Annemarieke Rutten

Multi-Atlas-Based Segmentation With Local Decision Fusion—Application to Cardiac and Aortic Segmentation in CT Scans

A novel atlas-based segmentation approach based on the combination of multiple registrations is presented. Multiple atlases are registered to a target image. To obtain a segmentation of the target, labels of the atlas images are propagated to it. The propagated labels are combined by spatially varying decision fusion weights. These weights are derived from local assessment of the registration success. Furthermore, an atlas selection procedure is proposed that is equivalent to sequential forward selection from statistical pattern recognition theory. The proposed method is compared to three existing atlas-based segmentation approaches, namely (1) single atlas-based segmentation, (2) average-shape atlas-based segmentation, and (3) multi-atlas-based segmentation with averaging as decision fusion. These methods were tested on the segmentation of the heart and the aorta in computed tomography scans of the thorax. The results show that the proposed method outperforms other methods and yields results very close to those of an independent human observer. Moreover, the additional atlas selection step led to a faster segmentation at a comparable performance.

Detection of coronary calcifications from computed tomography scans for automated risk assessment of coronary artery disease

A fully automated method for coronary calcification detection from non-contrast-enhanced, ECG-gated multi-slice computed tomography (CT) data is presented. Candidates for coronary calcifications are extracted by thresholding and component labeling. These candidates include coronary calcifications, calcifications in the aorta and in the heart, and other high-density structures such as noise and bone. A dedicated set of 64 features is calculated for each candidate object. They characterize the objects spatial position relative to the heart and the aorta, for which an automatic segmentation scheme was developed, its size and shape, and its appearance, which is described by a set of approximated Gaussian derivatives for which an efficient computational scheme is presented. Three classification strategies were designed. The first one tested direct classification without feature selection. The second approach also utilized direct classification, but with feature selection. Finally, the third scheme employed two-stage classification. In a computationally inexpensive first stage, the most easily recognizable false positives were discarded. The second stage discriminated between more difficult to separate coronary calcium and other candidates. Performance of linear, quadratic, nearest neighbor, and support vector machine classifiers was compared. The method was tested on 76 scans containing 275 calcifications in the coronary arteries and 335 calcifications in the heart and aorta. The best performance was obtained employing a two-stage classification system with a k-nearest neighbor (k-NN) classifier and a feature selection scheme. The method detected 73.8% of coronary calcifications at the expense of on average 0.1 false positives per scan. A calcium score was computed for each scan and subjects were assigned one of four risk categories based on this score. The method assigned the correct risk category to 93.4% of all scans.

Noise Reduction in Computed Tomography Scans Using 3-D Anisotropic Hybrid Diffusion With Continuous Switch

Noise filtering techniques that maintain image contrast while decreasing image noise have the potential to optimize the quality of computed tomography (CT) images acquired at reduced radiation dose. In this paper, a hybrid diffusion filter with continuous switch (HDCS) is introduced, which exploits the benefits of three-dimensional edge-enhancing diffusion (EED) and coherence-enhancing diffusion (CED). Noise is filtered, while edges, tubular structures, and small spherical structures are preserved. From ten high dose thorax CT scans, acquired at clinical doses, ultra low dose ( 15 mAs ) scans were simulated and used to evaluate and compare HDCS to other diffusion filters, such as regularized Perona-Malik diffusion and EED. Quantitative results show that the HDCS filter outperforms the other filters in restoring the high dose CT scan from the corresponding simulated low dose scan. A qualitative evaluation was performed on filtered real low dose CT thorax scans. An expert observer scored artifacts as well as fine structures and was asked to choose one of three scans (two filtered (blinded), one unfiltered) for three different settings (trachea, lung, and mediastinal). Overall, the HDCS filtered scan was chosen most often.

Coronary Artery Calcification in Hemophilia A: No Evidence for a Protective Effect of Factor VIII Deficiency on Atherosclerosis

Objective—Ischemic heart disease mortality is lower in hemophilia patients than in the general male population. As coagulation plays a role in the inflammatory pathways involved in atherogenesis, we investigated whether the clotting factor deficiency protects hemophilia patients from developing atherosclerosis. Methods and Results—Coronary artery calcification, measured with multidetector-row computed tomography, was compared between 42 men, ≥59 years, with severe or moderate hemophilia A, and 613 nonhemophilic men from the Rotterdam Study, a prospective population-based study. None of the study subjects were HIV infected or had a history of cardiovascular disease. Coronary artery calcification was quantified by calculating the Agatston score and calcification mass. Data were analyzed using linear regression. Mean difference (&bgr;) of the natural log–transformed Agatston score between men with and without hemophilia was 0.141 (95% CI −0.602 to 0.885, P=0.709). Results did not change after adjustment for age, body mass index, hypercholesterolemia, hypertension, and use of antidiabetic medication (&bgr;=0.525, 95% CI −0.202 to 1.252, P=0.157). Comparable results were found for calcification mass. Conclusion—The extent of coronary artery atherosclerosis is comparable between elderly men with and without hemophilia. Results from this study underline the importance of screening and treating atherosclerosis risk factors in hemophilia patients.

