Quantification of the accuracy limits of image registration using peak signal-to-noise ratio
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A new method was developed for quantifying the accuracy limits of image registration devices and the distortion of anatomical structures in verification images without image registration. A correlation was found between peak signal-to-noise ratio (PSNR) and the amount of parallel movement (1–10 mm at 1-mm intervals) of a rectangular parallelepiped phantom [correlation coefficient (CC) −0.91, contribution ratio (CR) 0.83]. Rotating the phantom from 1° to 10° at 1° intervals produced a similar correlation with PSNR (CC −0.91, CR 0.83). To allow for manual registration, the grid pattern of the Mylar top plate was extracted from 455 pelvic portal images of 21 patients using a band-pass filtering technique. This revealed a different correlation between the original data (CC −0.62, CR 0.38) and averaged data (CC −0.96, CR 0.92), but this is considered to have been caused by structural distortion and manual matching errors. Thus, PSNR can be used to evaluate the accuracy limits of image registration and provide a judgment index that can be used in re-planning or re-setup in adaptive radiotherapy.
KeywordsSetup accuracy Peak signal-to-noise ratio Image registration Image-guided radiotherapy Geometric uncertainty Adaptive radiotherapy
Compliance with ethical standards
This study was funded by a Kazuya Yamashita Grant of the Japanese Society of Radiological Technology (Grant Number 1).
Conflict of interest
The authors declare that they have no conflict of interest.
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