Biomedical subjects

G J Streekstra

Publications and source records attributed to G J Streekstra.

6 recordsLinked to original sources

PubMed2005

Interactive 3D segmentation using connected orthogonal contours.

This paper describes a new method for interactive segmentation that is based on cross-sectional design and 3D modelling. The method represents a 3D model by a set of connected contours that are planar and orthogonal. Planar contours overlayed on image data are easily manipulated and linked contours reduce the amount of user interaction.1 This method solves the contour-to-contour correspondence problem and can capture extrema of objects in a more flexible way than manual segmentation of a stack of 2D images. The resulting 3D model is guaranteed to be free of geometric and topological errors. We show that manual segmentation using connected orthogonal contours has great advantages over conventional manual segmentation. Furthermore, the method provides effective feedback and control for creating an initial model for, and control and steering of, (semi-)automatic segmentation methods.

Algorithms↗

PubMed2004

Validation and application of an automated rheoscope for measuring red blood cell deformability distributions in different species.

BACKGROUND: The deformability of red blood cells (RBCs) is of great importance for the conservation of oxygen delivery in the microcirculation. Even a small fraction of rigid cells is considered to harm the exchange of respiratory gases. Techniques that measure RBC deformability often provide an indication of the mean deformability. It may not be possible, however, to assess whether this mean value is reduced by the presence of a small rigid cell fraction or by a slight overall reduction in RBC deformability. A technique that provides a deformability distribution would be of great value to study diseases that are marked by subpopulations with a reduced deformability. METHODS: This paper describes a rheoscope system that uses advanced image analysis techniques to quickly quantify the deformability of many individual cells in shear flow, in order to find the RBC-deformability distribution. Since variations in the shear stress are responsible for variations in cell elongation, and hence introduce an additional spread in the cell deformability distribution, we first determined the spread caused by instrumental error. We then utilized the technique to investigate the relation between cell deformability and cell size of single blood samples of different species (human, pig, rat and rabbit). RESULTS: The spread caused by instrumental error was small compared to the actual RBC-deformability spread in blood samples. The deformability distribution of human and pig cells are alike although their cell sizes are different. Rat and rabbit cells show comparable deformability and size distributions. With this technique no correlation was found between cell deformability and cell size in animal RBCs. In the human sample a minor correlation was found between cell deformability and cell size. CONCLUSIONS: The automated rheoscope enables us to study the mechanical properties of RBCs more thoroughly by their deformability distribution. These deformability distributions are hardly influenced by the technique or by cell size.

Animals↗

PubMed2002

Measurement of the distribution of red blood cell deformability using an automated rheoscope.

BACKGROUND: Red blood cells (RBCs) have to deform markedly to pass through the smallest capillaries of the microcirculation. Techniques for measuring RBC deformability often result in an indication of the mean value. A deformability distribution would be more useful for studying diseases that are marked by subpopulations of less deformable cells because even small fractions of rigid cells can cause circulatory problems. METHODS: We present an automated rheoscope that uses advanced image analysis techniques to determine a RBC deformability distribution (RBC-DD) by analyzing a large number of individual cells in shear flow. The sensitivity was measured from density-separated fractions of one blood sample and from cells rendered less deformable by heat treatment. A preliminary experiment included the RBC-DDs of a patient with sickle cell anemia, one on dialysis and being treated with erythropoietin, and one with elliptocytosis. RESULTS: Measurement of the RBC-DD was highly reproducible. The sensitivity test showed markedly different deformability distributions of density-separated cells and yielded distinct RBC-DDs after each additional minute of heat treatment. CONCLUSION: The automated rheoscope enabled the determination of RBC-DDs from which less deformable subpopulations can be established. The shape of an RBC-DD may be valuable in assessing cell fractions with normal and anomalous deformability within pathologic blood samples.

Erythrocyte Deformability↗

PubMed2001

Velocity estimation of spots in three-dimensional confocal image sequences of living cells.

BACKGROUND: The analysis of three-dimensional (3D) motion is becoming increasingly important in life cell imaging. A simple description of sometimes complex patterns of movement in living cells gives insight in the underlying mechanisms governing these movements. METHODS: We evaluate a velocity estimation method based on intensity derivatives in spatial and temporal domain from 3D confocal images of living cells. Cells of the sample contain intense spots throughout the cell nucleus. In simulations, we model these spots as Gaussian intensity profiles which are constant in intensity and shape. To quantify the quality of the estimated velocity, we introduce a reliability measure. RESULTS: For constant linear velocity, the velocity estimation is unbiased. For accelerated motion paths or when a neighboring spot disturbs the intensity profile, the method results are biased. The influence of the point-spread function on the velocity estimation can be compensated for by introducing anisotropic derivative kernels. The insight gained in the simulations is confirmed by the results of the method applied on an image sequence of a living cell with fluorescently labeled chromatin. CONCLUSIONS: With the velocity estimation method, a tool for estimating 3D velocity fields is described which is successfully applied to a living cell sequence. With the estimated velocity fields, motion patterns can be observed, which are a useful starting point for the analysis of dynamic processes in living cells.

Animals↗

PubMed1995

A new method to study shape recovery of red blood cells using multiple optical trapping.

In this new method for studying the shape recovery of deformed red blood cells, three optical traps ("optical tweezers") induce a parachute-shaped red cell deformation, which is comparable to the deformation in small capillaries. The shape recovery is recorded, and a relaxation time is obtained for each individual red blood cell. The sensitivity of this technique for the detection of differences in relaxation times is demonstrated on subpopulations of density-separated red blood cells: "young" cells have shorter (162 ms) and "old" cells have longer (353 ms) relaxation times compared with the total population (271 ms). The relaxation time is remarkably shorter (114 ms) when the plasma surrounding the cells is replaced by a phosphate-buffered saline solution. The main advantages of this technique are the relatively short measuring and preparation time and the physiological type of deformation and shape recovery in which all relevant cell properties play a role. Therefore, especially when automated further, the technique may be a powerful tool for the study of (sub)populations of pathological red blood cells.

Biophysical Phenomena↗

PubMedDate not supplied

Analyzing red blood cell-deformability distributions.

BACKGROUND: Red blood cells (RBCs) must deform to pass the smallest capillaries of the microcirculation. Available techniques for measuring RBC deformability often provide an indication of the mean deformability. The latter may be decreased either by a slight overall deformability reduction or by the presence of a small fraction of rigid cells. A distinction between these two cases can be made with a RBC-deformability distribution (RBC-DD). METHODS: This paper explores RBC-DDs of healthy individuals and of cells with anomalous mechanical properties (sickle cell disease, dialysis patients, elliptocytosis, and cultivated malaria tropica). The distributions were measured with an automated rheoscope, which uses advanced image analysis techniques to obtain the deformability index of a large number of individual cells subjected to simple shear flow. RESULTS: The RBC-DD of healthy volunteers is close to a normal distribution. In the investigated patients, distributions were markedly different and yielded significant changes in the mean, in the standard deviation, or in both. The presence of hypodeformable and hyperdeformable cell fractions can qualitatively and quantitatively be assessed from the deformability distribution (DD). In elliptocytosis, cells orient differently with respect to the streamlines, compared to normal cells. This causes the DD to be biased. CONCLUSIONS: The RBC-DD is a powerful representation to establish subpopulations with anomalous deformability. Fractions of hypodeformable and hyperdeformable cells and the standard deviation of the DD are new and excellent quantitative parameters to assess alterations in RBC deformability.

Anemia, Sickle Cell↗