High Blood Pressure in Pregnancy and Coronary Calcification

A considerable proportion of pregnant women develop high blood pressure in pregnancy. Although it is assumed that this condition subsides after pregnancy, many of these women develop the metabolic syndrome later in life and are at increased risk to develop coronary heart disease. Atherosclerosis development is considered in between risk factors and occurrence of vascular symptoms. We set out to cross-sectionally study the relation of high blood pressure during pregnancy with risk of coronary calcification. The study population was composed 491 healthy postmenopausal women selected from a population-based cohort study. Information on high blood pressure during pregnancy was obtained using a questionnaire. Between 2004 and 2005, the women underwent a multidetector computed tomography (Philips Mx 8000 IDT 16) to assess coronary calcium. The Agatston score, volume, and mass measurements were used to quantify coronary calcium. A total of 30.7% of the women reported to have had high blood pressure in pregnancy. Body mass index (odds ratio [OR]: 1.05; 95% CI: 1.01 to 1.09) and diastolic blood pressure (OR: 1.03; 95% CI: 1.01 to 1.05) were significantly related to a history of high blood pressure in pregnancy. Age was significantly related to increased coronary calcification. Women with a history of high blood pressure during pregnancy had a 57% increased risk of having coronary calcification compared with those women without this condition (OR: 1.57; 95% CI: 1.04 to 2.37). After adjusting for age, the relation did not change (OR: 1.64; 95% CI: 1.07 to 2.53). We concluded that high blood pressure during pregnancy is associated with an increased risk of coronary calcification later in life.

Pilot study of dynamic cine CT angiography for the evaluation of abdominal aortic aneurysms: Implications for endograft treatment

Purpose: To utilize 40-slice electrocardiographically (ECG)-gated cine computed tomographic angiography (CTA) to characterize normal aortic motion during the cardiac cycle at relevant anatomical landmarks in preoperative abdominal aortic aneurysm (AAA) patients. Methods: In 10 consecutive preoperative AAA patients (10 men; mean age 78.8 years, range 69–86), an ECG-gated CTA dataset was acquired on a 40-slice CT scanner using a standard radiation dose. CTA quality was graded and scan time was measured. Pulsatility measurements at multiple relevant anatomical levels were performed in the axial plane. Changes in aortic circumference were determined for both the aortic wall and the luminal diameter. Results: All 10 CT scans were of good quality. All patients could be scanned in 14 to 33 seconds (mean 21). At each anatomical level measured, there was a 2.2- to 3.4-mm increase in the aortic wall circumference per cardiac cycle. A similar increase was observed in luminal circumference, with a 2.4- to 3.6-mm increase per cycle. Conclusion: This study introduces the concept of dynamic cine CTA imaging of aortic motion, providing insight into the pathophysiology of abdominal aortic and iliac pulsations. Patients with AAAs selected for EVAR demonstrate changes in aortic circumference with each cardiac cycle that may have consequences for endograft sizing and future design. The potential for graft migration, intermittent type I endoleak, and poor patient outcome following EVAR can be anticipated. Complex aortic dynamics deserve increased scrutiny in an effort to prevent potential complications.

Contrast agents in X-ray computed tomography and its applications in oncology.

Intravascular iodinated contrast agents are required for a large proportion of computed tomography (CT) studies. Contrast media are indispensable to more clearly differentiate anatomic structures and to detect and characterize abnormalities. Depending on the indication up to 200 ml of these agents are injected during CT. Despite these large amounts adverse effects are rare and have further decreased with the introduction of non-ionic substances. However, it took 10 to 20 years until these non-ionic agents replaced the older ionic agents in clinical practice. In recent years no new substance has been brought to the market. The introduction of rapid scanning using multislice CT technology, however, has led to the development of more sophisticated contrast injection techniques. Current research focuses on optimizing contrast application techniques and on further evaluating the safety profiles of the various substances. The amount of contrast enhancement obtained in individual patients for instance depends on the contrast agent characteristics, such as iodine concentration, and the parameters of the contrast injection protocol, such as iodine flux and iodine dose. Meanwhile, contrast agent characteristics such as osmolality and viscosity play a role in the safety profile of an agent. This paper provides a current overview of CT contrast media, CT contrast dynamics, and CT contrast applications with a special focus on oncological imaging.

Reproductive factors, metabolic factors, and coronary artery calcification in older women.

