Characterization and evaluation of tissue-mimicking gelatin phantoms for use with MRgFUS (original) (raw)
Related papers
MR relaxation times of agar‐based tissue‐mimicking phantoms
Journal of Applied Clinical Medical Physics
Agar gels were previously proven capable of accurately replicating the acoustical and thermal properties of real tissue and widely used for the construction of tissue-mimicking phantoms (TMPs) for focused ultrasound (FUS) applications. Given the current popularity of magnetic resonance-guided FUS (MRgFUS), we have investigated the MR relaxation times T1 and T2 of different mixtures of agar-based phantoms. Nine TMPs were constructed containing agar as the gelling agent and various concentrations of silicon dioxide and evaporated milk. An agar-based phantom doped with wood powder was also evaluated. A series of MR images were acquired in a 1.5 T scanner for T1 and T2 mapping. T2 was predominantly affected by varying agar concentrations. A trend toward decreasing T1 with an increasing concentration of evaporated milk was observed. The addition of silicon dioxide decreased both relaxation times of pure agar gels.The proposed phantoms have great potential for use with the continuously emerging MRgFUS technology. The MR relaxation times of several body tissues can be mimicked by adjusting the concentration of ingredients, thus enabling more accurate and realistic MRgFUS studies.
MRI-compatible bone phantom for evaluating ultrasonic thermal exposures
Ultrasonics, 2016
Objective: The goal of the proposed study was the development of a magnetic resonance imaging (MRI) compatible bone phantom suitable for evaluating focused ultrasound protocols. Materials and methods: High resolution CT images were used to segment femur bone. The segmented model was manufactured with (Acrylonitrile Butadiene Styrene) ABS plastic using a 3-D printer. The surrounding skeletal muscle tissue was mimicked using an agar-silica-evaporated milk gel (2% w/v-2% w/ v-40% v/v). MR thermometry was used to evaluate the exposures of the bone phantom to focused ultrasound. Results: The estimated agar-silica-evaporated milk gel's T 1 and T 2 relaxation times in a 1.5 T magnetic field were 776 ms and 66 ms respectively. MR thermometry maps indicated increased temperature adjacent to the bone, which was also shown in situations of real bone/tissue interfaces. Conclusion: Due to growing interest of using MRI guided Focused Ultrasound Surgery (MRgFUS) in palliating bone cancer patients at terminal stages of the disease, the proposed bone phantom can be utilized as a very useful tool for evaluating ultrasonic protocols, thus minimizing the need for animal models. The estimated temperature measured and its distribution near the bone phantom/agar interface which was similar to temperatures recorded in real bone ablation with FUS, confirmed the phantom's functionality.
Tissue-mimicking gel phantoms for thermal therapy studies
Ultrasonic imaging, 2014
Tissue-mimicking phantoms that are currently available for routine biomedical applications may not be suitable for high-temperature experiments or calibration of thermal modalities. Therefore, design and fabrication of customized thermal phantoms with tailored properties are necessary for thermal therapy studies. A multitude of thermal phantoms have been developed in liquid, solid, and gel forms to simulate biological tissues in thermal therapy experiments. This article is an attempt to outline the various materials and techniques used to prepare thermal phantoms in the gel state. The relevant thermal, electrical, acoustic, and optical properties of these phantoms are presented in detail and the benefits and shortcomings of each type are discussed. This review could assist the researchers in the selection of appropriate phantom recipes for their in vitro study of thermal modalities and highlight the limitations of current phantom recipes that remain to be addressed in further studies.
International Journal of Thermophysics, 2012
Tissue-mimicking phantoms, including bovine serum albumin phantoms and egg white phantoms, have been developed for, and in laboratory use for, realtime visualization of high intensity focused ultrasound-induced thermal coagulative necrosis since 2001. However, until now, very few data are available concerning their thermophysical properties. In this article, a step-wise transient plane source method has been used to determine the values of thermal conductivity, thermal diffusivity, and specific heat capacity of egg white phantoms with elevated egg white concentrations (0 v/v% to 40 v/v%, by 10 v/v% interval) at room temperature (∼20 • C). The measured thermophysical properties were close to previously reported values; the thermal conductivity and thermal diffusivity were linearly proportional to the egg white concentration within the investigation range, while the specific heat capacity decreased as the egg white concentration increased. Taking account of large differences between real experiment and ideal model, data variations within 20 % were accepted.
MRI-compatible breast/rib phantom for evaluating ultrasonic thermal exposures
The International Journal of Medical Robotics and Computer Assisted Surgery, 2017
Introduction: The target of this study was the development of a magnetic resonance imaging (MRI) compatible breast phantom for focused ultrasound which includes plastic (ABS) ribs. The objective of the current study was the evaluation of a focused ultrasound procedure using the proposed phantom that eliminates rib heating. Material and Methods: The proposed phantom was evaluated using two different focused ultrasound exposures. The surrounding breast tissue was mimicked using an agar-silica-evaporation milk gel (2% w/v-2% w/v-40% v/v). Results: The attenuation of the ABS was similar to that of ribs. MR thermometry of focused ultrasound exposures were acquired using the breast/rib phantom. In one exposure focused ultrasound was applied with far-field targeting of the ribs. In the other exposure, the transducer was positioned laterally, thus avoiding exposure of the rib to focused ultrasound. Conclusions: Due to growing interest in using MRI guided focused ultrasound (MRgFUS) for patients with breast cancer, the proposed breast/rib phantom can be utilized as a very useful tool for evaluating ultrasonic protocols.
