Original Research
Pediatric Imaging
January 2009

CT with a Computer-Simulated Dose Reduction Technique for Detection of Pediatric Nephroureterolithiasis: Comparison of Standard and Reduced Radiation Doses

Abstract

OBJECTIVE. The purpose of this study was to compare the diagnostic capabilities of standard- and reduced-dose CT in the detection of nephroureterolithiasis in children.
MATERIALS AND METHODS. Forty-five patients 20 years old or younger divided into two groups weighing 50 kg or less and more than 50 kg underwent unenhanced 16-MDCT in the evaluation of acute flank pain. An investigational computer-simulated tube current reduction tool was used to produce additional 80- and 40-mA examination sets (total number of image sets = 135). Three independent blinded readers ranked random images for stones (confidence scale, 1-5, least to most), hydronephrosis, noise-based image quality, and presence of nonrenal lesions.
RESULTS. Compared with the standard tube current used for the original CT scans, there was no significant reduction (p = 0.37) in detection of renal stones at the 80-mA setting (mean dose reduction, 67%; range, 43-81%); and at the 40-mA setting (mean dose reduction, 82%; range, 72-90%), the detection rate was significantly lower (p = 0.05). At the 40-mA setting, there was no significant difference among the children weighing 50 kg or less (p = 0.4). Detection of ureteral stones and hydronephrosis was not significantly different at 80 and 40 mA; however, disease frequency was low, and no definite conclusion can be made.
CONCLUSION. Simulated dose reduction is a useful tool for determining diagnostic thresholds for MDCT detection of renal stones in children. Use of the 80-mA setting for all children and 40 mA for children weighing 50 kg or less does not significantly affect the diagnosis of pediatric renal stones.

Introduction

Unenhanced abdominal CT examinations have become the preferred diagnostic method for evaluation of nephroureterolithiasis in both adults and children [1, 2]. CT has the advantage of a high rate of detection of renal and ureteral stones and shows other pathologic changes that can mimic renal colic. There is no need for IV contrast media and therefore no risk of side effects related to contrast media [1, 2]. The main concern with abdominal CT examinations, however, is radiation exposure, especially with the possibility of cumulative doses because renal calculi can be a recurring problem. The risks of radiation-related bioeffects are greater among children than among adults, and there is growing concern about the long-term risk of neoplasm development associated with radiation exposure [3, 4].
A reduction in tube current is one method of lowering radiation exposure during CT [5]. The disadvantage of a decrease in tube current is an increase in noise, which can reduce the radiologist's ability to detect disease [6]. Investigational repeated scanning of children with lower doses is not justifiable. One option is to use a computer to simulate a tube current lower than that used for the original CT examinations [7]. Although this simulation tool has been investigated for systematic reduction in tube current in the adult population with nephroureterolithiasis [8], similar investigations have not been performed for evaluation of nephroureterolithiasis in the more radiation-sensitive pediatric population. The purpose of our study was to determine how tube current reduction affects the diagnostic yield in CT examinations for suspected renal or ureteral stones in children.

Materials and Methods

Patient Population

The study was approved by our institutional review board with waiver of informed consent. From April 2005 to May 2006, we identified all patients 20 years old or younger in a tertiary care children's hospital who underwent abdominopelvic MDCT without contrast enhancement for a clinical indication of suspected nephro ureterolithiasis. Scan indications included acute flank pain with or without hematuria, painless hematuria, and history of renal calculi. The clinical indication was documented, as were age, sex, and body weight. Repeated MDCT examinations of any patient for possible nephroureterolithiasis were not included in the study set. The number of CT studies performed for evaluation of nephroureterolithiasis was recorded.

