Single shot MR tagging to quantify local tissue deformation during MRI-guided needle interventions: A feasibility study
(a) Block diagram of the intervention protocol and (b) Schematic overview of the proposed single shot tagging sequence. The red lines indicate the sample periods. Tag delay is defined as the time between the simulated trigger event and the application of the 1331-pulse, while the trigger delay determines the time between the trigger event and the center of the excitation pulse that samples the central line in k-space (k = 0).
Relative tag contrast in time for several flip angles, assuming the imaging takes place directly after magnetization preparation, n = t/TR, TR = 4 ms, (a) T1 = 1000 ms and T2 = 100 ms and (b) T1 = 600 ms and T2 = 40 ms.
(a) translation phantom, (b) rotation phantom, (c) needle intervention phantom without plastic cover, and (d) needle intervention phantom with plastic cover.
Tag pattern after meat displacement of (a) 0 mm and (b) 6 mm. The white lines indicate corresponding tag lines. (c) Scatter plot of the measured and actual displacements. The error bars equal a voxel. Tag pattern after meat rotation of (d) 0° and (e) 10°. (f) Scatter plot of the measured and actual rotations. The error bars indicate the minimum and maximum obtained values. The reported values for the mean values, the magnitude of the upper bar and the magnitude of the lower bar are rounded to the first decimal.
Tag pattern (a) with 14 G titanium needle situated in the meat, (b) during needle insertion and (c) during needle retraction. The dashed line mimics an undeformed tagging line (reference).
(a–l) Tagging images of the pelvic area of the volunteer using different scan parameters. The signal intensities on the red line are used to construct the line profile. The pink crosses on the line profile represent the minima, while the black crosses indicate the maxima. The minimum and maximum values are used to window a small area which is created by extending the red line by two voxels in all directions. The line profiles are scaled to the maximum image tag contrast, which was obtained for profile order low-high, α = 140°, and Δ = 0.5 s. Graphs show the relative tag contrast versus Δ for different flip angles, using (m) the profile order: linear, (n) the profile order: low-high.
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