Publications

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    ABSTRACT: Purpose To determine the intervendor variability of Agatston scoring determined with state-of-the-art computed tomographic (CT) systems from the four major vendors in an ex vivo setup and to simulate the subsequent effects on cardiovascular risk reclassification in a large population-based cohort. Materials and Methods Research ethics board approval was not necessary because cadaveric hearts from individuals who donated their bodies to science were used. Agatston scores obtained with CT scanners from four different vendors were compared. Fifteen ex vivo human hearts were placed in a phantom resembling an average human adult. Hearts were scanned at equal radiation dose settings for the systems of all four vendors. Agatston scores were quantified semiautomatically with software used clinically. The ex vivo Agatston scores were used to simulate the effects of different CT scanners on reclassification of 432 individuals aged 55 years or older from a population-based study who were at intermediate cardiovascular risk based on Framingham risk scores. The Friedman test was used to evaluate overall differences, and post hoc analyses were performed by using the Wilcoxon signed-rank test with Bonferroni correction. Results Agatston scores differed substantially when CT scanners from different vendors were used, with median Agatston scores ranging from 332 (interquartile range, 114-1135) to 469 (interquartile range, 183-1381; P < .05). Simulation showed that these differences resulted in a change in cardiovascular risk classification in 0.5%-6.5% of individuals at intermediate risk when a CT scanner from a different vendor was used. Conclusion Among individuals at intermediate cardiovascular risk, state-of the-art CT scanners made by different vendors produced substantially different Agatston scores, which can result in reclassification of patients to the high- or low-risk categories in up to 6.5% of cases. © RSNA, 2014.
    Radiology 08/2014; · 6.34 Impact Factor
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    ABSTRACT: Optimizing CT brain perfusion protocols is a challenge because of the complex interaction between image acquisition, calculation of perfusion data, and patient hemodynamics. Several digital phantoms have been developed to avoid unnecessary patient exposure or suboptimum choice of parameters. The authors expand this idea by using realistic noise patterns and measured tissue attenuation curves representing patient-specific hemodynamics. The purpose of this work is to validate that this approach can realistically simulate mean perfusion values and noise on perfusion data for individual patients.
    Medical physics. 07/2014; 41(7):071907.
  • Medical Image Analysis. 07/2014;
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    ABSTRACT: We evaluated the effects of hybrid and model-based iterative reconstruction (IR) algorithms from different vendors at multiple radiation dose levels on image quality of chest phantom scans.
    Journal of computer assisted tomography. 06/2014;
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    ABSTRACT: To analyse the effects of radiation dose reduction and iterative reconstruction (IR) algorithms on coronary calcium scoring (CCS).
    European radiology. 06/2014;
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    ABSTRACT: Lung cancer is the most frequent cause of tumor-associated death and only has a good prognosis if detected at a very early tumor stage. For the first time the American National Lung Screening Trial (NLST) could prove that low-dose computed tomography (CT) screening is able to reduce lung cancer mortality by 20 %. To date, however, three much smaller and therefore statistically underpowered European trials could not confirm the positive results of the NLST. The results of the largest European trial NELSON are expected within the next 2 years. In addition, there are a number of open or not yet satisfactorily answered questions, such as the definition of the appropriate screening population, the management of nodules detected by screening, the effects of over-diagnosis and the risk of cumulative radiation exposure. The success of the NLST prompted several predominantly American professional societies to issue a positive recommendation about the implementation of lung cancer screening in a population at risk. However, potentially conflicting results of European studies and a number of not yet optimized issues justify caution and call for a pooled analysis of European studies in order to provide statistically sound results and to ensure a high efficiency of screening with respect to the radiation applied, mental and physical patient burden and, last but not least, the financial efforts.
    Der Radiologe 05/2014; 54(5):462-9. · 0.47 Impact Factor
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    ABSTRACT: Subsolid pulmonary nodules occur less often than solid pulmonary nodules, but show a much higher malignancy rate. Therefore, accurate detection of this type of pulmonary nodules is crucial. In this work, a computer-aided detection (CAD) system for subsolid nodules in computed tomography images is presented and evaluated on a large data set from a multi-center lung cancer screening trial. The paper describes the different components of the CAD system and presents experiments to optimize the performance of the proposed CAD system. A rich set of 128 features is defined for subsolid nodule candidates. In addition to previously used intensity, shape and texture features, a novel set of context features is introduced. Experiments show that these features significantly improve the classification performance. Optimization and training of the CAD system is performed on a large training set from one site of a lung cancer screening trial. Performance analysis on an independent test from another site of the trial shows that the proposed system reaches a sensitivity of 80% at an average of only 1.0 false positive detections per scan. A retrospective analysis of the output of the CAD system by an experienced thoracic radiologist shows that the CAD system is able to find subsolid nodules which were not contained in the screening database.
