Jing Bai

Threshold selection by clustering gray levels of boundary

In this paper, threshold selection is considered in the continuous image rather than in digital image. We prove that, for each given object within 2D image, its optimal threshold is determined by the mean of the gray values of the points lying on its continuous boundary. Thus, we try to deduce threshold from the gray values of the boundary rather from the gray values of the given discrete sampling points (pixels or edge pixels). By the scheme, we well overcome some disadvantages existing in the threshold methods based on the histogram of edge pixels. Besides, the proposed method has the ability to well handle the image whose histogram has very unequal peaks and broad valley.

Automatic segmentation technique for acetabulum and femoral head in CT images

Abstract Segmentation of the femoral head and proximal acetabulum from three dimensional (3D) CT data is essential for patient specific planning and simulation of hip surgery whereas it still remains challenging due to deformed shapes and extremely narrow inter-bone regions. In this paper, we present an accurate, automatic and fast approach for simultaneous segmentation of the femoral head and proximal acetabulum in the hip joint from 3D CT data. First valley-emphasized image is constructed from original images so that valleys stand out in high relief and initial thresholding segmentation is performed to divide the image set into bone (femoral head and acetabulum) and non-bone classes. It is employed as an initial boundary of the femoral head and acetabulum for further processing in the segmentation procedures. In the subsequent iterative process, the bone regions are further segmented with consideration of the narrow joint space, the neighborhood information and the partial volume effect. Finally, the segmented bone boundaries are corrected based on the normal direction of vertices of the 3D bone surface. Evaluation of the method is performed on the 110 hips including pathologies. Experimental results indicate that our method rapidly leads to very accurate segmentations of the femoral head and acetabulum in the hip joint and can be applied as a tool in the clinical practice.

Cardiovascular responses to external counterpulsation: a computer simulation.

A mathematical model of the human cardiovascular system is presented which includes a simulation of cardiac assistance by external counterpulsation. The model was established to study the effects of external counterpulsation on cardiovascular haemodynamics. The closed simulation includes both the left and the right heart and the pulmonary circulation. The model is able to provide data for the behaviour of the system under varying modes of assistance. Our results suggest that control of external counterpulsation is more difficult than control of the intra-aortic balloon pump and requires regulation of a larger number of variables. The results also suggest that a tradeoff exists between improved oxygen delivery to the heart and reduction in the oxygen consumption of the myocardium, an observation similar to that reported for the intra-aortic balloon pump.

Optimum control of the Hemopump as a left-ventricular assist device

A general framework for designing an optimum control strategy for the Hemopump is described. An objective function was defined that includes four membership functions, each constructed based on the desired values of one of the four members: stroke volume, mean left atrial pressure, aortic diastolic pressure and mean pump rotation speed. The Hemopump was allowed to operate either at a constant speed or at two different speeds during a cardiac cycle. The goal was to maximise the objective function by varying the magnitude and timing of the pump speed. Using a canine circulatory model, it was demonstrated that, in general, different cardiac conditions or different clinical objectives require different operation parameters. For example, when a left ventricle with minor ischaemia was simulated, and the main objective was to increase stoke volume, the objective function was maximised, from a value of 0.877 when the pump was off, to 0.946 when the pump was operated at speed 2 (18 500-revolutions min−1). On the other hand, for a severely ischaemic heart, the optimum pump speed became speed 3 (20 000 revolutions min−1), which maximized the objective function to 0.943 (from 0.707 when the pump was off). The results also suggest that it is more beneficial to operate the Hemopump at two different speeds during a cardiac cycle (a higher speed during systole and early diastole, and a lower speed during late diastole) than to maintain a constant speed throughout the cardiac cycle.

Adaptive approximation of the boundary surface of a neuron in confocal microscopy volumetric images

In biomedical visualisation, the isosurface is usually used to represent (approximate) the boundary surface of the structure within biomedical volumetric images. However, in many confocal microscopy volumetric images of neurons, the grey values of the object and/or background are usually uneven. Therefore a fixed isosurface is not suitable for use in approximating the boundary surface of the neuron. A method is proposed to construct the adaptively approximating surface of the boundary surface of the neuron. In this method, the boundary surface of the neuron could be locally and adaptively approximated with different surface patches in different local regions. Consequently, the approximation accuracy has been considerably improved.

