Subtraction Iodine Imaging Generated from Dual-Energy CT: Optimal Energy Determination and Evaluation of Sinonasal and Nasopharyngeal Malignancies.

Abstract

Background and purpose: Subtraction iodine imaging (SII) and dual-energy CT-derived iodine imaging (DEII) have been proposed to enhance tumor delineation in head and neck cancers. However, the optimal energy for SII and the added diagnostic value of SII or DEII combined with conventional CT (CCT) remain uncertain. We aimed to determine the optimal energy for SII and to evaluate its incremental diagnostic benefits, as well as those of DEII.

Materials and methods: Thirty-nine patients with histologically confirmed sinonasal or nasopharyngeal malignancies who underwent dual-energy CT (DECT) and contrast-enhanced MRI were included in this retrospective study. SII was generated by subtracting pre- and postcontrast virtual monochromatic images from the DECT images (45-75 keV, in 5-keV increments). Contrast-to-noise ratios (CNRs) were measured in the brain, prevertebral muscles, and skull base. Tumor delineation was assessed on a 5-point scale by 2 blinded radiologists, and the diagnostic performance for local tumor extension was evaluated using clustered receiver operating characteristic analysis with bootstrap resampling.

Results: The highest CNR across all anatomic sites was consistently achieved with SII at 65 keV. Tumor delineation scores were significantly higher with SII than with DEII (median, 4.5 versus 2.0; P < .001). Receiver operating characteristic analysis showed that CCT combined with SII yielded the highest diagnostic accuracy (area under the curve [AUC], 0.954), significantly outperforming CCT alone (AUC, 0.929; difference in AUC = 0.024; P = .02). The CCT combined with DEII did not show any significant improvements.

Conclusions: SII at 65 keV provided optimal image quality, superior tumor delineation, and significantly improved diagnostic accuracy more than CCT did. Incorporating this imaging technique into CCT protocols may enhance the evaluation of tumor extension in sinonasal and nasopharyngeal malignancies.