Yazhu Chen

Mutual information-based multimodal image registration using a novel joint histogram estimation

Mutual information (MI)-based image registration has been proved to be very effective in multimodal medical image applications. For computing the mutual information between two images, the joint histogram needs to be estimated. As we know, the joint histogram estimation through linear interpolation and partial volume (PV) interpolation methods may result in the emergency of the local extreme in mutual information registration function. The local extreme is likely to hamper the optimization process and influence the registration accuracy. In this paper, we present a novel joint histogram estimation method (HPV) by using an approximate function of Hanning windowed sinc as kernel function of partial volume interpolation. We apply it to both rigid registration and non-rigid registration. In addition, we give a new method estimating the gradient of mutual information with respect to the model parameters during non-rigid registration. By the experiments on both synthetic and real images, it is clearly shown that the new algorithm has the ability to reduce the local extreme, and the registration accuracy is improved.

The shape of the acetabular cartilage surface: a geometric morphometric study using three-dimensional scanning.

The acetabular cartilage surface plays an important role in hip joint biomechanics, locomotion and lubrication, but few studies has focused on its geometric morphometry. The aim of this study was to present a novel, accurate mathematical representation of the acetabular cartilage surface based on a new method, combined with a reverse engineering technique, surface-fitting algorithms and mathematical curve surface theory. By using a three-dimensional (3D) laser scanner, a 3D triangulated mesh surface approximation of acetabular cartilage was created. Using surface-fitting algorithms and mathematical curve surface theory, two main curvature parameters, Gaussian curvature and mean curvature at each point on the surface of the acetabular cartilage, were calculated. The distribution patterns of both parameters over the curved surface were elucidated and the eigenvalues of the surface were calculated to determine the shape of the acetabular cartilage surface. By statistically analyzing 25 specimens, it was found that the shape of the acetabular cartilage surface was not theoretically spherical but rotational ellipsoidal, which is a novel mathematical description. The surface-fitting error of a rotational ellipsoid shape was significantly smaller than that of a spherical shape for representing the acetabular cartilage surface (p<0.001). The highest surface-fitting error for a spherical shape was seen in the roof area of the acetabular cartilage, where a rotational ellipsoid surface presented a better anatomical fit. The results will not only be helpful in gaining a new anatomical understanding of the acetabular cartilage surface, but will also be usable in the construction of a precise 3D numerical model in simulation studies of the hip joint.

A high-resolution three-dimensional far-infrared thermal and true-color imaging system for medical applications

As the needs for various kinds of body surface information are wide-ranging, we developed an imaging-sensor integrated system that can synchronously acquire high-resolution three-dimensional (3D) far-infrared (FIR) thermal and true-color images of the body surface. The proposed system integrates one FIR camera and one color camera with a 3D structured light binocular profilometer. To eliminate the emotion disturbance of the inspector caused by the intensive light projection directly into the eye from the LCD projector, we have developed a gray encoding strategy based on the optimum fringe projection layout. A self-heated checkerboard has been employed to perform the calibration of different types of cameras. Then, we have calibrated the structured light emitted by the LCD projector, which is based on the stereo-vision idea and the least-squares quadric surface-fitting algorithm. Afterwards, the precise 3D surface can fuse with undistorted thermal and color images. To enhance medical applications, the region-of-interest (ROI) in the temperature or color image representing the surface area of clinical interest can be located in the corresponding position in the other images through coordinate system transformation. System evaluation demonstrated a mapping error between FIR and visual images of three pixels or less. Experiments show that this work is significantly useful in certain disease diagnoses.

A Computer-based Diagnosis System for Early Glaucoma Screening

Glaucoma is a serious eye disease and the major cause of blindness worldwide. Glaucoma screening is a useful way in detecting the disease at an early stage. This paper presents a computer-based glaucoma screening system in which optic nerve defects detection, visual field examination, and expert system rules are combined to increase the sensitivity and specificity. Several fundus image processing methods are used and a histogram model is given especially for combed hair retinal nerve fiber layer defect. A visual field test performed on computer monitor is adopted to reduce the cost for other perimetry equipments. The assistant diagnostic module can give a primary diagnosis based on a set of fuzzy rules. The system is cost effective and suitable for detecting early stage glaucoma, especially for large-scale screening

Contributions of non-spherical hip joint cartilage surface to hip joint contact stress

