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(Radiology. 2000;217:430-435.)
© RSNA, 2000

Medical Physics

Technique Factors and Image Quality as Functions of Patient Weight at Abdominal CT1

Walter Huda, PhD, Ernest M. Scalzetti, MD and Galina Levin, BS

1 From the Department of Radiology, SUNY Upstate Medical University, 750 E Adams St, Syracuse, NY 13210. Received December 28, 1999; revision requested February 21, 2000; revision received April 18; accepted May 1. Address correspondence to W.H. (e-mail: hudaw@mail.upstate.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
PURPOSE: To investigate how changes in kilovolt peak and milliampere second settings, and patient weight affect transmitted x-ray energy fluence and the image contrast-to-noise ratio (CNR) at abdominal computed tomography (CT).

MATERIALS AND METHODS: Cylinders of water were used as patient models, and x-ray spectra, including x-ray tube potentials of 80–140 kVp, were investigated. The mean photon energy and energy fluence transmitted through water cylinders with varying diameters and the image contrast for fat, muscle, bone, and iodine relative to water were determined. The effect of changing the x-ray tube potential on CNR also was investigated.

RESULTS: At a constant kVp, increasing patient weight from 10 kg to 120 kg reduced the transmitted energy fluence by two orders of magnitude. Changing the x-ray tube potential from 80 kVp to 140 kVp increased the mean photon energy from approximately 52 keV to approximately 72 keV and thus reduced the image contrast relative to water by 12% for muscle, 21% for fat, 39% for bone, and 50% for iodine (approximate reduction values). Increasing the x-ray tube potential from 80 kVp to 140 kVp increased the CNR by a factor of 2.6 for muscle and by a factor of 1.4 for iodine.

CONCLUSION: With changes in patient weight at abdominal CT, x-ray tube potentials must be varied to maintain a constant detector energy fluence. Increasing the x-ray tube potential generally improves CNR.

Index terms: Abdomen, CT, 70.12111 • Dosimetry, 70.12111 • Computed tomography (CT), image quality, 70.12111 • Computed tomography (CT), physics, 70.12111 • Computed tomography (CT), radiation exposure, 70.12111 • Radiations, exposure to patients and personnel


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
In screen-film radiography, a constant exposure is required to generate a satisfactory film density. For example, for a 400-speed screen-film system, an exposure of approximately 0.5 mR (1.3 x 10-7 C kg-1) is required to generate a film density of about 1.4 (1). Any radiation exposure substantially higher or lower will overexpose or underexpose, respectively, the radiograph, with a concomitant reduction in image contrast. On the other hand, the radiation detector used in computed tomography (CT) provides an output signal that can be digitized and stored in a computer. CT detectors can therefore enable one to acquire images with a relatively wide range of exposure levels. For CT image acquisition, the lowest radiation exposure should be larger than the intrinsic detector noise level, and the largest exposure should not exceed the detector saturation level.

The use of a digital detector at CT decouples the typical relationship between radiation exposure and resultant film density encountered at screen-film radiography. At CT, the acquired image data can be modified by using window and level settings to change the gray-scale appearance of the displayed image. Appropriate adjustment of window and level settings should permit the displayed image intensities to be optimal, irrespective of the choice of technique factors used to generate the digital image data. As a result, CT images may be acquired with a wide range of exposure levels without resulting in overexposed or underexposed scans. However, this ability to adjust the image display with CT is also a potential weakness. Given that almost any technique factor can be used to acquire a CT image, it is not clear which factors should be used for any given type of clinical examination (2–4).

At CT, patient weight can vary substantially—from low weight in young infants to very large weight in oversized adults. The modification of technique factors (eg, kilovolt peak and milliampere second settings) to account for these differences in patients is problematic, and to our knowledge, little attention has been given to this topic in the scientific literature. Most types of conventional radiologic examinations are performed with the use of a photo-timing system, which maintains a constant film density at radiography or a constant light output from the image intensifier at fluoroscopy. Commercial CT scanners generally do not possess an automatic exposure control system to regulate selected technique factors, and the choice of technique factors is left to the operator of the scanner. The current practice for CT scanning at many institutions is to use the same technique factors regardless of the patient’s weight (5,6). Failure to account specifically for patient weight when setting CT protocols can lead to patients being unnecessarily exposed (7) or, if the radiation amount used is too low (8), possibly generate suboptimal image quality.

