69 research outputs found
High-resolution diffusion-weighted imaging at 7 Tesla: single-shot readout trajectories and their impact on signal-to-noise ratio, spatial resolution and accuracy
Diffusion MRI (dMRI) is a valuable imaging technique to study the brain in
vivo. However, the resolution of dMRI is limited by the low signal-to-noise
ratio (SNR) of this technique. Various acquisition strategies have been
developed to achieve high resolutions, but they require long scan times.
Imaging at ultra-high fields (UHF) could further increase the SNR of
single-shot dMRI; however, the shorter T2* and the greater field
non-uniformities will degrade image quality. In this study, we investigated the
trade-off between the SNR and resolution of different k-space trajectories,
including echo planar imaging (EPI), partial Fourier EPI, and spiral, over a
range of resolutions at 7T. The effective resolution, spatial specificity and
sharpening effect were measured from the point spread function (PSF) of the
simulated diffusion sequences for a nominal resolution range of 0.6-1.8 mm.
In-vivo scans were acquired using the three readout trajectories. Field probes
were used to measure dynamic magnetic fields up to the 3rd order of spherical
harmonics. Using a static field map and the measured trajectories image
artifacts were corrected, leaving T2* effects as the primary source of
blurring. The effective resolution was examined in fractional anisotropy (FA)
maps. In-vivo scans were acquired to calculate the SNR. EPI trajectories had
the highest specificity, effective resolution, and image sharpening effect, but
also had substantially lower SNR. Spirals had significantly higher SNR, but
lower specificity. Line plots of the in-vivo scans in phase and frequency
encode directions showed ~0.2 units difference in FA values between the
different trajectories. The difference between the effective and nominal
resolution is greater for spirals than for EPI. However, the higher SNR of
spiral trajectories at UHFs allows us to achieve higher effective resolutions
compared to EPI and PF-EPI trajectories
Up the leash: Exploring canine handlers’ perceptions of volunteering in canine-assisted interventions
To date, research on university and college based canine-assisted interventions for post-secondary students have focused on identifying the effects of spending time with therapy dogs on the well-being of participants and, to a lesser extent, exploring the effects of canine-assisted interventions on therapy dogs as a means of safeguarding canine welfare. Little empirical attention has focused on understanding the experience of volunteer canine handlers – agents at the heart of the success of canine-assisted interventions. The aim of this exploratory research was to first capture the voice of these key stakeholders to better understand their experience as canine handler volunteers and second to provide preliminary insights into their well-being. Sixty volunteer handlers with varying volunteer experience with a canine therapy program at a mid-size Canadian university responded to a series of open-ended prompts related to their volunteer work and completed a battery of well-being measures. Qualitative findings revealed that most participants identified social benefits to volunteering for themselves (64%) and for their dog (55%). The perceived impact on students (33%) and the ability to help university students (36%) were the most rewarding aspects of volunteering. Though enticed to volunteer by qualities of the CAI program (36%), participant motivations to continue volunteering were predominantly associated with personal benefits of volunteering (44%). Most handlers reported no challenges associated with volunteering (73%) and described their dog as happy after sessions (71%). Participants commonly described good therapy dogs as relaxed, calm, and respectful (66%) and strong handlers as having good awareness of their dog (48%). Quantitative findings revealed volunteer handlers reported elevated levels of positive affect (p = < 0.001, d = 1.19), greater satisfaction with life (p = < 0.001, d = 0.85) and lower levels of avoidant attachment to their therapy dog (p = < 0.001, d = -1.16) when compared to normative samples. Implications for the governing of university and college based programs and handler well-being are discussed
Optimization of acquisition parameters for cortical inhomogeneous magnetization transfer (ihMT) imaging using a rapid gradient echo readout
Purpose: Imaging biomarkers with increased myelin specificity are needed to
better understand the complex progression of neurological disorders.
Inhomogeneous magnetization transfer (ihMT) imaging is an emergent technique
that has a high degree of specificity for myelin content but suffers from low
signal-to-noise ratio (SNR). This study used simulations to determine optimal
sequence parameters for ihMT imaging for use in high-resolution cortical
mapping. Methods: MT-weighted cortical image intensity and ihMT SNR were
simulated using modified Bloch equations for a range of sequence parameters.
The acquisition time was limited to 4.5 min/volume. A custom MT-weighted RAGE
sequence with center-out k-space encoding was used to enhance SNR at 3 Tesla.
Pulsed MT imaging was studied over a range of saturation parameters and the
impact of the turbo-factor on effective ihMT was investigated. 1 mm isotropic
ihMTsat maps were generated in 25 healthy adults using an optimized protocol.
