Ponencia presentada en el XIX Congreso Internacional de Acústica (ICA2007), Madrid, 2-7 Sep 2007.-- PACS: 43.80.Ev.A time delay technique that relates the temperature changes with the time shifts (delays) presented in echoes coming from a simulated and experimental body immersed in a thermal bath is developed and analyzed. Both simulated and experimental signals were obtained from a numeric and experimental phantom respectively. Results of the time domain analysis for two transducer frequencies in a temperature interval ranging from 25°C to 42°C are presented. Performance in the technique is evaluated by calculating the correlation coefficient between the lineal regression and the real values obtained for the temperature estimation. A comparison between simulated and experimental data for two transducer frequencies is presented.This work was supported by the Acoustics Institute (CSIC) in Madrid (R&D National Plan of the Spanish Ministry of Education & Science, Project PN-DPI2005-00124), and the Bioelectronics Section (CINVESTAV) in Mexico. The stay of M. Sc. I. Bazán in CSIC, during 2006, was financed by ALFA-PETRA-II, U.E contract AML/B7-11/97/0666/II-0343 FA-FCD-FI.Peer reviewed