A fat-water-iron phantom comprised of forty-nine 20mL scintillation vials in varying true fat volume percentages (0, 2.5, 5, 10, 20, 30, 40, 50 and 100%) and iron concentrations (0, 10, 20, 30, 40, and 50 μg/mL) was constructed, based on a modified version of the phantom described by Bernard et al(17 (link)). In addition, the phantom described by Bernard et al did not contain iron. These fat percentages and iron concentrations were chosen to reflect the range of values seen in patients with hepatic steatosis (0-50%)(18 (link), 19 (link)), and values seen arising from adipose tissue (~100%). T2* values in healthy livers range between 25 and 35ms, although T2* values less than a few milliseconds can been observed in patients with very severe hepatic iron overload(20 (link)).
Appropriate volumes of peanut oil were dispensed by weight into vials, assuming the density of peanut oil (0.916 g/cm3). Peanut oil was chosen because it has a proton NMR spectrum similar to that of triglyceride protons in adipose tissue(11 (link)). Peanut oil is comprised of approximately 9% palmitic, 4% stearic, 55% oleic, and 27% linoleic acids (21 ). Aliquots of superparamagnetic iron oxide (SPIO) (Feridex, Bayer Healthcare) were added to the vials to shorten T2* values.
A “water solution” comprising the water fraction of the phantom contained the following in distilled, deionized water: 43mM sodium dodecyl sulfate (surfactant, Sigma Aldrich, St. Louis, MO), 43mM sodium chloride, 3.75mM sodium azide, and 0.3mM gadobenate dimeglumine (MultiHance, Bracco Inc.). Agar (2.0% w/v) was added over heat with stirring until melted. Volumes of the water solution were poured into vials containing pre-measured peanut oil and SPIO volumes, mixed through gentle inversion for approximately two minutes, and formed a solid gel when cooled to room temperature. Fat-fractions (0.0, 2.7, 5.4, 10.7, 21.2, 31.6, 41.8, 51.9, and 100.0%) and iron concentrations were re-calculated to reflect the actual volume of the water mixture present due to losses in transfer and cooling.
Micrographs of examples of the phantom (50% fat with 20 μg Fe/mL, and 10% fat with 20 μg Fe/mL) were created on a separate day to investigate the microscopic behavior of the emulsion at a low and high fat-fraction. A drop of the fresh emulsion was placed onto a slide with a coverslip before complete cooling occurred. Photographs and measurements of structure size at 40x magnification were taken using MicroSuite (Basic Edition v 2.3 (Build 1121), Olympus America Inc., Center Valley, PA).
Appropriate volumes of peanut oil were dispensed by weight into vials, assuming the density of peanut oil (0.916 g/cm3). Peanut oil was chosen because it has a proton NMR spectrum similar to that of triglyceride protons in adipose tissue(11 (link)). Peanut oil is comprised of approximately 9% palmitic, 4% stearic, 55% oleic, and 27% linoleic acids (21 ). Aliquots of superparamagnetic iron oxide (SPIO) (Feridex, Bayer Healthcare) were added to the vials to shorten T2* values.
A “water solution” comprising the water fraction of the phantom contained the following in distilled, deionized water: 43mM sodium dodecyl sulfate (surfactant, Sigma Aldrich, St. Louis, MO), 43mM sodium chloride, 3.75mM sodium azide, and 0.3mM gadobenate dimeglumine (MultiHance, Bracco Inc.). Agar (2.0% w/v) was added over heat with stirring until melted. Volumes of the water solution were poured into vials containing pre-measured peanut oil and SPIO volumes, mixed through gentle inversion for approximately two minutes, and formed a solid gel when cooled to room temperature. Fat-fractions (0.0, 2.7, 5.4, 10.7, 21.2, 31.6, 41.8, 51.9, and 100.0%) and iron concentrations were re-calculated to reflect the actual volume of the water mixture present due to losses in transfer and cooling.
Micrographs of examples of the phantom (50% fat with 20 μg Fe/mL, and 10% fat with 20 μg Fe/mL) were created on a separate day to investigate the microscopic behavior of the emulsion at a low and high fat-fraction. A drop of the fresh emulsion was placed onto a slide with a coverslip before complete cooling occurred. Photographs and measurements of structure size at 40x magnification were taken using MicroSuite (Basic Edition v 2.3 (Build 1121), Olympus America Inc., Center Valley, PA).
