First published online September 17, 2007
British Journal of Radiology (2007) 80, 902-910
© 2007 British Institute of Radiology
doi: 10.1259/bjr/88577258
Imaging the neonate in the incubator: an investigation of the technical, radiological and nursing issues
S J Mutch, BSc(HONS), MSc, MIPEM
1 and
S D P Wentworth, BSc(HONS), PhD, MIPEM
2
1 Department of Medical Physics & Clinical Engineering, The Churchill Hospital, Old Road, Headington, Oxford OX3 7L J, 2 Department of Medical Physics and Clinical Engineering, Rehabilitation Engineering Unit, Rookwood Hospital, Llandaff, Cardiff CF5 2YN, UK
Correspondence: Steven J Mutch, Department of Medical Physics & Clinical Engineering, The Churchill Hospital, Old Road, Headington, Oxford OX3 7LJ, UK. E-mail: steven.mutch{at}orh.nhs.uk
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Abstract
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Modern neonatal incubators incorporate an X-ray tray device into the mattress support structure to facilitate patient examination with minimal disturbance and distress. However, the usual method of examination is to place the image plate directly underneath the baby. Users often cite radiological reasons for not using X-ray trays but modern quantitative evidence is lacking. This work looks at the technical and clinical aspects of imaging neonates in incubators and the impact that these may have in determining the imaging protocol. A number of hospitals were surveyed to determine their current method of examination and the reasons for their preference. Experimental measurements of the radiological impact of using (or not using) the X-ray tray were performed for a range of neonatal incubators. The average dose to the image plate was 5.9 µGy (range 5.4–6.4 µGy) for the "plate on mattress" method and 3.0 µGy (2.0–3.8 µGy) when using the tray — a 49% reduction owing to the mattress support materials. However, when using a computed radiography (CR) imaging system, the image quality differences were marginal. Survey results indicated that nurses preferred to use the tray but that radiographers were reluctant. We conclude that incubator manufacturers could do much to improve the radiological performance of their equipment and we offer recommendations. We also conclude that, with appropriate nurse and radiographer training and the advent of CR imaging systems, use of X-ray tray facilities may optimize imaging of the neonate in the incubator.
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Introduction
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Incubators are used for the care and treatment of premature babies. They are designed to provide a stable, protective environment whilst facilitating patient monitoring (e.g. temperature, oxygen supply) and treatment [1]. As part of the care regime, X-ray images are often required for optimal treatment and any one patient may have several examinations [2, 3]. The normal method of examination traditionally involves placing an image receptor (i.e. film cassette or computed radiography (CR) imaging plate) directly beneath the infant. Neonatal patients are by definition fragile; any undue disturbance and movement should be minimized. In particular, neonatal skin is sensitive and may easily dry out. This potential problem is greatly reduced by maintaining a stable environment inside the incubator [4, 5]. In addition, infection control is much better managed when cot sides remain closed [6]. Thus, to avoid undue patient disruption, many modern state-of-the-art neonatal incubators provide an X-ray imaging facility. This may take the form of a slot under the mattress support into which one slides the imaging plate or, as in the latest incubator models, a dedicated X-ray imaging plate tray incorporated into the mattress support structure [7].
User feedback in recent UK Department of Health incubator evaluations indicated that X-ray trays are not utilized by the majority of incubator users [8–11]. Responses also indicated that users preferred an X-ray tray device to an X-ray slot or recess [8]. Users often cite radiological reasons (e.g. increased radiation dose, reduced image quality) for deciding not to use X-ray tray mechanisms, and continue to place the image plate directly under the patient. Nevertheless, as outlined above, there are distinct benefits to not disturbing neonates and their environment unnecessarily. Each point of view is valid but somewhat conflicting. A method of imaging the neonate that not only satisfies the radiological requirements but also the nursing needs would be most beneficial to the patient. Modern quantitative evidence is so far lacking, and preliminary work on the use of incubator X-ray trays showed that a more in-depth study of the technical and user issues was required [12]. This work looks closely at two aspects of imaging the neonate in the incubator: technical aspects (incubator construction, imaging system, etc) and clinical care (patient risk and procedural aspects, which affect the choice of imaging method employed). Furthermore, to have a fully informed choice, both nursing and radiographical considerations must be considered. In bringing together both views, this work attempts to highlight the common ground and, where contradictory needs arise, it hopes to indicate how changes and improvements in current technology (e.g. incubators, imaging systems) could solve these problems.
