Investigation of Microwave Ablation Process in Sweet Potatoes as Substitute Liver

The microwave ablation technique to destroy cancer tissues in liver is practiced clinically and is the subject of ongoing research, e.g., ablation monitoring. For studies, liver tissue from cattle or pigs is often used as a substitute material. In this work, sweet potato is presented as an alternative material for microwave ablation experiments in liver due to similar material properties. Sweet potatoes as a substitute for liver have the advantages of better handling, easy procurement and stable material properties over time for microwave ablation experiments. The dielectric constant and electrical conductivity of sweet potato are characterized for temperature variation with the help of high-temperature dielectric probe. Furthermore, a test setup is presented for microwave ablation experiments in which a bowtie slot antenna matched to sweet potato is placed on its surface to directly receive the microwave power from a self-developed microwave applicator inserted into a sweet potato 4 cm below the surface antenna. A high-power source was used to excite the microwave powers up to 80 W and a spectrum analyzer was used to measure the signal received by the surface antenna. The experiments were performed in an anechoic chamber for safety reasons. Power at 50 W and 80 W was stimulated for a maximum of 600 s at the 2.45 GHz ISM band in different sweet potato experiments. A correlation is found between the power received by the surface antenna and rise of temperature inside sweet potato; relative received power drops from 1 at 76 ∘C to 0.6 at 88 ∘C (max. temperature) represents a 40% relative change in a 50 W microwave ablation experiment. The received power envelope at the surface antenna is between 10 mW and 32 mW during 50 W microwave ablation. Other important results for 10 min, 80 W microwave ablation include: a maximum ablation zone short axis diameter of 4.5 cm and a maximum ablation temperature reached at 99 ∘C, 3 mm away from the applicator’s slot. The results are compared with the state of the art in microwave ablation in animal liver. The dielectric constant and electrical conductivity evolution of sweet potato with rising temperature is comparable to animal liver in 50–60 ∘C range. The reflection loss of self-developed applicator in sweet potato is below 15 dB which is equal to reflection loss in liver experiments for 600 s. The temperature rise for the first 90 s in sweet potato is 76 ∘C as compared to 73 ∘C in liver with 50 W microwave ablation. Similarly, with 80–75 W microwave ablation, for the first 60 s, the temperature is 98 ∘C in sweet potato as compared to 100 ∘C in liver. The ablation zone short-axis diameter after 600 s is 3.3 cm for 50 W microwave ablation in sweet potato as compared to 3.5 cm for 30 W microwave ablation in liver. The reasons for difference in microwave ablation results in sweet potato and animal liver are discussed. This is the first study to directly receive a signal from microwave applicator during a microwave ablation process with the help of a surface antenna. The work can be extended to multiple array antennas for microwave ablation monitoring.

Determination of Aflatoxins and Ochratoxin a in Animal Liver Using HPLC-FD Method with Immunoaffinity Column Clean-Up

Analytical methods based on immunoaffinity column clean-up and quantitative determination with liquid chromatography-fluorescence detection were used to determine aflatoxins and ochratoxin A in liver samples. The validation of the procedures was performed. The linearity of the methods was checked, and a good coefficient of correlation was found for all aflatoxins and OTA as well. The LOD and LOQ were acceptable: 0.003 µg/kg and 0.009 µg/kg for AFB1; 0.001 µg/kg and 0.005 µg/kg for AFB2; 0.006 µg/kg and 0.020 µg/kg for AFG1; 0.007 µg/kg and 0.022 µg/kg for AFG2; 0.08 µg/kg and 0.27 µg/kg for OTA. The results for the repeatability estimated by the relative standard deviation (RSDr) were satisfactory and the obtained values were in the acceptable range (1.97–14.41% for all aflatoxins and 3.76-8.31% for OTA) at three proposed concentration levels. RSDR values showed acceptable correlation between two analysts for all four aflatoxins and OTA. The RSDR values were as followed: 2.37% and 5.60% for AFB1, 6.71% and 8.78% for AFB2, 4.40% and 7.00% for AFG1 and 10.30% and 13.91% for AFG2 (for the first and second analyst, respectively). The RSDR values for OTA were 4.91% and 3.15% (1 µg/kg); 3.76% and 4.12% (5 µg/kg) and 8.31% and 8.21% (10 µg/kg). The mean recovery for total aflatoxins and OTA were 78.10% and 93.34%, respectively. All validation parameters were in accordance to European legislation. They indicate that the proposed analytical procedures are suitable and they could be methods of choice for the determination of aflatoxins and OTA in liver samples.