First published online September 17, 2007
British Journal of Radiology (2007) 80, 807-815
© 2007 British Institute of Radiology
doi: 10.1259/bjr/77948690
Dose and image quality optimization in neonatal radiography
E D Dougeni, MSc
1
H B Delis, PhD
1
A A Karatza, MD, PhD
2
C P Kalogeropoulou, MD, PhD
3
S G Skiadopoulos, PhD
1
S P Mantagos, MD, PhD
2 and
G S Panayiotakis, PhD
1
Departments of 1 Medical Physics, 2 Paediatrics and 3 Radiology, School of Medicine, University of Patras, 265 00 Patras, Greece
Correspondence: George S Panayiotakis, Department of Medical Physics, School of Medicine, University of Patras, 265 00 Patras, Greece. E-mail: panayiot{at}upatras.gr
 |
Abstract
|
|---|
In a special care baby unit, neonates, mainly premature, encounter serious to life-threatening diseases, the timely diagnosis and treatment of which may require a large number of radiographs. Increased neonatal radiosensitivity and longer life expectancy increase the risk of radiation-induced cancer, which emphasizes the importance of minimizing dose while maintaining clinically satisfactory image quality. An optimization study on radiation dose and image quality in neonatal radiography is presented. Neonates were categorized into four groups depending on birthweight. For a total of 378 chest and chest–abdomen radiographs, exposure parameters were recorded. Entrance surface dose (ESD) was estimated and dose–area product (DAP) was measured. Image quality evaluation was performed by two observers and was based on the visibility of certain anatomical features and catheters placed during treatment using a five-grade scale. ESD values increased with neonatal weight and demonstrated wide variation (16.4–76.9 µGy, mean 38.2 µGy). A wide variation was also observed in DAP values (1.2–15.0 mGycm2, mean 7.2 mGycm2). Image quality evaluation revealed the feasibility of achieving a diagnostically satisfactory image (score >70%) using both low and high tube voltage techniques, with the latter resulting in reduced ESDs. The majority of estimated ESDs are in accordance with the reference level of 50 µGy recommended by the National Radiological Protection Board for neonatal radiography. The results suggest that the use of high tube voltage techniques could result in further reductions in neonatal dose, without image quality degradation, underlying the requirement for establishing standard examination protocols for neonatal radiography with respect to neonatal weight.
|
Introduction
|
|---|
In the special care baby unit (SCBU), neonates, and especially those born prematurely, with a gestational age (GA) as low as 24 weeks and a birthweight (BW) as low as 600 g, often suffer from a variety of serious to life-threatening complications, which usually result from diseases in the respiratory and cardiovascular system. Increasing the survival rate of neonates depends upon both timely diagnosis and prompt therapy. Neonatal radiography is an indispensable tool that contributes significantly not only to the initial clinical diagnosis and evaluation of common neonatal diseases (e.g. pneumothorax, meconium aspiration syndrome, hyaline membrane disease, respiratory distress syndrome, bowel obstruction, necrotizing enterocolitis) but also to the assessment and confirmation of the position of percutaneous intravenous long lines, umbilical catheters and endotracheal tubes that are inserted during hospitalization in the SCBU. Consequently, depending on the clinical symptoms that neonates present, they often undergo a considerable number of chest radiographs and "babygrams" (simultaneous chest and abdominal radiography) before their discharge from the SCBU.
Premature neonates are far more susceptible than adults to the chromosome-damaging effects of radiation because of the highly mitotic state of their cells; in general, the sensitivity of a tissue to radiation is directly proportional to its rate of proliferation [1]. In addition, apart from the breast, other critical organs such as the thyroid, the gonads and a large fraction of blood forming red bone marrow are also frequently directly irradiated. Furthermore, because of the longer life expectancy of neonates compared with any other patient group, there is a greater period for the potential expression of delayed detrimental radiation-related effects, such as cancer and particularly leukaemia [2, 3], thus the risk of a radiation-induced malignancy is increased [4, 5]. However, the benefit to neonates from the use of ionizing radiation is indisputable, as long as the examinations are absolutely justified and in accordance with the As Low As Reasonably Achievable (ALARA) principle. In view of the increased radiation risk, examinations of neonates merit special consideration and, thus, radiation protection is of paramount importance [6, 7].