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Methods and materials
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Incubator design and construction have a significant effect on imaging of the neonate. A range of commonly used incubator models was assessed with regard to radiological imaging performance and these are listed in Table 1
; each was assessed for its suitability and usability. When using the X-ray tray for imaging, the radiation beam must not only pass through the patient but must also penetrate the incubator canopy, the patient mattress and the mattress support. The impact of these components on beam attenuation and quality varies by incubator type. The degree of radiation attenuation (reduction of beam intensity) exhibited by the canopy, mattress and its support was measured for each incubator. Experimental measurements of the radiological impact of using (and not using) the X-ray tray were performed. Patient dose and image quality data were recorded for a standard neonatal imaging exposure derived from European guidelines on quality criteria for paediatric imaging (EUR16261) [13]. The effectiveness of these exposure recommendations have been tested in a number of studies and many have suggested that significant patient dose saving can be made by following them [14–16].
Current working practices and preferences were investigated. A number of hospitals were surveyed as to their current method of examination. Radiology and nursing staff were asked, by questionnaire, to detail their reasoning, opinions, experiences and desires so that we could build a fuller and better understanding of all aspects of imaging the neonate in the incubator.
As the technical study was conducted at three different hospital sites, three different X-ray units were used for exposure. The units used were a Siemens Mobilett mobile X-ray unit (Siemens Medical Solutions, Erlangen, Germany), a Philips Optimus over-table X-ray unit and a Philips Practix mobile X-ray unit (Philips Medical Systems, Eindhoven, Holland). The radiation output and half value layer (HVL) for each unit was measured. The average HVL at 81 kV was 3.0±0.1 mmAl, indicating that the beam quality was similar for all units. The average radiation output was measured as: 11.2±1.5 µGy mAs–1 for 60 kV, 100 cm tube focus to chamber distance, and additional filtration of 1 mm aluminium and 0.11 mm copper. All dose measurements were normalized to this output to allow a direct comparison of the doses measured at the phantom, mattress and slot/tray position for each incubator. The close similarity of the X-ray unit outputs indicates that any variation in image plate exposure, for any incubator, will be caused overwhelmingly by variations in incubator attenuation properties.
Assessment of incubator radiological imaging performance
Each incubator was inspected closely with regard to its radiographic imaging capability. The design and operation of the X-ray tray or slot was noted (Table 1
) and the thicknesses of the canopy and mattress support were recorded.
The definition of a standard exposure was based on the recommendations in the EUR16261 criteria [13]. The exposure conditions used were 60 kV, 1 mAs, 90 cm focus to phantom surface distance (FSD), and additional beam filtration of 1 mmAl and 0.11 mmCu. A 5 cm thick polymethylmethacrylate (PMMA) block (30 cmx30 cm) was used as a phantom to simulate the neonatal patient. Dose measurements were performed at the phantom surface, the mattress surface, and at the image plate position or tray surface. Distances to these positions were also recorded. The measurements were made using a Keithley 96035B 15 cc ionization chamber with a Keithley 35050A dosemeter (Keithley Instruments Inc, Cleveland, OH). Three readings were taken for each measurement and the average calculated. The chamber was placed directly onto the phantom for surface dose measurements and thus dose readings include the backscattered radiation. For the mattress dose measurements, the chamber was placed directly between the phantom and mattress. For tray/slot measurements, the chamber was placed centrally in the tray or slot area. The measurement set-up is shown in Figure 1. The uncertainty in the dose measurements was estimated to be ±6%. The canopy radiation attenuation (percentage reduction) was determined from dose measurements taken with the canopy in, and then out, of the beam. The reduction in dose by moving from the mattress surface position to the tray position was determined from the ratio of the dose measurements at these points; this is the attenuation of the beam due to all factors, e.g. inverse square law reduction, absorption and scatter by materials of the mattress and its support. The percentage total reduction in radiation beam intensity at the tray position due to all factors was calculated for each incubator from dose measurements at the tray position and at the tray position distance free in air.
