Laser Ablation of Liver Tumors with Realtime Monitoring

More than two-thirds of primary liver cancer patients and 90% of patients with secondary liver cancer are inoperable because the tumors are in the vicinity of or have invaded into major blood vessels or other adjacent vital structures. Image-guided percutaneous laser ablation (LA) has been increasingly used as a minimally invasive therapy for unresectable primary and secondary liver tumors. In current practice, CT, MRI or US imaging allows the operator to locate the tumor and precisely place the probe, but monitoring of the tumor during ablation is extremely difficult.

Monitoring tissue status during ablation is critical to ensure complete destruction of the cancer cells while avoiding charring and excessive damage to healthy tissues and important structures. Although magnetic resonance thermometry (MRT) or thermocouples are often used to monitor temperature, most damage assessment is done at the end of the initial treatment. The temperature-based damage assessment (the Arrhenius model) also requires priori knowledge of tissue contents, which is generally unknown. More importantly, the most commonly used MRT/MRI method is expensive and requires at least one MR physicist and one radiologist in the operation room at the same time, making it inaccessible to many liver cancer patients.

To address this clinical need, we have developed an integrated laser ablation (iLA) solution (as illustrated in Fig. 3) that can be operated by a radiologist alone to effectively kill cancer cells in the liver while minimizing unnecessary damage to healthy tissues. Under US-guidance, the iLA probe can ablate a tumor with a high-power NIR laser while continuously monitoring the tumor temperature (using a fiber optic sensor) and optical properties using DRS. In our recent studies, we have observed that the absorption and reduced scattering coefficients (µa and µs') of ex vivo porcine muscle and liver tissues measured with DRS changed drastically in a reproducible manner during heating.

 

Data from thermal ablation

 
Fig. 6:  Relative changes in (a) µa and (b) µs' compared with the natural logarithm of Arrhenius tissue damage index Fd; (c) continuous measurement of relative changes in µa and µs', and Fd at different temperatures; (d) comparison of relative changes in µa and µs' at Level 1 (37° C), 2 (55° celsius), 3 (65° C) and 4 (75° C), respectively. (* indicates p<0.0003, and ** indicates p<0.001).

 

Selected Publications

Vivek Krishna Nagarajan, Jerrold M. Ward, and Bing Yu, “Association of Liver Tissue Optical Properties and Thermal Damage”, Lasers in surgery and medicine 52 (8), 779-787.

Vivek K. Nagarajan, Venkateswara R. Gogineni, Sarah B. White and Bing Yu, "Real time evaluation of tissue optical properties during thermal ablation of ex vivo liver tissues," International Journal of Hyperthermia, 35(1):176-182, 2019, DOI: 10.1080/02656736.2018.1488278.

Vivek K. Nagarajan and Bing Yu, "Monitoring of tissue optical properties during thermal coagulation of ex vivo tissues," Lasers Surg. Med., June 1, 2016. DOI: 10.1002/lsm.22541.

 

 

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