Reliable preparation of agarose phantoms for use in quantitative magnetic resonance elastography

McIlvain, Grace; Ganji, Elahe; Cooper, Cyrus; Killian, Megan L.; Ogunnaike, Babatunde A.; Johnson, Curtis L.

doi:10.1016/j.jmbbm.2019.05.001

Cited by 24 publications

(18 citation statements)

References 53 publications

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“…As aforementioned, the storage modulus was shown to dominate the loss modulus in agar and agar-doped phantoms. More specifically, around an order of magnitude difference can be observed between these two parameters 39 , 40 . The storage moduli at both frequencies were then fixed from the shear modulus distributions in Fig.…”

Section: Methodsmentioning

confidence: 98%

“…The forward problem relating harmonic displacements to tissue mechanical properties is described by the Navier’s equation: where ρ is the material’s density [kg m −3 ], ω the motion angular velocity [rad s −1 ], u the motion field [m], λ [N m −2 ] the first Lamé coefficient 38 and G [N m −2 ] the complex shear modulus. In agar and agar-doped phantoms, the real part of the complex shear modulus (storage modulus) was shown to considerably dominate the imaginary part (loss modulus) 39 , 40 . The LFE, which ignores the loss modulus, was then chosen to retrieve first elasticity information from Lorentz force induced displacements in agar phantoms, given its availability and wide use in the MRE community.…”

Section: Methodsmentioning

confidence: 99%

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Lorentz force induced shear waves for magnetic resonance elastography applications

Flé

Gilbert

Grasland-Mongrain

et al. 2021

Sci Rep

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Quantitative mechanical properties of biological tissues can be mapped using the shear wave elastography technique. This technology has demonstrated a great potential in various organs but shows a limit due to wave attenuation in biological tissues. An option to overcome the inherent loss in shear wave magnitude along the propagation pathway may be to stimulate tissues closer to regions of interest using alternative motion generation techniques. The present study investigated the feasibility of generating shear waves by applying a Lorentz force directly to tissue mimicking samples for magnetic resonance elastography applications. This was done by combining an electrical current with the strong magnetic field of a clinical MRI scanner. The Local Frequency Estimation method was used to assess the real value of the shear modulus of tested phantoms from Lorentz force induced motion. Finite elements modeling of reported experiments showed a consistent behavior but featured wavelengths larger than measured ones. Results suggest the feasibility of a magnetic resonance elastography technique based on the Lorentz force to produce an shear wave source.

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Section: Methodsmentioning

confidence: 98%

Section: Methodsmentioning

confidence: 99%

Lorentz force induced shear waves for magnetic resonance elastography applications

Flé

Gilbert

Grasland-Mongrain

et al. 2021

Sci Rep

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“…The in vivo data for sample group (1) for rat cortical brain tissue were taken from [25], which used the same protocol used for sample group (2) and (3). Agarose hydrogels are widely used as brain phantoms [52][53][54]. Briefly, a stainless steel conical probe was used to penetrate the material and the material relaxation forces imposed on the probe were measured using a 10 g load cell at a sampling frequency of 54 Hz.…”

Section: Mechanical Characterizationmentioning

confidence: 99%

Soft, Conductive, Brain-Like, Coatings at Tips of Microelectrodes Improve Electrical Stability under Chronic, In Vivo Conditions

Sridharan

Muthuswamy

2021

Micromachines

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Several recent studies have reported improved histological and electrophysiological outcomes with soft neural interfaces that have elastic moduli ranging from 10 s of kPa to hundreds of MPa. However, many of these soft interfaces use custom fabrication processes. We test the hypothesis that a readily adoptable fabrication process for only coating the tips of microelectrodes with soft brain-like (elastic modulus of ~5 kPa) material improves the long-term electrical performance of neural interfaces. Conventional tungsten microelectrodes (n = 9 with soft coatings and n = 6 uncoated controls) and Pt/Ir microelectrodes (n = 16 with soft coatings) were implanted in six animals for durations ranging from 5 weeks to over 1 year in a subset of rats. Electrochemical impedance spectroscopy was used to assess the quality of the brain tissue–electrode interface under chronic conditions. Neural recordings were assessed for unit activity and signal quality. Electrodes with soft, silicone coatings showed relatively stable electrical impedance characteristics over 6 weeks to >1 year compared to the uncoated control electrodes. Single unit activity recorded by coated electrodes showed larger peak-to-peak amplitudes and increased number of detectable neurons compared to uncoated controls over 6–7 weeks. We demonstrate the feasibility of using a readily translatable process to create brain-like soft interfaces that can potentially overcome variable performance associated with chronic rigid neural interfaces.

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“…Therefore, most of the existing MRI phantoms are composed of tissue-mimicking materials, such as water, fat, and agarose gel. [24][25][26] In terms of phantom building techniques and materials, the design criteria for quantitative MRI phantoms are well-characterized MRI properties and stability of the used materials. It is also recommended avoiding fillable compartments to ensure traceability and consistency of the phantom characteristics.…”

Section: Mr Imaging Phantomsmentioning

confidence: 99%

“…However, if the relaxation times are too short, as it is the case in most solid materials, MRI systems will not produce sufficiently high signals for detection. Therefore, most of the existing MRI phantoms are composed of tissue‐mimicking materials, such as water, fat, and agarose gel . In terms of phantom building techniques and materials, the design criteria for quantitative MRI phantoms are well‐characterized MRI properties and stability of the used materials.…”

Section: Mr Imaging Phantomsmentioning

confidence: 99%

Physical imaging phantoms for simulation of tumor heterogeneity in PET, CT, and MRI: An overview of existing designs

2020

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Background: In oncology, lesion characterization is essential for tumor grading, treatment planning, and follow-up of cancer patients. Hybrid imaging systems, such as Single Photon Emission Computed Tomography (SPECT)/CT, Positron Emission Tomography (PET)/CT, or PET/magnetic resonance imaging (MRI), play an essential role for the noninvasive quantification of tumor characteristics. However, most of the existing approaches are challenged by intra-and intertumor heterogeneity. Novel quantitative imaging parameters that can be derived from textural feature analysis (as part of radiomics) are promising complements for improved characterization of tumor heterogeneity, thus, supporting clinically relevant implementations of personalized medicine concepts. Nevertheless, establishing new quantitative parameters for tumor characterization requires the use of standardized imaging objects to test the reliability of results prior to their implementation in patient studies. Methods: In this review, we summarize existing reports on heterogeneous phantoms with a focus on simulating tumor heterogeneity. We discuss the techniques, materials, advantages, and limitations of the existing phantoms for PET, CT, and MR imaging modalities. Conclusions: Finally, we outline the future directions and requirements for the design of cross modality imaging phantoms.

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Reliable preparation of agarose phantoms for use in quantitative magnetic resonance elastography

Cited by 24 publications

References 53 publications

Lorentz force induced shear waves for magnetic resonance elastography applications

Lorentz force induced shear waves for magnetic resonance elastography applications

Soft, Conductive, Brain-Like, Coatings at Tips of Microelectrodes Improve Electrical Stability under Chronic, In Vivo Conditions

Physical imaging phantoms for simulation of tumor heterogeneity in PET, CT, and MRI: An overview of existing designs

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