Our purpose in this study was to investigate how changes in kilovolt peak and milliampere second settings and patient weight affected the x-ray energy fluence transmitted through cylindrical water phantoms used to simulate patients undergoing abdominal CT. In addition, we examined how changes in the x-ray tube potential affected the image contrast-to-noise ratio (CNR) at abdominal CT when the x-ray tube current was kept constant.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
X-ray Spectra and Image Contrast
The values of the four spectra used in this study, which were generated by using a Tungsten target and a 17° anode angle, are summarized in Table 1. The total aluminum filtration, peak x-ray tube potential, and computed values of mean photon energy and the first, second, and third half-value layers, all as supplied by Birch et al (9), are given. The values of the four x-ray spectra used in this study are representative of those used with modern CT scanners (10). Computations for each of these four x-ray spectra were performed by using a spreadsheet format and energy increments of 1 keV.


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  		TABLE 1. Summary of the Four X-ray Spectra Used to Compute the Relative Energy Fluence Transmitted through Patients with Various Weights
 
Because the x-ray tube on a given CT scanner has a fixed filtration, the 80-kVp spectrum listed in Table 1 was attenuated by an additional 1 mm Al. In addition, all four spectra were attenuated by using 3.8-mm polytetrafluoroethylene to simulate the attenuation along the central axis of a clinical CT scanner (10). Attenuation coefficients for aluminum (11) and polytetrafluoroethylene (12) were obtained from the scientific literature. The published attenuation coefficients were fitted to second-order polynomials over the 20–150-keV energy range to yield an analytical expression for use in a spreadsheet program.

The output of a given x-ray tube is directly proportional to the mAs value, but it increases supralinearly with increasing x-ray tube potential. For example, for a CT Advantage HiSpeed scanner (GE Medical Systems, Milwaukee, Wis), the x-ray tube output as a function of x-ray tube potential was taken to be proportional to the mean CT dose index values measured in a head CT dosimetry phantom. Thus, relative to 80 kVp, the x-ray output was 1.5 at 100 kVp, 2.5 at 120 kVp, and 3.4 at 140 kVp (13).

X-ray Transmission and Patient Weight
The relationship between a patient with a given mass M (in kg) and a cylinder of water with a given radius r (in mm) that was used to model a patient’s abdomen for the purposes of CT dosimetry is expressed by the equation (6) r = 63.3 + 1.12 M - 0.000635 M2. This equation was obtained by using empirical data on 99 patients who underwent abdominal CT. An average-sized adult has a mass of 70 kg (14), and the above equation indicates that the abdomen of a patient of this mass can be modeled by a 27.7-cm water cylinder. The diameter of water cylinders used in this study ranged from 14.9 cm for a 10-kg patient to 37.7 cm for a 120-kg patient. Twelve patient weights ranging from 10 kg to 120 kg in 10-kg increments were modeled.

The number of x-ray photons at each photon energy, N(E), transmitted along the central axis of a water cylinder of r was determined from the number of incident photons, No(E), by using the equation N(E) = [No(E)]e-2rµ, where E is a given photon energy value and µ is the linear attenuation coefficient for water at E. Attenuation coefficients for water were fit to a second-order polynomial over the 20–150-keV energy range to yield an analytical expression for use in a spreadsheet program.

Detector Energy Fluence
In this study, relative changes in energy fluence were investigated with results that were normalized for a constant x-ray detector energy fluence. This normalization criterion is the same as that in screen-film radiography, in which a constant radiation exposure is required to produce a given film density. For a constant x-ray tube potential, a technique factor of 200 mAs was considered to result in a satisfactory abdominal CT examination in a 70-kg individual. When the x-ray tube potential was changed, operating the CT scanner at 120 kVp and 200 mAs was considered to result in satisfactory abdominal CT images.

