HIGH-FREQUENCY ULTRASOUND PROPERTIES OF MULTICELLULAR SPHEROIDS DURING HEATING

High-frequency ultrasound monitoring is a possible method for real-tim e imaging of thermal therapy in tissues at microscopic resolution, The objective of this work was to measure changes in the ultrasound prope rties of V79 spheroids (grown from Chinese Hamster lung fibroblasts) e xposed to heating, Spheroids are clonal aggregates of cells that provi de a useful model for investigating the ultrasound properties of cells in the absence of connective tissue, Relative echo signal power and a ttenuation coefficients were measured over the frequency range 30 MHz to 70 MHz, from spheroids heated from 37 degrees C to 50 degrees C or 60 degrees C, Echo signal power from the viable rim decreased during t he first 5 min by a factor of 1.08 before the spheroid reached 50 degr ees C, For the next 25 min, echo signal power rose to a factor of 1.27 above the initial level, after which it remained relatively constant over the remainder of the 50 degrees C heating period, At 60 degrees C , echo signal from the viable rim remained relatively constant, althou gh it appeared to have possibly decreased slightly over the duration o f the heating period, Echo signal power from the necrotic core fell to a factor of 1.4 and 1.54 below the initial level at 50 degrees C and 60 degrees C, respectively, First-order chemical rate analysis applied to the echo signal power results in the viable rim at 50 degrees C re vealed a rate constant for the 5-15-min heating interval, Interpretati on of the echo signal power results in terms of histological stains in dicates that the rise in echo signal power at 50 degrees C was due to a loss of cell cohesion, and the possible drop in echo signal power at 60 degrees C was due to spheroid coagulation, Attenuation coefficient s decreased by up to 1.54 dB mm(-1) over a 30-min period at 60 degrees C, The appearance of a real-time ultrasound image of lesion formation in cells is discussed. (C) 1998 World Federation for Ultrasound in Me dicine & Biology.