Three-dimensional Automated Breast US: Facts and Artifacts.

As automated breast (AB) US becomes more integrated into the daily practice of breast imaging, the need to address the artifacts that interfere with AB US image interpretation is becoming more important. Learning methods to detect and subsequently resolve artifacts such as shadowing can enhance the reader's confidence and ability to differentiate artifacts and true abnormalities. Understanding the basic principles of AB US and its image acquisition process are key elements in resolving artifacts. Gaining familiarity with the common patterns of AB US artifacts and placing them into categories of technical, software, physiologic, and breast lesion-related causes can aid in image interpretation. Recognizing specific artifacts, such as dropout and lack of contact, and the ability to distinguish them from true abnormalities, such as surgical scars and suspicious lesions, can help minimize preventable false-positive interpretations. Applying methods to confirm shadowing as artifactual, including the use of a second view, additional planes, and software-related tools such as the rotational tool, can aid the radiologist in resolving artifacts and avoiding preventable recalls, potentially resulting in increased specificity. Presented is a methodical approach to recognizing AB US artifacts and their causes; analyzing shadowing, a challenging entity in the interpretation of AB US imaging studies; differentiating artifact from true abnormality; and reviewing characteristic patterns and basic techniques to resolve artifacts. The goal of this article is to enable the radiologist in applying these methods to help reduce preventable false-positive recommendations and increase efficiency in AB US image interpretation. Online supplemental material is available for this article. ©RSNA, 2019.

Development of a nomogram to predict the clinical impact of a postexcision preirradiation mammogram.

We aimed to better quantify the impact of a postexcision preirradiation mammogram (PPM), first by identifying factors associated with abnormal results and then incorporating these findings into a nomogram. Beginning February 2011, our institution made a practice change to obtain a PPM on all patients with any calcifications identified. A total of 530 patients underwent a PPM. Suspicious abnormalities were reported in 61 patients (11.5%), with the PPM leading to a change in management in 47 instances (8.9%). A nomogram was created based on patient and tumor characteristics to identify patients most likely to have an abnormal PPM.

How grow-and-switch gravitropism generates root coiling and root waving growth responses in Medicago truncatula.

Experimental studies show that plant root morphologies can vary widely from straight gravity-aligned primary roots to fractal-like root architectures. However, the opaqueness of soil makes it difficult to observe how environmental factors modulate these patterns. Here, we combine a transparent hydrogel growth medium with a custom built 3D laser scanner to directly image the morphology of Medicago truncatula primary roots. In our experiments, root growth is obstructed by an inclined plane in the growth medium. As the tilt of this rigid barrier is varied, we find Medicago transitions between randomly directed root coiling, sinusoidal root waving, and normal gravity-aligned morphologies. Although these root phenotypes appear morphologically distinct, our analysis demonstrates the divisions are less well defined, and instead, can be viewed as a 2D biased random walk that seeks the path of steepest decent along the inclined plane. Features of this growth response are remarkably similar to the widely known run-and-tumble chemotactic behavior of Escherichia coli bacteria, where biased random walks are used as optimal strategies for nutrient uptake.

3D imaging and mechanical modeling of helical buckling in Medicago truncatula plant roots.

We study the primary root growth of wild-type Medicago truncatula plants in heterogeneous environments using 3D time-lapse imaging. The growth medium is a transparent hydrogel consisting of a stiff lower layer and a compliant upper layer. We find that the roots deform into a helical shape just above the gel layer interface before penetrating into the lower layer. This geometry is interpreted as a combination of growth-induced mechanical buckling modulated by the growth medium and a simultaneous twisting near the root tip. We study the helical morphology as the modulus of the upper gel layer is varied and demonstrate that the size of the deformation varies with gel stiffness as expected by a mathematical model based on the theory of buckled rods. Moreover, we show that plant-to-plant variations can be accounted for by biomechanically plausible values of the model parameters.

Classical topological order in Abelian and non-Abelian generalized height models.

