Abstract
Fabrication of a spherical multi-compartment MRI phantom is demonstrated that can be used to validate magnetic resonance (MR)-based susceptibility imaging reconstruction. The phantom consists of a 10 cm diameter gelatin sphere that encloses multiple smaller gelatin spheres doped with different concentrations of paramagnetic contrast agents. Compared to previous multi-compartment phantoms with cylindrical geometry, the phantom provides the following benefits: (1) no compartmental barrier materials are used that can introduce signal voids and spurious phase; (2) compartmental geometry is reproducible; (3) spherical susceptibility boundaries possess a ground-truth analytical phase solution for easy experimental validation; (4) spherical geometry of the overall phantom eliminates background phase due to air-phantom boundary in any scan orientation. The susceptibility of individual compartments can be controlled independently by doping. During fabrication, formalin cross-linking and water-proof surface coating effectively blocked water diffusion between the compartments to preserve the phantom's integrity. The spherical shapes were realized by molding the inner gel compartments in acrylic spherical shells, 3 cm in diameter, and constructing the whole phantom inside a larger acrylic shell. From gradient echo images obtained at 3T, we verified that the phantom produced phase images in agreement with the theoretical prediction. Factors that limit the agreement include: air bubbles trapped at the gel interfaces, imperfect magnet shimming, and the susceptibility of external materials such as the phantom support hardware. The phantom images were used to validate publicly available codes for quantitative susceptibility mapping. We believe that the proposed phantom can provide a useful testbed for validation of MR phase imaging and MR-based magnetic susceptibility reconstruction.
Highlights
We have demonstrated fabrication of a spherical gelatin phantom with spherical inclusions with different magnetic susceptibilities for possible use as a testbed for magnetic resonance (MR)-based susceptibility imaging
Non-spherical phantoms have been successfully used for multi-center quantitative susceptibility mapping (QSM) validation [7], we believe that spherical phantoms have merit for volumetric measurements and phase imaging with available "ground truth"
It is our expectation that the proposed spherical inclusion phantom could be of use to validate
Summary
Static magnetic susceptibility is an important magnetic resonance imaging (MRI) biomarker that carries information about iron deposit in tissue as well as myelin density and hemorrhage. Since the susceptibility-induced phase maps are strongly orientation dependent, a phantom that can be imaged in any scan plane is desirable for volumetric susceptibility imaging validation With these points in mind, here we demonstrate fabrication of a spherical phantom with spherical inner compartments ("inclusions"), in which a 10 cm-diameter spherical gelatin body encloses smaller spherical gelatin balls at controlled locations without using foreign barrier or support materials. The spherical shape of the overall phantom served to eliminate bulk background phase caused by the air-phantom boundary, whereas the spherical inner compartments produced 3D phase variation according to a known analytical solution These beneficial features hold regardless of the phantom’s physical orientation in the magnet bore or the scan plane choice. We demonstrate use of our phantom to validate publicly available QSM reconstruction software
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