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. 2022 Feb 2;9(12):2105333. doi: 10.1002/advs.202105333

Figure 2.

Figure 2

Locating the thermoseed. a) Distortion MRI artifact caused by the ferromagnetic properties of the thermoseed. Image of a 0.5 mm diameter chrome steel sphere acquired with a fast spin‐echo pulse sequence. b) Simulated map of resonance frequencies surrounding a 0.5 mm diameter thermoseed. c) Discrete bands can be selectively excited using a frequency‐selective MRI pulse sequence.[ 30 , 31 ] The signal can be projected onto a 2D plane or 1D axis, from which the thermoseed's location can be determined. d) An agar phantom consisting of three plastic fiducial markers and one thermoseed was used to assess the accuracy of the frequency‐selective MRI method. e) Ground truth distances between each thermoseed‐marker pair were calculated from CT images. f) Marker coordinates were determined from fast spin‐echo MR images. Thermoseed coordinates were calculated using the frequency‐selective MRI method, and thermoseed‐marker distances were compared with CT values to assess method accuracy.