Abstract
The problem of detecting and identifying the heat transfer processes in living tissues using a noninvasive ultrasound technique is discussed. An optimal method, which is optimal in terms of maximum of likelihood, is proposed to detect the temperature variations within internal layers of the living tissue. The properties of signals returned from different tissues are examined. The ultrasound velocity for different temperatures and the salt composition of a specimen under study is estimated. Results of the algorithm simulation are given.
TopPhysical Principles Of The Proposed Technique
A plot of the sound wave velocity as a function of temperature c(T) for homogeneous media (say, water) and for different sounding signal frequencies using the data drawn from the reference (Hutte,1934), is presented on Figure 1.
Figure 1. The temperature-dependent sound propagation velocity in water
As far as medical applications are concerned, hyperthermia in particular, the temperature interval between 390 and 450 C is of certain interest. The experimental studies indicated that the derivative of sound velocity with respect to 
over this particular temperature interval is insignificant (Figure 2), and for the carrier frequency of sounding signal 
MHz yields an increment of a complete returned-signal phase 
on the order of 0,1 of phase degree (or 1,8*10-3 rad) by a temperature degree according to the Celsius scale.
Key Terms in this Chapter
S/N Ratio: Is a ratio of acoustic signal power to dispersion of noise.
Ultrasound Wave Acoustothermometer: Is a device which radiate ultrasound waves to living tissue and calculate the temperature gradient as a function of time using information from reflected signal.
Kalman Filter: Is dynamic adaptive filter the amplifier factor of which calculated from the Riccati differential equation using statistical information of signal and noise.
Hyperthermia: A method of treating cancer (malignant tumors), in which the patient's body, parts thereof, or individual organs are exposed to high temperatures (above 39 ° C, to 44-45 ° C).
Sound Velocity: Is a velocity of ultrasound wave front in homogeneous tissue.
Increment of the Total Phase of the Signal: Is the phase change of the signal due to the propagation delay of the signal to the target and back, expressed in radians (or degrees).
Acousto-Brightness Temperature: Is gradient amplitude of reflected acoustic signal.