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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    ABSTRACT: Minimally invasive therapies such as radiofrequency ablation have been developed to treat cancers of the liver, prostate and kidney without invasive surgery. Prior work has demonstrated that ultrasound echo shifts due to temperature changes can be utilized to track the temperature distribution in real time. In this paper, a motion compensation algorithm is evaluated to reduce the impact of cardiac and respiratory motion on ultrasound-based temperature tracking methods. The algorithm dynamically selects the next suitable frame given a start frame (selected during the exhale or expiration phase where extraneous motion is reduced), enabling optimization of the computational time in addition to reducing displacement noise artifacts incurred with the estimation of smaller frame-to-frame displacements at the full frame rate. A region of interest that does not undergo ablation is selected in the first frame and the algorithm searches through subsequent frames to find a similarly located region of interest in subsequent frames, with a high value of the mean normalized cross-correlation coefficient value. In conjunction with dynamic frame selection, two different two-dimensional displacement estimation algorithms namely a block matching and multilevel cross-correlation are compared. The multi-level cross-correlation method incorporates tracking of the lateral tissue expansion in addition to the axial deformation to improve the estimation performance. Our results demonstrate the ability of the proposed motion compensation using dynamic frame selection in conjunction with the two-dimensional multilevel cross-correlation to track the temperature distribution.
    Physics in Medicine and Biology 08/2010; 55(16):4735-53. DOI:10.1088/0031-9155/55/16/008 · 2.76 Impact Factor
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    ABSTRACT: La lutte contre le cancer a vu l'émergence de nouvelles technologies permettant d'améliorer le soin aux patients. Parmi celles-ci, la thermo-ablation par laser est une des techniques de destruction in situ des tumeurs les plus récentes. Elle consiste à plonger la fibre optique au cœur d'une tumeur en insérant un guide au travers de la peau. La diode laser émettrice de lumière permet ensuite de brûler localement la tumeur sans abord chirurgical, le patient pourra ainsi quitter plus rapidement l'hôpital. Les énormes avantages de cette thérapie sont cependant limités par la difficulté du geste à réaliser. Pour se guider durant les différentes étapes, le chirurgien pourra utiliser l’imagerie par résonance magnétique. L'objectif de cette thèse, qui bénéficie du soutien de la Région Nord Pas de Calais et du CHRU de Lille de 2005 à 2007, est de fournir des outils pour l’assistance par IRM de la thermo-ablation par laser. Les différents développements offriront ainsi non seulement un outil de préparation à cet acte complexe (visualisation en trois dimensions des tumeurs du patient, calcul de la trajectoire optimale pour éviter la perforation de structures anatomiques vitales …) mais également des outils d’assistance per-opératoire (positionnement du guide assisté par la stéréovision sur les premiers centimètres, évaluation des dommages thermiques de la zone traitée…). Lors de cette première phase, nous nous sommes concentrés sur les tumeurs hépatiques, qui demeurent une réelle difficulté, tout en proposant un système pouvant être adapté à toute tumeur abdominale.
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