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In contemporary practice, multidetector computed tomography plays a critical role in the diagnostic evaluation of patients with suspected acute mesenteric and bowel trauma. Although less common than solid organ injuries, it may be seen in up to 5% of blunt trauma patients. Evaluation with CT remains challenging even with improvements in technology. The major imaging signs of mesenteric and bowel trauma and what is known about their applicability in clinical practice are reviewed here. Examples illustrate both the subtlety and variable significance of many of the key signs as well as how these are typically integrated into clinical practice.

Constraints on the proximity of the carboxyl carbons of the Asp-85 and Asp-212 side chains to the 14-carbon of the retinal chromophore have been established for the bR(555), bR(568), and M(412) states of bacteriorhodopsin (bR) using solid-state NMR spectroscopy. These distances were examined via (13)C-(13)C magnetization exchange, which was observed in two-dimensional RF-driven recoupling (RFDR) and spin diffusion experiments. A comparison of relative RFDR cross-peak intensities with simulations of the NMR experiments yields distance measurements of 4.4 +/- 0.6 and 4.8 +/- 1.0 A for the [4-(13)C]Asp-212 to [14-(13)C]retinal distances in bR(568) and M(412), respectively. The spin diffusion data are consistent with these results and indicate that the Asp-212 to 14-C-retinal distance increases by 16 +/- 10% upon conversion to the M-state. The absence of cross-peaks from [14-(13)C]retinal to [4-(13)C]Asp-85 in all states and between any [4-(13)C]Asp residue and [14-(13)C]retinal in bR(555) indicates that these distances exceed 6.0 A. For bR(568), the NMR distance constraints are in agreement with the results from recent diffraction studies on intact membranes, while for the M state the NMR results agree with theoretical simulations employing two bound waters in the region of the Asp-85 and Asp-212 residues. The structural information provided by NMR should prove useful for refining the current understanding of the role of aspartic acid residues in the proton-pumping mechanism of bR.

Solid–state NMR evidence for an antibody–dependent conformation of the V3 loop of HIV–1 gp120

We discuss several aspects of homonuclear recoupling and longitudinal exchange using rotor-synchronized spin echo sequences in solid state magic-angle spinning (MAS) experiments. These include the accurate measurement of weak dipole–dipole couplings between rare spins, the behavior of dipolar trajectories in multiple spin environments, and chemical shift correlation spectroscopy via polarization exchange. To describe dipolar trajectories accurately, we adopt an approach to the simulation of these experiments which includes finite pulses and the influence of coherence decay. The latter effect becomes competitive with the strength of weak couplings in many experiments, and a simple empirical approach is outlined for the selection of decay parameters. Dipolar trajectories are shown to be dominated by the largest couplings in multiple spin systems via comparison of two and three interacting spins. Two-dimensional correlation spectroscopy based on dipolar exchange among proximate nuclei is illustrated with a uniformly 15N,13C-labeled sample of the tetrapeptide achatin-II (Gly-L-Phe-L-Ala-L-Asp). In addition, a frequency-selective approach to recoupling dipolar interactions among homonuclear spins is introduced; selective approaches have possible utility in examining weak dipole–dipole couplings in the presence of strong interactions.

Diagnostic imaging features of the most commonly performed types of bariatric surgery, which are gastric banding, sleeve gastrectomy, and Roux-en-Y gastric bypass, are reviewed as well as imaging diagnosis of their complications. Although upper gastrointestinal series remains the first-line imaging test for assessing postoperative anatomy and complications, the important role of multidetector computed tomography in diagnosis of serious complications is highlighted.

Transjugular intrahepatic portosystemic shunts (TIPS) are an effective method for treating the complications of portal hypertension. Specific indications for TIPS include secondary prevention of variceal bleeding and refractory ascites. The purpose of this review is to summarize the role of diagnostic radiology in the creation and assessment of TIPS, to highlight the complications that can occur post-TIPS, and to critically evaluate the literature regarding ultrasound evaluation of TIPS.

The role of diagnostic imaging in liver transplantation is reviewed with a focus on assessing for postoperative complications after adult orthotopic transplant. The normal postoperative appearance after liver transplant and imaging appearances of both vascular and nonvascular complications are discussed. The key role of Doppler ultrasound as the first-line imaging modality is highlighted.

A compensated pulse sequence for the spectrally selective reintroduction of heteronuclear dipole–dipole interactions (frequency‐selective dipolar recoupling) into solid state magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments is described and shown to provide frequency‐selective dipolar dephasing in weakly coupled spin systems. The experimental dipolar spin evolution is interpreted via analytical and numerical calculations, which include a simple model for the observed losses of spin coherence in the multiple pulse experiments. In the peptide glycylglycine, the selective dipolar evolution of two spins is observed while the influence of larger internuclear couplings is suppressed. This approach is aimed at obtaining several quantitative internuclear distances independently in dipolar ‘‘recoupling’’ MAS experiments by reducing multiple spin effects in the observed dipolar evolution. Similar frequency‐selective dephasing experiments are also introduced for static solids, where an efficie...