A Computational Framework for Approximating Boundary Surfaces in 3-D Biomedical Images

We propose a new method for detecting and approximating the boundary surfaces in three-dimensional (3-D) biomedical images. Using this method, each boundary surface in the original 3-D image is normalized as a zero-value isosurface of a new 3-D image transformed from the original 3-D image. A novel computational framework is proposed to perform such an image transformation. According to this framework, we first detect boundary surfaces from the original 3-D image and compute discrete samplings of the boundary surfaces. Based on these discrete samplings, a new 3-D image is constructed for each boundary surface such that the boundary surface can be well approximated by a zero-value isosurface in the new 3-D image. In this way, the complex problem of reconstructing boundary surfaces in the original 3-D image is converted into a task to extract a zero-value isosurface from the new 3-D image. The proposed technique is not only capable of adequately reconstructing complex boundary surfaces in 3-D biomedical images, but it also overcomes vital limitations encountered by the isosurface-extracting method when the method is used to reconstruct boundary surfaces from 3-D images. The performances and advantages of the proposed computational framework are illustrated by many examples from different 3-D biomedical images.

Computer simulation of the baroregulation in response to moderate dynamic exercise

A baroregulation model, based on a previous pulsatile non-linear multielement cardiovascular model, is extended and used to study short-term regulation mechanisms. Using this model, the responses of several cardiovascular variables to different exercise levels are simulated and compared with the experimental data reported in the literature. The impact of physiological or pathological changes on the short-term regulation of arterial pressure under the stimulus of moderate dynamic exercise is then studied. The simulation results indicate that baroreflex feedback plays a critical role in the short-term regulation of arterial pressure. When the baroreflex gain decreases to one-third of the normal value, the response of the mean arterial pressure to moderate dynamic exercise and post-exercise recovery time increases by factors of 1.7 and 2.3, respectively. Clinical data from 36 subjects (two groups: normal and hypertensive) are collected to validate the model. Computer simulations for the hypertensive group show that the elastic modulus of the arterial vessel wall is increased by 1.5 times, and peripheral resistance is increased by 1.3 times the normal value, and the baroreflex gain decreases from 0.55 (for the normal group) to 0.40. The simulation results for normal and hypertensive groups agree well with the clinical data.

An analysis algorithm for accurate determination of articular cartilage thickness of hip joint from MR images

To test the accuracy of the most widely used technique based on edge detection for thickness measurement of the hip joint cartilage in MR images, and to improve the measurement accuracy by developing a new measurement method based on a model of the MRI process.

Simulation Study and Function Analysis of Micro-axial Blood Pumps

During past decades, various micro-axial blood pumps were invented and have gained widespread acceptance as prospective devices as circulatory support of failing hearts. Studies concerned with the effects of the pumps can be divided into two categories: in vivo studies and simulation studies using mathematical model of the pumps and circulatory system. A new mathematical model of the micro-axial blood pumps is established, which can be applied to various micro-axial blood pumps. By inserting the pump model into the model of canine circulatory system according to clinic setting, the pumps effects can be investigated. In this paper, simulation studies of two types of micro-axial blood pumps, Hemopump and dynamic aortic valve (DAV), are made and the results verified that blood pumps decrease the workload of the heart by increasing pump flux, stroke volume, aortic pressure and decreasing left ventricular pressure and volume, left atrial pressure, the blood pumped by the left ventricle. With the increasing of rotation speed, the benefit effects are enhanced, however, too high rotation speed may cause left ventricular collapse. For Hemopump at above 24500 rpm left ventricular collapse is observed and for DAV it is not obtained below 9000 rpm. The simulation results are found in good agreement with the in vivo experimental results

Novel ultrasonic fusion imaging method based on cyclic variation in myocardial backscatter

Quantitative ultrasonic tissue characterisation of the myocardium based on integrated backscatter (IB) has the potential of becoming an effective method for detecting and evaluating myocardial ischaemia. To facilitate IB-based clinical applications, a new imaging method has been developed that combines the anatomical information of a B-mode image with the contractile performance of a selected myocardial region. To produce such a fusion image, a region of interest (ROI) in a B-mode cardiac image was first selected by the user. Algorithms for detection of the endocardium andepicardium were developed, and the resulting mean distance between the computer-detected curve and the manually traced curve was 0.83 mm for the endocardium and 0.58 mm for the epicardium. The cyclic variation of IB (CVIB) of each myocardial tissue element within the ROI was then calculated over one cardiac cycle. Finally, a grey-scale B-mode image at the end of diastole was displayed as a still image, and the pixels representing the myocardial tissue in the ROI colour-coded according to the corresponding CVIB over the past heart cycle. Both the B-mode image and the colour-coded region were refreshed (up-dated) at the next end-of-diastole. Preliminary results from normal (CVIB=10–12dB) and ischaemic (CVIB=5–7 dB) canine hearts are presented that demonstrate the utility of this new imaging method.