Biomedical subjects

R Stokking

Publications and source records attributed to R Stokking.

13 recordsLinked to original sources

PubMed2001

Integrated volume visualization of functional image data and anatomical surfaces using normal fusion.

A generic method, called normal fusion, for integrated three-dimensional (3D) visualization of functional data with surfaces extracted from anatomical image data is described. The first part of the normal fusion method derives quantitative values from functional input data by sampling the latter along a path determined by the (inward) normal of a surface extracted from anatomical data; the functional information is thereby projected onto the anatomical surface independently of the viewpoint. Fusion of the anatomical and functional information is then performed with a color-encoding scheme based on the HSV model. This model is preferred over the RGB model to allow easy, rapid, and intuitive retrospective manipulation of the color encoding of the functional information in the integrated display, and two possible strategies for this manipulation are explained. The results first show several clinical examples that are used to demonstrate the viability of the normal fusion method. These same examples are then used to evaluate the two HSV color manipulation strategies. Furthermore, five nuclear medicine physicians used several other clinical cases to evaluate the overall approach for manipulation of the color encoded functional contribution to an integrated 3D visualization. The integrated display using the normal fusion technique combined with the added functionality provided by the retrospective color manipulation was highly appreciated by the clinicians and can be considered an important asset in the investigation of data from multiple modalities.

Adult↗

PubMed2000

Automatic morphology-based brain segmentation (MBRASE) from MRI-T1 data.

A method called morphology-based brain segmentation (MBRASE) has been developed for fully automatic segmentation of the brain from T1-weighted MR image data. The starting point is a supervised segmentation technique, which has proven highly effective and accurate for quantitation and visualization purposes. The proposed method automates the required user interaction, i.e., defining a seed point and a threshold range, and is based on the simple operations thresholding, erosion, and geodesic dilation. The thresholds are detected in a region growing process and are defined by connections of the brain to other tissues. The method is first evaluated on three computer simulated datasets by comparing the automated segmentations with the original distributions. The second evaluation is done on a total of 30 patient datasets, by comparing the automated segmentations with supervised segmentations carried out by a neuroanatomy expert. The comparison between two binary segmentations is performed both quantitatively and qualitatively. The automated segmentations are found to be accurate and robust. Consequently, the proposed method can be used as a default segmentation for quantitation and visualization of the human brain from T1-weighted MR images in routine clinical procedures.

Adolescent↗

PubMed2000

Reproducibility of serial peri-ictal single-photon emission tomography difference images in epilepsy patients undergoing surgical resection.

Peri-ictal single-photon emission tomography (SPET) difference images co-registered to magnetic resonance imaging (MRI) visualize regional cerebral blood flow (rCBF) changes and help localize the epileptogenic area in medically refractory epilepsy. Few reports have examined the reproducibility of SPET difference image results. Epilepsy patients having two peri-ictal and at least one interictal SPET scan who later underwent surgical resection were studied. Localization accuracy of peri-ictal SPET difference images results, interictal electroencephalography (EEG), and ictal EEG from the first (seizure 1) and second (seizure 2) seizure, as well as MRI and positron emission tomography (PET) findings, were compared using surgical resection site as the standard. Thirteen patients underwent surgical resection (11 temporal lobe and 2 extratemporal). SPET results from seizure 1 were localized to the surgical site in 12/13 (92%) patients, while SPET results from seizure 2 were localized in 13/13 (100%) patients. All other modalities were less accurate than the SPET results interictal EEG--seizure 1 6/13 (46%); ictal EEG--seizure 1 5/13 (38%); interictal intracranial EEG--seizure 2 4/9 (44%); ictal intracranial EEG--seizure 2 results 8/9 (89%); MRI 6/13 (46%); PET 9/13 (69%)[. SPET results were reproducible in 12/13 (92%) patients. SPET difference images calculated from two independent peri-ictal scans appear to be reproducible and accurately localize the epileptogenic area. While SPET difference images visualize many areas of rCBF change, the quantification of these results along with consideration of injection time improves the diagnostic interpretation of the results.

Adult↗

PubMed2000

Decreased cerebral blood flow during seizures with ictal SPECT injections.

