Convolutional Neural Network to Stratify the Malignancy Risk of Thyroid Nodules: Diagnostic Performance Compared with the American College of Radiology Thyroid Imaging Reporting and Data System Implemented by Experienced Radiologists

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FIG 1.
Flowchart of the study population. AUS/FLUS indicates atypia of undetermined significance/follicular lesion of undetermined significance.
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FIG 2.
Comparison of ROC curves between the CNN (solid line) and ACR TI-RADS categories (dotted line). The area under the ROC curve of the CNN (0.917; 95% confidence interval, 0.895–0.936) was higher than that in the ACR TI-RADS categories (0.891; 95% confidence interval, 0.867–0.912) (P = .017). The areas under the ROC curve of the CNN using a malignancy risk percentage between 0 and 100 and ACR TI-RADS categories using a TR category from 1 to 5 were compared as continuous values.

Table 1:

Patient demographics and distribution of ACR TI-RADS features in benign and malignant thyroid nodules (n = 760)^{^a}

Characteristics	All (n = 760)	Benign Nodules (n = 584)	Malignant Nodules (n = 176)	P Value
Sex				.035
Women	587	462 (79.4%)	125 (71.4%)
Men	170	120 (20.6%)	50 (28.6%)
Age (median) (interquartile range) (yr)	51 (39–61)	52 (41–61)	45 (34–60)	<.001
Nodule size (median) (interquartile range) (mm)	20 (14–30)	23 (15–32)	14 (11–20)	<.001
Nodule features
Composition				<.001
Cystic or almost completely cystic	50	47 (8.0%)	3 (1.7%)
Spongiform	1	1 (0.2%)	0
Mixed cystic and solid	234	222 (38.0%)	12 (6.8%)
Solid or almost completely solid	475	314 (53.8%)	161 (91.5%)
Echogenicity				<.001
Anechoic		0	0
Hyperechoic or isoechoic	410	387 (66.3%)	23 (13.1%)
Hypoechoic	329	191 (32.7%)	138 (78.4%)
Very hypoechoic	21	6 (1.0%)	15 (8.5%)
Shape				<.001
Wider-than-tall	671	554 (94.9%)	117 (66.5%)
Taller-than-wide	89	30 (5.1%)	59 (33.5%)
Margin				<.001
Smooth	579	535 (91.6%)	44 (25.0%)
Ill-defined	0	0	0
Lobulated or irregular	181	49 (8.4%)	132 (75.0%)
Extrathyroidal extension	0	0	0
Echogenic foci				<.001
None or large comet-tail artifacts	536	477 (81.7%)	59 (33.5%)
Macrocalcifications	91	69 (11.8%)	22 (12.5%)
Peripheral (rim) calcifications	10	10 (1.7%)	0
Punctate echogenic foci	123	28 (4.8%)	95 (54.0%)

Table 2:

Calculated malignancy risk of each category according to the risk stratification of ACR TI-RADS

	TR1	TR2	TR3	TR4	TR5	Total
Suggested risk of malignancy (%)^20,24	≤2	≤2	2< and ≤5	5< and ≤20	>20
ACR TI-RADS category
No. of malignant nodules	0	4	9	33	130	176
Assigned total nodules	41	158	185	209	167	760
Calculated risk of malignancy (%)	0	2.5	4.9	15.8	77.8	23.2
CNN^{^a}
No. of malignant nodules	0	0	0	9	167	176
Assigned total nodules	0	5	45	307	403	760
Calculated risk of malignancy (%)	0	0	0	2.9	41.4	23.2

↵a Malignancy percentages provided by the CNN were re-categorized according to the suggested cancer risk levels of ACR TI-RADS.

Table 3:

Comparison of diagnostic performance between CNN and ACR TI-RADS

↵a The AUCs of the CNN using a malignancy risk percentage between 0 and 100 and ACR TI-RADS categories using a TR category from 1 to 5 were compared as continuous values.