Quantitative analysis and application value of CT spectral parameter in lung cancer

Objective To analyze the characteristics and to evaluate the application of quantitative CT spectral parameters in patients with suspected lung cancer. Methods One hundred and thirty two patients with occupying lesions of the lung underwent chest plain and two-phase contrast enhanced CT scan with gemstone spectral imaging (GSI) mode. The CT images of patients with confirmed lung cancer by pathological evidence were analyzed with GSI viewer. Optimal energy value supplying optimal contrast-to-noise ratio (CNR) was recorded. The CT values of lesions at 40 keV, 70 keV and optimal energy level were measured. Spectral curve slope at different intervals of 40-70 keV, 40-100 keV and 40-140 keV was computed. Effective atomic number (Zeff), iodine concentration (IC) and water concentration (WC) were measured and analyzed by statistical methods. Results Sixty six patients with confirmed lung cancer were included in the analysis. The optimal energy values for optimal CNR on plain scan, arterial phase and venous phase were (63.09±5.33) keV, (52.65±6.44) keV and (54.06±5.53) keV, respectively. The difference of CT values at different energy levels on each scan phase was statistically significant (F=4.561, P=0.025). The spectral curve slope values among three different energy intervals were significantly different (F=2.137, P<0.001). The differences of the slope between arterial phase and venous phase at same energy interval were not significant (40-70 keV: t=1.165, P=0.248; 40-100 keV: t=1.102, P=0.274; 40-140 keV: t=1.118, P=0.268). Zeff on plain scan, arterial phase and venous phase was 7.73±0.14, 8.35±0.37 and 8.39±0.30, respectively. There was positive correlation between IC and Zeff on enhanced phase (arterial phase: r=0.998, P<0.001; venous phase: r=0.998, P<0.001). Conclusion CT spectral imaging can supply the optimal energy value for optimal CNR. CT value at optimal energy level and spectral curve slope at 40-140 keV are suitable for analysis. IC and Zeff can be used jointly in evaluation of patients with suspected lung cancer. Key words: Lung neoplasms; Tomography, X-ray; Dual-energy scanned projection