    Medical image analysis 12/2013; 18(2):374-384. · 3.09 Impact Factor
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    ABSTRACT: MR angiography is proposed as a safer and less expensive alternative to the reference standard, DSA, in the follow-up of intracranial aneurysms treated with endovascular coil occlusion. We performed a systematic review and meta-analysis to evaluate the accuracy of TOF-MRA and contrast-enhanced MRA in detecting residual flow in the follow-up of coiled intracranial aneurysms. Literature was reviewed through the PubMed, Cochrane, and EMBASE data bases. In comparison with DSA, the sensitivity of TOF-MRA was 86% (95% CI: 82-89%), with a specificity of 84% (95% CI: 81-88%), for the detection of any recurrent flow. For contrast-enhanced MRA, the sensitivity and specificity were 86% (95% CI: 82-89%) and 89% (95% CI: 85-92%), respectively. Both TOF-MRA and contrast-enhanced MRA are shown to be highly accurate for detection of any recanalization in intracranial aneurysms treated with endovascular coil occlusion.
    American Journal of Neuroradiology 09/2013; · 3.17 Impact Factor
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    ABSTRACT: Finding phenotypes within COPD patients may prove imperative for optimizing treatment and prognosis. We hypothesized that it would be possible to discriminate emphysematous, large airway wall thickening and small airways disease dominant phenotypes. Inspiratory and expiratory CTs were performed in 1140 male smokers without or with mild COPD to quantify emphysema, airway wall thickness and air trapping. Spirometry, residual volume to total lung capacity (RV/TLC) and diffusion capacity (Kco) were measured. Dominant phenotype (emphysema, airway wall thickening or air trapping dominant) was defined as one of the respective CT measure in the upper quartile, with the other measures not in the upper quartile. 573 subjects had any of the three CT measures in the upper quartile. Of these, 367 (64%) were in a single dominant group and 206 (36%) were in a mixed group. Airway wall thickening dominance was associated with younger age (p < 0.001), higher body mass index (p < 0.001), more wheezing (p < 0.05) and lower FEV1 %predicted (p < 0.001). Emphysema dominant subjects had lower FEV1/FVC (p < 0.05) and Kco %predicted (p < 0.05). There was no significant difference in respiratory related hospitalizations (p = 0.09). CT measures can discriminate three different CT dominant groups of disease in male smokers without or with mild COPD. ISRCTN63545820, registered at www.trialregister.nl.
    Respiratory medicine 08/2013; · 2.33 Impact Factor
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    ABSTRACT: OBJECTIVES: Despite extensive research aimed at clarifying (failing) pelvic organ support, the complete aetiology of pelvic organ prolapse (POP) is still not fully understood. During vaginal delivery, the pelvic floor can be irreversibly traumatised, resulting in pubovisceral muscle avulsions. The aetiology of these avulsions is discussed in this pictorial overview. Normal female pelvic floor anatomy is described and variations are exemplified using magnetic resonance (MR) images. The clinical relevance of detecting pubovisceral muscle avulsions is specified. METHODS: T2-weighted MR imaging has multiplanar capabilities with high diagnostic accuracy allowing for detailed visualisation of the pelvic floor. Together with the use of a three-dimensional (3D) post-processing program, the presence and severity of pubovisceral muscle avulsions can be quantified. RESULTS: Pelvic floor MR imaging is a non-invasive method that enables adequate identification of pubovisceral muscle avulsions which are known risk factors for the development of POP. They can be scored with good to excellent inter- and intra-observer reliability. CONCLUSIONS: Radiologists and urogynaecology subspecialists should be familiar with MR imaging findings of pubovisceral muscle avulsions as this birth-related trauma is observed in over 36 % of vaginally parous women. TEACHING POINTS: • Pelvic organ prolapse (POP) is a growing problem for both patients and for our healthcare system • Pubovisceral muscle avulsions are known risk factors for pelvic organ prolapse (POP) • T2-weighted MR imaging visualises pubovisceral muscle avulsions adequately • Pubovisceral muscle avulsions are scored with good to excellent inter- and intra-observer reliability.
