HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) All Versions of this Article: 2403050993v1 240/3/828    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Tsapaki, V. Articles by Prokop, M. Search for Related Content PubMed PubMed Citation Articles by Tsapaki, V. Articles by Prokop, M.

Dose Reduction in CT while Maintaining Diagnostic Confidence: Diagnostic Reference Levels at Routine Head, Chest, and Abdominal CT—IAEA-coordinated Research Project¹

¹ From the CT Department, Konstantopoulio Agia Olga Hospital, 1 Ifaistou St, 14569 Anixi, Athens, Greece (V.T., C.T., P.N.M., J.P.); Department of Radiology, Vancouver Hospital, Vancouver, British Columbia, Canada (J.E.A.); Department of Radiology, All India Institute of Medical Sciences, New Delhi, India (R.S.); Poland Radiation Protection Department, Nofer Institute of Occupational Medicine, Lodz, Poland (M.A.S.); Department of Radiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand (A.K.); International Atomic Energy Agency, Vienna, Austria (M.R.); North Western Medical Physics, Christie Hospital NHS Trust, Manchester, England (A.H.); and Department of Radiology, University Medical Center Utrecht, Utrecht, the Netherlands (M.P.). Received June 14, 2005; revision requested August 12; revision received September 2; accepted September 22; final version accepted November 23. Supported in part by the International Atomic Energy Agency through the coordinated research project Dose Reduction in Computed Tomography while Maintaining Diagnostic Confidence. Address correspondence to V.T. (e-mail: virginia{at}otenet.gr).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 
Purpose: To measure radiation doses for computed tomography (CT) of the head, chest, and abdomen and compare them with the diagnostic reference levels, as part of the International Atomic Energy Agency Research coordination project.

Materials and Methods: The local ethics committees of all participating institutions approved the study protocol. Written informed consent was obtained from all patients. All scanners were helical single-section or multi–detector row CT systems. Six hundred thirty-three patients undergoing head (n = 97), chest (n = 243), or abdominal (n = 293) CT were included. Collected data included patient height, weight, sex, and age; tube voltage and tube current–time product settings; pitch; section thickness; number of sections; weighted or volumetric CT dose index; and dose-length product (DLP). The effective dose was also estimated and served as collective dose estimation data.

Results: Mean volumetric CT dose index and DLP values were below the European diagnostic reference levels: 39 mGy and 544 mGy · cm, respectively, at head CT; 9.3 mGy and 348 mGy · cm, respectively, at chest CT; and 10.4 mGy and 549 mGy · cm, respectively, at abdominal CT. Estimated effective doses were 1.2, 5.9, and 8.2 mSv, respectively.

Conclusion: Comparison of CT results with diagnostic reference levels revealed the need for revisions, partly because the newer scanners have improved technology that facilitates lower patient doses.

© RSNA, 2006

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 
Because of rapid advances in computed tomographic (CT) technology, this modality has become a very robust and versatile examination that has replaced many radiologic techniques (1,2). CT applications have expanded with the introduction of helical and multi–detector row systems (3). However, this expansion of CT techniques has resulted in substantial increases in radiation doses to patients that have not been fully appreciated (2,4). According to the National Radiological Protection Board, CT performed in the United Kingdom accounted for approximately 40% of the medical exposure to x-rays for the general population, although this percentage represents only 4% of the exposure from all radiologic procedures (5). This was the situation in the early 1990s, whereas there has been a fast increase in the frequency of CT examinations performed and a substantial increase in the collective dose, as reported by international organizations (6,7). In one report from the United States (4), CT scanning was estimated to account for more than 10% of all radiologic examinations performed and for approximately two-thirds of the overall radiation dose to patients (4). Furthermore, modern CT scanners have a wide variety of exposure factors and involve techniques that can drastically change the radiation dose to the patient (8,9).