Factors affecting radiation dose during radiographic examinations include applied tube voltage (kVp), tube current (mA), exposure time (s), filtration, focal spot to skin distance (FFD), film–screen speed, collimation and patient size. Neonatal entrance surface dose (ESD) is the principal dosimetric index employed for radiographic audit, for comparison of different studies and for setting diagnostic reference levels (DRLs) for common radiographic examinations. A number of dosimetric studies have been published describing the theoretical estimation of ESD during radiographic examinations [8–17], as well as the direct measurement of ESD utilizing thermoluminescent dosemeters (TLDs) [17–21], suggested methods of dose reduction [8, 9, 15, 18] and the risk of cancer following exposures during the neonatal period [9, 10, 14, 16]. Dosimetric studies on phantoms that simulate neonates have also been reported [16, 18, 22, 23]. Furthermore, surveys of external collimation and shielding of radiosensitive organs, such as the gonads and the thyroid, which are necessary in neonates, have been reported [9, 24, 25]. A few other studies have expressed dose in terms of dose–area product (DAP) [15, 17, 26] and effective dose [12, 16, 20, 26, 27].
Diagnostic reference levels (DRLs) for ESD have been proposed by the Commission of the European Communities (CEC) [5] and more recently by the National Radiological Protection Board (NRPB) [3], which recommend 80 µGy and 50 µGy, respectively, as the reference values for an anteroposterior (AP) neonatal chest radiograph. Recommendations for optimized radiological techniques and equipment have been proposed by the CEC in order to promote the optimization principle; they suggest that tube voltage should be in the range of 60–65 kVp, film–screen combination speed should be 200–400 and FFD should be between 100 cm and 150 cm [5].
Although the DRLs are rarely exceeded, European studies [21, 28–30] have revealed a wide interhospital variation in ESD values (11–386 µGy), originating from differences in radiographic techniques, equipment and staff training and a lack of radiographic protocols. A large percentage of participating hospitals (71%) applied tube voltages lower than 60 kVp, resulting in increased doses, whereas one-quarter of the exposures were made using low-speed film–screen combinations (<200) [21]. This has been regarded as a cause for concern, bearing in mind the requirement for adapting an optimized radiographic protocol for neonatal examinations with respect to birthweight.
The present study was carried out at the SCBU of the University Hospital of Patras. It examines the prospect of dose reduction through optimization of radiographic parameters in relation to image quality. Its dosimetric objectives were to determine the ESDs for different birthweight groups and to compare them with the current DRLs and to quantify exposure in terms of DAP for each technique. Radiographs were evaluated for various exposure parameters based on the CEC criteria, to balance the requirement for satisfactory image quality with minimum radiation dose, depending on neonatal weight.
|
Methods and materials
|
|---|
Neonates: radiographic sample
The sample consisted of 378 neonatal radiographic examinations (35% chest and 65% babygrams) of 123 neonates (64 male and 59 female) admitted and treated in the SCBU of the University Hospital of Patras. Lateral or other projections were excluded from the study because CEC and NRPB recommendations refer to AP projections of the chest and the abdomen, the most frequent examinations. The majority of the neonates (83%) were preterm, with a GA lower than 37 weeks. Specifically, GAs were in the range of 27–41 weeks, with a mean of 34.5 weeks. The birthweights of the neonates included in the study varied between 635 g and 4440 g, with a mean value of 2245 g. Because patient dose can be significantly dependent on patient size, it was considered necessary to study the variation in ESD and the quality of the image obtained for neonates of approximately the same weight. Neonates were categorized into the following four groups, depending on their birthweight (w) [22]: (1) extremely low birthweight (w
1000 g) (47 radiographs); (2) very low birthweight (1000 g<w1500 g) (67 radiographs); (3) low birthweight (1500 g<w2500 g) (138 radiographs); (4) normal birthweight (w>2500 g) (126 radiographs). The majority of the radiographs (36.5%) used in this study belonged in the third group.
The frequency of radiograph examinations is highly dependent upon the clinical situation of the neonate, thus the number of radiographs per neonate may be over 25 (Figure 1
). Although the majority of the neonates underwent one or two radiographs, the mean number was three radiographs per neonate. For each neonate the following data were collected: date of birth, date of entrance, duration of stay, gestational age, sex, height, weight, date and time of radiographic examination, number of radiographs taken and diagnosis. This is similar to the data used by Chapple et al [13], with some additions. Radiographic data for each exposure, such as projection, FFD, tube voltage, mAs settings, field size and examination inside or outside the closed incubator, were also recorded.
During radiographic set-up, the cassette was placed directly under the neonate, wrapped up in a clean thin linen cover. Radiographic examinations were performed by several radiographers, setting manually different exposure parameters (kVp and mAs) even for neonates of the same weight group. Radiographers were asked to use and record the techniques and the exposure parameters that would normally have been chosen, so that the results would be representative of routine practice.