For each of the four x-ray spectra used in this study, the energy fluence transmitted through each patient was determined to be a percentage of the energy fluence incident on the patient. At a constant mAs setting, OkVp is the output of the CT scanner at the selected kVp relative to the output at 120 kVp. F70,120 is the energy fluence transmitted through a 70-kg patient with CT technique factors of 120 kVp and 200 mAs. With any other kVp, the mAs required to maintain the same detector energy fluence on a patient of M, mAsM,kVp, is expressed as mAsM,kVp = (200 · F70,120)/(FM,kVp · OkVp), where FM,kVp is the energy fluence transmitted through a patient of M when scanned at 200 mAs and the specified kVp. At a constant x-ray tube potential, this equation is shortened to mAsM = 200 · F70/FM, where both F70 and FM are computed at the same mAs value.

Contrast and Noise
Image contrast depends on photon energy and the material(s) being imaged. The image contrast for any material relative to water is expressed as relative attenuation values (in Hounsfield units [HU]), which are a function of photon energy (15). Calculations were performed to determine the relative attenuation value of material X at E, (HUX,E), over the energy range of interest (30–100 keV) by using the equation HUX,E = [1,000 · (µX,E - µwater,E)]/µwater,E, where µX,E and µwater,E are the linear attenuation coefficients of material X and water at E, respectively.

Attenuation coefficients for muscle, fat, bone (11), and iodine (16), materials of clinical interest in abdominal CT, were obtained from the scientific literature. For iodine, computations were performed only above the K edge of iodine (ie, 33 keV). To estimate how contrast is affected by patient weight, a representative photon energy was determined for each spectrum by taking the arithmetic average of the input/output spectra values for the patient undergoing abdominal CT.

Image mottle in CT is dominated by quantum mottle, which is inversely proportional to the square root of the radiation exposure level absorbed by the x-ray detector (17). For a given patient weight, the relative noise was taken to be inversely proportional to the square root of the energy fluence incident on the CT detector. At a constant mAs value, the relationship between the CNR, computed CNR (CNRX), and x-ray tube potential is expressed as CNRX = k · HUX,E · (OkVp · FkVp)0.5, where k is a constant of proportionality.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
X-ray Transmission and Patient Weight
Figure 1 shows how the mean photon energy for each of the four spectrum values varied with patient thickness, with peak x-ray tube potentials ranging from 80 to 140 kVp. The data in Figure 1 indicate that the mean spectral photon energy increases as the x-ray beam passes through the patient (ie, beam hardening) and that no unique value can be assigned to an x-ray spectrum used in CT scanning.



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  		Figure 1. Graph illustrates mean photon energy versus patient thickness. As a result of beam hardening, the incident mean photon energy is lower than the exit mean photon energy, and the mean exit photon energy slowly increases with increasing patient thickness.

 
Figure 2 shows the percentage of energy fluence transmitted through patients of varying mass with each of the four x-ray spectrum values. At 80 kVp, the transmitted energy fluence was 3.1% for a 10-kg patient, and it decreased to 0.025% for a 120-kg patient. At 140 kVp, the transmitted energy fluence was 5.3% for a 10-kg patient, and it decreased to 0.080% for a 120-kg patient. For a 70-kg patient, increasing the x-ray tube potential from 80 kVp to 140 kVp increased the percentage of energy fluence transmitted by a factor of approximately 2.5. The corresponding absolute increase in energy fluence at the CT detector was a factor of approximately 8.5.



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  		Figure 2. Graph illustrates the percentages of energy fluence transmitted through patients of various masses. As the patient mass increases from 10 kg to 120 kg, the percentage of energy fluence transmitted is reduced by about two orders of magnitude.

