In vivo evaluation of non-invasive temperature monitoring with spectral CT thermometry

Thermal ablation of liver tumors has demonstrated effectiveness comparable to that of surgical resection but faces high local tumor recurrence rates largely associated with insufficient ablation of the tumor and surrounding safety margin of healthy tissue. Current standard of care for identifying ablation margins, including theoretical heat models and post-procedural imaging, remain insufficient. One method of ensuring the ablation of both tumor and safety margin, and thus reducing local tumor recurrences, is non-invasive temperature monitoring with spectral CT. It exploits spectral CT’s ability to separate composition changes and temperature changes to generate accurate volumetric temperature maps for visualization of the ablation zone intra-procedurally. Spectral CT thermometry’s utility has been previously established in ex vivo tissue and liver-mimicking phantoms, but not yet in in vivo liver. To assess the feasibility of spectral CT thermometry in in vivo liver, a microwave ablation probe and thermometers were inserted into the liver of a healthy Yorkshire pig. An ablation was performed at 65 W for 5 minutes and scanned with a dual-layer dual-energy CT every 30 seconds. Spectral results were reconstructed to calculate physical density maps, which were measured at each thermometer location to related temperature and physical density on the basis of thermal volumetric expansion. Over the course of the ablation, temperatures increased from 36.3 to 81.3 °C, corresponding to a decrease in physical density from 1.058 to 1.031 g/L. Physical density and temperature exhibited a strong fit to thermal volumetric expansion with a Pearson’s correlation coefficient of 0.8785. This study confirms the utility of spectral CT thermometry in monitoring temperature non-invasively during in vivo liver microwave ablation, further promoting its clinical translation.