For all of the techniques recorded, the tube voltage varied between 44 kVp and 66 kVp (mean value 53.1 kVp), with a range of 0.5–2.6 mAs (mean value 1.4 mAs).
All radiographic examinations were performed using the same capacitor discharge mobile unit (Mobilet II; Siemens, Erlangen, Germany) with total inherent filtration of 3.8 mm Al, focal spot size of 0.8 mm and tube target angle of 15°. This was exclusively used for neonatal radiography. Radiographs were acquired using Kodak Lanex regular screens and Kodak film and the films were processed with a daylight processor (X-OMAT 5000 RA Processor ML 700+; Kodak, Eastman Kodak Company, Rochester, NY). To ensure the correct performance of the equipment and the reliability and reproducibility of exposure parameters, a complete quality control check was initially and periodically performed, based on published protocols [31]. Additionally, daily quality control of the film processor was performed to ensure a high and stable performance.
Dose estimation
Because DRLs for neonatal radiography, as proposed by the CEC and NRPB, are expressed in terms of ESD, this quantity was estimated for each radiograph. The collected data were used to estimate retrospectively the ESD for each neonatal radiograph according to the following equation [8, 17]:
|
In this equation, U is the output of the mobile unit (µGy mAs–1) measured at 100 cm with an X-ray multimeter (Victoreen non-invasive X-ray test device, 4000M+; Victoreen LLC, Cleveland, OH) for various tube voltage values in the range of 40–102 kVp. (I•t) is the product of tube current (mA) and exposure time (s) required for the radiograph. BSF is the backscatter factor, which is applied to take into account the scattered radiation from the neonate. For examinations in children, BSFs vary from 1.1 to 1.36, depending on exposure factors, the patient's thickness and field size [13, 15]. Because of the small size of the neonates, a constant value of 1.1 was applied for the whole sample. ISL is the inverse square law factor, allowing for the correction of the output from the measured distance of 100 cm to a standard focus-to-skin distance of approximately 85 cm. TF is the transmission factor of 5 mm perspex, which was applied as the majority of neonates were cared for in closed incubators. The attenuation of the beam was estimated to be in the order of 10%, whereas the scattered radiation by the perspex was considered negligible. (µen/
)tisair is the mass energy absorption coefficient ratio of tissue over air, averaged over the X-ray energy spectrum used, and was evaluated for muscle as defined by the International Commission on Radiation Units and Measurements [32].
Direct dose measurements utilizing TLDs during the examination provide the best indication of actual clinical practice; however, this was not practically achievable in this study, mainly because of the limitations set by the infection control protocol of the SCBU. Also, unnecessary disturbance to the newborn can raise heartbeat and blood pressure and lower oxygenation. In addition, the doses involved are near the minimum detection level of common TLDs-100 (50 µGy) [18, 19].
Dose–area product measurements
Despite the fact that ESD is indicative of the techniques applied, it does not take into account the effect of field size variations. A small shift in the field margins will produce large differences in effective dose and organ dose, a problem that is magnified in neonates compared with adults because of their small size. Thus, beam limitation is a major criterion of the image quality according to the CEC guidelines. An appropriate dose index that can be correlated with field size is the DAP. DAP is increasingly used as it provides a convenient and accurate method for dose measurements and it is independent of the set-up. In addition, it allows comparison with other studies and effective dose can be deduced as well as the somatic risks introduced. This flexibility emphasizes the possibility of using DAP as a selected dose index for the DRLs.
A DAP meter (PTW Diamentor M4; Freiburg, Germany), initially calibrated by the manufacturer and periodically cross calibrated in situ [using a Victoreen non-invasive X-ray test device (4000M+)] was used to measure the dose in the centre of the field, at a distance of 100 cm, by attaching it directly to the light beam diaphragm on the tube head of the mobile unit. Slow radiotherapy films (Kodak EDR2) positioned directly on the top of the device were used to measure the irradiated area. DAP values were obtained under conditions simulating all neonatal chest and chest–abdomen (babygrams) radiographs. However, the lower limit of detectability of the DAP meter was very close to the DAP values that occur in neonatal radiography. Thus, for better accuracy, DAP values were measured for all tube voltages (from 44 to 64.5 kVp) for a 10 x 10 field at 90 cm and for 10 mAs. Finally, a correction was employed for the typically used mAs settings and the corresponding field sizes. For each radiograph, the field sizes were measured on the acquired films to determine the DAP values, taking into account the different degrees of collimation as well as the different technique parameters applied. Additionally, DAP measurements were used to deduce ESD values, taking into account the backscatter factor from the neonate and the various field sizes (for an anteroposterior thickness of 5 cm), as a validation of the formula used.
