Evaluation of lung cancer by enhanced dual-energy CT: association between three-dimensional iodine concentration and tumour differentiation

Abstract

Objective: To investigate the correlation between iodine concentration of dual-energy CT (DECT) and histopathology of surgically resected primary lung cancers.

Methods: We reviewed the medical records, post-operative pathological records and pre-operative DECT images of patients who underwent surgical lung resection for primary lung cancer. After injection of iodinated contrast media, arterial and delayed phases were scanned using 140- and 80-kV tube voltages. Three-dimensional iodine concentration (iodine volume) of primary tumours was calculated using lung nodule application software.

Results: A total of 60 patients (37 males and 23 females; age range, 39-84 years; mean age, 69 years) with 62 lung cancers were analysed. The resected tumours were histopathologically classified into well-differentiated (G1; n = 20), moderately differentiated (G2; n = 29), poorly differentiated (G3; n = 9) and undifferentiated (G4; n = 4) groups by degree of tumour differentiation (DTD). The mean ± standard deviation of iodine volume at the delayed phase was 59.6 ± 18.6 HU in G1 tumours, 46.5 ± 11.3 HU in G2 tumours, 34.3 ± 15.0 HU in G3 tumours and 28.8 ± 6.4 HU in G4 tumours; significant differences were observed between groups (p < 0.001). Univariate logistic regression analysis showed that iodine volumes both at the early and delayed phases were significantly correlated with DTD (p = 0.006 and p = 0.001, respectively), whereas gender, body weight and tumour size were not (p = 0.084, p = 0.062 and p = 0.391, respectively).

Conclusion: The iodine volume of lung cancers was significantly associated with their DTD. High-grade tumours tended to have lower iodine volumes than low-grade tumours.

Advances in knowledge: Iodine volume measured by DECT could be a valuable functional imaging method to estimate differentiation of primary lung cancer.

Figure 1.

Procedure for measuring the iodine volume of lung lesions. (a) At the delayed phase of contrast-enhanced CT, a solid-type adenocarcinoma is observed in the right upper lobe (arrow). (b) Iodine-enhanced images at the same level as shown in (a). (c) Three-dimensional measurement of the iodine value on an iodine-enhanced image. Automatic segmentation (double yellow line) and calculation of iodine volume can be performed using the “Lung Nodule” application of dual-energy CT. (d) Coronal view of iodine-enhanced image after segmentation.

Figure 2.

Study cohort flow chart. A total of 78 surgically resected pulmonary lesions were scanned pre-operatively with dual-phase contrast-enhanced CT using a dual-source technique. After exclusion, 62 primary lung cancers were included in the present analysis.

Figure 3.

A 62-year-old female patient. (a) Well-differentiated (G1) adenocarcinoma is in the right upper lobe. (b) Iodine-enhanced image at the delayed phase of contrast-enhanced CT. The iodine volume is 57 HU. (c) Positron emission tomography/CT shows low fludeoxyglucose uptake of the tumour and the maximal standard uptake value is 1.1.

Figure 4.

A 65-year-old male patient. (a) Poorly differentiated (G3) adenocarcinoma is in the right lower lobe. (b) Iodine-enhanced image at the delayed phase of contrast-enhanced CT. The iodine volume is 20 HU. (c) Positron emission tomography/CT shows high fludeoxyglucose uptake of the tumour and the maximal standard uptake value is 10.1.