Tissue mimicking materials for a multi-imaging modality prostate phantom

Materials that simultaneously mimic soft tissue in vivo for magnetic resona nce imaging (MRI), ultrasound (US), and computed tomography (CT) for use in a prostate phantom have been developed. Prostate and muscle mimicking mate rials contain water, agarose, lipid particles, protein, Cu++, EDTA, glass b eads, and thimerosal (preservative). Fat was mimicked with safflower oil su ffusing a random mesh (network) of polyurethane. Phantom material propertie s were measured at 22 degreesC. (22 degreesC is a typical room temperature at which phantoms are used.) The values of material properties should match , as well as possible, the values for tissues at body temperature, 37 degre esC. For MRI, the primary properties of interest are T1 and T2 relaxations times, for US they are the attenuation coefficient, propagation speed, and backscatter, and for CT, the x-ray attenuation. Considering the large numbe r of parameters to be mimicked, rather good agreement was found with actual tissue values obtained from the literature. Using published values for pro state parenchyma, T1 and T2 at 37 degreesC and 40 MKz are estimated to be a bout 1100 and 98 ms, respectively. The CT number for in vivo prostate is es timated to be 45 HU (Hounsfield units). The prostate mimicking material has a T1 of 937 ms and a T2 of 88 ms at 22 degreesC and 40 MHz; the propagatio n speed and attenuation coefficient slope are 1540 m/s and 0.36 dB/cm/MHz, respectively, and the CT number of tissue mimicking prostate is 43 HU. Tiss ue mimicking (TM) muscle differs from TM prostate in the amount of dry weig ht agarose, Cu++, EDTA, and the quality and quantity of glass beads. The 18 mum glass beads used in TM muscle increase US backscatter and US attenuati on; the presence of the beads also has some effect on T1 but no effect on T 2. The composition of tissue-mimicking materials developed is such that dif ferent versions can be placed in direct contact with one another in a phant om with no long term change in US, MRI, or CT properties. Thus, anthropomor phic phantoms can be constructed. (C) 2001 American Association of Physicis ts in Medicine.