MR Imaging of Magnetic Ink Patterns via Off-Resonance Sensitivity
The magnetic susceptibility effects of magnetic ink in MRI can be exploited to visualize magnetic ink patterns placed on the skin. Similar to metal, magnetic ink has a significant magnetic susceptibility difference compared to body tissues, which causes artifacts in MR images such as failure of fat suppression. In the case of magnetic ink, the susceptibility difference is small enough that a failure of fat suppression near a pattern placed on the skin can provide information about the shape of the pattern. Thus magnetic ink patterns can be used as MR-visible skin markers of arbitrary shape and size that are also visible by eye, which could be useful for fusion of MR data to the body via augmented reality, surgical planning, radiation therapy, tracking of joint movement, or other image registration scenarios. In this work, we evaluate the ability to use MRI with spectral presaturation to visualize magnetic ink patterns and assess the ability to use these patterns as MR-visible skin markers in vivo.
Perkins SL, Daniel BL, Hargreaves BA. MR imaging of magnetic ink patterns via off-resonance sensitivity. Magn Reson Med. 2018 Nov;80(5):2017-23.
A magnetic ink grid pattern applied to the chest of a male volunteer was imaged using spectral presaturation tuned to suppress fat and water, and the grid pattern can be identified in a maximum intensity project (MIP) of the MR images. The deformation of the grid pattern as the arm changes position can also be identified in both the reference photos and the MR data, which could be useful for image registration scenarios.
