Quantification and correction of geometric distortions in low-field MRI

Juan M. Parra Robles; William Dominguez; Evelio R Gonzalez M.D.; Ilse Berdellans

doi:10.1117/12.349545

28 May 1999 Quantification and correction of geometric distortions in low-field MRI

Juan M. Parra Robles, William Dominguez, Evelio R Gonzalez M.D., Ilse Berdellans

Proceedings Volume 3659, Medical Imaging 1999: Physics of Medical Imaging; (1999) https://doi.org/10.1117/12.349545
Event: Medical Imaging '99, 1999, San Diego, CA, United States

Abstract

Geometric distortions are one of the most important degrading factors in MRI. They usually do not greatly affect the clinical relevance of images, but their correction is indispensable for lesion volume measurements, radiotherapy and surgical planning. In this work, the main sources of geometric distortion in Cuban low-field MRI systems are studied. Geometric distortion models and correction algorithms are tested by means of computer simulation using theoretical distributions of the magnetic fields. The real distributions are determined from images of a grid phantom. Calculated static field distributions showed that the system magnetic center is shifted, relative to magnet geometric center. Quantitative measurements provided inhomogeneity values (93 ppm in a spherical region of diameter 256 mm) larger than calibration data (65 ppm) obtained 15 months ago. The shim settings must be readjusted. The temporal behavior of static field was also studied. The magnet heating produces a slow time variation in static field intensity, but field error distribution proved to be stable. In the images, geometric distortions increase with increasing distance from image center and ranged from -6 to 7 mm. The implemented correction procedure reduced distortions from maximally 7 mm to the order of pixel resolution (0.8 - 1 mm).

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Juan M. Parra Robles, William Dominguez, Evelio R Gonzalez M.D., and Ilse Berdellans "Quantification and correction of geometric distortions in low-field MRI", Proc. SPIE 3659, Medical Imaging 1999: Physics of Medical Imaging, (28 May 1999); https://doi.org/10.1117/12.349545

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KEYWORDS

Magnetism

Magnetic resonance imaging

Calibration

Nonlinear filtering

Silver

Digital filtering

Head

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