CT Technique

All studies were performed with a 16-MDCT scanner (LightSpeed, GE Healthcare). Imaging parameters were detector configuration, 16 × 0.625 mm; section thickness, 5 mm; interval, 2.5 mm; tube voltage, 120 kVp; gantry rotation time, 0.5 seconds for body weight less than 60 kg, 0.8 seconds for body weight 60 kg or greater; pitch, 1.375; matrix size, 512 × 512; standard reconstruction algorithm. The tube current depended on our institutional weight-adjusted MDCT protocols. For 37 children (82%) the tube current ranged from 140 to 260 mA (70-208 effective mAs) according to the CT renal stone protocol. Eight children (18%) underwent routine abdominal studies with up to 425 mA (340 effective mAs) according to the radiologist's discretion. No automatic tube current modulation was used.

Image Simulation

Simulated tube current reduction is a proprietary tool that operates with projectional scan data from diagnostic CT examinations. User-controlled random gaussian noise is added to the original scan data to simulate a reduction in tube current. The amount of simulated noise added to the scan data simulates the increased noise that would occur in scans actually obtained at these tube currents. This technique has been described in detail elsewhere [7].
All scan and patient identification was removed from the original CT images. Postprocessing of the original CT raw data was performed. Each CT study was reproduced to simulate tube currents of 80 and 40 mA, yielding three examinations (original and two simulated examinations) for each patient for a total of 135 image sets. Images from the original and simulated examinations were viewed on standard clinical PACS stations (Centricity, GE Healthcare) under clinical reading conditions.

Image Analysis

The images at the three tube current settings were viewed randomly. Each study was interpreted independently by three pediatric radiologists with 14-30 years of experience, all fellowship trained with a certificate of added qualification. The reviewers were blinded to all technical parameters. Observers could use the standard PACS tools to make the adjustments they would make during routine interpretation. There was no time limit for viewing a study. When a calculus was believed to be present, the window and level settings were standardized at width 650 HU and level 150 HU for measuring the maximum diameter of renal stones with PACS calipers. The reference standard was the observers' interpretations of the images from the original examination. Criteria for the presence of stones and hydronephrosis were at the discretion of the radiologist.
The reviewers rated each image on a modified 5-point Likert scale for the presence of stones in the right kidney, left kidney, right ureter, and left ureter (1, definitely no stone; 2, probably no stone; 3, uncertain finding; 4, probably stone; 5, definitely stone). The data were grouped as depicting stones if there was any rating of 4 or 5. If more than one stone was identified, the readers counted the number of stones present and measured the largest stone. Findings associated with renal obstruction, including hydronephrosis, hydroureter, and soft-tissue stranding in perirenal fat, were rated as present, uncertain, or absent.
The presence or absence of nonurologic abnormalities, such as bowel wall thickening and distention, enlarged lymph nodes 8 mm or more in short axis [9], adnexal mass, and adnexal cyst larger than 5 mm, and visualization of a normal appendix were rated with the same modified 5-point Likert scale. Each reviewer then evaluated the overall quality of the image as adequate, suboptimal, or nondiagnostic.

Statistical Analysis

For each qualitative variable, the mean responses from the three readers were compared at each tube current level by use of the paired Wilcoxon's signed rank test. The resulting p values were not adjusted for multiple comparisons. Reader agreement was measured with Cohen's kappa statistic. Standard errors of estimated kappa statistics and averages and differences of kappa statistics were computed by use of the statistical jackknife. A kappa value less than 0.2 indicated poor agreement; 0.21-0.40, fair agreement; 0.41-0.60, moderate agreement; 0.61-0.80, good agreement; and 0.81-1.00, excellent agreement. For all tests, statistical significance was set at p < 0.05. Statistical software was used (SAS version 9.1, SAS Institute).

Results

Study Group

The cases of 45 patients (18 boys, 27 girls) who met the entry criteria were identified. The median age was 13.2 years (range, 2.8-20 years), and the average body weight was 50 kg (range, 14-114 kg). Twenty-eight patients (62%) weighed 50 kg or less, and 17 patients (38%) weighed more than 50 kg. The most common indication for CT was evaluation of acute flank pain with or without hematuria (26 of 45 patients, 58%); other indications included follow-up of renal stones in 11 patients (24%) and painless hematuria in eight patients (18%). Thirteen (29%) of the patients underwent more than one unenhanced CT study (mean, 2.6 studies; range, 2-7 studies) for evaluation of nephroureterolithiasis.

