Mobile X-ray equipment

1. X-ray mobile and detector

Portable or mobile x-ray units are considered as mobile equipment as they are equipped with wheels that enable it to me moved to different locations with a Hospital or health care unit. These are powered by an electric motor supplied by a battery that assists the movement when the Radiographer drives the mobile unit with less effort.

Mobile x-ray systems are often used to perform chest radiography to patients who cannot be moved to the Radiology department. As such, a mobile x-ray equipment is designed with such unique characteristics to be able to be moved within limited spaces like in between hospital beds in small wards.

An x-ray mobile system consists of a motorized drive, compact wheelbase that includes the generator, an x-ray tube attached to a positioning column and an exposure control panel. As part of this system the image receptor plays a vital role in terms of the image quality and exposure safety (4). Also, different types of detectors can be used such digital radiography (DR) or computed radiography (CR) systems. DR systems have potential to perform examination at a lower dose, they present a high spatial resolution, image quality, lesion-signal response, and a wide dynamic display range when compared to CR systems. The workflow of DR systems is also better when both systems are compared(5).

Specifications of portable x-ray equipment are different among different vendors and the range of products available from the same vendor. Although, there are some common characteristics that could be highlighted as recommendation (Table 1).

1.1. Detector characteristics

Computed Radiography (CR) and Digital Radiography (DR) detectors are available as digital image receptors for radiography. CR systems use storage-phosphor image plates with a separate image readout process. DR technology converts x-rays into light and subsequently the TFT array will convert this light into electrical charges and finally to a digital image readily available (6).

CR technology uses an indirect conversion process using a two-stage technique. X-Rays are captured at a storage-phosphor screen (SPS) (ex: BaFBr:Eu2+) and then a photodetector captures the light emitted from the SPS and converts the captured luminescence into a corresponding digital image as a latent image result from the exposure. After the exposure, the image plate (IP) inside the cassete is scanned in a separate CR reader device. The readout is a process that follows exposure of the image plate and constitutes the second step of the CR imaging cycle.

Images of CR cassettes can be found in this page

DR technology use a two stage technique for conversion. They have a scintillator, such as Cesium Iodide (CsI) that converts X-Rays into visible light at a first stage. That light is then converted - at a second stage - into an electric charge by means of an amorphous silicon photodiode array, allowing the radiographic images to be readily available to the Radiographer in about 1 second.

One of the most interesting recent developments for DR detectors is the in-built wireless component. This allows the detector to be operated with no cable attached, allowing more flexibility in their use, especially in portable radiography.

Wireless DR detectors are battery-powered which allows multiple exposures and need a reliable wireless connectivity to the radiography environment and the portable x-ray mobile equipment.

Images of DR detectors can be found in this page

Different digital technologies are currently available for clinical practice in plain radiography. CR and DR technologies constitute a remarkable improvement based on detector technology developments. The specific properties and capabilities of a digital detector influences the choice of the radiographic technique, the radiation dose delivered to the patient and the diagnostic quality of radiographic.

Although CR and DR coexist at the present time the recommended technology to be used in a COVID-19 patient environment would be the wireless DR portable detector.

The use of a wireless DR detector will allow the Radiographer to have less contact time with potential infected patient, less exposure errors and less retakes, better image quality and rapid image sharing in the PACS system.

1.2. Sliding column X-ray tube arm

The sliding column is an important component of the mobile x-ray equipment. It allows the Radiographer to easily and effortlessly operate the system in different settings. With a small turning radius and cable-free design the sliding column integrates a flexible telescopic tube, with a broad extension range and wide degrees of rotation, allows to easily operate at the patient bedside.

Five major movements can hence be identified (4):

1.    Rotation around the center of the column;

2.    Cross arm movements – extension of the x-ray tube from the center of the column;

3.     Rotation around the axis of the cross-arm;

4.     Angulation across the long axis of the x-ray tube;

5.     Vertical movement up and down the main column.

The collimator box allows the Radiographer to move the x-ray tube head and collimator into the most appropriate positioning towards the patient and the detector. Fine positioning control on the tube head offers precise and accurate technique in terms of radiographic positioning.

