This study examined associations of neighbourhood walkability with cognitive functioning (i.e., global cognition, memory, language, attention-psychomotor speed, and executive functioning) in... Show moreThis study examined associations of neighbourhood walkability with cognitive functioning (i.e., global cognition, memory, language, attention-psychomotor speed, and executive functioning) in participants without or with either heart failure, carotid occlusive disease, or vascular cognitive impairment. Neighbourhood walkability at baseline was positively associated with global cognition and attention-psychomotor speed. These associations were stronger in patients with vascular cognitive impairment. Individuals who live in residential areas with higher walkability levels were less likely to have impairments in language and executive functioning at two-year follow-up. These findings highlight the importance of the built environment for cognitive functioning in healthy and vulnerable groups. Show less
In this dissertation non-parametric Bayesian methods are used in the application of robotic vision. Robots make use of depth sensors that represent their environment using point clouds. Non... Show moreIn this dissertation non-parametric Bayesian methods are used in the application of robotic vision. Robots make use of depth sensors that represent their environment using point clouds. Non-parametric Bayesian methods can (1) determine how good an object is recognized, and (2) determine how many objects a particular scene contains. When there is a model available for the object to be recognized and the nature of perceptual error is known, a Bayesian method will act optimally.In this dissertation Bayesian models are developed to represent geometric objects such as lines and line segments (consisting out of points). The infinite line model and the infinite line segment model use a non-parametric Bayesian model, to be precise, a Dirichlet process, to represent the number of objects. The line or the line segment is represented by a probability distribution. The lines can be represented by conjugate distributions and then Gibbs sampling can be used. The line segments are not represented by conjugate distributions and therefore a split-merge sampler is used.A split-merge sampler fits line segments by assigning points to a hypothetical line segment. Then it proposes splits of a single line segment or merges of two line segments. A new sampler, the triadic split-merge sampler, introduces steps that involve three line segments. In this dissertation, the new sampler is compared to a conventional split-merge sampler. The triadic sampler can be applied to other problems as well, i.e., not only problems in robotic perception.The models for objects can also be learned. In the dissertation this is done for more complex objects, such as cubes, built up out of hundreds of points. An auto-encoder then learns to generate a representative object given the data. The auto-encoder uses a newly defined reconstruction distance, called the partitioning earth mover’s distance. The object that is learned by the auto-encoder is used in a triadic sampler to (1) identify the point cloud objects and to (2) establish multiple occurrences of those objects in the point cloud. Show less
Demirkiran, A.; Amier, R.P.; Hofman, M.B.M.; Geest, R.J. van der; Robbers, L.F.H.J.; Hopman, L.H.G.A.; ... ; Nijveldt, R. 2021
The pathophysiology behind thrombus formation in paroxysmal atrial fibrillation (AF) patients is very complex. This can be due to left atrial (LA) flow changes, remodeling, or both. We investigated... Show moreThe pathophysiology behind thrombus formation in paroxysmal atrial fibrillation (AF) patients is very complex. This can be due to left atrial (LA) flow changes, remodeling, or both. We investigated differences for cardiovascular magnetic resonance (CMR)-derived LA 4D flow and remodeling characteristics between paroxysmal AF patients and patients without cardiac disease. In this proof-of-concept study, the 4D flow data were acquired in 10 patients with paroxysmal AF (age=61 +/- 8 years) and 5 age/gender matched controls (age=56 +/- 1 years) during sinus rhythm. The following LA and LA appendage flow parameters were obtained: flow velocity (mean, peak), stasis defined as the relative volume with velocities<10 cm/s, and kinetic energy (KE). Furthermore, LA global strain values were derived from b-SSFP cine images using dedicated CMR feature-tracking software. Even in sinus rhythm, LA mean and peak flow velocities over the entire cardiac cycle were significantly lower in paroxysmal AF patients compared to controls [(13.12.4 cm/s vs. 16.7 +/- 2.1 cm/s, p=0.01) and (19.3 +/- 4.7 cm/s vs. 26.8 +/- 5.5 cm/s, p=0.02), respectively]. Moreover, paroxysmal AF patients expressed more stasis of blood than controls both in the LA (43.2 +/- 10.8% vs. 27.8 +/- 7.9%, p=0.01) and in the LA appendage (73.3 +/- 5.7% vs. 52.8 +/- 16.2%, p=0.04). With respect to energetics, paroxysmal AF patients demonstrated lower mean and peak KE values (indexed to maximum LA volume) than controls. No significant differences were observed for LA volume, function, and strain parameters between the groups. Global LA flow dynamics in paroxysmal AF patients appear to be impaired including mean/peak flow velocity, stasis fraction, and KE, partly independent of LA remodeling. This pathophysiological flow pattern may be of clinical value to explain the increased incidence of thromboembolic events in paroxysmal AF patients, in the absence of actual AF or LA remodeling. Show less
