262 research outputs found
Towards 1H-MRSI of the human brain at 7T with slice-selective adiabatic refocusing pulses
Contains fulltext :
70576.pdf (publisher's version ) (Closed access)OBJECTIVE: To explore the possibilities of proton spectroscopic imaging (1H-MRSI) of the human brain at 7 Tesla with adiabatic refocusing pulses. MATERIALS AND METHODS: A combination of conventional slice selective excitation and two pairs of slice selective adiabatic refocusing pulses (semi-LASER) results in the formation of an echo from a localized volume. Depending on the used radio frequency (rf) coil efficiency and available rf power, the duration of the adiabatic full passage pulses (AFPs) is adapted to enable echo times down to 50 ms (head coil) or 30 ms (local surface coil). RESULTS: An AFP duration of 5 ms with a corresponding bandwidth of 5.1 kHz resulted in a chemical shift displacement error of 23% over 3.8 ppm at 7T. Using a local surface coil and an echo time down to 30 ms, we detected not only the three main metabolites (NAA, Cr and Cho), but also coupled signals from myo-inositol and glutamate/glutamine in spectra from 0.14 cc voxels with linewidths down to 10 Hz in 10 min measurement time. CONCLUSIONS: The semi-LASER pulse sequence enables 1H-MRSI of the human brain at 7T for larger parts of the brain as well as small localized areas with both a high spectral and spatial resolution
New MR sequences in daily practice: susceptibility weighted imaging. A pictorial essay
Background Susceptibility-weighted imaging (SWI) is a
relatively new magnetic resonance (MR) technique that
exploits the magnetic susceptibility differences of various
tissues, such as blood, iron and calcification, as a new
source of contrast enhancement. This pictorial review is
aimed at illustrating and discussing its main clinical
applications.
Methods SWI is based on high-resolution, threedimensional
(3D), fully velocity-compensated gradientecho
sequences using both magnitude and phase images.
A phase mask obtained from the MR phase images is
multiplied with magnitude images in order to increase the
visualisation of the smaller veins and other sources of
susceptibility effects, which are displayed at best after postprocessing
of the 3D dataset with the minimal intensity
projection (minIP) algorithm.
Results SWI is very useful in detecting cerebral microbleeds
in ageing and occult low-flow vascular malformations,
in characterising brain tumours and degenerative diseases of the brain, and in recognizing calcifications in
various pathological conditions. The phase images are
especially useful in differentiating between paramagnetic
susceptibility effects of blood and diamagnetic effects of
calcium. SWI can also be used to evaluate changes in iron
content in different neurodegenerative disorders.
Conclusion SWI is useful in differentiating and characterising
diverse brain disorders
Improved Measurement of the Pseudoscalar Decay Constant
We present a new determination of the Ds decay constant, f_{Ds} using 5
million continuum charm events obtained with the CLEO II detector. Our value is
derived from our new measured ratio of widths for Ds -> mu nu/Ds -> phi pi of
0.173+/- 0.021 +/- 0.031. Taking the branching ratio for Ds -> phi pi as (3.6
+/- 0.9)% from the PDG, we extract f_{Ds} = (280 +/- 17 +/- 25 +/- 34){MeV}. We
compare this result with various model calculations.Comment: 23 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
First Observation of and Decays
We have observed new channels for decays with an in the final
state. We study 3-prong tau decays, using the and
\eta\to 3\piz decay modes and 1-prong decays with two \piz's using the
channel. The measured branching fractions are
\B(\tau^{-}\to \pi^{-}\pi^{-}\pi^{+}\eta\nu_{\tau})
=(3.4^{+0.6}_{-0.5}\pm0.6)\times10^{-4} and \B(\tau^{-}\to
\pi^{-}2\piz\eta\nu_{\tau}
=(1.4\pm0.6\pm0.3)\times10^{-4}. We observe clear evidence for
substructure and measure \B(\tau^{-}\to
f_1\pi^{-}\nu_{\tau})=(5.8^{+1.4}_{-1.3}\pm1.8)\times10^{-4}. We have also
searched for production and obtain 90% CL upper limits
\B(\tau^{-}\to \pi^{-}\eta'\nu_\tau)<7.4\times10^{-5} and \B(\tau^{-}\to
\pi^{-}\piz\eta'\nu_\tau)<8.0\times10^{-5}.Comment: 11 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Search for the Decays B^0 -> D^{(*)+} D^{(*)-}
Using the CLEO-II data set we have searched for the Cabibbo-suppressed decays
B^0 -> D^{(*)+} D^{(*)-}. For the decay B^0 -> D^{*+} D^{*-}, we observe one
candidate signal event, with an expected background of 0.022 +/- 0.011 events.
