BACKGROUND AND PURPOSE: Cerebral small-vessel disease may alter cerebral blood flow (CBF) leading... more BACKGROUND AND PURPOSE: Cerebral small-vessel disease may alter cerebral blood flow (CBF) leading to brain changes and, hence, cognitive impairment and dementia. CBF and the spatial coefficient of variation can be measured quantitatively by arterial spinlabeling. We aimed to investigate the associations of demographics, vascular risk factors, location, and severity of cerebral small-vessel disease as well as the etiologic subtypes of cognitive impairment and dementia with CBF and the spatial coefficient of variation. MATERIALS AND METHODS: Three hundred ninety patients with a diagnosis of no cognitive impairment, cognitive impairment no dementia, vascular cognitive impairment no dementia, Alzheimer disease, and vascular dementia were recruited from the memory clinic. Cerebral microbleeds and lacunes were categorized into strictly lobar, strictly deep, and mixed-location and enlarged perivascular spaces into the centrum semiovale and basal ganglia. Total and region-specific white matter hyperintensity volumes were segmented using FreeSurfer. CBF (n ¼ 333) and the spatial coefficient of variation (n ¼ 390) were analyzed with ExploreASL from 2D-EPI pseudocontinuous arterial spin-labeling images in white matter (WM) and gray matter (GM). To analyze the effect of demographic and vascular risk factors as well as the location and severity of cerebral small-vessel disease markers on arterial spin-labeling parameters, we constructed linear regression models, whereas logistic regression models were used to determine the association between arterial spin-labeling parameters and cognitive impairment no dementia, vascular cognitive impairment no dementia, Alzheimer disease, and vascular dementia. RESULTS: Increasing age, male sex, hypertension, hyperlipidemia, history of heart disease, and smoking were associated with lower CBF and a higher spatial coefficient of variation. Higher numbers of lacunes and cerebral microbleeds were associated with lower CBF and a higher spatial coefficient of variation. Location-specific analysis showed mixed-location lacunes and cerebral microbleeds were associated with lower CBF. Higher total, anterior, and posterior white matter hyperintensity volumes were associated with a higher spatial coefficient of variation. No association was observed between enlarged perivascular spaces and arterial spin-labeling parameters. A higher spatial coefficient of variation was associated with the diagnosis of vascular cognitive impairment no dementia, Alzheimer's disease, and vascular dementia. CONCLUSIONS: Reduced CBF and an increased spatial coefficient of variation were associated with cerebral small-vessel disease, and more specifically lacunes, whereas cerebral microbleeds and white matter hyperintensities were associated with WM-CBF and GM spatial coefficient of variation. The spatial coefficient of variation was associated with cognitive impairment and dementia, suggesting that hypoperfusion might be the key underlying mechanism for vascular brain damage. ABBREVIATIONS: AD ¼ Alzheimer's disease; ASL ¼ arterial spin-labeling; ATT ¼ arterial transit time; CIND ¼ cognitive impairment no dementia; CMB ¼ cerebral microbleed; NCI ¼ no cognitive impairment; ePVS ¼ enlarged perivascular spaces; PLD ¼ post-labeling delay; sCoV ¼ spatial coefficient of variation; SVD ¼ cerebral small-vessel disease; VaD ¼ vascular dementia; VCIND ¼ vascular CIND; WMH ¼ white matter hyperintensities C BF ensures a constant delivery of oxygen and nutrients to brain tissue. 1 Recently, the assessment of CBF has become a common clinical investigation to evaluate vascular brain damage, 2 owing to the noninvasive and quantitative measurement by arterial spin-labeling (ASL). 1 Reduced CBF has been linked with normal aging 3 and systemic vascular risk factors such as
Studies in health technology and informatics, 2001
Early detection of polyps has proven to lead to a decrease in incidence of colon cancer. In the p... more Early detection of polyps has proven to lead to a decrease in incidence of colon cancer. In the past few years, virtual colonoscopy has been developed as a patient-friendly screen-ing technique. The procedure comprises the following steps. First, the patient's colon is cleansed and transanally inflated with air. Subsequently, a 3D image volume is acquired of the abdomen by CT or MRI. Finally, the bowel surface is extracted and visualized, after which the physician virtually navigates through the colon and examines the surface for abnormalities. This paper describes the progress in research for virtual colonoscopy.
