Abstract
In a general scenario, the brain images acquired from magnetic resonance imaging (MRI) may experience tilt, distorting brain MR images. The tilt experienced by the brain MR images may result in misalignment during image registration for medical applications. Manually correcting (or estimating) the tilt on a large scale is time-consuming, expensive, and needs brain anatomy expertise. Thus, there is a need for an automatic way of performing tilt correction in three orthogonal directions (X, Y, Z). The proposed work aims to correct the tilt automatically by measuring the pitch angle, yaw angle, and roll angle in X-axis, Z-axis, and Y-axis, respectively. For correction of the tilt around the Z-axis (pointing to the superior direction), image processing techniques, principal component analysis, and similarity measures are used. Also, for correction of the tilt around the X-axis (pointing to the right direction), morphological operations, and tilt correction around the Y-axis (pointing to the anterior direction), orthogonal regression is used. The proposed approach was applied to adjust the tilt observed in the T1- and T2-weighted MR images. The simulation study with the proposed algorithm yielded an error of 0.40 ± 0.09°, and it outperformed the other existing studies. The tilt angle (in degrees) obtained is ranged from 6.2 ± 3.94, 2.35 ± 2.61, and 5 ± 4.36 in X-, Z-, and Y-directions, respectively, by using the proposed algorithm. The proposed work corrects the tilt more accurately and robustly when compared with existing studies.
Highlights
Kalavathi et al [23] used skull stripped brain images, followed by curve fitting. Even though it is robust and straightforward compared with previous works, it fails to correct the tilt if the rotation angle exceeds 15°
This study has included fourteen epileptic patients brain magnetic resonance imaging (MRI) acquired in part of the magnetoencephalography (MEG) protocol at National Institute of Mental Health and Neurosciences (NIMHANS)
MR volume suffers from tilt when a subject may not correctly align inside the gantry
Summary
The brain images are tilted [1] when acquired through these modalities rather than aligned with the scanner. Visual inspection of such images by clinicians while diagnosis can lead to erroneous perception of abnormalities [2,3,4]. Content-based methods explore the brain’s bilateral symmetry by matching the intensities of one half of the brain with the other half of the brain. In 3D-based methods, the tilt correction is performed by the plane that maximizes the bilateral symmetry by considering the head as a whole volume [18]. The proposed study employed the content-based techniques to correct the tilt in X, Y, Z-directions of brain MR images
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