Osama M. Mukdadi

Abstract: Introduction The objective of this study was to demonstrate the potential of 3-dimensional modeling and finite element analysis as clinical tools in treatment planning for orthodontic tooth movement. High stresses in bone and miniscrew implants under load can cause fractures and trauma for orthodontic patients, and treatments are typically planned by using clinical experience or simple 2-dimensional radiographs. Methods Anatomically accurate 3-dimensional models reconstructed from cone-beam computed tomography scans were used to simulate the retraction of a single-rooted mandibular canine with a miniscrew placed as skeletal anchorage. Detailed stress distributions in the implant and peri-implant bone were found, in addition to the effect of the orthodontic bracket hook length and the angulation of retraction force on stress response in the periodontal ligament (PDL). Results The numeric results showed that the equivalent von Mises stress on the miniscrew under a 200-cN tangential load reached 42 MPa at the first thread recession, whereas von Mises stress in the peri-implant bone only reached 11 MPa below the neck. High tightening loads of 200 N·mm of torsion and 460 cN of axial compression resulted in much greater bone and implant von Mises stresses than tangential loading, exceeding the yield strengths of the titanium alloy and the cortical bone. Increasing the hook length on the orthodontic bracket effectively reduced the canine PDL stress from 80 kPa with no hook to 22 kPa with a hook 7 mm long. Angulating the force apically downward from 0° to 30° had a less significant effect on the PDL stress profile and initial canine deflection. The results suggest that stresses on miniscrew implants under load are sensitive to changes in diameter. Overtightening a miniscrew after placement might be a more likely cause of fracture failure and bone trauma than application of tangential orthodontic force. The reduction of stress along the PDL as a result of increasing the bracket hook length might account for steadier tooth translation by force application closer to the center of resistance of a single-rooted canine. The relatively minor effect of force angulation on the PDL response suggests that the vertical placement of miniscrews in keratinized or nonkeratinized tissue might not significantly affect orthodontic tooth movement. Conclusions This model can be adapted as a patient-specific clinical orthodontic tool for planning movement of 1 tooth or several teeth.

Abstract: Transient ultrasonic guided waves in anisotropic layered plates with finite and infinite width are presented in this article. A semianalytical finite-element method is adopted to study the guided waves in both infinite- and finite-width elastic plates. Three-noded beam elements in the thickness direction are used in infinite plate model, whereas the cross section of the finite-width plate is represented by nine-noded quadrilateral elements. Propagation in the axial direction is modeled by analytical wave functions. Elastodynamic Green’s functions are derived using modal summation in the frequency–wave number and time–space domains. Results for dispersion and transient analysis of guided waves in infinite nickel plates are presented and compared with those of finite-width plates. Group velocities are calculated and wave arrival times are computed for different plate cross sections. Numerical results show a significant influence of the plate aspect ratio on the dispersion and transient wave response. The co...

Abstract: Guided waves in a layered elastic plate of rectangular cross section (finite width and thickness) has been studied in this paper A semianalytical finite element method in which the deformation of the cross section is modeled by two-dimensional finite elements and analytical representation of propagating waves along the length of the plate has been used The method is applicable to arbitrary number of layers and general anisotropic material properties of each layer, and is similar to the stiffness method used earlier to study guided waves in a laminated composite plate of infinite width Numerical results showing the effect of varying the width of the plate on the dispersion of guided waves are presented and are compared with those for an infinite plate In addition, effect of thin anisotropic coating or interface layers on the guided waves is investigated

Abstract: The main objective of this article is to introduce a new nonlinear elastography based classification method for human breast masses. Multi-compression elastography imaging is elucidated in this study to differentiate malignant from benign lesions, based on their nonlinear mechanical behavior under compression. Three classification parameters were used and compared in this work: a new nonlinear parameter based on a power-law behavior of the strain difference between breast masses and healthy tissues, mass-soft tissue strain ratio and the mass relative volume between B-mode and elastography imaging. Using 3D elastography, these parameters were tested in vivo. A pilot study on 10 patients was performed, and results were compared with biopsy diagnosis as a gold standard. Initial elastography results showed a good agreement with biopsy outcomes. The new estimated nonlinear parameter had an average value of 0.163 ± 0.063 and 1.642 ± 0.261 for benign and malignant masses, respectively. Strain ratio values for the benign and malignant masses had an average value of 2.135 ± 0.707 and 4.21 ± 2.108, respectively. Relative mass volume was 0.848 ± 0.237 and 2.18 ± 0.522 for benign and malignant masses. In addition to the traditional normal axial strain, new strain types were used for elastography and constructed in 3D, including the first principal, maximum shear and Von Mises strains. The new strains provided an enhanced distinction of the stiff lesion from the soft tissue. In summary, the proposed elastographic techniques can be used as a noninvasive quantitative characterization tool for breast cancer, with the capability of visualizing and separating the masses in a three dimensional space. This may reduce the number of unnecessary painful breast biopsies.

