Abstract The potential of using a commercial ultra- sound transmission imaging system to quantitatively monitor tissue attenuation changes after thermal therapy was investigated. The ultrasound transmission imaging system used, the AcoustoCam (Imperium Inc., MD) allows ultrasonic images to be captured using principles similar to that of a CCD-type camera that collects light. Ultrasound energy is focused onto a piezoelectric array by an acoustic lens system, creating a gray scale acoustic image. In this work, the pixel values from the acoustic images were assigned acoustic attenuation values by imaging polyacrylamide phan- toms of varying known attenuation. After the calibra- tion procedure, data from heated polyacrylamide/ bovine serum albumin (BSA) based tissue-mimicking (TM) phantoms and porcine livers were acquired. Samples were heated in water at temperatures of 35, 45, 55, 65, and 75°C for 1 h. Regions of interest were chosen in the images and acoustic attenuation values before and after heating were compared. An increase in ultrasound attenuation was found in phantoms containing BSA and in porcine liver. In the presence of BSA, attenuation in the TM phantom increased by a factor of 1.5, while without BSA no significant changes were observed. The attenuation of the porcine liver increased by up to a factor of 2.4, consistent with previously reported studies. The study demonstrates the feasibility of using a quantitative ultrasound transmission imaging system for monitoring thermal therapy. Keywords Thermal therapy Æ Acoustic attenuation Æ Ultrasound phantoms Æ Gel attenuation Æ Ultrasound attenuation mapping 1 Introduction Thermal therapy is an attractive alternative to surgery and radiation therapy because of its ability to locally kill tumors while preserving surrounding normal tissues [27]. The target tissue is heated to high tem- peratures (between 50 and 100°C), leading to rapid destruction. An integral part of the success of thermal therapy is a real-time monitoring system to monitor tissue damage in order to control the area being heated and protects the surrounding normal tissue. Ultrasound (US) monitoring may be useful since it is non-invasive and it can be done in real-time. Several groups have investigated the change in acoustic properties of heated tissue, showing that tissue ultrasound attenua- tion rises for temperatures above 55°C. Worthington and Sherar [31] investigated changes in ultrasound backscatter and attenuation for 30 min exposure times at temperatures up to 65°C in porcine kidney. They found an increase in attenuation of a factor of ~1.9 after 30 min. Clarke et al. [3] and Gertner et al. [6] measured attenuation changes for higher temperature heating protocols (70–80°C) and found attenuation increases of up to 2.4 dB/cm. These studies show that N. Parmar Æ M. C. Kolios Department of Electrical and Computer Engineering, Ryerson University, 350 Victoria Street, Toronto, ON, Canada M5B-2K3 M. C. Kolios (&) Department of Physics, Ryerson University, 350 Victoria Street, Toronto, ON, Canada M5B-2K3 e-mail: mkolios@ryerson.ca URL: http://www.physics.ryerson.ca Med Bio Eng Comput (2006) 44:583–591 DOI 10.1007/s11517-006-0067-8 123 ORIGINAL ARTICLE An investigation of the use of transmission ultrasound to measure acoustic attenuation changes in thermal therapy Neeta Parmar Æ Michael C. Kolios Received: 29 January 2006 / Accepted: 20 April 2006 / Published online: 10 June 2006 Ó International Federation for Medical and Biological Engineering 2006