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.


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]
40, 25, 15, 7.5
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]

Note—Dash = not applicable for this reference.
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
    Jung et al. [60]2000 52170 (1 mm thick)40 (2 mm thick)12040
    Yi et al. [61]2003 20170a70a12070
    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]
Pulmonary emboli
mA (mAs not specified).
Simulated reduced dose images.
90 effective mAs (pitch, 1.75).
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


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


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


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Information & Authors


Published In

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


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


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



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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