CT reconstruction with thick slices not only underestimates lymph node size but also reduces data reproducibility in colorectal cancer.

Abstract

Reliable size measurement of lymph node (LN) metastases is important for the evaluation of cancer treatment. However, image analyses without proper settings may result in inappropriate diagnoses and staging. To investigate whether reconstruction slice thickness in computed tomography (CT) affects measurements of LN size and reproducibility. We analyzed 48 patients with histological diagnoses of sigmoid colon and rectal cancer who underwent contrast-enhanced CT colonography as part of a surgical treatment preparation. A board-certified radiologist selected 106 LNs whose short-axis diameter was ≥5 mm on 1-mm-thick images; the short-axis diameters were measured on 1- and 5-mm-thick images by the radiologist and residents and compared using Wilcoxon matched-pairs signed rank test. Data variation and reproducibility were evaluated using the F test and Bland-Altman analysis. P<0.05 was considered significant. Short-axis diameters measured on 5-mm-thick images were significantly lower than those measured on 1-mm-thick images (P<0.01), even in the LNs whose short-axis diameters were over twice the slice thickness (P<0.05). Of the 106 LNs, 57 showed short-axis diameter <5 mm on 5-mm-thick images; the maximum short-axis diameter was 6.7 mm on a 1-mm thick image. Data variation was significantly larger on 5-mm thick images than 1-mm-thick images in small LNs (P<0.05) and reproducibility on 5-mm-thick images was inferior to that on 1-mm-thick images. Thick reconstruction slices in CT can result in an underestimation of LN size and reduce data reproducibility. When measuring LN size, a thin reconstruction slice would be recommended based on targeted LN size.