The Decay of Unstable Noncommutative Solitons

We study the classical decay of unstable scalar solitons in noncommutative field theory in 2+1 dimensions. This can, but does not have to, be viewed as a toy model for the decay of D-branes in string theory. In the limit that the noncommutativity parameter \theta is infinite, the gradient term is absent, there are no propagating modes and the soliton does not decay at all. If \theta is large, but finite, the rotationally symmetric decay channel can be described as a highly excited nonlinear oscillator weakly coupled to a continuum of linear modes. This system is closely akin to those studied in the context of discrete breathers. We here diagonalize the linear problem and compute the decay rate to first order using a version of Fermi's Golden Rule, leaving a more rigorous treatment for future work.Comment: 36 pages, 7 figures, dedicated to Rudolf Haag. v2: uniform estimate for Weyl criterion provided, refs adde

MR motility imaging in Crohn's disease improves lesion detection compared with standard MR imaging

Objective: To evaluate retrospectively in patients with Crohn's disease (CD) if magnetic resonance (MR) motility alterations correlate with CD typical lesions leading to an increased detection rate. Methods: Forty patients with histologically proven CD underwent MR enterography (MRE), including coronal cine sequences (cine MRE), in addition to the standard CD MR protocol. Two blinded readings were performed with and without cine MRE. Locations presenting motility alterations on the cine sequences were analysed on standard MRE for CD-related lesions. This was compared with a second reading using the standard clinical MRE protocol alone. Results: The number of lesions localised by cine MRE and identified on standard MRE compared with standard MRE alone were 35/24 for wall thickening (p = 0.002), 24/20 for stenoses (p = 0.05), 17/11 for wall layering (p = 0.02), 5/3 for mucosal ulcers (p = 0.02) and 21/17 for the comb sign (p = 0.05). Overall, cine MRE detected 35 more CD-specific findings than standard MRE alone (124/89; p = 0.007) and significantly more patients with CD-relevant MR findings (34/28; p = 0.03). Conclusion: CD lesions seem to be associated with motility changes and this leads to an increased lesion detection rate compared with standard-MRE imaging alon

Aperistaltic effect of hyoscine N -butylbromide versus glucagon on the small bowel assessed by magnetic resonance imaging

The aim of this prospective study was to compare the intraindividual aperistaltic effect of 40mg hyoscine N-butylbromide (HBB/Buscopan) with that of 1mg glucagon on small bowel motility by using magnetic resonance imaging (MRI). Ten healthy volunteers underwent two separate 1.5-T MRI studies (HBB/glucagon) after a standardized oral preparation with an aqueous solution of Gd-DOTA and ispaghula (Metamucil). A 2D T1-w GRE sequence was acquired (TR 2.7ms/TE 1.3ms, temporal resolution 0.25s) before and after intravenous (i.v.) drug administration and motility was followed over 1h. On the resulting images the cross-sectional luminal diameters were assessed and plotted over time. Baseline motility frequency, onset of aperistalsis, duration of arrest, reappearance of motility and return to normal motility were analysed. Significant differences regarding reliability and duration of aperistalsis were observed. In the HBB group aperistalsis lasted a mean of 6.8 ± 5.3min compared with 18.3 ± 7min after glucagon (p < 0.0001). In 50% of cases HBB did not accomplish aperistalsis, whereas glucagon always succeeded (p = 0.05). There were no significant differences in terms of baseline and end frequencies for the onset of aperistalsis (22.2 ± 37.5s HBB/13.4 ± 9.2s glucagon, p = 0.1), nor for the return to normal motility. Arrest of small bowel motion is achieved more reliably and lasts significantly longer after i.v. administration of 1mg glucagon compared with 40mg HB

Gradient-enhanced volume rendering: an image processing strategy to facilitate whole small bowel imaging with MRI

MRI of the small bowel with positive contrast from orally administered contrast agent is a promising non-invasive imaging method. The aim of our study was to introduce small bowel MRI in a display format that clinicians are accustomed to and that maximizes the amount of information visualized on a single image. Twelve healthy volunteers, median age 32years (range 18-49 years) participated in the study. A mixture of 20ml Gd-DOTA (Dotarem), 0.8g/kg body weight psyllium fibre (Metamucil) and 1.2l water were sequentially administered over a period of 4h. Imaging was performed on a 1.5Tunit (Philips Gyroscan, Intera). Fat-saturated, 3D, gradient echo imaging was performed while the patient was in apnea (30s). Bowel motion was reduced with 40mg intravenously administered scopolamine (Buscopan). A 3D, gradient-enhanced, volume rendering technique was applied to the 3D data sets. Standard projections [left anterior oblique (LAO), right anterior oblique (RAO), supine and prone] resembling conventional enteroclysis were successfully generated within fewer than 10min processing time. Reconstructions were reproducible and provided an entire overview of the small bowel. In addition thin-slab volume rendering allowed an overlap-free display of individual structures. Positive contrast from orally administered contrast agent, combined with a gradient enhanced volume rendering method, allows the reconstruction of the small bowel in a pattern resembling conventional double-contrast enteroclysis. Segmental display without overlay is possibl

