Jahan Tavakkoli

Jahan Tavakkoli
Ryerson University · Department of Physics

PhD

About

96
Publications
18,089
Reads
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1,111
Citations
Additional affiliations
February 2011 - present
St. Michael’s Hospital
Position
  • Affiliate Scientist
June 2007 - present
Ryerson University
Position
  • Professor (Associate)

Publications

Publications (96)
Conference Paper
Full-text available
Nonlinear ultrasound modeling is finding an increasing number of applications in both medical and industrial areas where due to high pressure amplitudes the effects of nonlinear propagation are no longer negligible. Taking nonlinear effects into account makes the ultrasound beam analysis more accurate in these applications. One of the most widely u...
Article
Full-text available
A time-domain numerical model is presented for simulating the finite-amplitude focused acoustic pulse propagation in a dissipative and nonlinear medium with a symmetrical source geometry. In this method, the main effects responsible in finite-amplitude wave propagation, i.e., diffraction, nonlinearity, and absorption, are taken into account. These...
Article
Full-text available
A computationally efficient model capable of simulating finite-amplitude ultrasound beam propagation in water and in tissue from phased linear arrays and other transducers of arbitrary quasiplanar geometry is described. It is based on a second-order operator splitting approach [Tavakkoli et al., J. Acoust. Soc. Am. 104, 2061-2072 (1998)], with a fr...
Article
Purpose A real-time and non-invasive thermometry technique is essential in thermal therapies to monitor and control the treatment. Ultrasound is an attractive thermometry modality due to its relatively high sensitivity to change in temperature and fast data acquisition and processing capabilities. A temperature-sensitive acoustic parameter is requi...
Article
Full-text available
Objective: This work aims to determine whether photoacoustic (PA) thermometry from a commercially available PA imaging system can be used to control the temperature in nanoparticle-mediated thermal therapies. Methods: The PA imaging system was interfaced to obtain PA images while scanning ex-vivo tissue. These images were then used to obtain tem...
Article
Skull bone represents a highly acoustical impedance mismatch and a dispersive barrier for the propagation of acoustic waves. Skull distorts the amplitude and phase information of the received waves at different frequencies in a transcranial brain imaging. We study a novel algorithm based on vector space similarity model for the compensation of the...
Article
Full-text available
The pathophysiological events of secondary brain injury contribute to poor outcome after traumatic brain injury (TBI). The neuroprotective effects of mesenchymal cells have been extensively studied and evidence suggests that their effects are mostly mediated through paracrine effects. Human umbilical cord perivascular cells (HUCPVCs) are mesenchyma...
Article
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Traumatic brain injury due to primary blast exposure is a major cause of ongoing neurological and psychological impairment in soldiers and civilians. Animal and human evidence suggests that low-level blast exposure is capable of inducing white matter injury and behavioural deficits. There are currently no effective therapies to treat the underlying...
Article
Full-text available
This paper proposes a new numerical framework to simulate ultrasound wave propagation in 3D viscoelastic heterogeneous media based on the elastodynamic wave equation including a 3D second-order time-domain perfectly matched layer formulation. A finite difference discretization of this formulation is presented, along with a stability analysis. The r...
Article
Full-text available
Although transcranial photoacoustic imaging has been previously investigated by several groups, there are many unknowns about the distorting effects of the skull due to the impedance mismatch between the skull and underlying layers. The current computational methods based on finite-element modeling are slow, especially in the cases where fine grids...
Article
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Background The main goal of ultrasound therapy is to have clinical effects in the tissue without damage to the intervening and surrounding tissues. Treatments have been developed for both in vitro and in clinical applications. HIFU therapy is one of these. Non-invasive surgeries, such as HIFU, have been developed to treat tumors or to stop bleeding...
Article
Full-text available
Purpose: A real-time noninvasive thermometry technique is required to estimate the temperature distribution during hyperthermia to monitor and control the treatment. The main objective of this study is to demonstrate the possibility of detecting change in backscatter energy (CBE) of acoustic harmonics in tissue-mimicking gel phantoms and ex vivo bo...
Thesis
An axial-transmission ultrasound device (Omnisense Quantitative Ultrasound Bone Sonometer [Omnisense, Sunlight, Medical Ltd., Rehovot, Israel]) was used in this study to measure the speed of sound along bone-mimicking phantoms and ex vivo animal bone samples. The clinical objectives were to determine if sound waves could be used to detect and quant...