    Insights into imaging. 06/2013;
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    ABSTRACT: BACKGROUND AND PURPOSE: Although collateral vessels have been shown to be an important prognostic factor in acute ischemic stroke, patients with lack of collaterals on standard imaging techniques may still have good clinical outcome. We postulate that in these cases collateral vessels are present though not visible on standard imaging techniques that are based on a single time frame. METHODS: This study included 40 consecutive patients with acute ischemic stroke with a large-vessel occlusion. Standard computed tomography angiography (CTA, single time frame) and CT perfusion (multiple time frames) were obtained at admission and timing-invariant (TI)-CTA was created from the CT perfusion data. Clinical outcome data (modified Rankin Scale) were assessed at 3-month follow-up. Four experienced observers independently assessed collateral status twice on both standard CTA and TI-CTA in an independent, blinded, randomized manner. Collateral status was rated as good if ≥50% and poor if <50% of collaterals were present compared with the contralateral hemisphere. RESULTS: Collateral status was rated higher on TI-CTA (good in 84%) compared with standard CTA (good in 49%; P<0.001). Thirty-one percent of patients with poor collateral status on standard CTA still had good clinical outcome. All of those patients, however, showed good collaterals on TI-CTA. All cases with poor collateral status rated on TI-CTA had poor clinical outcome. CONCLUSIONS: Collateral vessels may not always be visible on standard single time-frame CTA because of delayed contrast arrival. Future prognostic studies in acute stroke should consider delay-insensitive techniques, such as TI-CTA, instead of standard single time-frame imaging, such as standard CTA.
    Stroke 06/2013; · 6.16 Impact Factor
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    ABSTRACT: OBJECTIVES: The aim of this study was to derivate and validate a prediction model for cardiovascular events based on quantification of coronary and aortic calcium volume in lung cancer screening chest computed tomography (CT). BACKGROUND: CT-based lung cancer screening in heavy smokers is a very timely topic. Given that the heavily smoking screening population is also at risk for cardiovascular disease, CT-based screening may provide the opportunity to additionally identify participants at high cardiovascular risk. METHODS: Inspiratory screening CT of the chest was obtained in 3,648 screening participants. Next, smoking characteristics, patient demographics, and physician-diagnosed cardiovascular events were collected from 10 years before the screening CT (i.e., cardiovascular history) until 3 years after the screening CT (i.e., follow-up time). Cox proportional hazards analysis was used to derivate and validate a prediction model for cardiovascular risk. Age, smoking status, smoking history, and cardiovascular history, together with automatically quantified coronary and aortic calcium volume from the screening CT, were included as independent predictors. The primary outcome measure was the discriminatory value of the model. RESULTS: Incident cardiovascular events occurred in 145 of 1,834 males (derivation cohort) and 118 of 1,725 males and 2 of 89 females (validation cohort). The model showed good discrimination in the validation cohort with a C-statistic of 0.71 (95% confidence interval: 0.67 to 0.76). When high risk was defined as a 3-year risk of 6% and higher, 589 of 1,725 males were regarded as high risk and 72 of 118 of all events were correctly predicted by the model. CONCLUSIONS: Quantification of coronary and aortic calcium volumes in lung cancer screening CT images-information that is readily available-can be used to predict cardiovascular risk. Such an approach might prove useful in the reduction of cardiovascular morbidity and mortality and may enhance the cost-effectiveness of CT-based screening in heavy smokers.
    JACC. Cardiovascular imaging 06/2013; · 14.29 Impact Factor
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    ABSTRACT: BACKGROUND: Beyond lung cancer, screening CT contains additional information on other smoking related diseases (e.g. chronic obstructive pulmonary disease, COPD). Since pulmonary function testing is not regularly incorporated in lung cancer screening, imaging biomarkers for COPD are likely to provide important surrogate measures for disease evaluation. Therefore, this study aims to determine the independent diagnostic value of CT emphysema, CT air trapping and CT bronchial wall thickness for COPD in low-dose screening CT scans. METHODS: Prebronchodilator spirometry and volumetric inspiratory and expiratory chest CT were obtained on the same day in 1140 male lung cancer screening participants. Emphysema, air trapping and bronchial wall thickness were automatically quantified in the CT scans. Logistic regression analysis was performed to derivate a model to diagnose COPD. The model was internally validated using bootstrapping techniques. RESULTS: Each of the three CT biomarkers independently contributed diagnostic value for COPD, additional to age, body mass index, smoking history and smoking status. The diagnostic model that included all three CT biomarkers had a sensitivity and specificity of 73.2% and 88.%, respectively. The positive and negative predictive value were 80.2% and 84.2%, respectively. Of all participants, 82.8% was assigned the correct status. The C-statistic was 0.87, and the Net Reclassification Index compared to a model without any CT biomarkers was 44.4%. However, the added value of the expiratory CT data was limited, with an increase in Net Reclassification Index of 4.5% compared to a model with only inspiratory CT data. CONCLUSION: Quantitatively assessed CT emphysema, air trapping and bronchial wall thickness each contain independent diagnostic information for COPD, and these imaging biomarkers might prove useful in the absence of lung function testing and may influence lung cancer screening strategy. Inspiratory CT biomarkers alone may be sufficient to identify patients with COPD in lung cancer screening setting.