Renal and Ureteral Stones

The median diameter of the renal stones was 3 mm (range, 1-12 mm). In kidneys with multiple stones, the largest stone was measured. For each tube current level, the percentages of kidneys rated as having stones are listed in Table 1. Figures 1A, 1B, and 1C shows a renal stone at the three tube current settings. In the original image sets, the mean of the three readers was detection of stones in 32% of kidneys, compared with 29% at 80 mA (p = 0.37) and 23% at 40 mA (p = 0.05). Table 2 summarizes the rate of detection of renal stones in patients weighing 50 kg or less (n = 28) and patients weighing more than 50 kg. Among patients weighing 50 kg or less, the mean rating was 33% on the original studies, compared with 32.1% at 80 mA (p = 1.0) and 29.8% at 40 mA (p = 0.4). Among patients with a body weight more than 50 kg, the mean detection rate was 29.4% on the original studies, compared with 17.6% at 80 mA (p = 0.4) and 11.8% at 40 mA (p = 0.06).
TABLE 1 : Percentage of Kidneys in Which at Least One Stone Was Detected (Rating 4 or 5)
Tube Current Setting (mA)Percentage of Kidneys with Stones (n = 90)
Reader 1Reader 2Reader 3Averagepa
40242420230.05
80312927290.37
Original
29
36
31
32

a
Wilcoxon signed rank test comparing the average number of kidneys in which stones were detected at the low tube current setting versus the original setting.
TABLE 2 : Percentage of Kidneys with Stones (Rating 4 or 5) According to Body Weight (n = 90)
Percentage of Kidneys with Stones
Tube Current Setting (mA)Reader 1Reader 2Reader 3Averagepa
Body weight ≤ 50 kg (n = 28)     
    4032.132.1525.029.850.4
    8032.132.132.132.11.0
    Original32.135.732.15  
Body weight > 50 kg (n = 17)     
    4011.211.811.811.80.06
    8029.423.517.623.50.39
    Original
23.5
35.3
29.4
29.4

Note—Comparison of average number of kidneys in which stones were detected at the low tube current setting versus the original setting.
Fig. 1A —13-year-old 49-kg boy with renal stone manifesting as acute flank pain and hematuria. Unenhanced MDCT scans show right renal stone identified by only one reader at 40-mA setting (A) and by all three readers at 80-mA setting (B) and at original setting of 250 mA (C).
Fig. 1B —13-year-old 49-kg boy with renal stone manifesting as acute flank pain and hematuria. Unenhanced MDCT scans show right renal stone identified by only one reader at 40-mA setting (A) and by all three readers at 80-mA setting (B) and at original setting of 250 mA (C).
Fig. 1C —13-year-old 49-kg boy with renal stone manifesting as acute flank pain and hematuria. Unenhanced MDCT scans show right renal stone identified by only one reader at 40-mA setting (A) and by all three readers at 80-mA setting (B) and at original setting of 250 mA (C).
With the original study as the reference standard, the sensitivity and specificity in the detection of renal stones were 85% and 97% for the 80-mA image sets and 69% and 97% for the 40-mA sets. Interobserver agreement for the presence of renal stones was good to excellent for all tube current groups (κ = 0.68-0.87), and no significant differences were found between readers.
Only eight ureteral stones were detected in our study group. There was no significant difference between tube current groups regarding detection of ureteral stones. The interobserver agreement was low to moderate, ranging from 0.20 to 0.64, but no significant differences were found between readers.
Fig. 2A —12-year-old, 59-kg boy with ureteral stone manifesting as acute left renal colic and hematuria. Unenhanced MDCT scans show left obstructing ureteral stone at ureterovesical junction identified with confidence level of 4 or 5 by one reader at 40 mA (A) and 80 mA (B) and by two readers at original setting of 250 mA (C).
Fig. 2B —12-year-old, 59-kg boy with ureteral stone manifesting as acute left renal colic and hematuria. Unenhanced MDCT scans show left obstructing ureteral stone at ureterovesical junction identified with confidence level of 4 or 5 by one reader at 40 mA (A) and 80 mA (B) and by two readers at original setting of 250 mA (C).
Fig. 2C —12-year-old, 59-kg boy with ureteral stone manifesting as acute left renal colic and hematuria. Unenhanced MDCT scans show left obstructing ureteral stone at ureterovesical junction identified with confidence level of 4 or 5 by one reader at 40 mA (A) and 80 mA (B) and by two readers at original setting of 250 mA (C).
Fig. 2D —12-year-old, 59-kg boy with ureteral stone manifesting as acute left renal colic and hematuria. In unenhanced MDCT scan at 40 mA, secondary left hydronephrosis was not identified.
Fig. 2E —12-year-old, 59-kg boy with ureteral stone manifesting as acute left renal colic and hematuria. Unenhanced MDCT scan shows secondary left hydronephrosis identified by one reader at 80 mA (E) and 250 mA (F).
Fig. 2F —12-year-old, 59-kg boy with ureteral stone manifesting as acute left renal colic and hematuria. Unenhanced MDCT scan shows secondary left hydronephrosis identified by one reader at 80 mA (E) and 250 mA (F).

