Abbas Samani - Academia.edu (original) (raw)

Papers by Abbas Samani

Proc. ISMRM 11th Annual Meeting, 2003

Synopsis To increase the displacement SNR in breast MR elastography, tissues are compressed signi... more Synopsis To increase the displacement SNR in breast MR elastography, tissues are compressed significantly. As a result, breast tissues undergo large deformations. This leads to significant geometric and material nonlinearities. In this study, methods for treating ...

2022 44th Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC)

2020 42nd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC)

Many types of cancers are associated with changes in tissue mechanical properties. This has led t... more Many types of cancers are associated with changes in tissue mechanical properties. This has led to the development of elastography as a clinically viable method where tissue mechanical properties are mapped and visualized for cancer detection and staging. In quasi-static ultrasound elastography, a mechanical stimulation is applied to the tissue using ultrasound probe. Using ultrasound radiofrequency (RF) data acquired before and after the stimulation, the tissue displacement field can be estimated. Elasticity image reconstruction algorithms use this displacement data to generate images of the tissue elasticity properties. The accuracy of the generated elasticity images depends highly on the accuracy of the tissue displacement estimation. Tissue incompressibility can be used as a constraint to improve the estimation of axial and, more importantly, the lateral displacements in 2D ultrasound elastography. Especially in clinical applications, this requires accurate estimation of the out-of-plane strain. Here, we propose a method for providing an accurate estimate of the out-of-plane strain which is incorporated in the incompressibility equation to improve the axial and lateral displacements estimation before elastography image reconstruction. The method was validated using in silico and tissue mimicking phantom studies, leading to significant improvement in the estimated displacement.

Tomography

Purpose: The aortic time-enhancement curve obtained from dynamic CT myocardial perfusion imaging ... more Purpose: The aortic time-enhancement curve obtained from dynamic CT myocardial perfusion imaging can be used to derive the cardiac output (CO) index based on the indicator dilution principle. The objective of this study was to investigate the effect of cardiac phase at which CT myocardial perfusion imaging is triggered on the CO index measurement with this approach. Methods: Electrocardiogram (ECG) gated myocardial perfusion imaging was performed on farm pigs with consecutive cardiac axial scans using a large-coverage CT scanner (Revolution, GE Healthcare) after intravenous contrast administration. Multiple sets of dynamic contrast-enhanced (DCE) cardiac images were reconstructed retrospectively from 30% to 80% R-R intervals with a 5% phase increment. The time-enhancement curve sampled from above the aortic orifice in each DCE image set was fitted with a modified gamma variate function (MGVF). The fitted curve was then normalized to the baseline data point unaffected by the streak a...

2019 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2019

Radiation therapy (RT) is an important component of treatment for lung cancer. However, the accur... more Radiation therapy (RT) is an important component of treatment for lung cancer. However, the accuracy of this method can be affected by the complex respiratory motion/deformation of the target tumor during treatment. To improve the accuracy of RT, patient-specific biomechanical models of the lung have been proposed for estimating the tumor’s respiratory motion/deformation. Chronic obstructive pulmonary disease (COPD) has a high incidence among lung cancer patients and is associated with heterogeneous destruction of lung parenchyma. This key heterogeneity element, however, has not been incorporated in lung biomechanical models developed in previous studies. In this work, we have developed a physiologically and patho-physiologically realistic lung biomechanical model that accounts for lung tissue heterogeneity. Four-dimensional computed tomography (4DCT) images were used to build a patient-specific finite element (FE) model of the lung. Image information was used to identify and incorporate inhomogeneities within the model. Mechanical properties of normal and diseased regions in the lung and the transpulmonary pressure driving the respiratory motion were estimated using an optimization algorithm that maximizes the similarity between the actual and simulated tumor and lung image data. Results from this proof of concept study on a lung cancer patient indicated improved accuracy of tumor motion estimation when COPD-induced lung tissue heterogeneities were incorporated in the model.