    Respiratory research 05/2013; 14(1):59. · 3.64 Impact Factor
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    ABSTRACT: OBJECTIVES: To assess radiation exposure due to CT in the Netherlands. METHODS: Twenty-one hospitals participated in a dose survey for the 21 most frequently used CT protocols. Hospitals completed a Web survey with detailed parameters for one patient per protocol, including the dose length product (DLP) from the scanner dose report. Only standard-sized patients (1.74 m and 77 kg and BMI 25.4 kg/m(2) ± 15 %) for each protocol and available scanner were considered. Effective dose (E) per protocol was estimated using ICRP-103-based E/DLP coefficients. Dose levels were compared to surveys from other countries and to diagnostic reference levels. RESULTS: Data of 186 patients (247 scan phases) from 14 hospitals and 19 scanners were used for final analysis of DLP and E. Effective doses varied from 0.2 mSv in sinus CT to 19.4 mSv for multiphase liver. The most frequent exams were brain (1.5 mSv), abdomen (8.0 mSv), and thorax-abdomen (11.5 mSv). These results are lower than in Germany and comparable to those in the UK, and are within reference levels. Results between hospitals varied, with per protocol minimum/maximum E ratios ranging from 1.1-5.4. CONCLUSIONS: Compared to surrounding countries, CT in the Netherlands is associated with relatively low radiation doses in standard patients. Important differences remain between hospitals. MAIN MESSAGES : • A national dose survey providing updated, detailed data for patient dose in the most frequently used CT protocols. • CT in the Netherlands is associated with relatively low individual radiation doses in standard patients compared to surrounding European countries. • Considerable differences remain between hospitals for the most frequently used CT protocols, indicating the need for further optimisation.
    Insights into imaging. 05/2013;
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    ABSTRACT: OBJECTIVES: The aim of this study was to assess the inter- and intraobserver reliability for diagnosing pubovisceral muscle avulsions and measurements of the levator hiatus on magnetic resonance (MR) imaging. Women with recurrent POP or in whom there was a discrepancy between clinical signs and symptoms of pelvic floor dysfunction were potentially eligible to participate. METHODS: Magnetic resonance imaging datasets of the pelvic floor of 262 women were obtained and scored by two observers. A random sample of 100 patients was reviewed a second time by one of the observers. Intraclass correlation coefficient with 95% confidence interval (ICC 95%CI) of all measurements were calculated. Furthermore, mean differences with accompanying limits of agreement were calculated to estimate agreement between two measurements and to detect possible systematic biases. RESULTS: Good interobserver reliability for pubovisceral muscle avulsions was found (ICC 0.76 - 0.79) and excellent agreement for measurements of the levator hiatus (ICC 0.85 - 0.89). The intraobserver reliability for pubovisceral muscle avulsions and other levator hiatus measurements also showed to be excellent (ICC 0.80 - 0.97). A significant systematic bias was observed in the mean difference of levator hiatus transverse diameter when measured by both observers, however, narrow limits of agreement were observed. CONCLUSIONS: Pubovisceral muscle avulsions and levator hiatus measurements can be assessed with good to excellent reliability.
    Ultrasound in Obstetrics and Gynecology 03/2013; · 3.56 Impact Factor
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    ABSTRACT: PURPOSE:: To assess the effect of computer-assisted detection (CAD) on diagnostic accuracy, reader confidence, and reading time when used as a concurrent reader for the detection of acute pulmonary embolism in computed tomography pulmonary angiography. MATERIALS AND METHODS:: In this institutional review board-approved retrospective study, 6 observers with varying experience evaluated 158 negative and 38 positive consecutive computed tomography pulmonary angiographies (mean patient age 60 y; 115 women) without and with CAD as a concurrent reader. Readers were asked to determine the presence of pulmonary embolism, assess their diagnostic confidence using a 5-point scale, and document their reading time. Results were compared with an independent standard established by 2 readers, and a third chest radiologist was consulted in case of discordant findings. RESULTS:: Using logistic regression for repeated measurements, we found a significant increase in readers' sensitivity (P<0.001) without loss of specificity (P=0.855) with the effects being reader dependent (P<0.001). Sensitivities varied from 68% to 100% without CAD and from 76% to 100% with CAD. A 2-way analysis of variance showed a small but significant decrease in reading time (P<0.001), with the duration varying between 24 and 208 seconds without CAD and between 17 and 196 seconds with CAD, and a significant increase in readers' confidence scores using CAD as a concurrent reader (P<0.001). CONCLUSIONS:: CAD as a concurrent reader has the potential to increase readers' sensitivity and confidence with a decrease in reading time without loss of specificity. The differences between readers, however, require further evaluation of CAD as a concurrent reader in a larger trial before stronger conclusions can be drawn.