International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, as developed in cooperation with the World Health Organization, the Pan American Health Organization, the International Labour Organization (10), and European Council Directive 97/43 (11), require that a radiologic examination be performed only in the case of a justifiable clinical indication and, in that case, that the patient's radiation exposure should be limited to the amount required to meet the specific clinical objective. There is a growing realization that the image quality at CT often exceeds the level required for a confident diagnosis and that patient doses are higher than necessary. This concern was emphasized in a Food and Drug Administration notification in regard to the exposure of pediatric patients and small adult patients to radiation at CT (12).

Guidelines to optimize the protection of patients during CT procedures have been provided by various international organizations (6,13,14). All guidelines include reference doses that are described as diagnostic reference levels (DRLs) (13) or guidance levels (10,14) that assist in the optimization of patient protection and permit comparisons of the performance of different CT scanners and techniques. The dose parameters suggested in the guidelines are the weighted CT dose index for a single section and the dose-length product (DLP) for the entire examination. The International Atomic Energy Agency (IAEA) and the International Commission on Radiation Units and Measurements recently pointed out that in measurements obtained by using an air-kerma calibrated ionization chamber, the measured quantity is air kerma and that in air-tissue interfaces (such as the air cavity in a CT phantom), the absorbed dose in air is impractical to measure. For this reason, the IAEA and the International Commission on Radiation Units and Measurements have proposed using the CT air-kerma index (15) rather than the weighted CT dose index. However, since this recommendation has not yet been stated in relevant International Commission on Radiation Units and Measurements reports and IAEA codes of practice, terminology based on weighted CT dose index measurements has been used in this article.

In recent years, investigators in a number of studies (16–19) have measured radiation doses in terms of weighted CT dose index and DLP values and compared these measurements with the European DRLs. Such studies have been performed mostly in only a limited number of countries, and in many cases in only one country (20–23). Investigators in one published study reported the weighted CT dose index and DLP results from two European countries (24). In another study, the results from five countries in the Nordic region were reported (25). With the advent of multi–detector row systems, the term volumetric CT dose index, which is derived by dividing the weighted CT dose index by pitch, was introduced to account for variations in radiation exposure in the z direction when the pitch is not equal to 1 (25,26). With use of a single-section helical system, the volumetric CT dose index is equal to the weighted CT dose index. In the same way, with use of a multi–detector row system, the DLP is estimated as the product of the volumetric CT dose index and the length of the irradiated object. The results obtained by using the recently developed multi–detector row technology have been presented in a limited number of studies in the literature (9,27–29).

In keeping with its mandate of the application of basic safety standards (10), the IAEA has initiated a number of coordinated research projects for radiation safety in diagnostic radiology. One of these IAEA coordinated research projects was focused on the general aspects of optimization of radiologic protection in radiography and included some primary results for chest CT (14). There is a requirement for reduction of CT radiation dose, especially in view of the fact that the use of helical and multi–detector row technologies is expanding rapidly. Aware of this requirement, the IAEA supported another coordinated research project, which was dedicated to the assessment of these CT systems. The purpose of this coordinated research project, titled Dose Reduction in Computed Tomography while Maintaining Diagnostic Confidence, was to study the CT radiation doses administered in different countries and then develop and evaluate dose reduction methods while maintaining diagnostic confidence. The purpose of our study was to measure radiation doses for CT of the head, chest, and abdomen and compare them with the DRLs, as part of the International Atomic Energy Agency Research Coordination Project titled Dose Reduction in Computed Tomography while Maintaining Diagnostic Confidence.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 
Selection of CT Scanners
Six countries participated in this research project: Canada, Greece, India, Poland, United Kingdom, and Thailand. All the CT scanners chosen for this study were manufactured after 1997 and were single-section or helical multi–detector row systems.

Patient Examinations
Adult head, chest, and abdominal CT examinations were chosen for the evaluations because they are commonly performed in most radiology departments. The local ethics committees of all participating institutions approved the study protocol. Informed consent was obtained from all study subjects.

