| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Gastrointestinal Imaging |
1 From the Department of Radiology, Division of Abdominal Imaging and Intervention, Massachusetts General Hospital and Harvard Medical School, White 270-E, 55 Fruit St, Boston, MA 02114 (M.K.K., M.M.M., R.S.K., E.F.H., S.S.); GE Yokogawa Medical Systems, Tokyo, Japan (T.H.); and GE Medical Systems, Waukesha, Wis (T.L.T.). From the 2003 RSNA scientific assembly. Received September 17, 2003; revision requested December 2; revision received January 6, 2004; accepted February 2. Address correspondence to M.K.K. (e-mail: mannudeep_k_kalra@yahoo.com).
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
|---|
MATERIALS AND METHODS: Ninety-five patients underwent 16-section multi–detector row CT of the abdomen and pelvis with z-axis modulation at noise indexes of 10.5, 11.0, 11.5, and 12.0 HU with 10–380 mA. Subsequently, 58 patients were scanned at noise indexes of 12.5 and 15.0 HU with 75–380 mA. The weights of all subjects were recorded, and transverse and anteroposterior diameters were measured. The CT images were evaluated for abnormalities and graded for image quality in terms of noise and diagnostic acceptability by using a five-point scale. Objective noise in the liver parenchyma was measured, and the tube current was recorded at each section in all 153 patients. Statistical analyses were performed to determine the appropriate noise index and to assess the effect of patient weight and abdominal diameters on image noise and diagnostic acceptability at different noise indexes. Tube current–time products (in milliampere seconds) at various noise indexes were compared with those at CT previously performed without z-axis modulation.
RESULTS: No significant difference in subjective image noise or diagnostic acceptability was found at noise indexes of 10.5–15.0 HU (P = .14), and objective noise was significantly inferior only at a noise index of 15.0 HU (P = .009). Compared with CT scanning at a 10.5-HU noise index, CT scanning at 12.5- and 15.0-HU noise indexes yielded, respectively, 10.0% and 41.3% reductions in radiation exposure. Patient weight and abdominal diameters affected subjective image quality.
CONCLUSION: Use of a 15.0-HU noise index at 75–380 mA results in acceptable subjective image noise and diagnostic acceptability but significantly greater objective image noise at routine abdominal-pelvic CT. For greater image quality demands, a noise index of 12.5 HU results in acceptable image quality and a 19.6% reduction in radiation exposure.
© RSNA, 2004
Index terms: Abdomen, CT, 70.12111 • Computed tomography (CT), image quality • Computed tomography (CT), radiation exposure • Pelvis, CT, 813.12111
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
|---|
Automatic tube current modulation is a method of adjusting the tube current according to the changing patient anatomy and quantum noise in the projections to maintain a selected level of noise in the image and improve radiation dose efficiency (2). The two tube current modulation methods used on CT scanners today—angular (ie, x-axis and y-axis) modulation and z-axis modulation—are complementary in minimizing radiation dose. The z-axis modulation technique enables one to adjust the CT tube current and regulate the noise on the final image to a level (ie, noise index) selected by the user.
The purpose of our study was to retrospectively determine the optimal noise indexes required to obtain diagnostically acceptable abdominal-pelvic CT images with z-axis modulation.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
|---|
Ninety-five patients underwent 16-section multi–detector row abdominal-pelvic CT with z-axis modulation at noise indexes of 10.5 (n = 21), 11.0 (n = 20), 11.5 (n = 32), and 12.0 (n = 22) HU, with minimal and maximal tube current thresholds of 10 and 380 mA, respectively. The remaining scanning parameters were held constant and included 140 kVp, a 0.5-second gantry rotation time, a beam pitch of 0.938:1, 16 x 1.25-mm detector collimation, and an 18.75-mm table feed per rotation. All image data were reconstructed by using a standard reconstruction algorithm to obtain a reconstructed section thickness of 5 mm. Fifty-eight patients were scanned at noise indexes of 12.5 (n = 32) and 15.0 (n = 26) HU, with minimal and maximal tube current thresholds of 75 and 380 mA, respectively. The remaining parameters were identical to those used to scan the previously described 95 patients.
