MEASUREMENT OF TEMPERATURE DISTRIBUTION IN PHANTOM BODY BY AN ULTRASONIC CT METHOD

摘要

It is becoming important to measure the interior temperature of the human body since the appearance of hyperthermia in the treatment of cancer. During such treatment, it is important to keep the temperature of the tumor over 42.5°C and the temperature of normal tissue below 42.5°C to avoid heat damage. We anticipate technology being able to measure indirectly the interior temperature distribution of an arbitrary transverse section of the body and to display the image for monitoring. This paper discusses ultrasonic CT (Computed Tomography) for indirect measuring the interior temperature distribution from a series of sound projections that are taken at several different orientations relative to a phantom body. Like X-ray CT, Ultrasonic CT is mainly one of the methods of getting a transverse image of the body. The advantages of ultrasonic CT include simpler instruments and the absence of radiation injury from X-ray CT. We can obtain the sound speed distribution within the object by measuring the arrival time of a sound wave with ultrasonic CT. The purpose of this study is to develop a method of measuring indirectly the interior temperature distribution of an object using the difference of sound speed before and after heating, using the characteristics of the sound speed that depends on the temperature. First, we compared three reconstruction algorithms to minimize a number of required projections. Then, a phantom made of agar was placed in a water bath as shown in Fig. A-1, and a series of sound projections were measured when a pair of ultrasonic detectors were both translated and rotated. We obtained the temperature distribution in the phantom with accuracy about 0.1°C by subtracting the sound speed before heating from the sound speed after heating. Figure A-2(1) shows the sound speed distribution before heating. Figure A-2(2) shows the temperature distribution after heating. The structure differences of watery tissue like blood, musculature, and the viscera did not have an effect on the measurement of the temperature distribution, because they were eliminated by subtracting the sound speed before heating from the sound speed after heating.