This yield corresponds to a branching fraction of Br(B^0 -> D^{*+} D^{*-}) =
(5.3^{+7.1}_{-3.7}(stat) +/- 1.0(syst)) x 10^{-4} and an upper limit of Br(B^0
-> D^{*+} D^{*-}) D^{*\pm} D^\mp and
B^0 -> D^+ D^-, no significant excess of signal above the expected background
level is seen, and we calculate the 90% CL upper limits on the branching
fractions to be Br(B^0 -> D^{*\pm} D^\mp) D^+
D^-) < 1.2 x 10^{-3}.Comment: 12 page postscript file also available through
http://w4.lns.cornell.edu/public/CLNS, submitted to Physical Review Letter
Production in Two-Photon Interactions at CLEO
Using the CLEO detector at the Cornell storage ring, CESR, we study
the two-photon production of , making the first
observation of . We present the
cross-section for as a function of
the center of mass energy and compare it to that predicted by
the quark-diquark model.Comment: 10 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Observation of the Decay
Using e+e- annihilation data collected by the CLEO~II detector at CESR, we
have observed the decay Ds+ to omega pi+. This final state may be produced
through the annihilation decay of the Ds+, or through final state interactions.
We find a branching ratio of [Gamma(Ds+ to omega pi+)/Gamma(Ds+ to eta
pi+)]=0.16+-0.04+-0.03, where the first error is statistical and the second is
systematic.Comment: 9 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Evaluation of Brain Iron Content Based on Magnetic Resonance Imaging (MRI): Comparison among Phase Value, R2* and Magnitude Signal Intensity
Background and Purpose: Several magnetic resonance imaging (MRI) techniques are being exploited to measure brain iron levels increasingly as iron deposition has been implicated in some neurodegenerative diseases. However, there remains no unified evaluation of these methods as postmortem measurement isn’t commonly available as the reference standard. The purpose of this study was to make a comparison among these methods and try to find a new index of brain iron. Methods: We measured both phase values and R2 * in twenty-four adults, and performed correlation analysis among the two methods and the previously published iron concentrations. We also proposed a new method using magnitude signal intensity and compared it with R2 * and brain iron. Results: We found phase value correlated with R2 * in substantia nigra (r = 20.723, p,0.001) and putamen (r = 20.514, p = 0.010), while no correlations in red nucleus (r = 20.236, p = 0.268) and globus pallidus (r = 20.111, p = 0.605). And the new magnitude method had significant correlations in red nucleus (r = 20.593, p = 0.002), substantia nigra (r = 20.521, p = 0.009), globus pallidus (r = 20.750, p,0.001) and putamen (r = 20.547, p = 0.006) with R2*. A strong inverse correlation was also found between the new magnitude method and previously published iron concentrations in seven brain regions (r = 20.982, P,0.001). Conclusions: Our study indicates that phase value may not be used for assessing the iron content in some brain region
Daf-2 Signaling Modifies Mutant SOD1 Toxicity in C. elegans
The DAF-2 Insulin/IGF-1 signaling (IIS) pathway is a strong modifier of Caenorhabditis elegans longevity and healthspan. As aging is the greatest risk factor for developing neurodegenerative diseases such as Amyotrophic Lateral Sclerosis (ALS), we were interested in determining if DAF-2 signaling modifies disease pathology in mutant superoxide dismutase 1 (SOD1) expressing C. elegans. Worms with pan-neuronal G85R SOD1 expression demonstrate significantly impaired locomotion as compared to WT SOD1 expressing controls and they develop insoluble SOD1 aggregates. Reductions in DAF-2 signaling, either through a hypomorphic allele or neuronally targeted RNAi, decreases the abundance of aggregated SOD1 and results in improved locomotion in a DAF-16 dependant manner. These results suggest that manipulation of the DAF-2 Insulin/IGF-1 signaling pathway may have therapeutic potential for the treatment of ALS
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