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We compare the performance of eight parallel transmit (pTx) body arrays with up to 32 channels and a standard birdcage design. Excitation uniformity, local specific absorption rate (SAR), global SAR, and power metrics are analyzed in the torso at 3 T for radiofrequency (RF)-shimming and 2-spoke excitations.We used a fast cosimulation strategy for field calculation in the presence of coupling between transmit channels. We designed spoke pulses using magnitude least squares optimization with explicit constraint of SAR and power and compared the performance of the different pTx coils using the L-curve method.PTx arrays outperformed the conventional birdcage coil in all metrics except peak and average power efficiency. The presence of coupling exacerbated this power efficiency problem. At constant excitation fidelity, the pTx array with 24 channels arranged in three z-rows could decrease local SAR more than 4-fold (2-fold) for RF-shimming (2-spoke) compared to the birdcage coil for pulses of equal duration. Multi-row pTx coils had a marked performance advantage compared to single row designs, especially for coronal imaging.PTx coils can simultaneously improve the excitation uniformity and reduce SAR compared to a birdcage coil when SAR metrics are explicitly constrained in the pulse design.

AbstractPlant cell walls constitute the majority of lignocellulosic biomass and serve as a renewable resource of biomaterials and biofuel. Extensive interactions between polysaccharides and the aromatic polymer lignin make lignocellulose recalcitrant to enzymatic hydrolysis, but this polymer network remains poorly understood. Here we interrogate the nanoscale assembly of lignocellulosic components in plant stems using solid-state nuclear magnetic resonance and dynamic nuclear polarization approaches. We show that the extent of glycan-aromatic association increases sequentially across grasses, hardwoods, and softwoods. Lignin principally packs with the xylan in a non-flat conformation via non-covalent interactions and partially binds the junction of flat-ribbon xylan and cellulose surface as a secondary site. All molecules are homogeneously mixed in softwoods; this unique feature enables water retention even around the hydrophobic aromatics. These findings unveil the principles of polymer interactions underlying the heterogeneous architecture of lignocellulose, which may guide the rational design of more digestible plants and more efficient biomass-conversion pathways.

Au-FexOy composite nanoparticles (NPs) are of great technological interest due to their combined optical and magnetic properties. However, typical syntheses are neither simple nor ecologically friendly, creating a challenging situation for process scale-up. Here we describe conditions for preparing Au-FexOy NPs in aqueous solutions and at ambient temperatures, without resorting to solvents or amphiphilic surfactants with poor sustainability profiles. These magnetic gold nanoclusters (MGNCs) are prepared in practical yields with average sizes slightly below 100 nm, and surface plasmon resonances that extend to near-infrared wavelengths, and sufficient magnetic moment (up to 6 emu g-1) to permit collection within minutes by handheld magnets. The MGNCs also produce significant photoluminescence when excited at 488 nm. Energy dispersive X-ray (EDX) analysis indicates a relatively even distribution of Fe within the MGNCs, as opposed to a central magnetic core.

Present a novel method for rapid prediction of temperature in vivo for a series of pulse sequences with differing levels and distributions of specific energy absorption rate (SAR).After the temperature response to a brief period of heating is characterized, a rapid estimate of temperature during a series of periods at different heating levels is made using a linear heat equation and impulse-response (IR) concepts. Here the initial characterization and long-term prediction for a complete spine exam are made with the Pennes' bioheat equation where, at first, core body temperature is allowed to increase and local perfusion is not. Then corrections through time allowing variation in local perfusion are introduced.The fast IR-based method predicted maximum temperature increase within 1% of that with a full finite difference simulation, but required less than 3.5% of the computation time. Even higher accelerations are possible depending on the time step size chosen, with loss in temporal resolution. Correction for temperature-dependent perfusion requires negligible additional time and can be adjusted to be more or less conservative than the corresponding finite difference simulation.With appropriate methods, it is possible to rapidly predict temperature increase throughout the body for actual MR examinations.

The study of brain connectivity plays an important role in understanding the functional organizations of the brain. It also helps to identify connectivity signatures that can be used for evaluating neural disorders and monitoring treatment efficacy. In this work, age-related changes in brain connectivity are studied to obtain aging signatures based on various modeling techniques. These include an energy-based machine learning technique to identify brain network interaction differences between two age groups with a large (30 years) age gap between them. Disconnectivity graphs and activation maps of the seven prominent resting-state networks (RSN) were obtained from functional MRI data of old and young adult subjects. Two-sample t-tests were performed on the local minimums with Bonferroni correction to control the family-wise error rate. These local minimums are connectivity states showing not only which brain regions but also how strong they are working together. They work as aging signatures that can be used to differentiate young and old groups. We found that the attention network’s connectivity signature is a state with all the regions working together and young subjects have a stronger average connectivity among these regions. We have also found a common pattern between young and old subjects where the left and right brain regions of the frontal network are sometimes working separately instead of together. In summary, in this work, we combined machine learning and statistical approaches to extract connectivity signatures, which can be utilized to distinguish aging brains and monitor possible treatment efficacy.