Retrospective analysis of patients for development of nephrogenic systemic fibrosis following conventional angiography using gadolinium-based contrast agents

Purpose: The purpose was to retrospectively review the data of 27 patients with renal insufficiency who underwent conventional angiography with gadolinium-based contrast agents (GDBCA) as alternative contrast agents and assess the occurrence of nephrogenic systemic fibrosis (NSF) together with associated potential risk factors. Methods: This HIPAA-compliant study had institutional review board approval, and informed consent was waived. Statistical analysis was performed for all available laboratory and clinical data, including dermatology reports. Type and amount of the GDBCA used were recorded for angiography and additional MRI studies, if applicable. Serum creatinine levels (SCr) pre- and post-angiography were recorded, and estimated glomerular filtration rates (eGFR) were calculated. Results: Ten female and 17 male patients who underwent angiography with GDBCA were included. The mean amount of GDBCA administered was 44 ± 15.5ml (range 15-60ml) or 0.24 + 0.12mmol/kg (range 0.1-0.53mmol/kg). At the time of angiography all patients had renal insufficiency (eGFR <60ml/min/1.73m2). Mean eGFR pre-angiography was 26ml/min/1.73m2 and 33ml/min/1.73m2 post-angiography. The mean follow-up period covers 28months, range 1-84months. Additional MRI studies with GDBCA administration were performed in 15 patients. One patient with typical skin lesions had developed biopsy-confirmed NSF. Conclusion: Conventional arterial angiography with GDBCA may play a role in the development of NSF in patients with renal insufficiency. Alternative contrast agents, such as CO2 angiography or rather the use of low doses of iodinated contrast agents, should be considered in these patient

A Hierarchical Diffusion Model Analysis of Age Effects on Visual Word Recognition

Reading is one of the most popular leisure activities and it is routinely performed by most individuals even in old age. Successful reading enables older people to master and actively participate in everyday life and maintain functional independence. Yet, reading comprises a multitude of subprocesses and it is undoubtedly one of the most complex accomplishments of the human brain. Not surprisingly, findings of age-related effects on word recognition and reading have been partly contradictory and are often confined to only one of four central reading subprocesses, i.e., sublexical, orthographic, phonological and lexico-semantic processing. The aim of the present study was therefore to systematically investigate the impact of age on each of these subprocesses. A total of 1,807 participants (young, N = 384; old, N = 1,423) performed four decision tasks specifically designed to tap one of the subprocesses. To account for the behavioral heterogeneity in older adults, this subsample was split into high and low performing readers. Data were analyzed using a hierarchical diffusion modeling approach, which provides more information than standard response time/accuracy analyses. Taking into account incorrect and correct response times, their distributions and accuracy data, hierarchical diffusion modeling allowed us to differentiate between age- related changes in decision threshold, non-decision time and the speed of information uptake. We observed longer non-decision times for older adults and a more conservative decision threshold. More importantly, high-performing older readers outperformed younger adults at the speed of information uptake in orthographic and lexico-semantic processing, whereas a general age- disadvantage was observed at the sublexical and phonological levels. Low- performing older readers were slowest in information uptake in all four subprocesses. Discussing these results in terms of computational models of word recognition, we propose age-related disadvantages for older readers to be caused by inefficiencies in temporal sampling and activation and/or inhibition processes

The protein and contrast agent-specific influence of pathological plasma-protein concentration levels on contrast-enhanced magnetic resonance imaging