Data Collected
The collected data included patient height, weight, sex, and age; tube voltage and tube current–time product settings; pitch; section thickness; and number of sections. Patients with gross abnormalities and those who required examinations involving special parameters to visualize special details were excluded.

Radiation Dose Calibration
Before patient data were collected, CT dose index measurements (weighted and volumetric CT dose indexes) were performed with all of the participating CT scanners by using a pencil-shaped ionization chamber with an appropriate calibration certificate, either in air or in a dedicated head-equivalent (16-cm-diameter) or body-equivalent (32-cm-diameter) polymethylmethacrylate phantom. The dosimetry method used was based on the technique proposed in the European guidelines (13). Then, individual patient dose data (weighted CT dose index or volumetric CT dose index and DLP) either were estimated from the phantom measurements or were documented from the scanner console.

Effective Dose Estimate
The effective dose estimate was determined by using DLP measurements and appropriate normalized coefficients found in the European guidelines for CT (0.0023 mSv · mGy^–1 · cm^–1 for head CT, 0.017 mSv · mGy^–1 · cm^–1 for chest CT, and 0.015 mSv · mGy^–1 · cm^–1 for abdominal CT) (13). All data were evaluated by all authors both independently and in consensus during an extensive meeting that was part of the coordinated research project.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 
Data in regard to 633 examinations in patients who underwent routine head, chest, or abdominal CT were collected. These subjects included 97 patients who underwent head CT, 243 who underwent chest CT, and 293 who underwent abdominal CT. Basic demographic data can be found in Table 1. The average weight for the combined sample of patients who underwent chest CT and those who underwent abdominal CT was slightly lower than 70 kg because the average weight of Asian individuals is lower than that of European and American individuals.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 
Our analysis of the technical factors for CT scanning at the participating centers revealed that the section thickness used at the centers in Greece, Poland, and Thailand conformed to the corresponding European recommendations of 7–10 mm. The center in Canada, on the other hand, reported using a thinner section thickness, particularly when imaging of lung nodules was performed. It should be noted, however, that at the Canadian center that participated in the study, a 16-section helical system was used; this system provided the opportunity to obtain thinner section thickness and low tube current–time values without any substantial loss of diagnostic information on the image. The center in India also applied a thinner section thickness (2.5 mm) for chest and abdominal CT. The facility in the United Kingdom reported using even thinner sections for chest (1.5 mm) and abdominal (0.75 mm) CT. It appears that variations in section thickness were as high as a value of approximately 10. In terms of pitch values, the European guidelines recommend a pitch value of 1 for small lesions and that of 1.5 for large lesions to achieve a good imaging technique (13). The centers in India and Thailand reported using larger pitch values for both chest and abdominal CT examinations. The reason for these elevated values is that there are two definitions of pitch available for use with multisection scanners, and these definitions depend on whether single-section collimation, with pitch that is independent of the number of detector rows, is chosen as the reference standard or the total collimation of the detector array, with volumetric pitch that increases as the number of detector rows increases, is chosen (30). It appears that the manufacturers of the scanners used in India and Thailand applied the volumetric pitch. The mean pitch values for the center in India were 1.50 for chest CT and 1.25 for abdominal CT. The mean pitch values for the center in Thailand were 1.25 for chest CT and 1.4 for abdominal CT.

In terms of the radiation doses used in individual countries, lower volumetric CT dose index values were reported at both chest and abdominal CT performed with multi–detector row systems (India, Canada, United Kingdom, and Thailand), partly because more appropriate technical factors were used. The center in Greece reported the highest volumetric CT dose index values, which were more than double the values reported by the centers in Thailand and the United Kingdom. These higher volumetric CT dose index values could be attributed, to some extent, to the design of the scanner, which has xenon detectors instead of solid-state technology. Another important fact was that all participating centers separately reported radiation doses that were lower than the DRLs for all three CT examinations. In a way, this finding shows the awareness and effort of users to keep doses low and, on the other hand, indicates the need to modify the European guidelines and recommendations accordingly.

