title: A versatile high-permittivity phantom for EIT.
abstract: Phantoms are frequently used in medical imaging systems to test hardware, reconstruction algorithms, and the interpretation of data. This report describes and characterizes the use of powdered graphite as a means of adding a significant reactive component or permittivity to useful phantom media for electrical impedance imaging. The phantom materials produced have usable complex admittivity at the electrical impedance tomography (EIT) frequencies from a few kilohertz to 1 MHz, as measured by our EIT system (ACT4) and by a commercial bioimpedance analyzer (BIS 4000, Xitron). We have also studied a commercial ultrasound coupling gel, which is highly electrically conductive and semisolid but that permits objects to move within it. The mixture of agar-graphite and gel-graphite, increases in permittivity and conductivity are proportional to the graphite concentration. We also report the use of a porous polymer membrane to simulate skin. A thin layer of this membrane increased resistance and the characteristic frequency of the phantoms, providing a promising candidate to simulate the effect of skin and the layered structure of a breast or other anatomical structure. The graphite also provides a realistic level of "speckle" in ultrasound images of the phantom, which may be useful in developing dual-mode imaging systems with ultrasound and the EIT.
authors.affiliation: Department of Biomedical Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA. kaot@rpi.edu
authors.forename: Tzu-Jen
authors.initials: TJ
authors.lastname: Kao
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Saulnier
authors.forename: David
authors.initials: D
authors.lastname: Isaacson
authors.forename: Tomas L
authors.initials: TL
authors.lastname: Szabo
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Newell
mesh_terms: D000362:Agar; D017097:Electric Impedance; D005782:Gels; D006108:Graphite; D006801:Humans; D019047:Phantoms, Imaging; D011108:Polymers; D016062:Porosity; D013450:Sulfones; D014054:Tomography / Q000379:methods*
chemical_list: D005782:Gels; D011108:Polymers; D013450:Sulfones; C022840:polyether sulfone; D006108:Graphite; D000362:Agar