Comparison of image quality and radiation dose between split-filter dual-energy images and single-energy images in single-source abdominal CT.

OBJECTIVES: To compare image quality and radiation dose of abdominal split-filter dual-energy CT (SF-DECT) combined with monoenergetic imaging to single-energy CT (SECT) with automatic tube voltage selection (ATVS). METHODS: Two-hundred single-source abdominal CT scans were performed as SECT with ATVS (n = 100) and SF-DECT (n = 100). SF-DECT scans were reconstructed and subdivided into composed images (SF-CI) and monoenergetic images at 55 keV (SF-MI). Objective and subjective image quality were compared among single-energy images (SEI), SF-CI and SF-MI. CNR and FOM were separately calculated for the liver (e.g. CNRliv) and the portal vein (CNRpv). Radiation dose was compared using size-specific dose estimate (SSDE). Results of the three groups were compared using non-parametric tests. RESULTS: Image noise of SF-CI was 18% lower compared to SEI and 48% lower compared to SF-MI (p < 0.001). Composed images yielded higher CNRliv over single-energy images (23.4 vs. 20.9; p < 0.001), whereas CNRpv was significantly lower (3.5 vs. 5.2; p < 0.001). Monoenergetic images overcame this inferiority in CNRpv and achieved similar results compared to single-energy images (5.1 vs. 5.2; p > 0.628). Subjective sharpness was equal between single-energy and monoenergetic images and diagnostic confidence was equal between single-energy and composed images. FOMliv was highest for SF-CI. FOMpv was equal for SEI and SF-MI (p = 0.78). SSDE was significant lower for SF-DECT compared to SECT (p < 0.022). CONCLUSIONS: The combined use of split-filter dual-energy CT images provides comparable objective and subjective image quality at lower radiation dose compared to single-energy CT with ATVS. KEY POINTS: • Split-filter dual-energy results in 18% lower noise compared to single-energy with ATVS. • Split-filter dual-energy results in 11% lower SSDE compared to single-energy with ATVS. • Spectral shaping of split-filter dual-energy leads to an increased dose-efficiency.

Impact of model-based iterative reconstruction on low-contrast lesion detection and image quality in abdominal CT: a 12-reader-based comparative phantom study with filtered back projection at different tube voltages.

OBJECTIVES: To evaluate the impact of model-based iterative reconstruction (MBIR) on image quality and low-contrast lesion detection compared with filtered back projection (FBP) in abdominal computed tomography (CT) of simulated medium and large patients at different tube voltages. METHODS: A phantom with 45 hypoattenuating lesions was placed in two water containers and scanned at 70, 80, 100, and 120 kVp. The 120-kVp protocol served as reference, and the volume CT dose index (CTDIvol) was kept constant for all protocols. The datasets were reconstructed with MBIR and FBP. Image noise and contrast-to-noise-ratio (CNR) were assessed. Low-contrast lesion detectability was evaluated by 12 radiologists. RESULTS: MBIR decreased the image noise by 24% and 27%, and increased the CNR by 30% and 29% for the medium and large phantoms, respectively. Lower tube voltages increased the CNR by 58%, 46%, and 16% at 70, 80, and 100 kVp, respectively, compared with 120 kVp in the medium phantom and by 9%, 18% and 12% in the large phantom. No significant difference in lesion detection rate was observed (medium: 79-82%; large: 57-65%; P > 0.37). CONCLUSIONS: Although MBIR improved quantitative image quality compared with FBP, it did not result in increased low-contrast lesion detection in abdominal CT at different tube voltages in simulated medium and large patients. KEY POINTS: • MBIR improved quantitative image quality but not lesion detection compared with FBP. • Increased CNR by low tube voltages did not improve lesion detection. • Changes in image noise and CNR do not directly influence diagnostic accuracy.

Transatlantic Comparison of CT Radiation Doses in the Era of Radiation Dose-Tracking Software.