The mean weighted CT dose index (39 mGy) for head CT in the entire sample was comparable to values reported by other authors (34–56 mGy) (28,30–34) and almost half the DRL value (60 mGy) recommended in the European guidelines (13). Despite new advances in CT techniques, most users still prefer to perform head examinations in the conventional way, without using the helical technique. The mean DLP (544 mGy · cm) for head CT was lower than the results reported by other authors such as Torp et al (740 mGy · cm) (25), Hidajat et al (587 mGy · cm) (31), and Shrimpton et al (787 mGy · cm) (29). It should be noted, however, that all of these authors reported values that were much lower than the European DRL (1050 mGy · cm).

The mean weighted CT dose index (9.3 mGy) for chest CT was lower than the value reported in the previous IAEA-coordinated research project (16.2 mGy) (14). Since the weighted CT dose index reflects the radiation output characteristics of each particular scanner, this difference can be explained by the fact that, in that particular coordinated research project (14), both newer CT equipment and older CT equipment were included. In our study, only scanners produced after 1997 were involved in the project. In addition, the weighted CT dose index for chest CT was lower than that reported by Papadimitriou et al (21 mGy) (24), who reported results for a total of 46 scanners used at facilities in Italy and Greece. This difference was probably because some of these systems were units with older technology. Torp et al (25) reported results from five countries in the Nordic region; weighted CT dose index values ranged from 10.5 to 11.7 mGy. The scanners in that study were helical units developed during the past decade, but no details about the technical factors used were provided. Hidajat et al (31) reported results from a study that involved conventional and helical scanners and compared their results with those of other authors (31–34). The range of values presented in that comparison was 13–22 mGy, with the lower values reported for helical chest CT. One should bear in mind that all of the studies described had results that were, at maximum (in 22 of 30 cases), 30% lower than the DRLs. Fridberg et al (28) reported values that were obtained by using both transverse scanners manufactured before 1995 and single-section helical and multi–detector row scanners manufactured after 1995. Their results also indicated a substantial decrease in the radiation doses used at routine chest CT examinations performed with newer equipment. Reduced doses were more prominent with use of the multi–detector row scanners, especially for chest CT.

The mean DLP (348 mGy · cm) for chest CT was lower than the IAEA-reported value (455 mGy · cm) (14), and the corresponding values reported by Papadimitriou et al—429 mGy · cm for centers in Greece and 483 mGy · cm for centers in Italy (24). The DRL DLP in European guidelines for chest CT is 650 mGy · cm, which is approximately 46% (302 of 650) higher than the corresponding value in this study. The large range of results reported reveals the differences in the techniques used at each center. Since the DLP is the product of the volumetric CT dose index and the length of the patient undergoing irradiation, the extent of the examination seems to differ between centers because of a number of reasons, such as the given patient's abnormality, the experience of the user, and/or even the demographics for the given region (ie, height of the population).

The mean weighted CT dose index for abdominal CT was 10.4 mGy, which is lower than the range of values (16–29 mGy) reported by a number of other authors (24,29,30–34). On the other hand, the mean DLP for abdominal CT (549 mGy · cm) is comparable to the values reported by Papadimitriou et al (493–551 mGy · cm) (24). It should be noted, however, that their values were obtained in the upper part of the abdomen and not in the entire abdominal region, so the scanned region in the patient was substantially decreased. On the other hand, all of the abdominal CT examinations performed in the Canadian center were in fact abdominal-pelvic examinations, and this partially explains why the mean DLP for abdominal CT (696 mGy · cm) at the Canadian center was higher than the mean DLP for our entire sample (549 mGy · cm). Hidajat et al (31) reported a lower DLP with use of the helical technique—247 mGy · cm, which is more than half the corresponding value in our study, showing once more the great importance of deciding the length of the irradiated subject.