An objective image noise level that demarcates a threshold of minimal acceptable image quality achieved with the lowest possible radiation dose has not been defined (2). The selection of scanning parameters, particularly the tube current, has been based largely on the preference of individual CT centers or technologists. Therefore, the z-axis modulation technique enables one to address the important task of selecting the appropriate noise levels on reconstructed images. The z-axis modulation technique assessed in the present study is used to adjust the tube current to maintain a user-selected quantum noise level on reconstructed CT images. With use of this technique, the attenuation and shape of scout projections obtained in the patient are used to determine the extent of tube current modulation for each CT image obtained in the scanning direction within the anatomic region being scanned.
The system determines the tube current by using the patient’s scout projection data and a set of empirically determined noise prediction coefficients as the reference technique parameters, which consist of an arbitrary 2.5-mm section thickness at the selected peak kilovoltage and 200 mAs. The noise index is approximately equal to the image noise (ie, the standard deviation) in the central region of an image obtained by scanning a uniform phantom. With every 5% decrease in noise index (in Hounsfield units), image quality improves, but the radiation exposure is expected to increase by 10%. Conversely, with every 5% increase in noise index, the radiation exposure is expected to decrease by 10%, with a concomitant decrease in image quality. Thus, selecting the appropriate noise index is fundamental to obtaining images of acceptable quality at an optimal radiation exposure with the z-axis modulation technique because a low noise index may yield higher image quality, but it will also cause the delivery of excess radiation to the patient. Conversely, a high noise index will result in radiation savings at the price of "noisier" images.
Of the 153 patients in the study cohort, 81 had been examined previously with the 16-section multi–detector row CT scanner (GE LightSpeed 4.X), a fixed–tube-current technique (120–240 mAs), and remaining scanning parameters that were identical to those used to perform CT with the z-axis modulation technique—specifically, 140 kVp, a 0.5-second gantry rotation time, a beam pitch of 0.938:1, 16 x 1.25-mm detector collimation, and an 18.75-mm table feed per rotation.
Qualitative CT Image Analysis
The CT images were reviewed on a digital picture-archiving system diagnostic workstation (AGFA Impax RS 3000 1K review station; AGFA Technical Imaging Systems, Richfield Park, NJ) by two abdominal radiologists (M.M.M. with 5 years experience and M.K.K. with 3 years experience) who were blinded to the scanning techniques used. Each radiologist independently graded the images for noise and diagnostic acceptability by using a five-point scale: Grade 1 meant unacceptable; grade 2, suboptimal; grade 3, acceptable; grade 4, above average; and grade 5, excellent. These two image features were graded at five anatomic levels: the upper part of the liver at the level of the diaphragm, the porta hepatis, the right kidney hilum, the iliac crest, and the upper margin of the acetabulum.
Diagnostic acceptability scores were based on the contrast of soft tissues, the sharpness of tissue interfaces, lesion conspicuity, and the degree of image degradation caused by noise streaking or beam-hardening artifacts. Diagnostic acceptability was judged to be acceptable when the sharpness of different structures, the soft-tissue contrast, and lesion visualization were satisfactory; unacceptable when these image attributes were deemed unsatisfactory; and excellent when these image attributes were deemed superior. Acceptable image noise was defined as an average amount of mottle or graininess associated with satisfactory visualization of small anatomic structures, such as blood vessels and the interfaces between structures with variable attenuation. Unacceptable image noise was defined as mottle that impaired the visualization of these structures. Excellent image noise was characterized by the presence of minimal or no appreciable mottle. In addition, both readers were asked to record the abnormality seen on each image.
Quantitative Data
The weights of all the subjects (mean weight, 78 kg; weight range, 45–132 kg) were recorded before they underwent CT. For each patient, the maximal transverse (mean, 32.72 cm; range, 23.3–44.5 cm) and anteroposterior (mean, 25.2 cm; range, 15.8–36.8 cm) diameters of the abdomen were measured from transverse images obtained at the level of the upper pole of the right kidney by using software on the digital picture-archiving system diagnostic workstation (AGFA Impax RS 3000 1K review station). Quantitative image noise—that is, the standard deviation of the mean attenuation coefficient values—was measured (by R.S.K.) at the level of the porta hepatis in the liver parenchyma by using a region of interest with a constant shape (circular) and size (40 square pixels). The tube current was recorded in each section in all 153 patients—a total of 13 822 sections—and a mean milliampere value for each examination was calculated from these data.
The tube current and gantry rotation time in the 81 patients who had previously undergone abdominal-pelvic CT with the fixed–tube-current technique were also recorded. Subsequently, the tube current–time product for each examination was calculated by multiplying the tube current by the tube rotation time.
