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Abstract
Purpose
The purpose of this study is to develop a simple method to measure magnetic susceptibility of arbitrarily shaped materials through MR imaging and numerical modeling.
Materials and Methods
Our 3D printed phantom consists of a lower compartment filled with a gel (gel part) and an upper compartment for placing a susceptibility object (object part). The B0 maps of the gel with and without the object were reconstructed from phase images obtained in a 3T MRI scanner. Then, their difference was compared with a numerically modeled B0 map based on the geometry of the object, obtained by a separate MRI scan of the object possibly immersed in an MR-visible liquid. The susceptibility of the object was determined by a least-squares fit.
Results
A total of 18 solid and liquid samples were tested, with measured susceptibility values in the range of −12.6 to 28.28 ppm. To confirm accuracy of the method, independently obtained reference values were compared with measured susceptibility when possible. The comparison revealed that our method can determine susceptibility within approximately 5%, likely limited by the object shape modeling error.
References
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Fig. 1.
(a, b) Pictures of the phantom. The phantom consists of an object part (i), gel part (ii), cap for the gel part (iii), supporter (iv), and the object (vi), and is placed in the posterior half of a head coil (v). The gel part and the object part can be detached as shown in (b).
Fig. 3.
Images of the object part (a) and the gel part (b) of the phantom, and their combination obtained by post-processing (c). (a) and (b) correspond to the third and the first images, respectively, on the transverse plane.
Fig. 4.
Reduction of susceptibility artifacts on the object immersed in paramagnetic Gadolinium solution. (a) Magnitude image of a grey 3D printing material in tap water. (b) Magnitude image of the same material in a gadolinium solution (χ = 8.54 ppm). Red arrows indicate signal loss artifacts. Images are shown on a coronal plane.
Fig. 5.
B0 map comparison: measured B0 maps (a, b), simulated B0 maps (c, d), and error (= simulated minus measured) maps (e, f). Note differences in color scales. (a, c, e) are from the ivory cuboid sample and (b, d, f) are from ceramic screws which had fine features.
Table 1.
(a) Magnetic susceptibility of several materials measured by the proposed method. (b, c) Comparison between the reference and measured values
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