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Suitability of miniature inductively coupled RF coils as MR‐visible markers for clinical purposes
Author(s) -
Garnov Nikita,
Thörmer Gregor,
Trampel Robert,
Gründer Wilfried,
Kahn Thomas,
Moche Michael,
Busse Harald
Publication year - 2011
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 - 10.1118/1.3655027
Subject(s) - steady state free precession imaging , electromagnetic coil , scanner , signal (programming language) , physics , radio frequency , nuclear magnetic resonance , optics , radiofrequency coil , magnetic resonance imaging , flip angle , pulse sequence , computer science , medicine , radiology , telecommunications , quantum mechanics , programming language
Purpose: MR‐visible markers have already been used for various purposes such as image registration, motion detection, and device tracking. Inductively coupled RF (ICRF) coils, in particular, provide a high contrast and do not require connecting wires to the scanner, which makes their application highly flexible and safe. This work aims to thoroughly characterize the MR signals of such ICRF markers under various conditions with a special emphasis on fully automatic detection.Methods: The small markers consisted of a solenoid coil that was wound around a glass tube containing the MR signal source and tuned to the resonance frequency of a 1.5 T MRI. Marker imaging was performed with a spoiled gradient echo sequence (FLASH) and a balanced steady‐state free precession (SSFP) sequence (TrueFISP) in three standard projections. The signal intensities of the markers were recorded for both pulse sequences, three source materials (tap water, distilled water, and contrast agent solution), different flip angles and coil alignments with respect to the B 0 direction as well as for different marker positions in the entire imaging volume (field of view, FOV). Heating of the ICRF coils was measured during 10‐min RF expositions to three conventional pulse sequences. Clinical utility of the markers was assessed from their performance in computer‐aided detection and in defining double oblique scan planes.Results: For almost the entire FOV (±215 mm) and an estimated 82% of all possible RF coil alignments with respect to B 0 , the ICRF markers generated clearly visible MR signals and could be reliably localized over a large range of flip angles, in particular with the TrueFISP sequence (0.3°–4.0°). Generally, TrueFISP provided a higher marker contrast than FLASH. RF exposition caused a moderate heating (≤5 °C) of the ICRF coils only.Conclusions : Small ICRF coils, imaged at low flip angles with a balanced SSFP sequence showed an excellent performance under a variety of experimental conditions and therefore make for a reliable, compact, flexible, and relatively safe marker for clinical use.