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Original Report |
1 Department of Neuroradiology, National Neuroscience Institute, Level B1,
Irrawaddy Block, 11 Jalan Tan Tock Seng, 308433 Singapore.
2 Department of Diagnostic Radiology, Tan Tock Seng Hospital, Singapore.
Received May 16, 2003;
accepted after revision August 1, 2003.
Address correspondence to T. C. C. Lim
(tchoyoson_lim{at}ttsh.com.sg).
Abstract
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CONCLUSION. Mobile CT may be used to provide dedicated radiology services to seriously ill patients requiring strict isolation during an infectious disease outbreak.
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Imaging studies, including chest radiography and CT, are important in the diagnosis and follow-up of SARS. However, our challenge was to provide radiology services in adherence with the isolation requirements for the containment of this new pneumonia. Dedicated SARS portable radiography and sonography scanners were readily made available at the point of care, but implementing CT service required more planning and mobilization to maintain strict isolation. Although mobile CT scanners have been successfully used during intracranial and craniocervical surgery [5] and in imaging critically ill patients in intensive care units [6, 7], we have seen no reports of their use in an infectious disease epidemic. We report the use of mobile CT in a viral outbreak that required strict isolation of the patients.
We describe the hospital isolation procedure and room preparation for the mobile CT scanner, with an emphasis on radiation protection and isolation. We also review the CT request patterns during the initial 5 weeks after deployment (Table 1), including reason for request, type of CT study, and technical adequacy of images.
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Placement and access routes to the scanner were arranged to bring patients to it from the ICU and other SARS isolation wards with minimal contact with other patients and health care workers during transit. This special area also had separate entrances that were accessible only to the involved health personnel and duty staff of the radiology department. Three radiographers were assigned exclusively to the mobile CT unit, each working a schedule with an 8-hr shift daily for 1 week, followed by 2 weeks on standby. Strict temperature monitoring and isolation from the rest of the radiology department were observed. Barrier nursing was carried out during all examinations, and radiographers in direct contact during patient positioning wore N95 masks, gowns, gloves, and goggles (Fig. 2). Disposable plastic covers were used on control surfaces of the scanner console during each study. The scanner gantry and bed were thoroughly disinfected with sodium dichloroisocyanurate (5,000 ppm) after each patient left. All studies performed by our scanner were routed to the PACS (picture archiving and communication system) (Pathspeed 8.12, General Electric Medical Systems, Milwaukee, WI) on the hospital local area network and were reviewed on remote PACS workstations.
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All patients tolerated their examinations well; no studies failed because of patient movement. The average procedure took 13 min; times ranged from 7 min for an unenhanced CT brain study to 26 min for a contrast-enhanced abdominopelvic study. The unprotected scatter radiation dose at the CT console, calculated 7 m from the isocenter of the scanner, was 0.05 µSv per scan. In the 5-week period reviewed (including a 10-day incubation period), no health care worker involved in the mobile CT service was cross infected from a SARS patients. No suspected or documented cases were reported of patients developing SARS after being examined on the mobile CT scanner.
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SARS is a new form of atypical and potentially fatal pneumonia that is caused by a novel coronavirus [3]. It has emerged as a worldwide public health hazard, with modern air travel facilitating its rapid spread to many parts of Asia, North America, and Europe [1–3]. In the diagnosis and follow-up of SARS, chest radiography and CT are important [10–13], so demand for radiology support for these patients is increasing. At the same time, a characteristic feature of this outbreak was that health care workers were being infected when in close contact with SARS patients before they were diagnosed as having the disease [14]. Hence, isolation, containment, and a high index of suspicion are crucial to protect health care workers, and a flexible response was needed to provide uninterrupted radiology services. It was decided to deploy the SARS CT scanner and radiographers in isolation from the rest of the radiology department to prevent spread to the rest of the staff. That way, if any of the three radiographers on the SARS roster (who worked alone) became infected, a new team could be deployed.
The mobile CT service performed an average of 3.2 and a maximum of six studies during each 8-hr shift. The productivity was affected by the low demand in a crisis situation and the necessity to take extra precautions such as disinfecting the scanner after each patient. Although this level of service was comfortable for the radiographers, some form of triage might have been needed if the demand had exceeded the capability of the scanner.
The pattern of requests for the mobile SARS CT scanner was similar to that in a general radiology department, with a wide variety of indications, ranging from stroke to pelvic abscess. The reason for this pattern was that the suspected SARS ward included patients from entire general surgical and neurology wards who had to be placed in isolation. Hence, even though the circumstances were caused by a pneumonia outbreak, the dedicated scanner was called on to perform a wide range of studies.
The major limitation of the battery-powered mobile CT scanner is its lower heat-loading and X-ray tube power compared with that of state-of-the-art MDCT scanners. However, motion blurring caused by longer acquisition times did not pose enough of a problem to render any study uninterpretable.
A more difficult challenge was interpreting studies of suspected pulmonary embolism obtained with the mobile CT scanner. When postmortem reports appeared describing deep venous thrombosis and pulmonary embolism in SARS patients, and deep vein thrombosis of the leg veins began to be detected on Doppler sonography (Wan G, unpublished data), it became necessary to perform these studies. However, of 18 studies for pulmonary embolism, we found no cases of thromboembolism in the main pulmonary arteries or its branches at the lobar and segmental levels. Available scanner protocols made it impossible for us to discern the smaller subsegmental arteries and segmental lung parenchyma perfusion, especially in patients with breathing difficulties. Furthermore, we do not know the sensitivity and specificity of these studies or whether prophylactic anticoagulation therapy was effective in preventing pulmonary embolism (Tai DYH, personal communication). More research needs to be conducted to ascertain if the observed phenomenon of coagulopathy is a feature of this novel disease.
The radiation dose delivered to the patient by the portable CT scanner is similar to that delivered by fixed CT scanners [6]. The low calculated dose of 0.05 µSv per scan received by the radiographer in our setup is well within the limit per year recommended by the International Commission on Radiological Protection [15], and the dose may be even lower because portable lead shields were always used.
In conclusion, our experience suggests that it is feasible to rapidly deploy a mobile CT system in an isolation ward during an infectious disease outbreak. This arrangement enables radiology services to continue uninterrupted and minimizes the risk of infection to health care workers. We hope the lessons learned will be useful in preparing radiology departments to face similar crises in the future.
Acknowledgments
We thank the frontline radiographers Muhd Avin Look, Ho Thye Sin, Hong
Tshun Vun, and all our colleagues who have been affected by this outbreak.
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