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16-slice CT: achievable effective doses of common protocols in comparison with recent CT dose surveys

Department of Radiology C-2S, Leiden University Medical Center, Albinusdreef 2, NL-2333 ZA Leiden, The Netherlands

Correspondence: A J van der Molen. E-mail: molen{at}lumc.nl

	Abstract

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The aim of the study was to investigate achievable dose levels in 16-slice CT by evaluating CT dose indices (CTDI) and effective doses of dose-optimized protocols compared with 4-slice dose surveys. Normalized CTDI free in air and in 16 cm and 32 cm diameter phantoms were measured on four different 16-slice CT scanners in the Netherlands. All collimation and tube potential settings were analysed. Volume CTDI was calculated for adult protocols for brain, chest, pulmonary angiography (CTPA), abdomen and biphasic liver CT. Effective doses were calculated first using volume CTDI with conversion factors and second from CTDIair values using the ImPACT dose calculator. Average results of the 16-slice scanners were correlated to results of dose surveys with predominantly 4-slice scanners. Statistical analysis was done with Student t-tests with a Bonferroni correction; therefore p < 0.017 was significant. The results of CTDIair and weighted CTDI were documented for all scanners. Effective doses averaged over four scanners for brain, chest, CTPA, abdomen and biphasic liver protocols were 1.9±0.4, 3.8±0.4, 3.0±0.2, 7.2±0.9 and 10.2±1.3 mSv, respectively. Compared with dose surveys achievable effective doses were equal (p = 0.069) to significantly lower (p < 0.017) for chest and abdomen protocols. For 16-slice spiral brain CT there was a trend of equal doses compared with sequential brain CT in the dose surveys. Thus, with dose-optimized protocols 16-slice CT can achieve equal to lower effective doses in examinations of the chest and abdomen compared with 4-slice CT, while doses can remain stable in the brain.

	Introduction

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Computed tomography (CT) is an important diagnostic imaging modality with rapid technical developments [1]. The number of CT examinations performed is increasing, with recent estimates in the USA in the range 50–58 million examinations per year [2, 3] and estimated growth of 4–10% per year [2, 4–6]. In a representative large university hospital in the USA, CT made up 10–15% of all radiology procedures while accounting for 67–75% of the effective dose [5, 6]. Therefore, there is a growing trend of CT being the major source of patient exposure.

Since 2001 radiation dose in CT has received special attention after the publication of unwanted high dose levels in the paediatric subpopulation [7]. Since then, much work has been done on optimization of scanning techniques [8–10], usually focusing on 4-slice units. However, insight into the dose effects of the newer 16-slice CT scanners in general practice is lagging behind, and only a few comprehensive dose surveys including multislice scanners are available to date [11–13]. In all these studies, 4-slice systems represent the majority of scanner types with only very few 16-slice systems included.

The aim of our study was to investigate achievable effective dose levels in commonly used 16-slice CT scanners in comparison with published survey data on multislice scanners by documenting CT dose indices (CTDI) and relating these to dose-optimized protocol suggestions for a number of frequently used scan protocols.

	Materials and methods

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Examined CT scanner types
Between October 2003 and August 2004, four 16-slice CT systems of different vendors at four institutions in the Netherlands were evaluated in this study: (a) General Electric Lightspeed 16 operating with 4.1 software (GE Healthcare, Waukesha, MI), (b) Philips MX8000IDT operating with 2.5 software (Philips Medical Systems, Best, The Netherlands), (c) Siemens Sensation 16 operating with VA70B software (Siemens Medical Solutions, Forchheim, Germany), and (d) Toshiba Aquilion 16CFX (Toshiba Medical Systems, Otawara, Japan) operating with 1.4 software.

Measurement technique
Dose measurements were made using a 102 mm pencil ionization chamber (model CP-4C; Capintec, Ramsey, NJ) connected to a multipurpose dosimeter (model 35050A; Keithley Instruments, Cleveland, OH). The chamber/dosemeter system had a traceable calibration.