2018 IEEE International Symposium on Medical Measurements and Applications (MeMeA), 2018

This paper presents an accurate technique for measuring electrical permittivity (EP) of small bio... more This paper presents an accurate technique for measuring electrical permittivity (EP) of small biological tissue specimens at low frequencies while measurement sensitivity to specimen geometry and tissue specimen inhomogeneity is investigated. Accurate EP measurement of various biological tissues, including healthy and pathological tissues, can pave the way for a wide range of medical applications. This novel technique utilizes a high precision hardware for impedance measurement of a capacitive structure formed by two conductive plates and the tissue specimen as its dielectric. The capacitance part of the measured impedance is processed using an inverse finite element framework to determine the tissue electrical permittivity. This framework considers specimen's accurate geometry and boundary conditions. After successful validation, the technique was employed to measure electrical permittivity of several specimens of bovine heart, liver and bone tissues. The proposed technique is reliable and is expected to offer improved measurement accuracy and repeatability of electrical permittivity of multi-layered tissue specimens, especially at low frequencies.

Lung Imaging and CADx, 2019

هلاقم تاعلاطا هدیکچ لماک یشهوژپ هلاقم :تفایرد 20 دنفسا 1395 :شریذپ 24 تشهبیدرا 1396 :تیاس رد هئار... more هلاقم تاعلاطا هدیکچ لماک یشهوژپ هلاقم :تفایرد 20 دنفسا 1395 :شریذپ 24 تشهبیدرا 1396 :تیاس رد هئارا 09 ریت 1693 تمسق رد هک تسا مرن یلیخ دنبمه تفاب زا یعون ،یبرچ تفاب نآ زا .تسا هدش عیزوت ندب فلتخم یاه یکیژولوتاپ طیارش زا یرایسب رد هک ییاج یرامیب و یم رییغت شوختسد یبرچ تفاب راتخاسزیر یکیناکم صاوخ ،یبرچ تفاب هب طوبرم یاه قیقد لدم کی هئارا ،دوش تهج یراتخاس هصخشم نیا زا .تسا دنمشزرا رایسب یبرچ تفاب راتخاسزیر یکیناکم صاوخ یبای یژولوفروم و یژولوتسیه تاعلاطا زا هدافتسا اب هلاقم نیا رد ،ور مهرب لح شور یانبمرب یراتخاس لدم کی ،یبرچ تفاب لولس لدم نیا رد .تسا هدش هئارا دماج و لایس شنک هب یبرچ یاه هرک تروص زا ییاه نیب سیرتام و لایس سنج هب یلولس نیب سیرتام راتفر فیصوت یارب .تسا هدش لدم دماج تروص لدم زا یلولس کیتسلاارپیاه یداینب یاه لدم نیا زا کی ره هب طوبرم یاهرتماراپ .تسا هدش هدافتسا هداد زا هدافتسا اب سوکعم هلأسم لح اب اه کت راشف شیامزآ هب طوبرم یبرجت یاه هنومن یور رب یروحم هب یبرچ تفاب یاه هب جیاتن .دندمآ تسد یم ناشن هدمآ تسد هداد اب بسانم قباطت هب هجوت اب هدش هئارا لدم هک دهد یاه لدم رد ییلااب...

2020 42nd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), 2020

Cancer is known to induce significant structural changes to tissue. In most cancers, including br... more Cancer is known to induce significant structural changes to tissue. In most cancers, including breast cancer, such changes yield tissue stiffening. As such, imaging tissue stiffness can be used effectively for cancer diagnosis. One such imaging technique, ultrasound elastography, has emerged with the aim of providing a low-cost imaging modality for effective breast cancer diagnosis. In quasi-static breast ultrasound elastography, the breast is stimulated by ultrasound probe, leading to tissue deformation. The tissue displacement data can be estimated using a pair of acquired ultrasound radiofrequency (RF) data pertaining to pre- and post-deformation states. The data can then be used within a mathematical framework to construct an image of the tissue stiffness distribution. Ultrasound RF data is known to include significant noise which lead to corruption of estimated displacement fields, especially the lateral displacements. In this study, we propose a tissue mechanics-based method aiming at improving the quality of estimated displacement data. We applied the method to RF data acquired from a tissue-mimicking phantom. The results indicated that the method is effective in improving the quality of the displacement data.

