Validation of continuously tagged MRI for the measurement of dynamic 3D skeletal muscle tissue deformation

Purpose: Typically spatial modulation of the magnetization (SPAMM) tagged magnetic resonance imaging (MRI) requires many repeated motion cycles limiting the applicability to highly repeatable tissue motions only. This paper describes the validation of a novel SPAMM tagged MRI and post-processing framework for the measurement of complex and dynamic 3D soft tissue deformation following just three motion cycles. Techniques are applied to indentation induced deformation measurement of the upper arm and a silicone gel phantom. Methods: A SPAMM tagged MRI methodology is presented allowing continuous (3.3-3.6 Hz) sampling of 3D dynamic soft tissue deformation using non segmented 3D acquisitions. The 3D deformation is reconstructed by the combination of three mutually orthogonal tagging directions, thus requiring only three repeated motion cycles. In addition a fully automatic post-processing framework is presented employing Gabor scale-space and filter-bank analysis for tag extrema segmentation and triangulated surface fitting aided by Gabor filter bank derived surface normals. Deformation is derived following tracking of tag surface triplet triangle intersections. The dynamic deformation measurements were validated using indentation tests (similar to 20 mm deep at 12 mm/s) on a silicone gel soft tissue phantom containing contrasting markers which provide a reference measure of deformation. In addition, the techniques were evaluated in vivo for dynamic skeletal muscle tissue deformation measurement during indentation of the biceps region of the upper arm in a volunteer. Results: For the phantom and volunteer tag point location precision were 44 and 92 mu m, respectively resulting in individual displacements precisions of 61 and 91 mu m, respectively. For both the phantom and volunteer data cumulative displacement measurement accuracy could be evaluated and the difference between initial and final locations showed a mean and standard deviation of 0.44 and 0.59 mm for the phantom and 0.40 and 0.73 mm for the human data. Finally accuracy of (cumulative) displacement was evaluated using marker tracking in the silicone gel phantom. Differences between true and predicted marker locations showed a mean of 0.35 mm and a standard deviation of 0.63 mm. Conclusions: A novel SPAMM tagged MRI and fully automatic post-processing framework for the measurement of complex 3D dynamic soft tissue deformation following just three repeated motion cycles was presented. The techniques demonstrate dynamic measurement of complex 3D soft tissue deformation at subvoxel accuracy and precision and were validated for 3.3-3.6 Hz sampling of deformation speeds up to 12 mm/s. (C) 2012 American Association of Physicists in Medicine. [DOI: 10.1118/1.3685579

A scale space based algorithm for automated segmentation of single shot tagged MRI of shearing deformation

This study proposes a scale space based algorithm for automated segmentation of single-shot tagged images of modest SNR. Furthermore the algorithm was designed for analysis of discontinuous or shearing types of motion, i.e. segmentation of broken tag patterns. The proposed algorithm utilises non-linear scale space for automatic segmentation of single-shot tagged images. The algorithm's ability to automatically segment tagged shearing motion was evaluated in a numerical simulation and in vivo. A typical shearing deformation was simulated in a Shepp-Logan phantom allowing for quantitative evaluation of the algorithm's success rate as a function of both SNR and the amount of deformation. For a qualitative in vivo evaluation tagged images showing deformations in the calf muscles and eye movement in a healthy volunteer were acquired. Both the numerical simulation and the in vivo tagged data demonstrated the algorithm's ability for automated segmentation of single-shot tagged MR provided that SNR of the images is above 10 and the amount of deformation does not exceed the tag spacing. The latter constraint can be met by adjusting the tag delay or the tag spacing. The scale space based algorithm for automatic segmentation of single-shot tagged MR enables the application of tagged MR to complex (shearing) deformation and the processing of datasets with relatively low SN

Use of continuously MR tagged imaging for automated motion assessment in the abdomen: A feasibility study

Purpose: To investigate the feasibility of measuring motion in the abdomen using a continuously tagged magnetic resonance imaging sequence. Materials and Methods: To assess (nonperiodic) motion in the abdomen, a nontriggered, continuously tagged transient field echo (TFE) sequence was implemented that acquires one complete 3D dataset per prepulse after a fixed delay. In postprocessing, a frequency analysis approach was developed for compact reviewing of the data and noise suppression. For proof of principle, a simulation was made and one free-breathing dynamic in vivo scan was acquired in a healthy volunteer. During the dynamic scan the volunteer received glucagon intravenously. Results: The simulation showed that this frequency analysis enables the extraction of motion at low signal-to-noise ratio levels. Motion information was successfully gathered from the in vivo scan. The decline in bowel motion caused by the administration of glucagon could be quantitatively measured using the continuously tagged sequence. Conclusion: Continuously tagged imaging in the abdomen for the purpose of automated gathering of motion information is feasible and could aid the study of bowel motion. J. Magn. Reson. Imaging 2012;36:492497. (c) 2012 Wiley Periodicals, In