Tissue-mimicking agar/gelatin materials for use in heterogeneous elastography phantoms

Madsen, Ernest L.; Hobson, Maritza A.; Shi, Hu; Varghese, Tomy; Frank, Gary R.

doi:10.1088/0031-9155/50/23/013

Cited by 203 publications

(188 citation statements)

References 11 publications

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“…Oil-in-agar, oil-in-gelatin and agar dispersions can achieve Young's modulus values ranging from 5 -135 kPa, which is representative of soft tissue (de Korte et al, 1997;Madsen et al, 2005Madsen et al, , 2006. Copolymer-in-oil TMM phantoms can achieve optimal mechanical properties (Oudry et al, 2009); however, the range of acoustic velocities achievable with this material (1420 -1464 m/s) is much lower than that of soft tissue (Szabo, 2004).…”

Section: Introductionmentioning

confidence: 99%

Assessment of the accuracy of an ultrasound elastography liver scanning system using a PVA-cryogel phantom with optimal acoustic and mechanical properties

Cournane¹,

Cannon²,

Browne³

et al. 2010

Phys. Med. Biol.

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The accuracy of a transient elastography liver-scanning ultrasound system was assessed using a novel application of PVA-cryogel as a tissue-mimicking material with acoustic and shear elasticity properties optimized to best represent those of liver tissue. Although the liver-scanning system has been shown to offer a safer alternative for diagnosing liver cirrhosis through stiffness measurement, as compared to the liver needle biopsy exam, the scanner's accuracy has not been fully established. The Young's elastic modulus values of 5-6wt% PVA-cryogel phantoms, also containing glycerol and 0.3μm Al 2 O 3 and 3μm Al 2 O 3 , were measured using a 'gold standard' mechanical testing technique and transient elastography. The mechanically measured values and acoustic velocities of the phantoms ranged between 1.6-16.1kPa and 1540-1570m/s, respectively, mimicking those observed in liver tissue. The values reported by the transient elastography system overestimated the Young's elastic modulus values representative of the progressive stages of liver fibrosis by up to 32%. These results were attributed to the relative rather than absolute nature of the measurement arising from the singlepoint acoustic velocity calibration of the system, rendering the measurements critically dependent on the speed of sound of the sample under investigation. Given the wide range of acoustic velocities which exist in the liver, spanning healthy tissue to cirrhotic pathology, coupled with the system's assumption that the liver is approximately elastic when it is rather highly viscoelastic, care should be exercised when interpreting the results from this system in patient groups.2

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Section: Introductionmentioning

confidence: 99%

Assessment of the accuracy of an ultrasound elastography liver scanning system using a PVA-cryogel phantom with optimal acoustic and mechanical properties

Cournane¹,

Cannon²,

Browne³

et al. 2010

Phys. Med. Biol.

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“…Shear modulus can be recovered from MR-measured internal tissue displacements via either a direct or an iterative inversion scheme. 6,[8][9][10][11][12][13] The direct approach is appealing because it is linear, efficient, and can be localized by assuming piecewise homogeneity in the mechanical properties. However, the direct approach to image reconstruction can be sensitive to measurement noise.…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, several groups, including our own, have described methods for fabricating phantoms from gelatin and/or agar gels with realistic imaging ͑i.e., acoustic and MR relaxation times͒ and shear-modulus properties. [9][10][11][12][13] Gelatin displays a linearly elastic response, with relatively low viscosity and frequency dependency, while agar displays a slightly nonlinear-elastic signature that is more viscous ͑see Fig. 1͒.…”

