Yuan Aaron Feng

Shanghai Jiao Tong University | SJTU · Department of Biomedical Engineering (BME)

Purposes To enhance the functional capability of MRI, this study aims to develop a novel MR elastography (MRE) sequence that achieves rapid acquisition without distortion artifacts. Methods A displacement‐encoded stimulated echo (DENSE) with multiphase acquisition scheme was used to capture wave images. A center‐out golden‐angle stack‐of‐stars sam...

Background and purpose: Preoperative assessment of meningioma consistency is beneficial for optimizing surgical strategy and prognosis of patients. We aim to develop a non-invasive prediction model for meningioma consistency utilizing magnetic resonance elastography (MRE) and diffusion tensor imaging (DTI). Materials and methods: Ninety-four pat...

Background Cushing disease (CD) is a rare clinical neuroendocrine disease. CD is characterized by abnormal hypercortisolism induced by a pituitary adenoma with the secretion of adrenocorticotropic hormone. Individuals with CD usually exhibit atrophy of gray matter volume. However, little is known about the alterations in topographical organization...

Magnetic resonance elastography (MRE) of brain relies on inducing and measuring shear waves in the brain. However, studies have shown vibration could induce changes in cerebral blood flow (CBF), which has a modulation effect and can affect the biomechanical properties measured. Objective: This work demonstrates the initial prototype of the indirect...

Background Different MR elastography (MRE) systems may produce different stiffness measurements, making direct comparison difficult in multi‐center investigations. Purpose To assess the repeatability and reproducibility of liver stiffness measured by three typical MRE systems. Study Type Prospective. Population/Phantoms Thirty volunteers without...

Accurate navigation and targeting are critical for neurological interventions including biopsy and deep brain stimulation. Real-time image guidance further improves surgical planning and MRI is ideally suited for both pre- and intra-operative imaging. However, balancing spatial and temporal resolution is a major challenge for real-time intervention...

Purpose: Patients with metabolic dysfunction-associated steatohepatitis (MASH) and significant fibrosis (fibrosis stage≥2), known as Fibro-MASH, are at increased risk of liver-related outcomes and lower rates of spontaneous disease regression. The aim was to investigate three-dimensional MR elastography (3D-MRE) combining proton-density fat fracti...

Magnetic Resonance Imaging (MRI) is now a widely used modality for providing multimodal, high-quality soft tissue contrast images with good spatiotemporal resolution but without subjecting patients to ionizing radiation. In addition to its diagnostic potential, its future theranostic value lies in its ability to provide MRI-guided robot interventio...

Neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD) present a major health burden to society. Changes in brain structure and cognition are generally only observed at the late stage of the disease. Although advanced magnetic resonance imaging (MRI) techniques such as diffusion imaging may allow identification of...

Magnetic Resonance Elastography (MRE) can characterize biomechanical properties of soft tissue for disease diagnosis and treatment planning. However, complicated wavefields acquired from MRE coupled with noise pose challenges for accurate displacement extraction and modulus estimation. Using optimization-based displacement extraction and Traveling...

White matter in the brain is structurally anisotropic consisting of large bundle of aligned axonal fibers. Hyperelastic, transversely isotropic constitutive models are typically used in the modeling and simulation of such tissues. However, most studies constrain the material models to describe the mechanical behavior of white matter in the limit of...

Human brain experiences vibration of certain magnitude and frequency during various physical activities such as vehicle transportation and machine operation, which may cause traumatic brain injury or other brain diseases. However, the mechanisms of brain pathogenesis due to vibration are not fully elucidated due to the lack of techniques to study b...

Magnetic Resonance Elastography (MRE) can characterize biomechanical properties of soft tissue for disease diagnosis and treatment planning. However, complicated wavefields acquired from MRE coupled with noise pose challenges for accurate displacement extraction and modulus estimation. Here we propose a pipeline for processing MRE images using opti...

Human brain experiences vibration of certain frequency during various physical activities such as vehicle transportation and machine operation or accidents, which may cause traumatic brain injury or other brain diseases. However, little is known about what happened to brain after vibration stimuli. Here, with a custom-built electromagnetic actuator...

It is known that biomechanical and structural properties of tumor tissues are potential biomarkers for the diagnosis and prognosis of tumors such as Hepatocellular carcinoma (HCC). Although there are many studies on the characterization of biomechanical properties of HCC at the cellular level, limited information is known from in vitro studies. Her...

The brain contains a tree of vasculature that contributes not only oxygen and nutrients but also structural integrity to the brain parenchyma. The structure formed by this vasculature affects the mechanical response of brain tissue both before and after injury, and maybe a determinant of an individual’s injury susceptibility. To investigate structu...

