Using a low-amplitude RF pulse at echo time (LARFET) for device localization in MRI
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We describe a new method for frequency down-conversion of MR signals acquired with the radio-frequency projections method for device localization. A low-amplitude, off-center RF pulse applied simultaneously with the echo signal is utilized as the reference for frequency down-conversion. Because of the low-amplitude and large offset from the Larmor frequency, the RF pulse minimally interfered with magnetic resonance of protons. We conducted an experiment with the coil placed at different positions to verify this concept. The down-converted signal was transformed into optical signal and transmitted via fiber-optic cable to a receiver unit placed outside the scanner room. The position of the coil could then be determined by the frequency analysis of this down-converted signal and superimposed on previously acquired MR images for comparison. Because of minimal positional errors (≤0.8 mm), this new device localization method may be adequate for most interventional MRI applications.
KeywordsInterventional MRI Device localization Catheter tracking Frequency down-conversion Self-mixing
The authors thank Umut Cindemir and Berk Camli for their efforts during experiments, Mr. Francis Payne and Dr. Can Akgün for their valuable editorial support. The experiments were conducted at National Magnetic Resonance Research Center (UMRAM) at Bilkent University, Ankara and Acıbadem Kozyatağı Hospital, Istanbul. This study was supported by The Scientific and Technological Research Council Of Turkey (TUBITAK, Project 111E197) and Boğaziçi University LifeSci Center (Ministry of Development, 2009K1200520), and EU Marie Curie Actions IRSES Project 269300 (TAHITI, Improving Therapy and Intervention through Imaging).
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