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Optimized Noninvasive Monitoring of Thermal Changes on Digital B-Mode Renal Sonography During Revascularization Therapy

Department of Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran (M.D.A.); Department of Electrical and Computer Engineering, University of Louisville, Louisville, Kentucky USA (V.T.); and Science and Research Branch, Islamic Azad University, Tehran, Iran (N.S.).

Address correspondence to Vahid Tavakoli, MD, MS, Department of Electrical and Computer, Engineering, University of Louisville, Medical Image, Computing Laboratory, Lutz Hall, Room 308, Louisville, KY 40292 USA. E-mail: v0tava01i{at}louisville.edu

Objective. Noninvasive real-time thermal change monitoring of human internal organs can play a critical role in diagnosis and treatment of many disorders, including reperfusion of renal arteries during anticoagulation therapy. Methods. This article focuses on tissue temperature detection using ultrasound velocity changes in different structures and their related speckle shift from their primary locations on high-quality B-mode digital sonography. We evaluated different speckle-tracking techniques and optimized them using appropriate motion estimation methods to determine the best algorithm and parameters. Results. Performing thermal detection methods on simulated phantoms showed a good correlation between speckle shifts and the ground truth temperature. For the simulated images, average thermal error was 0.5°C with an SD of 0.5°C, where lower errors can be obtained in noiseless (motionless) data. The proposed technique was evaluated on real in vivo cases during surgical occlusion and reopening of the renal segmental artery and showed the potential of the algorithm for observation of internal organ changes using only digital ultrasound systems for diagnosis and therapy. Conclusions. The adaptive Rood pattern search proved to be the best block-matching technique, whereas the multiresolution Horn-Schunck technique was the best gradient optical flow method. The extracted thermal change during in vivo revascularization therapy is promising. In addition, we present an evaluation of several block-matching and optical flow motion estimation techniques.

Key Words: block matching • optical flow • reperfusion therapy • speckle tracking • ultrasound thermometry

Abbreviations: ARPS, adaptive Rood pattern search • ES, exhaustive search • 4SS, 4-step search • MAD, mean absolute difference • MSE, mean square error • PSF, point spread function • ROI, region of interest • 3SS, 3-step search • 2D, 2-dimensional