key: cord-327543-kibjwfad
authors: Ong, S. J.; Renfrew, I.; Gopinathan, A.; Tan, A. P.; Sia, S. Y.; Low, C. K.; Hoon, H. X.; Ang, B.W.L.; Quek, S. T.
title: SIR HELMET (Safety In Radiology HEalthcare Localised Metrological EnviromenT): a low-cost negative-pressure isolation barrier for shielding MRI frontline workers from COVID-19 exposure
date: 2020-07-01
journal: Clin Radiol
DOI: 10.1016/j.crad.2020.06.015
sha: 
doc_id: 327543
cord_uid: kibjwfad

• Low cost reusable acrylic and silicone rubber barrier shield design. • Localised negative pressure environment simulating isolation rooms. • Does not affect MRI image quality even on the most sensitive sequences. • Additional personal protective equipment for frontline healthcare professionals.

COVID-19 is a highly infective infectious disease caused by a novel coronavirus first identified in Wuhan, China, in December 2019. It has now evolved into a pandemic affecting at least 216 countries. The precise incidence of stroke in COVID-19 patients is unknown but is thought to affect up to 5.7% of severely affected individuals [1] . It is also being recognised as the first clinical presentation of COVID-19, especially in young patients [2, 3] . Although computed tomography (CT) is the first-line technique to assess patients presenting with acute stroke symptoms, many centres prefer to evaluate further with magnetic resonance imaging (MRI) [4] . Hence, more patients with COVID-19 are attending for MRI examinations.

In well-resourced hospitals, infective COVID-19 patients are nursed within negativepressure rooms. Even within these negative-pressure rooms, research has shown extensive environmental contamination when occupied by infected patients [5] .

Although patients can be provided with filtering face piece (FFP) masks to reduce their infectivity, studies have demonstrated high rates (up to 87%) of poor fit of the face masks among untrained non-healthcare professionals [6].

Most MRI rooms are not built with negative-pressure ventilation systems. In addition, there are limitations to the use of personal protective equipment (PPE) by both patients and staff within the magnetic field of the MRI room. Therefore, each time a patient with COVID-19 undergoes MRI, there is a real risk of MRI room contamination and exposure of both staff and subsequent patients to the virus.

To address the above problem, a low-cost physical barrier was designed and developed for use within the MRI machine that could produce a localised negativepressure containment area around the patient's head. The barrier has been named "SIR HELMET" from Safety In Radiology HEalthcare Localised Metrological EnviromenT. The "helmet" can potentially reduce the spread of pathogens via the patient's breath. In addition to assessing its functionality, the present study also evaluates the impact of the shield on MRI image quality.

The SIR HELMET is a dome shaped, re-useable barrier that fits into MRI machines with a bore size of ≥65 mm. It is made of 3 mm clear acrylic with chloroform used as the primary adhesive. The access port on the front of the "helmet" is covered with a 1.5 mm silicone rubber membrane with slits for access and clamped to the main structure with another layer of 3 mm acrylic, held together by plastic screws (Fig. 1) .

The calculated raw volume of the helmet is 139 l with an effective net gas volume of approximately 130 l or less depending on patient position within the barrier shield.

Negative pressure within the "helmet" is generated by connecting a standard medical gas wall vacuum using extension tubing via a port in the barrier shield. Continuous For this study, two healthy volunteers were scanned in a 3 T MAGNETOM SKYRA MRI unit (Siemens, Munich, Germany) and a 1.5 T Optima MRI unit (GE Healthcare, Chicago, IL, USA) using standard head and neck sequences (eight sets of examinations in total; four of the head and four of the cervical spine). Each participant was scanned using each machine by the same senior MRI radiographer with and without the "helmet".

Images were loaded onto a standalone staging picture archiving and retrieval system, Centricity Universal Viewer (GE Healthcare). The eight anonymised sets of images were reviewed on diagnostic-quality monitors by two consultant musculoskeletal radiologists, two consultant neuroradiologists, and two consultant clinical diagnostic radiologists, blinded to the acquisition history of the images.

