Global registration matrices values.
Transformations values for the registration used for the T1W (top row – a and b) and T2W (low row – c and d) and for 7T/PS (left column – a and c) and 7T/AS (right column – b and d) images, as derived from the corresponding transformation matrices. The transformation values are measured as maximum scaling change (deviation of the scaling form 1), maximum skew (measured as the tangent of the skew angle), and volume change (deviation of the transformation determinant form 1) that were needed for global registration between 7 T and 1.5 T images. The values indicate that the registration operators are essentially rigid body transformations with negligible linear corrections in scaling, skew, and the transformation determinant. Given the high degree of correspondence between the registered images, these values indicate minimal amount of geometric distortion between the 1.5 T and 7 T images. Greater amount of scaling and skew was recorded for the 7T/AS T2-weighted images (5d). This is due to a stronger gradient employed in the 7T/AS MR system.