Computers in biology and medicine, 2021

Medical imaging derived cardiac biomechanical models offer a wealth of new information to be used... more Medical imaging derived cardiac biomechanical models offer a wealth of new information to be used in diagnosis and prognosis of cardiovascular disease. A noteworthy feature of such models is the ability to predict myofiber contraction stresses during acute or chronic ischemic events. Current techniques for heterogeneous contraction models require tissue motion tracking capabilities which are neither available on all imaging modalities, nor currently used in the clinic. Proposed in this article is a proof of concept of a tissue tracking independent technique focused on shape optimization to predict the contraction stresses of in-silico left ventricle models simulating various acute myocardial infarction events. The technique involves three variables defined in the left ventricle muscle. Two of the variables represent the contraction stresses in the healthy and infarct regions while the third is a novel periinfarct variable defining a non-contracting myofiber state allowing finer clas...

Lung’s air volume estimation is of great importance in lung disease diagnosis. In this paper a fu... more Lung’s air volume estimation is of great importance in lung disease diagnosis. In this paper a fully automatic algorithm, which we presented recently to estimate the lung’s air volume from CT-images, is more developed. In this algorithm, first a suitable cost function is introduced based on the long parenchyma physics to determine the voxels of lung’s air region. In this paper, a fully automatic framework is proposed to calculate the initial guess for the solution of the optimization problem. Moreover, a 3D model reconstruction technique is utilized to determine spatial localization of the lung’s air region in 3D CT-images. Furthermore, the performance of the whole-lung-volume-based methods and direct lung’s air volume measurment methods are compared and investigated. In order to evaluate the accuracy, porcine’s lung images and clinical human’s lung images from reliable databases are fed to the proposed algorithm. The significant accuracy and robust performance of the proposed algor...

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2021

Computerized Medical Imaging and Graphics, 2021

Dual-modality 4D cardiac data visualization can convey a significant amount of complementary imag... more Dual-modality 4D cardiac data visualization can convey a significant amount of complementary image information from various sources into a single and meaningful display. Even though there are existing publications on combining multiple medical images into a unique representation, there has been no work on rendering a series of cardiac image sequences, acquired from multiple sources, using web browsers and synchronizing the result over the Internet in real time. The ability to display multi-modality beating heart images using Web-based technology is hampered by the lack of efficient algorithms for fusing and visualizing constantly updated multi-source images and streaming the rendering results using internet protocols. To address this practical issue, in this paper we introduce a new Internet-based algorithm and a software platform running on a Node.js server, where a series of registered cardiac images from both magnetic resonance (MR) and ultrasound are employed to display dynamic fused cardiac structures in web browsers. Taking advantage of the bidirectional WebSocket protocol and WebGL-based graphics acceleration, internal cardiac structures are dynamically displayed, and the results of rendering and data exploration are synchronized among all the connected client computers. The presented research and software have the potential to provide clinicians with comprehensive information and intuitive feedback relating to cardiac behavior and anatomy and could impact areas such as distributed diagnosis of cardiac function and collaborative treatment planning for various heart diseases.

Computer Methods in Biomechanics and Biomedical Engineering, 2017

Computational models are effective tools to study cardiac mechanics under normal and pathological... more Computational models are effective tools to study cardiac mechanics under normal and pathological conditions. They can be used to gain insight into the physiology of the heart under these conditions while they are adaptable to computer assisted patient-specific clinical diagnosis and therapeutic procedures. Realistic cardiac mechanics models incorporate tissue active/passive response in conjunction with hyperelasticity and anisotropy. Conventional formulation of such models leads to mathematically-complex problems usually solved by custom-developed non-linear finite element (FE) codes. With a few exceptions, such codes are not available to the research community. This article describes a computational cardiac mechanics model developed such that it can be implemented using off-the-shelf FE solvers while tissue pathologies can be introduced in the model in a straightforward manner. The model takes into account myocardial hyperelasticity, anisotropy, and active contraction forces. It follows a composite tissue modeling approach where the cardiac tissue is decomposed into two major parts: background and myofibers. The latter is modelled as rebars under initial stresses mimicking the contraction forces. The model was applied in silico to study the mechanics of infarcted left ventricle (LV) of a canine. End-systolic strain components, ejection fraction, and stress distribution attained using this LV model were compared quantitatively and qualitatively to corresponding data obtained from measurements as well as to other corresponding LV mechanics models. This comparison showed very good agreement.

