What is the role of imaging in combatting covid-19 pulmonary infections?
Covid-19 has officially been declared a global pandemic. The UK now potentially stands on the precipice of a major covid-19 outbreak that could threaten to overrun hospitals, schools, and communities. At the time of writing we are moving from “contain” to “delay” in our approach. Numbers of confirmed UK cases continue to rise, with Public Health England reporting 456 positive cases and 8 deaths on 10 March 2020  With reports of protective equipment such as facemasks for healthcare workers already in short supply, the concern is that we may soon face a surge in covid-19 infections that could overwhelm existing hospital resources.  Early diagnosis is absolutely critical to containment. Radiology services have found themselves at the centre of a debate on how to approach diagnosis of this novel coronavirus.
Provided that RT-polymerase chain reaction (RT-PCR) test kits (currently used to diagnose covid-19 from throat swabs) remain available in sufficient numbers, and laboratories processing the results are able to cope with the expected increased demand, CT scanning has only a limited role in diagnosing covid-19 . However, should RT-PCR results continue to have a prolonged delay (24-48 hours), or be unavailable, the implementation of CT imaging as a frontline diagnostic tool, as rolled-out in China, requires urgent discussion.
It is widely accepted among chest radiologists at the heart of national covid-19 planning that CT diagnosis for covid-19 pulmonary infection would not have a role in the context of a rapidly available PCR test result.  Advocates for a straight-to-CT approach would point to the surge in diagnoses of covid-19 on 12 Feb 2020 in Hubei following the introduction of new diagnostic criteria that included CT changes.  In a study of 1,014 patients with both CT chest and PCR, the sensitivity of CT was 97% relative to positive RT-PCR.  In patients with initial negative RT-PCR but positive CT scans, 81% were reclassified as “highly likely” or “probable” cases with covid-19 by analysis of clinical symptoms, typical CT manifestations and longitudinal CT follow-up. It is speculated that this approach may have facilitated timely treatment and isolation measures. However, given that changes on CT from covid-19 may only appear gradually, it would be prudent to avoid being overly reassured by a normal-appearing early CT in a clinical context suggestive of covid-19. The primary advantage of CT imaging is its speed of diagnosis. Yet even when CT is available, the current lack of specialist chest radiologists in the UK may provide a barrier to timely diagnosis of covid-19, particularly when findings are subtle (seen in early disease) and/or atypical. 
Only 3% of NHS imaging departments are able to report routinely-performed scans within normal working hours. [7,8] The UK also trails behind most European counterparts (including Greece and Estonia) in CT scanner availability with only 8.4 CT scanners per million population.  In the covid-19 crisis, radiology finds itself in a remarkable situation. To combat this imaging shortfall would require a truly heroic logistical effort by NHS Trusts. One solution would be to utilise mobile CT scanners on hospital sites and designate scanners as either “clean” or “dirty.” Dirty scanners would be commandeered for scanning suspected covid-19 patients. Clean scanners would perform non-covid-related urgent inpatient and outpatient work. Undoubtedly, such measures would have massive consequences for staffing and routine hospital workloads. Yet, as crisis point approaches, we need to start planning for this eventuality now whilst putting aside the deep-seated frustration held by UK radiologists who have consistently argued the need for greater radiology investment. 
From a chest radiologist perspective, we fear that without appropriate planning and infrastructure placement for large volume CT imaging of covid-19 cases, we ultimately risk: (i) potential contamination of CT scanners: as there may be insufficient time in an already overworked system to provide thorough repeated deep cleaning of machines between CT examinations; and more importantly (ii) potential infection of suspected covid-19 patients who are negative for infection at the time of scanning. Yet even these concerns do not address the lack of specialist chest radiologists actually required to examine the scans and provide both accurate diagnosis and risk stratification for covid-19 infected patients.
Investment in rapid turnaround covid-19 RT-PCR testing is essential to limit spread of the disease. While CT scanning may pick up abnormalities in the lungs with high sensitivity, the specificity for covid-19 diagnosis on CT alone is limited. Furthermore, this simply reflects the “tip of an iceberg phenomenon” whereby a chronic dearth of investment into UK radiology has led to a critical shortage of both CT scanning equipment and radiologists, specifically specialist chest imagers whose expertise would critically drive early diagnosis and high-quality care. Yet there are scenarios where CT imaging may be required earlier in the covid-19 diagnostic pathway. In spite of limitations, radiology departments around the country remain ready as ever to answer the call and must actively prepare to deal with the covid-19 crisis, a disease for which imaging appears to play an emerging role. A provision for more CT access—possibly with mobile CT scanners—may be a step in the right direction.
Samanjit S Hare, Consultant Chest Radiologist, Royal Free London NHS Foundation Trust. Twitter @lungdiagnosis
Joseph Jacob, Consultant Chest Radiologist, University College London.
Annette Johnstone, Consultant Chest Radiologist, Leeds Teaching Hospital NHS Trust.
Graham Robinson, Consultant Chest Radiologist, Royal United Bath Hospitals Bath NHS Foundation Trust.
All four authors are committee members of the British Society of Thoracic Imaging. Twitter: @BSTIImaging
Competing interests: Joseph Jacob reports fees from Boehringer Ingelheim and Roche unrelated to the current submission and is supported by a Clinical Research Career Development Fellowship 209553/Z/17/Z from the Wellcome Trust.
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