Image quality evaluation
To quantitate image quality and the amount of diagnostic information received, a visual grading analysis of the radiographs was performed in accordance with the CEC guidelines, which define the acceptability of radiographs [5]. A radiologist and a paediatrician, experienced in reading radiographs, interpreted the images in a random order, independently and blinded to the technique used.
The image quality assessment criteria used (Table 1) were based on the CEC guidelines with the addition of four more criteria concerning the visibility of bowel loops and the tips of the various tubes and lines inserted in the body of a neonate during treatment in the SCBU. Malposition or displacement of venous and arterial long lines can result in severe complications for the neonate, including perforation, pleural and pericardial effusions and cardiac tamponade [33], whereas, because of their short airways, dislocation of the endotracheal tube is crucial as it may result in inadequate mechanical ventilation [34]. The additional criteria were considered necessary because a large number of radiographical examinations are performed to ensure the accurate placement of these devices.
Apart from the exposure parameters that are discussed in the present work, other CEC criteria, such as reproduction of the thorax without rotation and tilting, whether the radiograph is performed at peak inspiration and whether the field size is appropriate (from above the apices of the lungs to T12/L1 for chest examinations), are equally important. The inability of neonates to follow directions (e.g. stop breathing) produces inevitable immobilization difficulties. Nevertheless, premature neonates who are ill are not very active and settle after a while. The most frequent cause of clinically unacceptable image quality in neonatal radiography is incorrect positioning, which can lead to diagnostic errors because of organ overlapping and shape distortion. However, this aspect is outside the main focus of this work and only criteria that could be affected by the radiographic technique were included and investigated. All indices for image quality criteria were equally weighted, assuming that the anatomical details described in the image quality criteria are of comparable significance. The visibility of the features was assessed using a five-grade scale (Table 2), enabling quantitative evaluation of the image quality criteria [35, 36]. The maximum possible total image quality score for each image was 65, if all criteria were applicable. The final total score for each image was acquired by summing the mean scores of the two observers for each feature.
Images were excluded from the study when the presence of severe underlying pathology in the patient (e.g. atelectasis, transient tachypnea of the newborn, bronchopulmonary dysplasia and pneumothorax) led to some features not being visualized, resulting in the failure to fulfil a criterion (11 radiographs). Also, in some cases a criterion could not be applied because of the absence of the feature (e.g. bowel loops for chest radiographs or absence of tubes and catheters). In these cases, the criterion was characterized as non-applicable (N/A). Four more radiographs were excluded from the study as their image quality was characterized by the physicians as "unacceptable"; these radiographs were included in the neonate's file to enable the exact number of exposures that the neonate had undergone to be recorded. In total, 363 radiographs were evaluated. During evaluation the room illumination was dimmed and kept constant, whereas the reading time and observer-to-image distance were not restricted.
|
Results
|
|---|
Entrance surface doses
The exposure parameters (kVp and mAs) and the corresponding values of ESD for each birthweight group, as calculated from Equation (1), are presented in Table 3. A relatively wide variation in ESD values is observed, not only among different weight groups but also within the same weight group. This reflects the lack of standardization of the exposure parameters applied in all of the procedures performed. In Group four, in particular, the ratio of the maximum to minimum value is 3.5:1, ranging from 21.1 to 74.9 µGy. However, the acquired ESD values are lower than the DRL of 80 µGy proposed by the CEC [5], and the majority are in accordance with the more recent and strict reference value of 50 µGy proposed by the NRPB [3] for neonatal chest radiography. The distribution of ESD values as a function of tube voltage is presented in Figure 2. The data are in two groups because radiographers applied high or low tube voltage techniques according to their own judgment, training and experience, rather than following a particular protocol. In general, older radiographers tended to use lower tube voltage techniques (approximately 44–53.5 kVp) with decreased mAs, whereas younger radiographers used higher tube voltage techniques (approximately 55–63.5 kVp) because of the better training they had received in radiation protection issues. It was observed, as anticipated, that ESD values tended to increase with neonatal birthweight, because neonates of increased weight require increased exposures. The correlation between mean ESD values and mean birthweight of neonates from each birthweight group (876 g, 1289 g, 1994 g, 3198 g, respectively) is shown in Figure 3 (R2 = 0.9995).