Phantom Experiment
To corroborate the effect of patient size (weight or cross-sectional abdominal diameters) on image quality with z-axis modulation, a cone-shaped polypropylene phantom (AutomA cone phantom; GE Yokogawa Medical Systems, Tokyo, Japan) that was 30 cm in diameter at the base and 30 cm in height was scanned with the 16-section multi–detector row CT scanner (GE LightSpeed 4.X). The following scanning parameters were used: a constant noise index of 10.0 HU; minimal and maximal tube current thresholds of 10 and 440 mA, respectively; 120 kVp; a 1-second gantry rotation time; and variable pitch and table feed per rotation combinations, including, respectively, 0.562:1 and 5.62 mm, 0.562:1 and 11.25 mm, 0.938:1 and 9.38 mm, 0.938:1 and 18.75 mm, 1.375:1 and 13.75 mm, 1.375:1 and 27.5 mm, 1.750:1 and 17.5 mm, and 1.750:1 and 35.0 mm. Image noise was measured (by T.H.) in the center of CT images acquired at 15 and 30 cm of the phantom’s diameter to study the effect of phantom size on image noise at a constant noise index.
In addition, to corroborate the effect of patient miscentering in the gantry isocenter on image quality with z-axis modulation, an elliptical polypropylene phantom (GE Medical Systems) with 30 x 21.5-cm cross-sectional diameters and an attenuation coefficient equivalent to –100 HU was scanned in an axial mode at different positions with the 16-section multi–detector row CT scanner. After the initial scanning of the phantom with its center perfectly aligned with the gantry isocenter, subsequent images were acquired with the phantom center shifted from the gantry isocenter in vertical and horizontal directions to variable extents. Image noise was measured (by T.L.T.) in the center of the images; rectangular regions of interest that measured 50 x 50 square pixels and were laterally centered but positioned 2.5 cm above the vertical center of the phantom were imaged.
Statistical Analysis of Patient Imaging Data
The Student t test was performed by using computer software (Excel; Microsoft, Redmond, Washington) to assess differences in age between the male and female patients in the study cohort. Mean values of subjective image noise and diagnostic acceptability ± standard deviations were determined for individual noise index categories by using the Excel software. The Wilcoxon signed rank test was performed by using computer software (SAS/STAT; SAS, Cary, NC) to compare subjective image noise and diagnostic acceptability at different noise indexes. The mean values of objective noise ± standard deviations in different noise index categories were determined. In addition, the objective image noises at different noise indexes were compared by using the Student t test.
The association between patient weight and anteroposterior and transverse diameters was determined by using the Pearson correlation test. To assess the homogeneity of the study cohort, significant differences in weight and anteroposterior and transverse diameters were calculated by using the Student t test. Subsequently, the mean patient weights and cross-sectional diameters, ± the standard deviations, associated with mean subjective image quality (image quality = [mean subjective noise score + mean diagnostic acceptability score]/2) scores of 3 (acceptable quality) or higher and of lower than 3 were determined. Significant differences in image quality based on anthropometric parameters (patient weight and cross-sectional diameters) were determined by using one-way analysis of variance. The Mood median test was used to determine significant differences in objective noise values among patients with different anthropometric parameters.
Statistical linear correlations between the mean milliampere-second values used with z-axis modulation and the patient sizes (ie, weight and cross-sectional diameters) were determined. In addition, the mean milliampere-second values required to obtain images at different noise indexes were estimated by using the Excel software. Subsequently, the mean milliampere-second values for scans with significant decreases in image quality in terms of acceptable image quality score (ie, grade 3) were determined. Mean milliampere-second values and percentage changes (increase or decrease) in milliampere-second value at various noise indexes, relative to the values used at fixed–tube-current CT, were determined. P < .05 was considered to indicate a significant difference. The degree of interobserver concordance was determined by using the weighted 
test.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
|---|
|
The quantitative image noise measurements obtained at different noise indexes in the study are summarized in Table 1. As expected, the quantitative image noise at a noise index of 15.0 HU was significantly greater than that at lower noise indexes (P < .001). In addition, the scans of 57 (37.2%) of the 153 patients were assigned an image quality score of less than 3, whereas the scans of the remaining 96 (62.7%) patients were assigned an acceptable or above acceptable image quality score. We noted strong statistical correlations between patient weight and cross-sectional diameters (r = 0.82). We observed no significant differences in the weight or cross-sectional anteroposterior and transverse diameters of patients scanned at different noise indexes (P = .5 to P = .9). However, we observed significant differences (P = .007 to P < .001) in the mean weights and cross-sectional diameters (± standard deviations) between patients whose scans were assigned mean subjective image quality scores lower than 3 and patients whose scans were assigned mean subjective image quality scores equal to or higher than 3 (Tables 2–4).