The natural non-spherical incongruent hip joint cartilage surface is normally assumed as spherical in shape, which has been extensively applied in orthopedic clinic, hip joint simulation studies and hip joint prosthesis design. The aim of the study was to investigate the contributions of non-spherical incongruent hip joint cartilage surface to the hip joint contact stress, and to assess the effect of simplified spherical assumption on the predicted contact stress. Based on our previous anatomic studies that the acetabular cartilage surface was demonstrated as rotational ellipsoid in shape, three finite element (FE) models involving the natural hip joint cartilage shape, the hip joint cartilage shape replaced by the rotational ellipsoid and the sphere, respectively, were developed using the computed tomography (CT) image data of healthy volunteers. The FE predictions of contact stress on the replaced hip joint cartilage surface were compared with that on the natural hip joint cartilage surface. The result showed that the non-spherical hip joint cartilage surface contributed to the optimal contact stress magnitude and distribution. The replaced fitting spherical surface led to the increased contact stress of hip joint and the uneven distributed patterns of contact stress, whereas the replaced fitting rotational ellipsoid surface was comparatively more consistent with the natural results than the sphere one. The surface fitting error of the replaced rotational ellipsoid was fewer than that of the replaced sphere. These results indicate that the simplified spherical assumption will lead to misestimating the contact mechanics of hip joint, and the rotational ellipsoid model rather than the sphere model may represent the hip joint contact surface applied in the hip joint simulation study and the hip joint prosthesis design.

The shape of the acetabular cartilage surface and its role in hip joint contact stress

The acetabular cartilage is normally represented as a spherical shape in orthopedic clinic and related researches. The aim of the study was to present a new mathematic representation with better fit to the acetabular cartilage surface and to investigate the role of its shape on the hip joint contact stress.

High-intensity focused ultrasound with large scale spherical phased array for the ablation of deep tumors

Under some circumstances surgical resection is feasible in a low percentage for the treatment of deep tumors. Nevertheless, high-intensity focused ultrasound (HIFU) is beginning to offer a potential noninvasive alternative to conventional therapies for the treatment of deep tumors. In our previous study, a large scale spherical HIFU-phased array was developed to ablate deep tumors. In the current study, taking into account the required focal depth and maximum acoustic power output, 90 identical circular PZT-8 elements (diameter=1.4 cm and frequency=1 MHz) were mounted on a spherical shell with a radius of curvature of 18 cm and a diameter of 21 cm. With the developed array, computer simulations and ex vivo experiments were carried out. The simulation results theoretically demonstrate the ability of the array to focus and steer in the specified volume (a 2 cm×2 cm×3 cm volume) at the focal depth of 15 to 18 cm. Ex vivo experiment results also verify the capability of the developed array to ablate deep target tissue by either moving single focal point or generating multiple foci simultaneously.

Multi-Modality Medical Image registration Using Support Vector Machines

The registration of multi-modality medical images is an important tool in surgical application. We presented a method of computing different modality medical images registration of the same patient. It incorporates prior joint intensity distribution between the two imaging modalities based on registered training images. The prior joint intensity distribution is modeled by support vector machine. Results aligning CT/MR and PET/MR scans demonstrate that it can attain sub-voxel registration accuracy. Furthermore, it is a fast registration method because support vector machine solution is sparse

SVM for density estimation and application to medical image segmentation

A method of medical image segmentation based on support vector machine (SVM) for density estimation is presented. We used this estimator to construct a prior model of the image intensity and curvature profile of the structure from training images. When segmenting a novel image similar to the training images, the technique of narrow level set method is used. The higher dimensional surface evolution metric is defined by the prior model instead of by energy minimization function. This method offers several advantages. First, SVM for density estimation is consistent and its solution is sparse. Second, compared to the traditional level set methods, this method incorporates shape information on the object to be segmented into the segmentation process. Segmentation results are demonstrated on synthetic images, MR images and ultrasonic images.

A Study of Heating Duration and Scanning Path in Focused Ultrasound Surgery

A conventional method of avoiding normal tissue overheating during focused ultrasound surgery (FUS) is to apply equal heating duration for each sonication in between cooling intervals. However, this method is time-consuming and expensive. A novel method with unequal heating duration in different scanning paths without cooling intervals was investigated in this paper. This method was compared with the conventional method through the ablation of a 10 × 10 cm2 target. The simulation results indicated that the new method was able to reduce treatment time by more than 50%, with higher than 95% coverage index, and more uniform thermal dose distribution. The method was further verified through the ablation of a circular lesion. Ex vivo experiments were also performed to confirm the simulation results. Both simulation and experimental results have proven that the new method can increase heating efficiency, and are a promising new approach in FUS.