Investigating Ballistic Gelatin Based Phantom Properties for Ultrasound Training
2019
The simulation has become an important tool for healthcare practitioners who have difficulty in accessing patients to learn ultrasound imaging modes. The ultrasound phantoms are specially designed objects that are used or imagined to evaluate, analyze and adjust the performance of test devices. These phantoms for ultrasonography devices are expensive, and low-cost alternatives have provided an educational experience that does not give the best result. Ballistic gelatin is a member of the 250-Bloom hydrogel family that resembles human muscle tissue in terms of its mechanical properties. The 250-Bloom Ballistic Gelatin (BG) is prepared with different mixing ratios to be made the mechanical tests such as gunshot, compression and electrical conductivity measurement. The results are compared with the mechanical results of human muscle tissue in order to measure the similarity of the 250-Bloom BG we prepared to human muscle tissue. It is showed that the 250-Bloom BG phantom model has very...
IEEE Transactions on Biomedical Engineering, 2000
The present study aims to identify a new recipe for reusable tissue mimicking phantoms that allows the optical visualization of thermal lesions produced in various applications of therapeutic ultrasound where thermal mechanisms are important. The phantom was made of polyacrylamide hydrogel containing a nonionic surface-active agent (NiSAA) as a temperature-sensitive indicator. Threshold temperature above which a thermal lesion is regarded to be formed in the phantom is controlled by selecting an NiSAA. In the present study, three NiSAAs of polyoxyethylene alkyl ether series with nominal clouding points of 66 • C, 70 • C, and 80 • C were chosen. Test phantoms were prepared with polyacrylamide hydrogel, corn syrup and NiSAAs [5% (w/v)]. Key acoustic properties of the three NiSAA hydrogels were found to be similar to those of human liver. The phantoms were optically transparent at room temperature (25 • C) and became opaque after exceeding the clouding points. The transparency was recovered on cooling, although the system demonstrated hysteresis. The phantoms were tested both in their ability to provide visualization of thermal lesions produced by high-intensity focused ultrasound and also to examine any characteristic differences in the shape of the lesions formed at different threshold temperatures. The present study suggests that the NiSAA polyacrylamide hydrogel will be of a practical use in quality assurance in various applications of therapeutic ultrasound where thermal mechanisms are important.
Ultrasonics, 2009
Miniature flat ultrasound transducers have shown to be effective for a large variety of thermal therapies, but the associated superficial heating implicates developing original strategies in order to extend therapeutic depth. The goal of the present paper is to use ultrasound contrast agents (UCA) to increase remote attenuation and heating. Theoretical simulations demonstrated that increasing attenuation from 0.27 to 0.8 Np/cm at 10 MHz beyond a distance of 18 mm from the transducer should result in longer thermal damages due to protein coagulation in a tissue mimicking phantom. Contrast agents (BR14, Bracco, Plan-les-Ouates, Switzerland) were embedded in thermo-sensitive gel and attenuations ranging from 0.27 to 1.33 Np/cm were measured at 10 MHz for concentrations of BR14 between 0 and 4.8%. Thermal damages were then induced in several gels, which had different layering configurations. Thermal damages, 12.8 mm in length, were obtained in homogeneous gels. When mixing contrast agents at a concentration of 3.2% beyond a first 18 mm-thick layer of homogeneous gel, the thermal damages reached 21.5 mm in length. This work demonstrated that contrast agents can be used for increasing attenuation remotely and extending therapeutic depth induced by a non-focused transducer. Additional work must be done in vivo in order to verify the remote-only distribution of bubbles and associated increase in attenuation.
2009 IEEE International Ultrasonics Symposium, 2009
High intensity focused ultrasound (HIFU) is a noninvasive technique that has great potential for improving thermal therapies. To target specified regions accurately for treatment, a robust imaging technique is required to monitor HIFU application. Therefore, the development of an ultrasonic imaging technique for monitoring HIFU treatment is highly medically significant. Quantitative ultrasound (QUS) is a novel imaging technique that may improve monitoring of HIFU treatment by quantifying tissue changes. Ultrasonic backscatter experiments were performed on two types of phantoms to understand the variations in QUS parameters with increases in temperature from 36 to 50 • C. The phantoms were biological phantoms made of agar and containing either mouse mammary carcinoma cells (4T1) or chinese hamster ovary cells (CHO) as scatterers. All scatterers were uniformly distributed spatially at random throughout the phantoms. Sound speed and attenuation were estimated in the phantoms versus temperature using insertion loss methods. Two parameters were estimated from the backscatter coefficient (effective scatterer diameter (ESD) and effective acoustic concentration (EAC)) and two parameters were estimated from the envelope statistics (k parameter and µ parameter) of the backscattered echoes versus temperature. The results of this study suggest that QUS has the potential to be used for noninvasive monitoring of temperature changes in tissues.