We introduce a novel algorithm to reconstruct dynamic MRI data from under-sampled k-t space data. In contrast to classical model based cine MRI schemes that rely on the sparsity or banded structure in Fourier space, we use the compact representation of the data in the Karhunen Louve transform (KLT) domain to exploit the correlations in the dataset. The use of the data-dependent KL transform makes our approach ideally suited to a range of dynamic imaging problems, even when the motion is not periodic. In comparison to current KLT-based methods that rely on a two-step approach to first estimate the basis functions and then use it for reconstruction, we pose the problem as a spectrally regularized matrix recovery problem. By simultaneously determining the temporal basis functions and its spatial weights from the entire measured data, the proposed scheme is capable of providing high quality reconstructions at a range of accelerations. In addition to using the compact representation in the KLT domain, we also exploit the sparsity of the data to further improve the recovery rate. Validations using numerical phantoms and in-vivo cardiac perfusion MRI data demonstrate the significant improvement in performance offered by the proposed scheme over existing methods.

Digital breast tomosynthesis ͑DBT͒ is a three-dimensional ͑3D͒ x-ray imaging modality that reconstructs image slices parallel to the detector plane. Image acquisition is performed using a limited angular range ͑less than 50 degrees͒ and a limited number of projection views ͑less than 50 views͒. Due to incomplete data sampling, image artifacts are unavoidable in DBT. In this preliminary study, the image artifacts in DBT were investigated systematically using a linear system approximation. A cascaded linear system model of DBT was developed to calculate the 3D presampling modulation transfer function ͑MTF͒ with different image acquisition geometries and reconstruction filters using a filtered backprojection ͑FBP͒ algorithm. A thin, slanted tungsten ͑W͒ wire was used to measure the presampling MTF of the DBT system in the cross-sectional plane defined by the thickness ͑z-͒ and tube travel ͑x-͒ directions. The measurement was in excellent agreement with the calculation using the model. A small steel bead was used to calculate the artifact spread function ͑ASF͒ of the DBT system. The ASF was correlated with the convolution of the two-dimensional ͑2D͒ point spread function ͑PSF͒ of the system and the object function of the bead. The results showed that the cascaded linear system model can be used to predict the magnitude of image artifacts of small, high-contrast objects with different image acquisition geometry and reconstruction filters.

A three-dimensional ͑3D͒ linear model for digital breast tomosynthesis ͑DBT͒ was developed to investigate the effects of different imaging system parameters on the reconstructed image quality. In the present work, experimental validation of the model was performed on a prototype DBT system equipped with an amorphous selenium ͑a-Se͒ digital mammography detector and filtered backprojection ͑FBP͒ reconstruction methods. The detector can be operated in either full resolution with 85 m pixel size or 2 ϫ 1 pixel binning mode to reduce acquisition time. Twenty-five projection images were acquired with a nominal angular range of Ϯ20°. The images were reconstructed using a slice thickness of 1 mm with 0.085ϫ 0.085 mm in-plane pixel dimension. The imaging performance was characterized by spatial frequency-dependent parameters including a 3D noise power spectrum ͑NPS͒ and in-plane modulation transfer function ͑MTF͒. Scatter-free uniform x-ray images were acquired at four different exposure levels for noise analysis. An aluminum ͑Al͒ edge phantom with 0.2 mm thickness was imaged to measure the in-plane presampling MTF. The measured in-plane MTF and 3D NPS were both in good agreement with the model. The dependence of DBT image quality on reconstruction filters was investigated. It was found that the slice thickness ͑ST͒ filter, a Hanning window to limit the high-frequency components in the slice thickness direction, reduces noise aliasing and improves 3D DQE. An ACR phantom was imaged to investigate the effects of angular range and detector operational modes on reconstructed image quality. It was found that increasing the angular range improves the MTF at low frequencies, resulting in better detection of large-area, low-contrast mass lesions in the phantom. There is a trade-off between noise and resolution for pixel binning and full resolution modes, and the choice of detector mode will depend on radiation dose and the targeted lesion.

aWe present a new strategy for in situ transformation of metal-organic framework (MOF) crystals to hollow metal-organic structures through polycondensation of dopamine. The hollow metal-polydopamine (PDA) particles are formed by a coordination assembly of metal ions (Co and Zn) and PDA, inheriting the morphology of MOF (ZIF-67 and ZIF-8) crystals. The hollow porous metal/N-carbon particles morphosynthetically transformed from hollow metal-PDA particles exhibit excellent oxygen reduction electrocatalytic activity. The strategy presented here is promising for synthesizing hollow metal-organic polymer (metal-carbon) particles with diverse morphologies for energy and environmental applications.

Ultra large‐scale integration (ULSI) should lead to 100 nm production circuits by 2006 as predicted by the Semiconductor Industry Association (SIA). For sub‐100 nm lithography it is desirable to synthesize higher performance and higher contrast resists. An optimum combination of high contrast necessary for sub‐100 nm resolution, high sensitivity for high throughput can be achieved by carefully engineering organic–inorganic nanocomposites, acting as optimum resists for a given lithographic process. This review outlines emerging approaches towards the achievement of these goals. A section also highlights selected state‐of‐the‐art organic resists. Nanocomposite resists for sub‐100 nm features have included the incorporation of fullerene C60 in a commercial resist ZEP520 (see Figure). Alternatively, nanoscale silica particles were incorporated in the polymer backbone as covalently bonded pendant clusters. The dispersion of 8–10 nm silica particles in a chemically amplified resist has also been reported. In all these approaches, a higher softening temperature (Tg) and increased rigidity, due to increased density of the film resulted. Higher etch resistance as well as increased mechanical properties and also enhanced resist performance for nanometer pattern fabrication have been obtained in these nanocomposites. Alternative approaches to conventional lithography, based on self‐assembled nanostructures, incorporating inorganic features as well as nanoimprinting via silicon polymer precursors, are also discussed.

Nitrogen-doped hollow carbon spheres with uniform and tunable morphology can be facilely synthesized by the monodisperse silicatemplate carbonization followed by hydrofluoric acid etching. The hollow carbon spheres containing 3.2 wt% of nitrogen have a thin wall of 5-12 nm and mesoporous shell structure.

The problem of redistributing the work load on parallel computers is considered. An optimal redistribution algorithm, which minimises the Euclidean norm of the migrating load, is derived. The relationship between this algorithm and some existing algorithms is discussed and the convergence of the new algorithm is studied. Finally, numerical results on randomly generated graphs as well as on graphs related to real meshes are given to demonstrate the effectiveness of the new algorithm. © 1998 John Wiley & Sons, Ltd.

SPNs are rare neoplasms with malignant potential but excellent prognosis. Adequate surgical resection, including laparoscopic surgery, may therefore be performed safely and is associated with a long-term survival, even in invasive cases.