In Vivo MR-Tracking Based on Magnetic Signature Selective Excitation

• Published in: IEEE transactions on medical imaging Vol. 27; no. 1; pp. 28 - 35
• Main Authors: Felfoul, O., Mathieu, J.-B., Beaudoin, G., Martel, S.
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.01.2008; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Artificial Intelligence; Catheterization - methods; Ferromagnetic core tracking; Humans; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Imaging, Three-Dimensional - methods; In vivo; interventional magnetic resonance imaging (MRI); Magnetic cores; magnetic dipole; Magnetic noise; Magnetic resonance; Magnetic resonance imaging; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; medical nanorobots; passive tracking; Pattern Recognition, Automated - methods; Phantoms, Imaging; Radio frequency; Radio navigation; radio-frequency (RF) excitation frequencies; Reproducibility of Results; RF signals; Sensitivity and Specificity; Signal generators; Signal to noise ratio; Surgery, Computer-Assisted - methods
• ISSN: 0278-0062; 1558-254X
• DOI: 10.1109/TMI.2007.897375

A novel magnetic resonance (MR)-tracking method specifically developed to locate the ferromagnetic core of an untethered microdevice, microrobot, or nanorobot for navigation or closed-loop control purpose is described. The tracking method relies on the application of radio-frequency (RF) excitation signals tuned to the equipotential magnetic curves generated by the magnetic signature of the object being tracked. Positive contrast projections are obtained with reference to the position of the magnetic source. A correlation function performed on only one k-space line for each of the three axes and corresponding to three projections, is necessary to obtain a 3-D location of the device. In this study, the effects of the sphere size and the RF frequency offset were investigated in order to find the best contrast noise ratio (CNR) for tracking. Resolution and precision were also investigated by proper measurement of the position of a ferromagnetic sphere by magnetic resonance imaging (MRI) acquisition and by comparing them with the real position. This method is also tested for a moving marker where the positions found by MRI projections were compared with the ones taken with a camera. In vitro and in vivo experiments show the operation of the technique in tortuous phantom and in animal models. Although the method was developed in the prospect of new interventional MR-guided endovascular operations based on miniature untethered devices, it could also be used as a passive tracking method using tools such as catheters or guide wires.