Ultrasound single-phase CBE imaging for monitoring radiofrequency ablation

Abstract

Radiofrequency (RF) ablation (RFA) is the most commonly used minimally invasive procedure for thermal ablation of liver tumors. Ultrasound not only provides real-time feedback of the electrode location for RFA guidance but also enables visualization of the tissue temperature. Changes in backscattered energy (CBE) have been widely applied to ultrasound temperature imaging for assessing thermal ablation. Pilot studies have revealed that significant shadowing features appear in CBE imaging and are caused by the electrode and RFA-induced gas bubbles. To resolve this problem, the current study proposed ultrasound single-phase CBE imaging based on positive CBE values. An in vitro model with tissue samples derived from the porcine tenderloin was used to validate the proposed method. During RFA with various electrode lengths, ultrasound scans of tissue samples were obtained using a clinical ultrasound scanner equipped with a convex array transducer of 3 MHz. Raw image data comprising 256 scan lines of backscattered RF signals were acquired for B-mode, conventional CBE, and singlephase CBE imaging by using the proposed algorithmic scheme. The ablation sizes estimated using CBE imaging and gross examinations were compared to calculate the correlation coefficient. The experimental results indicated that single-phase CBE imaging largely suppressed artificial CBE information in the shadowed region. Moreover, compared with conventional CBE imaging, single-phase CBE imaging provided a more accurate estimation of ablation sizes (the correlation coefficient was higher than 0.8).

Frequency-domain CBE imaging for ultrasound localization of the HIFU focal spot: a feasibility study

“…The window then moves throughout R k and R 0 according to a window overlap ratio (WOR) for generating a CBE map. A spatial-domain CBE image with the same size as the original image can be obtained after data interpolation 24 :ˆˆη…”

“…In this study, the WOR was set at 50% to compromise CBE image resolution and computational complexity, and the side length corresponding to three times the pulse length of the ultrasound transducer (6.9 mm) was used to determine the dimension of the sliding window 24 .…”

“…The temperature changes, which were measured using the thermocouple, as functions of time under HIFU exposures using different output powers were plotted. According to the previous study 24 The changes in the contrast factor with time obtained from |η s | and |η f | images were plotted. The Pearson correlation coefficient r was calculated to evaluate the correlation between CBE values and temperature.…”

“…Conventionally, algorithms for ultrasound CBE imaging are designed in the spatial domain 24,25 . In general, a major drawback for spatial-domain CBE imaging is that the CBE computation is easily affected by noises, particularly when the CBE is measured in decibels (dB) to describe the intensity ratio on a logarithmic scale.…”

Deep heat therapy system with resonant cavity applicator for articular cartilage in knee osteoarthritis

“…Generally, the speed of sound is dependent on the temperature of the transmission medium 17) . However, commercially available ultrasound medical imaging systems reconstruct images assuming a constant speed of sound 18) . Accordingly, the resulting images will be slightly altered as the temperature changes.…”