Head and Neck

Key images

Findings

75-year-old male with left-sided oropharyngeal epidermoid carcinoma diagnosed in 2004 and treated with radiochemotherapy. Spectral CT was requested for monitoring of potential local progression.

Quantification of iodine uptake of the right-sided mass at the base of the tongue with iodine density and Z effective images. Better delineation of the left-sided oropharyngeal infiltration on iodine overlay images.

Axial images

Conventional CT with contrast showed a mass at the right side of the base of the tongue and left-sided oropharyngeal infiltration. Virtual monoenergetic images provided better delineation of the mass and oropharyngeal infiltration. Iodine density and Z effective images demonstrated increased iodine content (2.95 mg/ml) and higher effective atomic number (9.05) of the mass of the tongue quantitatively compared to unaffected left side of the tongue (iodine density: 1.42 mg/ml, effective atomic number: 8.24) and left submandibular lymph node (iodine content: 1.90 mg/ml, effective atomic number: 8.50). Iodine overlay images were helpful in better demonstrating the margins of the left oropharyngeal infiltration.

Discussion

Virtual monoenergetic images at lower keV could improve lesion enhancement in head and neck tumors. Iodine density and Z effective images quantitatively demonstrate the iodine content of a tongue mass and enlarged lymph nodes compared to unaffected adjacent structures. The quantification of the amount of iodine in head and neck masses and lymph nodes may be helpful in characterization of these lesions. Iodine overlay images also provide better delineation of the lesion and could be beneficial for demonstrating the tumor extent and invasion of the adjacent structures better, thus may help in staging.

Conventional CT with contrast, axial image at 120 kVp: right-sided mass of the base of the tongue (blue arrow) and left-sided submandibular lymph node (white arrow).

Virtual monoenergetic axial image at 50 keV: better demarcation of the mass (arrow).

Iodine density image: increased iodine content of the right-sided mass of the tongue (3.05 mg/ml, blue arrow) compared to left side (1.30 mg/ml, white arrow) and increased iodine content of the left submandibular lymph node (1.90 mg/ml).

Z effective image: mass of the right side of the tongue (blue arrow) with increased iodine content which is color coded in dark blue. The effective atomic number is higher (9.09) compared to left side of the tongue (8.19, white arrow) and left submandibular lymph node (8.50, curved arrow), appearing color coded in lighter blue.

Iodine density axial image: increased iodine content of the left-sided oropharyngeal infiltration (2.69 mg/ml, blue arrow) compared to right side of oropharynx (1.30 mg/ml, white arrow).

Z effective axial image: left side of oropharynx (blue arrow) with increased iodine content is color coded in dark blue and has higher effective atomic number (8.95) compared to right side of oropharynx (8.20) color coded in light blue-green (white arrow).

Iodine overlay axial image: better delineation of the extent of left-sided oropharyngeal and epiglottis infiltration (arrows).

History Benefits or pitfalls of dual-energy CT