OBJECTIVE: The objective of this study was to measure the protein-specific response of r1 and r2 relaxivities of commercially available gadolinium-based magnetic resonance imaging contrast agents to variation of plasma-protein concentrations. MATERIALS AND METHODS: In this in vitro study, contrast agent (gadofosveset trisodium, gadoxetate disodium, gadobutrol, and gadoterate meglumine) dilution series (0-2.5 mmol Gd/L) were prepared with plasma-protein (human serum albumin [HSA] and immunoglobulin G [IgG]) concentrations at physiological (42 and 10 g/L HSA and IgG, respectively, Normal) and at 3 pathological levels with HSA/IgG concentrations of 10/10 (solution Alb low), 42/50 (IgG mild), and 42/70 (IgG severe) g/L. Contrast-agent molar relaxivities and relaxivity-enhancing protein-contrast-agent interaction coefficients were determined on the basis of inversion-recovery and spin-echo data acquired at 1.5 and 3.0 T at 37°C. Protein-induced magnetic resonance imaging signal changes were calculated. RESULTS: The effective r1 and r2 molar relaxivities consistently increased with albumin and IgG concentrations. At 1.5 T, the r1 values increased by 10.2 (gadofosveset), 4.3 (gadoxetate), 1.3 (gadobutrol), and 1.1 L s mmol (gadoterate), respectively, from the Alb low to the IgG severe solution. At 3.0 T, the r1 values increased by 2.9 (gadofosveset), 2.3 (gadoxetate), 0.7 (gadobutrol), and 0.9 (gadoterate) L s mmol, respectively. An excess of IgG most strongly increased the r1 of gadoxetate (+40 and +19% at 1.5 and 3.0 T, respectively, from Normal to IgG severe). An albumin deficiency most strongly decreased the r1 of gadofosveset (-44% and -20% at 1.5 and 3.0 T, respectively, from Normal to Alb low). The modeling confirmed a strong gadofosveset r1 enhancement by albumin and suggested stronger IgG than albumin effects on the apparent molar relaxivity of the other agents per protein mass concentration at 1.5 T. CONCLUSIONS: Pathological deviations from normal plasma-protein concentrations in aqueous solutions result in changes of effective r1 and r2 contrast-agent relaxivities and projected signal enhancements that depend on the contrast agent, the blood-serum protein profile, and the field strength

Structural gray matter features and behavioral preliterate skills predict future literacy – A machine learning approach

When children learn to read, their neural system undergoes major changes to become responsive to print. There seem to be nuanced interindividual differences in the neurostructural anatomy of regions that later become integral parts of the reading network. These differences might affect literacy acquisition and, in some cases, might result in developmental disorders like dyslexia. Consequently, the main objective of this longitudinal study was to investigate those interindividual differences in gray matter morphology that might facilitate or hamper future reading acquisition. We used a machine learning approach to examine to what extent gray matter macrostructural features and cognitive-linguistic skills measured before formal literacy teaching could predict literacy 2 years later. Forty-two native German-speaking children underwent T1-weighted magnetic resonance imaging and psychometric testing at the end of kindergarten. They were tested again 2 years later to assess their literacy skills. A leave-one-out cross-validated machine-learning regression approach was applied to identify the best predictors of future literacy based on cognitive-linguistic preliterate behavioral skills and cortical measures in a priori selected areas of the future reading network. With surprisingly high accuracy, future literacy was predicted, predominantly based on gray matter volume in the left occipito-temporal cortex and local gyrification in the left insular, inferior frontal, and supramarginal gyri. Furthermore, phonological awareness significantly predicted future literacy. In sum, the results indicate that the brain morphology of the large-scale reading network at a preliterate age can predict how well children learn to read

MR motility imaging in Crohn's disease improves lesion detection compared with standard MR imaging

To evaluate retrospectively in patients with Crohn's disease (CD) if magnetic resonance (MR) motility alterations correlate with CD typical lesions leading to an increased detection rate

Suction against resistance: a new breathing technique to significantly improve the blood flow ratio of the superior and inferior vena cava

Objectives: Optimal contrast within the pulmonary artery is achieved by the maximum amount of contrast-enhanced blood flowing through the superior vena cava (SVC), while minimum amounts of non-contrasted blood should originate from the inferior vena cava (IVC). This study aims to clarify whether "suction against resistance” might optimise this ratio. Methods: Phase-contrast pulse sequences on a 1.5T MRI magnet were used for flow quantification (mean flow (mL/s), stroke volume (Vol) in the SVC and IVC in volunteers. Different breathing manoeuvers were analysed repeatedly: free breathing; inspiration; expiration; suction against resistance, and Valsalva. To standardise breathing commands, volunteers performed suction and Valsalva manoeuvers with an MR-compatible manometer. Results: Suction against resistance was associated with a significant drop of the IVC/SVC flow quotient (1.63 [range 1.3-2.0] p  0.05). Conclusions: Suction against resistance caused a significant drop in the IVC/SVC quotient. Theoretically, this breathing manoeuver might significantly improve the enhancement characteristics of CT angiography. Key Points: • Suction provokes reduction in blood flow in the inferior vena cava. • Ratio between the inferior and superior vena cava blood flow diminished during suction. • Manometer used during breathing standardises MR phase-contrast blood flow measurements