Results: Greater SNR was observed for larger number of bursts consisting of 6-8
saturation pulses each, combined with a high readout turbo-factor. However,
that protocol suffered from a point spread function that was more than twice
the nominal resolution. For high-resolution cortical imaging, we selected a
protocol with a higher effective resolution at the cost of a lower SNR. We
present the first group-average ihMTsat whole-brain map at 1 mm isotropic
resolution. Conclusion: This study presents the impact of saturation and
excitation parameters on ihMTsat SNR and resolution. We demonstrate the
feasibility of high-resolution cortical myelin imaging using ihMTsat in less
than 20 minutes
Correcting for T1 bias in Magnetization Transfer Saturation (MTsat) Maps Using Sparse-MP2RAGE
Purpose: Magnetization transfer saturation (MTsat) mapping is commonly used
to examine the macromolecular content of brain tissue. This study compared
variable flip angle (VFA) T1 mapping against compressed sensing (cs)MP2RAGE T1
mapping for accelerating MTsat imaging. Methods: VFA, MP2RAGE and csMP2RAGE
were compared against inversion recovery (IR) T1 in a phantom at 3 Tesla. The
same 1 mm VFA, MP2RAGE and csMP2RAGE protocols were acquired in four healthy
subjects to compare the resulting T1 and MTsat. Bloch-McConnell simulations
were used to investigate differences between the phantom and in vivo T1
results. Finally, ten healthy controls were imaged twice with the csMP2RAGE
MTsat protocol to quantify repeatability. Results: The MP2RAGE and csMP2RAGE
protocols were 13.7% and 32.4% faster than the VFA protocol, respectively. All
approaches provided accurate T1 values (<5% difference) in the phantom, but the
accuracy of the T1 times was more impacted by differences in T2 for VFA than
for MP2RAGE. In vivo, VFA generated longer T1 times than MP2RAGE and csMP2RAGE.
Simulations suggest that the bias in the T1 values between VFA and IR-based
approaches (MP2RAGE and IR) could be explained by the MT-effects from the
inversion pulse. In the test-retest experiment, we found that the csMP2RAGE has
a minimum detectable change of 3% for T1 mapping and 7.9% for MTsat imaging.
Conclusions: We demonstrated that csMP2RAGE can be used in place of VFA T1
mapping in an MTsat protocol. Furthermore, a shorter scan time and high
repeatability can be achieved using the csMP2RAGE sequence.Comment: 23 pages, 7 figures, 2 table
When Therapy Dogs Provide Virtual Comfort: Exploring University Students’ Insights and Perspectives
With the proliferation of canine-assisted interventions and the emphasis placed on the impact of these sessions in bolstering the well-being of visitors to sessions, especially university students, it can be easy to overlook just how participating in one of these sessions is experienced by participants. Capturing participants’ experiences is important as this holds the potential to inform program design and delivery and elucidate mechanisms within the intervention that were found to be especially efficacious. Forging new empirical terrain, this study explored the insights and perceptions of 469 undergraduate students who participated in a virtual canine-assisted stress-reduction intervention at a mid-size western Canadian university. Participants were randomly assigned to synchronous or asynchronous and dog or no-dog conditions and were asked to share their views of their experience by rating statements and responding to open-ended prompts. Thematic content analysis of findings revealed that a virtual canine-assisted intervention was well received by participants. Participants in the synchronous condition with a dog reported more favorable well-being benefits, as compared with participants in the asynchronous condition with a dog and with participants in both the synchronous and asynchronous conditions without a dog. Implications of these findings hold relevance for supporting geographically remote students and students for whom attending virtual sessions is the only option given barriers preventing them from in-person attendance. Correspondingly, considerations of the role of the handler and of animal welfare are presented
Dual-encoded magnetization transfer and diffusion imaging and its application to tract-specific microstructure mapping
We present a novel dual-encoded magnetization transfer (MT) and
diffusion-weighted sequence and demonstrate its potential to resolve distinct
properties of white matter fiber tracts at the sub-voxel level. The sequence
was designed and optimized for maximal MT contrast efficiency. The resulting
whole brain 2.6 mm isotropic protocol to measure tract-specific MT ratio (MTR)
has a scan time under 7 minutes. Ten healthy subjects were scanned twice to
assess repeatability. Two different analysis methods were contrasted: a
technique to extract tract-specific MTR using Convex Optimization Modeling for
Microstructure Informed Tractography (COMMIT), a global optimization technique;
and conventional MTR tractometry. The results demonstrate that the
tract-specific method can reliably resolve the MT ratios of major white matter
fiber pathways and is less affected by partial volume effects than conventional
multi-modal tractometry. Dual-encoded MT and diffusion is expected to both
increase the sensitivity to microstructure alterations of specific tracts due
to disease, ageing or learning, as well as lead to weighted structural
connectomes with more anatomical specificity.Comment: 26 pages, 7 figure
Decreased long‐range temporal correlations in the resting‐state functional magnetic resonance imaging blood‐oxygen‐level‐dependent signal reflect motor sequence learning up to 2 weeks following training
