-
[show abstract]
[hide abstract]
ABSTRACT: The advent of high angular resolution diffusion imaging (HARDI) has opened up new perspectives for the delineation of crossing and branching fiber pathways. However, image acquisition under clinical conditions with limited measurement time faces the problem of poor spatial and angular resolution and the technique's high susceptibility to noise. In this paper we present a straightforward spatial filter for ODF fields that uses the data-inherent structural information around a voxel as part of a directionally selective method for angular smoothing and radial regularization (ASRR). Especially in regions where fibers cross (multimodal voxels), the method allows us to reduce noise, improve the accuracy of ODF diffusion peaks, and strengthen signals of non-dominant fibers. Moreover, we propose a dynamic scheme in which regularization is applied only to ODFs classified as multimodal. The approach is quantitatively evaluated on synthetic datasets of various configurations. With an in vivo dataset of a human subject, measured under clinical imaging conditions, we demonstrate the method's ability to improve tractography of non-dominant transcallosal fiber pathways and the long fibers of the superior longitudinal fasciculus.
Physica Medica 11/2011; · 1.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Since the advent of high angular resolution diffusion imaging (HARDI) techniques in diffusion MRI great efforts have been
taken in order to reconstruct complex whitematter structures, such as crossing, branching and kissing fibers. However, even
highly sophisticated fiber tracking schemes, such as probabilistic tracking, suffer from the data’s poor signal-to-noise (SNR)
ratio. In this paper we present a novel regularization approach for q-ball fields, exploiting structural information within
the data. We also propose a straightforward deterministic tracking algorithm, allowing delineation of even non-dominant pathways
through crossing regions. Results from a phantom study with a biological phantom as well as a patient study, in which we reconstruct
a part of the pyramidal tract, emphasize the method’s efficiency.
KeywordsHARDI-ODF-Regularization-Fiber Tracking
01/2010: pages 845-848;
-
H H Ehricke
[show abstract]
[hide abstract]
ABSTRACT: This paper addresses the problem of sonography education and training. A method and software package for ultrasound simulation are presented. The latter is based on standard PC technology and allows graphical interaction with a virtual patient and transducer. The most essential component is an extensible case database with various cases from different clinical disciplines. A case consists mainly of a 3D image dataset, sonographically acquired from a patient or a healthy subject. It represents an anatomical region which may be investigated. Furthermore, a method for the geometric registration of the data volume of a new case with the model of the virtual patient is described. This enables the arbitrary extension of the case database.
European Journal of Ultrasound 09/1998; 7(3):225-300.
-
[show abstract]
[hide abstract]
ABSTRACT: In this work we focus on one of the key problems of scientific visualization, the object recognition dilemma. The necessity to pre-interpret application data in order to classify object surface voxels prior to rendering has prevented many visualization methods from becoming practical. We propose the concept of vision by visualization which integrates computer vision methods into the visualization process. Based on this, we present the vision camera, a new tool allowing for interactive object recognition during volume data walkthroughs. This camera model is characterized by a flexible front-plane which, under the control of user-specified parameters and image features elastically matches to object surfaces, while shifted through a data volume. Thus, objects are interactively carved out and can be visualized by standard volume visualization methods. Implementation and application of the model are described. Our results suggest that by the integration of human and machine vision new perspectives for data exploration are opened up
Visualization, 1993. Visualization '93, Proceedings., IEEE Conference on; 11/1993
-
[show abstract]
[hide abstract]
ABSTRACT: A treatment planning system based on magnetic resonance (MR) angiographic imaging data for the radiosurgery of inoperable cerebral arteriovenous malformations is reported. MR angiography was performed using a three-dimensional (3D) velocity-compensated fast imaging with steady-state precession (FISP) sequence. Depending on the individual MR system, inhomogeneities and nonlinearities induced by eddy currents during the pulse sequence can distort the images and produce spurious displacements of the stereotactic coordinates in both the x-y plane and the z axis. If necessary, these errors in position can be assessed by means of two phantoms placed within the stereotactic guidance system--a "2D-phantom" displaying "pincushion" distortion in the image, and a "3D-phantom" displaying displacement, warp, and tilt of the image plane itself. The pincushion distortion can be "corrected" (reducing displacements from 2-3 mm to 1 mm) by calculations based on modeling the distortion as a fourth order 2D polynomial. Displacement, warp, and tilt of the image plane may be corrected by adjustment of the gradient shimming currents. After correction, the accuracy of the geometric information is limited only by the pixel resolution of the image (= 1 mm). Precise definition of the target volume could be performed by the therapist either directly in the MR images or in calculated projection MR angiograms obtained by a maximum intensity projection algorithm. MR angiography provides a sensitive, noninvasive 3D method for defining target volume and critical structures, and for calculating precise dose distributions for radiosurgery of cerebral arteriovenous malformations.