For measurement of CTDI free in air (CTDIair), the ionization chamber was fixed to a special stand and was positioned along the central axis of the scanner. Hereby, the axis of rotation of the scanner coincided with the centre of the ionization chamber. Using a fixed scan length, dose readings at all available kilovoltage (kV) and slice collimation settings were made in spiral scan mode. The spiral scan mode guarantees that dose measurements of CTDIair exactly correspond to the actual acquisition conditions as for two scanners 16-slice scan mode was only available for spiral acquisitions. Moreover, our own validation showed that for equal beam collimation spiral CTDIair corresponded well with sequential CTDIair measurements (data not shown). Head and body modes were measured separately. The measurements were converted to dose per rotation and CTDIair. All measurements of CTDIair were normalized to 100 mAs and were done with pitch 1.

From the equivalence in spiral and sequential CTDIair measurements we concluded that measurements of CTDI in phantoms could be performed in sequential mode with the phantoms positioned on the table. Therefore, dose was measured in standard 16 cm and 32 cm diameter polymethylmethacrylate (PMMA) phantoms each 15 cm long in sequential mode. The ionization chamber was placed in holes at the centre and at peripheral 3, 6, 9 and 12 o'clock positions, and dose readings at all available tube voltages and slice collimation settings were made. CTDI₁₀₀ centre (CTDIc) and CTDI₁₀₀ periphery (CTDIp) were calculated. Weighted CTDI (CTDIw) values were derived from the formula: CTDIw = (1/3xCTDIc) + (2/3xCTDIp). Head and body scan modes were measured separately. All values of CTDIw were normalized to 100 mAs.

Evaluation of effective doses in common CT protocols
CTDI was calculated for adult dose-optimized CT protocol suggestions for helical brain (brain metastases), routine chest (lung metastases), CT pulmonary angiography (CTPA – pulmonary embolism), routine abdomen–pelvis (further abbreviated as abdomen – lymphoma staging) and biphasic liver (hypervascular tumours) studies. All protocols were defined single phase except the liver protocol. In this biphasic liver protocol, the portal phase always included the abdomen and pelvis.

Dose-optimized implied a practical balance between diagnostic image quality and dose reduction, not the ultimate in low dose. These suggestions were supplied to us by representatives of the various vendors based on cooperation with multiple clinical reference sites. As dose modulation techniques were not implemented in the same way on each scanner, dose modulation was not included in the comparison. Average planned scan length was set at 140 mm for non-tilted helical brain CT (125 mm for tilted scans), 270 mm for chest CT, 250 mm for CT pulmonary angiography, 420 mm for abdominal CT and 180 + 420 mm for biphasic liver CT. At the time of the study, only the Toshiba scanner allowed tilted helical brain scans in combination with a cone-beam reconstruction algorithm.

Our measured normalized CTDIw data were converted to volume CTDI (CTDIvol = CTDIw/pitch) and were used to calculate dose–length products (DLP), whereby DLP = CTDIvolxexposed scan length. The exposed scan length in this calculation incorporated the overrange length, based on our own data [14]. For brain CT only half of the overrange length was incorporated in the DLP calculations as the overrange above the vertex of the skull will only radiate air outside the patient. Effective dose was evaluated in two ways: (1) by converting DLP values to effective doses with the use of conversion factors for multislice CT taken from the 2004 Quality Criteria for Multislice CT [12], and (2) by using the ImPACT dose calculator (version 0.99X; ImPACT, London) in conjunction with our measured normalized CTDIair data. Effective doses were compared between the two methods and correlation was assessed (Figure 1). In our opinion, the CTDIair-based calculations of effective dose with the ImPACT calculator are better adapted to the characteristics of the specific scanners and are therefore expected to have a higher accuracy compared with the estimation of effective dose using conversion factors. Therefore, effective dose results from the ImPACT calculator were used for subsequent comparisons.

View larger version (11K): [in this window] [in a new window]   Figure 1. Scatterplot of all effective dose values estimated with conversion factors from DLP based on volume CTDI calculationsvs calculation with the ImPACT dose calculator (version 0.99X, 2006) based on normalized CTDIair measurements.

In 2002 a concerted action of the German Roentgen Society, the Federal Office for Radiation Protection and the Association of Manufacturers of Electromedical Equipment conducted a comprehensive dose survey among multislice CT users in Germany [11]. In this survey data on 14 standard and 4 special adult protocols from 113 scanners (55% of the installed base of 207 scanners) were evaluated. Scanner types included 39 2-slice (34.5%), 73 4-slice (64.6%) and one 8-slice scanner (0.9%).