Increased regional cerebral blood flow (rCBF) at the epileptogenic site has been consistently reported for single photon emission computed tomography (SPECT) injections made during seizure activity, and the increased rCBF has been shown to remain elevated at the epileptogenic site in some cases, even when SPECT injections are made after seizure termination (postictal). A sustained increase in rCBF after seizure cessation was recently confirmed, but for no more than 100 s from seizure onset [Avery, R.A., Spencer, S.S., Spanaki, M.V., Corsi, M., Seibyl, J.P., Zubal, I.G., 1999. Effect of injection time on postictal SPET perfusion changes in medically refractory epilepsy. Eur. J. Nucl. Med. 26, 830-836]. In the current study, it is examined whether ictal SPECT injections demonstrate a similar change in rCBF around 100 s from seizure onset. Twenty-one patients with medically refractory epilepsy and a known area of seizure onset receiving ictal and interictal 99mTc-Hexamethyl-propyleneamineoxime (HMPAO) SPECT scans were studied. The results of SPECT subtraction analysis which visualize increased and decreased rCBF were compared to seizure duration and HMPAO injection time. Five patients received ictal SPECT injections (during ongoing seizure activity) more than 90 s after seizure onset and demonstrated decreased rCBF. Two of these patients also demonstrated areas of increased rCBF. Decreased rCBF was localized to the epileptogenic lobe in four of the five patients. By examining ictal SPECT injections made 90 s after seizure onset, evidence was found that reduced rCBF may exist during ictus. The change in rCBF around 90 s is also observed in postictal injections, suggesting a common metabolic mechanism may be responsible.

Adolescent↗

PubMed2000

Ratio-images calculated from interictal positron emission tomography and single-photon emission computed tomography for quantification of the uncoupling of brain metabolism and perfusion in epilepsy.

PURPOSE: Image processing techniques were applied to interictal positron emission tomography (PET) and single-photon emission computed tomography (SPECT) brain images to aid in the localization of epileptogenic foci by calculating a functional image that represents the degree of coupling between perfusion and metabolism. Uncoupling of these two functions has been demonstrated to be a characteristic of epileptogenic tissue in temporal lobe epilepsy and has the potential to serve as a diagnostic measure for localization in other areas as well. METHODS: Interictal PET ((18)F-FDG) and interictal SPECT ((99m)Tc-HMPAO) scans were acquired from 11 epilepsy patients. The metabolism and perfusion images were three-dimensionally spatially registered, and a functional ratio-image was computed. These functional maps are overlaid onto a three-dimensional rendering of the same patient's magnetic resonance imaging anatomy. RESULTS: In all patients, an average uniform perfusion-to-metabolism ratio showed approximately constant values throughout most of the whole brain. However, the epileptogenic area (confirmed on surgery) demonstrated an area of elevated perfusion/metabolism in the grey matter. CONCLUSIONS: Although hypometabolism in the PET image was observed in most of these patients, the calculation of a functional ratio-image demonstrated localized foci that in some cases could not be observed on the PET image alone. The ratio-image also yields a quantitative measure of the uncoupling phenomenon.

Adolescent↗

PubMed1999

Integrated visualization of functional and anatomic brain data: a validation study.

UNLABELLED: Two-dimensional SPECT display and three methods for integrated visualization of SPECT and MRI patient data are evaluated in a multiobserver study to determine whether localization of functional data can be improved by adding anatomical information to the display. METHODS: SPECT and MRI data of 30 patients were gathered and presented using four types of display: one of SPECT in isolation, two integrated two-dimensional displays and one integrated three-dimensional display. Cold and hot spots in the peripheral cortex were preselected and indicated on black-and-white hard copies of the image data. Nuclear medicine physicians were asked to assign the corresponding spots in the image data on the computer screen to a lobe and a gyrus and give a confidence rating for both localizations. Interobserver agreement using kappa statistics and average confidence ratings were assessed to interpret the reported observations. RESULTS: Both the interobserver agreement and the confidence of the observers were greater for the integrated two-dimensional displays than for the two-dimensional SPECT display. An additional increase in agreement and confidence was seen with the integrated three-dimensional display. CONCLUSION: Integrated display of SPECT and MR brain images provides better localization of cerebral blood perfusion abnormalities in the peripheral cortex in relation to the anatomy of the brain than single-modality display and increases the confidence of the observer.

Cerebral Cortex↗

PubMed1998

Advances in three-dimensional diagnostic radiology.

The maturity of current 3D rendering software in combination with recent developments in computer vision techniques enable an exciting range of applications for the visualisation, measurement and interactive manipulation of volumetric data, relevant both for diagnostic imaging and for anatomy. This paper reviews recent work in this area from the Image Sciences Institute at Utrecht University. The processes that yield a useful visual presentation are sequential. After acquisition and before any visualisation, an essential step is to prepare the data properly: this field is known as 'image processing' or 'computer vision' in analogy with the processing in human vision. Examples will be discussed of modern image enhancement and denoising techniques, and the complex process of automatically finding the objects or regions of interest, i.e. segmentation. One of the newer and promising methodologies for image analysis is based on a mathematical analysis of the human (cortical) visual processing: multiscale image analysis. After preprocessing the 3D rendering can be acquired by simulating the 'ray casting' in the computer. New possibilities are presented, such as the integrated visualisation in one image of (accurately registered) datasets of the same patient acquired in different modality scanners. Other examples include colour coding of functional data such as SPECT brain perfusion or functional magnetic resonance (MR) data and even metric data such as skull thickness on the rendered 3D anatomy from MR or computed tomography (CT). Optimal use and perception of 3D visualisation in radiology requires fast display and truly interactive manipulation facilities. Modern and increasingly cheaper workstations ( < $10000) allow this to be a reality. It is now possible to manipulate 3D images of 256 at 15 frames per second interactively, placing virtual reality within reach. The possibilities of modern workstations become increasingly more sophisticated and versatile. Examples presented include the automatic detection of the optimal viewing angle of the neck of aneurysms and the simulation of the design and placement procedure of intra-abdominal aortic stents. Such developments, together with the availability of high-resolution datasets of modern scanners and data such as from the NIH Visible Human project, have a dramatic impact on interactive 3D anatomical atlases.