Abstract: Accurate measurement of velocity profiles, multiple velocity vectors and local shear stress in arteries is very important for a variety of cardiovascular diseases. We have recently developed an ultrasound based velocimetry technique, termed echo particle image velocimetry (echo PIV). This method takes advantage of the nonlinear backscatter characteristics of ultrasound contrast microbubbles when exposed to certain ultrasonic forcing conditions. Preliminary in vitro, animal and clinical studies have shown significant promise of this method for measuring multiple velocity components with good temporal (up to 2 ms) and spatial (<1 mm) resolution. However, there is still difficulty in maximizing the nonlinearity of bubble backscatter using conventional Gaussian-pulse excitation techniques because: (1) significant harmonic components may not be produced at modest pressure amplitudes; and (2) the higher incident pressure amplitudes required to induce nonlinear behavior may cause bubble destruction. We present here a potential solution to this problem through the use of multifrequency excitation, where rectangular and triangular pulses with four harmonics are used to drive the bubble. The nonlinear behavior of the microbubble, as well as fragility and backscatter, were studied through numerical modeling via a modified Rayleigh-Plesset equation. Results show that the rectangular wave is effective in improving the visibility of microbubbles, with effective scattering cross-section area significantly higher (up to 35 times) than the widely-used Gaussian waveform. However, velocity and acceleration analysis of the bubble wall shows that the rectangular wave may threaten bubble stability. Due to lower wall velocity and acceleration, the triangular wave should decrease the potential for bubble destruction yet maintain relatively high second harmonic backscatter components. The impact of higher harmonics was studied by examining backscatter differences from incident rectangular and triangular pulses with four and two harmonics. Results indicate that a two-frequency excitation (which may be easier to implement practically) may be sufficient to induce nonlinear behavior of the microbubbles at modest incident pressures. These predictions provide support for the use of multifrequency driving to enhance echo PIV applications.

Abstract: Two of the most important prognostic indicators for breast cancer are tumor size and extent of axillary lymph node involvement. Data on 24,740 cases recorded in the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute were used to evaluate the breast cancer survival experience in a representative sample of women from the United States. Actuarial (life table) methods were used to investigate the 5-year relative survival rates in cases with known operative/pathologic axillary lymph node status and primary tumor diameter. Survival rates varied from 45.5% for tumor diameters equal to or greater than 5 cm with positive axillary nodes to 96.3% for tumors less than 2 cm and with no involved nodes. The relation between tumor size and lymph node status was investigated in detail. Tumor diameter and lymph node status were found to act as independent but additive prognostic indicators. As tumor size increased, survival decreased regardless of lymph node status; and as lymph node involvement increased, survival status also decreased regardless of tumor size. A linear relation was found between tumor diameter and the percent of cases with positive lymph node involvement. The results of our analyses suggest that disease progression to distant sites does not occur exclusively via the axillary lymph nodes, but rather that lymph node status serves as an indicator of the tumor's ability to spread.

Abstract: This paper deals with a semi-analytical finite element (SAFE) method for modeling wave propagation in waveguides of arbitrary cross-section. The method simply requires the finite element discretization of the cross-section of the waveguide, and assumes harmonic motion along the wave propagation direction. The general SAFE technique is extended to account for viscoelastic material damping by allowing for complex stiffness matrices for the material. The dispersive solutions are obtained in terms of phase velocity, group velocity (for undamped media), energy velocity (for damped media), attenuation, and cross-sectional mode shapes. Knowledge of these properties is important in any structural health monitoring attempt that uses ultrasonic guided waves. The proposed SAFE formulation is applied to several examples, including anisotropic viscoelastic layered plates, composite-to-composite adhesive joints and railroad tracks.

Abstract: Nanoparticle-based contrast agents are quickly becoming valuable and potentially transformative tools for enhancing medical diagnostics for a wide range of in-vivo imaging modalities. Compared with conventional molecular-scale contrast agents, nanoparticles (NPs) promise improved abilities for in-vivo detection and potentially enhanced targeting efficiencies through longer engineered circulation times, designed clearance pathways, and multimeric binding capacities. However, NP contrast agents are not without issues. Difficulties in minimizing batch-to-batch variations and problems with identifying and characterizing key physicochemical properties that define the in-vivo fate and transport of NPs are significant barriers to the introduction of new NP materials as clinical contrast agents. This manuscript reviews the development and application of nanoparticles and their future potential to advance current and emerging clinical bioimaging techniques. A focus is placed on the application of solid, phase-separated materials, for example metals and metal oxides, and their specific application as contrast agents for in-vivo near-infrared fluorescence (NIRF) imaging, magnetic resonance imaging (MRI), positron emission tomography (PET), computed tomography (CT), ultrasound (US), and photoacoustic imaging (PAI). Clinical and preclinical applications of NPs are identified for a broad spectrum of imaging applications, with commentaries on the future promise of these materials. Emerging technologies, for example multifunctional and theranostic NPs, and their potential for clinical advances are also discussed.