Seminal vesicle intrafraction motion 79 Supplementary A Additional improvements were made to the original prostate registration algorithm to allow the method to more accurately track small volumes with relatively large displacements, such as the seminal vesicles. These improvements included the use of an additional metric (mean squared difference between the grey values of the voxels in the fixed and moving image), in addition to mutual information and the use of increased spatial sampling. Using increased spatial sampling allows the method to compare a relative higher number of voxels in the mask. This approach reduces the risk of mismatches but comes at the cost of increased processing times. To reduce the influence of banding artefacts with the used bTFE sequence, shimming was used. This was performed by using a shimbox centring the prostate. Description Value Sequence bTFE without fat suppression Time per dynamic 9.36 sec Relaxation time TR 4.7 ms Echo time TE 2.3 ms Field strength B0 1.5 T Flip angle 50˚ Field of view 448 x 448 x 45 voxels Acquired voxel spacing 2 x 2 x 2.2 mm Reconstructed voxel spacing 1.01 x 1.01 x 2.2 mm Bandwidth 434 Hz/px Table S1 – Imaging parameters used for the acquisition of the cine-MR images. The images were acquired with a 3D balanced turbo field echo (bTFE) without fat suppression. 4
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