OBJECTIVE: The purpose of this study is to compare diagnostic reference levels from a local European CT dose registry, using radiation-tracking software from a large patient sample, with preexisting European and North American diagnostic reference levels. MATERIALS AND METHODS: Data (n = 43,761 CT scans obtained over the course of 2 years) for the European local CT dose registry were obtained from eight CT scanners at six institutions. Means, medians, and interquartile ranges of volumetric CT dose index (CTDIvol), dose-length product (DLP), size-specific dose estimate, and effective dose values for CT examinations of the head, paranasal sinuses, thorax, pulmonary angiogram, abdomen-pelvis, renal-colic, thorax-abdomen-pelvis, and thoracoabdominal angiogram were obtained using radiation-tracking software. Metrics from this registry were compared with diagnostic reference levels from Canada and California (published in 2015), the American College of Radiology (ACR) dose index registry (2015), and national diagnostic reference levels from local CT dose registries in Switzerland (2010), the United Kingdom (2011), and Portugal (2015). RESULTS: Our local registry had a lower 75th percentile CTDIvol for all protocols than did the individual internationally sourced data. Compared with our study, the ACR dose index registry had higher 75th percentile CTDIvol values by 55% for head, 240% for thorax, 28% for abdomen-pelvis, 42% for thorax-abdomen-pelvis, 128% for pulmonary angiogram, 138% for renal-colic, and 58% for paranasal sinus studies. CONCLUSION: Our local registry had lower diagnostic reference level values than did existing European and North American diagnostic reference levels. Automated radiation-tracking software could be used to establish and update existing diagnostic reference levels because they are capable of analyzing large datasets meaningfully.

Bone subtraction radiography in adult patients with cystic fibrosis.

Background Bone subtraction radiography allows reading pulmonary changes of chest radiographs more accurately without superimposition of bones. Purpose To evaluate the value of bone subtraction chest radiography using dual energy (DE) bone subtracted lung images compared to conventional radiographs (CR) in adult patients with cystic fibrosis (CF). Material and Methods Forty-nine DE radiographs of 24 patients (16 men) with CF (mean age, 32 years; age range, 18-71 years) were included. Lung function tests were performed within 10 days of the radiographs. Two radiologists evaluated all CR, DE, and CR + DE radiographs using the modified Chrispin-Norman score (CNS) and a five-point score for the confidence. Findings were statistically evaluated by Friedman ANOVA and Wilcoxon matched-pairs test. Results There was significant difference of CNS between CR and DE ( P = 0.044) as well as CR and CR + DE ( P < 0.001). CNS of CR images showed moderate correlation with FEV1% (R = 0.287, P = 0.046) while DE and CR + DE correlated poorly with FEV1% (R = 0.023, P = 0.874 and R = 0.04, P = 0.785). A higher confidence was achieved with bone-subtracted radiographs compared to radiographs alone (median, CR 3.3, DE 3.9, CR + DE 4.1, for both P < 0.001). Conclusion DE radiographs are reliable for the evaluation of adult patients with CF in acute exacerbation. For yearly surveillance, CR and DE radiographs may play a limited role. However, in clinical routine, DE radiographs are useful for adult CF patients and may depict more accurately inflammatory changes than CR.

Organ-based tube current modulation in a clinical context: Dose reduction may be largely overestimated in breast tissue.

OBJECTIVES: Organ-based tube current modulation aims to reduce exposure to radiosensitive organs like the breasts by considering their anatomical location and altering tube current during rotation. Former phantom studies demonstrated a dose reduction of 20-37 %. Our study aimed to estimate the potential of dose reduction with this technique in relation to the actual location of breast tissue in a large clinical cohort. METHODS: A 1-year cohort of chest CTs of females (N=1,263) was retrospectively evaluated. To estimate the relative dose effect, breast location was analysed by measuring the angle range of glandular tissue within the different dose zones. Relative exposure compared with constant tube current was calculated. Descriptive statistics and Wilcoxon-test were applied. RESULTS: Only 63 % of angle range of glandular breast tissue was found inside the reduced dose zone. The estimated mean relative dose reduction was lower than observed in former phantom studies(16 % vs. 20-37 %) but still significant compared to constant tube current (p<0.0001). CONCLUSIONS: Although organ-based tube current modulation results in a significant reduction of breast exposure compared to non-modulated irradiation, the technique cannot unfold its full potential, because breast tissue is often located outside the reduced dose zone, resulting in significantly lower dose reduction than expected. KEY POINTS: • OBTCM results in significant dose reduction compared to constant tube current scans. • A substantial portion of glandular tissue lies outside the reduced dose zone. • Potential dose reduction using organ-based tube current modulation may be overestimated.

