Three commercial metal artifact reduction methods were evaluated for use in computed tomography (CT) imaging in the presence of clinically realistic metal implants: Philips O-MAR, GE's monochromatic Gemstone Spectral Imaging (GSI) using dual-energy CT, and GSI monochromatic imaging with metal artifact reduction software applied (MARs). Each method was evaluated according to CT number accuracy, metal size accuracy, and streak artifact severity reduction by using several phantoms, including three anthropomorphic phantoms containing metal implants (hip prosthesis, dental fillings, and spinal fixation rods). All three methods showed varying degrees of success for the hip prosthesis and spinal fixation rod cases, while none were particularly beneficial for dental artifacts. Limitations of the methods were also observed. MARs underestimated the size of metal implants and introduced new artifacts in imaging planes beyond the metal implant when applied to dental artifacts, and both the O-MAR and MARs algorithms induced artifacts for spinal fixation rods in a thoracic phantom. Our findings suggest that all three artifact mitigation methods may benefit patients with metal implants, though they should be used with caution in certain scenarios.

Purpose To determine whether in-house patient-specific IMRT QA results predict the Imaging and Radiation Oncology Core (IROC)-Houston phantom results. Methods and Materials IROC Houston’s IMRT head and neck phantoms have been irradiated by numerous institutions as part of clinical trial credentialing. We retrospectively compared these phantom results with those of in-house IMRT QA (following the institution’s clinical process) for 855 irradiations performed between 2003 and 2013. The sensitivity and specificity of IMRT QA to detect unacceptable or acceptable plans was determined relative to the IROC Houston phantom results. Additional analyses evaluated specific IMRT QA dosimeters and analysis methods. Results IMRT QA universally showed poor sensitivity relative to the head and neck phantom i.e., poor ability to predict a failing IROC Houston phantom result. Depending on how the IMRT QA results were interpreted, overall sensitivity ranged from 2% to 18%. For different IMRT QA methods, sensitivity ranged from 3% to 54%. Although the observed sensitivity was particularly poor at clinical thresholds (e.g., 3% dose difference or 90% of pixels passing gamma), receiver operator characteristic analysis indicated that no threshold showed good sensitivity and specificity for the devices evaluated. Conclusions IMRT QA is not a reasonable replacement for a credentialing phantom. Moreover, the particularly poor agreement between IMRT QA and the IROC Houston phantoms highlights surprising inconsistency in the QA process.

Biological exoskeletons, in particular those with unusually robust and multifunctional properties, hold enormous potential for the development of improved load-bearing and protective engineering materials. Here, we report new materials and mechanical design principles of the iron-plated multilayered structure of the natural armor of Crysomallon squamiferum, a recently discovered gastropod mollusc from the Kairei Indian hydrothermal vent field, which is unlike any other known natural or synthetic engineered armor. We have determined through nanoscale experiments and computational simulations of a predatory attack that the specific combination of different materials, microstructures, interfacial geometries, gradation, and layering are advantageous for penetration resistance, energy dissipation, mitigation of fracture and crack arrest, reduction of back deflections, and resistance to bending and tensile loads. The structure-property-performance relationships described are expected to be of technological interest for a variety of civilian and defense applications.exoskeleton | mollusc | biomechanics | nanomechanics | nanoindentation M any organisms have evolved robust protective exterior structures over millions of years to maximize survivability in their specific environments. Biological exoskeletons or "natural armor" must fulfill various performance requirements such as wear resistance, dissolution prevention, thermal and hydration regulation, and accommodations for feeding, locomotion, and reproduction. Another critical function of these systems is mechanical protection from predators that can induce damage from, for example, penetration, fatigue, drilling, peeling, chipping, hammering, crushing, and kinetic attacks (1). Hence, a diverse array of macroscopic geometries, sizes, and hierarchical, multilayered composite structures exist (2). The shells of gastropod molluscs have long provided key insights into the mechanical performance of biological armor materials. Early on, Wainwright carried out macroscopic mechanical experiments on bivalve shells and formulated important questions on the contributions of different crystal textures to their strength and other functional properties (3). Soon after, Currey and Taylor characterized the properties of numerous mollusc shell microstructures and determined that the inner nacreous layer had superior mechanical properties (4). Subsequently, three decades of investigations ensued on nacre (5-9), leading to the generalized concept of "mechanical property amplification;" i.e., order of magnitude increases in strength and toughness exhibited by biological composites compared to their individual constituent materials beyond simple rule of mixture formulations (10-12). These discoveries engendered numerous efforts to produce nacre-mimetic composite materials that also exhibit mechanical property amplification (12-15). Design, inspired by nature, of engineering materials with robust and multifunctional mechanical properties [i.e., those which sustain a variety of loading condi...