 
Detector Energy Fluence
For a fixed x-ray tube potential, mAsM is the tube-current product that should be selected, for a patient weighing M, to maintain the same detector dose as that achieved for a 70-kg individual and 200 mAs. Figure 3 shows how the mAsM for the four x-ray spectrum values considered in this study varied with patient mass. At 80 kVp, reducing the patient mass from 70 kg to 10 kg necessitated a 16-fold reduction in mAs to maintain the same transmitted energy fluence; at 140 kVp, this reduction in mass necessitated an 11-fold reduction in mAs. At 80 kVp, increasing the patient mass from 70 kg to 120 kg necessitated an eightfold increase in mAs to maintain the same transmitted energy fluence; at 140 kVp, this mass increase necessitated a sixfold increase in mAs.



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  		Figure 3. Values of mAsM plotted as a function of patient mass. The mAsM value determines how the mAs needs to be changed, as the mass of the patient varies, to maintain the same detector energy fluence as that achieved at 200 mAs. An increase in patient mass from 10 kg to 120 kg would necessitate an increase in mAs of about two orders of magnitude.

 
The data in Table 2 are mAsM,kVp parameters as a function of patient weight and x-ray tube potential. Use of the mAsM,kVp values listed in Table 2 would enable the operator to maintain the same detector energy fluence as that achieved in a 70-kg patient at 200 mAs and 120 kVp. The mAsM,kVp values that are achievable in practice with a typical generator, given a scanning time of 1 second and an x-ray tube with currents between approximately 40 mA and approximately 400 mA, are highlighted. For 10-kg patients, increasing the x-ray tube potential from 80 kVp to 140 kVp increased the energy fluence at the detector by a factor of about 6. For 120-kg patients, increasing the x-ray tube potential from 80 kVp to 140 kVp increased the energy fluence at the detector by about a factor of 10.


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  		TABLE 2. mAsM,kVp Values as a Function of Patient Weight and X-ray Tube Potential
 
Contrast and Noise
Figure 4 shows how the computed HUX,E values varied with photon energy in fat, muscle, bone, and iodine. Table 3 shows the representative photon energies for the four materials used in this study in a 70-kg patient. Increasing the x-ray tube potential from 80 kVp to 140 kVp increased the representative photon energy from approximately 52 keV to approximately 72 keV. The data in Table 3 show that increasing the x-ray tube potential from 80 kVp to 140 kVp reduced the image contrast relative to water by approximately 12% for muscle, approximately 21% for fat, approximately 39% for bone, and approximately 50% for iodine. Image contrast is a function of the effective atomic number (Z) of the object being imaged in a CT scanner, with high Z materials (eg, iodine) being affected to a greater extent than low Z materials (eg, muscle).



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  		Figure 4. Graphs illustrate computed Hounsfield unit values versus photon energy for fat, muscle, bone, and iodine. For low Z materials such as fat and muscle, increasing the photon energy results in a modest reduction in the Hounsfield unit value. For high Z materials such as bone and iodine, increasing the photon energy results in a rapid decrease in the Hounsfield unit value.

 

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  		TABLE 3. Variation in Attenuation Values and Representative Photon Energy with X-ray Tube kVp
 
Figure 5 shows how the computed CNR for each of the four materials varied as a function of x-ray tube potential. For all four materials, increasing the kVp resulted in a higher computed CNR, which was an indication that the increase in radiation transmitted to the CT detector more than offset the corresponding reduction in image contrast (Table 3). Increasing the x-ray tube potential from 80 kVp to 140 kVp increased the CNR by a factor of 2.6 for muscle and by a factor of 1.4 for iodine. At our institution, most CT examinations are performed at 120 kVp, but the CT scanner can be operated with a maximum of up to 140 kVp. For a 70-kg patient scanned at a constant mAs, using 140 kVp would improve the CNR for muscle by approximately 27% and improve that for iodine by approximately 9%.



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  		Figure 5. Graph illustrates relative CNR as a function of x-ray tube potential for four materials at CT in a 70-kg patient scanned at a constant mAs. The image quality, or CNR, always increases with increasing kVp, with the improvements in CNR being more notable for the low Z materials (ie, muscle and fat) than for the high Z materials (ie, bone and iodine).