Feasibility of Dose Optimization in a Second-Generation Dual-Source CT Scanner for a Manufacturer-Recommended Urolithiasis Protocol for Imaging Renal Stones.

OBJECTIVE: The purpose of this article is to investigate the magnitude of dose optimization for a manufacturer-recommended urolithiasis protocol in a second-generation dual-source CT scanner. MATERIALS AND METHODS: Custom renal phantoms with 24 stones were scanned using the manufacturer-provided dual-energy CT protocol (tube A, 100 kVp and 210 reference mAs; tube B, 140 kVp and 162 reference mAs) and seven dose-optimized protocols in which the reference tube current-time product setting of tube A was reduced stepwise by 20 mAs. Detection and characterization of the stones was assessed. In the patient study, 25 patients underwent the manufacturer-provided dual-energy protocol and 25 patients underwent imaging with a dose-optimized protocol (tube A, 100 kVp and 90 reference mAs; tube B, 140 kVp and 70 reference mAs). Dose-length product (DLP), image noise, and contrast-to-noise ratio (CNR) were assessed. Subjective image quality was analyzed by three independent radiologists. RESULTS: In the phantom study, the reference tube current-time product of tube A could be reduced from 210 to 90 mAs without losing the accuracy of detection or characterization of the calculi. In the patient study, the dose-optimized protocol resulted in a significant reduction of the average DLP by 51% compared with the standard protocol (219.4 vs 443.5 mGy·cm, respectively; p = 0.0001). The image noise was higher, and the CNR was lower, in the dose-optimized group than in the standard-dose group (p < 0.05). The subjective overall image quality of the dose-optimized CT examinations was rated as good, and that of the standard-dose CT examinations was rated as excellent (p = 0.001). CONCLUSION: The in vitro and in vivo assessment revealed a potential for a 51% dose reduction of the manufacturer-recommended dual-energy CT protocol for urolithiasis without compromising the accuracy.

Prospective randomised comparison of diagnostic confidence and image quality with normal-dose and low-dose CT pulmonary angiography at various body weights.

OBJECTIVES: To find a threshold body weight (BW) below 100 kg above which computed tomography pulmonary angiography (CTPA) using reduced radiation and a reduced contrast material (CM) dose provides significantly impaired quality and diagnostic confidence compared with standard-dose CTPA. METHODS: In this prospectively randomised study of 501 patients with suspected pulmonary embolism and BW <100 kg, 246 were allocated into the low-dose group (80 kVp, 75 ml CM) and 255 into the normal-dose group (100 kVp, 100 ml CM). Contrast-to-noise ratio (CNR) in the pulmonary trunk was calculated. Two blinded chest radiologists independently evaluated subjective image quality and diagnostic confidence. Data were compared between the normal-dose and low-dose groups in five BW subgroups. RESULTS: Vessel attenuation did not differ between the normal-dose and low-dose groups within each BW subgroup (P = 1.0). The CNR was higher with the normal-dose compared with the low-dose protocol (P < 0.006) in all BW subgroups except for the 90-99 kg subgroup (P = 0.812). Subjective image quality and diagnostic confidence did not differ between CT protocols in all subgroups (P between 0.960 and 1.0). CONCLUSIONS: Subjective image quality and diagnostic confidence with 80 kVp CTPA is not different from normal-dose protocol in any BW group up to 100 kg. KEY POINTS: • 80 kVp CTPA is safe in patients weighing <100 kg • Reduced radiation and iodine dose still provide high vessel attenuation • Image quality and diagnostic confidence with low-dose CTPA is good • Diagnostic confidence does not deteriorate in obese patients weighing <100 kg.