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Figure 1. General set-up for the incubator radiological imaging performance measurements. A fixed X-ray tube focus to phantom surface distance (FSD) of 90 cm was set for all incubators. Image quality was assessed for both imaging methods, namely with the image plate directly under the phantom (neonate) or when the plate is in the tray/slot mechanism.
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The average image quality for each examination method was assessed for each incubator. Leeds test object TO.12 (Leeds X-Ray Test Objects, Leeds, UK) was used to quantify the degree of threshold contrast in each image. The object was placed directly onto the imaging plate for each image taken at the mattress surface and at the X-ray tray position with the standard exposure. Three images were recorded for each image quality measurement, and the average score calculated. Each image was scored by one of the authors and the threshold detection index (HT(A)) determined for each detail size. These data were then demonstrated graphically by plotting this value against the square root of the detail area. This method of graphical representation is preferred, as HT(A) correlates with the level of image quality and more easily reveals reduced imaging performance [17].
All radiographs were acquired using a CR imaging system. Two of the three centres in the study used a Fuji FCR 5000 CR system (Fuji Photo Film Company Ltd, Tokyo, Japan) and the other used a Kodak DirectView 950 CR system (Eastman Kodak Company, Rochester, NY). Each of the centres confirmed that they were running their CR systems at roughly the equivalent of 400 speed film. This indicates a degree of cross-centre uniformity in CR system response. However, for comparing mattress with tray imaging methods in any one incubator, the relative response between CR systems is not critical. All images from the Fuji systems were processed using the Sensitivity protocol; those from the Kodak system were processed with the Pattern protocol. These protocols apply a linear greyscale look-up table to the image pixel value range, and thus allow the image processing and display to be as similar as is possible between differing CR systems. Displayed images were then windowed to optimize scoring of the TO.12 details. No further post-processing was applied and all images were scored on hardcopy format (dry laser printed film).
User response survey
To understand better the issues surrounding imaging of the neonate in the incubator, users' opinions were surveyed with a questionnaire. Two distinct staff groups (nursing staff and radiology staff, specifically radiographers) were identified as having a key influence on clinical practice. Each was asked:
- Which types of incubator are used in your hospital?
- How often were neonates X-rayed in an incubator?
- How would the X-ray be conducted (e.g. antero-posterior (AP) chest)?
- What advantages would using the tray have for you and your department?
If the user had used the tray, he or she was asked:
- On which incubator model?
- What was your experience of using the tray on these incubators?
- Did you obtain an image easily first time?
- What disadvantages, problems or difficulties have you encountered using the tray?
If the user had a tray, but did not use it routinely, he or she was asked:
- Have you ever considered using the tray?
- What factors influenced your decision not to use the tray?
- Do you have access to any sources of advice?
- What changes would you like to see that would encourage you to use the tray?
The questionnaire also asked users to grade the likelihood and severity of adverse incidents that might occur when imaging the neonate in an incubator with or without using a tray, i.e. a risk assessment. The events identified have either nursing or radiographical aspects and are shown in Table 2. These incidences were determined as the primary concern of each group following initial discussions with them during this and previous work [12]. The question of magnification of the image when using the tray was not considered important by radiographers. The actual numerical magnification for this set-up is little more than 9% and is not significant clinically; indeed, the small X-ray beam foci used in this type of imaging, usually 0.3 mm, means image resolution levels would remain unaffected. Questionnaires were sent to neonatal departments and radiography departments that had first been identified as willing to cooperate. As such, no response rate is meaningful, as users in all departments returned at least one questionnaire.