    Journal of thoracic imaging 03/2013; · 1.42 Impact Factor
  • Onno M Mets, Pim A de Jong, Mathias Prokop
    JAMA The Journal of the American Medical Association 02/2013; 309(7):656-7. · 29.98 Impact Factor
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    ABSTRACT: OBJECTIVES: Carotid siphon calcification is often visible on unenhanced head CT (UCT), but the relation to proximal carotid artery stenosis (CAS) is unclear. We investigated the association of carotid siphon calcification with the presence of CAS. METHODS: This IRB-waived retrospective study included 160 consecutive patients suspected of stroke (age 64 ± 14 years, 63 female) who underwent head UCT and CTA of the head and neck. CAS was rated on CTA as not present or present with non-significant (<50 %), moderate (50-69 %) or significant (≥70 %) stenosis. Presence, shape (on UCT) and volume (on CTA) of carotid siphon calcifications were related to CAS. RESULTS: Carotid siphon calcification was absent in 41 % of patients and bilateral in 94 % of those with calcifications. Presence, shape and volume of calcification resulted in odds ratios for having significant CAS of 10.1, 3.9 and 8.4, with 95 % CIs of 1.3-79.6, 1.1-14.1 and 2.6-26.8, respectively. Corresponding NPVs were 0.98, 0.98 and 0.96, while PPVs were 0.14, 0.07 and 0.29, respectively. CONCLUSION: Absence of calcification in the carotid artery siphon on UCT has high negative predictive value for carotid artery stenosis in patients with suspected stroke. However, siphon calcification is not a reliable indicator of significant carotid artery stenosis. KEY POINTS: • Many stroke patients do not have calcification in the carotid artery siphon. • Carotid stenosis ≥50 % is unlikely in stroke patients without siphon calcification. • Carotid siphon calcium is a poor indicator of significant carotid artery stenosis.
    European Radiology 01/2013; · 4.34 Impact Factor
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    ABSTRACT: OBJECTIVE AND METHODS: In the diagnostic work-up of patients suspected of a dural arteriovenous fistula (dAVF), imaging has a key role in order to diagnose the dAVF, assess its bleeding risk and choose optimal treatment strategy. Digital subtraction angiography (DSA) is the gold standard for the most detailed image of a dAVF. Nowadays four-dimensional CT angiography (4D-CTA) could possibly be an additional first-line tool in the work-up of a patient suspected of a dAVF. We describe three cases clinically suspected of a dAVF which had a diagnostic work-up with 4D-CTA as well as DSA. We evaluated the angioarchitecture of the dAVF both on 4D-CTA and DSA, with emphasis on the patterns of venous drainage as this is important in assessing the bleeding risk of a dAVF. RESULTS AND CONCLUSION: 4D-CTA identified the dAVF, revealed its angioarchitecture and correctly differentiated different patterns of venous drainage (Borden type I, II and III) as confirmed on DSA. Although DSA has the advantage of higher spatial and temporal resolution, 4D-CTA seems to be a new useful non-invasive tool in the diagnostic work-up of a patient suspected of a dAVF.
    Clinical neurology and neurosurgery 01/2013; · 1.30 Impact Factor
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    ABSTRACT: Objective: To compare various visualization techniques for the detection of non-solid nodules in low-dose lung cancer screening computed tomography (CT) scans. Methods: An enriched sample of 216 male lung cancer screening subjects aged 60.4 ± 6.0 years was used. Two blinded independent readers searched for non-solid nodules on 5-mm multiplanar reconstructions, 1-mm slices and 7-mm maximum intensity projections (trial protocol). The reference standard was a consensus diagnosis of all non-solid nodules reported at least once. Results: Twenty-three individuals (10.6%) had in total 34 non-solid nodules. Interobserver agreement was good (Cohen kappa 0.89-0.95). For both observers, we found no differences between the 3 viewing techniques (P > 0.13). Conclusion: In low-dose lung cancer screening CT scans, we were unable to find a viewing technique superior to that used in the trial by experienced observers who focused on non-solid nodule detection.
    Cancer Imaging 01/2013; 13(2):150-154. · 1.59 Impact Factor

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