Journal of Clinical Pediatrics and Neonatal Care

Neonatal Chest Radiography – Comparison of Exposure Protocols in Canada and Norway

*Johansen Safora
Department Of Pediatrics, Oslo Metropolitan University, Oslo, Norway

*Corresponding Author:
Johansen Safora
Department Of Pediatrics, Oslo Metropolitan University, Oslo, Norway
Email:Safora.johansen@oslomet.no

Published on: 2019-06-20

Abstract

Introduction: Neonates are highly sensitive and vulnerable to ionizing radiation, and as a result, at higher to develop cancer. It is crucial for the radiographer to adhere to the ALARA principle, while preserving image quality. This study aims to collect protocols from different hospitals in Norway and Canada and compare these to the guidelines by the European Commission.
Methods: Neonatal chest protocols from hospitals performing chest x-rays on neonates were collected. Information about exposure parameters, mobile equipment utilized, inherent filtration, added filtration, and the use of a grid or cassette tray were collected. A total of 31 hospitals in Canada and Norway participated in this study.
Results: The majority of hospitals in Canada and all of Norway use DR rather than CR. Most of the protocols for both countries are weight-based. Exposure factors differ between the two countries. Canada generally uses a lower kV than Norway, and Norway uses a lower mAs. Another difference between countries is that Canada typically obtains AP and lateral radiographs of the chest, while Norway performs a single AP projection.
Conclusion: Canada and Norway differ largely in kV and mAs usage as well as the routine projections performed. Canada was found to use protocols that result in higher radiation doses to neonates in comparison to protocols used in Norway. Protocols collected from both countries were compared to the European guidelines and results indicate that there is a need to re-model the Canadian protocols for neonatal chest imaging.

Keywords

Neonatal chest x-ray; pediatric; radiographic technique; exposure parameters; protocol

Copyright: © 2019 Safora

Introduction

chest x-rays are the most frequently requested imaging in neonatal intensive care units (NICUs), using mobile x-ray equipment. It is the most important diagnostic test to assist in diagnosis and treatment of respiratory difficulties in neonates [1-2]. Although respiratory distress syndrome (RDS), caused from a lack of surfactant in underdeveloped lungs [3] is the most common indication of chest radiography in the NICU [4], chest radiography is also used to determine the position of tubes and catheters used as well as general thoracic bone formation and anatomy.

The risk of developing respiratory distress syndrome is inversely proportional to gestational period. In addition, this syndrome is life-threatening and is a large contributor in death among neonates. Chest imaging is essential and is performed frequently within a short period of time [1, 4]. A standard chest x-ray includes an anteroposterior (AP) supine projection of the chest. This is sufficient for diagnosis of respiratory problems, however, it is necessary to include 2/3 of the abdomen in order to clarify that other factors, such as abdominal gas, are not causing the respiratory symptoms and also to check the position of umbilical venous and arterial catheters [5]

Children, especially neonates, are highly sensitive and vulnerable to ionizing radiation due to their small body size, high mitotic cell activity and their life expectancy. Furthermore, radiation affects cell functions and may induce cancerous cells [6]. The risk of developing cancer due to radiation exposure is therefore higher for neonates [7-8]. It is therefore crucial for the radiographer to adhere to the ALARA principle while preserving image quality [9]

Exposure parameters have a significant impact on both dose and image quality in neonatal chest radiographs. The European Commission (EC) has released European guidelines on quality criteria for diagnostic radiographic images in pediatrics [10]. The current study aims at collecting protocols used in pediatric departments in Canada and Norway and comparing them to the EC’s guidelines.

 

 

Methods

Data Collection

Managers or team leads from diagnostic imaging departments in hospitals across Canada and Norway were  .contacted via telephone. Written and oral information on the study was provided and their participation was requested.

A written request and consent to collect protocol data was provided for each hospital. The information was collected via questionnaire, which included information about current neonatal chest protocols, exposure parameters, type of mobile equipment, inherent and added filtration type and thickness, and the use of a grid or tray. Upon agreement to participate in the study, managers or team leads were given the option to participate via email, or telephone. Collected information was compiled and compared with international guidelines.

 

Target Population and Sample Size

The target population of this study is imaging de-partments representing all geographic regions in Canada and Norway that perform mobile chest radiographs. Hospi-tals were excluded if they did not have an x-ray department, a mobile x-ray machine, or refused participation.