A constant relative biological effectiveness (RBE) is used for clinical proton therapy; however, experimental evidence indicates that RBE can vary. We analyzed pediatric ependymoma patients who received proton therapy to determine if areas of normal tissue damage indicated by post-treatment image changes were associated with increased biological dose effectiveness.Fourteen of 34 children showed T2-FLAIR hyperintensity on post-treatment magnetic resonance (MR) images. We delineated regions of treatment-related change and calculated dose and linear energy transfer (LET) distributions with Monte Carlo. Voxel-level image change data were fit to a generalized linear model incorporating dose and LET. Cross-validation was used to determine model parameters and for receiver operating characteristic curve analysis. Tolerance dose (TD50; dose at which 50% of patients would experience toxicity) was interpolated from the model.Image changes showed dependence on increasing LET and dose. TD50 decreased with increasing LET, indicating an increase in biological dose effectiveness. The cross-validated area under the curve for the model was 0.91 (95% confidence interval 0.88-0.94).Our correlation of changes on MR images after proton therapy with increased LET constitutes the first clinical evidence of variable proton biological effectiveness.

Se ha planteado la hipótesis de que el suministro de energía química puede ser insuficiente para alimentar la función normal de la bomba mecánica en la insuficiencia cardíaca (IC). La reacción de la creatina quinasa (CK) sirve como reserva de energía primaria del corazón, y el suministro de trifosfato de adenosina (flujo de ATP) que proporciona se reduce en la IC humana. Sin embargo, la relación entre el suministro de energía CK y la energía mecánica gastada nunca se ha cuantificado en el corazón humano. Este estudio prueba si la reducción del suministro de energía de CK se asocia con una reducción del trabajo mecánico en pacientes con IC. El trabajo mecánico cardíaco y el flujo de CK en W/kg, y la eficiencia mecánica se midieron de forma no invasiva en reposo utilizando bucles de presión-volumen cardíaco, imágenes de resonancia magnética y espectroscopia de fósforo en 14 sujetos sanos y 27 pacientes con IC leve a moderada. En la IC, el flujo de CK en reposo (126 ± 46 frente a 179 ± 50 W/kg, p < 0,002), el promedio (6,8 ± 3,1 frente a 10,1 ± 1,5 W/kg, p <0,001) y el pico (32 ± 14 frente a 48 ± 8 W/kg, p < 0,001) las tasas de trabajo mecánico cardíaco, así como la eficiencia mecánica cardíaca (53% ± 16 frente a 79% ± 3, p < 0,001), se redujeron en un tercio en comparación con los sujetos sanos. Además, el flujo cardíaco de CK se correlacionó con el pico en reposo y la potencia mecánica promedio (p < 0.01), y con la eficiencia mecánica (p = 0.002). Estos primeros hallazgos no invasivos que muestran que el trabajo mecánico cardíaco y la eficiencia en la IC humana leve a moderada disminuyen proporcionalmente con el suministro de energía CK ATP, son consistentes con la hipótesis de privación de energía de la IC. El suministro de energía de CK supera el trabajo mecánico en reposo, pero se encuentra dentro de un rango que puede ser limitante con una actividad moderada y, por lo tanto, presenta un objetivo prometedor para el tratamiento de la IC. Identificador de ClinicalTrials.gov: NCT00181259 . Il a été émis l'hypothèse que l'apport d'énergie chimique peut être insuffisant pour alimenter le fonctionnement normal de la pompe mécanique en cas d'insuffisance cardiaque (IC). La réaction de la créatine kinase (CK) sert de réserve d'énergie primaire du cœur, et l'apport d'adénosine triphosphate (flux d'ATP) qu'elle fournit est réduit dans l'IC humain. Cependant, la relation entre l'approvisionnement en énergie CK et l'énergie mécanique dépensée n'a jamais été quantifiée dans le cœur humain. Cette étude teste si la réduction de l'apport d'énergie CK est associée à une réduction du travail mécanique chez les patients atteints d'IC. Le travail mécanique cardiaque et le flux CK en W/kg, et l'efficacité mécanique ont été mesurés de manière non invasive au repos en utilisant des boucles pression-volume cardiaque, l'imagerie par résonance magnétique et la spectroscopie du phosphore chez 14 sujets sains et 27 patients atteints