Interventional magnetic resonance imaging (i-MRI) for surgical guidance could help visualize the interventional process such as deep brain stimulation (DBS), improving the surgery performance and patient outcome. Different from retrospective reconstruction in conventional dynamic imaging, i-MRI for DBS has to acquire and reconstruct the interventio...

Objective: To achieve fast magnetic resonance elastography (MRE) at a low frequency for better shear modulus estimation of the brain. Approach: We proposed a multiphase radial DENSE MRE (MRD-MRE) sequence and an improved GRASP algorithm utilizing the sparsity of the harmonic motion (SH-GRASP) for fast MRE at 20 Hz. For the MRD-MRE sequence, the...

Objective: Interventional MRI (i-MRI) is crucial for MR image-guided therapy. Current image reconstruction methods for dynamic MR imaging are mostly retrospective that may not be suitable for i-MRI in real-time. Therefore, an algorithm to reconstruct images without a temporal pattern as in dynamic imaging is needed for i-MRI. Methods: We propose...

The cover image is based on the Research Article An electromagnetic actuator for brain magnetic resonance elastography with high frequency accuracy by Suhao Qiu et al., https://doi.org/10.1002/nbm.4592.

Objective: Interventional MRI (i-MRI) is crucial for MR image-guided therapy. Current image reconstruction methods for dynamic MR imaging are mostly retrospective that may not be suitable for i-MRI in real-time. Therefore, an algorithm to reconstruct images without a temporal pattern as in dynamic imaging is needed for i-MRI. Methods: We proposed a...

Our goal is to design, test and verify an electromagnetic actuator for brain magnetic resonance elastography (MRE). We proposed a grappler-shaped design that can transmit stable vibrations into the brain. To validate its performance, simulations were carried out to ensure the electromagnetic field generated by the actuator did not interfere with th...

Measurement the viscoelastic properties is important for studying the developmental and pathological behavior of soft biological tissues. Magnetic resonance elastography (MRE) is a non-invasive method for in vivo measurement of tissue viscoelasticity. As a flexible method capable of testing small samples, indentation has been widely used for charac...

Computational modeling of the brain is crucial for the study of traumatic brain injury. An anatomically accurate model with refined details could provide the most accurate computational results. However, computational models with fine mesh details could take prolonged computation time that impedes the clinical translation of the models. Therefore,...

Mechanical properties of brain tissue can provide vital information for understanding the mechanism of traumatic brain injury (TBI). As mouse models were commonly adopted for TBI studies, a method to produce injury to the brain and characterize the injured tissue is desired. In this paper, a complete workflow of TBI induction, sample preparation, a...

Real‐time interventional MRI (I‐MRI) could help to visualize the position of the interventional feature, thus improving patient outcomes in MR‐guided neurosurgery. In particular, in deep brain stimulation, real‐time visualization of the intervention procedure using I‐MRI could improve the accuracy of the electrode placement. However, the requiremen...

Background: Mechanical properties of the brain tissue are crucial to understand the mechanisms of traumatic brain injury (TBI). Injured brain tissue could induce changes of mechanical properties and anatomical structures. However, limited data is available for the injured tissue. New method: We developed a custom-built device to introduce contro...

Deep brain stimulation (DBS) is a neurosurgical procedure for treating neurodegenerative diseases and neurological disorders such as Parkinson's disease (PD) and epilepsy. Image guidance is crucial for the accurate placement of DBS electrodes. However, current surgical planning systems based on pre-operative MR and CT images of the brain cannot tak...

Liver cancer is one of the leading cancers, especially in developing countries. Understanding the biomechanical properties of the liver cancer cells can not only help to elucidate the mechanisms behind the cancer progression, but also provide important information for diagnosis and treatment. At the cellular level, we used well-established atomic f...

Purpose Biomechanical properties can be used as biomarkers to diagnose tumors, monitor tumor development, and evaluate treatment efficacy. The purpose of this preliminary study is to characterize the biomechanical environment of two typical liver tumors, hemangiomas (HEMs) and hepatocellular carcinomas (HCCs), and to investigate the potential of us...

Traumatic brain injury is one of the leading causes of injury and death in both developed and developing countries. Animal models are important preclinical tools for injury level studies. In this study, a finite element (FE) model of mouse brain was constructed to investigate the biomechanical responses of brain tissue during a controlled cortical...

Photothermal therapy (PTT) has been emerging as an effective, minimally invasive approach to treat cancers. However, a method to quantitatively evaluate the treatment effect after laser-induced thermotherapy (LITT) is needed. In this study, we used 808 nm laser radiation with three different power densities to treat the breast cancer tissue from 4T...

