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Published online before print July 12, 2002, 10.1148/radiol.2243010874
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(Radiology 2002;224:905-912.)
© RSNA, 2002

Technical Developments

Lung: Feasibility of a Method for Changing Tube Current during Low-Dose Helical CT1

Shigeki Itoh, MD, Mitsuru Ikeda, MD, Yoshine Mori, MD, Koujiro Suzuki, MD, Akiko Sawaki, MD, Shingo Iwano, MD, Hiroko Satake, MD, Shoji Arahata, MD, Takayuki Isomura, MD, Masahiro Ozaki, B.E. and Takeo Ishigaki, MD

1 From the Departments of Technical Radiology (S. Itoh), Medical Information and Medical Records (M.I.), and Radiology (Y.M., K.S., A.S., S. Iwano, H.S., T. Ishigaki), Nagoya University School of Medicine, Tsumai-cho 65, Showa-ku, Nagoya 466-8560, Japan; Department of Radiology, Komaki City Hospital, Japan (S.A.); Department of Radiology, Hokushin General Hospital, Nakano, Japan (T. Isomura); and Toshiba, Tokyo, Japan (M.O.). Received May 1, 2001; revision requested June 16; final revision received February 14, 2002; accepted March 21. Address correspondence to S. Itoh (e-mail: shigeito@met.nagoya-u.ac.jp).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 Materials and Methods
Results
Discussion
 REFERENCES
 
A method for changing the tube current during helical scanning was applied to low-dose computed tomography (CT) in the lung. The changing method resulted in significant equalization of image noise in various lung sections compared with that at scanning with constant tube current. Detectability of nodules was equivalent between 60 mA and the changing method, whereas degradation occurred at 20 mA. This method seems feasible for the low-dose CT of lung cancer screening.

© RSNA, 2002

Index terms: Cancer screening, 60.12115, 60.32 • Computed tomography (CT), helical, 60.12115 • Computed tomography (CT), image quality, 60.12115 • Lung neoplasms, CT, 60.12115, 60.32 • Lung neoplasms, diagnosis, 60.12115, 60.32


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
Materials and Methods
Results
Discussion
 REFERENCES
 
The most effective treatment for lung cancer is surgical resection. However, since early curable lung cancers usually produce no symptoms and are often missed at chest radiography (1), many tumors are not resectable at the time of diagnosis. Thus, the prognosis is poor. However, because the cure rate for non–small cell lung cancers smaller than 20 mm in diameter has been reported to be greater than 80% (2), earlier and more certain detection with more effective screening methods can be expected to improve the cure rate. Computed tomography (CT) is generally accepted as the most accurate imaging technique for the detection of pulmonary nodules (3). Furthermore, helical CT allows scanning of the entire lung during a single breath hold. Thus, attempts have recently been made to apply helical CT as a primary screening method for lung cancer (4). At most institutions in Japan in the beginning of this project, screening helical CT was performed with scanning parameters of 120 kVp, 50 mA, 1 second per rotation, 10-mm collimation, and a pitch of 2.0 to reduce both the scanning time and the radiation dose. However, since the dose with this method is about 10 times higher than that with conventional chest radiography (4), achievement of a further reduction in radiation dose in helical CT would be desirable.

In CT examinations, reduction of the tube current would result in a proportionate reduction in radiation dose. However, the reduction would also result in the degradation of image quality because noise is inversely proportional to the square root of current. Therefore, optimization of the low-dose CT protocol is important, with the goal of maintaining a level of image quality that is sufficient to depict curable lung cancers while minimizing radiation dose. Achievement of a reduction in radiation dose by using a lower tube current has been attempted (5,6). Results of these studies have demonstrated that, owing to the anatomic characteristics of the lung, the apex and base of the lung require a higher radiation dose to achieve image quality equivalent to that in other regions of the lung (5). Recently, attempts have been made to reduce the dose at CT without sacrificing image quality by reducing the tube current during tube rotation at the angular positions at which the diameter through the patient is smallest (7,8).

On the basis of results in these studies, we speculated that modulation of tube current for each location of the lung was critical in the optimal protocol for low-dose CT of the lung. The purpose of the present study was to establish the feasibility of a method for changing the tube current during helical scanning in low-dose CT for lung cancer screening.


