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WE‐G‐WAB‐03: 4D Composite MR Image Distortion Field: Quantification and Applications for MRI‐Guided Radiotherapy
Author(s) -
Stanescu T,
Tadic T,
Jaffray D
Publication year - 2013
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 - 10.1118/1.4815645
Subject(s) - distortion (music) , diaphragm (acoustics) , medical imaging , physics , nuclear medicine , artificial intelligence , medicine , computer science , acoustics , vibration , amplifier , optoelectronics , cmos
Purpose: To study the interplay effects of MR image distortion fields for moving/deformable anatomy and their implications for MR‐guided radiotherapy. Methods: The composite distortion field is given by the combination of two independent components a) the system‐related distortions due to B0 inhomogeneities and imaging gradients nonlinearities and b) the tissue magnetic susceptibility‐induced effects. Field a) is static while b) is dynamic, modifying as a function of tissue interface characteristics (shape, location, type of neighboring tissues). The field experienced by a moving or deformable (over time) target/organ can be very complex as entity changes location and shape. Field a) was measured with a linearity object in conjunction with a harmonic analysis. Field b) was computed numerically using a finite difference method. Both fields were quantified for moving/deformable anatomy using multiple image data bins derived from 4D CT and 4D MRI for several lung and liver cases. Results: The 4D composite field tools and methodology was validated in phantoms. The independent and combined distortion fields were quantified for several lung and liver patients. For a lung case with a target travelling 2.4 cm in the superior‐inferior direction, the susceptibility distortions for the inhale and exhale phases were 3.84 and 2.5 ppm, respectively. The system distortion difference for the two phases was about 1 mm. The maximum 4D composite distortion between the inhale and exhale was approximately 1.5 mm. For liver, the target experienced negligible distortions (embedded in soft‐tissue) and the diaphragm showed a local distortion larger than 1 mm. Conclusion: The combined effect due to various types of MR image distortions were quantified for organ motion/deformation. Geometric distortion introduced by the 4D composite field may be significant for certain scenarios. However, this can be mitigated by a careful selection of imaging and by implementing robust methods for image correction.