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
 
Maintaining constant technique factors at CT results in the level of image mottle being determined by the weight of the patient (18,19). It is more rational to adjust the x-ray techniques for each patient weight to ensure that the resultant image CNR is sufficient for the diagnostic task at hand. Ignoring patient weight in CT examination protocols is unlikely to meet the current requirements for ensuring that patient exposures are kept as low as reasonably achievable (7). At a fixed kVp, modification of the mAs will permit the operator to select the amount of mottle on the resultant CT image, whereas modification of the x-ray tube potential will affect the overall CNR value. Knowledge of the transmitted radiation intensities through patients of various weights is an essential prerequisite to the development of more rational CT protocols.

The representative photon energy for a given abdominal CT examination was obtained by taking the mean of the incident/exit spectrum values, which depends on both the x-ray tube potential and the weight of the patient being examined. The data in Figure 1 show that the selected x-ray tube potential is the most important factor in determining the representative photon energy in an abdominal CT examination. Increasing the mean photon energy reduces both image contrast and image noise. The CNR, however, increases with x-ray tube potential, as shown in Figure 5. Given that x-ray tube filtration also increases the mean photon energy, it would be interesting to study how modifying the x-ray tube filtration would affect the CNR values for current CT scanners.

The data shown in Figure 2 indicate that the radiation transmitted through patients with weights varying from 10 to 120 kg changes by about two orders of magnitude. This large dynamic range suggests that the current practice of using the same CT technique factors regardless of patient weight is suboptimal. Current commercial CT scanners do not have automatic exposure control systems, which would permit an empirical adjustment of radiologic technique factors according to patient weight. To achieve the same (or average) x-ray exposure level at the detector, the technique factors (ie, kVp and mAs) for CT scanners need to be modified. CT scanners have a limited range of x-ray tube current values—typically between approximately 40 mA and approximately 400 mA. CT scanners also attempt to minimize scanning times, so there are practical limitations to adjusting the mAs for different sized patients. As a result, to maintain a constant detector dose at CT scanning, the x-ray tube potential also must be adjusted. Adjusting kVp and mAs according to patient weight would bring CT into line with current practices in radiography and fluoroscopy.

For normalization purposes, technique factors of 120 kVp/200 mAs were adopted for a 70-kg patient because they are commonly used for abdominal CT (20). These technique factors, however, may not be optimal for abdominal CT performed in average-sized adult patients. The effect of changing the selected mAs value has been investigated in studies of CT imaging of the sinuses (21,22) and chest (23–25). In general, the results of these studies suggest that it should be possible to reduce the mAs without adversely affecting diagnostic imaging performance. For specialized imaging tasks such as the determination of adipose and muscle tissue area and volume, it is possible to achieve large dose radiation reductions in patients without adversely affecting diagnostic performance (26).

Although the data in Figure 5 show that increasing the x-ray tube potential improves the CNR, this does not necessarily imply that CT should be performed at the highest possible kVp value. Increasing the x-ray tube potential increases the radiation dose to the patient also, and the improvements in image quality would need to be sufficient to justify this additional exposure, particularly if a radiosensitive patient (eg, pregnant woman or pediatric patient) were being scanned. It is also important to note that if the image quality at a lower x-ray tube potential was adequate to achieve a high level of diagnostic accuracy, then any improvement in CNR would not translate into improved diagnostic performance. Additional factors to consider include the effect of the increased x-ray tube loading on the x-ray tube lifetime, as well as the additional anode heat loading and the total number of scans that could be obtained in the helical scanning mode. It is also possible that the use of high x-ray tube potentials may be justified in the detection of low Z materials but not required in the detection of high Z materials such as bone or iodine.

Our computations of image quality were restricted to relative changes in image contrast and noise for a fixed patient weight. A complete description of image signal-to-noise ratios for patients with differing weights is problematic because of corresponding changes in pixel size and the need to explicitly take into account the human visual system (27). In a complete analysis under these circumstances, one would also need to specify the type of lesion being detected (28). The data in Figure 5 show that the improvement in image CNR with increasing x-ray tube potential was most important for the low Z materials—that is, fat and muscle. The detection of small high-contrast lesions is generally related to spatial resolution, whereas the detection of large low-contrast objects generally is associated with a high CNR.