SSRN Electronic Journal, 2020

There is growing awareness that brain mechanical properties are important for neural development ... more There is growing awareness that brain mechanical properties are important for neural development and health. Yet, published values of brain stiffness differ by orders of magnitude from ex vivo to in vivo, pointing to a general lack of understanding of the complex mechanical behavior of brain tissue. We here show that there is no fundamental disparity between ex vivo and in vivo data when considering large-scale properties of the entire brain. Using numerical simulations and novel real-time magnetic resonance elastography we investigated the viscoelastic dispersion of the human brain in, so far, unexplored dynamic ranges from intrinsic brain pulsations at 1Hz to externally induced harmonic vibrations at 40Hz. Surprisingly, we observed variations in brain stiffness over more than two orders of magnitude, suggesting that the in vivo human brain is superviscous on large scales with very low shear modulus of 42±13 Pa and relatively high viscosity of 6.6±0.3 Pa•s according to the two-parameter solid model. Our data shed light on the crucial role of fluid compartments including blood vessels and cerebrospinal fluid (CSF) for whole brain properties and provide, for the first time, an explanation for the variability of the mechanical brain responses to manual palpation, local indentation, and high-dynamic tissue stimulation as used in elastography.

Computer Methods in Biomechanics and Biomedical Engineering, 2016

Abstract For studying cardiac mechanics, hyperelastic anisotropic computational models have been ... more Abstract For studying cardiac mechanics, hyperelastic anisotropic computational models have been developed which require the tissue anisotropic and hyperelastic parameters. These parameters are obtained by tissue samples mechanically testing. The validity of such parameters are limited to the specific tissue sample only. They are not adaptable for pathological tissues commonly associated with tissue microstructure alterations. To investigate cardiac tissue mechanics, a novel approach is proposed to model hyperelasticity and anisotropy. This approach is adaptable to various tissue microstructural constituent’s distributions in normal and pathological tissues. In this approach, the tissue is idealized as composite material consisting of cardiomyocytes distributed in extracellular matrix (ECM). The major myocardial tissue constituents are mitochondria and myofibrils while the main ECM’s constituents are collagen fibers and fibroblasts. Accordingly, finite element simulations of uniaxial and equibiaxial tests of normal and infarcted tissue samples with known amounts of these constituents were conducted, leading to corresponding tissue stress–strain data that were fitted to anisotropic/hyperelastic models. The models were validated where they showed good agreement characterized by maximum average stress-strain errors of 16.17 and 10.01% for normal and infarcted cardiac tissue, respectively. This demonstrate the effectiveness of the proposed models in accurate characterization of healthy and pathological cardiac tissues.

IEEE Transactions on Instrumentation and Measurement, 2019

This paper proposes a technique aimed at accurate measurement of electrical permittivity (EP) of ... more This paper proposes a technique aimed at accurate measurement of electrical permittivity (EP) of small tissue specimens at low frequencies. Accurate measurement of EP of healthy and pathological tissues can facilitate the establishment of many medical applications such as electrical impedance imaging. The proposed novel technique employs hardware with high precision for impedance measurement of capacitive structures formed by the tissue specimen as its dielectric combined with two conductive plates placed at two ends of the specimen. To determine the EP of the tissue specimen, the capacitance part of the measured impedance is processed using an inverse finite-element framework. In this framework, accurate geometry and boundary conditions of the specimen are considered. The proposed technique was validated before it was employed to measure EP of several tissue specimens including bovine heart, liver, and bone. Results obtained in this investigation indicate that the proposed technique is reliable as it provides improved EP measurement accuracy and repeatability of homogeneous or multilayered tissue specimens, especially at low-frequency range.