In Canada, 33 hospitals were contacted initially as potential participants. In total, 15 data collection forms were returned, eight representing central Canada (Ontario and Quebec), four representing the Atlantic provinces (Nova Scotia, New Brunswick, Prince Edward Island, and Newfoundland & Labrador), two representing Western Canada (British Columbia), and one representing the Prairies (Alberta, Saskatchewan and Manitoba). The Northern Territories are not represented in this study due to lack of pediatric hospitals in these regions

 

Ethics

Ethics approval in Norway was not required for this study; however ethics approval was required and obtainedin Canada. No patient information was collected. Participa tion was voluntary, and participating hospitals were been identified. 

Results

CanadaAcross Canada, most neonatal mobile chest x-rays include an AP and a lateral image. Occasionally just an AP is obtained, and other times an AP and a dorsal decubitus is obtained. One hospital stated an AP chest and abdomen are performed initially, and all subsequent images are AP only. Detector sizes varied, with the four main sizes being, 18x24 cm, 24x30 cm, 35x43 cm and 25x30 cm. The source-image distance (SID) varies greatly across Canada due to varied types of incubators and space available. The most common SID is 100 cm, followed by 110-120 cm. The most common inherent filtration amongst the data collected is 2.0 mm Al. Only one hospital in Canada used added filtration, and reported 1.2 mm Al additional filtration on their GE AMX4+ mobile. The most commonly used peak tube voltage (kVp) range is between 52-66 kV while the tube current-time product (mAs) was 1.0-2.5 mAs.

ian results show that there is some variation across the country (Table 1).In terms of equipment, the most commonly used is Care stream and General Electric (GE). The majority of the detectoCanadrs used in Canada are digital and no hospitals used a grid. Most Canadian hospitals use the cassette tray to hold the detector underneath the incubator. It is unclear if this is mandatory for every neonatal mobile chest x-ray, or if used only when requested. Canadian protocols are mostly weight-based. One hospital commented that they base their exposure parameter selection on available clinical information and two hospitals did not indicate what their protocol selection was based on

Table 1: Study results retrieved from hospitals in Canada.

Norway

Norwegian results are shown in Table 2. Protocols were collected from 16 hospitals. Decotron and Carestream are the most commonly used equipment Digital radiography (DR) is used in all hospitals included in this study. The majority of the hospitals prefer not to use the detector tray, laying the detector directly under the neonate. Protocols across Norway are weight based. Standard projections are AP for all hospitals included in this study. Some hospitals commented lateral projections are ordered only on suspicion of pneumothorax. Exposure parameters vary between hospitals, but almost all have a kV range of 60-80. The tube current-time product (mAs) lies between 0.1-0.71 mAs. In contrast, there is little variation in the SID, which most hospitals reporting 100 cm. The most common inherent filtration is 2.5 mm Al and five hospitals reported using additional filtration. Two use a combination of 0.1 mm Cu and 1.0 mm Al, one uses a combination 0.2 mm Cu and 0.3 mm Al and one uses 0.2 mm Cu and one uses 2.0 mm of Cu. None of the hospitals use a grid.

Table 2: Study results retrieved from hospitals in Norway.

Comparison

Similarities included the majority of Canada and all of Norway use DR. Most protocols are weight based in both countries, and 50% of the hospitals reported using the incubator tray. Neither country uses grids. The most common detector size in both Canada and Norway is 24x30 cm, followed by 25x30 cm. Differences between Canada and Norway are that AP and lateral radiographs of the chest are routine in Canada, while Norway does only an AP projection. There are also differences in exposure factors between the two countries. Canada uses lower kV (Figure 1), but Norway uses lower mAs (Figure 2). The median exposure parameters in Canada for mobile neonatal chest imaging are 60 kV at 1.5 mAs with an inherent filtration of 2.0 mm Al (Figure 3). In Norway, the median exposure parameters are 70 kV at 0.45 mAs with an inherent filtration of 2.5 mm Al (Figure 3)

Figure 1: Comparison of kVp usage in Canada vs. Norway with difference of CR and DR demonstrated.

Figure 2: Comparison of mAs usage in Canada vs Norway with difference between CR and DR demonstrated.