Many physical problems are reducible to two dimensions which facilitate their eventual solution. If there is no traction on one plane passing through the body, this state is known as plane stress since all nonzero stresses are confined to planes parallel to the traction-free plane. This is an obvious possibility for bodies with one dimension much s...

The equilibrium equations derived in Chap. 2 must be connected with the kinematic relations developed in Chap. 3. This coupling is accomplished by considering the mechanical properties of the materials for which the theory of elasticity is to be applied and is expressed by constitutive or material laws. Beginning with the generalized Hooke’s law, t...

An approach to the solution of problems in solid mechanics is to establish relationships first between applied loads and internal stresses and, subsequently, to consider deformations. Another way is to examine deformations initially and then proceed to the stresses and applied loads. Regardless of the eventual solution path selected, it is necessar...

Some classical problems that may be solved within the assumptions of the strength of materials are examined by applying the theory of elasticity. It is anticipated that the elementary solutions are approximately correct but deficient or incomplete in some way. In each case the isotropic material law is assumed to be applicable. The problems conside...

The stress–strain relationships derived in Chap. 4 pertain to elastic materials that respond immediately to the load applied. Viscous materials also resist loading but undergo strain with a time lag. For such viscoelastic systems, the stress at a particular time depends on the strain rate in addition to the strain itself. Viscoelastic materials exh...

Since the theory of elasticity originated primarily in the first half of the nineteenth century, most of the original work supporting the presentation in this introductory text is many decades old. Occasionally, new developments emerge, even in a mature field. A recent contribution, countering the classical notion that a material cannot have a nega...

The strains in an elastic body may be computed from a specified displacement field using the equations of compatibility, regardless of whether the displacements arise from static or dynamic excitation. The corresponding stresses and, indeed, the displacements themselves may be dependent on the rate characteristics of the loading function. Therefore...

The application of the rigorous methods of analysis embodied in the theory of elasticity is naturally of interest to engineers. Within this largely theoretical subject, it is of interest to introduce the fundamental basis of such applications, namely, the comparison of the analytical results obtained from an elasticity solution to the expected capa...

When a thin plate is loaded transverse to the plane, the plate bends and the deflection of the surface in the normal direction is predominant, similar to a gridwork of beams. Correspondingly a distributed transverse loading can be efficiently resisted by an initially curved thin surface structure such as a cylindrical or spherical tank. The initial...

Displacements with respect to a reference coordinate system may be physically observed, calculated, or measured for a deformed elastic body. Each displacement may be considered to have two components, one of which is due to relative movements or distortions within the body and the other which is uniform throughout the body, the so-called rigid body...

The theory of elasticity may also be developed from energy considerations, leading to the field equations in the form of differential equations. This approach does not promise any obvious computational advantage from the standpoint of analytical solutions. However energy methods are extensively developed for the pursuit of numerical solutions and a...

The theory of elasticity comprises a consistent set of equations which uniquely describe the state of stress, strain, and displacement at each point within an elastic deformable body. Engineering approaches are often based on a strength-of-materials formulation with its various specialized derivatives such as the theories of rods, beams, plates, an...

The essential equations of the linear theory of elasticity have been derived. Restated concisely are the equilibrium conditions, the kinematic relations with the compatibility constraints, and the constitutive law for isotropic materials. These equations are combined in force, displacement, and mixed formulations. Also the necessary and sufficient...

This augmented and updated fourth edition introduces a new complement of computational tools and examples for each chapter and continues to provide a grounding in the tensor-based theory of elasticity for students in mechanical, civil, aeronautical and biomedical engineering and materials and earth science. Professor Gould’s proven approach allows...

Breast cancer is one of the leading cancer forms affecting females worldwide. Characterizing the mechanical properties of breast cancer tissue is important for diagnosis and uncovering the mechanobiology mechanism. Although most of the studies were based on human cancer tissue, an animal model is still describable for preclinical analysis. Using a...

Simulations of soft tissues rely on constitutive models whose form must be generated by in-vitro experimentation. For membranes and thin specimens, planar biaxial testing systems have been used, but remain limited in their ability to fully prescribe in-plane F2D, in the homogeneity of the applied F2D and in the size of specimens they can accommodat...

Rapid clearance of nanoagents is a critical criterion for their clinical translation. Herein, it is reported that biodegradable and renal clearable nanoparticles are potentially useful for image-guided photothermal therapy of tumors. The multifunctional nanoparticles with excellent colloidal stability are synthesized through coordination reactions...

Purpose: Ultrasound (US) imaging has been widely used in breast tumor diagnosis and treatment intervention. Automatic delineation of the tumor is a crucial first step, especially for the computer-aided diagnosis (CAD) and US-guided breast procedure. However, the intrinsic properties of US images such as low contrast and blurry boundaries pose chal...

