Showing papers by "Osama M. Mukdadi published in 2009"

In vivo vascular wall tissue characterization using a strain tensor measuring (STM) technique for flow-mediated vasodilation analyses.

Abstract: Endothelial dysfunction is considered to be a key factor in the development of atherosclerosis, and the measurement of flow-mediated vasodilation (FMD) in brachial and other conduit arteries has become a common method to assess the status of endothelial function in vivo. Based on the direct relationship between the FMD response and local shear stress on the conduit brachial artery endothelium, we hypothesize that measuring relevant changes in the brachial wall strain tensor would provide a non-invasive tool for assessing vascular mechanics during post-occlusion reactive hyperemia. Direct measurement of the wall strain tensor due to FMD has not yet been reported in the literature. In this work, a noninvasive direct ultrasound-based strain tensor measuring (STM) technique is presented to assess changes in the mechanical parameters of the vascular wall during post-occlusion reactive hyperemia and/or FMD, including local velocities and displacements, diameter change, local strain tensor and strain rates. The STM technique utilizes sequences of B-mode ultrasound images as its input with no extra hardware requirement, and its algorithm starts with segmenting a region of interest within the artery and providing the acquisition parameters. Then a block matching technique based on speckle tracking is employed to measure the frame-to-frame local velocities. Displacements, diameter change, local strain tensor and strain rates are then calculated by integrating or differentiating velocity components. The accuracy of the STM algorithm was assessed in vitro using phantom studies, where an average error of 7% was reported using different displacement ranging from 100 µm to 1000 µm. Furthermore, in vivo studies using human subjects were performed to test the STM algorithm during pre- and post-occlusion. Good correlations (|r| >0.5, P < 0.05) were found between the post-occlusion responses of diameter change and local wall strains. Results indicate the validity and versatility of the STM algorithm and describe how parameters other than the diameter change are sensitive to reactive hyperemia following occlusion. This work suggests that parameters such as local strains and strain rates within the arterial wall are promising metrics for the assessment of endothelial function, which can then be used for accurate assessment of atherosclerosis. In summary, this study describes a simple and computationally efficient algorithm that can be integrated with ultrasound machines for vascular research. Moreover, it suggests that monitoring the local strain and strain rates of the brachial artery wall can replace or augment the measurement of arterial diameter in FMD studies.

High-Frequency Ultrasound Tissue Classification of Atherosclerotic Plaques in an APOE-KO Mouse Model Using Spectral Analysis

Abstract: Small animal models have been widely used in cardiovascular research when studying the development and treatment of different diseases. This kind of research has promoted the development of noninvasive techniques to assess cardiac tissue and blood vessels of small animals. Recently, we have developed a high-frequency ultrasound imaging system for small animals, in particular, mouse and rat models. In this work, we aim to elucidate the usefulness of using spectral analysis of the received radiofrequency (RF) ultrasound signals to extract quantitative parameters to assess mechanical properties of cardiac and vascular tissues. A custom system that employs high-frequency single-element ultrasound transducers (30–120 MHz) is used for scanning. Various signal and image processing techniques are applied on the received ultrasound signals to reconstruct high resolution B-mode and spectral images. In vitro imaging of isolated heart and vessels of APOE-KO “knock-out” mouse model with atherosclerosis was performed. Power spectral densities (PSD) of RF signals were evaluated within various regions of interests (ROI) including degassed water, normal cardiac tissue, and cardiac tissue with atheroma. Various parameters were extracted from the power spectrum such as the maximum power (Pmax ), the frequency at maximum power (Fpeak ), and the variance of power spectrum (Pvar ). Results of the preliminary spectral analysis indicated larger values for the Pmax , Fpeak , and Pvar parameters for ROI contains atheroma than other regions. For example using the envelop data, the normalized maximum power (Pmax ) value for cardiac tissue with atheroma was 0.0 ± 0.789 (dB), whereas for normal tissues it was about −13.71± 0.267 (dB). These results suggest the use spectral images as a quantitative method when assessing mouse hearts and blood vessels noninvasively.Copyright © 2009 by ASME