As part of the fifth research framework of the European Commission, a CT Working Group performed a multinational dose survey in eight countries in 2003 [12]. Data on 10 adult and 4 paediatric protocols from 53 hospitals were evaluated and formed the basis for the 2004 Quality Criteria on Multislice CT. Scanner types were not specified but the majority were 4-slice systems. The number of multislice CT scanners per protocol varied between 50% and 70%.

In 2003 a new CT survey was performed in the UK by the National Radiological Protection Board, CT Users Group and ImPACT and laid down in NRPB report W-67 [13]. Detailed data from six adult and six paediatric protocols of 126 scanners at 118 institutions were evaluated, being 26.8% (126/471) of CT scanners in use. Among the multislice scanners were seven 2-slice, 32 4-slice, six 8-slice and two 16-slice scanners.

Statistical analysis
Results of the effective dose calculations are reported as mean±SD of the four scanners evaluated. The two methods of effective dose calculation were analysed for correlation by linear regression. Differences in average effective dose between our measurements and published dose survey results were analysed for significance by two-tailed, paired Student t-tests. To reduce Type I errors in multiple comparisons, a Bonferroni correction (for n = 3 comparisons) was applied. A p-value lower than 0.017 (0.05/3) was considered significant for each comparison to maintain a global 0.05 significance level. As brain CT in the dose surveys was predominantly sequential, brain CT had to be excluded from the significance analysis.

	Results

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The results of the calculations of CTDI free in air and weighted CTDI in PMMA phantoms normalized to 100 mAs for all available tube voltage and slice collimation settings of the four 16-slice scanners are summarized in Tables 1 and 2. Differences in CTDIair data primarily reflect differences in scanner geometry (focus–isocentre distance) and inherent and additional filtration in the centre of the beam (Table 3). Based on these vendor specifications, interpretation is not straightforward, e.g. due to differences in filter materials or measurement conditions. In addition, normalized CTDIw differences are even harder to interpret due to variable shapes of bow-tie filters between scanners while details of these remain confidential.

The results of our CTDIair-ImPACT calculation method and the results of the dose surveys that we compare against are summarized in Table 5. For body CT protocols, differences between our and the mean values of the survey by Brix et al [11] and the MSCT Working Group survey [12] were significant (p = 0.0003 and p = 0.013, respectively). Differences from the mean 4-slice values of the survey by Shrimpton et al [13] did not reach significance (p = 0.069).

Shrimpton et al also evaluated a number of 8+ slice scanners and quoted effective dose values for head (94% axial CT), chest and abdomen of 1.7 mSv, 3.7 mSv and 7.1 mSv, respectively [13]. These data are in good agreement with the average results from our 16-slice protocols.

	Discussion

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With the increasing use of multislice CT, controlling the radiation dose remains an important issue. Radiation dose is best characterized by CTDI DLP and effective dose. It is recommended that protocol optimization of multislice CT is best done by using volume CTDI [15]. The CTDIvol integrates the effect of beam geometry, beam filtration, kVp, mAs, collimation and pitch on dose. Our comparative measurements of CTDIw provide the multislice CT user with tools to compare published protocols of all vendors and adapt them for dose optimization to their own practice [8]. CTDIvol can also be used to approximate effective dose, which is more accurately calculated using CTDIair and calculating software as the CTDIair approach, in combination with organ dose conversion factors and the ImPACT factor, is particular to the scanner used. Our correlation shows that the use of CTDIvol, DLP and conversion factors results in a good approximation of true effective dose.

The data on tube geometry and filtration do not completely explain CTDIair differences between scanners. The factors that influence CTDIair and weighted CTDI are complex, such as dependence of effective tube filtration on tube voltage and differing wedge filter geometries. However for clinical purposes, scanner types that are associated with higher values of (normalized) CTDI do not necessarily show higher effective doses in the protocol calculations.

Radiation dose should always be viewed in relation to image quality. We elected to correlate our dose measurements to dose-optimized protocol suggestions for patients with normal postures provided by the vendors based on experiences from multiple reference sites. These suggestions balance reduced radiation dose with clinically acceptable image quality. We believe that this traditional subjective measure of image quality involving multiple radiologists from different institutions, although imperfect, is justified given the fact that our focus is on average effective dose values for 16-slice CT and not on a detailed scanner comparison. Also, currently no generally accepted objective measure of image quality exists. Our collection of protocol suggestions shows lower settings than in recently published clinical 16-slice protocols [16, 17], which is indicative of the ongoing process of dose reduction efforts. For CT pulmonary angiography, only one protocol recommendation used 100 kV tube voltage that may be used for improved contrast-to-noise ratio of enhanced pulmonary structures at reduced dose [18].