Imaging protocols should also account for the radiation doses delivered to the patient. With conventional screen-film radiography, the use of high kVps reduces both patient radiation dose and subject contrast. As a result, the choice of x-ray tube potential needs to be determined by balancing image quality requirements with radiation dose considerations. For CT in a given-sized patient, the radiation dose will be directly proportional to the selected mAs. At a constant mAs, increasing the x-ray tube potential from 80 kVp to 140 kVp increased the radiation dose by a factor of about 3.4 in the current study. In addition, CT examination protocols need to consider image quality and radiation dose, which may be combined to generate an overall value as a guide to protocol optimization (29). For a given clinical application, it is essential that any increase in patient radiation exposure is justified by improved diagnostic imaging performance. In practice, the radiation exposure might be reduced in high-risk patients, such as pregnant women, and in the detection of high-contrast lesions but increased in the detection of subtle low-contrast lesions.

The data presented in this study indicate how radiologic technique factors should be modified to maintain a constant detector energy fluence. The rationale behind this normalization criterion is based partially on radiologic practice during the past 100 years, during which radiologic technique factors that keep the image brightness constant have been used in screen-film radiography and fluoroscopy. The data presented in Figure 3 and Table 2 offer a first approximation as to how CT technique factors might be changed as a function of patient weight. At our institution, these factors are intended to incrementally modify current practice while we develop objective criteria to monitor the corresponding CT image quality. In determining the appropriate CT technique factors as a function of patient weight, we also intend to take into account changes in x-ray tube potential and the corresponding radiation dose values. The data presented in this study will serve as a guide to empirical studies to ensure that CT protocols explicitly take patient weight into account without compromising overall diagnostic imaging performance and while keeping patient radiation exposures as low as reasonably possible.


   FOOTNOTES
 
Abbreviations: CNR = contrast-to-noise ratio, Z = effective atomic number

Author contributions: Guarantor of integrity of entire study, W.H.; study concepts and design, W.H., E.M.S.; definition of intellectual content, W.H.; literature research, W.H.; data acquisition, W.H., G.L.; data analysis, W.H., E.M.S., G.L.; manuscript preparation, editing, and review, W.H., E.M.S., G.L.


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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 

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C. Herzog, D. M. Mulvihill, S. A. Nguyen, G. Savino, B. Schmidt, P. Costello, T. J. Vogl, and U. J. Schoepf
Pediatric Cardiovascular CT Angiography: Radiation Dose Reduction Using Automatic Anatomic Tube Current Modulation
Am. J. Roentgenol., May 1, 2008; 190(5): 1232 - 1240.
[Abstract] [Full Text] [PDF]

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 RadiologyHome page
C. T. Hsu, Z. J. Wang, A. S. L. Yu, R. G. Gould, Y. Fu, B. N. Joe, A. Qayyum, R. S. Breiman, F. V. Coakley, and B. M. Yeh
Physiology of Renal Medullary Tip Hyperattenuation at Unenhanced CT: Urinary Specific Gravity and the NaCl Concentration Gradient
Radiology, April 1, 2008; 247(1): 147 - 153.
[Abstract] [Full Text] [PDF]

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 Eur Heart JHome page
L. Husmann, I. Valenta, O. Gaemperli, O. Adda, V. Treyer, C. A. Wyss, P. Veit-Haibach, F. Tatsugami, G. K. von Schulthess, and P. A. Kaufmann
Feasibility of low-dose coronary CT angiography: first experience with prospective ECG-gating
Eur. Heart J., January 2, 2008; 29(2): 191 - 197.
[Abstract] [Full Text] [PDF]

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 RadiologyHome page
S. T. Schindera, R. C. Nelson, S. Mukundan Jr, E. K. Paulson, T. A. Jaffe, C. M. Miller, D. M. DeLong, K. Kawaji, T. T. Yoshizumi, and E. Samei
Hypervascular Liver Tumors: Low Tube Voltage, High Tube Current Multi Detector Row CT for Enhanced Detection Phantom Study
Radiology, December 1, 2007; 246(1): 125 - 132.
[Abstract] [Full Text] [PDF]