Overall, eight examination sets were read independently by six different readers to provide 48 total sets for scoring. Images were scored on a scale of 1 to 4 regarding diagnostic quality, structural delineation, and severity of artefacts for each set of images as per Ryu et al. [7] with area for free-text comment.

Negative pressure airflow rates of >20 l/min was obtained with the underwater seal filter system and at 40 l/min without. This allowed at least 9.2 full gas exchanges per hour for the underwater seal filtered system and at least 18.5 for the other one.

There was consensus regarding scoring of all eight sets of images among all the readers with full points for diagnostic quality, delineation of structural margins, and complete lack of MRI-related artefacts (Fig. 2) . Post-scoring, the readers were informed that half of the image sets were performed with the "helmet", but they were not able to identify these sets from those scanned without the helmet.

Although transmission of COVID-19 is predominantly via direct contact or aerosol inhalation, it may also occur via indirect delayed contact, for example, through the use of the same physical seat [8] . Droplet transmission enhanced by air-conditioning airflow creating super spreaders is also documented [9] . Hence, isolation of the most infective patients is essential [10] . Nevertheless, when an infected patient is brought outside their isolation ward to other clinical areas, such as radiology departments, this "isolation" is interrupted, creating potential opportunities for virus dissemination.

As the COVID-19 pandemic continues, there is high likelihood that more coronavirus-infected patients would present with stroke or stroke-like symptoms, thereby increasing the need to perform MRI examinations in these patients. As a limited resource, it may not possible to reserve an MRI machine exclusively to image COVID-19 patients. Hence, it is essential to explore alternative ways to control the spread of infection from transit of an infected patient through an MRI room. The effort of thoroughly cleaning the shield between patients is much less than that of cleaning the bore of the MRI machine.

Using the ubiquitous medical gas wall vacuum apparatus, the "helmet" can provide at least 9.2 full gas exchange per hour with the afore-described filtration system or 18.5 full gas exchanges per hour without filtration. This gas exchange rate is similar to or above that of the requirements of a negative-pressure isolation facility, which is usually 10 to 15 exchanges per hour. Hence, use of this helmet would effectively provide frontline healthcare staff and patients with an added layer of protection against airborne pathogens. This can also avoid the cost and time required in installing negative-pressure ventilation systems within an MRI room.

Use of the helmet without suction is not recommended due to concerns regarding carbon dioxide retention during long examinations. In an unvented system, there are also concerns of a high concentration of aerosolised pathogen that the MRI technician would be exposed to, while removing the "helmet" from the patient. The decision to vent the suction via an underwater seal sterilisation scrub or directly to the wall vacuum port would depend on the local hospital infection-control policy and the underlying infrastructure of the vacuum system.

To improve patient comfort and to reduce claustrophobia, the helmet was intentionally fabricated using flame-polished translucent acrylic, using the biggest arc possible to maximise the sense of space. Given the multitude of different scanner and coil configurations, the length of the "helmet" was increased intentionally to fit across all the MRI machines within our institution. If required, it is possible to customise this shield for individual scanners with shorter lengths to increase the air exchange rates. Acrylic is cheap and can be fabricated quickly, and in addition, is suitable for cleaning with most of the usual disinfectants.

The image quality of MRI examinations was not affected by scanning with the helmet on. The adoption of this or similar barriers would provide frontline healthcare staff and patients with an additional level of protection without prohibitive financial costs to the institution. Highlights: 1 • Low cost reusable acrylic and silicone rubber barrier shield design 2 • Localised negative pressure environment simulating isolation rooms 3 • Does not affect MRI image quality even on the most sensitive sequences 4 • Additional personal protective equipment for frontline healthcare professionals

COVID-19-related stroke

Large-vessel stroke as a presenting feature of Covid-19 in the Young

COVID-19 presenting as stroke

Imaging of acute stroke prior to treatment: current

Clinical feasibility of 1-min ultrafast brain MRI compared with routine brain MRI using synthetic MRI: a single center pilot study

Investigation of three clusters of COVID-19 in Singapore: implications for surveillance and response measures

COVID-19 outbreak associated with air conditioning in restaurant

Rapid expansion of temporary, reliable airborne-infection isolation rooms with negative air machines for critical COVID-19 patients