Even though we included the effect of overrange, for chest and abdomen protocols the average 16-slice effective doses in our study were all lower than average values for comparable protocols in all dose surveys under evaluation [11–13]. Most of our 16-slice protocols employ beam widths of 16–24 mm with Z-axis geometric efficiencies of 80–95% [19], improved compared with efficiencies of 70–85% for beam widths of 8–10 mm (4x2–2.5 mm) employed in 4-slice body CT [19, 20]. We found significance between our results and two dose surveys [11, 12], but not with the most recent third dose survey [13]. This is probably due to an ongoing effort for dose reduction since 2001 and the more limited number of protocols that were comparable with that newest study [13]. Also, country of origin plays a role. As already noted in the UNSCEAR 2000 report, average doses in the UK are generally lower than in Germany or southern European countries [21]. For brain CT, the situation was different and our results were lower [11], equal to [12] or higher [13] than average results in the dose surveys. In most dose surveys brain CT was largely sequential, which is associated with lower dose than spiral scanning due to a lack of overrange rotations and penumbra effects. This suggests that 16-slice spiral brain CT can be done at equal dose to 4-slice sequential brain CT.

Our comparison with the surveys by Brix et al [11] and the EC Working Group [12] using mean values averaged over different multislice scanner types may have underestimated the real differences from 4-slice scanners. For instance, Brix et al [11] noted that 4-slice units showed significantly higher volume CTDI, DLP and effective doses than their 2-slice counterparts. The graphs in their report show that 4-slice DLP per series was 20%, 50% and 65% higher than the study average for brain, liver and pulmonary angiography, respectively. Cohnen et al also performed phantom dose measurements of several protocols on a Siemens 4-slice system [22]. They found average calculated effective dose values for routine chest and abdomen protocols of 12.5 mSv and 12.3 mSv, respectively, which are 3.0 and 1.7 times higher than our Siemens 16-slice values. Especially their high values in chest CT are due to the use of 140 kV tube voltage and a relatively long scan length.

Four-slice CT may be viewed as an early generation of multislice CT in which scanner designs and scan protocol implementation may not have been optimally suited for efficient use of the radiation given to the patient. This has improved in 16-slice CT and given the fact that we included the effect of overrange and taking the limitations of our study design mentioned below into consideration, we think that compared with earlier dose survey results a dose reduction for 16-slice body CT exams in the order of 5–15% would be feasible. With proper optimization, reference effective doses in the order of 1.5–2.3 mSv for spiral brain CT, 3.5–4.0 mSv for chest CT, 3.0–3.5 mSv for CTPA, 6.0–8.0 mSv for abdominal CT and 9.0–11.5 mSv for biphasic liver CT should be routinely possible in average-sized patients while maintaining clinically acceptable image quality. That this is feasible is supported by the 8+ slice data from the dose survey from the UK [13].

There are limitations to our study design. First, our detailed CTDI measurements were performed in only one institution per vendor. Practical issues prevented us from performing the same extensive measurements at multiple different sites for each vendor. However, comparison of our CTDI with data from ImPACT showed consistency with variations within 10% in almost all cases. Nevertheless, newer dose surveys focusing on 16-slice CT in actual clinical practice for corroboration of our data are eagerly awaited. Second, our dose calculations with strictly defined, optimized protocol suggestions were correlated with published dose surveys averaging many different techniques. It is known from dose surveys and other studies [11–13, 23] that important variations in dose values exist between institutions. However, by using mean dose values and where possible comparable mean scan lengths in the comparisons the effect of these variations was minimized as much as possible. Proper feedback, increased education and application of reference dose levels will be important tools to further reduce such institutional differences [11, 24, 25]. Also, only a limited number of protocols could be included in the comparisons, thereby limiting statistical power. Third, our protocol suggestions only apply to patients with normal postures (or normal body mass indices) and our data do not take into account necessary adaptations of scanning parameters to the patient physique. Other phantoms needed for such an evaluation have not been generally validated and adaptation to patient physique per se will not be different with dose-optimized compared with non-optimized scanning protocols. Also, some of our protocol suggestions show variability based on country of origin or have been optimized in more or less obese populations, but this will make our average values even more representative of clinical practice. Finally, in our protocol suggestions we did not take newer dose reduction features like adaptive data filtering or dose modulation techniques into account in order to get a fair comparison. Three-dimensional data filtering can effectively reduce noise especially in difficult regions like the shoulders and hips, as shown by Kachelriess et al [26] and Kalra et al [27]. Angular or longitudinal dose modulation software (or combinations thereof) varies tube current according to online attenuation measurements or information from scanned projection radiographs. Studies by Greess et al [28] and Kalra et al [29] indicate that significant dose reductions equal to or better than our results were possible when compared with conventional scanning techniques. As the conventional protocols were often not fully optimized for dose, early results may have been optimistic. As pointed out by Tack et al [30], initial decreased presets such as used in our suggestions should be the primary dose reduction tool, and dose modulation may serve in addition to improve image quality or further reduce patient dose.

