76 research outputs found
Search for Extra Dimensions at CDF
This poster, presented at the 2006 Duke Hadron Collider Symposium, presents the results from searches for large extra dimensions, as proposed by Arkani-Hamed, Dimopoulos and Dvali (ADD), and Randall-Sundrum (RS) model warped extra dimensions, at CDF
Assessment of MRI scanner performance for preclinical functional studies
Functional Magnetic Resonance Imaging (fMRI) based studies are rapidly expanding in the
field of preclinical research. The majority of these studies use Echo Planar Imaging (EPI) to
measure Blood Oxygenation Level Dependent (BOLD) signal contrasts in the brain. In such
studies the magnitude and statistical significances of these contrasts are then related to brain
function and cognition. It is assumed that any observed signal contrast is ultimately due to
differences in biological state and that scanner performance is stable and repeatable between
subjects and studies. However, due to confounding issues introduced by in vivo subjects,
little work has been undertaken to test this basic assumption. As the BOLD signal contrasts
generated in such experiments are often very low, even small changes in scanner
performance may dominate the BOLD contrast, distorting any biological conclusions drawn.
A series of fMRI phantoms were produced to measure scanner performance independent of
biological subjects. These phantoms produce specified signal contrast levels on demand
during an fMRI scan by means of current-induced magnetic field gradients. These were used
to generate data sets that emulated the BOLD signal contrast of in vivo imaging. Two studies
examining scanner performance were then conducted on high-field preclinical MRI scanners.
Firstly, in a longitudinal study on a single scanner, measurements were taken over a number
of days across a week long period and then every two months over a year long period.
Secondly, the behaviour of four preclinical scanners (three at 7T, one at 9.4T) was
comparatively assessed. Measurements of several imaging parameters including contrast
generated and functional contrast to noise ratio (fCNR) were obtained in both studies. If the
scanners involved are truly comparable then they should generate similar measurement
values.
Across both studies parameter measurements showed significant differences for identical
contrast settings on the phantom. Although signal contrast itself proved very comparable
across the studies fCNR proved to be highly variable. As well as these measurements of
longer tem behaviour proving variable, short and mid-term signal stability displayed a wide
range of variability. Variations in the level and quality of both signal and noise were
observed. Modelling of signal changes based on fundamental physical principles was also
performed for comparison.
The impact of these behaviours and variations on in vivo studies could result in skewed
biological conclusions at any single site, with some sites exhibiting greater problems than
others. The multisite results suggest potential difficulties when comparing biological
conclusions between sites, even when using identical imaging parameters.
In summary, these results suggest that a cautious approach should be taken with the
conclusions of both fMRI and associated resting state connectivity studies that use EPI as
their acquisition sequence. Improvements to both the experimental design of studies and
regular quality monitoring of scanners should be undertaken to minimise these effects.
Clinical MRI scanners should also be assessed for similar aberrations in behaviour
Effects of early life stress on brain activation.
<p>Within and between group analysis comparing BOLD response to first CS presentation over baseline in rats previously exposed to early life stress (ELS) compared to unstressed controls (CON). KE  =  cluster extent in voxels. T  =  peak voxel t-statistic. Clusters reaching <i>P</i><sub>corrected</sub> <0.05 are shown. R =  right, L =  left, RSG =  retrospenial granular cortex. CON, n =  14; ELS, n = 8.</p
Training and scanning procedure.
<p>Animals were acclimatised to the scanning procedure using a mock scanner, conditioned and then tested during retrieval in the scanner 24 h later.</p
Consequence of early life stress on fear associated brain activation.
<p>Greater activation in response to CS presentation is observed in right and left lateral amygdalae (LA), hypothalamus (Hyp) and optic grey (optic) when ELS is compared to CON. (a) Coronal, (b) axial and (c) sagittal sections of rat brain. Control, n = 14; ELS, n = 8.</p
Brain activation during first CS presentation versus baseline.
<p>Significant regional brain activation (BOLD responses) to the first CS presentation compared to baseline. PG  =  paired group, UG  =  unpaired group. KE  =  cluster extent in voxels. T  =  peak voxel t-statistic. Clusters reaching <i>P</i><sub>corrected</sub> <0.05 are shown.*  =  significant (<i>P</i><sub>corrected</sub> <0.05) within lateral amygdala ROI. R =  right, L =  left, PVN =  paraventricular nucleus. PG, n =  14; UG, n = 10.</p
Brain activation maps in response to a fear conditioned stimulus.
<p>(a) Activation in PG in response to CS presentation is observed in right lateral amygdala (LA) and hypothalamus (Hyp). (b) Comparison of response between groups (PG:UG) confirms LA, Hyp and granular insular cortex (GI) activation in PG in response to the CS presentation. Extinction modeling of (c) the response across CS presentations within the PG or (d) between PG and UG groups reveals right LA, Hyp, GI and somatosensory cortex activation (SSC). PG, n = 14; UG, n = 10.</p
Heart rate levels obtained during preliminary testing using a mock scanner.
<p>Data Mean ±SEM, n = 6 rats. Previous telemetry evidence suggests a resting heart rate of around 300–380 bpm in adult rats.</p
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