Combining automated attenuation-based tube voltage selection and iterative reconstruction: a liver phantom study.

OBJECTIVES: To determine the value of combined automated attenuation-based tube-potential selection and iterative reconstructions (IRs) for optimising computed tomography (CT) imaging of hypodense liver lesions. METHODS: A liver phantom containing hypodense lesions was imaged by CT with and without automated attenuation-based tube-potential selection (80, 100 and 120 kVp). Acquisitions were reconstructed with filtered back projection (FBP) and sinogram-affirmed IR. Image noise and contrast-to-noise ratio (CNR) were measured. Two readers marked lesion localisation and rated confidence, sharpness, noise and image quality on a five-point scale (1 = worst, 5 = best). RESULTS: Image noise was lower (31-52%) and CNR higher (43-102%) on IR than on FBP images at all tube voltages. On 100-kVp and 80-kVp IR images, confidence and sharpness were higher than on 120-kVp FBP images. Scores for image quality score and noise as well as sensitivity for 100-kVp IR were similar or higher than for 120-kVp FBP and lower for 80-kVp IR. Radiation dose was reduced by 26% at 100 kVp and 56% at 80 kVp. CONCLUSIONS: Compared with 120-kVp FBP images, the combination of automated attenuation-based tube-potential selection at 100 kVp and IR provides higher image quality and improved sensitivity for detecting hypodense liver lesions in vitro at a dose reduced by 26%. KEY POINTS: • Combining automated tube voltage selection/iterative CT reconstruction improves image quality. • Attenuation values remain stable on IR compared with FBP images. • Lesion detection was highest on 100-kVp IR images.

Hybrid iterative reconstruction technique for abdominal CT protocols in obese patients: assessment of image quality, radiation dose, and low-contrast detectability in a phantom.

OBJECTIVE: The purpose of this study was to assess the impact of a noise reduction technique on image quality, radiation dose, and low-contrast detectability in abdominal CT for obese patients. MATERIALS AND METHODS: A liver phantom with 12 different tumors was designed, and fat rings were added to mimic intermediately sized and large patients. The intermediate and large phantoms were scanned with our standard abdominal CT protocol (image noise level of 15 HU and filtered back projection [FBP]). The large phantom was scanned with five different noise levels (10, 12.5, 15, 17.5, and 20 HU). All datasets for the large phantom were reconstructed with FBP and the noise reduction technique. The image noise and the contrast-to-noise ratio (CNR) were assessed. Tumor detection was independently performed by three radiologists in a blinded fashion. RESULTS: The application of the noise reduction method to the large phantom decreased the measured image noise (range, -14.5% to -37.0%) and increased the CNR (range, 26.7-70.6%) compared with FBP at the same noise level (p < 0.001). However, noise reduction was unable to improve the sensitivity for tumor detection in the large phantom compared with FBP at the same noise level (p > 0.05). Applying a noise level of 15 HU, the overall sensitivity for tumor detection in the intermediate and large phantoms with FBP measured 75.5% and 87.7% and the radiation doses measured 42.0 and 23.7 mGy, respectively. CONCLUSION: Although noise reduction significantly improved the quantitative image quality in simulated large patients undergoing abdominal CT compared with FBP, no improvement was observed for low-contrast detectability.

Iterative reconstruction algorithm for CT: can radiation dose be decreased while low-contrast detectability is preserved?