2. Quality control

The quality control tests that a mobile x-ray unit should be submitted do not differ from those that currently performed in a routine setting. At acceptance and as routine the main quality control tests are (7):

• tube and generator performance;
• radiation output;
• half value layer;
• beam alignment;
• focal spot size;
• dose area product (DAP) metre accuracy;
• mechanical safety;
• equipment condition.

The electrical safety and tube leakage radiation are additional testes that must be performed at acceptance only (7)

3. Safe use and Infection Control

A multidisciplinary panel comprised mainly by radiologists and pulmonologists with experience managing COVID-19 patients evaluated the utility of imaging considering the variation of risk factors, community conditions and resource constraints (8). This group of experts considered that chest radiography (CXR) and computed tomography (CT) are important in this scenario except on patients with mild clinical features unless they are at risk for disease progression. CXR are performed daily in many intensive care units but there are studies showing evidence of the limited efficacy of this type of examination even outside the COVID-19 setting (9, 10, 11). The examination is useful for COVID-19 patients but if they present severe conditions and if they are well justified.

However, to perform any type of imaging there is a need for strict adherence to infection control protocols designed to minimize risk of transmission and protect healthcare personnel(8)

The protection of professionals varies according to each country but Centers of Disease Control (CDC) guidelines recommend radiology staff wear a mask, goggles or face shield, gloves, and an isolation gown at least. According to the Radiology Scientific Expert Panel(12), the main strategies to work safely in this scenario consider the decontamination of the equipment and the rooms used to imaging positive patients for COVID-19 (Table 2).

Outside the radiology department, when mobile equipment for chest x-rays is used with COVID-19 patients is also necessary to perform decontamination before its use in other patients to avoid the spread of disease. Appropriate manipulation involves a minimum contact with the different components of the equipment namely to the x-ray tube, detector and console for exposure parameters selection. The detector should be protected with the available materials at the intensive care unit. After the verification of the image, the equipment should be removed from the room to be clean with an appropriated agent to not damage the equipment (mobile x-ray and the detector itself).

4. Patient demographics

According to Huang et al (13), the majority of patients are male, having other primary diseases, including diabetes, hypertension and cardiovascular problems. In this study, it was observed that the average age was 49 years-old (IQR 41–58). The main symptoms presented by the patients were fever, cough, dyspnoea and myalgia or fatigue. Other symptoms less frequent included sputum production, headache, haemoptysis and diarrhea (13,14,15). The patients with dyspnoea had computed tomography (CT) presenting signs of pneumonia (Tables 3 and 4).

Table 3 – Patient demographics: age and gender (adapted from The Novel Coronavirus Pneumonia Emergency Response Epidemiology Team (16)

Table 4 – Patient demographics – previous illness (adapted from The Novel Coronavirus Pneumonia Emergency Response Epidemiology Team (16))

5. Exposure factor selection

Typically, a mobile CXR in this scenario is performed in antero-posterior (AP), in an intensive and less critical scenario (17). Mobile equipment due to its less performer generator (compared to a stationary generator), requires longer exposure times (18).  In a study performed with mobile X-ray equipment, the mean values used to expose an average adult chest were: 96 kVp, 1.25 mAs, 30 msec, no filtration and no grid (18). Other guidelines referred that kVp can varied between 70 or greater than 100 kVp, depending on patient thickness and on the use of scatter radiation grid. The beam intensity needs to be as short as possible to reduce the probability of having movement artefacts(19). Increasing the kVp can reduce the dose and the signal-to-noise ratio (SNR). Lowering x-ray tube potential from 80 to 60 kVp improved the SNR by 30–40 %, with a corresponding increase in phantom dose of 40–50 %. If patients are obese the use of grid can improve image quality of thicker regions (20). If it involves peadiatric patients with less than 14 cm the use of grids must be minimized(19).

