An MPI-Compatible HIFU Transducer: Experimental Evaluation of Interferences

Tim C. Kranemann, Thomas Ersepke, Thomas Friedrich, Jochen Franke, Alexander Neumann, Thorsten Buzug, Georg Schmitz

Int. J. Mag. Part. Imag. 4(2), 2018, DOI: 10.18416


High intensity focused ultrasound (HIFU) is an early-stage therapeutic technology that allows for non-invasive cancer treatment by delivering heat to the target tissue. Monitoring the tissue temperature is challenging and remains a key element for accurate tumor ablation. Recently, the ability of magnetic particle imaging (MPI) to measure the nanoparticle temperature was demonstrated. This can be utilized for measuring the surrounding tissue temperature during HIFU ablation. To evaluate MPI as a HIFU monitoring modality, a first MPI-compatible HIFU transducer is presented. Its MPI-compatibility was experimentally examined, whereby heating of conducting transducer parts as well as interferences with the MPI receive signal chain were addressed. Thermometry measurements showed that temperature rise (<5 K) of transducer electrodes due to eddy current heating during MPI acquisition can be neglected. Measurements of transfer functions between the transducer and the MPI low-noise amplifier outputs and acquisition of MPI spectra during HIFU operation confirmed that concurrent MPI reconstruction is feasible during HIFU operation. The resulting sound field of the presented HIFU transducer was measured and extrapolation of the applied electrical power confirms that acoustic intensities necessary for rapid tissue ablation can be easily achieved without causing an MPI signal overload. By operating a HIFU transducer inside the MPI scanner, the feasibility of a HIFU-MPI combination has been confirmed.