Keywords:
Experimental, Not applicable, Tissue characterisation, Technical aspects, CT, Animal (veterinary) studies, Performed at one institution
Authors:
S. Mizukami, H. Hara, D. Hatakeyama, E. Kanai, D. Yokoyama, H. Muraishi, T. Gomi; Sagamihara, Kanagawa/JP
DOI:
10.26044/ecr2020/C-07853
Methods and materials
1. Theoretical background of CT based thermometry
CT based thermometry is obtained indirectly the temperature information from CT values of the subject. CT value is calculated from the linear attenuation coefficient of subject and water. Moreover, the linear attenuation coefficient varies with physical density and the mass attenuation coefficient for a given material. Because the physical density of a material is affected by temperature due to thermal expansion, the CT value depends on temperature. Therefore if temperature increases, thermal expansion causes the decrease of density and the CT value decreases (Fig. 3).
2. Histological sample study
As the histological samples, liver, kidney, muscle and fat obtained from swine were used in this study (Fig. 4). Temperature of the samples was changed in the range of -20 to 60 °C, measured with an optical fiber thermometer inserted. CT images were acquired every time the temperature of the samples changed by 1 °C. CT scans were acquired with the following protocol: 120 kV, 300 mA, 1.0 s, a slice thickness of 4 mm, a FOV of 240 mm. The CT value at the image close to the sensor and measured temperature was used to create a CT value-temperature conversion table (CT-Temp conversion table) for each sample.
3. Living swine study
After approval from Azabu University Animal Experiment Committee in Japan (No. 180806-2), in vivo experiment was made using swine (three yuan swine, 23 days old, 7.58 kg). The temperature of swine living organs (liver, kidney, muscle, and fat) under anesthesia was measured with an optical fiber thermometer inserted (Fig. 5). CT images were acquired at the following settings: 120 kV, 300 mA, 1.0 s, a slice thickness of 4 mm, a FOV of 240 mm. CT-Temp conversion table of living swine was obtained by correcting the conversion table of the histological sample using measured CT value and temperature, because the swine body temperature was not changed in this study.
4. Temperature mapping
CT values displayed in gray scale were converted into temperature information displayed in color look-up table by a first order approximation of CT-Temp conversion table corresponding to a sample or a living organ (Fig. 6). The look-up table was colored with changed at 5 °C intervals. The look-up table was colored by changing from low temperature purple to high temperature red at 5 °C intervals.