Magnetic Resonance Imaging 02/1992; 10(4):609-21. · 1.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In many clinical situations neuroradiologists and neurosurgeons are keenly interested in images displaying both brain structures and intracranial vessels in an integrative manner. In this paper an approach to three-dimensional visualization of brain and vascular structures from magnetic resonance (MR) volume data is reported. It has been designed with the aim of providing a robust and reliable image processing tool for routine clinical applications. The method has been made possible by recent developments in MR image acquisition, especially MR angiography and rapid gradient-echo sequences (Turbo-fast low angle shot). On the basis of the ray-tracing principle, integration of brain and vessel anatomy into a single 3D image is achieved. Image data are acquired with flow-compensated gradient-echo pulse sequences. Even slow flow in venous structures may be demonstrated using a two-dimensional sequential-slice scanning method. Finally, if incorporated into an interactive image processing system, this technique may be used as a planning tool allowing a surgical "rehearsal" prior to actual operative exposure and resection of a lesion.
Journal of Computer Assisted Tomography 14(5):846-52. · 1.22 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: With the introduction of MR angiography (MRA) into clinical routine MR protocols, it has become possible now to image flowing as well as stationary tissue with excellent contrast using a single modality. This has opened up new perspectives for planning stereotactic approaches, which are characterized by high risks for damaging intracerebral vessels or vital brain structures. In this article we present an MRA based planning method for the treatment of arteriovenous malformations by stereotactic radiosurgery. It includes flow compensated gradient echo pulse sequences for the acquisition of angiographic MR datasets, a stereotactic MR marker system, an algorithm for the correction of geometric distortion of MR image data, and a three-dimensional workstation system for the creation and evaluation of treatment plans. The latter is based on the concept of simultaneously displaying both MR slice and angiographic projection images. This allows the evaluation of intracerebral vasculature together with brain anatomy. The MRA guided planning approach was tested and compared to a conventional X-ray angiographic technique in a clinical study. Our satisfactory results suggest that MRA is a technique that can be used advantageously for stereotactic planning.
Journal of Computer Assisted Tomography 16(1):35-40. · 1.22 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Stereotactic neurosurgical interventions are characterized by a high risk of rupturing intracranial vessels or damaging vital brain structures. By MRI and MRA, the anatomic information necessary for stereotactic treatment planning may be assessed with a single modality as a high-resolution digital image volume. The adequacy of MR as a modality for stereotactic guidance is demonstrated by the example of the radiosurgical treatment of cerebral angiomas. An optimized acquisition protocol, a stereotactic apparatus, a distortion correction and minimization method, and a 3D treatment planning workstation are elements of a proposed preoperative approach which in a clinical study met with good acceptance.
Computerized Medical Imaging and Graphics 16(2):65-71. · 1.47 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present a medical workstation for the efficient implementation of research ideas related to image processing and computer graphics. Based on standard hardware platforms the software system encompasses two major components: A turnkey application system provides a functionally kernel for a broad community of clinical users working with digital imaging devices, including methods of noise suppression, interactive and automatic segmentation, 3D surface reconstruction and multi-modal registration. A development toolbox allows new algorithms and applications to be efficiently implemented and consistently integrated with the common framework of the turnkey system. The platform is based on an elaborate object class structure describing objects for image processing, computer graphics, study handling and user interface control. Thus expertise of computer scientists familiar with this application domain is brought into the hospital and can be readily used by clinical researchers.
Computerized Medical Imaging and Graphics 18(6):403-11. · 1.47 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present a workstation-based research platform with two major components. A turnkey application system provides a functionality kernel for a broad community of clinical users with an interest in digital imaging. A development toolbox allows efficient implementation of research ideas and consistent integration of new applications with the common framework of the turnkey system. The platform is based on an elaborate object class structure describing objects for image processing, computer graphics, study handling and user interface control. Thus expertise of computer scientists familiar with this application domain is brought into the hospital and can be readily used by clinical researchers.
Computer Methods and Programs in Biomedicine 48(1-2):157-62. · 1.52 Impact Factor