|
|
|
|
|
|
|
|
The mean milliampere-second values (± standard deviations) at different noise indexes, as well as the mean radiation dose savings relative to the radiation dose delivered at CT examinations previously performed in 81 of the same patients with the fixed–tube-current technique, are summarized in Table 5. Compared with the reduced mean milliampere-second value achieved with a noise index of 10.5 HU, 10.0% and 41.3% reductions in mean milliampere-second values were achieved at CT examinations performed with 12.5- and 15.0-HU noise indexes, respectively. The CT scans with mean subjective image quality scores significantly lower than 3 (P < .001) were obtained with a mean tube current of 75 mA. There was significant interobserver concordance between the two readers (weighted coefficient, 0.7; P < .05).
|
|
.01). Image noise increased by 22% and 30% when the phantom was vertically miscentered by 4 and 6 cm, respectively. The tube current would need to be increased by 64% and 100%, respectively, to obtain a noise level similar to that in a properly centered phantom (Fig 4). With lateral miscentering of the phantom, the noise increased by 13% and 17%, respectively, at 4- and 6-cm shifts from the gantry isocenter. With lateral miscentering, the tube current would need to be increased by 32% and 45%, respectively, to achieve a similar noise level.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
|---|
The present study results show that acceptable subjective image noise and diagnostic acceptability can be achieved with a minimal tube current threshold of 75 mA and at noise indexes of 12.5 and 15.0 HU, as compared with the noise indexes recommended by the vendor (10.5–12.0 HU). The greater milliampere-second savings noted with noise indexes of 11.0–12.0 HU, 37.6%–51.2%, as compared with the 19.6% savings at a noise index of 12.5 HU, can be attributed to the higher minimal tube current threshold of 75 mA used at examinations performed with 12.5 HU, as compared with the 10-mA threshold used with 11.0–12.0 HU. Indeed, all CT examinations that resulted in significant deteriorations in subjective image noise and diagnostic acceptability were performed at noise indexes of 11.0–12.0 HU, with a mean milliampere-second value of less than 37.5 mAs (<75 mA). Therefore, to avoid unexpected decreases in tube current and image quality, we set a minimal tube current threshold of 75 mA according to the vendor’s recommendation (60–80 mA) and increased the noise indexes to 12.5 and 15.0 HU.
Despite our selection of a higher minimal tube current threshold, at 12.5 HU there was a 19.6% reduction in the mean milliampere-second value without an increase in objective noise, as compared with a 16.6% reduction in the mean milliampere-second value at 10.5 HU. On the other hand, a 55.2% reduction in the mean milliampere-second value was noted at a noise index of 15.0 HU, as compared with the 16.6% reduction at the 10.5-HU noise index. These radiation savings with use of z-axis modulation are consistent with the effective milliampere-second reductions reported in previous studies in which the angular modulation technique was used (6–8). Compared with fixed–tube-current CT, angular modulation CT examinations of the abdomen and pelvis in patients and cadavers performed in earlier studies have reportedly yielded 15%–23% reductions in radiation dose (7,8).
In view of concerns about increasing radiation doses at CT, radiologists have begun to consider some noisier images that were acquired at lower radiation doses to be diagnostically acceptable. Consequently, the overall image quality scores of less than 3 in 57 (37.2%) patients in the current study were largely due to diagnostically acceptable images that had more noise than was acceptable.