Eight neonatal nurses and eight radiographers from six centres completed the questionnaire. At least one nurse from each of the six centres responded, and at least one radiographer from four of the six centres. Their comments were collated and their perception of the risks described in Table 2 were analysed. They were asked to rate the probability of an event occurring on a scale of 1 to 5, where 1 indicated a low probability of occurrence and 5 indicated a high probability of occurrence. They were also asked to rate the severity of the events in Table 2 from a rating of 1 (indicating "insignificant") to 5 (indicating "catastrophic"). The risk rating was then calculated by multiplying the probability by the severity:
This method of risk analysis is derived from a standard risk assessment system used throughout the NHS and is described by The Institute of Risk Management in their joint publication [18].
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Results
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Assessment of incubator radiological imaging performance
The measured thicknesses of the canopy and mattress support are shown in Table 3, together with the focus to tray/slot distances for each incubator when a 90 cm FSD is set. The average canopy thickness was 5.6 mm (range 4.5–8.0 mm), whereas the average mattress support thickness was 9.5 cm (range 9.0–10.0 cm). The results show that, with respect to these parameters, incubator design is relatively similar across the range included in this study. Other than the patient, the two other factors that will influence the number of X-rays reaching the image plate when it is placed in the tray/slot are the canopy and the mattress support mechanism. The percentage reduction in the radiation beam owing to these components is shown in Table 4. The average reduction caused by the canopy was 17% (range 11–24%) and for the mattress support 49% (range 40–65%). Significant variation comes from the Hill-Rom Air Shields C200 incubator, which has a markedly reduced dose to the tray/slot position. This unit has a greater canopy thickness of 8.0 mm compared with 4.5–6.0 mm for the others, and a markedly higher attenuation (65%) from the mattress support than the rest (40–49%). The results for the other incubators are much more closely grouped together. However, the importance of how construction materials can influence dosimetry is shown here. The Caleo incubator has the largest mattress support thickness of 10 cm but it has the lowest attenuation factor of 40%. Therefore, not only are the construction material attenuation properties important but also the design of the structure. Of particular interest is the size of air gap between the physical structure of the mattress support (which will be responsible for most of the scattered radiation) and the imaging plate. A small increase in this air gap can notably reduce the scattered radiation reaching the plate.
These design differences are reflected further in the dose measurements at the phantom surface, the mattress surface and the tray/slot position (Table 4). For the standard set-up, the average dose at the phantom surface (an indication of patient entrance skin dose) was 15.0 µGy (range 14.2–16.1 µGy). This value is well within the maximum of 80 µGy recommended by the European Commission criteria. The mean dose to the image plate when placed at the mattress surface was 5.9 µGy (range 5.4–6.4 µGy) and 3.0 µGy (range 2.0–3.8 µGy) when in the tray/slot position. There is an average 49% reduction between the dose to the image plate at the mattress surface (behind the phantom) and that at the tray/slot position. For the distances shown, the reduction due to the inverse square law would account for only one-fifth of this. The remaining additional decrease must result from the attenuation by the materials between these two positions.
The average image quality at each position for each incubator was determined. As would be expected from the dose results, image quality results for each incubator are very similar. The average threshold detection index (TDI) curves for images obtained by the direct exposure method for each incubator are shown in Figure 2. In all cases, the results from three scored films were averaged to produce each curve. The curves are all tightly grouped in the graph; this indicates that the threshold contrast rendition is similar in all of the images. In Figure 3, the TDI curves for the tray/slot imaging method are shown. Here, there is a little more variation than in Figure 2, which is almost entirely due to the C200 incubator results. As the dose measurements show, the image plate dose in this incubator is approximately one-third lower than the average for the rest, and this is shown by a reduced threshold contrast rendition. Noise in these images is higher, although contrast values are reduced across all detail sizes. All of the other curves are tightly grouped showing very similar image quality.
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Figure 2. Threshold detection index diagram showing the image quality results from exposing the plate by the direct method(plate under phantom/neonate) for each incubator.
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Figure 3. Threshold detection index diagram showing the image quality results when the plate is exposed in the incubator tray/slot device for each incubator.
