Unsurprisingly, errors were found predominantly near the areas of large phase change and discontinuity in the base phase image. This is an order of magnitude better than required for this algorithm to work well, and therefore this method should be both accurate and robust for phase images acquired with typical MR sequences.
The speed of the two algorithms varied markedly. There are two potential weaknesses of the current approach.
The first arises during the creation of the initial regions. This dramatically reduces the likelihood of finding connecting tracks within noisy areas. In fact, we have not found any phase maps in which two sizable areas have been incorrectly connected using this method. Other methods, such as splitting regions into convex components possibly using morphological operations , could also be pursued.
That is, always choosing the best least opportunity cost candidate pair at each stage, and so can get stuck in a local minimum.
Comparison between the residue-vector map and existing quality maps for phase unwrapping
It would be possible to use alternative optimization methods to solve the cost function minimization e. For both methods the accuracy degraded gradually with decreasing SNR. It is hoped that this will enable more users in the MR community to develop applications for fast, automated phase unwrapping, and to assist in the evaluation and improvement of this algorithm. Volume 49 , Issue 1. If you do not receive an email within 10 minutes, your email address may not be registered, and you may need to create a new Wiley Online Library account.
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Please review our Terms and Conditions of Use and check box below to share full-text version of article. That is: 1. Creating the Initial Regions Many different approaches could be taken to determine the initial regions.
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Many robust phase unwrapping algorithms rely on having good quality or weighting maps. In essence, we present a general comparison between the residue-vector map and existing quality maps for phase unwrapping to evaluate the importance of the newly established residue-vector technique in the phase unwrapping context. Such quality maps used for comparison are phase derivative variance, maximum phase gradient, pseudo-correlation, weighted phase derivative variance and second difference. Flynn's minimum discontinuity phase unwrapping algorithm was used on the same wrapped phase but with different quality maps for result evaluation.
It was found that the residue-vector map was the most robust of all. Google Scholar.