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Optimal matrix size of chest radiographs for computer-aided detection on lung nodule or mass with deep learning



To investigate the optimal input matrix size for deep learning-based computer-aided detection (CAD) of nodules and masses on chest radiographs.


We retrospectively collected 2088 abnormal (nodule/mass) and 352 normal chest radiographs from two institutions. Three thoracic radiologists drew 2758 abnormalities regions. A total of 1736 abnormal chest radiographs were used for training and tuning convolutional neural networks (CNNs). The remaining 352 abnormal and 352 normal chest radiographs were used as a test set. Two CNNs (Mask R-CNN and RetinaNet) were selected to validate the effects of the squared different matrix size of chest radiograph (256, 448, 896, 1344, and 1792). For comparison, figure of merit (FOM) of jackknife free-response receiver operating curve and sensitivity were obtained.


In Mask R-CNN, matrix size 896 and 1344 achieved significantly higher FOM (0.869 and 0.856, respectively) for detecting abnormalities than 256, 448, and 1792 (0.667–0.820) (p < 0.05). In RetinaNet, matrix size 896 was significantly higher FOM (0.906) than others (0.329–0.832) (p < 0.05). For sensitivity of abnormalities, there was a tendency to increase sensitivity when lesion size increases. For small nodules (< 10 mm), the sensitivities were 0.418 and 0.409, whereas the sensitivities were 0.937 and 0.956 for masses. Matrix size 896 and 1344 in Mask R-CNN and matrix size 896 in RetinaNet showed significantly higher sensitivity than others (p < 0.05).


Matrix size 896 had the highest performance for various sizes of abnormalities using different CNNs. The optimal matrix size of chest radiograph could improve CAD performance without additional training data.

Key Points

• Input matrix size significantly affected the performance of a deep learning-based CAD for detection of nodules or masses on chest radiographs.

• The matrix size 896 showed the best performance in two different CNN detection models.

• The optimal matrix size of chest radiographs could enhance CAD performance without additional training data.

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Area under the curve


Computer-aided detection


Convolutional neural network


Figure of merit


Feature pyramid network


Jackknife alternative free-response receiver operating characteristic curve


Region-based convolutional neural network


Receiver operating characteristic


Region of interest


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This study has received funding by the Industrial Strategic Technology Development program (10072064, Development of Novel Artificial Intelligence Technologies To Assist Imaging Diagnosis of Pulmonary, Hepatic, and Cardiac Diseases and Their Integration into Commercial Clinical PACS Platforms) funded by the Ministry of Trade Industry and Energy (MI, Korea).

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Corresponding authors

Correspondence to Sang Min Lee or Namkug Kim.

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The scientific guarantor of this publication is Sang Min Lee.

Conflict of interest

The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.

Statistics and biometry

Jung Bok Lee, PhD kindly provided statistical advice for this manuscript.

Informed consent

Written informed consent was waived by the Institutional Review Board.

Ethical approval

Institutional Review Board approval was obtained.

Study subjects or cohorts overlap

Study subjects have been previously reported in Park et al study (Deep learning-based detection system for multiclass lesions on chest radiographs: comparison with observer readings. Eur Radiol. 2020 Mar;30(3):1359–1368).


• Retrospective

• Diagnostic or prognostic study

• Performed at one institution

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Kim, YG., Lee, S.M., Lee, K.H. et al. Optimal matrix size of chest radiographs for computer-aided detection on lung nodule or mass with deep learning. Eur Radiol 30, 4943–4951 (2020).

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  • Thoracic radiography
  • Lung
  • Computer-assisted diagnosis
  • Deep learning
  • Algorithms