Emmanuel Christodoulou

Accuracies of the synthesized monochromatic CT numbers and effective atomic numbers obtained with a rapid kVp switching dual energy CT scanner

PURPOSE This study was performed to investigate the accuracies of the synthesized monochromatic images and effective atomic number maps obtained with the new GE Discovery CT750 HD CT scanner. METHODS A Gammex-RMI model 467 tissue characterization phantom and the CT number linearity section of a Phantom Laboratory Catphan 600 phantom were scanned using the dual energy (DE) feature on the GE CT750 HD scanner. Synthesized monochromatic images at various energies between 40 and 120 keV and effective atomic number (Z(eff)) maps were generated. Regions of interest were placed within these images/maps to measure the average monochromatic CT numbers and average Z(eff) of the materials within these phantoms. The true Z(eff) values were either supplied by the phantom manufacturer or computed using Mayneords equation. The linear attenuation coefficients for the true CT numbers were computed using the NIST XCOM program with the input of manufacturer supplied elemental compositions and densities. The effects of small variations in the assumed true densities of the materials were also investigated. Finally, the effect of body size on the accuracies of the synthesized monochromatic CT numbers was investigated using a custom lumbar section phantom with and without an external fat-mimicking ring. RESULTS Other than the Z(eff) of the simulated lung inserts in the tissue characterization phantom, which could not be measured by DECT, the Z(eff) values of all of the other materials in the tissue characterization and Catphan phantoms were accurate to 15%. The accuracies of the synthesized monochromatic CT numbers of the materials in both phantoms varied with energy and material. For the 40-120 keV range, RMS errors between the measured and true CT numbers in the Catphan are 8-25 HU when the true CT numbers were computed using the nominal plastic densities. These RMS errors improve to 3-12 HU for assumed true densities within the nominal density +/- 0.02 g/cc range. The RMS errors between the measured and true CT numbers of the tissue mimicking materials in the tissue characterization phantom over the 40-120 keV range varied from about 6 HU-248 HU and did not improve as dramatically with small changes in assumed true density. CONCLUSIONS Initial tests indicate that the Z(eff) values computed with DECT on this scanner are reasonably accurate; however, the synthesized monochromatic CT numbers can be very inaccurate, especially for dense tissue mimicking materials at low energies. Furthermore, the synthesized monochromatic CT numbers of materials still depend on the amount of the surrounding tissues especially at low keV, demonstrating that the numbers are not truly monochromatic. Further research is needed to develop DE methods that produce more accurate synthesized monochromatic CT numbers.

Use of Medical Imaging Procedures With Ionizing Radiation in Children: A Population-Based Study

OBJECTIVE To determine population-based rates of the use of diagnostic imaging procedures with ionizing radiation in children, stratified by age and sex. DESIGN Retrospective cohort analysis. SETTING All settings using imaging procedures with ionizing radiation. PATIENTS Individuals younger than 18 years, alive, and continuously enrolled in UnitedHealthcare between January 1, 2005, and December 31, 2007, in 5 large US health care markets. MAIN OUTCOME MEASURES Number and type of diagnostic imaging procedures using ionizing radiation in children. RESULTS A total of 355 088 children were identified; 436 711 imaging procedures using ionizing radiation were performed in 150 930 patients (42.5%). The highest rates of use were in children older than 10 years, with frequent use in infants younger than 2 years as well. Plain radiography accounted for 84.7% of imaging procedures performed. Computed tomographic scans-associated with substantially higher doses of radiation-were commonly used, accounting for 11.9% of all procedures during the study period. Overall, 7.9% of children received at least 1 computed tomographic scan and 3.5% received 2 or more, with computed tomographic scans of the head being the most frequent. CONCLUSIONS Exposure to ionizing radiation from medical diagnostic imaging procedures may occur frequently among children. Efforts to optimize and ensure appropriate use of these procedures in the pediatric population should be encouraged.

Model-based Iterative Reconstruction: Effect on Patient Radiation Dose and Image Quality in Pediatric Body CT