Renal Obstruction

The mean rating by the three readers for all studies revealed only seven kidneys with hydronephrosis (n = 6) or hydroureter (n = 2). No significant difference in the number of obstructed kidneys was found between 40 mA (p = 1.00) or 80 mA (p = 0.61) and the original images. The presence of hydronephrosis was not always rated similarly by the three observers (Figs. 2A, 2B, 2C, 2D, 2E, and 2F). Soft-tissue stranding in perirenal fat was found in only one kidney.

Nonurologic Abnormalities

Only a few patients had non-urinary system abnormalities. On the original studies, the mean rating for the presence of bowel wall thickening or distention was 1.9; enlarged lymph nodes, 2.0; and adnexal mass or cyst, 1.3. There was no statistical difference in the number of such abnormalities detected with 40 mA and 80 mA compared with the original tube current level (p = 0.39 and p = 0.59, respectively).
The mean visualization of the normal appendix ranged from 23% to 42% (Table 3). The mean detection rate on images obtained at the original CT settings was higher than that on images obtained at 80 and 40 mA (p < 0.01 for each). The decreased detection of the appendix also was significant in the subgroup of patients weighing 50 kg or less in comparisons of either 40- or 80-mA simulated studies with the original studies (p = 0.001 and p = 0.004, respectively). Detection of the appendix was decreased in patients weighing more than 50 kg in comparisons of 40- or 80-mA simulated studies with the original studies. The decreased detection, however, was statistically significant (p = 0.03) only for the 40-mA image sets.
TABLE 3 : Frequency of Identification of Normal Appendix at Unenhanced MDCT (n = 45)
Tube Current Setting (mA)Percentage Detection of Normal Appendix
Reader 1Reader 2Reader 3Averagepa
4013362023<0.01
8027382430<0.01
Original
42
51
33
42

Note—Readers used scale of 1 (cannot be identified) to 5 (definitely present); appendix was classified as detected if rating was 4 or 5.
a
Original tube current setting compared with the lower settings.

Image Quality

The original CT examinations were considered of adequate quality more frequently than were either the 80- or 40-mA image sets (p < 0.01 for each). There was marked interobserver variability in rating the quality of the studies (Table 4). The mean rating for optimal studies increased from 34% to 56% to 67%, respectively, with the increase in tube current from 40 to 80 mA to the original setting. In the cases of children weighing 50 kg or less, image quality was significantly lower between the original and the 40-mA image sets (p < 0.01) but did not vary between the original and the 80-mA image sets (p = 0.3). Among patients with higher body weight, image quality was significantly lower between the original and both the 40- and 80-mA image sets (p < 0.01 for both).
TABLE 4 : Comparison of Percentages of Unenhanced CT Scans of the Abdomen Graded with Optimal Quality at Different Tube Current Settings (n = 45)
Tube Current Setting (mA)Percentage of Studies with Optimal Quality
Reader 1Reader 2Reader 3Averagepa
4031692340.001
8069917560.001
Original
78
93
31
67

a
Average number of CT scans graded as optimal compared with original setting.