Objective: Metabolic disturbances may explain the increased cardiovascular risk associated with reproductive factors. This cohort study investigated the relationship between reproductive factors and coronary artery calcification in elderly women and whether this relationship could be explained by metabolic disturbances. Design: In total, 568 postmenopausal women were included in this cross-sectional study. Information about the womens reproductive life was obtained by a questionnaire. Metabolic factors were measured during a single visit. Coronary artery calcification was assessed with a multislice computed tomography scanner and dichotomized as absent or present. Logistic regression analysis was used to assess the relationship between reproductive factors and coronary artery calcification. Crude and multivariate adjusted odds ratios (ORs) with corresponding 95% confidence intervals (CIs) were calculated. In addition, ORs were adjusted for several metabolic and cardiovascular risk factors. Results: The mean age was 66.9 (± 5.5) years. Women with a history of irregular menstrual cycle lengths, as opposed to women with a history of regular menstrual cycles (26-30 d), had an increased risk of coronary artery calcification; multivariate-adjusted OR = 2.73 (95%CI: 1.24-5.98). Four or more pregnancies, compared with never pregnant, yielded an multivariate-adjusted OR of 1.89 (95% CI: 1.00-3.58). Having four children or more, compared with having no children, yielded a multivariate-adjusted OR of 1.97 (95% CI: 1.00-3.89). Adjustment for metabolic factors and other cardiovascular risk factors did not fully explain theses relationships. Conclusion: Multigravidity (more than four pregnancies), multiparity (more than four births), and irregular menstrual cycle lengths were related to an increased risk of coronary artery disease. These associations could not be explained by metabolic abnormalities.

Automated aortic calcium scoring on low-dose chest computed tomography

PURPOSE Thoracic computed tomography (CT) scans provide information about cardiovascular risk status. These scans are non-ECG synchronized, thus precise quantification of coronary calcifications is difficult. Aortic calcium scoring is less sensitive to cardiac motion, so it is an alternative to coronary calcium scoring as an indicator of cardiovascular risk. The authors developed and evaluated a computer-aided system for automatic detection and quantification of aortic calcifications in low-dose noncontrast-enhanced chest CT. METHODS The system was trained and tested on scans from participants of a lung cancer screening trial. A total of 433 low-dose, non-ECG-synchronized, noncontrast-enhanced 16 detector row examinations of the chest was randomly divided into 340 training and 93 test data sets. A first observer manually identified aortic calcifications on training and test scans. A second observer did the same on the test scans only. First, a multiatlas-based segmentation method was developed to delineate the aorta. Segmented volume was thresholded and potential calcifications (candidate objects) were extracted by three-dimensional connected component labeling. Due to image resolution and noise, in rare cases extracted candidate objects were connected to the spine. They were separated into a part outside and parts inside the aorta, and only the latter was further analyzed. All candidate objects were represented by 63 features describing their size, position, and texture. Subsequently, a two-stage classification with a selection of features and k-nearest neighbor classifiers was performed. Based on the detected aortic calcifications, total calcium volume score was determined for each subject. RESULTS The computer system correctly detected, on the average, 945 mm3 out of 965 mm3 (97.9%) calcified plaque volume in the aorta with an average of 64 mm3 of false positive volume per scan. Spearman rank correlation coefficient was p = 0.960 between the system and the first observer compared to p = 0.961 between the two observers. CONCLUSIONS Automatic calcium scoring in the aorta thus appears feasible with good correlation between manual and automatic scoring.

Variability of coronary calcium scores throughout the cardiac cycle: implications for the appropriate use of electrocardiogram-dose modulation with retrospectively gated computed tomography.

Objective:To study how much the calcium scores at various phases throughout the cardiac cycle deviate from the score in the most motionless phase during retrospectively electrocardiogram (ECG)-gated multidetector row computed tomography (MDCT) of the heart and to evaluate how to optimize ECG-based tube current modulation so that errors in calcium scoring can be minimized while dose savings can be maximized. Materials and Methods:In 73 subjects with known or suspected coronary artery disease we performed retrospectively ECG-gated 64-detector row computed tomography for calcium scoring. Four subjects were excluded after scanning because of breathing artifacts or lack of coronary calcification. The scans of 69 subjects (46 men, mean age 62 ± 6 years) were used for further analysis. Heart rate during the scan was recorded. In each patient, calcium scoring [Agatston score (AS), mass score (MS), and volume score, (VS)] was performed on 10 data sets reconstructed at 10%-intervals throughout the cardiac cycle. The most motionless phase was subjectively determined and used as the reference phase. For the score in each phase, deviation from the score in the reference phase was determined. An ECG-simulator was used to determine the amount of dose saving while scanning with dose modulation and applying diagnostic dose during 1 or several phases. Results:Mean heart rate was 63 (±13) beats per minute (bpm). In 51% of patients the reference phase was the 70% phase. Using the calcium score in the 70% phase (mid-diastole) instead of the reference at heart rates below 70 bpm would have induced a median score deviation of 0% [interquartile range: 0%–6% (AS, MS, and VS)] and using the calcium score in the 40% phase (end-systole) at heart rates ≥70 bpm would also have induced a median score deviation of 0% [interquartile range: 0%–7% (AS), 0%–5% (MS), and 0%–3% (VS)]. Errors in calcium scores of more than 10% occur in around 10% of subjects for all 3 scoring algorithms. Dose savings increased with lower heart rates and shorter application of diagnostic dose. Conclusions:The optimum phases for dose modulation are 70% (mid-diastole) at heart rates below 70 bpm and 40% (end-systole) at heart rates above 70 bpm. Under these conditions dose saving is maximum and a median error of 0% is found for the various calcium scoring techniques with score errors of more than 10% in around 10% of subjects.