PURPOSE To retrospectively compare image quality and radiation dose between a reduced-dose computed tomographic (CT) protocol that uses model-based iterative reconstruction (MBIR) and a standard-dose CT protocol that uses 30% adaptive statistical iterative reconstruction (ASIR) with filtered back projection. MATERIALS AND METHODS Institutional review board approval was obtained. Clinical CT images of the chest, abdomen, and pelvis obtained with a reduced-dose protocol were identified. Images were reconstructed with two algorithms: MBIR and 100% ASIR. All subjects had undergone standard-dose CT within the prior year, and the images were reconstructed with 30% ASIR. Reduced- and standard-dose images were evaluated objectively and subjectively. Reduced-dose images were evaluated for lesion detectability. Spatial resolution was assessed in a phantom. Radiation dose was estimated by using volumetric CT dose index (CTDI(vol)) and calculated size-specific dose estimates (SSDE). A combination of descriptive statistics, analysis of variance, and t tests was used for statistical analysis. RESULTS In the 25 patients who underwent the reduced-dose protocol, mean decrease in CTDI(vol) was 46% (range, 19%-65%) and mean decrease in SSDE was 44% (range, 19%-64%). Reduced-dose MBIR images had less noise (P > .004). Spatial resolution was superior for reduced-dose MBIR images. Reduced-dose MBIR images were equivalent to standard-dose images for lungs and soft tissues (P > .05) but were inferior for bones (P = .004). Reduced-dose 100% ASIR images were inferior for soft tissues (P < .002), lungs (P < .001), and bones (P < .001). By using the same reduced-dose acquisition, lesion detectability was better (38% [32 of 84 rated lesions]) or the same (62% [52 of 84 rated lesions]) with MBIR as compared with 100% ASIR. CONCLUSION CT performed with a reduced-dose protocol and MBIR is feasible in the pediatric population, and it maintains diagnostic quality.

Radiation dosimetry in digital breast tomosynthesis: Report of AAPM Tomosynthesis Subcommittee Task Group 223

The radiation dose involved in any medical imaging modality that uses ionizing radiation needs to be well understood by the medical physics and clinical community. This is especially true of screening modalities. Digital breast tomosynthesis (DBT) has recently been introduced into the clinic and is being used for screening for breast cancer in the general population. Therefore, it is important that the medical physics community have the required information to be able to understand, estimate, and communicate the radiation dose levels involved in breast tomosynthesis imaging. For this purpose, the American Association of Physicists in Medicine Task Group 223 on Dosimetry in Tomosynthesis Imaging has prepared this report that discusses dosimetry in breast imaging in general, and describes a methodology and provides the data necessary to estimate mean breast glandular dose from a tomosynthesis acquisition. In an effort to maximize familiarity with the procedures and data provided in this Report, the methodology to perform the dose estimation in DBT is based as much as possible on that used in mammography dose estimation.

Imaging Trends and Radiation Exposure in Pediatric Inflammatory Bowel Disease at an Academic Children's Hospital

OBJECTIVE The purpose of this study was to retrospectively evaluate diagnostic imaging trends and radiation exposure in pediatric inflammatory bowel disease (IBD) at a U.S. academic childrens hospital between 2001 and 2010. MATERIALS AND METHODS Pediatric IBD patients within our health system during the 2001, 2006, and 2010 calendar years were identified. The number of abdominopelvic radiologic and endoscopic examinations (total and by modality) performed during each 1-year-period was recorded for each subject. Means were compared using the Wilcoxon rank sum test. The cumulative lifetime number of diagnostic examinations by modality and estimated effective radiation dose (using Monte Carlo simulation software and CT dose-length product values) was calculated for the 2010 IBD subject cohort. RESULTS There was a 53% increase in the average number of abdominopelvic diagnostic examinations obtained per pediatric IBD patient comparing 2001 with 2010 (1.29 ± 2.19 vs 1.98 ± 3.46, p = 0.004). Abdominal radiography (p = 0.02), MRI (p < 0.0001), and esophagogastroduodenoscopy (EGD) (p = 0.01) showed significantly increased use. The increase in use of CT and ileocolonoscopy was not significant (p > 0.05). There was significantly reduced use of contrast enema, small-bowel follow-through (SBFT), and upper gastrointestinal (UGI) series (all, p < 0.0001). The average pediatric IBD patient seen in 2010 (mean age, 13.9 years) had undergone 1.08 CT, 0.82 MRI, 1.36 abdominal radiographic, 0.14 contrast enema, 0.52 SBFT, 0.54 UGI, 1.00 ileocolonoscopy, and 0.72 EGD examinations during his or her lifetime, with an average cumulative lifetime estimated effective radiation dose of 4.6 mSv. CONCLUSION Although the number of yearly diagnostic examinations performed for pediatric IBD patients increased significantly between 2001 and 2010, the cumulative lifetime estimated effective radiation dose is relatively low in most of these patients.