Effect of subdicing on the dispersion and resonance behavior of elastic guided waves in 1D array ultrasound transducers

Abstract: 1D array ultrasound subdicing is a common fabrication practi ce to avoid the presence of lateral modes near the center frequency of the transducer The objective of this study is to theoretically analyze the effect of subdicing depth and width on the dispersion and resonance behavior of elastic guided wave propagation in 1D array transducers The transducer is modeled as a periodic structure with the representative cell composed of one element A semi-analytical finite-element (SAFE) method is derived to obtain the disper sion curves, group velocity and resonance mode shapes of a piezoelectric structure with arbitrary cross-section and periodic boundary conditions Results indicate that resonant modes can occur at cutoff frequencies (wavenumber k = 0), where the phase velocity is infinite Moreover, another interesting resonance behavior at zero-group-velocity (ZGV) points (wavenumber k  0) is observed where the phase velocity is finite Theoretical results show that subdicing increases the number of wavegui de modes, lowers the cut-off frequencies, increases the number of ZGV points and lowers the group velocities for flexural and extensional modes Lower values of subdicing depth tend to increase the cut-of f frequencies, but subdicing widt h has a minor effect on the dispersion curves These important changes of the dispersion behavior are likely to influence the resonance characteristics and the bandwidth of the transducer The analysis presented in this study provides a useful tool to optimize the design of 1D array ultrasound transducers and to gain better understanding of the complicated acoustic behavior of 1D array ultrasound transducers Keywords: Guided Waves Dispersion, Zero-Group Velocity, 1D Ultrasound Transducer Array

Patient-Specific 3D Finite-Element Analysis of Miniscrew Implants During Orthodontic Treatment

Abstract: Miniscrew implants have seen increasing clinical use as orthodontic anchorage devices with demonstrated stability. The focus of this study is to develop and simulate operative factors, such as load magnitudes and anchor locations to achieve desired motions in a patient-specific 3D model undergoing orthodontic treatment with miniscrew implant anchorage. A CT scan of a patient skull was imported into Mimics software (Materialise, 12.1). Segmentation operations were performed on the images to isolate the mandible, filter out noise, then reconstruct a smooth 3D model. A model of the left canine was reconstructed with the PDL modeled as a thin solid layer. A miniscrew was modeled with dimensions based on a clinical implant (BMK OAS-T1207) then inserted into the posterior mandible. All components were volumetrically meshed and optimized in Mimics software. Elements comprising the mandible bone and teeth were assigned a material based on their gray value ranges in HU from the original scan, and meshes were exported into ANSYS software. All materials were defined as linear and isotropic. A nonlinear PDL was also defined for comparison. For transverse forces applied on the miniscrew, maximum stresses increased linearly with loading and appeared at the neck or first thread and in the cortical bone. A distal tipping force was applied on the canine, and maximum stresses appeared in the tooth at the crown and apex and in the bone at the compression surface. Under maximum loading, stresses in bone were sufficient for resorption. The nonlinear PDL exhibited lower stresses and deflections than the linear model due to increasing stiffness. Numerous stress concentrations were seen in all models. Results of this study demonstrate the potential of patient-specific 3D reconstruction from CT scans and finite-element simulation as a versatile and effective pre-operative planning tool for orthodontists.© 2009 ASME

High frequency 3D echodentographic imaging modality for early assessment of periodontal diseases: in vitro study

