**Abstract**

Coronavirus disease-19 (COVID-19), a highly contagious viral disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) affects many organ systems causing a vast range of clinical manifestations. However, involvement of lungs is the most common manifestation and is the main cause of mortality. Detection of viral nucleic acid in the respiratory secretions is the corner stone of the diagnosis of COVID-19 infection; however, imaging plays a critical role in clinching diagnosis of reverse transcriptase polymerase chain reaction (RT-PCR) negative cases and those with atypical presentation. More importantly imaging has a pivotal role in the detection of complications and their appropriate management. Chest radiography, computed tomography (CT) and magnetic resonance imaging (MRI) all have a role in the diagnosis of COVID-19 pneumonia and detection of various thoracic complications related to this disease. This chapter comprehensively discusses the thoracic manifestations of COVID-19 and the role of imaging in their diagnosis and effective management.

**Keywords:** COVID-19, chest manifestations, CXR, CT, MRI, CT perfusion, PET-CT

### **1. Introduction**

Coronavirus disease 2019 (COVID-19) first emerged in Wuhan, China in late 2019 and spread rapidly across the world. COVID-19 has touched vast swathes of land affecting 220 countries across the world. The disease has infected an estimated 57.7 million people and claimed 1.37 million lives as on 23 November, 2020. The World Health Organization (WHO) declared COVID-19 a pandemic on 11 March, 2020 [1].

COVID-19 is a viral disease. The causative agent is a novel enveloped singlestranded RNA virus belonging to betacoronavirus group and is referred to as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [2]. SARS-CoV-2 is believed to have originated from bats which act as the natural reservoir. The disease spreads through human-to-human contact via respiratory route [3]. Coronaviruses (CoVs) are classified into three genera of alphacoronavirus, betacoronavirus, and gammacoronavirus [4]. CoVs infect animals and humans and cause respiratory, gastrointestinal and neurological diseases of various degrees of severity. CoVs exhibit the genetic characteristics of mutation and recombination which confers them the ability to adapt to new hosts and ecological niches [5].

Respiratory system is the primary target organ of SARS-CoV-2 [6]. However, the virus also affects other organ systems including gastrointestinal system, neurological system, cardiac and vascular systems [7–11]. Many infected patients do not

develop any symptoms. 19–50% patients have been reported to have an asymptomatic infection [12]. Asymptomatic patients act as covert transmitters and constitute a potential contagious source of SARS-CoV-2 as they unknowingly transmit the virus to others [13–17]. However, many patients who are asymptomatic at the time of initial diagnosis become symptomatic later and are referred to as pre-symptomatic cases [16].

Detection of viral nucleic acid in the respiratory secretions by reverse transcriptase polymerase chain reaction (RT-PCR) is the mainstay of diagnosis [13, 15]. RT-PCR has a reported sensitivity of 60–71 percent with a very high specificity [17]. However, the performance of RT-PCR is limited by various factors including specimen collection, type of specimen, transportation of specimen and the processing time which results in many false negative results [18, 19].

Imaging plays a key role in the diagnosis of various manifestations of COVID-19 and detection of its associated complications. An effective utilization of imaging would require a comprehensive understanding and appropriate interpretation of the typical and atypical imaging features of the disease. In this chapter we first elaborate chest manifestations of COVID-19 and subsequently we discuss the role of various chest imaging modalities in their management.