Figure 3:Comparison of median exposure parameters used in Canada vs Norway

Discussion

Tube Current-time Product (mAs) and Peak Tube Voltage (kVp)

Tube kilo voltage controls the quality of the radiation produced [7] and tube current-time product (mAs) utilized indicates the quantity of radiation produced. Higher mAs results in higher dose [7]. Canada utilizes higher mAs and lower kV than Norway resulting in a higher quantity of radiation and incidence of photoelectric effect (radiation absorption). It can be concluded that based on kV and mAs, Canada’s neonatal dose is higher than Norway. The European Guidelines on Quality Criteria for Diagnostic Radiographic Images in Pediatrics recommends a kV range of 60-65 kV be utilized on newborn AP projections [10]. While this recommended range is utilized in both countries, it represents the average kV range in Norway whereas it represents the higher end of the average kV range in Canada.lized indicates the quantity of radiation produced. Higher mAs results in higher dose [7]. Canada utilizes higher mAs and lower kV than Norway resulting in a higher quantity of radiation and incidence of photoelectric effect (radiation absorption). It can be concluded that based on kV and mAs, Canada’s neonatal dose is higher than Norway. The European Guidelines on Quality Criteria for Diagnostic Radiographic Images in Pediatrics recommends a kV range of 60-65 kV be utilized on newborn AP projections [10]. While this recommended range is utilized in both countries, it represents the average kV range in Norway whereas it represents the higher end of the average kV range in Canada.

ProjectionsThe Canadian standard is both AP and lateral projections (Figure 4). In Norway, the AP projection alone is standard unless a pneumothorax is suspected or the ordering physician requests it. In Canada, the lateral projection is valued to assist RDS diagnosis by demonstrating existing hyperinflation and cardiomegaly [11]. The lateral projection while beneficial doubles radiation dose [11]. Based on routine projections, Norway has a lower radiation dose than Canada, as only a single AP projection is obtained. It would be beneficial for future studies to examine why Canadian hospitals perform two projections in the NICU and limit the projections to a single AP. Guidelines set by the European Commission state that a lateral projection should not be done routinely and only after the initial AP view has been evaluated [10].

Figure 4: Routine projections performed in each country. One hospital in the study did not report the routine projections they perform for mobile neonatal chest radiographs.

Source to image distance

Increasing the source to image distance (SID) is an effective technique to decrease patient dose during radiological examinations [12]. Increasing SID reduces geometric blur and magnification, while minimizing distortion, thus reducing dose to the patient while maintaining image quality [13]. The European Guidelines on Quality Criteria for Diagnostic Radiographic Images in Pediatrics recommend an SID between80-100 cm for newborn imaging [10]. The most common SID used in Canada and Norway is 100 cm. Fifteen of the hospitals included in this study have an SID within the recommended European guidelines. The remaining 17 hospitals are above the recommended distance. Three hospitals stand out with a SID of 130 cm, 165 cm and 180 cm respectively. A study by Karami, et al. [12] investigates the efficacy of SID in patient dose and image quality in pediatric chest x-rays. They examined the difference of increasing the distance from 100 cm to 130 cm and the effect on dose and image quality. Patients included in this study were >1 year and all exposures were performed
with no grid. Voltage for 100 cm was 53 kV, and 54 kV for
130 cm. The mAs were constant at 3.8 mAs for both SIDs.
They concluded that an increase in SID to 130 cm resulted in a reduction in the entrance skin dose (ESD) by 32.2%
without any significant difference in image quality.
Other studies of pelvic, skull and lumbar spine radiography also report dose reduction as a result of increasing
SID from 100 cm to 130 cm [13-15]. Unfortunately, there are
no studies looking at how an increase of 165 cm or 180 cm
affects the dose and image quality in chest radiographs of
neonates.

CR versus DR

Digital radiography has also been shown to provide superior image quality and further reduces radiation dose to the patient in comparison to CR technology [16]. Earlier reports proved that DR systems require 30 % less exposure than those needed in CR [16]. Five of the hospitals included in this study use CR, while the remaining 27 hospitals use DR (Figure 5). As figure 5 shows, all 16 hospitals in Norway and 11 Canadian hospitals use DR.

Figure 5: Comparison of the use of CR versus DR systems reported by hospitals in Canada and Norway.

For consistency, CR exposures were compared with DR exposures in Canada. When the kV ranges of DR and CR systems were compared, a median value of 60 kVp was noted for both systems (Figure 3). However, when mAs were compared, CR systems had a higher median of 1.6 mAs in comparison to 1.2 mAs with DR systems (Figure 4). This difference represents a 33% increase in mAs exposure used in CR systems, which is in keeping with the reports that DR systems require 30% less exposure [16]. When averages are used for comparison, rather than the median, a more conservative increase in mAs exposure of 13.6% is noted. However, the comparison between the median values will be considered more relevant for this study because the DR systems have significantly more data to contribute to the averages calculated than the CR systems.

Both CR and DR introduce the potential for overexposure without necessarily compromising the image quality [17]. As a result of the overexposure, the CR and DR images can result in sharp and noise free diagnostic images. Underexposure causes image noise and decreased diagnostic value [17]. The principle of ALARA is important to take into consideration regarding CR and DR systems ensuring the lowest possible doses are used while preserving image quality [18].