The source-to-image distance (SID) needs also to be considered since it will have impact on dose and image quality. Images can be underpenetrated, mainly in lower lung fields and in obese patients, or they can be overpenetrated if the beam energy is too high or if the SID is to short(21). Using a longest SID magnification and unsharpness can be reduced. According to the recommendations of American College of Radiology (19)for mobile chest X-rays, SID must be at least 40 inches (1 meter) with the optimal distance as close as possible to 72 inches (1,8m).

If the context involves uncooperative or pediatric patients, the images can be performed in supine or semi-erect with one meter or greater SID. Increasing the SID from 1 to 1.3 m the entrance skin dose (ESD) can be reduced by 32.2% without lost of image quality (22).

Table 5 – Comparison of two phantoms image quality and dose based the use/no use of a grid and for different mAs  for CR mobile  system f (adapted from(20))

6. References

1. Simpson S, Kay FU, Abbara S, Bhalla S, Chung JH, Chung M, et al. Radiological Society of North America Expert Consensus Statement on Reporting Chest CT Findings Related to COVID-19. Endorsed by the Society of Thoracic Radiology, the American College of Radiology, and RSNA. Radiol Cardiothorac Imaging [Internet]. 2020 Apr 1;2(2):e200152. Available from: http://pubs.rsna.org/doi/10.1148/ryct.2020200152
2. Wong HYF, Lam HYS, Fong AH-T, Leung ST, Chin TW-Y, Lo CSY, et al. Frequency and Distribution of Chest Radiographic Findings in COVID-19 Positive Patients. Radiology [Internet]. 2019 Mar 27;201160. Available from: http://pubs.rsna.org/doi/10.1148/radiol.2020201160
3. Jacobi A, Chung M, Bernheim A, Eber C. Portable chest X-ray in coronavirus disease-19 (COVID-19): A pictorial review. Clin Imaging [Internet]. 2020 Aug;64:35–42. Available from: https://linkinghub.elsevier.com/retrieve/pii/S0899707120301017
4. Russo P. Handbook of X-ray Imaging [Internet]. Russo P, editor. CRC Press; 2017. Available from: https://www.taylorfrancis.com/books/9781498741545
5. Audin CR, Aran S, Muse V V., Abbott GF, Ackman JB, Sharma A, et al. Bedside Chest Radiographs in the Intensive care Setting: Wireless Direct Radiography Compared to Computed Radiography. Curr Probl Diagn Radiol [Internet]. 2018 Nov;47(6):397–403. Available from: https://linkinghub.elsevier.com/retrieve/pii/S0363018817301603
6. Lanca L, Silva A. Digital Imaging Systems for Plain Radiography [Internet]. New York, NY: Springer New York; 2013. Available from: http://link.springer.com/10.1007/978-1-4614-5067-2
7. Gray L, Dowling A, Gallagher A, Gorman D, O’Connor U, Devine M, et al. Acceptance testing and routine quality control in general radiography: mobile units and film/screen fixed systems. Radiat Prot Dosimetry [Internet]. 2008 Feb 18;129(1–3):276–8. Available from: https://academic.oup.com/rpd/article-lookup/doi/10.1093/rpd/ncn033
8. Rubin GD, Haramati LB, Kanne JP, Schluger NW, Yim J-J, Anderson DJ, et al.The Role of Chest Imaging in Patient Management during the COVID-19 Pandemic: A Multinational Consensus Statement from the Fleischner Society. Radiology [Internet]. 2020 Apr 7;201365. Available from: http://pubs.rsna.org/doi/10.1148/radiol.2020201365
9. Hendrikse KA, Gratama JWC, ten Hove W, Rommes JH, Schultz MJ, Spronk PE. Low Value of Routine Chest Radiographs in a Mixed Medical-Surgical ICU. Chest [Internet]. 2007 Sep;132(3):823–8. Available from: https://linkinghub.elsevier.com/retrieve/pii/S0012369215366460