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 Am. J. Roentgenol.Home page
C. L. Hollingsworth, T. T. Yoshizumi, D. P. Frush, F. P. Chan, G. Toncheva, G. Nguyen, C. R. Lowry, and L. M. Hurwitz
Pediatric Cardiac-Gated CT Angiography: Assessment of Radiation Dose
Am. J. Roentgenol., July 1, 2007; 189(1): 12 - 18.
[Abstract] [Full Text] [PDF]

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 Am. J. Roentgenol.Home page
G. Hur, S. W. Hong, S. Y. Kim, Y. H. Kim, Y. J. Hwang, W. R. Lee, and S. J. Cha
Uniform Image Quality Achieved by Tube Current Modulation Using SD of Attenuation in Coronary CT Angiography
Am. J. Roentgenol., July 1, 2007; 189(1): 188 - 196.
[Abstract] [Full Text] [PDF]

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 RadiologyHome page
F. H. Fahey, M. R. Palmer, K. J. Strauss, R. E. Zimmerman, R. D. Badawi, and S. T. Treves
Dosimetry and Adequacy of CT-based Attenuation Correction for Pediatric PET: Phantom Study
Radiology, April 1, 2007; 243(1): 96 - 104.
[Abstract] [Full Text] [PDF]

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 Am. J. Roentgenol.Home page
W. Huda and A. Vance
Patient Radiation Doses from Adult and Pediatric CT
Am. J. Roentgenol., February 1, 2007; 188(2): 540 - 546.
[Abstract] [Full Text] [PDF]

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 Am. J. Roentgenol.Home page
D. V. Sahani, S. P. Kalva, P. F. Hahn, and S. Saini
16-MDCT Angiography in Living Kidney Donors at Various Tube Potentials: Impact on Image Quality and Radiation Dose
Am. J. Roentgenol., January 1, 2007; 188(1): 115 - 120.
[Abstract] [Full Text] [PDF]

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 RadioGraphicsHome page
N. C. Dalrymple, S. R. Prasad, F. M. El-Merhi, and K. N. Chintapalli
Price of Isotropy in Multidetector CT
RadioGraphics, January 1, 2007; 27(1): 49 - 62.
[Abstract] [Full Text] [PDF]

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 RadiologyHome page
W. C. Chan, B. N. Joe, F. V. Coakley, E. L. Prien Jr, R. G. Gould, S. Prevrhal, W. C. Barber, K. S. Kirkwood, A. Qayyum, and B. M. Yeh
Gallstone Detection at CT in Vitro: Effect of Peak Voltage Setting.
Radiology, November 1, 2006; 241(2): 546 - 553.
[Abstract] [Full Text] [PDF]

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 Am. J. Roentgenol.Home page
Y. Nakayama, K. Awai, Y. Funama, D. Liu, T. Nakaura, Y. Tamura, and Y. Yamashita
Lower tube voltage reduces contrast material and radiation doses on 16-MDCT aortography.
Am. J. Roentgenol., November 1, 2006; 187(5): W490 - W497.
[Abstract] [Full Text] [PDF]

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 CirculationHome page
J. Hausleiter, T. Meyer, M. Hadamitzky, E. Huber, M. Zankl, S. Martinoff, A. Kastrati, and A. Schomig
Radiation Dose Estimates From Cardiac Multislice Computed Tomography in Daily Practice: Impact of Different Scanning Protocols on Effective Dose Estimates
Circulation, March 14, 2006; 113(10): 1305 - 1310.
[Abstract] [Full Text] [PDF]

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V. L. Ward, C. E. Barnewolt, K. J. Strauss, R. L. Lebowitz, V. Venkatakrishnan, M. Stehr, D. L. McLellan, C. A. Peters, D. Zurakowski, P. S. Dunning, et al.
Radiation Exposure Reduction during Voiding Cystourethrography in a Pediatric Porcine Model of Vesicoureteral Reflux
Radiology, January 1, 2006; 238(1): 96 - 106.
[Abstract] [Full Text] [PDF]