A simple two pulse phase modulation (TPPM) scheme greatly reduces the residual linewidths arising from insufficient proton decoupling power in double resonance magic angle spinning (MAS) experiments. Optimization of pulse lengths and phases in the sequence produces substantial improvements in both the resolution and sensitivity of dilute spins (e.g., 13C) over a broad range of spinning speeds at high magnetic field. The theoretical complications introduced by large homo‐ and heteronuclear interactions among the spins, as well as the amplitude modulation imposed by MAS, are explored analytically and numerically. To our knowledge, this method is the first phase‐switched sequence to exhibit improvement over continuous‐wave (cw) decoupling in a strongly coupled homogeneous spin system undergoing sample spinning.

We present a new method of performing chemical shift correlation spectroscopy in solids with magic angle spinning (MAS). Its key feature is a longitudinal mixing period of π pulses that recouples the dipolar interaction. We discuss experimental results for triply‐13C‐labeled alanine and a theory combining MAS and π pulses.

An overview of the normal anatomy of the anus and rectum is provided with an emphasis on correlative imaging, including computed tomography, magnetic resonance, and ultrasound. The major clinically important structures that can be assessed with these imaging modalities are reviewed.

The sections in this article are 1 Introduction 2 Dipolar Hamiltonian Under Magic Angle Spinning 3 Rotor-Driven Homonuclear Recoupling 4 Homonuclear Recoupling Via Spin Echoes 5 Direct Recoupling Sequences: DRAMA and USEME 6 Emerging Techniques 7 Concluding Remarks 8 Acknowledgements 9 Biographical Sketches Related Articles

Experiments which require mixing among spins with large frequency differences are generally performed with sequences based on composite pulses or computer-optimized cycles. Adiabatic pulses generally offer several advantages over other approaches, including greater single spin inversion bandwidths and tolerance to RF inhomogeneity. Here, a novel theoretical framework is presented in order to understand how spin–spin interactions are influenced by adiabatic inversion pulses, and insights from this approach are used to design more efficient adiabatic coherence exchange experiments. For very large frequency differences, this new approach generally offers improved results over previously applied mixing sequences, as applied to 13C–13C experiments which are the basis of modern sidechain assignment techniques in proteins. It is also anticipated that the approach presented here will be applicable to the analysis of various alternative approaches to adiabatic mixing.

In solid state nuclear magnetic resonance spectroscopy, several methods have recently been introduced for the purpose of restoring dipolar couplings into magic angle spinning experiments. These powerful techniques are useful for the measurement of internuclear distances and, more generally, for filtering and correlation experiments in noncrystalline materials. In the case of heteronuclear spins, the rotational echo double resonance experiment provides an elegant and practical approach to the spectrally nonselective reintroduction of dipolar interactions. In this article, we describe an approach to restore heteronuclear couplings which is spectrally selective—in particular we recouple the observed spins only with those nonobserved spins lying at exact resonance (and at multiples of the spinning frequency) in the triple resonance experiment. We refer to the technique as frequency‐selective dipolar recoupling.

The measurement of homo- and heteronuclear dipolar couplings by nuclear magnetic resonance (NMR) techniques is an important tool for the determination of molecular structure in solids. In a static polycrystalline solid, the dipolar coupling between two magnetically dilute spins results in the characteristic “Pake pattern” [1], first observed in the 1H spectrum of gypsum, CaSo4-2H2O, which arises from the interaction between the two protons in the water molecules of hydration. The splitting between the singularities provides a straightforward measurement of the dipolar coupling constant and therefore the internuclear distance between the two spins. Unfortunately, in the more general case, the structural information revealed by internuclear distances cannot be obtained directly from the static 1H NMR spectrum because of the multiplicity of couplings. In situations involving other nuclei, such as 13C, 15N, and 31P, large chemical shift anisotropics, as well as other line-broadening mechanisms, obscure the lineshape perturbations from the through-space dipolar couplings.

Within the framework of many‐body perturbation theory, the total correlation energy can be partitioned into: intraorbital pair energies, eii; interorbital pair energies, αβeij and ααeij; double‐excitation pair‐coupling terms eij,kl(D); and higher‐excitation pair‐coupling terms, eij,kl(S,T,Q,...). The asymptotic convergence of pair natural orbital expansions for each of these terms is determined for the model problem of n infinitely separated helium‐like ions with infinite nuclear charge. For example, the asymptotic form of the basis set truncation error in an αβ‐interorbital pair energy is LimitNij→∞Δαβeij =αβfij (Jμ=1Nij Cμij)2 ((−225/ 4608)) (Nij+δij)−1 , where Nij is the number of pair natural orbitals and Cμij is the coefficient of pair natural orbital configuration μij. Numerical studies of the neon atom verify that this model behavior applies to real many‐electron systems. The pair‐coupling terms beyond third‐order contribute less than 1% of the total correlation energy in a variety of atoms and mo...

The major source of errror in most ab initio calculations of molecular energies is the truncation of the one‐electron basis set. A complete basis set model chemistry is defined to include corrections for basis set truncation errors. This model uses double zeta plus polarization level atomic pair natural orbital basis sets to calculate molecular self‐consistent‐field (SCF) energies and correlation energies. The small corrections to give the complete basis set SCF energies are then estimated using the l−6 asymptotic convergence of the multicenter angular momentum expansion. The calculated correlation energies of the atoms He, Be, and Ne, and of the hydrides LiH, BH3, CH4, NH3, H2O, and HF, using the double zeta plus polarization basis sets vary from 83.0% to 91.2% of the experimental correlation energies. However, extrapolation of each of the pair energies and pair‐coupling terms to the complete basis set values using the asymptotic convergence of pair natural orbital expansions retrieves from 99.5±0.7% to ...