PURPOSE: To compare the low-contrast detectability and image quality of computed tomography (CT) at different radiation dose levels reconstructed with iterative reconstruction (IR) and filtered back projection (FBP). MATERIALS AND METHODS: A custom liver phantom with 12 simulated hypoattenuating tumors (diameters of 5, 10, 15, and 20 mm; tumor-to-liver contrast values of -10, -20, and -40 HU) was designed. The phantom was scanned with a standard abdominal CT protocol with a volume CT dose index of 21.6 mGy (equivalent 100% dose) and four low-dose protocols (20%, 40%, 60%, and 80% of the standard protocol dose). CT data sets were reconstructed with IR and FBP. Image noise was measured, and the tumors' contrast-to-noise ratios (CNRs) were calculated. Tumor detection was independently assessed by three radiologists who were blinded to the CT technique used. A total of 840 simulated tumors were presented to the radiologists. Statistical analyses included analysis of variance. RESULTS: IR yielded an image noise reduction of 43.9%-63.9% and a CNR increase of 74.1%-180% compared with FBP at the same dose level (P < .001). The overall sensitivity for tumor detection was 64.7%-85.3% for IR and 66.3%-85.7% for FBP at the 20%-100% doses, respectively. There was no significant difference in the sensitivity for tumor detection between IR and FBP at the same dose level (P = .99). The sensitivity of the protocol at the 20% dose with FBP and IR was significantly lower than that of the protocol at the 100% dose with FBP and IR (P = .019). CONCLUSION: As the radiation dose at CT decreases, the IR algorithm does not preserve the low-contrast detectability. SUPPLEMENTAL MATERIAL: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13122349/-/DC1.

Comparison of dual-energy subtraction and electronic bone suppression combined with computer-aided detection on chest radiographs: effect on human observers' performance in nodule detection.

OBJECTIVE: The objective of our study was to compare the effect of dual-energy subtraction and bone suppression software alone and in combination with computer-aided detection (CAD) on the performance of human observers in lung nodule detection. MATERIALS AND METHODS: One hundred one patients with from one to five lung nodules measuring 5-29 mm and 42 subjects with no nodules were retrospectively selected and randomized. Three independent radiologists marked suspicious-appearing lesions on the original chest radiographs, dual-energy subtraction images, and bone-suppressed images before and after postprocessing with CAD. Marks of the observers and CAD marks were compared with CT as the reference standard. Data were analyzed using nonparametric tests and the jackknife alternative free-response receiver operating characteristic (JAFROC) method. RESULTS: Using dual-energy subtraction alone (p = 0.0198) or CAD alone (p = 0.0095) improved the detection rate compared with using the original conventional chest radiograph. The combination of bone suppression and CAD provided the highest sensitivity (51.6%) and the original nonenhanced conventional chest radiograph alone provided the lowest (46.9%; p = 0.0049). Dual-energy subtraction and bone suppression provided the same false-positive (p = 0.2702) and true-positive (p = 0.8451) rates. Up to 22.9% of lesions were found only by the CAD program and were missed by the readers. JAFROC showed no difference in the performance between modalities (p = 0.2742-0.5442). CONCLUSION: Dual-energy subtraction and the electronic bone suppression program used in this study provided similar detection rates for pulmonary nodules. Additionally, CAD alone or combined with bone suppression can significantly improve the sensitivity of human observers for pulmonary nodule detection.

Focal and diffuse myocardial fibrosis both contribute to regional hypoperfusion assessed by post-processing quantitative-perfusion MRI techniques.