The finding of a substantial correlation between mean milliampere-second value selected by using z-axis modulation and patient anthropometric size is consistent with the effective modulation of the tube current in the scanning direction and with the results of previous studies reported in the literature, in which a correlation between reduced tube current with angular modulation and body mass index was documented (8). However, contrary to previous study results, the small (<68 kg) patients in our study who were scanned at a mean of 63.4 mAs with z-axis modulation had significant decreases in subjective image noise (P = .005). Also, the mean patient weight and cross-sectional diameter values associated with scans with an image quality score lower than 3 were significantly lower than those associated with scans with an image quality score of 3 or higher. This finding was supported by a slight (9.1%) increase in noise on the CT images acquired at small cross-sectional diameters of the AutomA cone phantom, although the objective noise measurements on the patient images did not show any significant difference between the small and large patients (P = .545). This decreased image quality may have had a number of causes, including a disproportionate decrease in tube current with the current version of the z-axis modulation technique; selective miscentering of small patients in the gantry isocenter; inherently poor-contrast images due to a paucity of fat in small patients; and inadequate x-ray beam energy with a substantially reduced tube current.
The strong statistical evidence of a correlation between the tube current modulation achieved by using the described technique and patient anthropometric size suggests that the decrease in subjective image quality for small patients may not have been a result of an overly reduced tube current with use of the technique. Indeed, results of previous studies with adults have shown that a 50% reduction in tube current is possible in patients with small anthropometric size—albeit at tube currents greater than those used in the present study (96–120 mAs vs 63.4 mAs) (9).
Small patients are more likely to be miscentered in the scanner gantry isocenter. This miscentering can lead to inadvertent x-ray beam attenuation by the bow-tie filters and increased image noise or to the estimation of lower tube currents with use of the technique. Indeed, the results of experiments with the phantom positioned at different locations in the scanner gantry in the present study showed a significant increase in objective noise when the phantom was miscentered in the gantry isocenter. Although a lack of fat tissue in small patients can result in poor background contrast, which can make CT images of certain regions difficult to interpret, this explanation does not explain the compromise in objective noise observed in the cone phantom experiment.
Substantially decreased signal is a well-known phenomenon that occurs in regions such as the shoulders because of x-ray beam attenuation in a particular projection that results in photon noise contamination from the electronic noise of the data acquisition system (10). Special reconstruction algorithms and projective space adaptive filters are used to improve image quality in highly asymmetric situations (10). The substantial increase in noise caused by vertical phantom miscentering can be explained by the long axis of the phantom being positioned in high-attenuation regions of the "bow tie" for the long-axis projections. With the lower milliampere values used for small patients, this vertical miscentering can produce enhanced long attenuation and streaking noise effects similar to those at shoulder scanning.
Our phantom experiment results suggest that patient centering is a critical factor in maintaining the image quality of scans obtained in small patients. Indeed, the most intensive objective noise outliers were observed in only the small patients. Miscentering may be an explanation for these cases. Further studies are needed to investigate the phenomena that lead to decreased image quality at substantially reduced tube currents. Alternatively, special reconstruction algorithms and noise reduction filters may be needed to reduce the effect of substantial tube current reductions on image quality (10–12).
At present, two techniques can be used to prevent inadvertent decreases in image quality for small patients: stressing the importance of small patient centering and increasing the minimal tube current threshold to above 63.4 mAs. On the basis of the present study results, we recommend using a noise index of 15.0 HU with a minimal tube current threshold of 75 mA for routine abdominal-pelvic CT examinations. However, because objective image noise is substantially greater on images acquired with a 15.0-HU noise index, we use a noise index of 12.5 HU with a minimal tube current threshold of 75 mA for examinations, such as renal mass CT, that require greater image quality or thinner sections. In such circumstances, nonenhanced images are acquired at a 15-HU noise index to reduce the radiation dose. Further studies are needed to establish protocols for examinations performed with low radiation doses and fixed tube currents, such as CT of kidney stones and CT colonography, so that a higher noise index (>15.0 HU) can be selected, with resultant reductions in radiation dose (13,14).
There were limitations to our study. The effect of noise indexes greater than 15.0 HU on the image quality of abdominal-pelvic CT scans was not evaluated. Although further noise index reductions—especially for follow-up and high-contrast CT examinations such as CT of renal calculi and CT colonography—warrant investigation, the present study results indicate that substantial decreases in objective image noise can be achieved at a noise index of 15.0 HU. In addition, we did not compare the image quality of scans obtained at various noise indexes with those obtained by using the fixed–tube-current technique.
Another probable limitation is that for noise indexes greater than 12.0 HU, a minimal tube current threshold of 75 mA was chosen on the basis of the vendor’s recommendation to keep the lower tube current threshold between 60 and 80 mA and thus avoid an inadvertent decrease in tube current. Conversely, although the user can use the z-axis modulation technique to "cap" the maximal tube current threshold at any level or at the tube current level that he or she might have used with the fixed–tube-current technique to avoid an unexpected increase in tube current, we did not cap the maximal tube current threshold. By capping the maximal tube current we could have limited the capability of the technique in enabling us to obtain the desired image quality along the scanning direction (z-axis).