Discussion

MDCT without contrast enhancement has become the primary diagnostic test for evaluation of renal and ureteral calculi [1, 2]. Unenhanced CT is accurate, can be rapidly performed, produces images that can be rapidly interpreted, and does not involve the risk of IV administration of contrast medium [1, 2]. However, the increasing use of MDCT for disease diagnosis, especially in children, has led to concerns about radiation exposure [3, 4]. Radiation doses to patients who undergo CT have been estimated to increase the lifetime risk of cancer death [5, 10, 11]. This finding has generated a call for further investigation of the contribution of various parameters, especially tube current reduction, to reducing radiation exposure [5, 10, 11]. This issue is especially important in children being evaluated for renal stones because some of these patients undergo numerous follow-up CT studies. In our study, approximately one third of the children underwent several (average, 2.6; range, 2-7) unenhanced abdominal CT studies for evaluation of renal stones.
The as-low-as-reasonably-achievable standard asserts that the radiation dose necessary to generate diagnostic CT scans be kept to a minimum. There is a linear relation between tube current and radiation dose. In addition, for a given tube current setting, pediatric doses are much larger than adult doses because a child's thinner torso provides less shielding of organs from radiation exposure. A reduction in the tube current setting proportionately reduces the dose and the risk. However, with decreased tube current, image noise increases, possibly reducing examination quality and diagnostic capability. Therefore, reductions in tube current should be balanced with the increased risk of an incorrect diagnosis [6, 7, 10, 11].
Studies have been conducted with adult subjects to compare routine- and low-dose-radiation CT [12, 13]. This paradigm would be difficult to apply to children because of radiation concerns. The use of a computer-simulated, low tube current (dose) reduction technique eliminates these difficulties. With this technique, there is no need to expose a child to additional radiation. It is possible to simulate multiple tube current reductions. This technique can be used for any CT study, and a prototype of this technology has been tested on children [7]. A study of this simulation tool technique showed that a tube current of 35 mA is acceptable for evaluation of nephrolithiasis in the size spectrum of adults [8]. We used the computer-simulated low-dose technique in our study and thus were able to compare the diagnostic performance of unenhanced MDCT studies at different tube current settings for evaluation of renal and ureteral calculi.
Studies of unenhanced MDCT for evaluation of nephroureterolithiasis in adult populations have shown that unenhanced MDCT at low tube current (reductions of 25-66%) can be used without loss of diagnostic quality [8, 12-16]. It is difficult to extend these results to children because the pediatric population is more heterogeneous in body size and fat distribution. With the increased incidence of obesity among children (5% of our patients weighed > 100 kg), adjusting CT parameters to body size becomes even more challenging.
Our results show that the difference in detection of renal stones was not significant at 80 mA compared with the original settings. Using the 80-mA setting would reduce CT dose an average of 67% (43-81%). In patients weighing 50 kg or less, using the 40-mA setting did not significantly decrease renal stone detection. Using the 40-mA setting in this group of patients would reduce CT dose an average of 82% (range, 71-90%). In patients weighing more than 50 kg, use of the 40-mA setting was accompanied by a marginally significant (p = 0.06) decrease in renal stone detection. This is likely related to the small sample size.
A potential concern with decreased tube current settings is false diagnosis of renal stones that may alter management. However, with the original studies as the reference standard, the specificity of both 40- and 80-mA imaging was very high (97%). Moreover, interobserver agreement was good to excellent for each tube current setting (κ = 0.68-0.87). This finding is supported by those of previous studies [12, 13] that showed a high sensitivity of 30 effective mAs MDCT in the detection of nephroureterolithiasis in adults. Poletti and colleagues [13], however, found that MDCT at 30-effective-mAs was limited in the detection of renal stones with a diameter less than 3 mm. The number of ureteral stones in our study was too small for statistical evaluation, and there was also poor interobserver variability (κ = 0.20-0.64). We cannot conclude from our results whether low tube current settings influence detection of ureteral stones.