Introduction: Indications for stress-cardiovascular magnetic resonance imaging (CMR) to assess myocardial ischemia and viability are growing. First pass perfusion and late gadolinium enhancement (LGE) have limited value in balanced ischemia and diffuse fibrosis. Quantitative perfusion (QP) to assess absolute pixelwise myocardial blood flow (MBF) and extracellular volume (ECV) as a measure of diffuse fibrosis can overcome these limitations. We investigated the use of post-processing techniques for quantifying both pixelwise MBF and diffuse fibrosis in patients with clinically indicated CMR stress exams. We then assessed if focal and diffuse myocardial fibrosis and other features quantified during the CMR exam explain individual MBF findings. Methods: This prospective observational study enrolled 125 patients undergoing a clinically indicated stress-CMR scan. In addition to the clinical report, MBF during regadenoson-stress was quantified using a post-processing QP method and T1 maps were used to calculate ECV. Factors that were associated with poor MBF were investigated. Results: Of the 109 patients included (66 ± 11 years, 32% female), global and regional perfusion was quantified by QP analysis in both the presence and absence of visual first pass perfusion deficits. Similarly, ECV analysis identified diffuse fibrosis in myocardium beyond segments with LGE. Multivariable analysis showed both LGE (ß = -0.191, p = 0.001) and ECV (ß = -0.011, p < 0.001) were independent predictors of reduced MBF. In patients without clinically defined first pass perfusion deficits, the microvascular risk-factors of age and wall thickness further contributed to poor MBF (p < 0.001). Discussion: Quantitative analysis of MBF and diffuse fibrosis detected regional tissue abnormalities not identified by traditional visual assessment. Multi-parametric quantitative analysis may refine the work-up of the etiology of myocardial ischemia in patients referred for clinical CMR stress testing in the future and provide a deeper insight into ischemic heart disease.

Extracardiac findings detected by cardiac magnetic resonance imaging.

OBJECTIVE: To determine the prevalence and importance of extracardiac findings (ECF) in patients undergoing clinical CMR and to test the hypothesis that the original CMR reading focusing on the heart may underestimate extracardiac abnormalities. METHODS: 401 consecutive patients (mean age 53 years) underwent CMR at 1.5 T. Main indications were ischaemic heart disease (n = 183) and cardiomyopathy (n = 164). All CMR sequences, including scout images, were reviewed with specific attention to ECF in a second reading by the same radiologist who performed the first clinical reading. Potentially significant findings were defined as abnormalities requiring additional clinical or radiological follow-up. RESULTS: 250 incidental ECF were detected, of which 84 (34%) had potentially significant ECF including bronchial carcinoma (n = 1), lung consolidation (n = 7) and abdominal abnormalities. In 166 CMR studies (41%) non-significant ECF were detected. The number of ECF identified at second versus first reading was higher for significant (84 vs. 47) and non-significant (166 vs. 36) findings (P < 0.00001). CONCLUSIONS: About one fifth of patients undergoing CMR were found to have potentially significant ECF requiring additional work-up. The second dedicated reading detected significantly more ECF compared with the first clinical reading emphasising the importance of active search for extracardiac abnormalities when evaluating CMR studies. KEY POINTS: • Many patients undergoing cardiac MR have significant extracardiac findings (ECF) • These impact on management and require additional work-up. • Wide review of scout and cine sequences will detect most ECFs. • Education of radiologists is important to identify ECFs on CMR studies.

Iterative reconstruction algorithm for abdominal multidetector CT at different tube voltages: assessment of diagnostic accuracy, image quality, and radiation dose in a phantom study.

PURPOSE: To assess the diagnostic accuracy, image quality, and radiation dose of an iterative reconstruction algorithm compared with a filtered back projection (FBP) algorithm for abdominal computed tomography (CT) at different tube voltages. MATERIALS AND METHODS: A custom liver phantom with 45 simulated hypovascular liver tumors (diameters of 5, 10, and 15 mm; tumor-to-liver contrast of 10, 25, and 50 HU) was placed in a cylindrical water container that mimicked an intermediate-sized patient. The phantom was scanned at 120, 100, and 80 kVp. The CT data sets were reconstructed with FBP and iterative reconstruction. The image noise was measured, and the contrast-to-noise ratio (CNR) of the tumors was calculated. The radiation dose was assessed with the volume CT dose index. Tumor detection was independently performed by three radiologists. Statistical analysis included analysis of variance. RESULTS: Compared with the FBP data set at 120 kVp, the iterative reconstruction data set collected at 100 kVp demonstrated significantly lower mean image noise (20.9 and 16.7 HU, respectively; P < .001) and greater mean CNRs for the simulated tumors (P < .001). The iterative reconstruction data set collected at 120 kVp yielded the highest sensitivity for tumor detection, while the FBP data set at 80 kVp yielded the lowest. The sensitivity for the iterative reconstruction data set at 100 kVp was comparable with that for the FBP data set at 120 kVp (79.3% and 74.9%, respectively; P > .99). The volume CT dose index decreased by 39.8% between the 120-kVp protocol and the 100-kVp protocol and by 70.3% between the 120-kVp protocol and the 80-kVp protocol. CONCLUSION: Results of this phantom study suggest that a 100-kVp abdominal CT protocol with an iterative reconstruction algorithm for simulated intermediate-sized patients increases the image quality and maintains the diagnostic accuracy at a reduced radiation dose when compared with a 120-kVp protocol with an FBP algorithm.

