Initial Characterization of Healthy and Malignant in vivo and ex vivo Human Colon Tissues under Surgery Procedures

The dielectric characterization of human tissues can play a crucial role in the development of new medical diagnostic tools. In particular, the characterization of healthy and pathological tissues can provide vital information for diagnosis. In this paper, preliminary results from a small-scale measurement campaign conducted in 0.5-26.5GHz during real surgeries on healthy and malignant human colon tissues are presented. Those measurements were carried out externally to the colon, without direct contact to the tumor growing inside the colon. Furthermore, different tumor stages are taken into account. Initial findings reveal that advanced tumor stages are related with increased higher values of dielectric properties in malignant tumor tissues compared to the healthy ones.

💡 Research Summary

This paper presents a preliminary investigation into the dielectric properties of human colon tissue measured during actual surgical procedures, aiming to differentiate healthy tissue from malignant tumors and to assess how tumor stage influences these properties. The authors employed an open‑ended coaxial probe connected to a Keysight FieldFox N9918A vector network analyzer (VNA) to acquire broadband (0.5–26.5 GHz) reflection data. Measurements were performed in two distinct scenarios: (1) in vivo, where the probe was placed on the external wall of the colon after the patient was anesthetized and the abdomen opened; and (2) ex vivo, where resected colon segments containing tumor and surrounding healthy tissue were measured immediately after removal.

In the in vivo setting, the probe was sterilized and inserted through a sterile bag, and because pre‑surgical calibration was not feasible, a pre‑set calibration was used followed by post‑measurement correction. Twenty‑seven measurements were collected from seven patients (one T4b, two T4a, four T3). In the ex vivo setting, a full calibration was performed before the surgery, and measurements were taken on the outer surface of the resected specimen. Thirty‑seven measurements were obtained from eight patients (one T4b, two T4a, five T3).

For each measurement point three sweeps were averaged, and the resulting complex permittivity εr(f)=ε′(f)−jε″(f) was extracted using the four‑point calibration method (air, short, water, methanol). To reduce noise, the mean permittivity data for each tissue type were fitted with a two‑pole Cole‑Cole model, which adequately captured the dispersion without over‑parameterization. Differences between tumor and healthy tissue (Δε′ and Δε″) were calculated at representative frequencies (2.45 GHz, 12.5 GHz, 18 GHz) and plotted as cubic fits for each patient, then grouped by measurement scenario and tumor stage.

When all data were pooled regardless of stage, the average dielectric constant and loss factor of tumor and healthy tissue were virtually indistinguishable, contradicting earlier literature that reported higher permittivity in malignant tissue. The authors attribute this discrepancy to the fact that their measurements were taken from the outer colon wall, whereas previous studies accessed tissue directly from the lumen. However, when the data were stratified by tumor stage, a clear trend emerged. Advanced stages (T4b) exhibited markedly higher Δε′ and Δε″ values in both in vivo and ex vivo conditions. For example, in the ex vivo scenario at 18 GHz, Δε′ reached 7.38 and Δε″ 1.75 for T4b tumors, while T3 tumors showed negative or near‑zero differences across all frequencies. In the in vivo scenario, T4a tumors displayed a substantial Δε′ of 3.98 at 2.45 GHz, and T4b tumors showed Δε″ of 2.66 at 18 GHz. These findings suggest that as a tumor grows outward toward the serosal surface, its dielectric signature becomes more detectable from the exterior, overcoming the limited penetration depth of the coaxial probe (a few millimetres).

The paper highlights two key implications. First, dielectric contrast between malignant and healthy colon tissue becomes measurable from the outside only for sufficiently advanced tumors that have breached deeper layers of the bowel wall. Second, the limited probing depth of the current open‑ended coaxial sensor restricts detection of early‑stage (T3) tumors, indicating a need for sensors with greater penetration or higher‑frequency operation to enhance sensitivity. The authors also note sources of variability such as patient‑specific anatomy, intra‑operative temperature, and blood perfusion, recommending larger cohorts, temperature compensation, and multi‑point sampling in future work.

In conclusion, this study demonstrates the feasibility of real‑time, broadband dielectric measurements of colon tissue during surgery and provides quantitative evidence that tumor stage influences the measurable dielectric contrast. The results lay groundwork for developing non‑invasive diagnostic tools or intra‑operative guidance systems that exploit dielectric properties, while also identifying technical challenges—particularly probe penetration depth and calibration under sterile conditions—that must be addressed to translate these findings into clinical practice. Future research directions include refined probe designs, expanded clinical trials, and integration of machine‑learning algorithms for automated tissue classification based on the measured dielectric spectra.