View this table:
[in this window]
[in a new window]
|
Table 3. Range and mean value(in parentheses) of exposure parameters and corresponding entrance surface dose (ESD) values for each birthweight group
|
|
View larger version (19K):
[in this window]
[in a new window]
|
Figure 2. Distribution of entrance surface dose(ESD) as a function of tube voltage for all birthweight groups. The dotted line represents the dose reference level (DRL) value recommended by the National Radiological Protection Board.
|
|
View larger version (13K):
[in this window]
[in a new window]
|
Figure 3. Mean entrance surface dose(ESD) values with respect to mean birthweight for each birthweight group.
|
|
Dose–area product measurements
DAP values were obtained for a fixed field size of 10 x 10 cm and were corrected for the field size and the exposure parameters applied to give the DAP values for all neonatal chest radiographs and babygrams performed. The range of the derived DAP values and the corresponding mean values for each birthweight group are presented in Table 4. A relatively wide variation is observed within groups because of the different tube voltages and mAs settings applied. Concurrently, DAP values also varied widely because of differences in body size and mainly because of the varying degree of collimation used for each examination. The distribution of the DAP values as a function of weight is presented in Figure 4. There is a broad range with the maximum DAP value being over five times the minimum. From the mean values it is observed, as expected, that DAP values increase with increasing weight because of the increased field size, mAs settings and tube voltage values.
View larger version (16K):
[in this window]
[in a new window]
|
Figure 4. Distribution of dose–area product (DAP) values with neonatal birthweight for all radiographs.
|
|
The acquired ESD values, as derived from the DAP values, are presented as a function of the theoretically estimated ESD values in Figure 5. The two sets of values were found to be strongly correlated (R2 = 0.957).
View larger version (12K):
[in this window]
[in a new window]
|
Figure 5. Entrance surface dose values as deduced from the dose–area product values (ESDDAP) as a function of those theoretically estimated (ESDTHEOR.).
|
|
Evaluation of image quality
The normalized total image quality score for chest radiographs and babygrams as a function of tube voltage for all weight groups is presented in Figures 6 and 7, respectively. In the SCBU both high and low tube voltage techniques were performed by different radiographers; however, a preference for low tube voltage techniques was observed. Figures 6 and 7 reveal the feasibility of achieving high total image quality scores, which means diagnostically acceptable images, using both techniques; these data demonstrate the fact that high kV techniques result in no clinically significant image quality degradation whereas they decrease dose. Thus, comparison of the imaging techniques indicates that a significant dose reduction (by a factor of approximately 3) may be achieved (Table 3
). The variations seen in Figures 6 and 7 may be partially attributed to difficulties in positioning the neonate. However, the major factor affecting image quality is considered to be the exposure parameters, because in all radiographs no significant positioning errors (cables, holder's hands, tilting) were observed that could obstruct the evaluation of the visibility of various anatomical details and the placement of catheters.
View larger version (17K):
[in this window]
[in a new window]
|
Figure 6. Normalized total image quality score of chest radiographs for all birthweight groups as a function of tube voltage.
|
|
View larger version (19K):
[in this window]
[in a new window]
|
Figure 7. Normalized total image quality score of babygrams for all birthweight groups as a function of tube voltage.
|
|
|
Discussion
|
|---|
The ESD values obtained in the present study are lower than, or comparable to, the values obtained in studies in other European countries. Comparative results with other studies are presented in Table 5. Although, in general, mAs settings decrease with increasing tube voltage, the lack of a standard protocol, in conjunction with the unavailability of an automatic exposure control system, results in overexposed or underexposed films. High dose values are generally associated with high mAs settings. In Figure 2, a trend of ESD reduction is observed for higher tube voltage values. This means that harder X-ray beams with increased penetrating ability are preferable because, in conjunction with the lower mAs settings required, they result in lower ESD values.