Abstract: The use of ultrasound in dentistry is still an open growing area of research. Currently, there is a lack of imaging modalities to accurately predict minute structures and defects in the jawbone. In particular, the inability of 2D radiographic images to detect bony periodontal defects resulted from infection of the periodontium. This study investigates the feasibility of high frequency ultrasound to reconstruct high resolution 3D surface images of human jawbone. Methods: A dentate and non-dentate mandibles were used in this study. The system employs high frequency single-element ultrasound focused transducers (15-30 MHz) for scanning. Continuous acquisition using a 1 GHz data acquisition card is synchronized with a high precision two-dimensional stage positioning system of ±1 µm resolution for acquiring accurate and quantitative measurements of the mandible in vitro. Radio frequency (RF) signals are acquired laterally 44-45.5 µm apart for each frame. Different frames are reconstructed 500 µm apart for the 3D reconstruction. Signal processing algorithms are applied on the received ultrasound signals for filtering, focusing, and envelope detection before frame reconstruction. Furthermore, an edge detection technique is adopted to detect the bone surface in each frame. Finally, all edges are combined together in order to render a 3D surface image of the jawbone. Major anatomical landmarks on the resultant images were confirmed with the anatomical structures on the mandibles to show the efficacy of the system. Comparison were also made with conventional 2D radiographs to show the superiority of the ultrasound imaging system in diagnosing small defects in the lateral, axial and elevation planes of space. Results: The landmarks on all ultrasound images matched with those on the mandible, indicating the efficacy of the system in detecting small structures in human jaw bones. Comparison with conventional 2D radiographic images of the same mandible showed superiority of the 3D ultrasound images in detecting defects in the elevation plane of space. These results suggest that the high frequency ultrasound system shows great potential in providing a non-invasive method to characterize the jawbone and detect periodontal diseases at earlier stages.

Surface Acoustic Wave Sensors Deposited on AlN Thin Films

Abstract: Over the past few decades, there has been considerable research and advancement in surface acoustic wave (SAW) technology. At present, SAW devices have been highly successful as frequency band pass filters for the mobile telecommunications and electronics industries. In addition to their inherent frequency selectivity, SAW devices are also highly sensitive to surface perturbations. This sensitivity, along with a relative ease of manufacture, makes SAW devices ideally suited for many sensing applications including mass, pressure, temperature, and biosensors. In the area of biosensing, surface plasmon resonance (SPR) and quartz crystal microbalances (QCM) are still in the forefront of research and development, but advancement in SAW sensors could prove to have significant advantages over these technologies. This study investigates the advantages of using aluminum nitride (AlN) as a material for SAW sensors. AlN retains its piezoelectric properties at relatively high temperatures when compared to more common piezoelectric materials such as lead zirconium titanate (PZT), lithium tantalate (LiTaO3) and zinc oxide (ZnO). AlN is also a very robust material making it suitable for biosensing applications where the sensing target is selectively absorbed by an active layer on the device which may attack the piezoelectric layer. AlN thin films of different thicknesses have been deposited on Si substrates by DC reactive sputtering. Rayleigh-wave SAW devices have been fabricated by the deposition of platinum contacts and interdigital transducers (IDTs) onto AlN thin films using standard photolithographic processes. Experiments have been conducted to measure Rayleigh velocities, resonant frequencies, and insertion loss. Experimental results are compared to theoretical calculations.

Simple fast noninvasive technique for measuring brachial wall mechanics during flow mediated vasodilatation analysis

Abstract: Measurement of flow-mediated vasodilatation (FMD) in brachial and other conduit arteries has become a common method to asses the status of endothelial function in vivo. In spite of the direct relationship between the arterial wall multi-component strains and FMD responses, direct measurement of wall strain tensor due to FMD has not yet been reported in the literature. In this work, a noninvasive direct ultrasound-based strain tensor measuring (STM) technique is presented to assess changes in the mechanical parameters of the vascular wall during FMD. The STM technique utilizes only sequences of B-mode ultrasound images, and starts with segmenting a region of interest within the artery and providing the acquisition parameters. Then a block matching technique is employed to measure the frame to frame local velocities. Displacements, diameter change, multi-component strain tensor and strain rates are then calculated by integrating or differentiating velocity components. The accuracy of the STM algorithm was assessed using a phantom study, and was further validated using in vivo data from human subjects. Results indicate the validity and versatility of the STM algorithm, and describe how parameters other than the diameter change are sensitive to pre- and post-occlusion, which can then be used for accura te assessment of atherosclerosis. Keywords: Atherosclerosis; Vascular Wall Mechanics; Flow Me diated Vasodilatation; Strain Tensor Measurement