Purpose: To optimize the binary detection of Chronic Obstructive Pulmonary
Disease (COPD) based on emphysema presence in the lung with convolutional
neural networks (CNN) by exploring manually adjusted versus automated
window-setting optimization (WSO) on computed tomography (CT) images.
Methods: 7,194 CT images (3,597 with COPD; 3,597 healthy controls) from 78
subjects (43 with COPD; 35 healthy controls) were selected retrospectively
(10.2018-12.2019) and preprocessed. For each image, intensity values were
manually clipped to the emphysema window setting and a baseline 'full-range'
window setting. Class-balanced train, validation, and test sets contained
3,392, 1,114, and 2,688 images. The network backbone was optimized by comparing
various CNN architectures. Furthermore, automated WSO was implemented by adding
a customized layer to the model. The image-level area under the Receiver
Operating Characteristics curve (AUC) [lower, upper limit 95% confidence] and
P-values calculated from one-sided Mann-Whitney U-test were utilized to compare
model variations.
Results: Repeated inference (n=7) on the test set showed that the DenseNet
was the most efficient backbone and achieved a mean AUC of 0.80 [0.76, 0.85]
without WSO. Comparably, with input images manually adjusted to the emphysema
window, the DenseNet model predicted COPD with a mean AUC of 0.86 [0.82, 0.89]
(P=0.03). By adding a customized WSO layer to the DenseNet, an optimal window
in the proximity of the emphysema window setting was learned automatically, and
a mean AUC of 0.82 [0.78, 0.86] was achieved.
Conclusion: Detection of COPD with DenseNet models was improved by WSO of CT
data to the emphysema window setting range