10. Krivopal M, Shlobin OA, Schwartzstein RM. Utility of Daily Routine Portable Chest Radiographs in Mechanically Ventilated Patients in the Medical ICU. Chest [Internet]. 2003 May;123(5):1607–14. Available from: https://linkinghub.elsevier.com/retrieve/pii/S0012369215336965
11. Ganapathy A, Adhikari NK, Spiegelman J, Scales DC.Routine chest x-rays in intensive care units: a systematic review and meta-analysis. Crit Care [Internet]. 2012;16(2):R68. Available from: http://ccforum.biomedcentral.com/articles/10.1186/cc11321
12. Mossa-Basha M, Meltzer CC, Kim DC, Tuite MJ, Kolli KP, Tan BS. Radiology Department Preparedness for COVID-19: Radiology Scientific Expert Panel. Radiology [Internet].2020 Mar 16;200988. Available from: http://pubs.rsna.org/doi/10.1148/radiol.2020200988
13. Huang C, Wang Y, Li X, Ren L, Zhao J, Hu Y, et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet [Internet]. 2020 Feb;395(10223):497–506. Available from: https://linkinghub.elsevier.com/retrieve/pii/S0140673620301835
14. Kanne JP, Little BP, Chung JH, Elicker BM, Ketai LH.Essentials for Radiologists on COVID-19: An Update— Radiology Scientific Expert Panel. Radiology [Internet]. 2020 Feb 27;200527. Available from: http://pubs.rsna.org/doi/10.1148/radiol.2020200527
15. The Novel Coronavirus Pneumonia Emergency Response Epidemiology Team. The Epidemiological Characteristics of an Outbreak of 2019 Novel Coronavirus Diseases (COVID-19) — China, 2020. Web [Internet]. 2020;2(8):113–22. Available from: http://weekly.chinacdc.cn/en/article/id/e53946e2-c6c4-41e9-9a9b-fea8db1a8f51?utm_source=TrendMD&utm_medium=cpc&utm_campaign=China_CDC_Weekly_TrendMD_1
16. The Novel Coronavirus Pneumonia Emergency Response Epidemiology Team. The Epidemiological Characteristics of an Outbreak of 2019 Novel Coronavirus Diseases (COVID-19) — China, 2020. Vol. 2, China CDC Weekly. 2020.
17. Kelly A, Toomey R. Protocols and guidelines for mobile chest radiography in Irish public hospitals. Radiography [Internet]. 2015 Feb;21(1):3–6. Available from: https://linkinghub.elsevier.com/retrieve/pii/S1078817414000558
18. Precht H, Hansen DL, Ring-Pedersen BM, Møller Hansen LF, Waaler D, Tingberg A, et al.Comparison of image quality in chest, hip and pelvis examinations between mobile equipment in nursing homes and static indirect radiography equipment in the hospital. Radiography [Internet]. 2020 May;26(2):e31–7. Available from: https://linkinghub.elsevier.com/retrieve/pii/S1078817419301531
19. American College of Radiology. ACR-SPR-STR Practice parameter for the performance of portable (mobile unit) chest radiography. Am Coll Radiol [Internet]. 2017;1076(Revised 2008):1–8. Available from: https://www.acr.org/-/media/ACR/Files/Practice-Parameters/Port-Chest-Rad.pdf
20. Rill LN, Brateman L, Arreola M. Evaluating radiographic parameters for mobile chest computed radiography: Phantoms, image quality and effective dose. Med Phys [Internet]. 2003 Sep 18;30(10):2727–35. Available from: http://doi.wiley.com/10.1118/1.1611291
21. Jensen L, Meyer C. Reducing errors in portable chest radiography. Appl Radiol. 2015;44(4):7–15.
22. Karami V, Zabihzadeh M, Danyaei A, Shams N. Efficacy of Increasing Focus to Film Distance (FFD) for Patient’s Dose and Image Quality in Pediatric Chest Radiography. Int J Peadiatrics. 2016;4(3):3421–9.