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C. H. McCollough
Automatic Exposure Control in CT: Are We Done Yet?
Radiology, December 1, 2005; 237(3): 755 - 756.
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Y. Funama, K. Awai, Y. Nakayama, K. Kakei, N. Nagasue, M. Shimamura, N. Sato, S. Sultana, S. Morishita, and Y. Yamashita
Radiation Dose Reduction without Degradation of Low-Contrast Detectability at Abdominal Multisection CT with a Low-Tube Voltage Technique: Phantom Study
Radiology, December 1, 2005; 237(3): 905 - 910.
[Abstract] [Full Text] [PDF]

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 RadiologyHome page
J. Menke
Comparison of Different Body Size Parameters for Individual Dose Adaptation in Body CT of Adults
Radiology, August 1, 2005; 236(2): 565 - 571.
[Abstract] [Full Text] [PDF]

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 Am. J. Roentgenol.Home page
T. Irie and H. Inoue
Individual Modulation of the Tube Current-Seconds to Achieve Similar Levels of Image Noise in Contrast-Enhanced Abdominal CT
Am. J. Roentgenol., May 1, 2005; 184(5): 1514 - 1518.
[Abstract] [Full Text] [PDF]

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 Am. J. Roentgenol.Home page
W. D. Middleton, S. A. Teefey, and K. Yamaguchi
Sonography of the Rotator Cuff: Analysis of Interobserver Variability
Am. J. Roentgenol., November 1, 2004; 183(5): 1465 - 1468.
[Abstract] [Full Text] [PDF]

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 RadiologyHome page
M. J. Siegel, B. Schmidt, D. Bradley, C. Suess, and C. Hildebolt
Radiation Dose and Image Quality in Pediatric CT: Effect of Technical Factors and Phantom Size and Shape
Radiology, November 1, 2004; 233(2): 515 - 522.
[Abstract] [Full Text] [PDF]

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 RadiologyHome page
S. Saini
Multi-Detector Row CT: Principles and Practice for Abdominal Applications
Radiology, November 1, 2004; 233(2): 323 - 327.
[Abstract] [Full Text] [PDF]

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 Am. J. Roentgenol.Home page
D. D. Cody, D. M. Moxley, K. T. Krugh, J. C. O'Daniel, L. K. Wagner, and F. Eftekhari
Strategies for Formulating Appropriate MDCT Techniques When Imaging the Chest, Abdomen, and Pelvis in Pediatric Patients
Am. J. Roentgenol., April 1, 2004; 182(4): 849 - 859.
[Abstract] [Full Text] [PDF]

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 RadiologyHome page
A. B. Sigal-Cinqualbre, R. Hennequin, H. T. Abada, X. Chen, and J.-F. Paul
Low-Kilovoltage Multi-Detector Row Chest CT in Adults: Feasibility and Effect on Image Quality and Iodine Dose
Radiology, April 1, 2004; 231(1): 169 - 174.
[Abstract] [Full Text] [PDF]

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 Br. J. Radiol.Home page
J Pages, N Buls, and M Osteaux
CT doses in children: a multicentre study
Br. J. Radiol., November 1, 2003; 76(911): 803 - 811.
[Abstract] [Full Text] [PDF]

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J. M. Boone, E. M. Geraghty, J. A. Seibert, and S. L. Wootton-Gorges
Dose Reduction in Pediatric CT: A Rational Approach
Radiology, August 1, 2003; 228(2): 352 - 360.
[Abstract] [Full Text] [PDF]

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M. F. McNitt-Gray
AAPM/RSNA Physics Tutorial for Residents: Topics in CT: Radiation Dose in CT
RadioGraphics, November 1, 2002; 22(6): 1541 - 1553.
[Abstract] [Full Text] [PDF]

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 Br. J. Radiol.Home page
A Khursheed, M C Hillier, P C Shrimpton, and B F Wall
Influence of patient age on normalized effective doses calculated for CT examinations
Br. J. Radiol., October 1, 2002; 75(898): 819 - 830.
[Abstract] [Full Text] [PDF]