Korean J Radiol.  2018 Jun;19(3):516-525. 10.3348/kjr.2018.19.3.516.

Nodule Classification on Low-Dose Unenhanced CT and Standard-Dose Enhanced CT: Inter-Protocol Agreement and Analysis of Interchangeability

• Lee KH
• Lee KW
• Park JH
• Han K
• Kim J
• Lee SM
• Park CM

• KMID: 2410823
• DOI: http://doi.org/10.3348/kjr.2018.19.3.516

Abstract

OBJECTIVE
To measure inter-protocol agreement and analyze interchangeability on nodule classification between low-dose unenhanced CT and standard-dose enhanced CT.
MATERIALS AND METHODS
From nodule libraries containing both low-dose unenhanced and standard-dose enhanced CT, 80 solid and 80 subsolid (40 part-solid, 40 non-solid) nodules of 135 patients were selected. Five thoracic radiologists categorized each nodule into solid, part-solid or non-solid. Inter-protocol agreement between low-dose unenhanced and standard-dose enhanced images was measured by pooling κ values for classification into two (solid, subsolid) and three (solid, part-solid, non-solid) categories. Interchangeability between low-dose unenhanced and standard-dose enhanced CT for the classification into two categories was assessed using a pre-defined equivalence limit of 8 percent.
RESULTS
Inter-protocol agreement for the classification into two categories {κ, 0.96 (95% confidence interval [CI], 0.94-0.98)} and that into three categories (κ, 0.88 [95% CI, 0.85-0.92]) was considerably high. The probability of agreement between readers with standard-dose enhanced CT was 95.6% (95% CI, 94.5-96.6%), and that between low-dose unenhanced and standard-dose enhanced CT was 95.4% (95% CI, 94.7-96.0%). The difference between the two proportions was 0.25% (95% CI, −0.85-1.5%), wherein the upper bound CI was markedly below 8 percent.
CONCLUSION
Inter-protocol agreement for nodule classification was considerably high. Low-dose unenhanced CT can be used interchangeably with standard-dose enhanced CT for nodule classification.

Keyword

Pulmonary nodules; Classification; Subsolid nodule; Ground-glass nodule; Computed tomography; Low-dose CT

MeSH Terms

Classification*
Humans
Tomography, X-Ray Computed

Figure

• 

  Fig. 1 Flowchart of nodule selection.Numbers in parentheses represent number of patients.

• 

  Fig. 2 Heatmap showing results of nodule classification.160 nodules included 80 subsolid (non-solid [No. 1–40] and part-solid [No. 41–80]) and 80 solid nodules (No. 81–160) that were selected by stratified random sampling from nodule libraries. Five radiologists classified nodules as subsolid (non-solid [displayed as light green], part-solid [displayed as green],) or solid [displayed as dark green] using standard-dose enhanced and low-dose unenhanced CT images during two reading sessions. In this figure, nodules are arranged in order of increasing size in each of three classification categories, regardless of reading order and reading session.

• 

  Fig. 3 Axial CT images of 14.6-mm nodule in right upper lobe (No. 68).Each of five radiologists indicated same classification for this nodule (arrows), either using low-dose unenhanced CT images (A) or standard dose enhanced CT images (B) (Reader 2–5: part-solid; Reader 1: solid).

• 

  Fig. 4 Axial CT images of 18-mm nodule in left upper lobe (No. 36).A. Using low-dose unenhanced CT images, three radiologists classified nodule (arrow) as non-solid nodule, whereas two radiologists regarded this as part-solid nodule. B. All five of radiologists classified nodule (arrow) as non-solid nodule using standard-dose enhanced CT images.

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