We present Monte Carlo simulations on a new class of lattice models in which the degrees of freedom are elements of an Abelian or non-Abelian finite symmetry group G, placed on directed edges of a two-dimensional lattice. The plaquette group product is constrained to be the group identity. In contrast to discrete gauge models (but similar to past work on height models), only elements of symmetry-related subsets S∈G are allowed on edges. These models have topological sectors labeled by group products along topologically nontrivial loops. Measurement of relative sector probabilities and the distribution of distance between defect pairs are done to characterize the types of order (topological or quasi-long-range order) exhibited by these models. We present particular models in which fully local non-Abelian constraints lead to global topological liquid properties.

Emergent spin excitations in a Bethe lattice at percolation.

We study the spin-1/2 quantum Heisenberg antiferromagnet on a Bethe lattice diluted to the percolation threshold. Dilution creates areas of even or odd sublattice imbalance resulting in "dangling spins" [L. Wang and A. W. Sandvik, Phys. Rev. Lett. 97, 117204 (2006); Phys. Rev. B 81, 054417 (2010)]. These collectively act as "emergent" spin-1/2 degrees of freedom and are responsible for the creation of a set of low-lying "quasidegenerate states." Using density matrix renormalization group calculations, we detect the presence and location of these emergent spins. We find an effective Hamiltonian of these emergent spins, with Heisenberg interactions that decay exponentially with the distance between them.

Total hip arthroplasty in patients with bone deficiency of the acetabulum.

Total hip replacement (THR) requires revision in only a minority of cases (approximately 17% of prosthetic hips fail), but when THR failures occur there may be significant acetabular bone deficiency. There is a variety of surgical hardware and strategies available to address this problem. The causes of primary THR revision include aseptic loosening or particle disease, infection, recurrent dislocation, implant failure, periprosthetic fracture, and leg length discrepancy. Almost all patients who need THR revision undergo a standard radiographic evaluation of the pelvis and hip. In general, CT is an excellent tool for evaluating loosening of the prosthesis caused by either mechanical reasons or infection, and MR imaging is best suited for evaluating the soft tissues surrounding the prosthesis. Nuclear medicine studies are performed when results of CT and MR imaging are inconclusive. When patients are evaluated for revision THR, radiologists must check for acetabular cup loosening, the amount and type of bone stock loss, the amount of component migration, and the presence or absence of liner wear. Before revision hardware is placed, bone stock loss must be repaired, either by using bone grafting or by placing accessory acetabular hardware such as cups, rings, or cages. The long-term success of revision acetabular surgery varies; there is acetabular cup presence at 5 years after surgery in 60%-94% of cases. Complications include postoperative infections, repeat liner wear, bone graft failure, periprosthetic or prosthetic fractures, dislocation, vascular injury, and nerve injury.

Structure of Periodic Crystals and Quasicrystals in Ultrathin Films of Ba-Ti-O.

We model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O, and with Ba occupying the larger. mainly Ti7O7, pores. The quasicrystal structue is a simple decoration of three types of tiles: square, triangle and 30° rhombus, with edge lengths 6.85 Å, joined edge-to-edge in a quasicrystalline pattern; observed periodic crystals in ultrathin film Ba-Ti-O are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally, and identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.

Classical height models with topological order.

I discuss a family of statistical-mechanics models in which (some classes of) elements of a finite group G occupy the (directed) edges of a lattice; the product around any plaquette is constrained to be the group identity e. Such a model may possess topological order, i.e. its equilibrium ensemble has distinct, symmetry-related thermodynamic components that cannot be distinguished by any local order parameter. In particular, if G is a non-Abelian group, the topological order may be non-Abelian. Criteria are given for the viability of particular models, in particular for Monte Carlo updates.

Order by disorder and gaugelike degeneracy in a quantum pyrochlore antiferromagnet.

The (three-dimensional) pyrochlore lattice antiferromagnet with Heisenberg spins of large spin length S is a highly frustrated model with a macroscopic degeneracy of classical ground states. The zero-point energy of (harmonic-order) spin-wave fluctuations distinguishes a subset of these states. I derive an approximate but illuminating effective Hamiltonian, acting within the subspace of Ising spin configurations representing the collinear ground states. It consists of products of Ising spins around loops, i.e., has the form of a Z2 lattice gauge theory. The remaining ground-state entropy is still infinite but not extensive, being O(L) for system size O(L3). All these ground states have unit cells bigger than those considered previously.