Journal of the Mechanical Behavior of Biomedical Materials, 2018

Finite element (FE)-based biomechanical simulations of the upper airway are promising computation... more Finite element (FE)-based biomechanical simulations of the upper airway are promising computational tools to study abnormal upper airway deformations under obstructive sleep apnea (OSA) conditions and to help guide minimally invasive surgical interventions in case of upper airway collapse. To this end, passive biomechanical properties of the upper airway tissues, especially oropharyngeal soft tissues, are indispensable. This research aimed at characterizing the linear elastic mechanical properties of the oropharyngeal soft tissues including palatine tonsil, soft palate, uvula, and tongue base. For this purpose, precise indentation experiments were conducted on freshly harvested human tissue samples accompanied by FE-based inversion schemes. To minimize the impact of the probable nonlinearities of the tested tissue samples, only the first quarter of the measured force-displacement data corresponding to the linear elastic regime was utilized in the FE-based inversion scheme to improve the accuracy of the tissue samples' Young's modulus calculations. Measured Young's moduli of the oropharyngeal soft tissues obtained in this study are presented. They include first estimates for palatine tonsil tissue samples while measured Young's moduli of other upper airway tissues were obtained for the first time using fresh human tissue samples.

The Journal of the Acoustical Society of America, 2017

Breast cancer is the most common cancer in women worldwide. Its early detection is paramount for ... more Breast cancer is the most common cancer in women worldwide. Its early detection is paramount for its successful treatment outcome. Among imaging techniques developed for breast cancer diagnosis, elastography has shown good promise. In this presentation, a breast ultrasound elastography method will be described, and its application in breast cancer patients will be demonstrated. The method follows the quasi-static elastography approach where the breast is stimulated using regular ultrasound transducer. RF data are utilized within a dynamic programming minimization algorithm for tissue motion tracking, leading to 2D (axial + lateral) strain field. This field is processed within a novel inverse finite-element reconstruction framework to reconstruct the breast Young's modulus distribution. The framework uses Hooke's law to obtain the Young's modulus distribution. It is iterative where the stress distribution is updated using finite element method at the end of each reconstruction iteration. To ensure converge...

Measurement, 2017

Previous studies have shown that dielectric properties of biological tissues can be imaged at hig... more Previous studies have shown that dielectric properties of biological tissues can be imaged at high frequencies (50 MHz-20 GHz) to detect abnormalities such as tumors. While evidence suggests that imaging these properties at low frequencies (e.g. below 1 MHz) holds a good potential in medical applications, less research efforts have been dedicated to explore these properties at such frequencies for medical imaging. This study uses a recently developed technique to measure tissue dielectric properties of normal and corresponding cancerous tissue at low frequencies. This was accomplished by using a preclinical animal tumor model. To develop this animal model, human breast cancer cell line (MDA-MB-231) was injected into hind legs of severely compromised immunodeficient (SCID) mice. As a result, tumors were developed while they were permitted to grow to the size of 8-10 mm in 8 weeks. The electrical conductivity and permittivity (EC and EP) of the grown xenograft tumors and their surrounding normal tissue were measured at 100 Hz-1 MHz frequency using a measurement method which includes using a custom-made experimental setup in conjunction with an inverse finite element framework. Histological analysis was performed on the tumor and normal tissue specimens to assess differences in their micro-structure. Results indicated that both conductivity and permittivity of the tumors have significantly greater values than those of the surrounding normal tissue with average ratio values of 3.5:1 and 10.9:1 for the EC and EP, respectively. Results obtained in this study are consistent with microstructural changes observed by histological assessment. The substantially high EP ratios measured in this study suggests that electrical permittivity at low frequencies can potentially be used as a powerful biomarker for the detection of breast malignancies.