Article
Full-text available
Background During the past few decades, high-intensity focused ultrasound (HIFU) modality has been gaining surging interest in various therapeutic applications such as non- or minimally-invasive cancer treatment. Among other attributes, robust and real-time HIFU treatment monitoring and lesion detection have become essential issues for successful c...
Article
Compressive sensing theory has in recent years been increasingly used in various pattern recognition applications. Compressive sensing theory makes it possible, under certain assumptions, to recover a signal or an image sampled below the Nyquist sampling limit. In this work, a new application of compressive sensing based on the threshold algorithm,...
Article
Purpose: Dual-energy X-ray absorptiometry (DXA) is the gold standard technique to measure areal bone mineral density (aBMD) for the diagnosis of osteoporosis. Because DXA relies on the attenuation of photon to estimate aBMD, deposition of bone-seeking metallic elements such as strontium, lead and aluminum that differ in atomic numbers from calcium...
Conference Paper
This paper presents a method for modeling and simulation of shear wave generation from a nonlinear Acoustic Radiation Force Impulse (ARFI) that is considered as a distributed force applied at the focal region of a HIFU transducer radiating in nonlinear regime. The shear wave propagation is simulated by solving the Navier’s equation from the distrib...
Conference Paper
Non-invasive tissue temperature estimation is important in thermal therapies for having an efficient treatment. A noninvasive ultrasonic technique for monitoring tissue temperature changes is proposed based on the changes in the harmonics of ultrasoundbackscatter as a function of temperature. The backscatteredpressure amplitudes of the fundamental...
Article
Purpose:Bone quantity, as determined by the current gold standard, dual energy X-ray absorptiometry (DXA), through measured areal bone mineral density (aBMD), is subject to positive biases if bone strontium levels are high. This is of particular concern for populations administered strontium-based compounds for the treatment of osteoporosis. This s...
Article
Traumatic brain injury (TBI) is a leading cause of death and morbidity in industrialized countries with considerable associated healthcare costs. The cost and time associated with preclinical development of TBI therapeutics is lengthy and expensive with a poor track record of successful translation to the clinic. The zebrafish is an emerging model...
Article
Full-text available
High intensity focused ultrasound (HIFU) is a form of thermal ablation technique which can treat a variety of medical afflictions. One promising therapeutic use is the permanent destruction of nerves non-invasively in patients with severe spasticity or certain types of pain (e.g. phantom limb pain). To this end, HIFU requires ultrasound guidance wh...
Conference Paper
Shear Wave Elastography (SWE) is a quantitative ultrasound-based imaging modality for distinguishing normal and abnormal tissue types by estimating the local viscoelastic properties of the tissue. These properties have been estimated in many studies by propagating ultrasound shear wave within the tissue and estimating parameters such as speed of wa...
Conference Paper
Full-text available
In this study, the feasibility of obtaining 2D temperature change maps was investigated by estimating the change in backscattered energy of the acoustic harmonics and comparing it with the standard RF echo shift technique. A commercial high-frequency ultrasound scanner (Vevo R 770, Visualsonics Inc., Toronto, ON, Canada) with a 25-MHz center freque...
Conference Paper
The resolution of conventional single-element ultrasound imaging varies spatially and depends on several factors, such as the central frequency, bandwidth, and the transducer’s active aperture size. Synthetic aperture focusing techniques (SAFT) enable dynamic focusing, which, among others, could lead to improvements in the spatial resolution of ult...
Article
The Advanced Biomedical Ultrasound Imaging and Therapy Laboratory (ABUITL), a 1600 square-foot research laboratory jointly affiliated to Ryerson University and St. Michael's Hospital, is one of the leading research laboratories in the field of biomedical ultrasound in Canada. The laboratory was established in 2007 in the Dept. of Physics, Ryerson U...
Article
Full-text available
Ultrasound-based thermometry requires a temperature-sensitive acoustic parameter that can be used to estimate the temperature by tracking changes in that parameter during heating. The objective of this study is to investigate the temperature dependence of acoustic harmonicsgenerated by nonlinearultrasoundwave propagation in water at various pulse t...
Article
Full-text available
High-intensity focused ultrasound (HIFU) is a novel treatment modality used by scientists and clinicians in the recent decades. This modality has had a great and significant success as a noninvasive surgery technique applicable in tissue ablation therapy and cancer treatment. In this study, radio frequency (RF) ultrasound signals were acquired and...
Article
Full-text available
Hyperthermia is a cancer treatment technique that could be delivered as a stand-alone modality or in conjunction with chemotherapy or radiation therapy. Noninvasive and real-time temperature monitoring of the heated tissue improves the efficacy and safety of the treatment. A temperature-sensitive acoustic parameter is required for ultrasound-based...