   Materials and Methods
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
Discussion
 REFERENCES
 
Baseline Studies
We developed a prototype method for changing the tube current during helical CT. This method allows performance of helical scanning according to a tube current that is specified for each rotation before scanning. To confirm the changes in tube current, the relative exposure dose and time required for the changes were measured with a scintillation detector (BCF-10; Bicron, Ohio) that was secured at the center of the gantry with supporting bars. The magnitude of the value measured with this method was proportional to the dose; the method allowed us to monitor the value continuously and in real time during scanning (9). For these measurements, scanning was performed with the parameters of 120 kVp, 0.75 second per rotation, and 10-mm collimation. The objective was to change the tube current between 20 and 60 mA.

Clinical Studies
CT acquisition.—The study protocol was approved by the ethics committee of Nagoya University School of Medicine, and informed consent was obtained from all subjects after the purpose and protocol for this study had been fully explained. The study group comprised seven healthy male volunteers (age range, 35–48 years; mean age, 42 years). All volunteers were selected from our colleagues in the radiology department on the basis of the following criteria: (a) age older than 35 years, (b) no medical history of pulmonary disease, and (c) no disease requiring medical treatment. Two authors (S.Itoh, M.I.) ensured that no image depicted an abnormality that interfered with interpretation, such as a nodule greater than 5 mm in diameter.

All images were obtained with a commercially available helical CT scanner (Asteion; Toshiba, Tokyo, Japan) that was equipped with a prototype method for changing the tube current during helical scanning. Helical CT was performed with fixed scanning parameters of 120 kVp, 0.75 second per rotation, 10-mm collimation, and a pitch of 1.5 (table feed rate, 20 mm/sec); the entire lung was scanned during a single breath hold at maximum inspiration. Images were reconstructed at 10-mm intervals with 180° linear interpolation with lung window settings (window width, 1,600 HU; window level, -600 HU). The images in this study were viewed at lung window settings.

In each volunteer, three helical scans were obtained: one at tube current of 60 mA, one at tube current of 20 mA, and one at the tube current set with this method for changing the tube current. With the latter, the following protocol was used. Initially, the craniocaudal dimension of the lung for each volunteer was defined on the basis of a scout scan. The first four rotations (for scanning of the apex of the lung) and the last four rotations (for scanning of the base of the lung) were performed at a tube current of 60 mA; the middle region of the lung was scanned at a tube current 20 mA. In the transitional areas, the tube current was changed to a rate of 10 mA per rotation.

Noise evaluation.—On the basis of findings in previous studies (10,11), we used the SDs of the CT numbers to evaluate image noise. One author (S. Itoh) measured the SD of each CT number with three circular 36-pixel regions of interest at the following levels: (a) the apex of the lung, defined as the first section that contains lung parenchyma; (b) the section that is 20 mm below the apex of the lung; (c) the section that is 40 mm below the apex of the lung; (d) the level of the aortic arch; (e) the level of the bifurcation of the trachea; (f) the level of the right inferior pulmonary vein; (g) the section that is 40 mm above the base of the lung; (h) the section that is 20 mm above the base of the lung; and (i) the base of the lung, defined as the last section that contains lung parenchyma. Noise was evaluated in homogeneous attenuating structures so that the SD of the CT number precisely reflected the image noise. Thus, with a workstation (Alatoview; Toshiba), circular regions of interest were placed over the trachea at the four cranial levels, over the ascending aorta at the bifurcation of the trachea, and over the descending aorta at the four caudal levels, with care taken to minimize partial volume artifacts so that statistical data, including the mean and SD, were available. The following formula was used with the workstation:

where Xi is the CT number in each pixel, Xm is the mean value of Xi in a given region of interest, and n is the number of pixels in a given region of interest.

