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SU‐G‐IeP1‐08: MR Geometric Distortion Dependency On Imaging Sequence, Acquisition Orientation and Receiver Bandwidth of a Dedicated 1.5T MR‐Simulator
Author(s) -
Law M,
Yuan J,
Wong O,
Yu S
Publication year - 2016
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 - 10.1118/1.4956968
Subject(s) - imaging phantom , orientation (vector space) , distortion (music) , isotropy , computer science , physics , matlab , artificial intelligence , nuclear medicine , bandwidth (computing) , geometry , mathematics , optics , medicine , amplifier , computer network , operating system
Purpose: To investigate the 3D geometric distortion of four potential MR sequences for radiotheraptic applications, and its dependency on sequence‐type, acquisition‐orientation and receiver‐bandwidth from a dedicated 1.5T 700mm‐wide bore MR‐simulator (Magnetom‐Aera, Sienmens Healthcare, Erlangen, Germany), using a large customized geometric accuracy phantom. Methods: This work studied 3D gradient‐echo (VIBE) and spin‐echo (SPACE) sequences for anatomical imaging; a specific ultra‐short‐TE sequence (PETRA) potentially for bone imaging and MR‐based dosimetry; and a motion‐insensitive sequence (BLADE) for dynamic applications like 4D‐MRI. Integrated geometric‐correction was employed, three orthogonal acquisition‐orientations and up to three receiver‐bandwidths were used, yielding 27 acquisitions for testing (Table 1a).A customized geometric accuracy phantom (polyurethane, MR/CT invisible, W×L×H:55×55×32.5cm3) was constructed and filled with 3892 spherical markers (6mm diameter, MR/CT visible) arranged on a 25mm‐interval 3D isotropic‐grid (Fig.1). The marker positions in MR images were quantitatively calculated and compared against those in the CT‐reference using customized MatLab scripts. Results: The average distortion within various diameter‐of‐spherical‐volumes (DSVs) and the usable DSVs under various distortion limits were measured (Tables 1b‐c). It was observed that distortions fluctuated when sequence‐type, acquisition‐orientation or receiver‐bandwidth changed (e.g. within 300mm‐DSV, the lowest/highest average distortions of VIBE were 0.40mm/0.59mm, a 47.5% difference). According to AAPM‐TG66 (<1mm distortion, left‐most column of Table 1c), PETRA (Largest‐DSV:253.9mm) has the potential on brain treatment, while BLADE (Largest‐DSV:207.2mm) may need improvement for thoracic/abdominal applications. The results of VIBE (Largest‐DSVs:294.3mm, the best among tested acquisitions) and SPACE (Largest‐DSVs:267.7mm) suggests their potentials on head and neck applications. These Largest‐DSVs were attained on different acquisition‐orientations and receiver‐bandwidths. Conclusion: Geometric distortion was shown to be dependent on sequence‐type, acquisition‐orientation and receiver‐bandwidth. In the experiment, no configuration in any one of these factors could consistently reduce distortion while the others were varying. The distortion analysis result is a valuable guideline for sequence selection and optimization for MR‐aided radiotherapy applications.