Preliminary study on the diagnostic value of single-source dual-energy CT in diagnosing cervical lymph node metastasis of thyroid carcinoma

Abstract

Background: To investigate the value of single-source dual-energy spectral CT imaging in improving the accuracy of preoperative diagnosis of lymph node metastasis of thyroid carcinoma.

Methods: Thirty-four thyroid carcinoma patients were enrolled and received spectral CT scanning before thyroidectomy and cervical lymph node dissection surgery. Iodine-based material decomposition (MD) images and 101 sets of monochromatic images from 40 to 140 keV were reconstructed after CT scans. The iodine concentrations (IC) of lymph nodes were measured on the MD images and was normalized to that of common carotid artery to obtain the normalized iodine concentration (NIC). The CT number of lymph nodes as function of photon energy was measured on the 101 sets of images to generate a spectral HU curve and to calculate its slope λ_HU. The measurements between the metastatic and non-metastatic lymph nodes were statistically compared and receiver operating characteristic (ROC) curves were used to determine the optimal thresholds of these measurements for diagnosing lymph nodes metastasis.

Results: There were 136 lymph nodes that were pathologically confirmed. Among them, 102 (75%) were metastatic and 34 (25%) were non-metastatic. The IC, NIC and the slope λ_HU of the metastatic lymph nodes were 3.93±1.58 mg/mL, 0.70±0.55 and 4.63±1.91, respectively. These values were statistically higher than the respective values of 1.77±0.71 mg/mL, 0.29±0.16 and 2.19±0.91 for the non-metastatic lymph nodes (all P<0.001). ROC analysis determined the optimal diagnostic threshold for IC as 2.56 mg/mL, with the sensitivity, specificity and accuracy of 83.3%, 91.2% and 85.3%, respectively. The optimal threshold for NIC was 0.289, with the sensitivity, specificity and accuracy of 96.1%, 76.5% and 91.2%, respectively. The optimal threshold for the spectral curve slope λ_HU was 2.692, with the sensitivity, specificity and accuracy of 88.2%, 82.4% and 86.8%, respectively.

Conclusions: The measurements obtained in dual-energy spectral CT improve the sensitivity and accuracy for preoperatively diagnosing lymph node metastasis in thyroid carcinoma.

Keywords: Thyroid carcinoma; lymph node; metastasis; spectral CT.

Figure 1

Male, 44 years of age with thyroid papillary carcinoma. (A) L1 is the primary tumor in the left lobe of the thyroid, with irregular shape and unclear margin. IC, NIC and λ_Hu were 3.24, 0.42 and 3.83 mg/mL, respectively; (B) L2 is a right cervical region IV lymph node, with regular shape and clear margin. IC, NIC, and λ_HU were 4.72, 0.62, and 5.55 mg/mL, respectively. The pathology was confirmed to be metastatic; (C) L3 is a left cervical region III lymph node, with regular shape and clear margin. IC, NIC, and λ_HU were 1.24, 0.16, and 1.42 mg/mL. The pathology was confirmed to be non-metastatic; (D) the spectral curve between 40 and 100 keV shows that the curve of metastatic lymph node is above that of the primary lesion, whereas the curve of non-metastatic lymph node is below that of the primary lesion. IC, iodine concentration; NIC, normalized iodine concentration.

Figure 2

Female, 22 years with papillary thyroid carcinoma. (A) L1 is the primary tumor in the right lobe of the thyroid, with irregular shape and unclear margin. IC, NIC and λ_HU were 2.61, 0.37 and 3.09 mg/mL; (B) L2 is a right cervical region II lymph node, with regular shape and clear margin. IC, NIC, and λ_HU were 4.03, 0.57, and 4.97 mg/mL. The pathology was confirmed to be metastatic; (C) L3 is a right cervical region IV lymph node, with regular shape and clear margin. IC, NIC, and λ_HU were 4.32, 0.62, and 5.13 mg/mL. The pathology was confirmed to be metastatic; (D) L4 and L5 are left cervical region IV and V lymph nodes, both with regular shape and clear margin. IC, NIC, and λ_HU were 1.71, 0.24, 2.17 and 1.45, 0.20, 1.67 mg/mL, respectively. Both were confirmed to be non-metastatic; (E) the spectral curve between 40 and 100 keV shows that the spectral curve of metastatic lymph nodes (L2, L3) is above that of the primary lesion, while the spectral curve of non-metastatic lymph nodes (L4, L5) is below that of the primary tumor. IC, iodine concentration; NIC, normalized iodine concentration. IC, iodine concentration; NIC, normalized iodine concentration.