Two-way analysis of variance was performed to statistically analyze differences in the SDs of the CT numbers. The T2 method of Hochber and Tamhane (12) was used to analyze differences in the means of the SDs of the CT numbers among various sections of the lung. In this two-way analysis of variance, the following variables were used as the two fixed effects: (a) the nine section levels at which the SD was measured and (b) the three scanning conditions with which scanning was performed (tube currents of 60 mA, 20 mA, and values set with this method for changing the tube current). We also performed statistical analysis of the differences in the means of the SDs of the CT numbers among the three scanning conditions in each lung section. Dispersion of the SDs of the CT numbers with each set of scanning conditions was calculated with the following equation:

where SDd is the SD of dispersion, n is the number of regions of interest with each set of scanning conditions, SDi is the SD of the CT numbers measured in a given region of interest, and SDm is the mean value of SDi with each set of scanning conditions. The lower this score, the smaller the difference in the SDs of the CT numbers among various regions of the lung.

In this study, scans for all volunteers underwent collective statistical analysis, to determine whether there were any significant differences among the three scanning conditions in the dispersion of the SDs, by means of one-way analysis of variance. Differences with P < .05 were considered statistically significant.

Simulated nodules.—Computer-generated nodules that were about 7 mm in diameter were synthesized, and these simulated nodules were superimposed over the volunteer images. The superimpositions were performed by adding a nodule mask on the CT number data of original lung images. The radius of each simulated nodule was 6 pixels, and the CT numbers in the nodules were 250 and 80 HU higher than those in lung parenchyma at the center and edge of the nodules, respectively (Fig 1).



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  		Figure 1. Graph of CT numbers of simulated nodules. The radius of each simulated nodule is 6 pixels, and the CT numbers in the nodules are 250 and 80 HU higher than those in lung parenchyma at the center and edge of the nodule, respectively.

 
Seventeen to 19 nodules were added to the images obtained in each examination, and the locations of the nodules were equalized for the following parenchymal regions: (a) level of the nodules, as defined by dividing the scanned images into an upper zone (above the aortic arch), middle zone, and lower zone (below the right inferior pulmonary vein); (b) central or peripheral distribution of the nodules, in which the peripheral lung was defined as the outer 2 cm of lung parenchyma along the chest wall; and (c) ventral or dorsal distribution of the nodules, in which the border was defined as the center of the anteroposterior diameter of the thorax. The simulated nodules were placed at the same positions in each examination performed for the same volunteer to permit the effects of tube current on the images to be evaluated free of any possible effects due to differences in the locations of the nodules.

Image interpretation.—Seven experienced radiologists (Y.M., K.S., A.S., S. Iwano, H.S., S.A., T. Isomura), who were blinded to the scanning parameters used to acquire the CT images, were asked to report the location of each suspected nodule and to estimate and report the probability of the presence of this nodule. A continuous rating scale that ranged from 0 to 1 was used to represent these probability estimates regarding the presence of a nodule: 0 and 1 corresponded to the definite absence and definite presence, respectively, of simulated nodules on the CT images; the rating scales between 0 and 1 indicated intermediate levels of probability. For training before the study began, the observers viewed the sample images and were asked to report the locations of suspected nodules and the probabilities of the presence of the nodules.

To avoid any learning bias, the study was conducted in the following manner. To prevent the readers from learning where the nodules were located, the CT images obtained for the same volunteer were not evaluated successively in the reading order (ie, they were mixed with images from the other volunteers, with six other images interpreted between them). In addition, the reading order differed among the seven readers to compensate for any learning bias in each reader. On the basis of a preliminary study (S.Itoh, unpublished data), the reading time was limited to less than 8 minutes for each examination. This limitation allowed avoidance of the possibility that degradation on the image due to the reduction in tube current could be compensated for by extending the reading time.

Statistical analysis.—Each CT section was divided into eight compartments as follows: (a) right and left lungs, (b) ventral and dorsal, and (c) central and peripheral. Each reader’s judgement regarding the presence of the simulated nodules in each compartment was then based on the Brier score (13–15), which was calculated by using the following equation:

where n is the number of compartments on each image, Pi is the confidence level for the presence of a nodule in each compartment, and Ti is 1 if the compartment contained a simulated nodule or 0 if the compartment did not contain a simulated nodule. The lower this score, the better the reader’s judgement of the presence of a nodule.

All interpretations underwent collective statistical analysis to determine whether there were any significant differences among the three scanning conditions in the detectability of simulated nodules. Detection of nodules was evaluated with the Brier score. Statistical analysis of the differences among the three scanning conditions comprised analysis of variance of pseudovalues of the Brier scores computed by means of the jack-knife analysis method. The influence of the tube current on the detectability of simulated nodules was also analyzed for each zone of the lung. Differences with P < .05 were considered statistically significant.


   Results
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
Discussion
 REFERENCES
 
Baseline Studies
The method for changing the tube current during helical scanning was confirmed to permit the tube current to be precisely changed to match the value specified for each rotation before scanning (Fig 2). A time of 50 msec was needed to change the tube current by 10 mA.



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  		Figure 2a. Measurement of exposure dose. The y axis of the graphs show the relative exposure dose. Tube currents are seen to change between (a) 20 and (b) 60 mA. The tube currents change precisely according to the value specified for each rotation before scanning. A time of 50 msec is needed to change the tube current by 10 mA.

 


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  		Figure 2b. Measurement of exposure dose. The y axis of the graphs show the relative exposure dose. Tube currents are seen to change between (a) 20 and (b) 60 mA. The tube currents change precisely according to the value specified for each rotation before scanning. A time of 50 msec is needed to change the tube current by 10 mA.

 
Clinical Studies
Noise evaluation.—Results for the SDs of CT numbers are summarized in Tables 1–3 and Figures 3 and 4. At tube currents of 60 and 20 mA, the SDs in the two most cranial sections (the apex of the lung and 20 mm below the apex of the lung) and the two most caudal sections (the base of the lung and 20 mm above the base of the lung) were greater and more variable than those in other sections. The bias toward an increase in SD became more pronounced at 20 mA. With the method for changing the tube current during helical scanning, differences in the SDs among various sections of the lung were significantly smaller than those observed at 60 and 20 mA, and the SDs in the four most cranial sections and the three most caudal sections were not significantly different from those at 60 mA.


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  		TABLE 1. SDs of CT Numbers

 

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  		TABLE 2. Statistical Analysis for Differences in SDs of CT Numbers among Lung Sections

 

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  		TABLE 3. Dispersion of SDs of CT Numbers

 


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  		Figure 3. Graph of SDs of CT numbers. At tube currents of 60 and 20 mA, the SDs for the two most cranial sections and the two most caudal sections were greater and more variable than those for other sections, and the bias toward an increase became more pronounced at 20 mA.

 


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  		Figure 4. Graph of dispersion of SDs of CT numbers. With the method for changing the tube current during helical scanning, the difference in the SDs of the CT numbers among various sections of the lung is smaller than that at tube currents of 60 and 20 mA.

 
Nodule detection.—Results for the detectability of simulated nodules are summarized in Figure 5. Detectability of simulated nodules was significantly degraded when the tube current was reduced to 20 mA compared with that at 60 mA. Detectability of nodules with the method for changing the tube current during helical scanning was equivalent to that at 60 mA. In the analysis for each zone of the lung, no significant differences in the detectability of the nodules were seen among the three scanning conditions in the middle zone. In the upper and lower zones of the lung, however, detectability of nodules with the method for changing the tube current was equivalent to that at 60 mA, but the results at 20 mA showed significant degradation (Figs 6, 7).



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  		Figure 5. Graph depicts detectability of simulated nodules. Detectability of simulated nodules at tube current of 20 mA is significantly degraded compared with that at both 60 mA and the values set with the method for changing the tube current during helical scanning. In the middle zone of the lung, no significant differences are seen among the three scanning conditions in the detectability of the nodules. In the upper and lower zones, however, the detectability of nodules with the method for changing the tube current is equivalent to that at 60 mA, but the results at 20 mA show significant degradation.

 


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  		Figure 6. A-C, Upper zone of the lung. D-F, Middle zone of the lung. CT images were acquired in one volunteer at tube currents of 60 mA (A, D), 20 mA (B, E), and with the method for changing the tube current during helical scanning (C, F). Arrows in A and D indicate the simulated nodules. All simulated nodules can be detected in the middle zone, even in E, whereas in B, the nodule is hardly detectable owing to an increase in noise.

 


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  		Figure 7. A-C, Middle zone of the lung. D-F, Lower zone of the lung. CT images were acquired in another volunteer at tube currents of 60 mA (A, D), 20 mA (B, E), and with the method for changing the tube current during helical scanning (C, F). Arrows in A and D indicate the simulated nodules. All simulated nodules can be detected in the middle zone, even in B, whereas in E, the nodule is hardly detectable due to an increase in noise.

 

   Discussion
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
Discussion
REFERENCES
 
To reduce the radiation dose during helical CT for lung cancer screening, use of the lowest possible tube current is desirable. A reduction in tube current results in degradation of image quality due to the increase in noise, however, and some controversy remains concerning the minimum tube current required for CT of the chest (11,16,17). Thus, the limits of low-dose helical CT for lung cancer screening were investigated in the previous study (5). Results of that study showed that, because the apex and base of the lung require a higher radiation dose to achieve an image quality equivalent to that in other locations of the lung due to their anatomic characteristics, the minimum tube current required for helical CT in lung cancer screening differs for various locations in the lung. On the basis of these results, we developed a new method for changing the tube current during helical scanning and have attempted to apply this method to low-dose CT for lung cancer screening.

Haaga et al (18) reported that there appears to be a linear relationship between noise and body size. To assess the effects of tube currents on CT images, without any possible effects of differences among individual subjects, we elected to perform helical CT three times in the volunteers: at tube currents of 60 mA, 20 mA, and with the values set with our method for changing the tube current. Results in previous studies show that computer-generated nodules can be used to assess a large number of imaging variables (17,19,20). Therefore, to assess the image quality more objectively, we electronically superimposed simulated nodules over sets of normal lung CT images and evaluated the diagnostic capabilities for detection of the nodules. The image quality required for lung cancer screening with helical CT is the level needed to allow detection of cancers that can be confidently judged to be curable; such cancers have been reported to have a diameter of less than 15 mm (2) and to show little fibrosis (21). These tumors appear as small focal areas of ground-glass opacity on CT images (22). Therefore, we synthesized computer-generated nodules that were 7 mm in diameter to show ground-glass opacity.

Findings in previous studies demonstrate that the image quality obtained in low-dose CT performed at 50 mA, with 1 second per rotation, and a pitch of 2, is definitely sufficient for the detection of pulmonary nodules (23–25). Furthermore, these scanning parameters have been accepted as the standard in helical CT for lung cancer screening in Japan (4). Thus, in this study, we used scanning parameters of 60 mA, 0.75 second per rotation, and a pitch of 1.5 for comparison, because they allowed us to reduce substantially the radiation dose in the volunteers compared with that at 200 mA. On the basis of results in the previous study with a helical CT scanner with a scanning time of 1 second per rotation (5), the SD of the CT number at 50 mA at the apex and base of the lung is equivalent to that at about 15 mA at other locations in the lung. Therefore, since the scanning time of the CT scanner used in the present study was 0.75 second per rotation, we adopted 60 and 20 mA as the tube currents with which to scan the apex and base of the lung or other locations in the lung, respectively, in the method for changing the tube current during helical scanning.

In the present study, the method for changing the tube current resulted in significant equalization of image noise in various sections of the lung compared with that at scanning with tube currents of 20 and 60 mA and in achievement of a reduction in radiation dose compared with that at a tube current of 60 mA. With regard to detectability of simulated nodules, differences were not significant in the middle zone of the lung between 60 mA, 20 mA, and the values set with the method for changing the tube current. Although detectability of nodules with the method for changing the tube current was equivalent to that at 60 mA in the upper and lower zones of the lung, significant degradation was seen at 20 mA. The main reason for the degradation is that the increase in noise that results from the reduction in tube current is more pronounced at the apex and base of the lung owing to anatomic characteristics of the lung. Diederich et al (25) also reported that low-dose CT performed at 25 mA, with 1 second per rotation, 5-mm collimation, and a pitch of 2, is associated with a significant decrease in the number of nodules 5 mm or smaller that can be detected, possibly owing to artifacts. These results suggest that if we intend to reduce the tube current to less than 20 mA uniformly in the entire lung, the image quality at helical CT will not be acceptable for lung cancer screening at the apex and base of the lung. Furthermore, results of the present study demonstrate that our method for changing the tube current allows this limitation to be overcome. Specifically, this method allows us to maintain an acceptable level of image quality for lung cancer screening in the entire lung while avoiding any unnecessary increase in radiation dose.

One limitation of this method is that scout scanning is required to define the protocol for changing the tube current during helical scanning in each patient. To minimize the radiation dose and reduce the examination time, scout scanning should not be performed with helical CT for lung cancer screening. Instead of performing measurements with scout scanning, Kalender et al (7) and Greess et al (8) developed the technical approach of attenuation-based on-line modulation of tube current for each projection by analyzing CT projection data. We expect that application of this technique may allow determination of the optimal tube current for each section in low-dose CT of the lung without scout scanning.

In the present study, 10-mm collimation and 10-mm reconstruction intervals were used according to the scanning parameters used in screening helical CT at most institutions in Japan (4). Advanced helical CT technology such as half-second rotation and multisection detectors will allow use of thinner collimation and thinner reconstruction intervals. However, if helical CT is performed at the same tube current, use of thinner collimation may result in an increase in noise due to an insufficient dose; the resulting degradation in image quality may be aggravated at the apex and base of the lung in low-dose CT. Therefore, the method for changing the tube current during helical scanning will play a more important role in lung cancer screening when half-second rotation CT and multisection CT are used.

In conclusion, our method for changing the tube current during helical scanning seems feasible in low-dose CT for lung cancer screening.


   FOOTNOTES
 
Author contributions: Guarantors of integrity of entire study, S. Itoh, M.I.; study concepts and design, S. Itoh; literature research, S. Itoh, M.I.; clinical studies, S. Itoh, M.O.; data acquisition, S. Itoh, M.O.; data analysis/interpretation, S. Itoh, Y.M., K.S., A.S., S. Iwano, H.S., S.A., T. Isomura; statistical analysis, M.I.; manuscript preparation, S. Itoh, M.I.; manuscript definition of intellectual content, S. Itoh, M.I., T. Ishigaki; manuscript editing, S. Itoh; manuscript revision/review, S. Itoh, M.I., M.O., T. Ishigaki; manuscript final version approval, all authors.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
Discussion
 REFERENCES
 

  1. Soda H, Tomita H, Kohno S, Oka M. Limitation of annual screening chest radiography for the diagnosis of lung cancer. Cancer 1993; 72:2341-2346.[CrossRef][Medline]
  2. Kurokawa T, Matsuno Y, Noguchi M, Mizuno S, Shimosato Y. Surgically curable "early" adenocarcinoma in the periphery of the lung. Am J Surg Pathol 1994; 18:431-438.[Medline]
  3. Davis ST. CT evaluation for pulmonary metastases in patients with extrathoracic malignancy. Radiology 1991; 180:1-12.[Abstract/Free Full Text]
  4. Kaneko M, Eguchi K, Ohmatsu H, et al. Peripheral lung cancer: screening and detection with low-dose spiral CT versus radiography. Radiology 1996; 201:798-802.[Abstract/Free Full Text]
  5. Itoh S, Ikeda M, Arahata S, et al. Lung cancer screening: minimum tube current required for helical CT. Radiology 2000; 215:175-183.[Abstract/Free Full Text]
  6. Itoh S, Koyama S, Ikeda M, et al. Further reduction of radiation dose in helical CT for lung cancer screening using small tube current and a newly designed filter. J Thorac Imaging 2001; 16:81-88.[CrossRef][Medline]
  7. Kalender WA, Wolf H, Suess C, Gies M, Greess H, Bautz WA. Dose reduction in CT by on-line tube current control: principles and validation on phantoms and cadavers. Eur Radiol 1999; 9:323-328.[CrossRef][Medline]
  8. Greess H, Wolf H, Baum U, et al. Dose reduction in computed tomography by attenuation-based on-line modulation of tube current: evaluation of six anatomical regions. Eur Radiol 2000; 10:391-394.[CrossRef][Medline]
  9. Aoyama T, Koyama S, Maekoshi H. Small scintillation and PIN-photodiode dosimeters for measuring the dose delivered by transmission x-ray computed tomography. KEK Proc 1999; 99:1-8.
  10. Starck G, Lönn L, Cederblad A, Alpsten M, Sjöström L, Ekholm S. Radiation dose reduction in CT: application to tissue area and volume determination. Radiology 1998; 209:397-403.[Abstract/Free Full Text]
  11. Mayo JR, Hartman TE, Lee KS, Primack SL, Vedal S, Müller NL. CT of the chest: minimal tube current required for good image quality with the least radiation dose. AJR Am J Roentgenol 1995; 164:603-607.[Abstract/Free Full Text]
  12. Hochber Y, Tamhane AC. Multiple comparison procedures New York, NY: Wiley, 1987.
  13. Spiegelhalter DJ. Probabilistic prediction in patient management and clinical trials. Stat Med 1986; 5:421-433.[Medline]
  14. Redelmeier DA, Bloch DA, Hickam DH. Assessing predictive accuracy: how to compare Brier score. J Clin Epidemiol 1991; 44:1141-1146.[CrossRef][Medline]
  15. Ikeda M, Itoh S, Ishigaki T, Yamauchi K. Application of resampling techniques to the statistical analysis of the Brier score. Methods Inf Med 2001; 40:259-264.[Medline]
  16. Naidich DP, Marshall CH, Gribbin C, Arams R, McCauley DI. Low-dose CT of the lungs: preliminary observation. Radiology 1990; 175:729-731.[Abstract/Free Full Text]
  17. Henry R, Naidich DP, McGuinness G, et al. Pulmonary nodule detection: low-dose versus conventional CT. Radiology 1998; 209:243-249.[Abstract/Free Full Text]
  18. Haaga JR, Miraldi F, MacIntyre W, LiPuma JP, Bryan PJ, Wiesen E. The effect of mAs variation upon computed tomography image quality as evaluated by in vivo and in vitro studies. Radiology 1981; 138:449-454.[Abstract/Free Full Text]
  19. Naidich DP, Rusinek H, McGuinness G, Leitman B, McCauley DI, Henschke CI. Variable affecting pulmonary detection with computed tomography: evaluation with three-dimensional computer simulation. J Thorac Imaging 1993; 8:291-299.[Medline]
  20. Seltzer SE, Judy PF, Adams DF, et al. Spiral CT of the chest: comparison of cine and film-based viewing. Radiology 1995; 197:73-78.[Abstract/Free Full Text]
  21. Noguchi M, Morikawa A, Kawasaki M, et al. Small adenocarcinoma of the lung: histologic characteristics and prognosis. Cancer 1995; 75:2844-2852.[CrossRef][Medline]
  22. Jang HJ, Lee KS, Kwon OJ, Rhee CH, Shim YM, Han J. Bronchioloalveolar carcinoma: focal area of ground-glass attenuation at thin-section CT as an early sign. Radiology 1996; 199:485-488.[Abstract/Free Full Text]
  23. Mori K. Detection of pulmonary nodules using helical CT. Jpn J Lung Cancer 1995; 35:149-156[Japanese].
  24. Itoh S, Ikeda M, Isomura T, et al. Screening helical CT for mass screening of lung cancer: application of low-dose and single-breath-hold scanning. Radiat Med 1998; 16:75-83.[Medline]
  25. Diederich S, Lenzen H, Windmann R, et al. Pulmonary nodules: experimental and clinical studies at low-dose CT. Radiology 1999; 213:289-298.[Abstract/Free Full Text]



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K Imai, M Ikeda, S Wada, Y Enchi, and T Niimi
Analysis of streak artefacts on CT images using statistics of extremes
Br. J. Radiol., November 1, 2007; 80(959): 911 - 918.
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J. K. Leader, T. E. Warfel, C. R. Fuhrman, S. K. Golla, J. L. Weissfeld, R. S. Avila, W. D. Turner, and B. Zheng
Pulmonary Nodule Detection with Low-Dose CT of the Lung: Agreement Among Radiologists
Am. J. Roentgenol., October 1, 2005; 185(4): 973 - 978.
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G. Iinuma, N. Moriyama, M. Satake, K. Miyakawa, U. Tateishi, N. Uchiyama, T. Akasu, T. Fujii, and T. Kobayashi
Vascular Virtual Endoluminal Visualization of Invasive Colorectal Cancer on MDCT Colonography
Am. J. Roentgenol., April 1, 2005; 184(4): 1194 - 1198.
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D. Tack, V. De Maertelaer, and P. A. Gevenois
Dose Reduction in Multidetector CT Using Attenuation-Based Online Tube Current Modulation
Am. J. Roentgenol., August 1, 2003; 181(2): 331 - 334.
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