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Figure 4 shows the difference between the image quality at the mattress surface and that at the tray/slot. The average for each method for all incubators was plotted as a single curve. The figure shows that image quality, specifically contrast rendition, differences are marginal, even though there is a near 50% difference in dose to the image plate between each method. The CR imaging systems have normalized the greyscale rendition of the pixel values of the images, resulting in hardcopy films that have the same background optical density despite the very different image plate doses. Background density will affect contrast rendition but, with this variable removed, only image noise is left as an influencing factor. Although image noise is increased in tray/slot images, Figure 4 shows it has not significantly reduced the threshold contrast rendition.
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Figure 4. Threshold detection index diagram showing the average image quality from all incubators for each method of plate exposure.
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User response survey
Figures 5 and 6 show the risk rating for each of the nursing aspects and the radiological aspects, as perceived by the nurses and radiographers. They illustrate the nurses' and radiographers' perception of the risk if the tray is used and not used. For each bar, the risk ratings were summed; for example, the first bar represents the nurses' perceived risk rating for the nursing aspects if the tray was used. It can be seen from Figure 5 that the nurses perceived the nursing aspects risk as higher, ranging from 24 to 70 (maximum risk rating for four events = 100) if the tray is not used. Those who expressed an opinion also perceived a higher radiological risk if the tray was used. The radiographers consistently perceived a higher risk rating of the radiological aspects if the tray was used. Three of the radiographers rated the nursing aspects risk and in each case this was higher if the tray was not used.
These cumulative perceived risk ratings reflect well the comments made by both groups. Comments received on the questionnaire show that the nurses were most concerned about infection control and disturbing the neonate. When asked how the X-ray would be conducted, all of the nurses and radiographers described the "standard" method of X-raying a neonate in an incubator, i.e. to open the incubator and lift or slide the neonate onto the X-ray plate, which is covered in either paper towels, a pillow case or a sheet. Radiographers would then position and operate the X-ray machine but the nurses are often involved in the preparation and positioning of the neonate. In the users' experience, neonates in intensive care are sometimes X-rayed up to three times a day. One nurse noted that it can take a baby "an hour to recover from handling". The nurses were more aware of the incubator model used when a tray was employed; most had experience of the Draeger Caleo. Half of the radiographers were unsure what type of incubator was in use but positive comments were recorded about the Ohmeda Medical Giraffe incubator. In particular, the transparent section in the mattress base enabled easier checking of the position of the X-ray plate.
Nurses often assist the radiographers and observe them taking the X-ray. Six nurses had experience of using an incubator tray or slot: three considered it easy to use but three considered it "fiddly" and had problems positioning the plate and getting good quality images. One nurse who considered it very easy was using an Ohmeda Giraffe incubator; another who thought it easy to use was using a Drager Caleo incubator. The three nurses who considered it difficult to accurately place the plate were using Drager Caleo incubators. Four radiographers with experience of using a tray commented that it was difficult to line up the neonate and plate and they needed to avoid "debris" in the image. However, only one of these identified the incubator as a Giraffe incubator; they commented that it was "essential to position the film in the middle of the tray and make sure the baby is centrally placed". Two of the six nurses who had experience of observing the radiographers using the tray had seen acceptable images obtained first time, as had one radiographer. They accredited this to the clear Perspex window in the base of the mattress support. When asked about problems using the tray, the nurses again commented on the difficulty they had seen the radiographers experience in positioning the plate and the poor images thus obtained. The radiographers also commented on the positioning and image clarity, as well as the risk of increased dose due to the increased distance between the object and the plate.
All of the nurses and three of the radiographers would consider using a tray. The factors influencing the nurses' decision were based largely on information and policy from the radiology department, as well as practical issues already discussed. The radiographers were mostly influenced by practical issues of dose, image quality and image accuracy; one did comment that they were not aware that the tray option was available and neither were their nursing colleagues aware of how to access it. Very little advice was available to either group. The nurses considered looking to the manufacturer and the instruction book for help. When asked about what changes would encourage use of the X-ray tray, nursing staff looked for better communication between radiology and nursing staff and consultants. Practically, they also wanted more guidelines on the placement of the infant for the X-ray using the tray. The radiographers wanted clearer guidelines for placement of the X-ray plate and reducing the distance between the baby and the tray, as well as better communication.