Article
The thermal mechanism of acoustic modulation of the reversible electrical activities of peripheral nerves is investigated using the soliton model, and a numerical solution is presented for its non-homogenous version. Our results indicate that heating a small segment of the nerve will increase the action potential conduction velocity and decrease it...
Article
Full-text available
http://medicalxpress.com/news/2015-03-concussion.html
Conference Paper
Ultrasound is a unique mechanical wave-based modality with a number of applications in medicine and biology. Besides widespread diagnostic applications of ultrasound, its therapeutic usage has gained increasing interest in both scientific and clinical communities during past couple of decades. One of the most promising therapeutic ultrasound modali...
Article
Full-text available
http://www.ryersonian.ca/pivotal-cancer-research-explores-new-ways-to-detect-tumours/
Article
High-intensity focused ultrasound (HIFU) induces thermal lesions by increasing the tissue temperature in a tight focal region. The main ultrasound imaging techniques currently used to monitor HIFU treatment are standard pulse-echo B-mode ultrasound imaging, ultrasound temperature estimation and elastography-based methods. The present study was carr...
Article
Ultrasound thermal therapy is used for noninvasive treatment of cancer. For accurate ultrasound based temperature monitoring in thermal therapy, the temperature dependence of acoustic parameters is required. In this study, the temperature dependence of acoustic harmonics was investigated in water. The pressure amplitudes of the transmitted fundamen...
Article
Full-text available
The aims of this study are: (a) to investigate the capability of photoacoustic (PA) method in detecting high-intensity focused ultrasound (HIFU) treatments in muscle tissuesin vitro; and (b) to determine the optical properties of HIFU-treated and native tissues in order to assist in the interpretation of the observed contrast in PA detection of HIF...
Article
Full-text available
Ultrasound elastography is a non-invasive method which images the elasticity of soft-tissues. To make an image, pre and after a small compression, ultrasound radio frequency (RF) signals are acquired and the time delays between them are estimated. The first differentiation of displacement estimations is called elastogram. In this study, we are goin...
Article
Full-text available
High intensity focused ultrasound (HIFU) induces focalized tissue coagulation by increasing the tissue temperature in a tight focal region and has been successfully used as a new technique of tumor treatment or to stop bleeding in clinical applications. The main challenges of this technique are: adjusting the location of HIFU thermal ablation exact...
Article
Full-text available
High-intensity focused ultrasound induces focalized tissue coagulation by increasing the tissue temperature in a tight focal region. Several methods have been proposed to monitor high-intensity focused ultrasound-induced thermal lesions. Currently, ultrasound imaging techniques that are clinically used for monitoring high-intensity focused ultrasou...
Article
Full-text available
This study investigated the dynamic changes of tissue attenuation coefficients before, during, and after high-intensity focused ultrasound (HIFU) treatment at different total acoustic powers (TAP) in ex vivo porcine muscle tissue. It further assessed the reliability of employing changes in tissue attenuation coefficient parameters as potential indi...
Article
Full-text available
Various numerical algorithms have been developed to solve the Khokhlov-Kuznetsov-Zabolotskaya (KZK) parabolic nonlinear wave equation. In this work, a generalized time-domain numerical algorithm is proposed to solve the diffraction term of the KZK equation. This algorithm solves the transverse Laplacian operator of the KZK equation in three-dimensi...
Conference Paper
Full-text available
Ultrasound waves have been widely used in diagnostic and therapeutic medical applications. Accurate and effective simulation of ultrasound beam propagation and its interaction with tissue has been proved to be important. The nonlinear nature of the ultrasound beam propagation, especially in the therapeutic regime, plays an important role in the mec...
Article
Full-text available
Non-invasive ultrasound surgeries such as high intensity focused ultrasound have been developed to treat tumors or to stop bleeding. In this technique, incorporation of a suitable imaging modality to monitor and control the treatments is essential so several imaging methods such as X-ray, Magnetic resonance imaging and ultrasound imaging have been...
Article
In this study we have evaluated the parameter of nonlinearity (B/A) and the parameter of h by measuring the amplitudes of the fundamental and the second harmonic components of the ultrasound echo signal. This method is derived from the finite-amplitude variation method that has been developed for pulse echo measurements. In this study, we used norm...
Article
Full-text available
This work investigated the transient characteristics of tissue attenuation coefficient before, during and after HIFU treatment at different total acoustic powers (TAP) in ex vivo porcine muscle tissues. Dynamic changes of attenuation coefficient parameters were correlated with conventional B-mode ultrasound images over the whole HIFU treatment pro...
