Catálogo de publicaciones - libros

Recent research in biology has indicated correlations between the movement patterns of functional sites (such as replication sites in DNA) and zones of genetic activity within a nucleus. A detailed study and analysis of the motion dynamics of these sites can reveal an interesting insight into their role in DNA replication and function. In this paper, we propose a suite of novel techniques to determine, analyze, and interpret the mobility patterns of functional sites. Our algorithms are based on interesting ideas from theoretical computer science and database theory and provide for the first time the tools to interpret the seemingly stochastic motion patterns of the functional sites within the nucleus in terms of a set of tractable ‘patterns’ which can then be analyzed to understand their biological significance.

Multidimensional fluorescence imaging is a powerful molecular imaging modality that is emerging as an important tool in the study of biological tissues. Due to the large volume of multi-spectral data associated with the technique, it is often difficult to find the best combination of parameters to maximize the contrast between different tissue types. This paper presents a novel framework for the characterization of tissue compositions based on the use of time resolved fluorescence imaging without the explicit modeling of the decays. The composition is characterized through soft clustering based on manifold embedding for reducing the dimensionality of the datasets and obtaining a consistent differentiation scheme for determining intrinsic constituents of the tissue. The proposed technique has the benefit of being fully automatic, which could have significant advantages for automated histopathology and increasing the speed of intraoperative decisions. Validation of the technique is carried out with both phantom data and tissue samples of the human pancreas.

Diffusion weighted magnetic resonance (DWMR or DW) imaging is a fast evolving technique to investigate the connectivity of brain white matter by measuring the self-diffusion of the water molecules in the tissue. Registration is a key step in group analysis of the DW images that may lead to understanding of functional and structural variability of the normal brain, understanding disease process, and improving neurosurgical planning. In this paper, we present a new method for registering DW images. The method works directly on the diffusion weighted images without using tensor reconstruction, fiber tracking, and fiber clustering. Therefore, the performance of the method does not rely on the accuracy and robustness of these steps. Moreover, since all the information in the original diffusion weighted images is used for registration, the results of the method is robust to imaging noise. We demonstrate the method on intra-subject registration with an affine transform using DW images acquired on the same scanner with the same imaging protocol. Extension to deformable registration for images acquired on different scanners and/or with different imaging protocols is also discussed.

Rigid registration of pre-operative surgical plans to intra-operative coordinates of a patient is an important step in computer-assisted orthopaedic surgery. A good measure for registration accuracy is the target registration error (TRE) which is the distance after registration between a pair of corresponding points not used in the registration process. However, TRE is not a deterministic value, since there is always error in the localized features (points) utilized in the registration. In this situation, the distribution of TRE carries more information than TRE by itself. Previously, the distribution of TRE has been estimated with the accuracy of the first-order approximation. In this paper, we analytically approximate the TRE distribution up to at least the second-order accuracy based on the Unscented Kalman Filter algorithm.

A new method for elastic mono-modal image registration for adaptive fractionated radiotherapy is presented. Elastic registration is a prerequisite for many medical applications in diagnosis, therapy planning, and therapy. Especially for adaptive radiotherapy efficient and accurate registration is required. Therefore, we developed a fast block matching algorithm for robust image registration. Anatomical landmarks are automatically selected at tissue borders and relocated in the frequency domain. A smooth interpolation is calculated by modified thin-plate splines with local impact. The concept of the algorithm allows different handling of different image structures. Thus, more features were included, like handling of discontinuities (e. g. air cavities in the intestinal track or rectum, observable in only one image), which can not be registered in a conventional way. The planning CT as well as delineated structures of target volume and organs at risks are transformed according to deviations observed in daily acquired verification CTs prior each dose fraction. This way, the time consuming repeated delineation, a prerequisite for adaptive radiotherapy, is avoided. The total calculation time is below 5 minutes and the accurateness is higher than voxel precision, which allows to use this tool in the clinical workflow. We present results of prostate, head-and-neck, and paraspinal tumors with verification by manually selected landmarks. We think this registration technique is not only suitable for adaptive radiotherapy, but also for other applications which require fast registration and possibilities to process special structures (e. g. discontinuities) in a different way.

This paper presents a deformable registration method to co-register histological images with MR images of the same prostate. By considering various distortion and cutting artifacts in histological images and also fundamentally different nature of histological and MR images, our registration method is thus guided by two types of landmark points that can be reliably detected in both histological and MR images, i.e., prostate boundary points, and internal salient points that can be identified by a scale-space analysis method. The similarity between these automatically detected landmarks in histological and MR images are defined by geometric features and normalized mutual information, respectively. By optimizing a function, which integrates the similarities between landmarks with spatial constraints, the correspondences between the landmarks as well as the deformable transformation between histological and MR images can be simultaneously obtained. The performance of our proposed registration algorithm has been evaluated by various designed experiments. This work is part of a larger effort to develop statistical atlases of prostate cancer using both imaging and histological information, and to use these atlases for optimal biopsy and therapy planning.

We present a new algorithm for affine registration of diffusion tensor magnetic resonance (DT-MR) images. The method is based on a new formulation of a point-wise tensor similarity measure, which weights directional and magnitude information differently depending on the type of diffusion. The method is compared to a reference method, which uses normalized mutual information (NMI), calculated either from a fractional anisotropy (FA) map or a -weighted MR image. The registration methods are applied to real and simulated DT-MR images. Visual assessment is done for real data and for simulated data, registration accuracy is defined. The results show that the proposed method outperforms the reference method.

We propose and test analytic equations for approximating expected fiducial and surface target registration error (TRE). The equations are derived from a spatial stiffness model of registration. The fiducial TRE equation is equivalent to one presented by [1]. We believe that the surface TRE equation is novel, and we provide evidence from computer simulations to support the accuracy of the approximation.

This paper presents a method for tracking a bronchoscope based on motion prediction and image registration from multiple initial starting points as a function of a bronchoscope navigation system. We try to improve performance of bronchoscope tracking based on image registration using multiple initial guesses estimated using motion prediction. This method basically tracks a bronchoscopic camera by image registration between real bronchoscopic images and virtual ones derived from CT images taken prior to the bronchoscopic examinations. As an initial guess for image registration, we use multiple starting points to avoid falling into local minima. These initial guesses are computed using the motion prediction results obtained from the Kalman filter’s output. We applied the proposed method to nine pairs of X-ray CT images and real bronchoscopic video images. The experimental results showed significant performance in continuous tracking without using any positional sensors.

Measurements of cup alignment after total hip replacement (THR) surgery are typically performed on postoperative pelvic radiographs. Radiographic measurement of cup orientation depends on the position and orientation of the pelvis on the X-ray table, and its variability could introduce significant measurement errors. We have developed a tool to accurately measure 3D implant orientation from postoperative antero-posterior radiographs by registering to preoperative CT scans. The purpose of this study is to experimentally and clinically validate the automatic CT/X-ray matching algorithm by comparing the X-ray based measurements of cup orientation with direct 3D measurements from postoperative CT scans. The mean measurement errors (± stdev) found in this study were 0.4°±0.8° for abduction and 0.6°±0.8° for version. In addition, radiographic pelvic orientation measurements demonstrated a wide range of inter-subject variability, with pelvic flexion ranging from –5.9° to 11.2°.