Weight-Based Protocols

In Norway, all hospitals use weight-based protocolsas do all but two in Canada. H1 of the Canadian hospitals did not provide information on what their protocol was based on and H2 reported using available clinical information to determine protocol. Without further elaboration, it can only be assumed neonate size factors into clinical history. Studies demonstrate it is possible to choose exposure techniques based on clinical information as certain disease processes can cause the maximum entrance-surface dose to vary; therefore techniques selected would need to vary to achieve a diagnostic image [19]. Patient size is a major factor influencing dose and is limited by age or weight [10]. For neonates it is logical to use weight to determine the exposure parameters. It has been demonstrated that the equipment settings increase in direct proportion to the weight of the neonate [19]. Using the neonate’s weight to determine the tube voltage and tube current-time product will therefore determine the patients’ dose [2].

Detector Placement

In Norway, six hospitals place the cassette or detector in the incubator tray. The manufacturer Care stream can provide their customers incubators with trays custom made to fit their small detectors. In Canada, 12 hospitals use the tray, although four reported only using the tray occasionally based on the clinical situation. Detector placement has an effect on image quality. In a previous study, it was concluded that by using the under-tray technique one should consider increasing the exposure parameters due to the attenuation by the mattress and bed [1]. In addition, because of increased SID with tray use, radiation reaching the detector would be lower than if the detector was directly beneath the neonate with the same exposure settings. Exposure parameters should therefore be different when using the tray [1]. Another study discovered that equipment such as comfort pads and support trays attenuate the primary beam by 6-15%. By removing these items from the path of the x-ray beam, the detector entrance exposure was increased by 28-36% and increased the contrast-to-noise ratio by more than 21%. This demonstrated that patient dose can be reduced while maintaining image quality [20].

Filtration

Inherent filtration of the tube, tube housing, collimator and other components of the tube head function to filter out low energy x-ray photons that contribute to unnecessary patient dose [10]. Most X-ray tubes have a minimum inherent filtration of 2.5 mm Al and filtration greater than this can further reduce patient dose [10]. Low kV is frequently used for pediatric patients due to generators not being able to maintain short exposure times when using high kV ranges, thus resulting in higher patient doses. When an additional filtration is used in conjunction with inherent filtration, the use of higher kV ranges with the shortest exposure times available possible. Added filtration of 1 mm Al plus 0.1 mm or 0.2 mm Cu is oftentimes appropriate with pediatric imaging. Some generators on older X-ray equipment have pre-contact phases in which low energy photons may be emitted. These photons can be filtered out of the beam when added filtration is used [10]. In Canada, the most common inherent filtration of the mobiles was 2.0 mm Al with only one hospital (H9) reporting the use of additional filtration. In comparison, Norwegian hospitals more commonly reported inherent filtrations of 2.5 mm Al and a higher frequency of additional filtration use. The most commonly used additional filtration amount was a 0.1 mm Cu and 1.0 mm Al combination which is the recommended appropriate additional filtration amounts set the European Commission’s guidelines [10]. There did not appear to be trends or substantial differences in the inherent filtration amounts across mobile X-ray machines that were CR or DR. Although used more frequently in Norway, added filtration does not appear to be part of standard protocol and it may be beneficial for hospitals in both Norway and Canada to adopt use of additional filtration.

Limitations

Limitations of this study include inconsistency with some of the data returned (i.e. sections left blank, reported filtrations), hospitals that perform low and high volumes of x-rays on neonates were both included, large ranges of kV, mAs and SID were reported by some. Image quality was not assessed. 

 

Conclusion

This study examined protocols for mobile neonatal chest radiography between Norway and Canada and demonstrated the countries differ in kV and mAs usage as well as routine projections performed. Canada was found to use protocols that result in higher radiation doses to neonates in comparison to Norwegian protocols. When comparing the reported protocols in this study to radiographic image quality guidelines created by the European Commission, Norway adheres more closely to these guidelines supporting the ALARA principle. It is recommended that Canadian hospitals re-model their neonatal chest imaging protocols based on the European Guidelines on Quality Criteria for Diagnostic Radiographic Images in Pediatrics to reduce radiation dose to neonates. Canadian hospitals that use CR systems may also benefit by switching to a DR system to further reduce dose. In Norway, hospitals could further reduce dose by using additional filtration as standard protocol in mobile neonatal chest imaging. Furthermore, image quality was not assessed in this study and it may be beneficial to do this as a continuation of the study

Acknowledgment : We thank the involved Norwegian and Canadian radiography undergraduate students for their contribution to this study.

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