Article
Full-text available
Microbubble agents have been shown to increase therapeutic effect of HIFU (high intensity focused ultrasound). In this work, the effects of treatment parameters on HIFU thermal lesion volume and temperature are investigated. Ex vivo tissues were treated with a 2 MHz HIFU beam in absence and presence of the Artenga® microbubbles at varying HIFU foc...
Article
Microbubble agents have been shown to increase therapeuticeffect of HIFU (high intensity focused ultrasound). Here, the effects of treatment parameters on lesion volume and temperature are investigated. Ex vivo tissue was treated with a 2 MHz HIFU beam in absence and presence of the Artenga™ microbubbles at varying HIFU focal intensities (649-2316...
Article
Accurate simulation of an intensive ultrasound beam requires taking nonlinear propagation effects into account. A notable example in the field of biomedical ultrasound where the effect of nonlinearity may play a significant role is the high intensity focused ultrasound (HIFU) as a non-invasive energy-based treatment modality. In this work, a 3D num...
Article
Low Intensity Pulsed UltraSound (LIPUS) has been shown to improve bone fracture healing in in vivo animal and human clinical studies. In vitro, this improvement has been shown through improved mineralization in bone cells. Low level heat of bone fractures has also been shown to improve healing. Moreover, low level heat has been shown to improve min...
Conference Paper
In this study we evaluate parameter of nonlinearity by measuring of the amplitude of the second harmonic component and the fundamental component. This method is a variation of the finite-amplitude that has been adopted for pulse echo measurements. We used normal and cooked pork muscle invitro. The result showed that image of this parameter can dist...
Conference Paper
Full-text available
High-intensity focused ultrasound (HIFU) can produce therapeutic benefits in deep-seated tissues selectively and noninvasively, presenting promising medical applications that can lead to non-invasive, bloodless surgery. This study aims at investigating the dose-dependent biologic effects of HIFU on neural tissues using an ultrasound image-guided HI...
Article
High intensity focused ultrasound (HIFU) with microbubbles has demonstrated the enhancement of the therapeutic efficacy of HIFU. The ultrasonic intensity for inducing cavitational bioeffects can be reduced by orders of magnitude with administration of such an agent externally. The current study investigates the effects of ultrasound treatment param...
Conference Paper
In this study we have evaluated the parameter of h instead of parameter of nonlinearity by measuring of the amplitude of the slope of dividing of second harmonic component to the fundamental component. This method is a variation of the finite-amplitude that has been adopted for pulse echo measurements. We used normal and cooked pork muscle in-vitro...
Conference Paper
Full-text available
A model describing the acoustic field resulting from an acoustic source vibrating in a rigid planar baffle is found to be computationally intensive if the field values are computed sequentially. The temporal complexity of the model is firstly due to the large number of computations required to integrate over the surface area of an arbitrarily-shape...
Chapter
Full-text available
In recent years high intensity focused ultrasound (HIFU) research and development have experienced a resurgence of interest at the academic, clinical, industrial and commercial levels. The clinical communities are encouraged to perform thermal ablation based surgeries of benign and malignant pathologies using minimally or non-invasive modalities. H...
Article
In this paper, a new technique based on nonlinear resonance of microbubbles is investigated in order to estimate the amplitude of an ultrasound wave pressure field. First, the existing theoretical model is reviewed. Then, an experimental setup consisting of a bubble generator and transmitting/receiving ultrasound transducers operating in the 1 MHz...
Article
This article reviews 9th International Symposium on Therapeutic Ultrasound (ISTU 2009) by Kullervo Hynynen, Jacques Souquet
Article
A study was conducted to develop an enhanced numerical model to simulate nonlinear continuous wave ultrasound field. The model was based on a second-order operator splitting method where the acoustic field was propagated over incremental steps. The splitting method accounted the effects of diffraction, nonlinearity, and attenuation to help in devel...
Article
Full-text available
Nonlinear propagation has been demonstrated to have a significant impact on ultrasound imaging. An efficient computational algorithm is presented to simulate nonlinear ultrasound propagation through layered liquid and tissue-equivalent media. Results are compared with hydrophone measurements. This study was undertaken to investigate the role of non...
Conference Paper
Full-text available
We present a new model of nonlinear ultrasound propagation through multilayered liquid/tissue media. This model includes the effects of diffraction, attenuation, and nonlinearity, with refraction and energy conservation at layer boundaries. It is capable of simulating pulsed and continuous wave propagation from sources of arbitrary geometry and exc...