In general, the nurses preferred to use the tray to minimize handling of the baby, maintain the stability of the incubator environment and reduce the risk of infection. The radiographers were reluctant to use a tray because of the difficulty in obtaining an image of the anatomy required, as it was difficult to line up the plate and the baby. They were also aware of a need for a higher dose to obtain an image (an assumption made with reference to film-screen systems) and that the images obtained when using the tray could contain artefacts due to objects in the incubator. The radiographers have a duty to obtain the best quality image at the lowest dose used, in order to apply the "As Low As Reasonably Achievable" (ALARA) principle. A repeat radiograph, e.g. as a result of poor positioning, would double the patient dose and be unacceptable.
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Discussion
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Perhaps a little surprisingly, the dosimetry results for each incubator were very similar in the final analysis. From initial inspection, it was clear that incubator design and construction, and the materials used, were very similar across all manufacturers. Table 4 shows that the majority of the radiation beam attenuation is caused by the mattress support materials and that this is consistent across all incubator models in this study, with the Hill-Rom Air Shields C200 incubator being a slight outlier. Canopy attenuation values were, on average, around one-third of those for the mattress support (17% canopy, 49% mattress and support); nevertheless, they are not trivial. Clearly, there is an opportunity to decrease the attenuation from these components and, by doing so, reduce the dose required for imaging The radiation risks to neonates from imaging is considered to be fairly low when compared with the substantial benefits that should accompany the examination [19, 20]. However any reduction in patient dose is beneficial. Reducing the attenuation of intervening materials will also reduce the amount of scattered radiation generated when the X-ray beam passes through these materials, with benefits to patients, staff, comforters and carers. Using the tray/slot mechanism will help to reduce scattered radiation reaching the image plate by introducing a gap between the patient and the image receptor, thus improving image quality.
Image quality results were very similar for the direct exposure method. In this case, as the exposure to each incubator is the same, the only variation of dose to the plate is due to the canopy and, as has been shown, all the canopies were similar. Incubator design would appear to have only a small influence on patient dose and image quality for the direct exposure imaging method.
The similarity of the image quality results from both methods of imaging (direct and tray/slot) is a direct result of using a CR system for image processing. For the set exposure conditions, moving from a direct exposure imaging method (plate under neonate) to a method using the tray/slot will produce a near 50% drop in dose to the plate. Although this would be very significant for film-screen imaging methods (image quality would be severely compromised), for CR imaging the much greater exposure latitude allows image quality to remain diagnostic. If a film-screen system is used for imaging, then the fall in image quality will be unacceptable. A greater exposure would then be required to improve image quality to acceptable levels, resulting in a higher dose to the neonate. However, as shown, the reduction in image quality is minimal if a CR system is used. There is an average 10% reduction in TDI over all detail sizes — a change that would be practically unnoticeable in clinical images. The actual clinical significance has not been explored here but a small increase in image noise would not have a significant effect for high contrast details, e.g. chest lines. Given the strong similarity between the radiographical data obtained from the range of incubator models tested technically, the important factor remaining is the ease of use of the tray.
Positioning problems
Positioning problems have often been cited as a drawback to regular incubator tray/slot usage. The tray/slot inspection notes (Table 1) have shown that image plate positional aids are minimal or non-existent, making it hard to accurately position an image plate directly under a patient. This is important, as accurate plate position and tight collimation of the image are necessary to minimize the patient dose, minimize the scattered radiation produced and reduce the possibility of a repeat X-ray due to poor positioning, thereby minimizing the radiation risk [21, 22]. Thus, plate position must be relatively precise and easily checked in relation to the patient and the image field area. External positional indicators to aid alignment of the X-ray tube, field area, neonate and image plate would be of great benefit but none was seen in this study. The trays encountered are non-movable (along the patient axis) so, if the neonate is not over the centre of the tray, he or she may have to be moved, thus defeating the object of using the tray.