The numbers of obstructed kidneys were small in our study group. The most common finding that suggested obstruction was hydronephrosis. Whereas soft-tissue stranding in perirenal fat has been found to be sensitive for renal obstruction in adults [17], it was detected in only one patient in our study. It is possible that the small amount of perirenal fat in children, including obese children, makes detection of tissue stranding in the fat more challenging.
Although we detected few substantial non-urinary tract abnormalities, another indication for CT in these patients is to rule out appendicitis. A decrease in the ability of radiologists to confirm the presence of a normal appendix with low-dose CT would argue against its introduction. We found that the ability to confirm the presence of a normal appendix was significantly higher with the original tube current settings. Thus a reduced tube current level may be satisfactory for urinary tract stone detection but not for ruling out appendicitis, and the relative importance of these tasks must be considered before a low-dose protocol is introduced. However, the utility of low-dose imaging in the evaluation of appendicitis itself was not evaluated because there was no case of acute appendicitis in our study group.
When readers evaluated the quality of CT images, there were significantly fewer optimal studies at 80 and 40 mA than at the original tube current settings. Only 34% of the studies were rated technically adequate at 40 mA, compared with 67% at the original settings. This discrepancy was greater in patients with a large or very large body habitus. However, in the subgroup of children weighing 50 kg or less, image quality did not vary significantly between the original and the 80-mA image sets (p = 0.3). This finding is supported by those of other authors [15], who suggested not performing low-dose CT examinations on adults with large body habitus.
Our study had limitations. We did not have enough patients with ureteral stones and renal obstruction to evaluate differences in detection rates between the different tube current settings. In addition, it is conceivable that the few patients with hydronephrosis and ureteral stones were remembered by the readers, thus skewing the data. The studies were evaluated only in the axial plane and not on coronal or sagittal multiplanar reconstructions, use of which may increase detection of nephroureterolithiasis. We evaluated only one parameter that can reduce radiation exposure (tube current), yet there are other parameters, such as kilovoltage, that can influence radiation exposure and rate of detection of nephroureterolithiasis. Dose does not necessarily translate equally to tube current reduction. Although dose reduction was implied in this study of simulated tube current reduction, the actual dose differences were not measured or estimated. We did not specify how to evaluate the quality of the images, which may explain the high interobserver variability.
Our study showed the value of computer-simulated technique as a tool for evaluation of low tube current (low radiation dose) CT images without use of additional CT studies on pediatric patients. We found it possible to decrease the tube current setting to 80 mA for all children and to 40 mA for children weighing 50 kg or less without significant change in detection of renal stones in all children. Changing the tube current setting to 80 mA would decrease radiation exposure 67%, and changing it to 40 mA would decrease the exposure 82%. However, at this reduced dose, there was significantly decreased detection of normal appendixes, and fewer studies were graded optimal at subjective evaluation. In addition, we did not have enough cases to evaluate the change in rate of detection of ureteral stones and renal obstruction. Therefore, a prospective clinical trial is needed for evaluation of tube current reduction in acute renal colic. Our results are a scientific rationale for tube current reduction.