In conclusion, our comparative dose measurements provide CTDI data for protocol comparisons between scanners and to aid optimization. The dose calculations and comparisons demonstrate that, with proper parameter optimization in 16-slice CT, equal to lower effective doses in examinations of the chest and abdomen can be achieved in comparison with 4-slice scanners. In the brain, dose can remain stable even though spiral scanning will be employed more often. Further dose reductions or improved image quality may be achieved with carefully controlled implementation of dose modulation and raw data filtering techniques.

	Acknowledgments

 
We thank Ms Esther van Schrojenstein Lantman (MSc PDeng), medical physicist in-training at the Elkerliek Hospital in Helmond, the Netherlands, and Ms Jannie van den Tillaart (MSc, PDeng), medical physicist in-training at the Maxima Medical Center in Veldhoven, the Netherlands for their help in the acquisition of the data.

Received for publication January 20, 2006. Revision received July 6, 2006. Accepted for publication August 1, 2006.

	References

Top Abstract Introduction Materials and methods Results Discussion References

 

1. Flohr T, Stierstorfer K, Ulzheimer S, Bruder H, Primak AN, McCollough CH. Image reconstruction and image quality evaluation for a 64-slice CT scanner with z-flying focal spot. Med Phys 2005;32:2536–47.[CrossRef][Medline]
2. IMV Market Statistics CT Census 2004. Accessible at: www.auntminnie.com/index.asp?Sec = sup&Sub = bai&Pag = dis&ItemId = 65284. Accessed 28 May 2006
3. Stern SH, Kaczmarek RV, Spelic DC, Suleiman OH. Nationwide evaluation of X-ray trends 2000–2001 survey of patient radiation exposure from CT examinations in the United States. Poster AH-06 presented at the 2002 FDA Science Forum. Accessible at www.cfsan.fda.gov/frf/forum02/a185ah6.htm. Accessed 28 May 2006
4. Frush DP, Applegate K. Computed tomography and radiation: understanding the issues. J Am Coll Radiol 2004;1:113–19.[CrossRef][Medline]
5. Mettler FA, Wiest PW, Locken JA, Kelsey CA. CT scanning: patterns of use and dose. J Radiol Prot 2000;20:353–9.[CrossRef][Medline]
6. Wiest PW, Locken JA, Heintz PH, Mettler FA. CT scanning: a major source of radiation exposure. Semin Ultrasound CT MR 2002;23:402–10.[CrossRef][Medline]
7. Paterson A, Frush DP, Donnelly LF. Helical CT of the body: are settings adjusted for pediatric patients? AJR Am J Roentgenol 2001;176:297–301.[Abstract/Free Full Text]
8. Hamberg LM, Rhea JT, Hunter GJ, Thrall JH. Multidetector row CT: radiation dose characteristics. Radiology 2003;226:762–72.[Abstract/Free Full Text]
9. Jangland L, Sanner E, Persliden J. Dose reduction in computed tomography by individualized scan protocols. Acta Radiol 2004;45:301–7.[CrossRef][Medline]
10. Boone JM, Geraghty EM, Seibert JA. Dose reduction in pediatric CT: a rational approach. Radiology 2003;228:352–60.[Abstract/Free Full Text]
11. 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;13:1979–91.[CrossRef][Medline]
12. MSCT quality criteria for multislice computed tomography Results from a European Concerted Action on CT (FIGM-CT-2000-20078). Appendix B: European field survey on MSCT. Published January 2005. Accessible at: http://www.msct.info/PDF_FILES/Appendix%20Field%20Survey.pdf. Accessed 28 May 2006
