Program Information
SI-Traceable Imaging Phantoms for MRI
S Russek, M Boss, K Keenan, K Stupic, NIST, Boulder, CO,
Presentations
SU-K-708-5 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 708
Purpose: To develop primary calibration structures for MRI that have precisely defined properties traceable to the International System of Units (SI). Properties include T1 and T2 proton-spin relaxation times, apparent water diffusion coefficients (ADC), resolution, and geometric distortion. In addition to the primary measurands, the properties of the phantom structure, including dielectric constant, conductivity, and magnetic susceptibility must be determined to fully understand and model MRI-based measurements. Here, we review the challenges of this new class of phantoms as well as the initial use in clinical research and advanced imaging.
Methods: A suite of MRI phantoms have been designed, fabricated, and commercialized including a system phantom, a diffusion phantom and a breast phantom. These phantoms include paramagnetic solutions for T1 T2 arrays, polymer solutions for ADC calibration, fiducial spheres for geometric distortion, and fat/tissue mimics. The properties of phantom materials are determined through temperature-controlled variable-field NMR, imaging on a MRI metrology scanner, electromagnetic properties measurements, and SQUID magnetometry.
Results: Rigorous but pragmatic definitions of parameters for the major MRI biomarkers have been developed. SI traceable measurement protocols and initial measurements for T1, T2 and ADC have been completed. SI-traceable measurements, with the associated certificates, are expected within 12 months. The phantoms are currently being used at clinical research sites to evaluate new faster quantitative imaging techniques, to homogenize images across scanners, and to develop quality control guidlines for clinical trials evaluating diffusion-based imaging for cancer detection/monitoring. These initial uses have indicated that it is necessary to guarantee phantom-parameter accuracy and stability of 2%.
Conclusion: As medical imaging improves with increased reliance on quantitative measurement of critical biomarkers, there is an increasing need for more rigorous calibration structures with the associated SI-traceable measurement of their properties. We have developed a suite of phantoms and associated measurement structure to meet this need.
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