Footnotes

Address correspondence to B. Karmazyn.
Supported in part by a grant from GE Healthcare.
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References

1.
Sourtzis S, Thibeau JF, Damry N, Raslan A, Vandendris M, Bellemans M. Radiologic investigation of renal colic: unenhanced helical CT compared with excretory urography. AJR 1999; 172:1491-1494
2.
Smith RC, Rosenfield AT, Choe KA, et al. Acute flank pain: comparison of non-contrast-enhanced CT and intravenous urography. Radiology 1995; 194:789-794
3.
Brenner DJ, Elliston CD, Hall EJ, et al. Estimated risks of radiation-induced fatal cancer from pediatric CT. AJR 2001; 176:289-296
4.
Brenner DJ, Hall EJ. Computed tomography: an increasing source of radiation exposure. N Engl J Med 2007; 29:2277-2284
5.
Rogers LF. Taking care of children: check out the parameters used for helical CT. AJR 2001; 176:287
6.
Jurik AG, Jessen KA, Hansen J. Image quality and dose in computed tomography. Eur Radiol 1997; 7:77-81
7.
Frush DP, Slack CC, Hollingsworth CL, et al. Computer simulated radiation dose reduction for abdominal multidetector CT of pediatric patients. AJR 2002; 179:1107-1113
8.
Paulson EK, Weaver C, Ho LM, et al. Conventional and reduced radiation dose of 16-MDCT for detection of nephrolithiasis and ureterolithiasis. AJR 2008; 190:151-157
9.
Karmazyn B, Werner EA, Rejaie B, Applegate KE. Mesenteric lymph nodes in children: what is normal? Pediatr Radiol 2005; 35:774-777
10.
Brody AS, Frush DP, Huda W, Brent RL; American Academy of Pediatrics Section on Radiology. Radiation risk to children from computed tomography. Pediatrics 2007; 120:677-682
11.
Frush DP, Applegate K. Computed tomography and radiation: understanding the issues. J Am Coll Radiol 2004; 1:113-119
12.
Tack D, Sourtzis S, Delpierre I, de Maertelaer V, Gevenois PA. Low-dose unenhanced multidetector CT of patients with suspected renal colic. AJR 2003; 180:305-311
13.
Poletti PA, Platon A, Rutschmann OT, Schmidlin FR, Iselin CE, Becker CD. Low-dose versus standard-dose CT protocol in patients with clinically suspected renal colic. AJR 2007; 188:927-933
14.
Heneghan JP, McGuire KA, Leder RA, DeLong DM, Yoshizumi T, Nelson RC. Helical CT for nephrolithiasis and ureterolithiasis: comparison of conventional and reduced radiation-dose techniques. Radiology 2003; 229:575-580
15.
Hamm M, Knopfle E, Wartenberg S, Wawroschek F, Weckermann D, Harzmann R. Low dose unenhanced helical computerized tomography for the evaluation of acute flank pain. J Urol 2002; 167:1687-1691
16.
Kalra MK, Maher MM, D'Souza RV, et al. Detection of urinary tract stones at low-radiation-dose CT with z-axis automatic tube current modulation: phantom and clinical studies. Radiology 2005; 235:523-529
17.
Smith RC, Verga M, Dalrymple N, McCarthy S, Rosenfield AT. Acute ureteral obstruction: value of secondary signs of helical unenhanced CT. AJR 1996; 167:1109-1113

Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: 143 - 149
PubMed: 19098193

History

Submitted: June 13, 2008
Accepted: July 21, 2008

Keywords

  1. CT
  2. pediatric imaging
  3. radiation
  4. renal stones

Authors

Affiliations

Boaz Karmazyn
Department of Pediatric Radiology, Indiana University School of Medicine, Riley Hospital for Children, 702 Barnhill Dr., Rm. 1053, Indianapolis, IN 46202.
Donald P. Frush
Department of Radiology, Duke University School of Medicine, Durham, NC 27710.
Kimberly E. Applegate
Department of Pediatric Radiology, Indiana University School of Medicine, Riley Hospital for Children, 702 Barnhill Dr., Rm. 1053, Indianapolis, IN 46202.
Charles Maxfield
Department of Radiology, Duke University School of Medicine, Durham, NC 27710.
Mervyn D. Cohen
Department of Pediatric Radiology, Indiana University School of Medicine, Riley Hospital for Children, 702 Barnhill Dr., Rm. 1053, Indianapolis, IN 46202.
Robert P. Jones
Department of Radiology, Duke University School of Medicine, Durham, NC 27710.

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