View this table:
[in this window]
[in a new window]
|
Table 5. Comparison of the mean entrance surface dose(ESD) value obtained for all birthweights groups with the corresponding ESD values of other studies
|
|
High image quality scores were obtained for both low and high tube voltage techniques with the latter resulting in reduced ESDs. By increasing tube voltage the contrast of the image is reduced, and so an upper level has to be set. A study of the images that received the highest scores enabled the derivation of the optimum combination of exposure parameters. The optimum range of mAs settings for achieving high image quality scores (>70%) as a function of tube voltage is presented in Figure 8. The ideal combination of exposure parameters that would result in the maximum total image quality score is represented by the solid curve. This was deduced by fitting the curve of the mAs values, and the corresponding kVp values applied, for those radiographs that achieved high image quality scores (over 70%), assuming that the ideal combination would lie in the area between the almost equal number of underexposed and overexposed radiographs. However, high and satisfactory image quality is obtained for mAs settings in the range determined by the curves above and below the ideal. These curves represent the combination of values (kVp and mAs) that result in images having quality scores of 70% of the maximum, which was considered as clinically acceptable. Films irradiated with exposure parameters lying beyond these two curves are characterized as overexposed and underexposed, respectively, resulting in unacceptable degradation of image quality and possible repetition of the radiographic examination. The ideal parameters to be selected, as obtained from the image quality evaluation, are presented for each weight group separately in Figure 9. Similarly, the expected values of ESDs for images characterized by acceptable quality scores are presented in Figure 10 as a function of tube voltage. In Figure 10, the middle bold curve represents those ESDs estimated from the ideal parameters to achieve maximum image quality. In accordance with the previous figures, the curves over and below the central curve represent those ESDs that correspond to images achieving 70% of the maximum score, as a function of tube voltage. From the radiation protection point of view it can be seen that it is possible to further reduce the doses received by neonates and, as shown in Figure 10, the ESD may reach almost half the DRL value. Thus, selection of exposure parameters that correspond to more penetrating X-ray beams, with increased tube voltage, are preferable. The area that represents the best combination of exposure parameters, giving high image quality and lower radiation dose, is in the right hand part of the diagram and between the curves. For example, an increase in tube voltage from 50 to 60 kVp allows a decrease in mAs from 1.6 to 0.6, giving a maximum image quality score. This change of exposure parameters reduces the ESD by approximately 53.2% (from 42.1 to 22.4 µGy).
View larger version (10K):
[in this window]
[in a new window]
|
Figure 8. The required values of mAs settings(mAs) for achieving maximum image quality scores (solid line) and 70% of the maximum score (dotted lines) as a function of tube voltage for all neonatal birthweight groups.
|
|
View larger version (19K):
[in this window]
[in a new window]
|
Figure 9. The required values of mAs settings(mAs) for achieving maximum image quality scores (solid line) and 70% of the maximum score (dotted lines) as a function of tube voltage for each birthweight group separately.
|
|
View larger version (15K):
[in this window]
[in a new window]
|
Figure 10. Entrance surface doses(ESDs) for images receiving maximum image quality scores (solid line) and for images receiving 70% of the maximum score (dotted lines) as a function of tube voltage for all neonatal birthweight groups.
|
|
The visibility of the tips of endotracheal tubes, umbilical catheters and long lines was graded with a high score independently of tube voltage, except in conditions of underlying pathology. This could be a matter of concern because the dose from radiographs performed routinely and exclusively for ensuring accurate tube and catheter placement could be considerably lower than the dose arising from radiographs performed for strict diagnostic reasons.
The variability in the DAP values is attributed to differences not only in the technique parameters but also in field size. This is an area of concern as larger fields are frequently used, resulting in image contrast impairment because of increased scatter and, most importantly, in the unnecessary irradiation of adjacent organs and red bone marrow of the neonate outside the area of interest.
The results are comparable with other studies. For the chest radiograph, Jones et al [26] and Armpilia et al [17] reported mean DAP values of 8.3 mGy cm2 and 4.3 mGy cm2, respectively, whereas Wraith et al [15] reported a higher value of 12.3 mGy cm2. For the combined (babygram) technique they reported values of 18.7 mGy cm2, 5.5 mGy cm2 and 12.8 mGy cm2, respectively. The mean DAP values in this study are 7.4 mGy cm2 for chest radiographs and 8.1 mGy cm2 for babygrams. Babygrams are usually routinely performed in a neonatal unit when neonatal chest and abdominal radiographs are requested simultaneously. In the separate exposure technique there is usually a field overlap. Fields diverge with depth resulting in double irradiation of the overlapping area, thus contributing to an increase in effective dose of the neonate. In contrast, in a babygram the dose deposited is relatively more homogenous [18]. Additionally, neonates should be disturbed as little as possible, whereas the separate exposure technique increases the risk of chilling and cross-infection. However, the use of a single radiographic field can cause distortion of the shape, size and position of structures, which increases with distance from the centring point. Thus, undoubtedly, the separate exposure technique can produce images of higher quality because of the different exposure parameters required and the lower distortion. However, the priority is to minimize dose while producing acceptable rather than maximum image quality radiographs. The risk in the combined technique (babygram) does not differ significantly from that of separate exposures [26]. Because neonatal abdominal radiography is regularly requested in order to examine the presence of necrotizing enterocolitis, atresia or other pathological conditions of the intestine, a babygram centred at the chest should be adequate to answer the clinical questions.
