Dynamic Contrast-Enhanced MR Imaging in Head and Neck Cancer: Techniques and Clinical Applications

ABSTRACT SUMMARY: In the past decade, dynamic contrast-enhanced MR imaging has had an increasing role in assessing the microvascular characteristics of various tumors, including head and neck cancer. Dynamic contrast-enhanced MR imaging allows noninvasive assessment of permeability and blood flow, both important features of tumor hypoxia, which is a marker for treatment resistance for head and neck cancer. Dynamic contrast-enhanced MR imaging has the potential to identify early locoregional recurrence, differentiate metastatic lymph nodes from normal nodes, and predict tumor response to treatment and treatment monitoring in patients with head and neck cancer. Quantitative analysis is in its early stage and standardization and refinement of technique are essential. In this article, we review the techniques of dynamic contrast-enhanced MR imaging data acquisition, analytic methods, current limitations, and clinical applications in head and neck cancer. ABBREVIATIONS: AIF ϭ arterial input function; DCE-MR imaging ϭ dynamic contrast-enhanced MR imaging; EES ϭ extracellular extravascular space; GCA

Strain Sensor’s Network for Low-Velocity Impact Location Estimation on Carbon Reinforced Fiber Plastic Structures: Part-I

116-124In this work, we have investigated the strain response (angular/spatial) from fiber Bragg grating (FBG) sensor & resistance strain gauge (RSG) sensors bonded to the composite structure due to the projectile low velocity impact (LVI). The number of sensor & its orientating has been optimized based on such experimental data and designed an optimum sensor network for faithful LVI detection. In order to study the efficacy of the sensor network, an impact localization algorithm based on peak strain amplitude from the sensor bonded to the structure was used in this study. Further the detection efficiency of the algorithm has been improved using weighted average value around the peak amplitude of strain experienced by the sensor. We found that for the high energy (~35 J) LVI the maximum distance error (Euclidian distance) was 50 mm for 80% of total trail case. Furthermore, we have developed and compared the relative performance of the algorithm cited in the literature, will be presented in PART-II of the same Journal

Simulation and validation of disbond growth in co-cured composite skin-stringer specimens using cohesive elements

Separation of skin and stringer is likely to be a failure mode in co-cured composites stiffened panels where there isconsiderable out-of-plane deformation. Such deformations are possible when a stiffened skin structure is loaded incompression/shear beyond buckling or in structures which contain a disbond/delamination at the skin–stringer interface.Prediction of damage initiation and progressive growth in numerical simulations require parameters such as interfacefracture toughness which have to be obtained through specimen tests. Since interface toughness is generally modedependent, this study deals with the design and testing of three different configuration of blade stiffened co-curedcomposite skin–stringer specimens under mode-I and mode-II dominated loading. Finite element numerical modelsare developed using three-dimensional cohesive elements to predict the disbond growth under mode-I and mode-IIdominated loading. The work also addresses the complexities in the convergence of numerical simulations that arise dueto cohesive elements. A systematic way to obtain the best values for cohesive element parameters while finding a balancebetween accuracy of the results, computation time and numerical stability is presented. The present cohesive elementmodelling and analysis methodology successfully predicted the disbond growth in skin–stringer specimen and can be usedto predict disbond/delamination onset or growth in composite stiffened structures subjected to high bendin

Influence of stiffener configuration on post-buckled response of composite panels with impact damages

In this paper, the effect of T, I and J stiffer configurations on post-buckling response of composite stiffened panels with impact damage is investigated through experiments and numerical simulations. Two identical panels in all three configurations were designed and manufactured. Each panel has four stringers of the same type. All panels were designed to have a skin buckling load of 92 kN ± 5 kN and weight of 1.45 kg ± 0.05 kg to separate the effect of impact damage irrespective of stiffener type. One panel from each configuration is impacted with 50 J energy above stiffener flange from skin side to create a Barely Visible Impact Damage (BVID) and followed by a compression test till collapse. A comparative study between pristine and impacted panels is presented. The effect of impact damage on buckling load, post-buckling response, collapse load and end-shortening were investigated. Moreover, finite element numerical models were developed for all panels which include intra-laminar and inter-laminar damage initiation and growth models. Impact damage area measured from ultrasonic C-scan was modelled in commercial finite element software Abaqus®. Failure modes in pristine and impacted panels such as disbond, tearing of stiffener web and locations from experiments are discussed and validated by numerical simulations