Review of Machine Learning in Lung Ultrasound in COVID-19 Pandemic

Abstract

Ultrasound imaging of the lung has played an important role in managing patients with COVID-19-associated pneumonia and acute respiratory distress syndrome (ARDS). During the COVID-19 pandemic, lung ultrasound (LUS) or point-of-care ultrasound (POCUS) has been a popular diagnostic tool due to its unique imaging capability and logistical advantages over chest X-ray and CT. Pneumonia/ARDS is associated with the sonographic appearances of pleural line irregularities and B-line artefacts, which are caused by interstitial thickening and inflammation, and increase in number with severity. Artificial intelligence (AI), particularly machine learning, is increasingly used as a critical tool that assists clinicians in LUS image reading and COVID-19 decision making. We conducted a systematic review from academic databases (PubMed and Google Scholar) and preprints on arXiv or TechRxiv of the state-of-the-art machine learning technologies for LUS images in COVID-19 diagnosis. Openly accessible LUS datasets are listed. Various machine learning architectures have been employed to evaluate LUS and showed high performance. This paper will summarize the current development of AI for COVID-19 management and the outlook for emerging trends of combining AI-based LUS with robotics, telehealth, and other techniques.

Keywords: COVID-19; artificial intelligence (AI); deep learning; lung ultrasound; machine learning.

Figure 1

The number of COVID-19 AI publications based on ultrasound (orange bars) and CT, X-ray and ultrasound combined (blue bars) in PubMed Database, as of 17 January 2022.

Figure 2

The three standard BLUE points are illustrated (two anterior and one posterior) [modified from [40]]. Two hands are placed on the front chest such that the upper hand touches the clavicle, and the upper anterior BLUE-point is in the middle of the upper hand, while the lower anterior BLUE-point is in the middle of the lower palm. The PLAPS-point is vertically at the posterior axillary line and horizontally at the same level of the lower anterior BLUE-point.

Figure 3

Examples of (a) horizontal A-lines (yellow arrows) in a normal lung, (b) multiple B-lines (yellow arrows) with an irregular pleura line (red arrows) in a COVID-19 indicative lung, and (c) white lung (completely diffused B-lines) for severe COVID-19 pneumonia. Reprinted with permission from ref. [34,51]. Copyright 2020 John Wiley and Sons.