The results presented in this study could contribute to an agreed protocol among departments, with standardized techniques, comparable diagnostic quality of images and doses within published reference ranges for neonates. The use of standardized exposure tables can facilitate the adjustment of tube voltage and mAs settings according to neonatal weight. Overall, education, training and practical experience of staff in all departments examining neonates is essential in diminishing wide dose variations in this radiosensitive group of patients.
|
Conclusions
|
|---|
The fact that relative radiation risks increase with decreasing age reinforces the concept that optimization is essential in the special field of neonatal radiography. The majority of the estimated ESD values showed good compliance with the recommended diagnostic reference levels proposed by the CEC and the NRPB (95.7%) for neonatal radiography. However, the results show that the use of higher tube voltage techniques could lead to further reductions in the neonatal dose, and, although these techniques slightly compromise the visualization of anatomical details, the image quality is still adequate to answer the diagnostic question, thus adhering to the driving philosophy of the ALARA principle. However, a limitation of this study is the number of cases (radiographs) in each birthweight group, and more data are necessary to achieve a higher accuracy.
|
Acknowledgments
|
|---|
The authors would like to thank the staff of the Departments of Paediatrics and Radiology at the University Hospital of Patras for their contribution to this work.
Received for publication July 24, 2006.
Revision received March 9, 2007.
Accepted for publication March 21, 2007.
|
References
|
|---|
- Prasad KN, editor. Handbook of radiobiology. Boca Raton, FL: CRC Press, 1995
- United Nations Scientific Committee on the Effects of Atomic Radiation. Sources, effects and risks of ionizing radiation. UNSCEAR 2000 report, volume II: effects. New York, NY: United Nations, 2000
- Hart D, Wall BF, Shrimpton PC, Bungay DR, Dance DR. Reference doses and patient size in paediatric radiology. NRPB-R318. Chitton, UK: NRPB, 2000
- International Commission on Radiation Protection 1990. Recommendations of the International Commission on Radiation Protection. ICRP publication 60. Oxford: Pergamon, 1991
- Commission of European Communities. European guidelines on quality criteria for diagnostic radiographic images in paediatrics. Report EUR 16261. Luxemburg: Office for Official Publications of the European Communities, 1996
- Roebuck DJ. Risk and benefit in paediatric radiology. Pediatr Radiol 1999;29:637–40.[CrossRef][Medline]
- American Academy of Pediatrics, Committee on Environmental Health. Risk of ionizing radiation exposure to children: a subject review. Pediatrics 1998;101:717–9.[Abstract/Free Full Text]
- McParland BL, Gorka W, Lee R, Lewall DB, Omojola MF. Radiology in the neonatal intensive care unit: radiation dose reduction and image quality. Br J Radiol 1996;69:929–37.[Abstract/Free Full Text]
- Faulkner K, Barry JL, Smalley P. Radiation doses to neonates in a special baby care unit. Br J Radiol 1989;62:230–3.[Abstract/Free Full Text]
- Sutton PM, Arthur RJ, Taylor C, Stringer MD. Ionising radiation from diagnostic x rays in very low birthweight babies. Arch Dis Child Fetal Neonatal Ed 1998;78:227–9.
