High-frequency rapid B-mode ultrasound imaging for real-time monitoring of lesion formation and gas body activity during high-intensity focused ultrasound ablation

Abstract

The goal of this study was to examine the ability of high-frame-rate, high-resolution imaging to monitor tissue necrosis and gas-body activities formed during high-intensity focused ultrasound (HIFU) application. Ex vivo porcine cardiac tissue specimens (n = 24) were treated with HIFU exposure (4.33 MHz, 77 to 130 Hz pulse repetition frequency (PRF), 25 to 50% duty cycle, 0.2 to 1 s, 2600 W/cm(2)). RF data from B-mode ultrasound imaging were obtained before, during, and after HIFU exposure at a frame rate ranging from 77 to 130 Hz using an ultrasound imaging system with a center frequency of 55 MHz. The time history of changes in the integrated backscatter (IBS), calibrated spectral parameters, and echo-decorrelation parameters of the RF data were assessed for lesion identification by comparison against gross sections. Temporal maximum IBS with +12 dB threshold achieved the best identification with a receiver-operating characteristic (ROC) curve area of 0.96. Frame-to-frame echo decorrelation identified and tracked transient gas-body activities. Macroscopic (millimeter-sized) cavities formed when the estimated initial expansion rate of gas bodies (rate of expansion in lateral-to-beam direction) crossed 0.8 mm/s. Together, these assessments provide a method for monitoring spatiotemporal evolution of lesion and gas-body activity and for predicting macroscopic cavity formation.

Transmural Ultrasound Imaging of Thermal Lesion and Action Potential Changes in Perfused Canine Cardiac Wedge Preparations by High Intensity Focused Ultrasound Ablation

“…Wright et al introduced a novel system that combined ultrasound imaging with ring or TPX-covered RF catheters to directly visualize lesion formation in real time [15]. We have previously shown that high frequency imaging at 55 MHz combined with fast frame rate M-mode (1 kHz) and short time B-mode (STBM) (frame rate 70 – 130 Hz) can image HIFU lesion and gas body formation [17], [18] by tracking the temporal history of changes in ultrasound integrated backscatter ( IBS ) and frame-to-frame echo decorrelation. In the current study, we employed ultrasound imaging at 30 MHz with imaging depth (∼12.7 mm) with better imaging depth more suitable for imaging across the depth of human atrial tissue (5 – 7 mm).…”

“…Amplitudes of the Hilbert transformed RF signals of ultrasound images, or envelope data A ( x , y ; t ) ( x and y are the 2D locations, and t is a time index), were used to form various parametric images as described previously [18], [27], [28]. Briefly, an image parameter, X ( x , y ; t ) (e.g.…”

“…It is color-coded to overlay on the original unprocessed image (Figure S3). Gray scale (GS) and IBS images were computed as [18] …”

“…Kolios et al demonstrated high frequency ultrasound backscatter signals can be used to effectively detect apoptotic changes in cell nucleus using spectral analysis method [16], indicating changes in the nucleus, such as apoptotic, necrosis or other changes, many produce detectable signals for high frequency ultrasound imaging for monitoring events reflective of cellular level changes. We have previously shown that high frequency ultrasound imaging at 55 MHz combined with fast frame rate M-mode (1 kHz) and short time B-mode (70 – 130 frames/s) can image HIFU lesion and gas body formation [17], [18] with high accuracy and resolution by tracking the temporal history of ultrasound integrated backscatter (IBS) and frame-to-frame echo decorrelation. ICE-based acoustic radiation force impulse (ARFI) imaging also provided improved performance in identifying lesion boundaries and dimensions in RFA lesion lines [19], although motion artifacts sometimes led to false classification of lesions with low imaging frame rate (<4 frames/min).…”

Real-time Monitoring of High Intensity Focused Ultrasound (HIFU) Ablation of <em>In Vitro</em> Canine Livers Using Harmonic Motion Imaging for Focused Ultrasound (HMIFU)

“…MRI provides high spatial resolution images of the treated region with tissue displacement or thermal dose but has a frame rate of 0.1-1 Hz and is costly. Several ultrasound-based techniques such as B-mode imaging 4 , passive acoustic mapping 5 , shear wave imaging 6 and acoustic radiation force impulse 7 have been developed to guide and monitor thermal ablation. However, B-mode imaging and passive acoustic mapping do not provide imaging of mechanical properties of the ablated region which is useful to the operator to improve lesion delivery.…”