Keonho Son

Portable, high-intensity focused ultrasound system with 3D electronic steering for the pancreas: a preclinical study in a swine model

Purpose The aim of this animal study was to evaluate the safety and feasibility of a portable, ultrasonography-guided, high-intensity focused ultrasound (USg-HIFU) system to treat the pancreas. Methods Eight swine were included. Using a portable HIFU device (ALPIUS 900, Alpinion Medical Systems), ablations were performed on the pancreas in vivo. Different acoustic intensities were applied (1.7 kW/cm2 or 1.5 kW/cm2, n=2 [group A for a pilot study]; 1.5 kW/ cm2, n=3 [group B]; and 1.2 kW/cm2, n=3 [group C]). Magnetic resonance imaging (MRI) was performed immediately (group A) or 7 days (groups B and C) after HIFU treatment. In groups B and C, serum amylase and lipase levels were measured on days 0 and 7, and performance status was observed every day. Necropsy was performed on days 0 (group A) or 7 (groups B and C) to assess the presence of unintended injuries and to obtain pancreatic and peripancreatic tissue for histological analysis. Results Ablation was noted in the pancreas in all swine on MRI, and all pathologic specimens showed coagulation necrosis in the treated area. The mean ablation areas on MRI were 85.3±38.1 mm2, 90.7±21.2 mm2, and 54.4±30.6 mm2 in groups A, B, and C, respectively (P>0.05). No animals showed evidence of complications, except for one case of a pseudocyst in group B. Conclusion This study showed that pancreas ablation using a portable USg-HIFU system may be safe and feasible, and that coagulation necrosis of the pancreas was successfully achieved with a range of acoustic intensities.

Development of an algorithm for HIFU focus visualization

The ultrasound waves emitted from the HIFU transducer propagate through water and various tissue layers to a focus of the internal body. During propagation the multiple refractions and reflections occur due to in-homogeneity nature of the tissues. These cause the aberration of the focal location. Therefore, in the view of safety for the HIFU treatment it is important to know where the focus is exactly formed. In this study, the method of synchronization control between a HIFU and an imaging devices is proposed for the focus visualization. In order to get a clear focus image, the signal processing with the harmonics of the transmitted HIFU pulses is introduced. The convex imaging probe is installed at the center of the phased-array HIFU transducer. The time delays for the imaging probe as well as the HIFU array-elements are calculated along the HIFU focus location. The HIFU array elements send a short-pulse train of 1 MHz and the imaging probe starts receiving the echo-signal in sequence according to the delays. In this manner, the IQ data were collected using the ultrasound device, ECUBE 9 of ALPINION MEDICAL SYSTEMS. At this stage, the focus is not clear due to the random distribution of the scatters with non-uniform intensity. Through the FFT of the IQ data the spatial distribution of the amplitudes at the fundamental and the harmonic frequencies are extracted. The amplitudes at the harmonic frequencies are divided by the amplitude at the fundamental frequency. And then the results from the division are displayed on the B-mode ultrasound images. This algorithm was tested in ex-vivo and in-vivo. The algorithm was verified through the in-vivo and ex-vivo experiments. It is confirmed that the algorithm can provide the precise information of the focus location in a simple manner.

Coupled vibration analysis for a piezoelectric array element using superposition method

The coupled vibration was analyzed for a piezoelectric array element of two-dimensional structure whose vibration can be described by two coupled differential equations with coupled boundary conditions. The exact solutions satisfying both equations of motion and boundary conditions are not available. Therefore, the approximate solutions were obtained using the superposition method suggested for accurate vibration analysis of the elastic structures. To this end, the mechanical and electrical boundary conditions were satisfied approximately by summing the stress and the electric potential obtained from the displacements. The frequency spectrum and the electromechanical coupling factor of the element varying the width/thickness ratio were calculated and compared with the results of the finite element analysis and experiment. As the ratio of thickness to with increases, the fundamental frequency and the electromechanical coupling factor of the array element increase. The theoretically calculated results has shown good agreement with the results of the finite element analysis. The superposition method was verified to provide the accurate analysis for a piezoelectric array element.