13. Shrimpton PC, Hillier MC, Lewis MA, Dunn M. Doses from computed tomography examinations in the UK – 2003 review. Report NRPB-W67. Published March 2005. Accessible at: http://www.hpa.org.uk/radiation/publications/w_series_reports/2005/nrpb_w67.htm Accessed 28 May 2006
14. Van der Molen AJ, Geleijns J. Overranging in multislice CT: quantification and relative contribution to dose – A comparison of four 16-slice CT scanners. Radiology, in press
15. Prokop M. Radiation dose. In: Prokop M, Galanski M, van der Molen AJ, Schaefer-Prokop CM, editors. Spiral and multislice computed tomography of the body. Stuttgart/New York: Thieme Verlag, 2003: 131–60
16. Cademartiri F, Luccichenti G, van der Lugt A, et al. Sixteen-row multislice computed tomography: basic concepts, protocols and enhanced clinical applications. Semin Ultrasound CT MR 2004;25:2–16.[CrossRef][Medline]
17. Kulama E. Scanning protocols for multislice CT scanners. Br J Radiol 2004;77 (Special Issue):S2–S9.[Abstract/Free Full Text]
18. Sigal-Cinqualbre AB, Hennequin R, Abada HT, et al. Low-kilovoltage multi–detector row chest CT in adults: feasibility and effect on image quality and iodine dose. Radiology 2004;231:169–74.[Abstract/Free Full Text]
19. Platten D, Keat N, Lewis M, Edyvean S. Sixteen slice CT scanner comparison report version 11. MHRA Report 04115. London, UK: ImPACT/MHRA, 2004: 15
20. Platten D, Keat N, Lewis M, Edyvean S. Four slice CT scanner comparison report version 11. MHRA Report 04114. London, UK: ImPACT/MHRA, 2004: 12
21. UNSCEAR. Sources and effects of ionizing radiation. UNSCEAR 2000 report to the General Assembly, with scientific annex. Vol. I: Sources, Annex D. New York: United Nations, 2000
22. Cohnen M, Poll LW, Puettmann C, Ewen K, Saleh A, Mödder U. Effective doses in standard protocols for multislice CT scanning. Eur Radiol 2003;13:1148–53.[Medline]
23. Koller CJ, Eatough JP, Bettridge A. Variations in radiation dose between the same model of multislice CT scanner at different hospitals. Br J Radiol 2003;76:798–802.[Abstract/Free Full Text]
24. Clarke J, Cranley K, Robinson J, et al. Application of draft European Commission reference levels to a regional CT dose survey. Br J Radiol 2000;73:43–50.[Abstract]
25. Donelly LF. Reducing radiation dose associated with pediatric CT by decreasing unnecessary examinations. AJR Am J Roentgenol 2005;184:655–7.[Free Full Text]
26. Kachelriess M, Watzke O, Kalender WA. Generalized multi-dimensional adaptive filtering for conventional and spiral single-slice, multi-slice, and cone-beam CT. Med Phys 2001;28:475–90.[CrossRef][Medline]
27. Kalra MK, Maher MM, Sahani DV, et al. Low-dose CT of the abdomen: evaluation of image improvement with use of noise reduction filters – pilot study. Radiology 2003;228:251–6.[Abstract/Free Full Text]
28. Greess H, Lutze J, Nömayr A, et al. Dose reduction in subsecond multislice spiral CT examination of children by online tube current modulation. Eur Radiol 2004;14:995–9.[CrossRef][Medline]
29. Kalra MK, Maher MM, Kamath RS, et al. Sixteen-detector row CT of abdomen and pelvis: study for optimization of z-axis modulation technique performed in 153 patients. Radiology 2004;233:241–9.[Abstract/Free Full Text]
30. Tack D, De Maertelaer V, Gevenois PA. Dose reduction in multidetector CT using attenuation-based online tube current modulation. AJR Am J Roentgenol 2003;181:331–4.[Abstract/Free Full Text]

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