Relative brightness due to temperature changes with ultrasound image analysis during Radiofrequency ablation

Introduction: Diagnosis of primary and secondary cancers to treat patients with diffuse and malignant tumors is an important subject. The appropriate treatment will be eliminating primary and metastatic tumors. Radiofrequency ablation with localized heat induction in the target tissue causes irreversible cellular damage and tissue coagulation. Estimation of tissue temperature changes is carried out under the guidance of ultrasound system. In addition to parameters such as variation in attenuation coefficient, acoustic power, thermal expansion, and variation in sound speed, the brightness of the ultrasound image shows a clear change in temperature. The aim of this study was to change brightness of ultrasound images in order to evaluate the thermal variations of tissue by Radiofrequency method.
Materials and Methods: With the fixation of ultrasound probe on the target tissue, all transverse cross- sectional images are visible from tip of the Radiofrequency electrodes and thermal sensor. DICOM images were transferred to PC and analyzed with RADWORKS Diagnostic 5.1 software. In order to estimate brightness of images for every degree temperature variation, ROI was plotted in desired areas, and average brightness values in pixels were assessed as a parameter without unit. In ultrasonic image processing, Circular ROIs was placed on both sides of thermal sensor, dimensions of each window were 2000 pixels (size of each pixel 0.05mm). To evaluation relative brightness, increasing temperature from 22˚C to 70 ˚C and reducing the temperature from 70 to 30 ˚C on reference image (with 22 ˚C) was drawn.
 Results: brightness value for each temperature was normalized to mean brightness of reference image and relative brightness variation was calculated. Results for each temperature were calculated as mean and standard deviation with descriptive analysis. Then, to verify the correlation between brightness and temperature variations, Pearson correlation analysis was performed with 95% confidence. As temperature rises, relative brightness parameter increased linearly (R> 0.99 and P<< 0.005) with cooling tissue, slop of brightness images decreased faster in linear phase of 22 to 50 ˚C (R> 0.98). During heating of the tissue at 22 ˚C until 60 ˚C for every 13 ˚C, relative brightness increased by 25%. Then temperature range from 60 to 63 ˚C was quickly achieved maximum value. In cooling stage, until the temperature reaches 30 ˚C, it continued with 25% steps per 7 ˚C reduction of temperature. At 35 -33 ˚C, it has reached -50% and -52% of the initial value.
Conclusion: In this study, not only brightness of Ultrasound images can be used as a qualitative measure of tissue thermal variations but also it can be provided as a quantitative map of brightness variation during Radiofrequency ablatio