Decreased long-range temporal correlations (LRTC) in brain signals can be used to measure cognitive effort during task execution. Here, we examined how learning a motor sequence affects long-range temporal memory within resting-state functional magnetic resonance imaging signal. Using the Hurst exponent (HE), we estimated voxel-wise LRTC and assessed changes over 5 consecutive days of training, followed by a retention scan 12 days later. The experimental group learned a complex visuomotor sequence while a complementary control group performed tightly matched movements. An interaction analysis revealed that HE decreases were specific to the complex sequence and occurred in well-known motor sequence learning associated regions including left supplementary motor area, left premotor cortex, left M1, left pars opercularis, bilateral thalamus, and right striatum. Five regions exhibited moderate to strong negative correlations with overall behavioral performance improvements. Following learning, HE values returned to pretraining levels in some regions, whereas in others, they remained decreased even 2 weeks after training. Our study presents new evidence of HE's possible relevance for functional plasticity during the resting-state and suggests that a cortical subset of sequence-specific regions may continue to represent a functional signature of learning reflected in decreased long-range temporal dependence after a period of inactivity
Partial Deletion of Chromosome 8 β-defensin Cluster Confers Sperm Dysfunction and Infertility in Male Mice
β-defensin peptides are a family of antimicrobial peptides present at mucosal surfaces, with the main site of expression under normal conditions in the male reproductive tract. Although they kill microbes in vitro and interact with immune cells, the precise role of these genes in vivo remains uncertain. We show here that homozygous deletion of a cluster of nine β-defensin genes (DefbΔ9) in the mouse results in male sterility. The sperm derived from the mutants have reduced motility and increased fragility. Epididymal sperm isolated from the cauda should require capacitation to induce the acrosome reaction but sperm from the mutants demonstrate precocious capacitation and increased spontaneous acrosome reaction compared to wild-types but have reduced ability to bind the zona pellucida of oocytes. Ultrastructural examination reveals a defect in microtubule structure of the axoneme with increased disintegration in mutant derived sperm present in the epididymis cauda region, but not in caput region or testes. Consistent with premature acrosome reaction, sperm from mutant animals have significantly increased intracellular calcium content. Thus we demonstrate in vivo that β-defensins are essential for successful sperm maturation, and their disruption leads to alteration in intracellular calcium, inappropriate spontaneous acrosome reaction and profound male infertility
High spatial overlap but diverging age-related trajectories of cortical magnetic resonance imaging markers aiming to represent intracortical myelin and microstructure
ABSTRACT: Statistical effects of cortical metrics derived from standard T1- and T2-weighted magnetic resonance imaging (MRI) images, such as gray–white matter contrast (GWC), boundary sharpness coefficient (BSC), T1-weighted/T2-weighted ratio (T1w/T2w), and cortical thickness (CT), are often interpreted as representing or being influenced by intracortical myelin content with little empirical evidence to justify these interpretations. We first examined spatial correspondence with more biologically specific microstructural measures, and second compared between-marker age-related trends with the underlying hypothesis that different measures primarily driven by similar changes in myelo- and microstructural underpinnings should be highly related. Cortical MRI markers were derived from MRI images of 127 healthy subjects, aged 18–81, using cortical surfaces that were generated with the CIVET 2.1.0 pipeline. Their gross spatial distributions were compared with gene expression-derived cell-type densities, histology-derived cytoarchitecture, and quantitative R1 maps acquired on a subset of participants. We then compared between-marker age-related trends in their shape, direction, and spatial distribution of the linear age effect. The gross anatomical distributions of cortical MRI markers were, in general, more related to myelin and glial cells than neuronal indicators. Comparing MRI markers, our results revealed generally high overlap in spatial distribution (i.e., group means), but mostly divergent age trajectories in the shape, direction, and spatial distribution of the linear age effect. We conclude that the microstructural properties at the source of spatial distributions of MRI cortical markers can be different from microstructural changes that affect these markers in aging
Identification of a Sudden Cardiac Death Susceptibility Locus at 2q24.2 through Genome-Wide Association in European Ancestry Individuals
Sudden cardiac death (SCD) continues to be one of the leading causes of mortality worldwide, with an annual incidence estimated at 250,000–300,000 in the United States and with the vast majority occurring in the setting of coronary disease. We performed a genome-wide association meta-analysis in 1,283 SCD cases and >20,000 control individuals of European ancestry from 5 studies, with follow-up genotyping in up to 3,119 SCD cases and 11,146 controls from 11 European ancestry studies, and identify the BAZ2B locus as associated with SCD (P = 1.8×10−10). The risk allele, while ancestral, has a frequency of ∼1.4%, suggesting strong negative selection and increases risk for SCD by 1.92–fold per allele (95% CI 1.57–2.34). We also tested the role of 49 SNPs previously implicated in modulating electrocardiographic traits (QRS, QT, and RR intervals). Consistent with epidemiological studies showing increased risk of SCD with prolonged QRS/QT intervals, the interval-prolonging alleles are in aggregate associated with increased risk for SCD (P = 0.006)
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