- Robinson A, Dellagrammaticas HD. Radiation doses to neonates requiring intensive care. Br J Radiol 1983;56:397–400.[Abstract/Free Full Text]
- Mohamadain KEM, Da Rosa LAR, Azevedo ACP, Guebel MRN, Boechat MCB, Habani F. Dose evaluation for paediatric chest x-ray examinations in Brazil and Sudan: low doses and reliable examinations can be achieved in developing countries. Phys Med Biol 2004;49:1017–31.[CrossRef][Medline]
- Chapple CL, Faulkner K, Hunter EW. Energy imparted to neonates during x-ray examinations in a special baby care unit. Br J Radiol 1994;67:366[Abstract/Free Full Text]
- Fletcher EW, Bum JD, Draper G. The risk of diagnostic radiation of the newborn. Br J Radiol 1986;59:165–70.[Abstract/Free Full Text]
- Wraith CM, Martin CJ, Stockdale EJN, McDonald S, Farquhar B. An investigation into techniques for reducing doses from neonatal radiographic examinations. Br J Radiol 1995;68:1074–82.[Abstract/Free Full Text]
- Brindhaban A, Al-Khalifah K. Radiation dose to premature infants in neonatal intensive care units in Kuwait. Radiat Prot Dosimetry 2004;111:275–81.[Abstract/Free Full Text]
- Armpilia, CI, Fife IAJ, Croasdale PL. Radiation dose quantities and risk in neonates in a special baby care unit. Br J Radiol 2002;75:590–5.[Abstract/Free Full Text]
- Duggan L, Warren-Forward H, Smith T, Kron T. investigation of dose reduction in neonatal radiography using specially designed phantoms and LiF:Mg,Cu,P TLDs. Br J Radiol 2003;76:232–7.[Abstract/Free Full Text]
- Duggan L, Hood C, Warren-Forward H, Haque M, Kron T. Variations in dose response with x-ray energy of LiF:Mg,Cu,P thermoluminescense dosimeters: implications for clinical dosimetry. Phys Med Biol 2004;49:3831–45.[CrossRef][Medline]
- Arroe M. The risk of X-ray examinations of the lungs in neonates. Acta Paediatr Scand 1991;80:489–93.[Medline]
- Schneider K, Fendel H, Bakowski C, Stein E, Kohn M, Kellner M, et al. Results of a dosimetry study in the European Community on frequent X-ray examinations on infants. Radiat Prot Dosimetry 1992;43:31–6.[Abstract]
- Ono K, Akahane K, Aota T, Hada M, Takano Y, Kai M, et al. Neonatal doses from X-ray examinations by birth weight in a neonatal intensive care unit. Radiat Prot Dosimetry 2003;103:155–62.[Abstract]
- Duetting T, Foerste B, Knoch T, Darge K, Troeger J. Radiation exposure during chest X-ray examinations in a premature intensive care unit: phantom studies. Pediatr Radiol 1999;29:158–62.[CrossRef][Medline]
- Barcham N, Egan I, Down SB. Gonadal protection methods in neonatal chest radiography. Radiol Technol 1997;69:157–61.[Medline]
- Appleton MB, Carr SR. Radiation protection in a neonatal intensive care unit: a practical approach. Radiography 1984;50:137–41.[Medline]
- Jones NF, Palarm TW, Negus IS. Neonatal chest and abdominal radiation dosimetry: a comparison of two radiographic techniques. Br J Radiol 2001;74:920–5.[Abstract/Free Full Text]
- Wilson-Costelo D, Rao PS, Morrison S, Hack M. Radiation exposure from diagnostic radiographs in extremely low birth weight infants. Pediatrics 1996;97:369–74.[Abstract/Free Full Text]
- Schneider K, Kohn MM, Bakowski C, Stein E, Freidhof C, Horwitz AE. Impact of radiographic imaging criteria on dose and image quality in infants in an EC-wide survey. Radiat Prot Dosimetry 1993;49:73–6.[Abstract]
- Schneider K. Special exposures: paediatrics. Radiation Protection 102. Proceedings of the workshop on Implementation of the Medical Exposure Directive (97/43/ Euratom); 1998 April 27; Madrid. Luxembourg: European Commission, 1998. 103–13.
- Schneider K. Evolution of quality assurance in paediatric radiology. Radiat Prot Dosimetry 1995;57:119–23.[Abstract]
- Diagnostic X-ray Imaging Committee Task Group #12. Quality control in diagnostic radiology. Report of AAPM No. 74. Madison, WI: Medical Physics Publishing, 2002
- International Commission on Radiation Units and Measurements. Radiation quantities and units. ICRU Report 33. Washington, DC: ICRU, 15 April 1980: 25
- Goutail-Flaud MF, Sfez M, Berg A, Laguenie G, Couturier C, Barbotin-Larrieu F, et al. Central venous catheter-related complications in newborns and infants: a 587-case survey. J Pediatr Surg 1991;26:645–50.[CrossRef][Medline]
- Lange M, Jonat S, Nikischin W. Detection and correction of endotracheal tube position in premature neonates. Pediatr Pulmonol 2002;34:455–61.[CrossRef][Medline]
- Lowe A, Finch A, Boniface D, Chaudhuri R, Shekhdar J. Diagnostic image quality of mobile neonatal chest x-rays and the radiation exposure incurred. Br J Radiol 1999;72:55–61.[Abstract]
- Cook JV, Kyriou JC, Pettet A, Fitzgerald MC, Shah K, Pablot SM. Key factors in the optimization of paediatric X-ray practice. Br J Radiol 2001;74:1032–40.[Abstract/Free Full Text]
Top
Abstract
Introduction
