Head and Neck

Key images

Findings

85-year-old female with previously diagnosed thyroid carcinoma treated by surgery and radiotherapy presented with severe dysphagia. Evaluation with spectral CT.

Better delineation of the paratracheal mass and the cervical lymph node with lower keV virtual monoenergetic and iodine overlay images. Quantification of iodine uptake of these lesions by iodine density and Z effective images.

Axial and coronal images

Conventional CT with contrast demonstrated a small left paratracheal mass in left thyroid bed and left level IIa enlarged lymph node suspicious for recurrent thyroid carcinoma. Virtual monoenergetic images at 55 keV and iodine overlay images better delineated the lesions. Iodine density and Z effective images showed increased iodine content of the mass in left thyroid bed (5.27 mg/ml) and the level IIa enlarged lymph node (3.79 mg/ml) quantitatively. Similarly, PET/CT performed the next day demonstrated high metabolic activity within the left paratracheal mass and left level IIa lymph node (SUVmax 4.8 and 10.4 respectively). The patient underwent lymph node biopsy for suspected recurrence.

Discussion high metabolic activity within the left paratracheal mass in thyroid bed (SUVmax 4.8, blue arrows).

Iodine density and Z effective images could quantitatively demonstrate the iodine content of the paratracheal masses in thyroid bed after surgery and enlarged cervical lymph nodes suspicious of recurrence. Virtual monoenergetic images at low keV and iodine overlay images allow better delineation of these lesions with higher iodine content providing images similar to PET/CT.

Virtual monoenergetic image at 55 keV, axial image: better delineation of left paratracheal mass in thyroid bed (arrow).

Virtual non-contrast axial image: left paratracheal mass (arrow) with an attenuation value of 55.5 HU.

Iodine density axial image: increased iodine content of the left paratracheal mass in thyroid bed (5.27 mg/ml, arrow).

Z effective axial image: left paratracheal mass in thyroid bed (arrow) with increased iodine content is color coded in dark blue and has an effective atomic number of 9.64.

Virtual monoenergetic image at 55 keV, coronal image: better delineation of left level IIa enlarged lymph node (arrow).

Virtual non-contrast coronal image: left level IIa enlarged lymph node (arrow) with an attenuation value of 39.9 HU.

Iodine density coronal image: increased iodine content of the left level IIa enlarged lymph node (3.79 mg/ml, arrow).

Z effective coronal image: left level IIa enlarged lymph node (arrow) with increased iodine content is color coded in dark blue and has an effective atomic number of 9.13.

Iodine overlay axial image: better delineation of left paratracheal mass in thyroid bed with higher iodine content (arrow).

Iodine overlay coronal image: better delineation of left level IIa enlarged lymph node with higher iodine content (arrow).

History

Benefits or pitfalls of dual-energy CT

Key images

Findings

33-year-old testicular carcinoma patient with previously resected brain metastasis presented with seizures.

Identification of iodine in an area of hemorrhage.

Axial images

Conventional non-contrast CT scan showed an area of hemorrhage on the right parietal lobe. A small portion showed contrast enhancement on lateral aspect of the lesion. Virtual non-contrast images were comparable to true non-contrast images. Iodine density and Z effective images showed iodine uptake indicating a metastatic foci with hemorrhagic component. The mass was resected and metastasis was confirmed at pathology.

Discussion

Contrast uptake could be masked by hyperdense hemorrhage in a hemorrhagic mass lesion on conventional CT images. Iodine density and Z effective images are useful to identify the presence of iodine in the lesion, and allowing therefore a more confident diagnosis of an underlying mass. Virtual non-contrast images are comparable to true non-contrast images. A reduction of radiation dose to the patient is possible by omitting true non-contrast images.

Conventional CT non-contrast axial image: hyperdense area of hemorrhage (arrow).

Virtual non-contrast axial image: hyperdense area of hemorrhage (arrow).

Conventional CT axial image with contrast: enhancement of the lateral aspect of the mass (arrow), difficult to differentiate from the hemorrhagic background.

Iodine density image: iodine uptake of the lateral portion of the lesion; iodine concentration of the mass (1.93 mg/ml, blue arrow) is higher compared to adjacent brain parenchyma (1.00 mg/ml, white arrow).

Z effective image: effective atomic number of the lateral portion of the mass is higher (8.70, blue arrow) compared to adjacent brain parenchyma (8.03, white arrow), indicating iodine uptake of the lesion.

Pathology image: infiltration of cerebral parenchyma by very atypical neoplastic cells. Some glandular and pseudoglandular structures (red arrow) and necrotic areas (black arrows) (Hematoxylin-Eosin, x200).

Pathology image, immunochemistry: quite diffuse membranous staining of CD30 (x200).

History Benefits or pitfalls of dual-energy CT

Key images Findings