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Dynamic keyhole: A novel method to improve MR images in the presence of respiratory motion for real‐time MRI
Author(s) -
Lee Danny,
Pollock Sean,
Whelan Brendan,
Keall Paul,
Kim Taeho
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4883882
Subject(s) - keyhole , nuclear medicine , magnetic resonance imaging , medical imaging , medicine , motion (physics) , radiology , respiratory system , computer science , biomedical engineering , computer vision , materials science , anatomy , welding , metallurgy
Purpose: In this work, the authors present a novel magnetic resonance imaging reconstruction method to improve the quality of MR images in the presence of respiratory motion for real‐time thoracic image‐guided radiotherapy. Methods: This new reconstruction method is called dynamic keyhole and utilizes a library of previously acquired, peripheral k‐space datasets from the same (or similar) respiratory state in conjunction with central k‐space datasets acquired in real‐time. Internal or external respiratory signals are utilized to sort, match, and combine the two separate peripheral and central k‐space datasets with respect to respiratory displacement, thereby reducing acquisition time and improving image quality without respiratory‐related artifacts. In this study, the dynamic keyhole, conventional keyhole, and zero‐filling methods were compared to full k‐space acquisition (ground truth) for 60 coronal datasets acquired from 15 healthy human subjects. Results: For the same image‐quality difference from the ground‐truth image, the dynamic keyhole method reused 79% of the prior peripheral phase‐encoding lines, while the conventional keyhole reused 73% and zero‐filling 63% ( p ‐value < 0.0001), corresponding to faster acquisition speed of dynamic keyhole for real‐time imaging applications. Conclusions: This study demonstrates that the dynamic keyhole method is a promising technique for clinical applications such as image‐guided radiotherapy requiring real‐time MR monitoring of the thoracic region. Based on the results from this study, the dynamic keyhole method could increase the temporal resolution by a factor of five compared with full k‐space methods.