Establishment of sentinel lymph node detection using impedance CT

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Electrical evaluation of surgically resected organs was conducted to determine whether electrical differences exist between normal tissue and malignant lesions. Specifically, dielectric properties of normal gastric mucosa and malignant lesions were evaluated, and "tan δm", the maximum tan δ in the β dispersion range, was calculated. No significant differences were observed in "tan δm" between normal gastric mucosa and malignant lesions in patients with well-differentiated adenocarcinoma. However, in patients with poorly differentiated adenocarcinoma, "tan δm" was 3.35 ± 0.21 in normal gastric mucosa, 4.66 ± 0.79 in lesions with tumor depths of m to mp, and 7.60 ± 1.23 in areas with tumor depths of ss to se, indicating statistically significant differences. Histologically, "tan δm" was shown to be higher for markedly poorly differentiated or advanced tumors in terms of structural changes. Meanwhile, electrical detection of lymph node accumulation using iron colloids was attempted by altering colloid diameter, content, dose, administration time, and measurement time, but no electrical differences were observed between normal lymph nodes and lymph nodes containing iron. In addition, the dielectric properties of experimental animal stomachs and large intestines were measured in a multi-frequency range from 1 kHz to 1 MHz using electrodes for contact-type multiple-point measurements and an existing impedance analyzer (HP4194A). However, data reproducibility was poor, and the results were thought to reflect individual differences among animals. Although a conductivity distribution map of dielectric properties was created based on obtained data using equipotential back-projection, lymph nodes could not be visualized on obtained images due to insufficient spatial resolution. Based on the above, although electrical differences may exist between normal and cancer tissues, establishment of sentinel lymph node detection using impedance CT in practice may prove difficult.