Artefact generation
Artefact generation in images is another commonly cited factor in not using incubator X-ray trays [8]. There are a number of sources of artefact generation. Many canopies still have feeding holes in them, sometimes positioned centrally where they are likely to be in the image area. Bedding and other materials may also present problems. For example the SpencoTM Kare-4-Kids incubator mattress (Spenco Healthcare International Limited, Halifax, UK) consists of a corrugated fibre pad that presents differing mattress thickness over the image area. Unfortunately, this type of mattress may leave an artefact on radiological images such as that shown in Figure 7. Even without such items, artefacts may still be generated. A simple kink in the covering sheet of a normal mattress could, at this beam quality, show on the image. It is noted, however, that artefacts of this type can be eliminated by using appropriate mattress materials and user vigilance.
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Figure 7. Image artefact generated by a non-uniform mattress. Such materials must be carefully considered when using incubator X-ray trays for imaging.
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All of the users imaged neonates by placing the plate beneath the patient. This "standard" way of producing an image eliminates errors from misalignment of the plate and concerns about using the lowest dose possible, but it can be traumatic for the neonate. The environment is disturbed and the baby is handled, both of which introduce risks of infection and trauma to a fragile neonate [23]. The use of the tray or slot removes both of these risks but introduces the risk of misalignment between the plate and the anatomy of the neonate to be imaged. It is important that these risks are carefully considered for each case. If the baby has to be moved in order to ensure correct positioning over the X-ray plate when it is placed in the tray, or if the baby needs to be held in position for the X-ray, as is sometimes the case, then any advantage from using the tray is decreased because the incubator must be opened.
It would seem that the overall risk to a neonate from the imaging process may be minimized by using a CR imaging system combined with the X-ray tray/slot mechanism. Using the tray should help reduce cross-infection risk, desaturation and bradycardia caused by handling neonates [23], and is certainly something desired by those charged with the care of these patients. Radiation dose levels and image quality remain as for direct imaging methods used with film-screen systems. There is some possibility of artefact and positioning error that may force a re-imaging of the patient and this is a prominent fear for radiology staff. However, these factors can be minimized by good training of staff in imaging techniques [20, 24] and by further improvements to incubator (and accessories) design and construction.
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Conclusions
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Using an examination protocol similar to that recommended by EUR16261 and employing a CR image processing system allows the possibility of using the X-ray tray or slot facility in modern incubators for neonate imaging, with minimal increased patient radiation dose/risk and minimal patient disturbance. The following recommendations to incubator design may encourage X-ray tray usage:
- Thinner canopies, perhaps down to 2 mm thick, particularly in the central area.
- Offset canopy roof tubing ports or no roof ports at all (side ports only).
- Thinner mattress supports to reduce dose and magnification.
- Use of X-ray transparent materials for mattress supports, e.g. carbon fibre.
- Suitable external positioning aids, e.g. markings on canopy aligned to the tray.
- Uniform mattress materials and construction.
It is important that incubator manufacturers continue to address these issues and develop incubators that are better able to minimize patient dose and disturbance when imaging is undertaken. Suitable incubator materials and construction (scientifically demonstrated) are essential to achieve this. Equally important, in conjunction with these recommendations, is the training of nurses and radiographers in the use of X-ray trays and slots. Targeted training and clear protocols are required if optimal imaging techniques are to be developed and maintained.
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Acknowledgments
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The authors wish to thank the technical, nursing and radiology staff at The John Radcliffe Hospital, Oxford; The Gloucestershire Royal Hospital; The Royal United Hospital, Bath; University Hospital of Wales, Cardiff; King's College Hospital, London; Derriford Hospital, Plymouth; and The Royal Berkshire Hospital, Reading, for all their assistance during the technical evaluation of the incubators and completion of the survey questionnaires.
SDP Wentworth, formerly of CEDAR, Department of Health Device Evaluation Centre, Cardiff, would like to thank the Rehabilitation Engineering Unit, Rookwood Hospital, for allowing her to continue this work. Particular thanks to Dr C Gibson and Mr W Davies.
Received for publication May 25, 2006.
Revision received March 22, 2007.
Accepted for publication March 27, 2007.
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Abstract
Introduction
