Bone material analogues for PET/MRI phantoms

摘要

Purpose To develop bone material analogues that can be used in construction of phantoms for simultaneous PET/MRI systems. Methods Plaster was used as the basis for the bone material analogues tested in this study. It was mixed with varying concentrations of an iodinated CT contrast, a gadolinium‐based MR contrast agent, and copper sulfate to modulate the attenuation properties and MRI properties (T1 and T2*). Attenuation was measured with CT and 68 Ge transmission scans, and MRI properties were measured with quantitative ultrashort echo time pulse sequences. A proof‐of‐concept skull was created by plaster casting. Results Undoped plaster has a 511?keV attenuation coefficient (~0.14?cm ?1 ) similar to cortical bone (0.10–0.15?cm ?1 ), but slightly longer T1 (~500?ms) and T2* (~1.2?ms) MR parameters compared to bone (T1?~?300?ms, T2* ~ 0.4?ms). Doping with the iodinated agent resulted in increased attenuation with minimal perturbation to the MR parameters. Doping with a gadolinium chelate greatly reduced T1 and T2*, resulting in extremely short T1 values when the target T2* values were reached, while the attenuation coefficient was unchanged. Doping with copper sulfate was more selective for T2* shortening and achieved comparable T1 and T2* values to bone (after 1?week of drying), while the attenuation coefficient was unchanged. Conclusions Plaster doped with copper sulfate is a promising bone material analogue for a PET/MRI phantom, mimicking the MR properties (T1 and T2*) and 511?keV attenuation coefficient of human cortical bone.