On the other hand, the technologists were instructed to review the milliampere setting table on the console before performing transverse CT to determine whether the maximal tube current threshold had been reached—this may have precluded our achieving the desired image quality—and to increase the tube rotation time until the threshold was circumvented. This additional step ensures against compromises in image quality due to larger patient size while maintaining an equivalent effective radiation dose. We did not perform a power analysis to determine the sample size of our study cohort because we were not aware of any previous studies in which the described z-axis modulation technique was assessed.
In the present study we introduce important factors that should be considered when using the z-axis modulation technique, including the necessity of using a lower noise index for small patients and the need for dedicated procedures to optimize pediatric examinations. Although use of the described technique does facilitate reduced radiation doses, there is a learning curve for understanding and optimizing its use. Introduction of the z-axis modulation technique warrants considerable changes in the CT scanning approaches used for specific protocols and in the assessment of different clinical indications.
In summary, we observed no significant difference in the subjective noise or diagnostic acceptability of CT images obtained at noise indexes of 10.5 and 15.0 HU (P = .14), and objective noise was significantly inferior only at a noise index of 15.0 HU (P = .009). For routine abdominal-pelvic CT examinations, a noise index of 12.5 HU with a minimal setting of 37.5 mAs is sufficient, whereas a 15.0-HU noise index may yield satisfactory image quality at nonenhanced phase scanning. It is critical to center small patients in the gantry isocenter and to increase the minimal tube current threshold to above 63.4 mAs.
|
FOOTNOTES |
|---|
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  S. Singh, M. K. Kalra, M. A. Moore, R. Shailam, B. Liu, T. L. Toth, E. Grant, and S. J. Westra Dose Reduction and Compliance with Pediatric CT Protocols Adapted to Patient Size, Clinical Indication, and Number of Prior Studies Radiology, July 1, 2009; 252(1): 200 - 208. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Matsubara, K. Koshida, K. Ichikawa, M. Suzuki, T. Takata, T. Yamamoto, and O. Matsui Misoperation of CT Automatic Tube Current Modulation Systems with Inappropriate Patient Centering: Phantom Studies Am. J. Roentgenol., April 1, 2009; 192(4): 862 - 865. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. A. Jaffe Reply Am. J. Roentgenol., March 1, 2009; 192(3): W141 - W141. [Full Text] [PDF]
|
|
|
|
|
|
T. Miyoshi, M. Kanematsu, H. Kondo, S. Goshima, Y. Tsuge, A. Hatcho, Y. Shiratori, M. Onozuka, N. Moriyama, and K. T. Bae Abdomen: Angiography with 16-Detector CT--Comparison of Image Quality and Radiation Dose between Studies with 0.625-mm and those with 1.25-mm Collimation Radiology, October 1, 2008; 249(1): 142 - 150. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Roggenland, S. A. Peters, S. P. Lemburg, T. Holland-Letz, V. Nicolas, and C. M. Heyer CT Angiography in Suspected Pulmonary Embolism: Impact of Patient Characteristics and Different Venous Lines on Vessel Enhancement and Image Quality Am. J. Roentgenol., June 1, 2008; 190(6): W351 - W359. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
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]
|
|
|
|
|
|
T. A. Jaffe, T. T. Yoshizumi, G. I. Toncheva, G. Nguyen, L. M. Hurwitz, and R. C. Nelson Early First-Trimester Fetal Radiation Dose Estimation in 16-MDCT Without and With Automated Tube Current Modulation Am. J. Roentgenol., April 1, 2008; 190(4): 860 - 864. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. T. Schindera, R. C. Nelson, T. L. Toth, G. T. Nguyen, G. I. Toncheva, D. M. DeLong, and T. T. Yoshizumi Effect of Patient Size on Radiation Dose for Abdominal MDCT with Automatic Tube Current Modulation: Phantom Study Am. J. Roentgenol., February 1, 2008; 190(2): W100 - W105. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Matsubara, K. Koshida, M. Suzuki, H. Tsujii, T. Yamamoto, and O. Matsui Comparison between 3-D and z-axis automatic tube current modulation technique in multidetector-row CT Radiat Prot Dosimetry, January 1, 2008; 128(1): 106 - 111. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Coursey, D. P. Frush, T. Yoshizumi, G. Toncheva, G. Nguyen, and S. B. Greenberg Pediatric Chest MDCT Using Tube Current Modulation: Effect on Radiation Dose with Breast Shielding Am. J. Roentgenol., January 1, 2008; 190(1): W54 - W61. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
