341 research outputs found
Exchange-dependent relaxation in the rotating frame for slow and intermediate exchange - modeling off-resonant spin-lock and chemical exchange saturation transfer
Chemical exchange observed by NMR saturation transfer (CEST) and spin-lock
(SL) experiments provide an MRI contrast by indirect detection of exchanging
protons. The determination of the relative concentrations and exchange rates is
commonly achieved by numerical integration of the Bloch-McConnell equations. We
derive an analytical solution of the Bloch-McConnell equations that describes
the magnetization of coupled spin populations under radiofrequency
irradiation.As CEST and off-resonant SL are equivalent, their steady-state
magnetization and dynamics can be predicted by the same single eigenvalue: the
longitudinal relaxation rate in the rotating frame R1rho. For the case of
slowly exchanging systems, e.g. amide protons, the saturation of the small
proton pool is affected by transverse relaxation (R2b). It turns out, that R2b
is also significant for intermediate exchange, such as amine- or
hydroxyl-exchange or paramagnetic CEST agents, if pools are only partially
saturated. We propose a solution for R1rho that includes R2 of the exchanging
pool by extending existing approaches, and verify it by numerical simulations.
With the appropriate projection factors, we obtain an analytical solution for
CEST and SL for nonzero R2 of the exchanging pool, whilst considering the
dilution by direct water saturation across the entire Z-spectra. This allows
the optimization of irradiation parameters and the quantification of
pH-dependent exchange rates and metabolite concentrations. In addition, we
propose evaluation methods that correct for concomitant direct saturation
effects. It is shown that existing theoretical treatments for CEST are special
cases of this approach
Many faces of DAMPs in cancer therapy
A new concept of immunogenic cell death (ICD) has recently been proposed. The immunogenic characteristics of this cell death mode are mediated mainly by molecules called âdamage-associated molecular patternsâ (DAMPs), most of which are recognized by pattern recognition receptors. Some DAMPs are actively emitted by cells undergoing ICD (e.g. calreticulin (CRT) and adenosine triphosphate (ATP)), whereas others are emitted passively (e.g. high-mobility group box 1 protein (HMGB1)). Recent studies have demonstrated that these DAMPs play a beneficial role in anti-cancer therapy by interacting with the immune system. The molecular pathways involved in translocation of CRT to the cell surface and secretion of ATP from tumor cells undergoing ICD are being elucidated. However, it has also been shown that the same DAMPs could contribute to progression of cancer and promote resistance to anticancer treatments. In this review, we will critically evaluate the beneficial and detrimental roles of DAMPs in cancer therapy, focusing mainly on CRT, ATP and HMGB1
Entwicklung einer Messtechnik zur nicht-invasiven Bestimmung des Gesamtgehalts an N-Acetyl-L-Aspartat im Gehirn des Menschen in vivo
Lokalisierte 1H-MR-Spektroskopie (MRS) ermöglicht die nicht invasive Messung des Metaboliten N-Acetyl-L-Aspartat (NAA) in vivo im Gehirn des Menschen. Da neuronaler Zellverlust einher geht mit einer Abnahme des NAA-Gehalts, könnte der Verlauf von gehirnschĂ€digenden Erkrankungen mit diesem Parameter verfolgt werden. In dieser Arbeit werden neben einem Vorschlag von O. Gonen et al. eigene AnsĂ€tze zur Bestimmung des gesamt-Gehalts an NAA im Gehirn (WBNAA) entwickelt und auf 1,5-T-Ganzkörper-MR-Tomographen implementiert. Die Techniken wurden erfolgreich an Phantomen und Probanden getestet. Im Hinblick auf eine klinische Anwendung wurden zudem verschiedene Methoden der absoluten Quantifizierung entwickelt und experimentell ĂŒberprĂŒft
Umbrella sampling of proton transfer in a creatineâwater system
Proton transfer reactions are among the most common processes in chemistry and
biology. Proton transfer between creatine and surrounding solvent water is
underlying the chemical exchange saturation transfer used as a contrast in
magnetic resonance imaging. The free energy barrier, determined by first-
principles umbrella sampling simulations (View the MathML sourceEaDFT 3
kcal/mol) is in the same order of magnitude as the experimentally obtained
activation energy. The underlying mechanism is a first proton transfer from
the guanidinium group to the water pool, followed by a second transition where
a proton is âtransferred backâ from the nearest water molecule to the
deprotonated nitrogen atom of creatine
A common language to assess allergic rhinitis control : results from a survey conducted during EAACI 2013 Congress
Peer reviewedPublisher PD
Joint multi-contrast Variational Network reconstruction (jVN) with application to rapid 2D and 3D imaging
Purpose: To improve the image quality of highly accelerated multi-channel MRI
data by learning a joint variational network that reconstructs multiple
clinical contrasts jointly.
Methods: Data from our multi-contrast acquisition was embedded into the
variational network architecture where shared anatomical information is
exchanged by mixing the input contrasts. Complementary k-space sampling across
imaging contrasts and Bunch-Phase/Wave-Encoding were used for data acquisition
to improve the reconstruction at high accelerations. At 3T, our joint
variational network approach across T1w, T2w and T2-FLAIR-weighted brain scans
was tested for retrospective under-sampling at R=6 (2D) and R=4x4 (3D)
acceleration. Prospective acceleration was also performed for 3D data where the
combined acquisition time for whole brain coverage at 1 mm isotropic resolution
across three contrasts was less than three minutes.
Results: Across all test datasets, our joint multi-contrast network better
preserved fine anatomical details with reduced image-blurring when compared to
the corresponding single-contrast reconstructions. Improvement in image quality
was also obtained through complementary k-space sampling and
Bunch-Phase/Wave-Encoding where the synergistic combination yielded the overall
best performance as evidenced by exemplarily slices and quantitative error
metrics.
Conclusion: By leveraging shared anatomical structures across the jointly
reconstructed scans, our joint multi-contrast approach learnt more efficient
regularizers which helped to retain natural image appearance and avoid
over-smoothing. When synergistically combined with advanced encoding
techniques, the performance was further improved, enabling up to R=16-fold
acceleration with good image quality. This should help pave the way to very
rapid high-resolution brain exams
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