Feasibility of HIFU tissue ablation in the presence of ribs using a 2D random phased array

Abstract

The goal of the work was to demonstrate feasibility of HIFU tissue ablation through the rib cage using a high power 2D random phased array. A method to minimize heating ribs while maintaining high intensities at the focus of the array was proposed and tested theoretically and experimentally. A 2D 1-MHz phased array with 254 randomly distributed elements and a phantom of porcine rib cage were used in experiments. Intensity distributions were measured in the plane of the rib phantom and in the focal plane of the array using an infra-red camera. Theoretical and experimental results show that if the position and the shape of ribs are known it is possible to provide adequate focusing through the ribs without overheating them for a single focus, including steering at ± 10-15 mm off and ± 20 mm along the array axis. The results suggest that the method is potentially useful for clinical applications of HIFU for which the rib cage lies between the transducer and the targeted tissue.

Focus splitting associated with propagation of focused ultrasound through the rib cage

“…These questions became the subject of detailed studies presented in our recent publications [9, 10]. To prevent overheating of bones and overlying tissues, we used an approach based on switching off a part of the array elements located in front of the ribs [6].…”

Extracorporeal high intensity focused ultrasound for renal tumours: a 3‐year follow‐up

“…A laparoscopic approach is feasible and allows direct delivery of energy, but detracts significantly from the non‐invasiveness of the extracorporeal approach [25]. Techniques that switch off the elements that lie in the beam pathway of the ribs show promise and allow additional power to be diverted to those elements with a good acoustic view of the target [26]. Respiratory motion tracking and correction will also allow tissue temperatures to increase more rapidly, thus reducing insonication times and reducing the heating of the prefocal tissues [27,28].…”

Infrared mapping of ultrasound fields generated by medical transducers: Feasibility of determining absolute intensity levels

“…There has been considerable interest in using the infrared (IR) technique to investigate the acoustical fields of HIFU transducers [3][4][5] which seems to have increased in recent years. [6][7][8][9][10][11][12] The IR method has specific advantages in comparison with these other methods. Hydrophone field mapping in three dimensions is very slow, with even a single planar raster scan taking typically several hours.…”

“…7 The principle has been applied to measure the relative intensity distribution of a multiple element random phased array by measuring the distribution of the initial rate of temperature increase at the start of insonation. 6,11,12 The temperature rise was measured in a thin (<2 mm thick), highly absorbing (30 dB cm À1 MHz…”

“…In this study, the assumption was that the measured temperature rise at the surface of the absorber is proportional to the free field intensity. Other studies have extended the method to account for the effect of heat diffusion by introducing correction factors in the conversion of temperature images to intensity, 8,9,11,12 and measuring the temperature distribution on the surface of a thick (40 mm) less absorbing tissue mimicking gel (0.6 dB cm À1 MHz…”