Section: Introductionmentioning

confidence: 99%

The performance of steady‐state harmonic magnetic resonance elastography when applied to viscoelastic materials

et al. 2010

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Purpose:The clinical efficacy of breast elastography may be limited when the authors employ the assumption that soft tissues exhibit linear, frequency-independent isotropic mechanical properties during the recovery of shear modulus. Thus, the purpose of this research was to evaluate the degradation in performance incurred when linear-elastic MR reconstruction methods are applied to phantoms that are fabricated using viscoelastic materials. Methods: To develop phantoms with frequency-dependent mechanical properties, the authors measured the complex modulus of two groups of cylindrical-shaped gelatin samples over a wide frequency range ͑up to 1 kHz͒ with the established principles of time-temperature superposition ͑TTS͒. In one group of samples, the authors added varying amounts of agar ͑1%-4%͒; in the other group, the authors added varying amounts of sucrose ͑2.5%-20%͒. To study how viscosity affected the performance of the linear-elastic reconstruction method, the authors constructed an elastically heterogeneous MR phantom to simulate the case where small viscoelastic lesions were surrounded by relatively nonviscous breast tissue. The breast phantom contained four linear, viscoelastic spherical inclusions ͑10 mm diameter͒ that were embedded in normal gelatin. The authors imaged the breast phantom with a clinical prototype of a MRE system and recovered the shear-modulus distribution using the overlapping-subzone-linear-elastic image-reconstruction method. The authors compared the recovered shear modulus to that measured using the TTS method. Results: The authors demonstrated that viscoelastic phantoms could be fabricated by including sucrose in the gelation process and that small viscoelastic inclusions were visible in MR elastograms recovered using a linear-elastic MR reconstruction process; however, artifacts that degraded contrast and spatial resolution were more prominent in highly viscoelastic inclusions. The authors also established that the accuracy of the MR elastograms depended on the degree of viscosity that the inclusion exhibited. Conclusions:The results demonstrated that reconstructing shear modulus from other constitutive laws, such as viscosity, should improve both the accuracy and quality of MR elastograms of the breast.

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“…The 19-mm diameter spherical inclusion was formed and bonded round the hooked end of a stainless steel rod, the latter representing an ablation electrode. A storage modulus (real part of the complex Young's modulus) of 50 ± 2 kPa was measured at 1 Hz for the inclusion material using a Bose EnduraTEC ® model 3200 system (Madsen et al 2005b). The background, with a storage modulus of 11 ± 2 kPa, surrounds the inclusion and is bonded to it.…”

Section: Tissue Mimicking Phantommentioning

confidence: 99%

Three-Dimensional Electrode Displacement Elastography Using the Siemens C7F2 fourSight Four-Dimensional Ultrasound Transducer

Bharat

Fisher

Varghese

et al. 2008

Ultrasound in Medicine & Biology

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Because ablation therapy alters the elastic modulus of tissues, emerging strain imaging methods may enable clinicians for the first time to have readily available, cost effective, real-time guidance to identify the location and boundaries of thermal lesions. Electrode displacement elastography is a method of strain imaging tailored specifically to ultrasound-guided electrode-based ablative therapies (eg. radiofrequency ablation). Here tissue deformation is achieved by applying minute perturbations to the unconstrained end of the treatment electrode, resulting in localized motion around the end of the electrode embedded in tissue. In this paper, we present a method for 3D elastographic reconstruction from volumetric data acquired using the C7F2 fourSight 4D ultrasound transducer, provided by Siemens Medical Solutions. Lesion reconstruction is demonstrated for a spherical inclusion centered in a tissue-mimicking phantom, which simulates a thermal lesion embedded in a normal tissue background. Elastographic reconstruction is also performed for a thermal lesion created in vitro in canine liver using radiofrequency ablation. Post-processing is done on the acquired raw radiofrequency data to form surface-rendered 3D elastograms of the inclusion. Elastographic volume estimates of the inclusion compare reasonably well with the actual known inclusion volume, with 3D electrode displacement elastography slightly underestimating the true inclusion volume.

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Tissue-mimicking agar/gelatin materials for use in heterogeneous elastography phantoms

Cited by 203 publications

References 11 publications

Assessment of the accuracy of an ultrasound elastography liver scanning system using a PVA-cryogel phantom with optimal acoustic and mechanical properties

Assessment of the accuracy of an ultrasound elastography liver scanning system using a PVA-cryogel phantom with optimal acoustic and mechanical properties

The performance of steady‐state harmonic magnetic resonance elastography when applied to viscoelastic materials

Three-Dimensional Electrode Displacement Elastography Using the Siemens C7F2 fourSight Four-Dimensional Ultrasound Transducer

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