Dharshan Chandramohan1, Peng Cao1, Misung Han1, Hongyu An2, John J Sunderland3, Paul E Kinahan4, Richard Laforest2, Thomas A Hope1, Peder E Z Larson1. 1. Department of Radiology and Biomedical Imaging, University of California - San Francisco, San Francisco, CA, 94143, USA. 2. Department of Radiology, Washington University, St. Louis, MO, 63110, USA. 3. Departments of Radiology, Radiation Oncology, and Physics and Astronomy, University of Iowa, Iowa City, IA, 52242, USA. 4. Department of Radiology, University of Washington, Seattle, WA, 98195, USA.
Abstract
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.
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.
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