Elastography: A Quantitative Method for Imaging the Elasticity of Biological Tissues

A nuclear magnetic resonance imaging (MRI) method is presented for quantitatively mapping the physical response of a material to harmonic mechanical excitation. The resulting images allow calculation of regional mechanical properties. Measurements of shear modulus obtained with the MRI technique in gel materials correlate with independent measurements of static shear modulus. The results indicate that displacement patterns corresponding to cyclic displacements smaller than 200 nanometers can be measured. The findings suggest the feasibility of a medical imaging technique for delineating elasticity and other mechanical properties of tissue.

https://science.sciencemag.org/content/sci/269/5232/1854.full.pdf

Magnetic resonance elastography by direct visualization of propagating acoustic strain waves

http://disciplinas.stoa.usp.br/pluginfile.php/166516/mod_resource/content/1/Radiomics.pdf

Radiomics: the process and the challenges

Magnetic resonance elastography: Non-invasive mapping of tissue elasticity

Noninvasive assessment of bone mineral and structure: state of the art.

Up until now, no material has been found whose attenuation and speed of sound properties not only mimic those of human soft tissue, but are controllable in magnitude. We have discovered such a material in the form of water-based pharmaceutical gels containing uniform distributions of graphite powder and known concentrations of alcohol. The magnitude of the attenuation coefficient can be controlled easily between 0.2 and 1.5 dB/cm at 1 MHz, by varying the concentration of graphite. These attenuation coefficients are nearly proportional to the frequency. The speed of sound varies between 1520 and 1650 m/s at room temperature, depending primarily upon the concentration of alcohol. Bacterial invasion has been prevented by sterilization procedures and the introduction of appropriate preservatives. The ultrasonic properties exhibit temporal stability and change little over the range of room temperatures.

Tissue mimicking materials for ultrasound phantoms

http://www.brl.uiuc.edu/Publications/1990/Yao-UltrasonImag-58-1990.pdf

Backscatter Coefficient Measurements Using a Reference Phantom to Extract Depth-Dependent Instrumentation Factors:

Two limitations on the animal-hide gelatin and graphite powder tissue equivalent (TE) materials are that they cannot be produced consistently with speeds of sound less than 1,570 m/s at room temperature (22 degrees C) and that irreparable damage can result if the materials are raised to temperatures above 32.5 degrees C. An acceptable substitute polysaccharide gel (agar) has a high melting point (78 degrees C) and can be made to exhibit speeds of sound over the range 1,498 m/s to over 1,600 m/s at 22 degrees C. Thus TE material made with agar is environmentally stable and can be manufactured to exhibit the important speed of sound, 1,540 m/s.

A new ultrasound tissue-equivalent material.

In a study involving 10 different sites, independent results of measurements of ultrasonic properties on equivalent tissue-mimicking samples are reported and compared. The properties measured were propagation speed, attenuation coefficients, and backscatter coefficients. Reasonably good agreement exists for attenuation coefficients, but less satisfactory results were found for propagation speeds. As anticipated, agreement was not impressive in the case of backscatter coefficients. Results for four sites agreed rather well in both absolute values and frequency dependence, and results from other sites were lower by as much as an order of magnitude. The study is valuable for laboratories doing quantitative studies.

/pdf/interlaboratory-comparison-of-ultrasonic-backscatter-1xgmzgekfl.pdf

Interlaboratory comparison of ultrasonic backscatter, attenuation, and speed measurements.

A form of tissue-mimicking material is reported in which oil droplets are dispersed in a water-based gelatin. Broad ranges of ultrasonic parameters, including speed of sound, attenuation coefficient, density and backscatter level, exist for this material. Very important, the attenuation coefficients are nearly proportional to the frequency as in the case of mammalian tissue and the available attenuation coefficient slopes span the range of mammalian tissues. The available range of slopes is 0.1 dB/cm/MHz through at least 2.0 dB/cm/MHz. The available speeds of sound range from a minimum below that of mammalian fat (approximately 1460 m/s) to a maximum above the accepted average for human tissue (154o m/s). Densities available range from below that of fat (approximately 0.92 gm/cm3) through about 1.00 gm/cm3. Backscatter levels are easily made negligible compared to clinical levels and compared to those exhibited in previously reported tissue-mimicking materials in which the suspended particles are solid (Madsen et al. 1978; Burlew et al., 1980). Addition of solid or hollow glass scatterers allows backscatter levels to be made comparable to those clinically observed.

http://www.brl.uiuc.edu/brp/pdfs/Madsen-UMB-277-1982.pdf

James A. Zagzebski

Papers

Tissue mimicking materials for ultrasound phantoms

Backscatter Coefficient Measurements Using a Reference Phantom to Extract Depth-Dependent Instrumentation Factors:

A new ultrasound tissue-equivalent material.

Interlaboratory comparison of ultrasonic backscatter, attenuation, and speed measurements.

Oil-in-gelatin dispersions for use as ultrasonically tissue-mimicking materials.