Fiber Bragg gratings-based sensing for real-time needle tracking during MR-guided brachytherapy Maxence Borot de Battisti a) Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, The Netherlands Baudouin Denis de Senneville Imaging Division, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, The Netherlands and IMB, UMR 5251 CNRS/University of Bordeaux, Talence 33400, France Metha Maenhout, Jan J. W. Lagendijk, and Marco van Vulpen Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, The Netherlands Gilion Hautvast and Dirk Binnekamp Philips Group Innovation Biomedical Systems, Eindhoven 5656 AE, The Netherlands Marinus A. Moerland Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, The Netherlands (Received 21 March 2016; revised 18 July 2016; accepted for publication 13 August 2016; published 6 September 2016; corrected 13 September 2016) Purpose: The development of MR-guided high dose rate (HDR) brachytherapy is under investigation due to the excellent tumor and organs at risk visualization of MRI. However, MR-based localization of needles (including catheters or tubes) has inherently a low update rate and the required image interpretation can be hampered by signal voids arising from blood vessels or calcifications limiting the precision of the needle guidance and reconstruction. In this paper, a new needle tracking prototype is investigated using fiber Bragg gratings (FBG)-based sensing: this prototype involves a MR-compatible stylet composed of three optic fibers with nine sets of embedded FBG sensors each. This stylet can be inserted into brachytherapy needles and allows a fast measurement of the needle deflection. This study aims to assess the potential of FBG-based sensing for real-time needle (including catheter or tube) tracking during MR-guided intervention. Methods: First, the MR compatibility of FBG-based sensing and its accuracy was evaluated. Different known needle deflections were measured using FBG-based sensing during simultaneous MR-imaging. Then, a needle tracking procedure using FBG-based sensing was proposed. This proce- dure involved a MR-based calibration of the FBG-based system performed prior to the interventional procedure. The needle tracking system was assessed in an experiment with a moving phantom during MR imaging. The FBG-based system was quantified by comparing the gold-standard shapes, the shape manually segmented on MRI and the FBG-based measurements. Results: The evaluation of the MR compatibility of FBG-based sensing and its accuracy shows that the needle deflection could be measured with an accuracy of 0.27 mm on average. Besides, the FBG-based measurements were comparable to the uncertainty of MR-based measurements estimated at half the voxel size in the MR image. Finally, the mean(standard deviation) Euclidean distance between MR- and FBG-based needle position measurements was equal to 0.79 mm(0.37 mm). The update rate and latency of the FBG-based needle position measurement were 100 and 300 ms, respectively. Conclusions: The FBG-based needle tracking procedure proposed in this paper is able to deter- mine the position of the complete needle, under MR-imaging, with better accuracy and preci- sion, higher update rate, and lower latency compared to current MR-based needle localization methods. This system would be eligible for MR-guided brachytherapy, in particular, for an improved needle guidance and reconstruction. C 2016 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4961743] Key words: needle tracking, real-time, MR-guided intervention, fiber Bragg grating, optic fiber 1. INTRODUCTION HDR brachytherapy involves placement of needles (includ- ing catheters or tubes) into or close to the tumor, through which a radioactive source (e.g., Ir-192) irradiates the tu- mor for certain times at different positions according to a calculated dose plan. 1 In usual clinical practice, a dose plan is made at the beginning of the brachytherapy procedure. 2–4 5288 Med. Phys. 43 (10), October 2016 0094-2405/2016/43(10)/5288/10/$30.00 © 2016 Am. Assoc. Phys. Med. 5288