Referenceless MR Thermometry for Monitoring Thermal Ablation in the Prostate

Radiological Sciences Laboratory, Department of Radiology, Stanford University, Stanford, CA 94305, USA.
IEEE Transactions on Medical Imaging (Impact Factor: 3.39). 07/2007; 26(6):813-21. DOI: 10.1109/TMI.2007.892647
Source: PubMed


Referenceless proton resonance frequency (PRF) shift thermometry provides a means to measure temperature changes during minimally invasive thermotherapy that is inherently robust to motion and tissue displacement. However, if the referenceless method is used to determine temperature changes during prostate ablation, phase gaps between water and fat in image regions used to determine the background phase can confound the phase estimation. We demonstrate an extension to referenceless thermometry which eliminates this problem by allowing background phase estimation in the presence of phase discontinuities between aqueous and fatty tissue. In this method, images are acquired with a multiecho sequence and binary water and fat maps are generated from a Dixon reconstruction. For the background phase estimation, water and fat regions are treated separately and the phase offset between the two tissue types is determined. The method is demonstrated feasibile in phantoms and during in vivo thermal ablation of canine prostate.

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    • "In recent research on nanomagnetism MNPs have been used instead of hydrogen as a new temperature-sensing element. The signal obtained from an MNP is two to three orders of magnitude higher than that obtained from a hydrogen atom in MR experiments, when measured in terms of either magnetic moment or magnetic susceptibility [11] [12]. Using a relatively inexpensive system Weaver et al [9] proposed a real-time method for measuring the temperature using the monotonic relationship between temperature and the ratio of the fifth and third harmonics of the MNP's AC magnetization. "
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    ABSTRACT: This study describes an approach for remote measuring of on-site temperature and particle concentration using magnetic nanoparticles (MNPs) via simulation and also experimentally. The sensor model indicates that under different applied magnetic fields, the magnetization equation of the MNPs can be discretized to give a higher-order nonlinear equation in two variables that consequently separates information regarding temperature and particle concentration. As a result, on-site tissue temperature or nanoparticle concentration can be determined using remote detection of the magnetization. In order to address key issues in the higher-order equation we propose a new solution method of the first-order model from the perspective of the generalized inverse matrix. Simulations for solving the equation, as well as to optimize the solution of higher equations, were carried out. In the final section we describe a prototype experiment used to investigate the measurement of the temperature in which we used a superconducting magnetometer and commercial MNPs. The overall error after nine repeated measurements was found to be less than 0.57 K within 310-350 K, with a corresponding root mean square of less than 0.55 K. A linear relationship was also found between the estimated concentration of MNPs and the sample's mass.
    Nanotechnology 02/2012; 23(7):075703. DOI:10.1088/0957-4484/23/7/075703 · 3.82 Impact Factor
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    • "The results presented in this paper also compare well to those obtained using the promising PRF method of MR thermometry for both RF ablation of the liver (Seror et al 2006) and HIFU ablation of the prostate (Rieke et al 2004, Pauly et al 2006, Rieke et al 2007). MR thermometry has demonstrated the ability to track temperatures greater than 60 • C over the duration of a HIFU ablation procedure (Pauly et al 2006) as well as in the prostate which can undergo large amounts of motion during treatment (Rieke et al 2007). Ultrasound-based temperature imaging does have several advantages over MR thermometry however. "
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