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]
|
|
|
|
 |
|
 D. D. Cody and M. Mahesh AAPM/RSNA Physics Tutorials AAPM/RSNA Physics Tutorial for Residents: Technologic Advances in Multidetector CT with a Focus on Cardiac Imaging RadioGraphics, November 1, 2007; 27(6): 1829 - 1837. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A J Van Der Molen, W J H Veldkamp, and J Geleijns 16-slice CT: achievable effective doses of common protocols in comparison with recent CT dose surveys Br. J. Radiol., April 1, 2007; 80(952): 248 - 255. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Li, U. K. Udayasankar, T. L. Toth, J. Seamans, W. C. Small, and M. K. Kalra Automatic Patient Centering for MDCT: Effect on Radiation Dose Am. J. Roentgenol., February 1, 2007; 188(2): 547 - 552. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
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]
|
|
|
|
 |
|
 S. Namasivayam, M.K. Kalra, K.M. Pottala, S.M. Waldrop, and P.A. Hudgins Optimization of Z-Axis Automatic Exposure Control for Multidetector Row CT Evaluation of Neck and Comparison with Fixed Tube Current Technique for Image Quality and Radiation Dose AJNR Am. J. Neuroradiol., November 1, 2006; 27(10): 2221 - 2225. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Graser, B. J. Wintersperger, C. Suess, M. F. Reiser, and C. R. Becker Dose reduction and image quality in MDCT colonography using tube current modulation. Am. J. Roentgenol., September 1, 2006; 187(3): 695 - 701. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Rizzo, M. Kalra, B. Schmidt, T. Dalal, C. Suess, T. Flohr, M. Blake, and S. Saini Comparison of Angular and Combined Automatic Tube Current Modulation Techniques with Constant Tube Current CT of the Abdomen and Pelvis. Am. J. Roentgenol., March 1, 2006; 186(3): 673 - 679. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. K. Kalra, S. Rizzo, M. M. Maher, E. F. Halpern, T. L. Toth, J.-A. O. Shepard, and S. L. Aquino Chest CT Performed with Z-Axis Modulation: Scanning Protocol and Radiation Dose Radiology, October 1, 2005; 237(1): 303 - 308. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. M. Chapman, M. Kalra, E. Halpern, B. Grottkau, M. Albright, and D. Jaramillo 16-MDCT of the Posttraumatic Pediatric Elbow: Optimum Parameters and Associated Radiation Dose Am. J. Roentgenol., August 1, 2005; 185(2): 516 - 521. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. K. Kalra, M. M. Maher, R. V. D'Souza, S. Rizzo, E. F. Halpern, M. A. Blake, and S. Saini Detection of Urinary Tract Stones at Low-Radiation-Dose CT with Z-Axis Automatic Tube Current Modulation: Phantom and Clinical Studies Radiology, May 1, 2005; 235(2): 523 - 529. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. J. Vrtiska, J. G. Fletcher, and C. H. McCollough State-of-the-Art Imaging With 64-Channel Multidetector CT Angiography Perspectives in Vascular Surgery and Endovascular Therapy, March 1, 2005; 17(1): 3 - 8. [Abstract] [PDF]
|
|
|
|
|
|
S. M. R. Rizzo, M. K. Kalra, M. M. Maher, M. A. Blake, T. L. Toth, and S. Saini Do Metallic Endoprostheses Increase Radiation Dose Associated with Automatic Tube-Current Modulation in Abdominal-Pelvic MDCT? A Phantom and Patient Study Am. J. Roentgenol., February 1, 2005; 184(2): 491 - 496. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. K. Kalra, M. M. Maher, T. L. Toth, B. Schmidt, B. L. Westerman, H. T. Morgan, and S. Saini Techniques and Applications of Automatic Tube Current Modulation for CT Radiology, December 1, 2004; 233(3): 649 - 657. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| RADIOLOGY | RADIOGRAPHICS | RSNA JOURNALS ONLINE |