Comparison of the results reported in our study and in other studies in the literature with the European DRLs revealed the need for revision of these values. This need for revised dose values has arisen in part from the improved technology of the newer CT units that facilitates lower patient doses.

Mean effective dose values for head, chest, and abdominal CT in our study were lower than the effective dose derived from the European DRLs and the corresponding normalized coefficients. They were also in the lower range of the values presented by the United Nations Scientific Committee on the Effects of Atomic Radiation (7). This committee grouped the results of several national studies performed between 1991 and 1995 (0.8–5.0 mSv for head CT, 4.6–18.0 mSv for chest CT, and 6–24 mSv for abdominal CT), the highest values of which were reported by centers in the Netherlands. The main drawback of this report was that all of the studies included were performed more than 10 years ago, so updates are urgently required owing to the rapid evolution of CT technologies and practices. Olerud (35) estimated an approximate value of 2 mSv for head CT and 10–15 mSv for chest CT on the basis of data in the report from the United Nations Scientific Committee on the Effects of Atomic Radiation and presented corresponding Norwegian results (2.0 mSv for head CT, 11.5 mSv for chest CT, and 12.8 mSv for abdominal CT). The values presented in our study are similar to or slightly less than half of the Norwegian values.

Our study was limited by the decision to examine only patients from large hospitals, so the results may not be typical of smaller centers. Furthermore, the range of countries was chosen to reflect a diversity of health care systems in which CT is used.

Multi–detector row CT systems have opened the field for other, as well as improved, applications. Radiation dose data indicate that manufacturers are focusing their efforts toward improving image quality with reduced radiation doses compared with the doses required with the older-generation equipment in recognition of the idea that dose reduction has been an important issue for users in the past years. On the other hand, the ease and speed with which the CT systems with more advanced technology can be operated allow more use, and the exposure factors applied are usually higher than those actually required to acquire an image with diagnostic confidence. The European guidelines, DRLs (13), and guidance levels in the basic safety standards (10) were produced before the introduction and clinical use of modern CT scanners. Therefore, the need to develop new values that account for such innovations seems valid. Continuing developments in CT scanner technology will no doubt further extend the indications for and scope of CT examinations. Ongoing clinical studies, similar to this one, to monitor associated patient doses can play a role in achieving excellent imaging at reasonable patient doses.

	ADVANCES IN KNOWLEDGE

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 

• Mean volumetric CT dose index and dose-length product values were below the European diagnostic reference levels.
  
• Comparison of CT results with diagnostic reference levels revealed the need for revisions, partly because the newer scanners have improved technology that facilitates lower patient doses.
  

	ACKNOWLEDGMENTS

 
A large number of persons were associated with the work performed at each participating center, and their contributions are gratefully acknowledged.

	FOOTNOTES

 

Abbreviations: DLP = dose-length product • DRL = diagnostic reference level • IAEA = International Atomic Energy Agency

Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, all authors; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, all authors; clinical studies, all authors; experimental studies, all authors; statistical analysis, J.E.A.; and manuscript editing, all authors