d'IC légère à modérée. Dans l'IC, le flux CK au repos (126 ± 46 vs. 179 ± 50 W/kg, p < 0,002), la moyenne (6,8 ± 3,1 vs. 10,1 ± 1,5 W/kg, p <0,001) et le pic (32 ± 14 vs. 48 ± 8 W/kg, p < 0,001) les cadences de travail mécanique cardiaque, ainsi que l'efficacité mécanique cardiaque (53% ± 16 vs. 79% ± 3, p < 0,001), ont tous été réduits d'un tiers par rapport aux sujets sains. En outre, le flux CK cardiaque était corrélé avec le pic de repos et la puissance mécanique moyenne (p < 0,01), et avec l'efficacité mécanique (p = 0,002). Ces premiers résultats non invasifs montrant que le travail mécanique cardiaque et l'efficacité dans l'IC humaine légère à modérée diminuent proportionnellement à l'apport d'énergie CK ATP, sont cohérents avec l'hypothèse de privation d'énergie de l'IC. L'approvisionnement en énergie CK dépasse le travail mécanique au repos mais se situe dans une plage qui peut être limitante avec une activité modérée, et présente donc une cible prometteuse pour le traitement de l'IC.ClinicalTrials.gov Identifiant : NCT00181259 . It has been hypothesized that the supply of chemical energy may be insufficient to fuel normal mechanical pump function in heart failure (HF). The creatine kinase (CK) reaction serves as the heart's primary energy reserve, and the supply of adenosine triphosphate (ATP flux) it provides is reduced in human HF. However, the relationship between the CK energy supply and the mechanical energy expended has never been quantified in the human heart. This study tests whether reduced CK energy supply is associated with reduced mechanical work in HF patients.Cardiac mechanical work and CK flux in W/kg, and mechanical efficiency were measured noninvasively at rest using cardiac pressure-volume loops, magnetic resonance imaging and phosphorus spectroscopy in 14 healthy subjects and 27 patients with mild-to-moderate HF.In HF, the resting CK flux (126 ± 46 vs. 179 ± 50 W/kg, p < 0.002), the average (6.8 ± 3.1 vs. 10.1 ± 1.5 W/kg, p <0.001) and the peak (32 ± 14 vs. 48 ± 8 W/kg, p < 0.001) cardiac mechanical work-rates, as well as the cardiac mechanical efficiency (53% ± 16 vs. 79% ± 3, p < 0.001), were all reduced by a third compared to healthy subjects. In addition, cardiac CK flux correlated with the resting peak and average mechanical power (p < 0.01), and with mechanical efficiency (p = 0.002).These first noninvasive findings showing that cardiac mechanical work and efficiency in mild-to-moderate human HF decrease proportionately with CK ATP energy supply, are consistent with the energy deprivation hypothesis of HF. CK energy supply exceeds mechanical work at rest but lies within a range that may be limiting with moderate activity, and thus presents a promising target for HF treatment.ClinicalTrials.gov Identifier: NCT00181259 . تم افتراض أن إمدادات الطاقة الكيميائية قد تكون غير كافية لتغذية وظيفة المضخة الميكانيكية العادية في فشل القلب (HF). يعمل تفاعل كيناز الكرياتين (CK) كاحتياطي الطاقة الأساسي للقلب، ويتم تقليل إمداد الأدينوزين ثلاثي الفوسفات (تدفق ATP) الذي يوفره في HF البشري. ومع ذلك، فإن العلاقة بين إمدادات الطاقة CK والطاقة الميكانيكية المستهلكة لم يتم قياسها أبدًا في قلب الإنسان. تختبر هذه الدراسة ما إذا كان انخفاض إمدادات الطاقة CK مرتبطًا بانخفاض العمل الميكانيكي في مرضى HF. تم قياس العمل الميكانيكي القلبي وتدفق CK بالوزن/كجم، والكفاءة الميكانيكية بشكل غير جراحي في الراحة باستخدام حلقات حجم الضغط القلبي والتصوير بالرنين المغناطيسي ومطياف الفوسفور في 14 شخصًا سليمًا و 27 مريضًا يعانون من HF خفيف إلى متوسط. في HF، انخفض تدفق CK المستريح (126 ± 46 مقابل 179 ± 50 W/kg، p < 0.002)، والمتوسط (6.8 ± 3.1 مقابل 10.1 ± 1.5 W/kg، p <0.001) والذروة (32 ± 14 مقابل 48 ± 8 W/kg، p < 0.001) معدلات العمل الميكانيكي للقلب، وكذلك الكفاءة الميكانيكية للقلب (53 ٪ ± 16 مقابل 79 ٪ ± 3، p < 0.001)، بمقدار الثلث مقارنة بالمشاركين الأصحاء. بالإضافة إلى ذلك، يرتبط تدفق CK القلبي بذروة الراحة ومتوسط الطاقة الميكانيكية (p < 0.01)، وبكفاءة ميكانيكية (p = 0.002). هذه النتائج الأولى غير الغازية التي تظهر أن العمل الميكانيكي للقلب والكفاءة في HF البشري الخفيف إلى المتوسط تنخفض بشكل متناسب مع إمدادات طاقة CK ATP، تتوافق مع فرضية حرمان الطاقة من HF. يتجاوز إمداد الطاقة CK العمل الميكانيكي أثناء الراحة ولكنه يقع ضمن نطاق قد يكون محدودًا مع نشاط معتدل، وبالتالي يقدم هدفًا واعدًا لعلاج HF. معرّف ClinicalTrials.gov: NCT00181259 .