Pipeline for Advanced Contrast Enhancement (PACE) of Chest X-ray in Evaluating COVID-19 Patients by Combining Bidimensional Empirical Mode Decomposition and Contrast Limited Adaptive Histogram Equalization (CLAHE)

COVID-19 is a new pulmonary disease which is driving stress to the hospitals due to the
large number of cases worldwide. Imaging of lungs can play a key role in the monitoring of health
status. Non-contrast chest computed tomography (CT) has been used for this purpose, mainly in
China, with significant success. However, this approach cannot be massively used, mainly for
both high risk and cost, also in some countries, this tool is not extensively available. Alternatively,
chest X-ray, although less sensitive than CT-scan, can provide important information about the
evolution of pulmonary involvement during the disease; this aspect is very important to verify the
response of a patient to treatments. Here, we show how to improve the sensitivity of chest X-ray
via a nonlinear post-processing tool, named PACE (Pipeline for Advanced Contrast Enhancement),
combining properly Fast and Adaptive Bidimensional Empirical Mode Decomposition (FABEMD)
and Contrast Limited Adaptive Histogram Equalization (CLAHE). The results show an enhancement
of the image contrast as confirmed by three widely used metrics: (i) contrast improvement index,
(ii) entropy, and (iii) measure of enhancement. This improvement gives rise to a detectability of more
lung lesions as identified by two radiologists, who evaluated the images separately, and confirmed by
CT-scans. The results show this method is a flexible and an e ective approach for medical image
enhancement and can be used as a post-processing tool for medical image understanding and analysis.