We are sharing an online calculator for creating MRI phantoms that mimic the dielectric properties of human tissues.
Interest in dielectric phantoms has grown as whole-body devices have increased in static field strength from 1.5 T in the 1980s to 10.5 T today. Stronger magnets generate higher resonance frequencies associated with shorter wavelengths. Shorter wavelengths intensify interactions between an object and the electromagnetic field. These interactions cause constructive and destructive interference patterns that depend on the shape and dielectric properties of the object
Dielectric phantoms are useful in many MR applications such as RF coil development, thermometry, SAR estimation or electrical property mapping validation.
The generator is a result of collaboration between CAI2R scientists and colleagues at the Advanced MRI Laboratory, part of the National Institutes of Health, and is hosted by the NIH.
The tool can be used to determine the concentration of ingredients needed to obtain the desired relative permittivity and conductivity for a given resonance frequency (between 50 MHz and 4.5 GHz).
Our recipe comprises three ingredients:
- Distilled water as solvent
- NaCl (sodium chloride S9625: anhydrous, free-flowing, Redi-DriTM, ACS reagent, ≥ 99%, Sigma-Aldrich, St. Louis, MO) to control conductivity
- Polyvinylpyrrolidone (PVP-40: average molecular weight 40,000 g/mol, Sigma-Aldrich, St. Louis, MO) to control permittivity
PVP-based phantoms have several advantages, including straightforward fabrication, nontoxic character, and semitransparency that makes air bubbles easy to identify. Application of PVP-based phantoms is particularly valuable in MR thermometry due to their long T2* values and predominantly single spectral peak.
Synthesized tissue-equivalent dielectric phantoms using salt and polyvinylpyrrolidone solutions.
Magn Reson Med. 2018 Jul;80(1):413-419. doi: 10.1002/mrm.27005
Please cite this work if you are using the dielectric phantom recipe generator in your research.
Questions about this resource may be directed to Ryan Brown, PhD.