OBJECTIVES This study compared the performance of the quantitative flow ratio (QFR) with single-photon emission computed tomography (SPECT) and positron emission tomography (PET) myocardial... Show moreOBJECTIVES This study compared the performance of the quantitative flow ratio (QFR) with single-photon emission computed tomography (SPECT) and positron emission tomography (PET) myocardial perfusion imaging (MPI) for the diagnosis of fractional flow reserve (FFR)-defined coronary artery disease (CAD).BACKGROUND QFR estimates FFR solely based on cine contrast images acquired during invasive coronary angiography (ICA). Head-to-head studies comparing QFR with noninvasive MPI are lacking.METHODS A total of 208 (624 vessels) patients underwent technetium -99m tetrofosmin SPECT and [15O]H2O PET imaging before ICA in conjunction with FFR measurements. ICA was obtained without using a dedicated QFR acquisition protocol, and QFR computation was attempted in all vessels interrogated by FFR (552 vessels).RESULTS QFR computation succeeded in 286 (52%) vessels. QFR correlated well with invasive FFR overall (R = 0.79; p < 0.001) and in the subset of vessels with an intermediate (30% to 90%) diameter stenosis (R = 0.76; p < 0.001). Overall, per-vessel analysis demonstrated QFR to exhibit a superior sensitivity (70%) in comparison with SPECT (29%; p < 0.001), whereas it was similar to PET (75%; p = 1.000). Specificity of QFR (93%) was higher than PET (79%; p < 0.001) and not different from SPECT (96%; p = 1.000). As such, the accuracy of QFR (88%) was superior to both SPECT (82%; p = 0.010) and PET (78%; p = 0.004). Lastly, the area under the receiver operating characteristics curve of QFR, in the overall sample (0.94) and among vessels with an intermediate lesion (0.90) was higher than SPECT (0.63 and 0.61; p < 0.001 for both) and PET (0.82; p < 0.001 and 0.77; p = 0.002), respectively.CONCLUSIONS In this head-to-head comparative study, QFR exhibited a higher diagnostic value for detecting FFRdefined significant CAD compared with perfusion imaging by SPECT or PET. (J Am Coll Cardiol Img 2020;13:1976-85) (c) 2020 by the American College of Cardiology Foundation. Show less
Purpose To compare cardiac magnetic resonance imaging (CMR) with [O-15]H2O positron emission tomography (PET) for quantification of absolute myocardial blood flow (MBF) and myocardial flow reserve ... Show morePurpose To compare cardiac magnetic resonance imaging (CMR) with [O-15]H2O positron emission tomography (PET) for quantification of absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) in patients with coronary artery disease (CAD). Methods Fifty-nine patients with stable CAD underwent CMR and [O-15]H2O PET. The CMR imaging protocol included late gadolinium enhancement to rule out presence of scar tissue and perfusion imaging using a dual sequence, single bolus technique. Absolute MBF was determined for the three main vascular territories at rest and during vasodilator stress. Results CMR measurements of regional stress MBF and MFR showed only moderate correlation to those obtained using PET (r = 0.39; P < 0.001 for stress MBF and r = 0.36; P < 0.001 for MFR). Bland-Altman analysis revealed a significant bias of 0.2 +/- 1.0 mL/min/g for stress MBF and - 0.5 +/- 1.2 for MFR. CMR-derived stress MBF and MFR demonstrated area under the curves of respectively 0.72 (95% CI: 0.65 to 0.79) and 0.76 (95% CI: 0.69 to 0.83) and had optimal cutoff values of 2.35 mL/min/g and 2.25 for detecting abnormal myocardial perfusion, defined as [O-15]H2O PET-derived stress MBF <= 2.3 mL/min/g and MFR <= 2.5. Using these cutoff values, CMR and PET were concordant in 137 (77%) vascular territories for stress MBF and 135 (80%) vascular territories for MFR. Conclusion CMR measurements of stress MBF and MFR showed modest agreement to those obtained with [O-15]H2O PET. Nevertheless, stress MBF and MFR were concordant between CMR and [O-15]H2O PET in 77% and 80% of vascular territories, respectively. Show less
Everaars, H.; Hoeven, N.W. van der; Janssens, G.N.; Leeuwen, M.A. van; Loon, R.B. van; Schumacher, S.P.; ... ; Nijveldt, R. 2020
OBJECTIVES This study sought to determine the agreement between cardiac magnetic resonance (CMR) imaging and invasive measurements of fractional flow reserve (FFR) in the evaluation of nonculprit... Show moreOBJECTIVES This study sought to determine the agreement between cardiac magnetic resonance (CMR) imaging and invasive measurements of fractional flow reserve (FFR) in the evaluation of nonculprit lesions after ST-segment elevation myocardial infarction (STEMI). In addition, we investigated whether fully quantitative analysis of myocardial perfusion is superior to semiquantitative and visual analysis.BACKGROUND The agreement between CMR and FFR in the evaluation of nonculprit lesions in patients with STEMI with multivessel disease is unknown.METHODS Seventy-seven patients with STEMI with at least 1 intermediate (diameter stenosis 50% to 90%) nonculprit lesion underwent CMR and invasive coronary angiography in conjunction with FFR measurements at 1 month after primary intervention. The imaging protocol included stress and rest perfusion, cine imaging, and late gadolinium enhancement. Fully quantitative, semiquantitative, and visual analysis of myocardial perfusion were compared against a reference of FFR. Hemodynamically obstructive was defined as FFR <= 0.80.RESULTS Hemodynamically obstructive nonculprit lesions were present in 31 (40%) patients. Visual analysis displayed an area under the curve (AUC) of 0.74 (95% confidence interval [CI]: 0.62 to 0.83), with a sensitivity of 73% and a specificity of 70%. For semiquantitative analysis, the relative upslope of the stress signal intensity time curve and the relative upslope derived myocardial flow reserve had respective AUCs of 0.66 (95% CI: 0.54 to 0.77) and 0.71 (95% CI: 0.59 to 0.81). Fully quantitative analysis did not augment diagnostic performance (all p > 0.05). Stress myocardial blood flow displayed an AUC of 0.76 (95% CI: 0.64 to 0.85), with a sensitivity of 69% and a specificity of 77%. Similarly, MFR displayed an AUC of 0.82 (95% CI: 0.71 to 0.90), with a sensitivity of 82% and a specificity of 71%.CONCLUSIONS CMR and FFR have moderate-good agreement in the evaluation of nonculprit lesions in patients with STEMI with multivessel disease. Fully quantitative, semiquantitative, and visual analysis yield similar diagnostic performance. (C) 2020 by the American College of Cardiology Foundation. Show less