Encrypted login | home

Program Information

A Sequence Independent Approach for Quantification of MR Image Deformations From Brachytherapy Applicators

no image available
N van Wieringen

N van Wieringen*, L van Heerden , O Gurney-Champion , Z van Kesteren , A Houweling , B Pieters , A Bel , Academic Medical Center, Amsterdam, The Netherlands


SU-E-J-216 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

MRI is increasingly used as a single imaging modality for brachytherapy treatment planning. The presence of a brachytherapy applicator may cause distortions in the images, especially at higher field strengths. Our aim is to develop a procedure to quantify these distortions theoretically for any MR-sequence and to verify the estimated deformations for clinical sequences.

Image distortions due to perturbation of the B0-field are proportional to the ratio of the induced frequency shift and the read-out bandwidth of the applied sequence. By reconstructing a frequency-shift map from the phase data from a multi-echo sequence, distortions can be calculated for any MR-sequence.

Verification of this method for estimating distortions was performed by acquiring images with opposing read-out directions and consequently opposing distortions. The applicator shift can be determined by rigidly matching these images. Clinically, T2W-TSE-images are used for this purpose. For pre-clinical tests, EPI-sequences with narrow read-out bandwidth (19.5-47.5Hz), consequently large distortions, were added to the set of clinical MR-sequences.

To quantify deformations of the Utrecht Interstitial CT/MR applicator (Elekta Brachytherapy) on a Philips Ingenia 3T MRI, pre-clinical tests were performed in a phantom with the applicator in water, followed by clinical validation.

Deformations observed in the narrow bandwidth EPI-images were well predicted using the frequency-shift, the latter giving an overestimation up to 30%/up to 1 voxel. For clinically applied MR-sequences distortions were well below the voxel size.

In patient setup distortions determined from the frequency-shift map were at sub-voxel level (<0.7mm). Using T2W-images larger distortions were found (1-2mm). This discrepancy was caused by patient movement between/during acquisition of the T2W-images with opposing read-out directions.

Phantom experiments demonstrated the feasibility of a clinical procedure for quantification of MR-image distortions for any MR-sequence. In a clinical set-up the distortions from a Utrecht interstitial CT/MR applicator are sub-voxel level.

Funding Support, Disclosures, and Conflict of Interest: This work was partially funded by Elekta Brachytherpy

Contact Email: