Abstract

OBJECTIVE. This article aims to summarize the available data on reducing radiation dose exposure in routine chest CT protocols. First, the general aspects of radiation dose in CT and radiation risk are discussed, followed by the effect of changing parameters on image quality. Finally, the results of previous radiation dose reduction studies are reviewed, and important information contributing to radiation dose reduction will be shared.
CONCLUSION. A variety of methods and techniques for radiation dose reduction should be used to ensure that radiation exposure is kept as low as is reasonably achievable.

Introduction

CT is a powerful tool for the examination of chest disease because it can depict the disease process far more clearly than chest radiographs. Technical developments in CT scanners have enabled larger volume coverage with higher resolution and lower noise, but this has led to increased radiation exposure [14]. Studies in the United States, United Kingdom, Germany, and Japan have shown approximately twofold increases in the number of CT examinations performed between the late 1980s and the early 2000s [58]. The contribution of CT examinations to the collective dose from diagnostic radiation exposure is estimated to be 67% in the United States and 47% in the United Kingdom [5, 9]. Currently, the issue of radiation dose reduction draws wide attention. However, application of reduced-dose CT techniques in clinical practice varies among institutions [10, 11], which illustrates the lack of a standard protocol for effectively reducing radiation dose to patients in clinical settings.
The objective of this article is to present the available data on reducing radiation dose exposure in routine chest CT protocols. First, important aspects of radiation dose in CT will be discussed, followed by a review of previous studies of CT radiation dose reduction. Finally, important techniques and factors that contribute to radiation dose reduction in CT will be outlined.

Radiation Dose Issues in CT

Several points must be considered regarding CT radiation dose. First, there is an argument that radiation exposure in medical imaging has a significant impact on cancer risk related to radiation exposure. It is reported that exposure to ionizing radiation during diagnostic imaging may be responsible for 0.6–3.2% of malignant tumors in 15 developed countries [12], and CT examinations are responsible for most of the collective patient dose. Note, however, that the increased risk of malignancy related to radiation exposure is based on estimates derived from mathematic models and not on true epidemiologic proof that diagnostic radiation caused malignancy. Some argue that the method used by Berrington de Gonzalez and Darby [12] overestimates the mortality risk related to diagnostic radiology [13].
Second, a large variation in CT scanning parameters and radiation dose exists in chest CT [1417]. According to Diederich and Lenzen [17], tube voltage for typical standard chest CT protocols ranged from 120 to 140 kVp and current–time product (mAs) ranged from 100 to 533 mAs. These facts mean that there is large variation in scanning parameters and consequently in the patient dose delivered in chest CT.
Finally, we must understand correctly that CT examinations involve much more radiation exposure than radiographic examinations. Unfortunately, both patients and physicians often do not have correct knowledge about the radiation exposure caused by CT examinations [18, 19]. Lee et al. [19] showed that all patients and more than 70% of physicians in the emergency department underestimated the radiation dose in one abdominal CT examination (equivalent of 100–250 chest radiographs).
Fig. 1A 62-year-old man with pleural effusion. Standard-dose (A, 150 mA) and reduced-dose (B, 50 mA) CT images at same level. In 50-mA image, increased mottles and black streaks over mediastinum and soft tissues on right lung are noticeable. SD of CT attenuation in region of interest measured on ascending aorta (20 × 20 pixels) was 8.3 H for 150-mA image and 13.9 H for 50-mAs image.
Fig. 1B 62-year-old man with pleural effusion. Standard-dose (A, 150 mA) and reduced-dose (B, 50 mA) CT images at same level. In 50-mA image, increased mottles and black streaks over mediastinum and soft tissues on right lung are noticeable. SD of CT attenuation in region of interest measured on ascending aorta (20 × 20 pixels) was 8.3 H for 150-mA image and 13.9 H for 50-mAs image.

General Strategy for Radiation Dose Reduction in CT Examinations

Because radiation dose is determined by many factors [20, 21], there are various ways to reduce the radiation dose in chest CT. CT scanning parameters that can be changed in clinical practice are summarized in Appendix 1. Lowering tube current or tube voltage is the most direct way of achieving radiation dose reduction. Because tube current is easier to modify and the result is more predictable, modification of tube current is most widely used. Tube voltage reduction is particularly useful when patient body diameter is small or when the contrast of target objects is high. Higher helical pitch can contribute to radiation dose reduction by reducing exposure time, although the effect on image quality depends on the type of scanner used. In axial scans, radiation dose is closely related to section thickness and section spacing. Individualization of scanning parameters can also reduce radiation dose through optimization of dose because patient size varies greatly. This is most important to avoid overexposure in the examinations of children and small adults [22].
The advent of automatic exposure control for CT scanners has eased the task of scanning parameter individualization and enabled dynamic modulation of tube current [23]. Some image processing parameters that have a primary effect on image quality can also have an influence on radiation dose. The use of reconstruction algorithms and image filters can change the radiation dose needed to obtain clinically acceptable CT images.
Needless to say, radiation dose reduction should be attained without deterioration in the quality of the examination. In general, image noise is inversely proportional to the square root of the radiation dose (Fig. 1A, 1B). Consequently, reduced-dose CT images have a higher noise level than standard-dose CT images, and care must be exercised to ensure that the former remain suitable for diagnosis. Direct comparison between reduced-dose and standard-dose CT images of the same patient may address this issue. Comparisons of image quality or diagnostic results between standard-dose and reduced-dose CT images have been performed to investigate the feasibility of reduced-dose CT protocols.

Reduction of Tube Current

Modification of tube current is the simplest method of radiation dose reduction and has been a mainstay of radiation dose-reduction methods. Assessment of image quality in reduced-dose CT has been reported in several articles [2428] (Table 1). Overall impression of image quality, visualization of structures in the lung, level of noise (grainy or mottled), and severity of artifacts are assessed with scores and compared between reduced-dose and standard-dose CT images. The results of the studies indicate that current–time product can be reduced (from the typical 200 mAs) to 110–140 mAs without significant degradation of image quality [2527]. In one article, standard-dose CT images obtained at 400 mAs were compared with reduced-dose CT images obtained at 200, 140, 80, and 20 mAs [25]. The images obtained at 200 and 140 mAs showed no significant difference in quality compared with standard-dose CT images. In another study, comparison of images obtained with 40–280 mAs was performed in terms of perceived level of mottle [26]. The authors concluded that the dose could be reduced to 120 mAs without compromising image quality.
TABLE 1: Studies Evaluating Image Quality of CT Examinations with Reduced Tube Current
StudyYearNo. of PatientsStandard Current—Time Product (mAs)Reduced Current—Time Product (mAs)Peak Kilovoltage (kVp)Image Quality CriteriaSmallest Acceptable mAs
Naidich et al. [24]19901228020, 13120Identification of structures13
Mayo et al. [25]199530400200, 140, 80, 20120Overall140
Ravenel et al. [26]200110280220, 160, 120, 80, 40120Level of mottle120
Prasad et al. [27]200224220-280110-140140Normal structures (noise, contrast, and visibility)110-140
Zhu et al. [32]
2004
60
115
40, 25, 15, 7.5
120
Artifacts
25
These results suggest that a higher tube current–time product beyond the 110- to 140-mAs range will not translate into significant improvement of perceived image quality, although image noise will decrease further as radiation dose increases. Therefore, current–time product above the 110- to 140-mAs range may be unnecessary for routine chest CT. Most studies of reduced-dose CT below this mAs level have shown that the perceived image quality of reduced-dose CT is less than that of standard-dose CT [25, 2831], although some studies cited much lower acceptable mAs values [24, 32, 33]. These discrepant results most likely originate from differences in scoring criteria, which is the major limitation of studies using qualitative image analysis.

Assessment of Diagnostic Quality

Comparison of diagnostic results between standard-dose CT images and reduced-dose CT images has also been used to evaluate the diagnostic quality of reduced-dose chest CT images. Clinically speaking, diagnostic quality is more important than image quality in itself; as long as we can reach the same diagnosis with both standard-dose and reduced-dose CT images—even if the quality of reduced-dose CT image appears inferior.
Evaluation of the diagnostic quality of reduced-dose CT in general has been attempted [25, 28, 31]. Two studies showed no statistically significant difference in the detection of abnormalities between standard-dose and reduced-dose CT [25, 28]. On the other hand, one article suggested decreased diagnostic quality of reduced-dose CT [31]. In this study, 150 series of images obtained with a standard protocol of 200–320 mAs at 120 kVp were compared with simulated low-dose images (40 and 100 mAs) [31]. The authors concluded that both 40- and 100-mAs images had significantly lower detectability of lesions than standard-dose CT. Clearly, no consensus exists regarding minimal clinically acceptable scanning parameters for chest CT in general, which complicates clinical implementation of radiation dose reduction in chest CT examinations.

Evaluation of Diagnostic Quality for Pulmonary Nodule Detection

There is an alternative approach to evaluating diagnostic quality of reduced-dose CT images. Assessments of diagnostic quality of reduced-dose CT images for specific clinical indications have been undertaken by many groups, particularly detection of nodules in low-dose CT [3442] (Table 2). These studies suggest that a current–time product of 50–20 mAs was sufficient for the detection of pulmonary nodules [3438]. Most lung cancer screening programs using CT use a tube current–time product in this range [4349]. More aggressive reduction of radiation dose down to 5 and 6 mAs was also investigated with favorable results [39, 40]. However, very low mAs settings should be used cautiously because there have been reports of decreased nodule detectability in images obtained with less than 20 mAs of current–time product [41, 42].
TABLE 2: Studies of CT Examinations with Reduced Tube Current–Time Product for Pulmonary Nodules
StudyYearNo. of PatientsStandard Current—Time Product (mAs)Reduced Current—Time Product (mAs)Peak Kilovoltage (kVp)Smallest Acceptable mAsComments
Rusinek et al. [34]1998182002012020 
Gartenschlager et al. [35]1998712003012030 
Diederich et al. [36]1999801002512025 
Nitta et al. [39]1999565061206 
Itoh et al. [41]2000306-5012020 
Karabulut et al. [37]2002252005012050 
Hetmaniak et al. [42]20035825030, 1012030 
Weng et al. [38]20043013043120 or 140a43Metastatic lung tumor
Gergely et al. [40]
2005
72
150
5
120
5

Note—Dash = not applicable for this reference.
a
For kVp, 120 kVp was used for standard mAs (130 mAs) and 140 kVp was used in conjunction with reduced mAs (43 mAs).

Radiation Dose Reduction in the Evaluation of Pulmonary Embolism

Pulmonary embolism is a major health problem that is estimated to affect 575,000 patients in the United States each year [50]. CT pulmonary angiography (CTPA) has a high negative predictive value for pulmonary embolism and is replacing pulmonary angiography [51, 52]. The number of CTPA examinations has increased because of its noninvasiveness and ready availability, but the rate of positive CTPA examinations has reportedly diminished to 5.7% in 2003 [53]. In other words, detection of one pulmonary embolism takes approximately 17 times more CTPA examinations with negative findings, thereby inflating the cost of radiation exposure for the diagnosis of pulmonary embolism. Radiation dose reduction in examinations for possible pulmonary embolism cases is therefore important. Tack et al. [54] reported that images produced with 17.5 effective mAs were sufficient for the detection of pulmonary emboli. They compared image quality and radiation dose between a standard-dose protocol (140 kVp and 175 mAs) and a low-dose protocol (100 kVp and 125 mAs). They showed that a radiation dose reduction of 67% was achieved and depiction of peripheral pulmonary artery was improved [55]. From these results, there seems to be room for radiation dose reduction in CTPA, although it remains to be seen whether the low tube voltage protocol is applicable to large patients.

Reduced-Dose CT for Other Clinical Indications

Applications of reduced-dose CT for specific clinical indications other than detection of pulmonary nodules have also been reported (Table 3). Reduced-dose CT was reported to be useful in follow-up chest CT of oncology patients [30, 56]. Yamada et al. [30] noted no difference in terms of detectability of abnormal findings between standard-dose (140 kVp, 96 mAs) and low-dose (140 kVp, 45 mAs) CT images. Chiu et al. [56] found almost perfect concordance in image interpretation between standard-dose (120 kVp, 240 mAs with contrast enhancement) and reduced-dose (140 kVp, 43 mAs without contrast enhancement) CT. Dinkel et al. [29] investigated CT in follow-up studies of lymphomas and extrapulmonary primary tumors using a low-dose protocol (15 mAs at 120 kVp) and a standard-dose protocol (150 mAs at 120 kVp). Although disease conspicuity decreased in the lung apex and mediastinum, detectability of lesions was not affected in the reduced-dose CT images.
TABLE 3: Studies of CT Examinations with Reduced Tube Current–Time Product for Specific Clinical Indications Other Than Pulmonary Nodules
StudyYearIndicationsNo. of PatientsStandard Current—Time Product (mAs)Reduced Current—Time Product (mAs)Peak Kilovoltage (kVp)Smallest Acceptable mAs
Follow-up of malignant disease       
    Chiu et al. [56]2003Lung cancer3024043120/140 (standard/reduced)43
    Dinkel et al. [29]2003Lymphoma and extrathoracic malignancy401501512015
    Yamada et al. [30]2004 20964514045
Bronchiectasis       
    Jung et al. [60]2000 52170 (1 mm thick)40 (2 mm thick)12040
    Yi et al. [61]2003 20170a70a12070
Emphysema       
    Zompatori et al. [58]2002 184819212048
    Zaporozhan et al. [59]2006 3015010-100b12030-50
Other indications       
    Remy-Jardin et al. [57]2004Asbestosis8360-100 (1 mm thick)60-100 (5 mm thick)140/120 (standard/reduced)60-100
    Coppenrath et al. [33]2004Follow-up of nonmalignant disease411708014080
    Tack et al. [54]
2005
Pulmonary emboli
21
157.5c
17.5-105d
120
17.5
a
mA (mAs not specified).
b
Simulated reduced dose images.
c
90 effective mAs (pitch, 1.75).
d
Simulated reduced dose images, 10-60 effective mAs (pitch, 1.75).
There have also been reports of successful application of reduced-dose CT for evaluation of asbestosis [57], emphysema [58, 59], bronchiectasis [60, 61], and pulmonary embolism [54], citing a current–time product of 17.5–70 mAs as an adequate parameter for these indications.

Reduction of Tube Voltage

Tube voltage (peak kilovoltage) reduction is used less frequently than tube current modification because there are some limitations. Tube voltage changes are limited; usually, users can select from several preset peak kilovoltages (typically 80, 90/100, 120, or 135/140 kVp). Delicate adjustment of radiation dose cannot be achieved through manipulation of peak kilovoltage. Substantial decrease in radiation dose can occur by selecting a lower tube voltage setting. For example, 17% peak kilovoltage reduction from 120 to 100 kVp will result in a greater than 30% dose reduction [21] because radiation dose is proportional to peak kilovoltage to the power of more than 2 [62]. Moreover, a large decrease in radiation dose is inevitably accompanied by a considerable increase in image noise that can necessitate a compensatory increase in tube current. Reduction of peak kilovoltage from 120 to 80 kVp requires an almost fourfold increase in tube current to keep image noise constant [63]. Therefore, modifications of two factors (kVp and mAs) are usually involved in tube voltage reduction.
Fig. 2 Effect of helical pitch on radiation dose. A and B, Schematic presentations of scanning with standard (A) and high-pitch (×2) (B) protocols. Total scanning time (i.e., exposure time) for high-pitch protocol is half that of standard protocol. Consequently, total radiation dose will be halved in high-pitch protocol and tube current will be kept constant.
Despite these limitations, tube voltage reduction may be useful for selected applications. Decreased beam energy augments contrast created with the injection of iodine-containing contrast media because of the K-absorption edge of the iodine [64]. For contrast-enhanced chest CT, a reduced-dose protocol using a low tube voltage (80 kVp and 135 or 180 mAs) has been reported to compare favorably with standard-dose protocol (120 kVp and 90 mAs) [65]. Radiation dose was estimated to be reduced 56% and 41% with these two low-tube-voltage protocols. A recent study showed that pulmonary CT angiography performed with 100 kVp showed improved visualization of subsegmental arteries while radiation dose to the patient decreased significantly [55]. Reduced peak kilovoltage contrast-enhanced CT has also been applied to abdominal CT examinations [66, 67].
Low tube-voltage radiography may be useful for the detection of calcified tissue. One group of investigators reported a 57% dose reduction using 80 kVp instead of 120 kVp with almost the same accuracy of calcium detection [68].
Dion et al. [69] applied a low-tube-voltage protocol (100 kVp, 200 mAs) to examine smaller (< 55 kg) adult patients and showed image quality comparable to that of standard-voltage (120 kVp, 200 mAs) images and reduced-tube-current (120 kVp, 100 mAs) images. Tube voltage reduction may be applied to small adult patients and children.
Fig. 3 Functions of automatic exposure control. A, Exposure adjustment to overall size of patient's body. B, Modulation of z-axis: tube current occurs between rotations as patient couch moves. C, In angular modulation, tube current is modulated during one tube rotation to account for attenuation inconsistencies at different angles of gantry rotation. θ = location of X-ray tube in gantry measured as angle from arbitrary place.

Helical Pitch

Helical pitch (beam pitch) is defined as table increment (table feed) per gantry rotation divided by the X-ray beam width [70]. In principle, raising the pitch shortens the total scanning time and consequently decreases the radiation dose, which is inversely proportional to pitch [71] (Fig. 2). However, the implication of helical pitch modification is not the same for single-detector CT and MDCT scanners. Because image noise stays constant, change to a higher helical pitch in single-detector CT can be used as a method for radiation dose reduction, especially in pediatric CT examinations in which reduction of total scanning time is also beneficial [72, 73]. On the other hand, on MDCT scanners, higher pitch generally leads to increased noise. In fact, some CT scanner models compensate automatically for the increase in noise by increasing current–time product [74]. Therefore, increasing pitch is not a practical method of radiation dose reduction, at least not in MDCT.

Length of Scan

The longitudinal length of the scan should be kept to a minimum because total radiation dose (CTDIDLP: dose–length product) delivered to the patient increases linearly as total scan length is increased. Inclusion of upper abdominal and supraclavicular regions in the chest CT protocol would be meaningful for patients with malignant disease because these areas may harbor metastatic lesions. However, in examinations of noncancer patients, obtaining extra scans outside the lung should be avoided because they will lead to significant increases in radiation dose without resulting in clinically relevant information [75].

Individualization of Scanning Parameters

Image quality depends largely on the size of the patient. Therefore, application of a single protocol is inherently inefficient. Large patients will have images of poor quality and small patients will have excessive exposure to radiation. Therefore, scanning parameters must be adjusted according to body size. Methods of parameter adjustment have been studied by several groups [7682]. These studies suggest that body weight is the best index of body size for parameter adjustments. A linear formula balancing tube current and body weight has been proposed to obtain consistent image quality [76, 80]. Body circumference has also been reported to be a useful guide for scanning parameter modification [63].

Automatic Exposure Control

Automatic exposure control, which has been an essential function in conventional radiography systems, is now becoming an important function in CT scanners [23]. The automatic exposure system in CT scanners essentially provides programmed dynamic adjustment of the tube current. Tube current is adjusted to achieve consistent image quality between patients and within a single patient. Because CT images are degraded by underexposure but not by overexposure, there is a strong tendency toward overexposure. Therefore, automatic exposure control can contribute to dose reduction in CT examinations, although it can increase radiation dose in large patients who would suffer underexposure with a standard protocol.
Three types of automatic exposure control work on different levels (Fig. 3): exposure adjustment to the overall size of the patient's body, exposure adjustment along the craniocaudal axis of the patient (z-axis modulation), and exposure adjustment during gantry rotation (angular modulation). Usually, scan projection radiographs (also variously known as Scanogram [Toshiba], ScoutView [General Electric], Topogram [Siemens Medical Solutions], Surview [Philips Medical Systems], and so forth) are obtained in one or two projections to estimate the attenuation value of the patient, which is used to adjust tube current. Adjustment to the overall size of the patient is made to diminish the difference in noise among patients of different body sizes, thus contributing to individualization of the tube current. Modulation of the z-axis enables variable tube currents between rotations as the patient couch moves so that each axial slice has almost constant mean image noise. Angular modulation adjusts tube current in one tube rotation to account for attenuation inconsistencies at different angles of gantry rotation. To use automatic exposure control, users specify parameters such as “noise index,” “reference mAs,” or “reference image” to obtain images of desired quality, instead of setting actual current–time product.
Automatic exposure control techniques have been shown to be effective in radiation dose reduction [8388]. For chest CT examinations, a 22% radiation dose reduction was reported with angular modulation [85], and a 26% radiation dose reduction was reported with z-axis modulation [88], without significant changes in image quality.
Users of automatic exposure control should remember that target image quality must be selected by users. If the user-specified image quality setting is higher than is actually needed, overexposure to the patient ensues as a result of increased X-ray output by the scanner. Dose reduction with automatic exposure control is achieved only when the user selects the image quality appropriate to the clinical purpose of the examination.

Imaging Filters

Imaging filters are software applications designed to improve image quality by removing noise and artifacts. When filters work effectively, it is possible to reduce radiation dose without affecting image quality. There are two types of imaging filters: spatial domain filters, which manipulate data in the reconstructed images, and raw-data based filters, which modulate the data in raw-data (projection-data) domain before reconstruction. Kalra et al. [89] used six spatial domain–based filters for reduced-dose chest CT images and showed that for all filters, improved noise level was achieved at the cost of loss of sharpness. Therefore, these filters will be applicable to images reconstructed for soft-tissue interpretation when sharpness of images is not critical, although the role of the filters is limited for lung parenchymal interpretation because of loss of image sharpness.
Application of raw-data-based filters to reduced-dose chest CT has also been reported [90, 91]. The advantage of this type of filter is less degradation of spatial resolution, which is important in diagnosis of lung parenchyma [91]. Raw-data-based filtering seems to contribute to dose reduction by suppressing the streak artifacts that can be prominent in reduced-dose CT.

Simulation of Reduced-Dose CT Images

Images of reduced-dose CT can be simulated by adding noise to standard-dose CT images [92, 93]. Simulated images can be used to investigate the effect of parameter change in CT examinations without giving additional radiation to the patients. Mayo et al. [92] tested the feasibility of computer-based noise simulation technique, which was subsequently used in a clinical dose reduction study [31]. Simulation techniques were also used for the assessment of reduced-dose pulmonary arteriograms for the evaluation of pulmonary embolism [54] and emphysema [59]. Dose simulation technique is also useful in user education of the CT scanners, making selection of the parameters easier.

Conclusion and Future Directions

In this article, we covered topics radiologists must know in order to reduce radiation dose in chest CT. Because this review is not intended to be a systemic review of the topic, the references cited in this article may not reflect all issues related to radiation dose of chest CT. Readers are advised to refer to other articles for comprehensive coverage of the issue of radiation dose in CT [1, 2, 4].
Because the number of CT examinations is increasing rapidly, radiation dose reduction is a task that needs urgent attention. Radiation dose adjustment according to specific indication of the examination and patient size plays a pivotal role in radiation dose reduction in CT. Appropriate use of reduced-dose protocols for common clinical indications requires further investigation. Automatic exposure control facilitates radiation dose adjustment according to patient size and optimizes radiation dose within a single patient with dynamic tube current adjustment, enabling further reduction of radiation dose. Conceivably, benefits of radiation dose reduction in CT may include the use of saved radiation doseto acquire more information such as organ perfusion or motion analysis with fast volume coverage using MDCT scanners. Radiation dose reduction is key in the pursuit of novel applications of MDCT.
Medical personnel involved in radiologic imaging should be familiar with the variety of methods and techniques for radiation dose reduction to ensure that radiation exposure is kept as low as reasonably achievable.
APPENDIX 1: Operator-Selectable Factors Influencing Radiation Dose in CT Examinations

Factors having a direct effect on radiation dose
    X-ray tube current (milliampere [mA])
    X-ray beam energy (peak kilovoltage [kVp])
    Rotation or exposure time
    Helical pitch [70]
    Section thickness
    Section spacing
    Scan length
    Dose adjustment techniques (automatic exposure control)
Factors having an indirect effect on radiation dose
    Reconstruction algorithms
    Image filters

Acknowledgments

The authors thank Sumiaki Matsumoto and Shiva Gautam for manuscript preparation and Donna Wolfe and Alba Cid for editorial assistance.

Footnote

Address correspondence to H. Hatabu ([email protected]).

References

1.
Kalra MK, Maher MM, Rizzo S, Kanarek D, Shepard JA. Radiation exposure from chest CT: issues and strategies. J Korean Med Sci 2004; 19:159 –166
2.
Tack D, Gevenois PA. Radiation dose in computed tomography of the chest. JBR-BTR 2004; 87:281–288
3.
Maher MM, Kalra MK, Toth TL, Wittram C, Saini S, Shepard J. Application of rational practice and technical advances for optimizing radiation dose for chest CT. J Thorac Imaging 2004; 19:16 –23
4.
Mayo JR, Aldrich J, Muller NL; Fleischner Society. Radiation exposure at chest CT: a statement of the Fleischner Society. Radiology 2003; 228:15–21
5.
Mettler FA Jr, Wiest PW, Locken JA, Kelsey CA. CT scanning: patterns of use and dose. J Radiol Prot 2000; 20:3533 –3559
6.
Stern SH. Nationwide evaluation of X-ray trends (NEXT) survey of tabulation and graphical sum-mary of 2000 computed tomography (CRCPD publication E-07-02). Frankfort, KY: Conference of Radiation Control Program Directors, 2007
7.
BfS (Bundesamt für Strahlenschutz). Unterrichtung durch die Bundesregierung: Umweltradioaktivität und Strahlenbelastung im Jahr 2003 (Parlamentsbericht). Salzgitter, Germany: Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit,2003
8.
Nishizawa K, Matsumoto M, Iwai K, Maruyama T. Survey of CT practice in Japan and collective effective dose estimation [in Japanese]. Nippon Igaku Hoshasen Gakkai Zasshi 2004; 64:151–158
9.
Hart D, Wall BF. UK population dose from medical X-ray examinations. Eur J Radiol 2004; 50:285–291
10.
Karabulut N, Ariyurek M. Low dose CT: practices and strategies of radiologists in university hospitals. Diagn Interv Radiol 2006; 12:3 –8
11.
Galanski M, Nagel HD, Stamm G. CT radiation exposure risk in Germany [in German]. Rofo 2001; 173:R1–R66 (also available at www.tuev-nord.de)
12.
Berrington de Gonzalez A, Darby S. Risk of cancer from diagnostic X-rays: estimates for the UK and 14 other countries. Lancet 2004; 363:345 –351
13.
Herzog P, Rieger CT. Risk of cancer from diagnostic X-rays. Lancet 2004; 363:340 –341
14.
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
15.
McLean D, Malitz N, Lewis S. Survey of effective dose levels from typical paediatric CT protocols. Australas Radiol 2003; 47:135 –142
16.
Moss M, McLean D. Paediatric and adult computed tomography practice and patient dose in Australia. Australas Radiol 2006; 50:33 –40
17.
Diederich S, Lenzen H. Radiation exposure associated with imaging of the chest: comparison of different radiographic and computed tomography techniques. Cancer 2000; 89:2457 –2460
18.
Renston JP, Connors AF Jr, DiMarco AF. Survey of physicians' attitudes about risks and benefits of chest computed tomography. South Med J 1996; 89:1067 –1073
19.
Lee CI, Haims AH, Monico EP, Brink JA, Forman HP. Diagnostic CT scans: assessment of patient, physician, and radiologist awareness of radiation dose and possible risks. Radiology 2004; 231:393 –398
20.
Rothenberg LN, Pentlow KS. Radiation dose in CT. RadioGraphics 1992; 12:1225 –1243
21.
McNitt-Gray MF. AAPM/RSNA physics tutorial for residents: topics in CT—radiation dose in CT. RadioGraphics 2002; 22:1541 –1553
22.
Food and Drug Administration. FDA public health notification: reducing radiation risk from computed tomography for pediatric and small adult patients. Pediatr Radiol 2002; 32:314–316 (also available at www.fda.gov/cdrh/)
23.
Kalra MK, Maher MM, Toth TL, et al. Techniques and applications of automatic tube current modulation for CT. Radiology 2004; 233:649 –657
24.
Naidich DP, Marshall CH, Gribbin C, Arams RS, McCauley DI. Low-dose CT of the lungs: preliminary observations. Radiology 1990; 175:729 –731
25.
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 1995; 164:603–607
26.
Ravenel JG, Scalzetti EM, Huda W, Garrisi W. Radiation exposure and image quality in chest CT examinations. AJR 2001; 177:279 –284
27.
Prasad SR, Wittram C, Shepard JA, McLoud T, Rhea J. Standard-dose and 50%-reduced-dose chest CT: comparing the effect on image quality. AJR 2002; 179:461 –465
28.
Takahashi M, Maguire WM, Ashtari M, et al. Low-dose spiral computed tomography of the thorax: comparison with the standard-dose technique. Invest Radiol 1998; 33:68–73
29.
Dinkel HP, Sonnenschein M, Hoppe H, Vock P. Low-dose multislice CT of the thorax in follow-up of malignant lymphoma and extrapulmonary primary tumors. Eur Radiol 2003; 13:1241 –1249
30.
Yamada T, Ono S, Tsuboi M, et al. Low-dose CT of the thorax in cancer follow-up. Eur J Radiol 2004; 51:169–174
31.
Mayo JR, Kim KI, MacDonald SL, et al. Reduced radiation dose helical chest CT: effect on reader evaluation of structures and lung findings. Radiology 2004; 232:749–756
32.
Zhu X, Yu J, Huang Z. Low-dose chest CT: optimizing radiation protection for patients. AJR 2004; 183:809–816
33.
Coppenrath E, Mueller-Lisse UG, Lechel U, et al. Low-dose spiral CT of the lung in the follow-up of non-malignant lung disease [in German]. Rofo 2004; 176:522 –528
34.
Rusinek H, Naidich DP, McGuinness G, et al. Pulmonary nodule detection: low-dose versus conventional CT. Radiology 1998; 209:243 –249
35.
Gartenschlager M, Schweden F, Gast K, et al. Pulmonary nodules: detection with low-dose vs conventional-dose spiral CT. Eur Radiol 1998; 8:609 –614
36.
Diederich S, Lenzen H, Windmann R, et al. Pulmonary nodules: experimental and clinical studies at low-dose CT. Radiology 1999; 213:289–298
37.
Karabulut N, Toru M, Gelebek V, Gulsun M, Ariyurek OM. Comparison of low-dose and standard-dose helical CT in the evaluation of pulmonary nodules. Eur Radiol 2002; 12:2764 –2769
38.
Weng MJ, Wu MT, Pan HB, Kan YY, Yang CF. The feasibility of low-dose CT for pulmonary metastasis in patients with primary gynecologic malignancy. Clin Imaging 2004; 28:408–414
39.
Nitta N, Takahashi M, Murata K, Morita R. Ultra low-dose helical CT of the chest: evaluation in clinical cases. Radiat Med 1999; 17:1 –7
40.
Gergely I, Neumann C, Reiger F, Dorffner R. Lung nodule detection with ultra-low-dose CT in routine follow-up of cancer patients [in German]. Rofo 2005; 177:1077 –1083
41.
Itoh S, Ikeda M, Arahata S, et al. Lung cancer screening: minimum tube current required for helical CT. Radiology 2000; 215:175 –183
42.
Hetmaniak Y, Bard JJ, Albuisson E, et al. Pulmonary nodules: dosimetric and clinical studies at low dose multidetector CT [in French]. J Radiol 2003; 84:399 –404
43.
Sone S, Li F, Yang ZG, et al. Results of three-year mass screening programme for lung cancer using mobile low-dose spiral computed tomography scanner. Br J Cancer 2001; 84:25–32
44.
Nawa T, Nakagawa T, Kusano S, Kawasaki Y, Sugawara Y, Nakata H. Lung cancer screening using low-dose spiral CT: results of baseline and 1-year follow-up studies. Chest 2002; 122:15–20
45.
Sobue T, Moriyama N, Kaneko M, et al. Screening for lung cancer with low-dose helical computed tomography: anti-lung cancer association project. J Clin Oncol 2002; 20:911–920
46.
Diederich S, Wormanns D, Semik M, et al. Screening for early lung cancer with low-dose spiral CT: prevalence in 817 asymptomatic smokers. Radiology 2002; 222:773–781
47.
Swensen SJ, Jett JR, Hartman TE, et al. Lung cancer screening with CT: Mayo Clinic experience. Radiology 2003; 226:756 –761
48.
Henschke CI, McCauley DI, Yankelevitz DF, et al. Early Lung Cancer Action Project: a summary of the findings on baseline screening. Oncologist 2001; 6:147–152
49.
Garg K, Keith RL, Byers T, et al. Randomized controlled trial with low-dose spiral CT for lung cancer screening: feasibility study and preliminary results. Radiology 2002; 225:506–510
50.
Silverstein MD, Heit JA, Mohr DN, Petterson TM, O'Fallon WM, Melton LJ 3rd. Trends in the incidence of deep vein thrombosis and pulmonary embolism: a 25-year population-based study. Arch Intern Med 1998; 158:585 –593
51.
Schoepf UJ. Diagnosing pulmonary embolism: time to rewrite the textbooks. Int J Cardiovasc Imaging 2005; 21:155–163
52.
Weiss CR, Scatarige JC, Diette GB, Haponik EF, Merriman B, Fishman EK. CT pulmonary angiography is the first-line imaging test for acute pulmonary embolism: a survey of US clinicians. Acad Radiol 2006; 13:434 –446
53.
Prologo JD, Gilkeson RC, Diaz M, Asaad J. CT pulmonary angiography: a comparative analysis of the utilization patterns in emergency department and hospitalized patients between 1998 and 2003. AJR 2004; 183:1093 –1096
54.
Tack D, De Maertelaer V, Petit W, et al. Multi-detector row CT pulmonary angiography: comparison of standard-dose and simulated low-dose techniques. Radiology 2005; 236:318–325
55.
Schueller-Weidekamm C, Schaefer-Prokop CM, Weber M, Herold CJ, Prokop M. CT angiography of pulmonary arteries to detect pulmonary embolism: improvement of vascular enhancement with low kilo-voltage settings. Radiology 2006; 241:899–907
56.
Chiu CH, Chern MS, Wu MH, et al. Usefulness of low-dose spiral CT of the chest in regular follow-up of postoperative non-small cell lung cancer patients: preliminary report. J Thorac Cardiovasc Surg 2003; 125:1300 –1305
57.
Remy-Jardin M, Sobaszek A, Duhamel A, Mastora I, Zanetti C, Remy J. Asbestos-related pleuro-pulmonary diseases: evaluation with low-dose four-detector row spiral CT. Radiology 2004; 233:182 –190
58.
Zompatori M, Fasano L, Mazzoli M, et al. Spiral CT evaluation of pulmonary emphysema using a low-dose technique. Radiol Med (Torino) 2002; 104:13 –24
59.
Zaporozhan J, Ley S, Weinheimer O, et al. Multi-detector CT of the chest: influence of dose onto quantitative evaluation of severe emphysema—a simulation study. J Comput Assist Tomogr 2006; 30:460 –468
60.
Jung KJ, Lee KS, Kim SY, Kim TS, Pyeun YS, Lee JY. Low-dose, volumetric helical CT: image quality, radiation dose, and usefulness for evaluation of bronchiectasis. Invest Radiol 2000; 35:557 –563
61.
Yi CA, Lee KS, Kim TS, Han D, Sung YM, Kim S. Multidetector CT of bronchiectasis: effect of radiation dose on image quality. AJR 2003; 181:501 –505
62.
Hamberg LM, Rhea JT, Hunter GJ, Thrall JH. Multi-detector row CT: radiation dose characteristics. Radiology 2003; 226:762 –772
63.
Nyman U, Ahl TL, Kristiansson M, Nilsson L, Wettemark S. Patient-circumference-adapted dose regulation in body computed tomography: a practical and flexible formula. Acta Radiol 2005; 46:396 –406
64.
Kalva SP, Sahani DV, Hahn PF, Saini S. Using the K-edge to improve contrast conspicuity and to lower radiation dose with a 16-MDCT: a phantom and human study. J Comput Assist Tomogr 2006; 30:391–397
65.
Sigal Cinqualbre AB, Hennequin R, Abada HT, Chen X, Paul JF. Low-kilovoltage multi-detector row chest CT in adults: feasibility and effect on image quality and iodine dose. Radiology 2004; 231:169 –174
66.
Wintersperger B, Jakobs T, Herzog P, et al. Aortoiliac multidetector-row CT angiography with low kV settings: improved vessel enhancement and simultaneous reduction of radiation dose. Eur Radiol 2005; 15:334 –341
67.
Nakayama Y, Awai K, Funama Y, et al. Abdominal CT with low tube voltage: preliminary observations about radiation dose, contrast enhancement, image quality, and noise. Radiology 2005; 237:945–951
68.
Thomas CK, Muhlenbruch G, Wildberger JE, et al. Coronary artery calcium scoring with multislice computed tomography: in vitro assessment of a low tube voltage protocol. Invest Radiol 2006; 41:668 –673
69.
Dion AM, Berger F, Helie O, Ott D, Spiegel A, Cordoliani YS. Dose reduction at abdominal CT imaging: reduced tension (kV) or reduced intensity (mAs)? J Radiol 2004; 85:375–380
70.
Silverman PM, Kalender WA, Hazle JD. Common terminology for single and multislice helical CT. AJR 2001; 176:1135 –1136
71.
Hu H. Multi-slice helical CT: scan and reconstruction. Med Phys 1999; 26:5 –18
72.
Vade A, Demos TC, Olson MC, et al. Evaluation of image quality using 1:1 pitch and 1.5:1 pitch helical CT in children: a comparative study. Pediatr Radiol 1996; 26:891–893
73.
Donnelly LF, Emery KH, Brody AS, et al. Minimizing radiation dose for pediatric body applications of single-detector helical CT: strategies at a large children's hospital. AJR 2001; 176:303–306
74.
Mahesh M, Scatarige JC, Cooper J, Fishman EK. Dose and pitch relationship for a particular multislice CT scanner. AJR 2001; 177:1273 –1275
75.
Campbell J, Kalra MK, Rizzo S, Maher MM, Shepard JA. Scanning beyond anatomic limits of the thorax in chest CT: findings, radiation dose, and automatic tube current modulation. AJR 2005; 185:1525 –1530
76.
Wildberger JE, Mahnken AH, Schmitz Rode T, et al. Individually adapted examination protocols for reduction of radiation exposure in chest CT. Invest Radiol 2001; 36:604–611
77.
Wilting JE, Zwartkruis A, van Leeuwen MS, Timmer J, Kamphuis AG, Feldberg M. A rational approach to dose reduction in CT: individualized scan protocols. Eur Radiol 2001; 11:2627 –2632
78.
Jangland L, Sanner E, Persliden J. Dose reduction in computed tomography by individualized scan protocols. Acta Radiol 2004; 45:301 –307
79.
Jung B, Mahnken AH, Stargardt A, et al. Individually weight-adapted examination protocol in retrospectively ECG-gated MSCT of the heart. Eur Radiol 2003; 13:2560 –2566
80.
Das M, Mahnken AH, Muhlenbruch G, et al. Individually adapted examination protocols for reduction of radiation exposure for 16-MDCT chest examinations. AJR 2005; 184:1437 –1443
81.
Yoshimura N, Sabir A, Kubo T, Lin PJ, Clouse ME, Hatabu H. Correlation between image noise and body weight in coronary CTA with 16-row MDCT. Acad Radiol 2006; 13:324–328
82.
Menke J. Comparison of different body size parameters for individual dose adaptation in body CT of adults. Radiology 2005; 236:565–571
83.
Mulkens TH, Bellinck P, Baeyaert M, et al. Use of an automatic exposure control mechanism for dose optimization in multi-detector row CT examinations: clinical evaluation. Radiology 2005; 237:213 –223
84.
Kazama M, Tsukagoshi S, Okumura M. Image quality improvement and exposure dose reduction with the combined use of X-ray modulation and Boost3D. Proc SPIE Int Soc Opt Eng 2006; 6142:847 –855
85.
Greess H, Wolf H, Baum U, et al. Dose reduction in computed tomography by attenuation-based online modulation of tube current: evaluation of six anatomical regions. Eur Radiol 2000; 10:391 –394
86.
Greess H, Nomayr A, Wolf H, et al. Dose reduction in CT examination of children by an attenuation-based on-line modulation of tube current (CARE dose). Eur Radiol 2002; 12:1571 –1576
87.
Mastora I, Remy-Jardin M, Delannoy V, et al. Multi-detector row spiral CT angiography of the thoracic outlet: dose reduction with anatomically adapted online tube current modulation and preset dose savings. Radiology 2004; 230:116–124
88.
Kalra MK, Rizzo S, Maher MM, et al. Chest CT performed with z-axis modulation: scanning protocol and radiation dose. Radiology 2005; 237:303–308
89.
Kalra MK, Wittram C, Maher MM, et al. Can noise reduction filters improve low-radiation-dose chest CT images? Pilot study. Radiology 2003; 228:257–264
90.
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; 28:475–490
91.
Kubo T, Nishino M, Kino A, et al. 3-Dimensional adaptive raw-data filter: evaluation in low dose chest multidetector-row computed tomography. J Comput Assist Tomogr 2006; 30:933–938
92.
Mayo JR, Whittall KP, Leung AN, et al. Simulated dose reduction in conventional chest CT: validation study. Radiology 1997; 202:453 –457
93.
Britten AJ, Crotty M, Kiremidjian H, Grundy A, Adam EJ. The addition of computer simulated noise to investigate radiation dose and image quality in images with spatial correlation of statistical noise: an example application to X-ray CT of the brain. Br J Radiol 2004; 77:323 –328

Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: 335 - 343
PubMed: 18212218

History

Submitted: May 13, 2007
Accepted: August 15, 2007

Keywords

  1. cancer risk
  2. chest CT
  3. CT
  4. radiation dose
  5. radiation safety

Authors

Affiliations

Takeshi Kubo
Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA.
Present address: Department of Diagnostic Imaging and Nuclear Medicine, Kyoto University, Kyoto, Japan.
Pei-Jan Paul Lin
Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA.
Wolfram Stiller
Department of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
Masaya Takahashi
Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA.
Hans-Ulrich Kauczor
Department of Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
Yoshiharu Ohno
Department of Radiology, Kobe University Graduate School of Medicine, Kobe, Japan.
Hiroto Hatabu
Department of Radiology, Brigham and Women's Hospital, 75 Francis St., Boston, MA 02115.

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