For the segmentation of magnetic resonance brain images into anatomical regions, numerous fully a... more For the segmentation of magnetic resonance brain images into anatomical regions, numerous fully automated methods have been proposed and compared to reference segmentations obtained manually. However, systematic differences might exist between the resulting segmentations, depending on the segmentation method and underlying brain atlas. This potentially results in sensitivity differences to disease and can further complicate the comparison of individual patients to normative data. In this study, we aim to answer two research questions: 1) to what extent are methods interchangeable, as long as the same method is being used for computing normative volume distributions and patient-specific volumes? and 2) can different methods be used for computing normative volume distributions and assessing patient-specific volumes? To answer these questions, we compared volumes of six brain regions calculated by five state-of-the-art segmentation methods: Erasmus MC (EMC), FreeSurfer (FS), geodesic i...
We examined interethnic differences in the prevalence of neuroimaging markers of cerebrovascular ... more We examined interethnic differences in the prevalence of neuroimaging markers of cerebrovascular and neurodegenerative disease in 3 major Asian ethnicities (Chinese, Malays, and Indians), as well as their role in cognitive impairment. 3T MRI brain scans were acquired from 792 subjects (mean age: 70.0 ± 6.5years, 52.1% women) in the multi-ethnic Epidemiology of Dementia In Singapore study. Markers of cerebrovascular disease and neurodegeneration were identified. Cognitive performance was evaluated using Mini Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), and a neuropsychological assessment. Compared to Chinese, Malays had a higher burden of intracranial stenosis (OR: 2.28. 95%CI: 1.23–4.20) and cortical atrophy (β: −0.60. 95%CI: −0.78, −0.41), while Indians had a higher burden of subcortical atrophy (β: −0.23. 95%CI: −0.40, −0.06). Moreover, Malay and Indian ethnicities were likely to be cognitively impaired (OR for Malays: 3.79. 95%CI: 2.29–6.26; OR for India...
Background: Low haemoglobin is highly prevalent among the elderly and has been associated with de... more Background: Low haemoglobin is highly prevalent among the elderly and has been associated with dementia. However, the mechanisms underlying this association with cognitive dysfunction, either through cerebrovascular disease or neurodegeneration, remain poorly understood. We aimed to examine the association of decreased haemoglobin levels with markers of cerebral small vessel disease (CSVD), neurodegeneration and cognitive impairment in an elderly Asian population. Methods: A total of 796 Chinese, Malay and Indian participants aged 60 years and older from the Epidemiology of Dementia in Singapore study were included in this study. After providing information on demographics, anthropometry and cardiovascular risk factors, participants underwent 3-T brain magnetic resonance imaging (MRI) to measure markers of CSVD, including cerebral microbleeds, cortical cerebral microinfarcts, lacunes, enlarged perivascular spaces and white matter hyperintensities, as well as neurodegenerative markers, including cortical thickness and subcortical structure volumes quantified using FreeSurfer. Cognition was assessed using a detailed neuropsychological assessment. Logistic and linear regression models were constructed, adjusting for age, gender, education, race, body mass index, smoking, hypertension, hyperlipidaemia, diabetes, glomerular filtration rate and other MRI markers, to test the association between haemoglobin levels and the MRI markers and cognition. Results: Decreased haemoglobin levels were associated with cerebral microbleeds, specifically lobar microbleeds (OR, 1.21; 95% CI, 1.04-1.40; p = 0.015). Decreased haemoglobin levels were also associated with occipital cortical thinning (mean difference, − 0.011; 95% CI, − 0.019, − 0.004; p = 0.003) and smaller accumbens volume (mean difference, − 0.01; 95% CI, − 0.02, 0.00; p = 0.005). A significant association was also observed between decreased haemoglobin levels and poorer global cognitive performance (mean difference, − 0.04; 95% CI, − 0.09, 0.00; p = 0.048). In cognitive domain analysis, associations were again observed between decreased haemoglobin levels and worse performance on attention (mean difference, − 0.05; 95% CI, − 0.10, − 0.01; p = 0.028) and language (mean difference, − 0.06; 95% CI, − 0.12, 0.00; p = 0.048) domains; however, these associations did not survive multiple comparison.
MR guided interstitial laser therapy can be used to monitor the extent of tumor tissue coagulatio... more MR guided interstitial laser therapy can be used to monitor the extent of tumor tissue coagulation during thermal treatment based on a temperature map. In a non-stationary object that was influenced by respiratory motion, the temperature map may show errors due to incorrect spatial baseline images. Moreover, an unwanted phase shift due to object displacement contributes to errors in the temperature map, that must be suppressed. This paper describes a strategy which addresses the difficulties of MR guided interstitial laser therapy in the presence of respiratory motion. The multi-baseline images, supported by the displacement correction scheme, were used to improve the temporal resolution of a temperature map in the respiratory cycle. In the displacement correction scheme, the object coordinates that are provided by an active tracking coil were employed to support a matching strategy between the thermal and baseline images. To avoid errors in the temperature map due to the motion artifact, a detector of low quality images was proposed as part of the displacement correction scheme.
We evaluate a new method, called VAMPIRE, for automated definition of a center lumen line in vess... more We evaluate a new method, called VAMPIRE, for automated definition of a center lumen line in vessels in cardiovascular image data. VAMPIRE is based on detection of vessel-like structures by analyzing firstorder and second-order image derivatives combined with a minimal cost path algorithm. The image derivatives are obtained using Canny edge detection and an improved ridge filter for detecting elongated structures. We compared VAMPIRE with an established technique in a multi-observer evaluation study involving 40 tracings in slabbed MIP images of multislice CTA datasets of atherosclerotic carotid arteries. The results show that VAMPIRE, in comparison with the established technique, presents considerably more successful tracings and improved handling of stenosis, calcifications, multiple vessels and nearby bone structures. We conclude that VAMPIRE is highly suitable for automated path definition in vessels in (clinical) cardiovascular image data and we expect to improve VAMPIRE to yield paths that are adequate enough to directly serve as center lumen lines in accordance with standards provided by clinicians.
2012 9th IEEE International Symposium on Biomedical Imaging (ISBI), 2012
The capacity of recognizing the first signs of disease has enormous socio-economic benefits. Popu... more The capacity of recognizing the first signs of disease has enormous socio-economic benefits. Population studies have the potential to see disease develop before your eyes, and when including advanced imaging techniques in these studies, literally so. Population imaging studies, especially when complemented with other biomedical and genetic data, provide unique databases that can be exploited with advanced analysis and search
Objective: To evaluate the concordance of a volumetric method for measuring white matter lesion (... more Objective: To evaluate the concordance of a volumetric method for measuring white matter lesion (WML) change with visual rating scales.Methods: The authors selected a stratified sample of 20 elderly people (mean age 72 years, range 61 to 88 years) with an MRI examination at baseline and at 3-year follow-up from the community-based Rotterdam Scan Study (RSS). Four raters assessed WML change with four different visual rating scales: the Fazekas scale, the Scheltens scale, the RSS scale, and a new visual rating scale that was designed to measure change in WML. The authors assessed concordance with a volumetric method with scatter plots and correlations, and interobserver agreement with intraclass correlation coefficients.Results: For assessment of change in WML, the Fazekas, Scheltens, and periventricular part of the RSS scale showed little correlation with volumetrics, and low interobserver agreement. The authors’ new WML change scale and the subcortical part of the RSS scale showed g...
Background: Previous studies have assessed the association between ankle-brachial index (ABI) and... more Background: Previous studies have assessed the association between ankle-brachial index (ABI) and cognition, mainly using brief cognitive tests. We investigated whether ABI was associated with cognition independent of neuroimaging markers of cerebrovascular disease. Methods: Chinese subjects (n = 278, aged ≥60 years) were recruited from the ongoing Epidemiology of Dementia in Singapore (EDIS) Study. Ankle and brachial blood pressures were measured, and low ABI was defined as ≤0.9. A neuropsychological battery was utilized to determine cognition. Cognitive impairment no dementia (CIND) and dementia were diagnosed according to standard diagnostic criteria. Magnetic resonance imaging (MRI) was used to obtain semiquantitative and quantitative markers of cerebrovascular disease and atrophy. Results: A low ABI was related to the presence of intracranial stenosis (odds ratio, OR = 1.71; 95% confidence interval, CI: 1.13-2.59), but not with the presence of infarcts, microbleeds or grey matt...
Attaching tantalum markers to prostheses for Roentgen stereophotogrammetry (RSA) may be difficult... more Attaching tantalum markers to prostheses for Roentgen stereophotogrammetry (RSA) may be difficult and is sometimes even impossible. In this study, a model-based RSA method that avoids the attachment of markers to prostheses is presented and validated. This model-based RSA method uses a triangulated surface model of the implant. A projected contour of this model is calculated and this calculated model contour is matched onto the detected contour of the actual implant in the RSA radiograph. The difference between the two contours is minimized by variation of the position and orientation of the model. When a minimal difference between the contours is found, an optimal position and orientation of the model has been obtained. The method was validated by means of a phantom experiment. Three prosthesis components were used in this experiment: the femoral and tibial component of an Interax total knee prosthesis (Stryker Howmedica Osteonics Corp., Rutherfort, USA) and the femoral component of a Profix total knee prosthesis (Smith & Nephew, Memphis, USA). For the prosthesis components used in this study, the accuracy of the model-based method is lower than the accuracy of traditional RSA. For the Interax femoral and tibial components, significant dimensional tolerances were found that were probably caused by the casting process and manual polishing of the components surfaces. The largest standard deviation for any translation was 0.19 mm and for any rotation it was 0.528. For the Profix femoral component that had no large dimensional tolerances, the largest standard deviation for any translation was 0.22 mm and for any rotation it was 0.228. From this study we may conclude that the accuracy of the current model-based RSA method is sensitive to dimensional tolerances of the implant. Research is now being conducted to make model-based RSA less sensitive to dimensional tolerances and thereby improving its accuracy.
To develop a new automated calibration method for vessel measurements in vascular x-ray images. R... more To develop a new automated calibration method for vessel measurements in vascular x-ray images. Radiopaque marker bands mounted equidistantly on a small catheter were acquired in vitro at five image intensifier (II) sizes in x-ray projection images. The positions of the marker centers were detected by using a Hough transform and were computed at subpixel precision by using either a novel, iterative center-of-gravity approach (CGA) or a symmetry filter. Curve-fitting procedures were used to reject false-positive marker detections and to calculate intermarker distances. The calibration factor was calculated from the true marker distance and the average of the measured distances in pixels. Results were compared statistically with a grid calibration method, which was taken as the gold standard. A simulation study was performed to assess the influence of image noise on the CGA method. The iterative CGA method was convergent and faster than the symmetry-based technique. For four II sizes (17, 20, 25, and 31 cm), the results from the CGA method were not significantly different from the results obtained with grid calibration. For the II size of 38 cm, a significant difference (0.3% of the grid calibration factor) was found; however, this was caused by the quantification error in the image data and was not clinically relevant. In general, the performance of the CGA method improved with increasing signal-to-noise ratio. A practical new calibration method for small catheter sizes was developed and validated for quantitative vascular arteriography.
The authors developed an analytic software package for the objective and reproducible assessment ... more The authors developed an analytic software package for the objective and reproducible assessment of a single leg separation (SLS) in the outlet strut of Björk-Shiley convexoconcave (BSCC) prosthetic heart valves. The radiographic cinefilm recordings of 18 phantom valves (12 intact and 6 SLS) and of 43 patient valves were acquired. After digitization of regions of interest in a cineframe, several processing steps were carried out to obtain a one-dimensional corrected and averaged density profile along the central axis of each strut leg. To characterize the degree of possible separation, two quantitative measures were introduced: the normalized pit depth (NPD) and the depth-sigma ratio (DSR). The group of 43 patient studies was divided into a learning set (25 patients) and a test set (18 patients). All phantom valves with an SLS were detected (sensitivity, 100%) at a specificity of 100%. The threshold values for the NPD and the DSR to decide whether a fracture was present or not were 3.6 and 2.5, respectively. On the basis of the visual interpretations of the 25 patient studies (learning set) by an expert panel, it was concluded that none of the patients had an SLS. To achieve a 100% specificity by quantitative analysis, the threshold values for the NPD and the DSR were set at 5.8 and 2.5, respectively, for the patient data. Based on these threshold values, the analysis of patient data from the test set resulted in one false-negative detection and three false-positive detections. An analytic software package for the detection of an SLS was developed. Phantom data showed excellent sensitivity (100%) and specificity (100%). Further research and software development is needed to increase the sensitivity and specificity for patient data.
The aim of this study was to assess whether the computed tomography (CT) features of COVID-19 (CO... more The aim of this study was to assess whether the computed tomography (CT) features of COVID-19 (COVID+) ARDS differ from those of non-COVID-19 (COVID−) ARDS patients. Materials and methods: The study is a single-center prospective observational study performed on adults with ARDS onset ≤72 h and a PaO 2 /FiO 2 ≤ 200 mmHg. CT scans were acquired at PEEP set using a PEEP-FiO 2 table with VT adjusted to 6 ml/kg predicted body weight. Results: 22 patients were included, of whom 13 presented with COVID-19 ARDS. Lung weight was significantly higher in COVID− patients, but all COVID+ patients presented supranormal lung weight values. Noninflated lung tissue was significantly higher in COVID− patients (36 ± 14% vs. 26 ± 15% of total lung weight at endexpiration, p < 0.01). Tidal recruitment was significantly higher in COVID− patients (20 ± 12 vs. 9 ± 11% of VT, p < 0.05). Lung density histograms of 5 COVID+ patients with high elastance (type H) were similar to those of COVID− patients, while those of the 8 COVID+ patients with normal elastance (type L) displayed higher aerated lung fraction.
BACKGROUND AND PURPOSE: Cerebral small-vessel disease may alter cerebral blood flow (CBF) leading... more BACKGROUND AND PURPOSE: Cerebral small-vessel disease may alter cerebral blood flow (CBF) leading to brain changes and, hence, cognitive impairment and dementia. CBF and the spatial coefficient of variation can be measured quantitatively by arterial spinlabeling. We aimed to investigate the associations of demographics, vascular risk factors, location, and severity of cerebral small-vessel disease as well as the etiologic subtypes of cognitive impairment and dementia with CBF and the spatial coefficient of variation. MATERIALS AND METHODS: Three hundred ninety patients with a diagnosis of no cognitive impairment, cognitive impairment no dementia, vascular cognitive impairment no dementia, Alzheimer disease, and vascular dementia were recruited from the memory clinic. Cerebral microbleeds and lacunes were categorized into strictly lobar, strictly deep, and mixed-location and enlarged perivascular spaces into the centrum semiovale and basal ganglia. Total and region-specific white matter hyperintensity volumes were segmented using FreeSurfer. CBF (n ¼ 333) and the spatial coefficient of variation (n ¼ 390) were analyzed with ExploreASL from 2D-EPI pseudocontinuous arterial spin-labeling images in white matter (WM) and gray matter (GM). To analyze the effect of demographic and vascular risk factors as well as the location and severity of cerebral small-vessel disease markers on arterial spin-labeling parameters, we constructed linear regression models, whereas logistic regression models were used to determine the association between arterial spin-labeling parameters and cognitive impairment no dementia, vascular cognitive impairment no dementia, Alzheimer disease, and vascular dementia. RESULTS: Increasing age, male sex, hypertension, hyperlipidemia, history of heart disease, and smoking were associated with lower CBF and a higher spatial coefficient of variation. Higher numbers of lacunes and cerebral microbleeds were associated with lower CBF and a higher spatial coefficient of variation. Location-specific analysis showed mixed-location lacunes and cerebral microbleeds were associated with lower CBF. Higher total, anterior, and posterior white matter hyperintensity volumes were associated with a higher spatial coefficient of variation. No association was observed between enlarged perivascular spaces and arterial spin-labeling parameters. A higher spatial coefficient of variation was associated with the diagnosis of vascular cognitive impairment no dementia, Alzheimer's disease, and vascular dementia. CONCLUSIONS: Reduced CBF and an increased spatial coefficient of variation were associated with cerebral small-vessel disease, and more specifically lacunes, whereas cerebral microbleeds and white matter hyperintensities were associated with WM-CBF and GM spatial coefficient of variation. The spatial coefficient of variation was associated with cognitive impairment and dementia, suggesting that hypoperfusion might be the key underlying mechanism for vascular brain damage. ABBREVIATIONS: AD ¼ Alzheimer's disease; ASL ¼ arterial spin-labeling; ATT ¼ arterial transit time; CIND ¼ cognitive impairment no dementia; CMB ¼ cerebral microbleed; NCI ¼ no cognitive impairment; ePVS ¼ enlarged perivascular spaces; PLD ¼ post-labeling delay; sCoV ¼ spatial coefficient of variation; SVD ¼ cerebral small-vessel disease; VaD ¼ vascular dementia; VCIND ¼ vascular CIND; WMH ¼ white matter hyperintensities C BF ensures a constant delivery of oxygen and nutrients to brain tissue. 1 Recently, the assessment of CBF has become a common clinical investigation to evaluate vascular brain damage, 2 owing to the noninvasive and quantitative measurement by arterial spin-labeling (ASL). 1 Reduced CBF has been linked with normal aging 3 and systemic vascular risk factors such as
Studies in health technology and informatics, 2001
Early detection of polyps has proven to lead to a decrease in incidence of colon cancer. In the p... more Early detection of polyps has proven to lead to a decrease in incidence of colon cancer. In the past few years, virtual colonoscopy has been developed as a patient-friendly screen-ing technique. The procedure comprises the following steps. First, the patient's colon is cleansed and transanally inflated with air. Subsequently, a 3D image volume is acquired of the abdomen by CT or MRI. Finally, the bowel surface is extracted and visualized, after which the physician virtually navigates through the colon and examines the surface for abnormalities. This paper describes the progress in research for virtual colonoscopy.
For the segmentation of magnetic resonance brain images into anatomical regions, numerous fully a... more For the segmentation of magnetic resonance brain images into anatomical regions, numerous fully automated methods have been proposed and compared to reference segmentations obtained manually. However, systematic differences might exist between the resulting segmentations, depending on the segmentation method and underlying brain atlas. This potentially results in sensitivity differences to disease and can further complicate the comparison of individual patients to normative data. In this study, we aim to answer two research questions: 1) to what extent are methods interchangeable, as long as the same method is being used for computing normative volume distributions and patient-specific volumes? and 2) can different methods be used for computing normative volume distributions and assessing patient-specific volumes? To answer these questions, we compared volumes of six brain regions calculated by five state-of-the-art segmentation methods: Erasmus MC (EMC), FreeSurfer (FS), geodesic i...
We examined interethnic differences in the prevalence of neuroimaging markers of cerebrovascular ... more We examined interethnic differences in the prevalence of neuroimaging markers of cerebrovascular and neurodegenerative disease in 3 major Asian ethnicities (Chinese, Malays, and Indians), as well as their role in cognitive impairment. 3T MRI brain scans were acquired from 792 subjects (mean age: 70.0 ± 6.5years, 52.1% women) in the multi-ethnic Epidemiology of Dementia In Singapore study. Markers of cerebrovascular disease and neurodegeneration were identified. Cognitive performance was evaluated using Mini Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), and a neuropsychological assessment. Compared to Chinese, Malays had a higher burden of intracranial stenosis (OR: 2.28. 95%CI: 1.23–4.20) and cortical atrophy (β: −0.60. 95%CI: −0.78, −0.41), while Indians had a higher burden of subcortical atrophy (β: −0.23. 95%CI: −0.40, −0.06). Moreover, Malay and Indian ethnicities were likely to be cognitively impaired (OR for Malays: 3.79. 95%CI: 2.29–6.26; OR for India...
Background: Low haemoglobin is highly prevalent among the elderly and has been associated with de... more Background: Low haemoglobin is highly prevalent among the elderly and has been associated with dementia. However, the mechanisms underlying this association with cognitive dysfunction, either through cerebrovascular disease or neurodegeneration, remain poorly understood. We aimed to examine the association of decreased haemoglobin levels with markers of cerebral small vessel disease (CSVD), neurodegeneration and cognitive impairment in an elderly Asian population. Methods: A total of 796 Chinese, Malay and Indian participants aged 60 years and older from the Epidemiology of Dementia in Singapore study were included in this study. After providing information on demographics, anthropometry and cardiovascular risk factors, participants underwent 3-T brain magnetic resonance imaging (MRI) to measure markers of CSVD, including cerebral microbleeds, cortical cerebral microinfarcts, lacunes, enlarged perivascular spaces and white matter hyperintensities, as well as neurodegenerative markers, including cortical thickness and subcortical structure volumes quantified using FreeSurfer. Cognition was assessed using a detailed neuropsychological assessment. Logistic and linear regression models were constructed, adjusting for age, gender, education, race, body mass index, smoking, hypertension, hyperlipidaemia, diabetes, glomerular filtration rate and other MRI markers, to test the association between haemoglobin levels and the MRI markers and cognition. Results: Decreased haemoglobin levels were associated with cerebral microbleeds, specifically lobar microbleeds (OR, 1.21; 95% CI, 1.04-1.40; p = 0.015). Decreased haemoglobin levels were also associated with occipital cortical thinning (mean difference, − 0.011; 95% CI, − 0.019, − 0.004; p = 0.003) and smaller accumbens volume (mean difference, − 0.01; 95% CI, − 0.02, 0.00; p = 0.005). A significant association was also observed between decreased haemoglobin levels and poorer global cognitive performance (mean difference, − 0.04; 95% CI, − 0.09, 0.00; p = 0.048). In cognitive domain analysis, associations were again observed between decreased haemoglobin levels and worse performance on attention (mean difference, − 0.05; 95% CI, − 0.10, − 0.01; p = 0.028) and language (mean difference, − 0.06; 95% CI, − 0.12, 0.00; p = 0.048) domains; however, these associations did not survive multiple comparison.
MR guided interstitial laser therapy can be used to monitor the extent of tumor tissue coagulatio... more MR guided interstitial laser therapy can be used to monitor the extent of tumor tissue coagulation during thermal treatment based on a temperature map. In a non-stationary object that was influenced by respiratory motion, the temperature map may show errors due to incorrect spatial baseline images. Moreover, an unwanted phase shift due to object displacement contributes to errors in the temperature map, that must be suppressed. This paper describes a strategy which addresses the difficulties of MR guided interstitial laser therapy in the presence of respiratory motion. The multi-baseline images, supported by the displacement correction scheme, were used to improve the temporal resolution of a temperature map in the respiratory cycle. In the displacement correction scheme, the object coordinates that are provided by an active tracking coil were employed to support a matching strategy between the thermal and baseline images. To avoid errors in the temperature map due to the motion artifact, a detector of low quality images was proposed as part of the displacement correction scheme.
We evaluate a new method, called VAMPIRE, for automated definition of a center lumen line in vess... more We evaluate a new method, called VAMPIRE, for automated definition of a center lumen line in vessels in cardiovascular image data. VAMPIRE is based on detection of vessel-like structures by analyzing firstorder and second-order image derivatives combined with a minimal cost path algorithm. The image derivatives are obtained using Canny edge detection and an improved ridge filter for detecting elongated structures. We compared VAMPIRE with an established technique in a multi-observer evaluation study involving 40 tracings in slabbed MIP images of multislice CTA datasets of atherosclerotic carotid arteries. The results show that VAMPIRE, in comparison with the established technique, presents considerably more successful tracings and improved handling of stenosis, calcifications, multiple vessels and nearby bone structures. We conclude that VAMPIRE is highly suitable for automated path definition in vessels in (clinical) cardiovascular image data and we expect to improve VAMPIRE to yield paths that are adequate enough to directly serve as center lumen lines in accordance with standards provided by clinicians.
2012 9th IEEE International Symposium on Biomedical Imaging (ISBI), 2012
The capacity of recognizing the first signs of disease has enormous socio-economic benefits. Popu... more The capacity of recognizing the first signs of disease has enormous socio-economic benefits. Population studies have the potential to see disease develop before your eyes, and when including advanced imaging techniques in these studies, literally so. Population imaging studies, especially when complemented with other biomedical and genetic data, provide unique databases that can be exploited with advanced analysis and search
Objective: To evaluate the concordance of a volumetric method for measuring white matter lesion (... more Objective: To evaluate the concordance of a volumetric method for measuring white matter lesion (WML) change with visual rating scales.Methods: The authors selected a stratified sample of 20 elderly people (mean age 72 years, range 61 to 88 years) with an MRI examination at baseline and at 3-year follow-up from the community-based Rotterdam Scan Study (RSS). Four raters assessed WML change with four different visual rating scales: the Fazekas scale, the Scheltens scale, the RSS scale, and a new visual rating scale that was designed to measure change in WML. The authors assessed concordance with a volumetric method with scatter plots and correlations, and interobserver agreement with intraclass correlation coefficients.Results: For assessment of change in WML, the Fazekas, Scheltens, and periventricular part of the RSS scale showed little correlation with volumetrics, and low interobserver agreement. The authors’ new WML change scale and the subcortical part of the RSS scale showed g...
Background: Previous studies have assessed the association between ankle-brachial index (ABI) and... more Background: Previous studies have assessed the association between ankle-brachial index (ABI) and cognition, mainly using brief cognitive tests. We investigated whether ABI was associated with cognition independent of neuroimaging markers of cerebrovascular disease. Methods: Chinese subjects (n = 278, aged ≥60 years) were recruited from the ongoing Epidemiology of Dementia in Singapore (EDIS) Study. Ankle and brachial blood pressures were measured, and low ABI was defined as ≤0.9. A neuropsychological battery was utilized to determine cognition. Cognitive impairment no dementia (CIND) and dementia were diagnosed according to standard diagnostic criteria. Magnetic resonance imaging (MRI) was used to obtain semiquantitative and quantitative markers of cerebrovascular disease and atrophy. Results: A low ABI was related to the presence of intracranial stenosis (odds ratio, OR = 1.71; 95% confidence interval, CI: 1.13-2.59), but not with the presence of infarcts, microbleeds or grey matt...
Attaching tantalum markers to prostheses for Roentgen stereophotogrammetry (RSA) may be difficult... more Attaching tantalum markers to prostheses for Roentgen stereophotogrammetry (RSA) may be difficult and is sometimes even impossible. In this study, a model-based RSA method that avoids the attachment of markers to prostheses is presented and validated. This model-based RSA method uses a triangulated surface model of the implant. A projected contour of this model is calculated and this calculated model contour is matched onto the detected contour of the actual implant in the RSA radiograph. The difference between the two contours is minimized by variation of the position and orientation of the model. When a minimal difference between the contours is found, an optimal position and orientation of the model has been obtained. The method was validated by means of a phantom experiment. Three prosthesis components were used in this experiment: the femoral and tibial component of an Interax total knee prosthesis (Stryker Howmedica Osteonics Corp., Rutherfort, USA) and the femoral component of a Profix total knee prosthesis (Smith & Nephew, Memphis, USA). For the prosthesis components used in this study, the accuracy of the model-based method is lower than the accuracy of traditional RSA. For the Interax femoral and tibial components, significant dimensional tolerances were found that were probably caused by the casting process and manual polishing of the components surfaces. The largest standard deviation for any translation was 0.19 mm and for any rotation it was 0.528. For the Profix femoral component that had no large dimensional tolerances, the largest standard deviation for any translation was 0.22 mm and for any rotation it was 0.228. From this study we may conclude that the accuracy of the current model-based RSA method is sensitive to dimensional tolerances of the implant. Research is now being conducted to make model-based RSA less sensitive to dimensional tolerances and thereby improving its accuracy.
To develop a new automated calibration method for vessel measurements in vascular x-ray images. R... more To develop a new automated calibration method for vessel measurements in vascular x-ray images. Radiopaque marker bands mounted equidistantly on a small catheter were acquired in vitro at five image intensifier (II) sizes in x-ray projection images. The positions of the marker centers were detected by using a Hough transform and were computed at subpixel precision by using either a novel, iterative center-of-gravity approach (CGA) or a symmetry filter. Curve-fitting procedures were used to reject false-positive marker detections and to calculate intermarker distances. The calibration factor was calculated from the true marker distance and the average of the measured distances in pixels. Results were compared statistically with a grid calibration method, which was taken as the gold standard. A simulation study was performed to assess the influence of image noise on the CGA method. The iterative CGA method was convergent and faster than the symmetry-based technique. For four II sizes (17, 20, 25, and 31 cm), the results from the CGA method were not significantly different from the results obtained with grid calibration. For the II size of 38 cm, a significant difference (0.3% of the grid calibration factor) was found; however, this was caused by the quantification error in the image data and was not clinically relevant. In general, the performance of the CGA method improved with increasing signal-to-noise ratio. A practical new calibration method for small catheter sizes was developed and validated for quantitative vascular arteriography.
The authors developed an analytic software package for the objective and reproducible assessment ... more The authors developed an analytic software package for the objective and reproducible assessment of a single leg separation (SLS) in the outlet strut of Björk-Shiley convexoconcave (BSCC) prosthetic heart valves. The radiographic cinefilm recordings of 18 phantom valves (12 intact and 6 SLS) and of 43 patient valves were acquired. After digitization of regions of interest in a cineframe, several processing steps were carried out to obtain a one-dimensional corrected and averaged density profile along the central axis of each strut leg. To characterize the degree of possible separation, two quantitative measures were introduced: the normalized pit depth (NPD) and the depth-sigma ratio (DSR). The group of 43 patient studies was divided into a learning set (25 patients) and a test set (18 patients). All phantom valves with an SLS were detected (sensitivity, 100%) at a specificity of 100%. The threshold values for the NPD and the DSR to decide whether a fracture was present or not were 3.6 and 2.5, respectively. On the basis of the visual interpretations of the 25 patient studies (learning set) by an expert panel, it was concluded that none of the patients had an SLS. To achieve a 100% specificity by quantitative analysis, the threshold values for the NPD and the DSR were set at 5.8 and 2.5, respectively, for the patient data. Based on these threshold values, the analysis of patient data from the test set resulted in one false-negative detection and three false-positive detections. An analytic software package for the detection of an SLS was developed. Phantom data showed excellent sensitivity (100%) and specificity (100%). Further research and software development is needed to increase the sensitivity and specificity for patient data.
The aim of this study was to assess whether the computed tomography (CT) features of COVID-19 (CO... more The aim of this study was to assess whether the computed tomography (CT) features of COVID-19 (COVID+) ARDS differ from those of non-COVID-19 (COVID−) ARDS patients. Materials and methods: The study is a single-center prospective observational study performed on adults with ARDS onset ≤72 h and a PaO 2 /FiO 2 ≤ 200 mmHg. CT scans were acquired at PEEP set using a PEEP-FiO 2 table with VT adjusted to 6 ml/kg predicted body weight. Results: 22 patients were included, of whom 13 presented with COVID-19 ARDS. Lung weight was significantly higher in COVID− patients, but all COVID+ patients presented supranormal lung weight values. Noninflated lung tissue was significantly higher in COVID− patients (36 ± 14% vs. 26 ± 15% of total lung weight at endexpiration, p < 0.01). Tidal recruitment was significantly higher in COVID− patients (20 ± 12 vs. 9 ± 11% of VT, p < 0.05). Lung density histograms of 5 COVID+ patients with high elastance (type H) were similar to those of COVID− patients, while those of the 8 COVID+ patients with normal elastance (type L) displayed higher aerated lung fraction.
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Papers by H. Vrooman