	References

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 

1. Kalra MK, Maher MM, Toth TL, et al. Strategies for CT radiation dose optimization. Radiology 2004;230:619–628.[Abstract/Free Full Text]
2. Rehani M, Berry M. Radiation doses in computed tomography [editorial]. BMJ 2000;320:593–594.[Free Full Text]
3. Prokop M. Multidetector-row CT: technical principles and future trends. Eur Radiol 2003;13(suppl 5):M3–M13.
4. Mettler FA, Wiest PW, Locken JA, Kelsey CA. CT scanning: patterns of use and dose. J Radiol Prot 2000;20:353–359.[CrossRef][Medline]
5. National Radiological Protection Board. Protection of the patient in x-ray computed tomography and further statements on radon affected areas. Chilton, England: National Radiological Protection Board, 1992.
6. International Commission on Radiological Protection 2000: managing patient dose in computed tomography. In: Annals of International Commission on Radiological Protection. ICRP 84. Didcot, Oxfordshire, England: Pergamon, 2000.
7. United Nations Scientific Committee on the Effects of Atomic Radiation. 2000 report to the general assembly, annex D: medical radiation exposures. New York, NY: United Nations, 2000.
8. Jangland L, Sanner E, Persliden J. Dose reduction in computed tomography by individualised scan protocols. Acta Radiol 2004;45(3):301–307.[CrossRef][Medline]
9. Koller CJ, Eatough JP, Bettridge A. Variations in radiation dose between the same model of multidetector-row CT scanner at different hospitals. Br J Radiol 2003;76:798–802.[Abstract/Free Full Text]
10. International Atomic Energy Agency. International basic safety standards for protection against ionizing radiation and for the safety of radiation sources. IAEA safety series no. 115. Vienna, Austria: International Atomic Energy Agency, 1996.
11. European Union. Council Directive 97/43 Euratom of 30 June 1997. Health protection of individuals against the dangers of ionizing radiation in relation to medical exposure. (Repealing Directive 84/466 Euratom.) Official J European Communities 1997; L 180: 22–27.
12. U.S. Food and Drug Administration. Reducing the radiation risk from computed tomography for paediatric and small adult patients. U.S. Food and Drug Administration Web site. http://www.fda.gov/cdrh/safety/110201-ct.html. Accessed July 14, 2004.
13. European Guidelines on Quality Criteria for Computed Tomography. Report EUR 16262. Brussels, Belgium: European Commission, 1999.
14. International Atomic Energy Agency. Optimisation of the radiological protection of patients undergoing radiography, fluoroscopy and computed tomography. Document no. IAEA-TECDOC-1423. Vienna, Austria: International Atomic Energy Agency, 2004.
15. Zoetelief J, Pernicka F, Carlsson GA, et al. Dosimetry in diagnostic and interventional radiology: international commission on radiation units and measurements and IAEA activities. Proceedings of the International Symposium on Standards and Codes of Practice in Medical Radiation Dosimetry, Vienna, Austria: International Atomic Energy Agency, 2003.
16. Pages J, Buls N, Osteaux M. CT doses in children: a multicentre study. Br J Radiol 2003;76(911):803–811.[Abstract/Free Full Text]
17. Hatziioannou K, Papanastassiou E, Delichas M, Bousbouras P. A contribution to the establishment of diagnostic reference levels in CT. Br J Radiol 2003;76(908):541–545.[Abstract/Free Full Text]
18. Clarke J, Cranley K, Robinson J, Smith PH, Workman A. Application of draft European Commission reference levels to a regional CT dose survey. Br J Radiol 2000;73(865):43–50.[Abstract]
19. Tsapaki V, Kottou S, Papadimitriou D. Application of European Commission reference dose levels in CT examinations in Crete, Greece. Br J Radiol 2001;74:836–840.[Abstract/Free Full Text]
20. Staniszewska MA. Evaluation of patient exposure in computerized tomogram in Poland. Radiat Prot Dosimetry 2002;98(4):437–440.[Abstract]
21. Goddard CC, Al-Farsi A. Radiation doses in the Sultanate of Oman. Br J Radiol 1999;72(863):1073–1077.[Abstract]
22. Poletti JL. Doses to patients from CT scanning in New Zealand. Report NRL 1992/5. Christchurch, New Zealand: National Radiation Laboratory, 1992.
23. Jessen KA, Christensen JJ, Jorgensen J, Petersen J, Sorensen EW. Determination of collective effective dose equivalent due to computed tomography in Denmark in 1989. Radiat Prot Dosimetry 1992;43:37–40.[Abstract]
24. Papadimitriou D, Perris A, Manetou A, et al. A survey of 14 computed tomography scanners in Greece and 32 scanners in Italy: examination frequencies, dose reference values, effective doses and doses to organs. Radiat Prot Dosimetry 2003;104(1):47–53.[Abstract]
25. Torp C, Olerud H, Einarson G, Gron P, Leitz W, Servomaa A. Use of the EC quality criteria as a common method of inspecting CT laboratories: a pilot study by the Nordic Radiation Protection Authorities—radiological protection of patients in diagnostic and interventional radiology, nuclear medicine and radiotherapy. Document IAEA-CN-85-175. Vienna, Austria: International Atomic Energy Agency, 2001.
26. United Kingdom's CT scanner evaluation centre. ImPact Group Web site. http://www.impactscan.org. Accessed July 14, 2004.
27. Brix G, Nagel HD, Stamm G, et al. Radiation exposure in multi-slice versus single-slice spiral CT: results of a nationwide survey. Eur Radiol 2003;13(8):1979–1991.[CrossRef][Medline]
28. Fridberg E, Borretzen I, Olerud M. Dual and multidetector-row CT: what about the doses? Presented at the Radiation Protection Symposium of the North West European Radiation Protection Societies, Utrecht, the Netherlands, June 2–5, 2003.
29. Shrimpton PC, Hillier MC, Lewes MA, Dunn M. National Radiological Protection Board (NRPB): doses from computed tomography examinations in the UK—2003 review. Document NRPB-W67. Chilton, England: National Radiological Protection Board, 2005.
30. Prokop M, Galanski M. Spiral and multislice computed tomography of the body. Stuttgart, Germany: Thieme, 2003.
31. Hidajat N, Wolf M, Nunnemann A, et al. Survey of conventional and spiral CT doses. Radiology 2001;218:395–401.[Abstract/Free Full Text]
32. Smith A, Shah GA, Kron T. Variation of patient dose in head CT. Br J Radiol 1998;71:1296–1301.[Abstract]
33. Conway BJ, McCrohan JL, Antonsen RG, Rueter FG, Slayton RJ, Suleiman OH. Average radiation dose in standard CT examinations of the head: results of the 1990 NEXT survey. Radiology 1992;184:135–140.[Abstract/Free Full Text]
34. Scheck RJ, Coppenrath EM, Kellner MW, et al. Radiation dose and image quality in spiral computed tomography: multicentre evaluation at six institutions. Br J Radiol 1998;71:734–744.[Abstract]
35. Olerud M. CT dose surveys. Presented at the Radiation Protection Symposium of the North West European RP Societies, Utrecht, the Netherlands, June 2–5, 2003.

