions of stationarity and linearity for both task related and resting state analyses are violated using fast EPI methods. Discussion: Fast EPI sequences are now available for the investigation of resting state and task-related FC applications in cognitive neuroscience. Whilst assuming that resting state data are stationary, linear and phase consistent as is the case with cross-correlation based functional connectivity, the results of fast EPI methods reveal a deeper and richer non-linear, non-stationary structure. The temporal sampling resolution now achievable using fast EPI enables novel studies investigating the dynamics of resting state and potentially task related cognitive processes. Keywords: multiband epi, functional connectivity, fMRI, non-linear, Non-stationary Conference: ACNS-2013 Australasian Cognitive Neuroscience Society Conference, Clayton, Melbourne, Australia, 28 Nov - 1 Dec, 2013. Presentation Type: Poster Topic: Other Citation: Paton B, Raniga P and Egan G (2013). Non-linear and non-stationary resting state functional connectivity examined using fast (sub-second) functional MRI.. Conference Abstract: ACNS-2013 Australasian Cognitive Neuroscience Society Conference. doi: 10.3389/conf.fnhum.2013.212.00056 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 15 Oct 2013; Published Online: 25 Nov 2013. * Correspondence: Mr. Bryan Paton, Monash University, Monash Biomedical Imaging, Clayton, VIC, 3168, Australia, bryan.paton@newcastle.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Bryan Paton Parnesh Raniga Gary Egan Google Bryan Paton Parnesh Raniga Gary Egan Google Scholar Bryan Paton Parnesh Raniga Gary Egan PubMed Bryan Paton Parnesh Raniga Gary Egan Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.