Nonlinear three-dimensional noise filter with low-dose CT angiography: effect on the detection of small high-contrast objects in a phantom model.

PURPOSE: To study the effect of a nonlinear noise filter on the detection of simulated endoleaks in a phantom with 80- and 100-kVp multidetector computed tomographic (CT) angiography. MATERIALS AND METHODS: An aortic aneurysm phantom, including iodinated endoleaks, was constructed. Multidetector CT angiography with use of 80-, 100-, and 120-kVp tube voltages was performed for simulated intermediate-sized and large patients (estimated body weights, 72-85 kg and 118-142 kg, respectively). Images obtained with 80 and 100 kVp were postprocessed by using a nonlinear noise filter. CT images containing 1152 endoleaks and images with no endoleaks were randomized and independently analyzed by three radiologists blinded to the location of the endoleaks. Diagnostic confidence and image quality were rated by using subjective scales. Analysis of variance was used for statistical assessment. RESULTS: In simulated intermediate-sized patients, energy reduction from 120 to 100 kVp and from100 to 80 kVp did not decrease image quality when images with reduced kilovoltage were filtered (P = .2692 and P > .99, respectively). Readers detected more endoleaks on the filtered 100-kVp images than on the nonfiltered images in simulated large patients (83 vs 75 lesions, P = .041). The number of detected endoleaks and the confidence rate were similar at 100 kVp with a filter and at 120 kVp in simulated large patients (P = .339 and P = .211, respectively). CONCLUSION: In a phantom, the nonlinear noise filter can prevent decreased image quality with use of 80- and 100-kVp abdominal multidetector CT angiography at a wide range of simulated body weights and may facilitate a better detection rate of endoleaks in heavy patients.

An education and training programme for radiological institutes: impact on the reduction of the CT radiation dose.

OBJECTIVES: To establish an education and training programme for the reduction of CT radiation doses and to assess this programme's efficacy. METHODS: Ten radiological institutes were counselled. The optimisation programme included a small group workshop and a lecture on radiation dose reduction strategies. The radiation dose used for five CT protocols (paranasal sinuses, brain, chest, pulmonary angiography and abdomen) was assessed using the dose-length product (DLP) before and after the optimisation programme. The mean DLP values were compared with national diagnostic reference levels (DRLs). RESULTS: The average reduction of the DLP after optimisation was 37% for the sinuses (180 vs. 113 mGycm, P < 0.001), 9% for the brain (982 vs. 896 mGycm, P < 0.05), 24% for the chest (425 vs. 322 mGycm, P < 0.05) and 42% for the pulmonary arteries (352 vs. 203 mGycm, P < 0.001). No significant change in DLP was found for abdominal CT. The post-optimisation DLP values of the sinuses, brain, chest, pulmonary arteries and abdomen were 68%, 10%, 20%, 55% and 15% below the DRL, respectively. CONCLUSIONS: The education and training programme for radiological institutes is effective in achieving a substantial reduction in CT radiation dose.

Decreased detection of hypovascular liver tumors with MDCT in obese patients: a phantom study.