The aligned axonal fiber bundles in white matter make it suitable to be modeled as a transversely isotropic material. Recent experimental studies have shown that a minimal form, nearly incompressible transversely isotropic (MITI) material model, is capable of describing mechanical anisotropy of white matter. Here, we used a finite element (FE) comp...

Mechanical properties of brain tissue are crucial to understand the mechanism of traumatic brain injury (TBI). Over the past several decades, most of the studies focused on healthy brain tissues, while few of them are about the injured tissues. Therefore, limited knowledge is known about the mechanical properties of the injured brain tissues. In th...

The regulation of environmental pH is key to the health of an ecosystem, influencing the metabolic activity, growth, and development of organisms within it. Although pH values can be measured by a wide range of readily available technologies ranging from fluorescent dyes and nano-sensors, these cannot reveal the history of environmental pH from bef...

Characterizing the mechanical properties of white matter is important to understand and model brain development and injury. With embedded aligned axonal fibers, white matter is typically modeled as a transversely isotropic material. However, most studies characterize the white matter tissue using models with a single anisotropic invariant or in a s...

An accurate and noninvasive method for assessing treatment response following radiotherapy is needed for both treatment monitoring and planning. Measurement of solid tumor volume alone is not sufficient for reliable early detection of therapeutic response, since changes in physiological and/or biomechanical properties can precede tumor volume chang...

Purpose:Early detection of liver cancer improves patient prognosis dramatically. We propose a novel approach in which liver deformation is tracked during the cardiac cycle using tagged MRI. Strain concentrations that arise from material mismatches between the tumor and non-tumor regions were compared in patients with liver tumors. Methods:Tagged MR...

Background: In recent years, MR images have been increasingly used in therapeutic applications such as image-guided radiotherapy (IGRT). However, images with low contrast values and noises present challenges for image segmentation. Objective: The objective of this study is to develop a robust method based on fuzzy C-means (FCM) method which can...

Fiber reinforced structures are central to the form and function of biological tissues. Hyperelastic, transversely isotropic material models are used widely in the modeling and simulation of such tissues. Many of the most widely used models involve strain energy functions that include one or both pseudo-invariants (I4 or I5) to incorporate energy s...

On-board magnetic resonance (MR) image guidance during radiation therapy offers the potential for more accurate treatment delivery. To utilize the real-time image information, a crucial prerequisite is the ability to successfully segment and track regions of interest (ROI). The purpose of this work is to evaluate the performance of different segmen...

Supplementary Material Files

Anisotropy exists in many soft biological tissues. The most common anisotropy is transverse isotropy, which is typical for fiber-reinforced structures, such as the brain white matter, tendon and muscle. Although many methods have been proposed to determine tissue properties, techniques to characterize transversely isotropic materials remain limited...

Purpose: Evaluate commonly used segmentation algorithms on a commercially available real-time MR image guided radiotherapy (MR-IGRT) system (ViewRay), compare the strengths and weaknesses of each method, with the purpose of improving motion tracking for more accurate radiotherapy. Methods: MR motion images of bladder, kidney, duodenum, and liver tu...

In magnetic resonance elastography (MRE), displacement fields from shear waves are inverted to estimate underlying material properties. Modulus differences detected by MRE may be used to distinguish tumors or other localized pathology in tissue. The accuracy of modulus estimates depends on the choice of the assumed constitutive model, as well as on...

Experimental studies [1] have shown that white matter (WM) in the brain is mechanically anisotropic. Based on its fibrous structure, transversely isotropic (TI) material models have been suggested to capture WM behavior. TI hyperelastic material models involve strain energy density functions that depend on the I4 and I5 pseudo-invariants of the Cau...

Purpose: To validate the feasibility of using compressed sensing to improve spatial resolution and image quality of motion tracking images for MRI guided radiotherapy system. Methods: This study was performed on a commercial low field 0.35T MRI-guided radiotherapy system using the ACR phantom. The phantom was moved along the feet-head direction...

Purpose: Tour long‐term goal is to develop techniques for evaluating radiation injury based upon mechanical changes to tissue. Here, we study the mechanical response of white matter ex vivo using dynamic shear testing (DST) and indentation testing in an animal model, with the goals of establishing in normal (non‐radiation‐injured) tissue (1) a base...

Purpose: Investigate the potential of magnetic resonance elastography (MRE) to differentiate and delineate tissues with different viscoelastic properties, with the purpose of applying MRE to differentiate and delineate recurrent brain tumor and radiation necrosis. Methods: To simulate tumor or radiation necrosis inside normal brain tissue, a 10...