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Friday, January 7, 2011

"The MRI Photocopier"

A very interesting note* has recently been published in Concepts in Magnetic Resonance Part A by Joseph Hornak (generous provider of the two excellent free online text books, The Basics of NMR and The Basics of MRI ). In this work, it is demonstrated that an MRI scanner can be used to reproduce an image of printed text. The technique is based on the fact that the toner used to print text contains ferromagnetic particles and when placed in the uniform magnetic field of an MRI magnet, the magnetic field near the ferromagnetic toner is distorted. The "sample" is prepared by placing the printed page face up on a polycarbonate plate and covering it with a very thin sheet of polyethylene. The polyethylene is covered with water (doped with CuSO4 as a relaxation agent). The "sample" is placed in the magnet such that the plane of the page is perpendicular to the magnetic field. The text is "scanned" by taking a 2D proton MR image of a slice of the water near the surface of the polyethylene. The distortion in the magnetic field due to the ferromagnetic toner renders the text visible in the 2D magnetic resonance image. This is demonstrated in the figure below (from the reference) where a 2.5 mm thick slice above the polyethylene was imaged. The text was printed in #36 Arial font. The author speculates that this technique may be applied to the analysis of paintings.
* Joseph P. Hornak, "Magnetic Resonance Imaging of Printed Text", Concepts in Magnetic Resonance Part A. 36A, 347 (2010).

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