A prospective study of dual-energy computed tomography for differentiating metastatic and non-metastatic lymph nodes of colorectal cancer

Abstract

Background: Colorectal cancer (CRC) is the third most common malignancy worldwide, and lymph node metastasis is considered to be a risk factor for local recurrence and a poor prognosis in colorectal cancer. However, there remains a lack of reliable and non-invasive biomarkers to identify the lymph node status of CRC patients preoperatively. The purpose of this study was to explore the ability of dual-energy computed tomography (DECT) to differentiate metastatic from non-metastatic lymph nodes in colorectal cancer.

Methods: Seventy-one patients with primary colorectal cancer underwent contrast-enhanced dual-energy computed tomography imaging preoperatively. The colorectal specimen was scanned postoperatively, and lymph nodes were matched to the pathology report. The following dual-energy computed tomography quantitative parameters were analyzed: dual-energy curve slope value (λ_HU), standardized iodine concentration (n△HU), iodine water ratio (nIWR), electron density value (nρ_eff), and effective atom-number (nZ), based on metastatic and non-metastatic lymph node differentiation. Also, sensitivity and specificity analyses were performed using receiver operating characteristic curves.

Results: In all patients, one hundred and fifty lymph nodes, including 66 non-metastatic and 84 metastatic lymph nodes, were matched using the radiological-pathological correlation. Metastatic nodes had significantly greater λ_HU, n△HU, and nIWR values than non-metastatic nodes in both the arterial and venous phases (P<0.01). The area under curve (AUC), sensitivity, and specificity were 0.80, 80%, and 66% for λ_HU; 0.86, 70%, and 95% for n△HU; and 0.88, 71%, and 95% for nIWR in the arterial phase. There was no significant difference in electron density and effective Z values between metastatic and non-metastatic lymph nodes.

Conclusions: DECT quantitative parameters may help differentiate between metastatic and normal lymph nodes in patients with CRC.

Keywords: Computed tomography; colorectal cancer (CRC); dual-energy CT (DECT); lymph node; staging.

Figure 1

Measurement of lymph nodes; (A) dual-energy CT curve; (B) 69-KeV monochromatic image. Measurement using the tools contained in the system. ROI was selected on the lymph node and included the entire lymph node as much as possible. ROIs, regions of interest.

Figure 2

The method of λ_Hu calculation. The calculation method for the slope of the ROI curve is shown. The pink line is a dual-energy CT curve; the slope of the curve in the ROI is 8.91. λ_Hu, dual-energy curve slope value.

Figure 3

A 41-year-old man with colon cancer; (A) monochromatic obtained at 69 Kev energy level with the best signal-to-noise ratio: a mass shallow was visible in the descending colon (yellow arrow), with multiple lymph nodes of different sizes; (B) dual-energy iodine image; (C) representative images of hematoxylin and eosin (H&E) stains of normal lymph nodes (×40); (D,E) dual-energy curve: the dual energy curve of the tumor (yellow line) almost overlaps that of metastatic lymph node (cyan line), with the same slope. The slope of non-metastatic lymph nodes (pink line) was smaller than that of the metastatic lymph node; (F) representative images of the hematoxylin and eosin (H&E) stains of metastatic lymph nodes of adenocarcinoma, demonstrating gland formation by malignant cells (×40). DECT parameters were used to differentiate normal and metastatic lymph nodes.

Figure 4

Bland-Altman plots for interobserver agreements of DECT parameters (λ_HU, n△HU, nIWR, nρ_eff, and nZ) measurements in the arterial phase (A) and venous phase (B). The X-axis is the average of the DECT parameters values of the two readers and the Y-axis is the percentage difference in the DECT parameters values between the two readers. The solid line shows the mean difference, while the dashed lines show the 95% limits of agreement. A, arterial phase; V, venous phase; OB, observer. The plot is useful in revealing the relationship between the differences of the two interobservers.

Figure 5

Diagnostic efficiency of DECT parameters. ROC curves for dual-energy parameters (λ_HU, n△Hu, and nIWR) in the differentiation of metastatic and non-metastatic lymph nodes. (A) ROC curves in the arterial phase: nIWR value represents the highest diagnostic efficiency, followed by n△Hu and λ_Hu values; (B) ROC curves in the venous phase: nIWR value displays the highest diagnostic efficiency, followed by λ_Hu and n△Hu values. A, arterial phase; V, venous phase; λHU, dual-energy curve slope value; n△HU, standardized iodine concentration; nIWR, iodine water ratio.