Digital breast tomosynthesis: studies of the effects of acquisition geometry on contrast-to-noise ratio and observer preference of low-contrast objects in breast phantom images

The effect of acquisition geometry in digital breast tomosynthesis was evaluated with studies of contrast-to-noise ratios (CNRs) and observer preference. Contrast-detail (CD) test objects in 5 cm thick phantoms with breast-like backgrounds were imaged. Twelve different angular acquisitions (average glandular dose for each ~1.1 mGy) were performed ranging from narrow angle 16° with 17 projection views (16d17p) to wide angle 64d17p. Focal slices of SART-reconstructed images of the CD arrays were selected for CNR computations and the reader preference study. For the latter, pairs of images obtained with different acquisition geometries were randomized and scored by 7 trained readers. The total scores for all images and readings for each acquisition geometry were compared as were the CNRs. In general, readers preferred images acquired with wide angle as opposed to narrow angle geometries. The mean percent preferred was highly correlated with tomosynthesis angle (R = 0.91). The highest scoring geometries were 60d21p (95%), 64d17p (80%), and 48d17p (72%); the lowest scoring were 16d17p (4%), 24d9p (17%) and 24d13p (33%). The measured CNRs for the various acquisitions showed much overlap but were overall highest for wide-angle acquisitions. Finally, the mean reader scores were well correlated with the mean CNRs (R = 0.83).

The use of high resolution computerized tomography (HRCT) of the chest in evaluating the effect of tobramycin solution for inhalation in cystic fibrosis lung disease

To compare the usefulness of HRCT of the chest versus spirometric measures (PFTs) in evaluating the effect of tobramycin solution for inhalation (TSI) in cystic fibrosis (CF).

The predicted increased cancer risk associated with a single computed tomography examination for calculus detection in pediatric patients compared with the natural cancer incidence.

Objectives: The objective of the study was to estimate the increased lifetime cancer risk associated with a single computed tomography (CT) examination for calculus detection in pediatric patients and compare it with the lifetime natural cancer risk. Methods: We used the program CT-Expo to calculate the radiation doses to various abdominal and pelvic organs for age-appropriate pediatric renal stone CT examination protocols used at our institution. Using the Biological Effects of Ionizing Radiation (BEIR) VII report, we estimated the lifelong cancer risk for these organs and compared it with the natural cancer risk for the same organs as predicted by the Surveillance, Epidemiology and End Results data from the National Cancer Institute. Results: For children 10 years or younger at the time of the examination, about 3 radiation-induced cancers are predicted for every 1000 naturally occurring cancers, and for children 15 years old, about 2 radiation-induced cancers are predicted for every 1000 naturally occurring cancers. The radiation dose from this examination is approximately equivalent to 1 to 2 years of background radiation. Conclusions: The ratio of the risk for any abdominal and pelvic cancer due to a single CT examination for calculus detection to the risk of a naturally occurring cancer over the lifetime of a child is estimated to be 2/1000 to 3/1000. With this information, the emergency department pediatrician can more effectively counsel parents about the risk-benefit aspects of the CT examination for renal calculus disease in their children.

Raise the Bar and Lower the Dose: Current and Future Strategies for Radiation Dose Reduction in Head and Neck Imaging

SUMMARY: Technologic advances in CT have generated a dramatic increase in the number of CT studies, with a resultant increase in the radiation dose related to CT scanning. Such increase in radiation dose is becoming a concern for the radiology community, especially with increasing public awareness of the dose burden related to examinations. To cope with the increase in CT-related radiation exposure, it is becoming necessary to optimize CT imaging protocols and apply radiation dose reduction techniques to ensure the best imaging with the lowest radiation dose.

Radiation dose reduction during neurointerventional procedures by modification of default settings on biplane angiography equipment

Background Neurointerventional procedures represent a significant source of ionizing radiation. We sought to assess the effect during neurointerventional procedures of varying default rates of radiation dose in fluoroscopy (F) and image acquisition (IA) modes, and frame rates during cine acquisition (CINE) on total X-ray dose, acquisition exposures, fluoroscopy time, and complications. Methods We retrospectively reviewed procedures performed with two radiation dose and CINE settings: a factory setting dose cohort (30 patients, F 45 nGy/pulse, IA 3.6 μGy/pulse, factory CINE frame rate) and a reduced dose cohort (30 patients, F 32 nGy/pulse, IA 1.2 μGy/pulse, with a decreased CINE frame rate). Total radiation dose, dose area product, number of acquisition exposures, fluoroscopy time, and complications were compared between the groups. Means comparisons (t tests) were employed to evaluate differences in the outcome variables between the two groups. p Value <0.05 was considered significant. Results The reduced dose cohort had a significant reduction in mean radiation dose (factory, 3650 mGy; reduced, 1650 mGy; p=0.005) and dose area product (factory, 34 700 μGy×m2; reduced, 15 000 μGy×m2; p=0.02). There were no significant differences between cohorts in acquisition exposure (p=0.73), fluoroscopy time (p=0.45), or complications. Conclusions Significant reductions in radiation dose delivered by neurointerventional procedures can be achieved through simple modifications of default radiation dose in F and IA and frame rate during CINE without an increase in procedural complexity (fluoroscopy time) or rate of complications.