Abstract
Abstract During thermal ablation in a target tissue the information about temperature is crucial for decision making of successful therapy. An observable temporal and spatial temperature propagation would give a visual feedback of irreversible cell damage of the target tissue. Potential temperature features in ultrasound (US) B-Mode image sequences during radiofrequency (RF) ablation in ex-vivo porcine liver were found and analysed. These features could help to detect the transition between reversible and irreversible damage of the ablated target tissue. Experimental RF ablations of ex-vivo porcine liver were imaged with US B-Mode imaging and image sequences were recorded. Temperature was simultaneously measured within the liver tissue around a bipolar RF needle electrode. In the B-Mode images, regions of interest (ROIs) around the centre of the measurement spots were analysed in post-processing using average gray-level (AVGL) compared against temperature. The pole of maximum energy level in the time-frequency domain of the AVGL changes was investigated in relation to the measured temperatures. Frequency shifts of the pole were observed which could be related to transitions between the states of tissue damage.
Highlights
Thermal therapies such as laser, microwave, radiofrequency (RF) ablation and high-intensity focused US (HIFU) are applied in clinical settings mainly for treatment of small carcinoma and metastases
We address the correlation of temperatures up to 75 °C to the relative average gray-level (AVGL) change and their corresponding change in the frequency domain
As observed in the whole US image sequence, some bubble formation started from the needle electrodes and traversed towards this analysed regions of interest (ROIs)
Summary
Thermal therapies such as laser, microwave, radiofrequency (RF) ablation and high-intensity focused US (HIFU) are applied in clinical settings mainly for treatment of small carcinoma and metastases. These therapies are followed with image guidance for visualization of target. High cost of such a clinical MR procedure, restricted range of motion for handling therapy tools inside the bore and system availability led to a motivation to search for alternative temperature monitoring systems. Along the density change the acoustic impedance is meant to change which should affect the appearance of intensity, i.e. pixel gray-level in the US image. Gray-level changes during ablation could be used for correlation with temperature [6] or with ablation progression of the tissue. An average gray-level (AVGL) [7]
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