Tissue Simulation
CIRS' Material Technology
One of CIRS’ core technologies is our ability to formulate proprietary Tissue Equivalent (TE) materials for a wide variety of applications and modalities. We use refined and proprietary computer models to choose our raw materials based on the tissue to be mimicked, the intended modality (energy level) and other desired properties. CIRS also has an extensive library of standardized formulations, allowing us to tailor phantom designs to the unique needs of our customers. CIRS TE technology has been validated through specific testing, continuous monitoring of manufacturing applications, and worldwide use and acceptance of products for more than 35 years.
Simulation for Ionizing Radiation
Tissue equivalent materials (TEM) or tissue substitutes are defined as the materials that substitute original human tissue and organs for a given radiation type and energy by absorbing and scattering the radiation to the same extent as actual tissues within known and acceptable limits.
According to the International Commission on Radiation Units and Measurements (ICRU) Report 44, TEM for photon and electron radiation will be suitable for tissue substitution if their linear attenuation and stopping power coefficients respectively are within +/-1% of their reference tissues within the appropriate energy range. Similar criteria can be applied to proton radiation. It is often required to adjust physical density of a material when matching linear attenuation coefficients and electron densities such that physical densities of the material may vary from reference tissue densities by more than 1%.
CIRS has developed technology that allows for very accurate tissue substitution for a variety of applications including photon, electron and proton radiation therapy as well as x-ray imaging; including low energy breast imaging, computed tomography and nuclear imaging. CIRS Tissue Simulation Technology has been validated through specific independent studies, continuous monitoring and improvement of manufacturing processes and worldwide use of our TEM for over 35 years.
CIRS can simulate any tissue found in the human body with many of our phantoms containing multiple tissue substitutes including:
- Breast tissue substitutes – any ratio of adipose / glandular intended for use in low energy mammographic X-Ray imaging
- Bone substitutes – from trabecular to cortical bone with a wide range of mineral densities used for CT and Micro CT calibration
- Lung substitutes – in a range of densities from inhale to exhale
- Soft tissue substitutes – muscle, adipose, brain, liver, prostate, etc.
- Water-equivalent material
Proton Radiation
Proton RT is an emerging technology that requires phantoms for QA procedures. Numerous CIRS TEMs, Soft Tissues and Bone were independently studied for proton interaction and demonstrate good agreement with reference tissues within +/- 1.5%.
ICRU Report 44. Tissue Substitutes in Radiation Dosimetry and Measurement
Varchena, Vladimir. Tissue Equivalent Materials for Proton Therapy. 2016,
Simulation for Non-Ionizing Radiation
Zerdine® solid-elastic hydrogel is one of our most versatile materials, and can be formulated with a wide variety of acoustic, mechanical and thermal properties. Phantoms constructed from Zerdine hydrogel will not melt or leak when punctured and they do not require refrigeration. Zerdine is also more elastic than other materials and allows more pressure to be applied to the scanning surface without subsequent damage to the material.
Without any filler materials, Zerdine is water clear with a slight amber tint. Proprietary fabrication procedures enable close control over the homogeneity of Zerdine hydrogel and the reliability of its imaging characteristics from batch to batch.
Zerdine hydrogel can also be molded into very intricate shapes, and can be cured in layers allowing the production of “multi-tissue” phantoms. While Zerdine hydrogel will desiccate if unprotected, the phantom housings and storage containers have been engineered to allow the phantoms to last many years.
Applications of Zerdine®
The Zerdine formulation system established at CIRS is geared primarily to control acoustic specifications to these optimal ranges:
Speed of sound: 1480 – 1650 m/s
Attenuation coefficient: 0.1 to 1.5 dB./cm/MHz with a linear frequency response
Backscatter coefficient (independent of SoS and attenuation): 3×10-4 1/str*cm ± 12 dB
Young’s modulus(independent of SoS, attenuation and contrast): 3 – 200 kPa
Additional applications include:
Ionizing Radiation: The base Zerdine® material has a water-like response; specialized filler materials allow CIRS to tailor photon absorption coefficients for x-ray, CT and radiation therapy.
MRI: The base Zerdine material has a water-like MR signal. Filler materials or salts such as nickel chloride may be added to modify the T1 and T2 response.
Thermal Testing: The thermal properties are within the range of human tissue, and the base polymer has a melting point over 100°C, making it ideal for testing high intensity focused ultrasound and other thermal therapies.
Photoacoustic and Optics: Zerdine® can be doped with optical absorbing dyes and scattering pigments for use in photoacoustic imaging.
Z-Skin Elastomer™
CIRS also works with ATS Urethane and the Z-skin™ elastomer in many of its phantoms.
ATS Urethane was developed by Bill Claymon, the founder of ATS Laboratories, and is known for its exceptional durability.
With an oil-based construction, it will not dry out over time. Like Zerdine®, filler materials can be added to tailor its imaging response, albeit over a more narrow range of speed of sound (1400 – 1470 m/s) and attenuation coefficient (0.2 – 0.7 dB/cm/MHz). The base material has a fat-like response under most imaging modalities.
Z-skin™ elastomer provides an incredible life-like feel in simulation and training phantoms. Its self-healing properties make it ideal for teaching biopsy techniques, and a patented bonding process now allows CIRS to use this versatile material as a highly durable, elastic membrane for Zerdine® phantoms.