This article has been cited by other articles:

				A. Grgic, H. Wilkens, R. Kubale, A. Groschel, A. Buecker, and G. W. Sybrecht Low-Dose MDCT for Surveillance of Patients with Severe Homogeneous Emphysema After Bronchoscopic Airway Bypass Am. J. Roentgenol., September 1, 2008; 191(3): W112 - W119. [Abstract] [Full Text] [PDF]

				M. M. Rehani THE IAEA'S ACTIVITIES IN RADIOLOGICAL PROTECTION IN DIGITAL IMAGING Radiat Prot Dosimetry, June 3, 2008; (2008) ncn155v2. [Abstract] [Full Text] [PDF]

				T. C. Lauenstein, K. Salman, R. Morreira, T. Heffron, J. R. Spivey, E. Martinez, P. Sharma, and D. R. Martin Gadolinium-Enhanced MRI for Tumor Surveillance Before Liver Transplantation: Center-Based Experience Am. J. Roentgenol., September 1, 2007; 189(3): 663 - 670. [Abstract] [Full Text] [PDF]

				R. de Wit Cutting Back on Computed Tomography Scan Frequency in Curative Oncology: Get the Picture J. Clin. Oncol., April 10, 2007; 25(11): 1308 - 1309. [Full Text] [PDF]

This Article Abstract Full Text (PDF) All Versions of this Article: 2403050993v1 240/3/828    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Tsapaki, V. Articles by Prokop, M. Search for Related Content PubMed PubMed Citation Articles by Tsapaki, V. Articles by Prokop, M.