OBJECTIVE: The purpose of this article is to assess the impact of large patient size on the detection of hypovascular liver tumors with MDCT and the effect of a noise filter on image quality and lesion detection in obese patients. MATERIALS AND METHODS: A liver phantom with 45 hypovascular tumors (diameters of 5, 10, and 15 mm) was placed into two water containers mimicking intermediate and large patients. The containers were scanned with a 64-MDCT scanner. The CT dataset from the large phantom was postprocessed using a noise filter. The image noise was measured and the contrast-to-noise ratio (CNR) of the tumors was calculated. Tumor detection was independently performed by three radiologists in a blinded fashion. RESULTS: The application of the noise filter in the large phantom yielded a reduction of image noise by 42% (p < 0.0001). The CNR values of the tumors in the nonfiltered and filtered large phantom were lower than that in the intermediate phantom (p < 0.05). In the non-filtered and filtered large phantom, 25% and 19% fewer tumors, respectively, were detected on average compared with the intermediate phantom (p < 0.01). CONCLUSION: The risk of missing hypovascular liver tumors with CT is substantially increased in large patients. A noise filter improves image quality in obese patients.

Diagnostic accuracy of pulmonary CT angiography at low tube voltage: intraindividual comparison of a normal-dose protocol at 120 kVp and a low-dose protocol at 80 kVp using reduced amount of contrast medium in a simulation study.

OBJECTIVE: The purpose of this study was to simulate pulmonary emboli (PE) and image quality at low tube energy and reduced contrast material volume in normal-dose pulmonary CT angiography (CTA) images and to analyze the diagnostic accuracy with normal- and low-dose pulmonary CTA. MATERIALS AND METHODS: Normal-dose pulmonary CTA examinations using 120 kVp and 100 mL of contrast material in 10 patients with no PE were retrospectively selected. The image characteristics of an 80-kVp low-dose pulmonary CTA protocol (patient exposure reduction, 57%) with 75 mL of contrast material were simulated. Four different sets of filling defects were computer simulated in identical locations in each normal-dose and corresponding low-dose examination, equaling 783 PE in 40 normal-dose and 40 low-dose datasets. Ten normal-dose and 10 low-dose examinations contained no emboli and were used as controls. The 100 pulmonary CTA studies were randomly assessed by three readers blinded to PE location and image quality. The results were assessed by nonparametric tests and Student t tests. RESULTS: No difference was found between the CT protocols in terms of sensitivity, specificity, and positive and negative diagnostic likelihood ratios at all ramification levels of the pulmonary arteries (p = 0.343-1). The overall sensitivity and specificity with the normal and simulated low-dose protocols were 79.9% versus 81.3% and 98.0% versus 98.2% (p = 0.444 and 0.702), respectively. The diagnostic confidence (2.81 ± 0.39 vs 2.77 ± 0.47; p = 0.297) and overall image quality (3.92 ± 0.52 vs 3.83 ± 0.54; p = 0.216) were similar at 120 kV and 80 kV. CONCLUSION: The intraindividual comparison of diagnostic accuracy with normal-dose and simulated low-dose pulmonary CTA protocols revealed no difference under experimental conditions.

Evaluation of the new Statscan radiography device for ventriculoperitoneal shunt assessment.

OBJECTIVE: We assessed the diagnostic accuracy and time effectiveness of the Statscan low-dose full-body digital x-ray machine in the evaluation of ventriculoperitoneal (VP) shunt dysfunction. SUBJECTS AND METHODS: Twenty-five consecutive adults scheduled for a radiographic shunt series with the Statscan were prospectively selected (group 1). Another 21 consecutive patients who underwent conventional x-ray scanning served as controls (group 2) for blinded analysis. RESULTS: Image quality was sufficient for diagnosis in both groups (95.6% vs 95.1%). The quality of VP shunt delineation and contrast of anatomic structures was good or optimal in both groups (p > 0.05). The scan time was significantly lower for group 1 (p < 0.001). All images for group 2 exhibited overlapping of anatomic structures (25% of total coverage), whereas no technically determined overlapping occurred in group 1. CONCLUSION: The Statscan digital x-ray machine allows accurate assessment of VP shunt continuity at lower radiation dosages and in less time than conventional x-ray techniques.