Humans↗

PubMed1997

Integration of functional and anatomical brain images.

This article concerns the integration of functional and anatomical volumetric brain images. Integration consists of two steps: matching or registration, where the images are brought into spatial agreement, and fusion or simultaneous display where the registered multimodal image information is presented in an integrated fashion. Approaches to register multiple images are divided into extrinsic methods based on artificial markers, and intrinsic matching methods based solely on the patient related image data. The various methods are compared by a number of characteristics, which leads to a clear preference for one class of intrinsic methods, viz. voxel-based matching. Furthermore, two- and three-dimensional techniques to display multimodality image information are outlined.

Brain↗

PubMed1997

Computed tomographic angiographic imaging of abdominal aortic aneurysms: implications for transfemoral endovascular aneurysm management.

PURPOSE: To describe anatomic features pertinent to patient selection and graft design for transfemoral endovascular aneurysm management (TEAM) of the infrarenal aorta using computed tomographic (CT) angiography. METHODS: A prospective noncomparative analysis of 102 spiral CT scans of the abdominal aorta of patients with abdominal aortic aneurysms was performed. From the original CT data set, slices were reconstructed perpendicular to the vessel axis (central lumen line) at a 10 mm interval. In these reconstructed slices, diameter measurements were performed. Vessel length was measured along the central lumen line. In each patient possibilities for TEAM were analyzed. RESULTS: Because of technical reasons, 36 scans were excluded from the analysis. Of the remaining 66 patients, 18 could potentially be treated with a bifurcated endovascular device. The infrarenal aortic diameter-to-iliac artery diameter ratio was less than 2 in most patients. The vessel segments judged to be adequate for endovascular graft anchoring had a noncylindrical shape in the majority of cases. CONCLUSION: Only a minority of patients with abdominal aortic aneurysms can at this stage be treated with an endovascular graft. The ideal endovascular graft should be a combination of rigid and flexible components. The proximal and distal attachment systems should have some flexibility with an intrinsic maximum diameter while the midsection of the graft can be relatively rigid.

Adult↗

PubMed1997

Normal fusion for three-dimensional integrated visualization of SPECT and magnetic resonance brain images.

UNLABELLED: Multimodality visualization aims at efficiently presenting integrated information obtained from different modalities, usually combining a functional modality (SPECT, PET, functional magnetic resonance imaging) with an anatomical modality [CT, magnetic resonance imaging (MRI)]. This paper presents a technique for three-dimensional integrated visualization of SPECT and magnetic resonance brain images, where MRI is used as a framework of reference for the display of the SPECT data. METHODS: A novel technique for three-dimensional integrated visualization of functional and anatomical information, called normal fusion, is presented. With this technique, local functional information is projected onto an anatomic structure. RESULTS: The normal fusion technique is applied to three cases of SPECT/MRI integration. The results are presented, discussed and evaluated for clinical relevance. CONCLUSION: The results for three-dimensional integrated display of SPECT and MR brain images indicate that the normal fusion technique provides a potentially comprehensive and diagnostically valuable presentation of cerebral blood perfusion in relation to the anatomy of the brain.

Autistic Disorder↗

PubMed1994

Variations in venous and segmental anatomy of the liver: two- and three-dimensional MR imaging in healthy volunteers.

OBJECTIVE: The purpose of this study was to use two- and three-dimensional analysis of thin-slice MR imaging data to study the anatomic variations in the segmental anatomy of the liver. It is important to recognize these anatomic variations in order to ensure accurate localization of hepatic lesions and preoperative delineation of resection planes. SUBJECTS AND METHODS: T1-weighted MR images of contiguous 4-mm sections were obtained in 10 healthy subjects. We measured the orientations of external and internal hepatic landmarks that indicated segmental boundaries and created three-dimensional renderings of hepatic veins, intrahepatic portal branches, liver surface, and gallbladder. RESULTS: Variations in the portal branching pattern were seen in eight of 10 subjects. Most variations occurred in the right hemiliver and consisted of the absence of a right portal trunk or the presence of accessory portal branches. The division between right anterior and right posterior segments was inclined posteriorly (average, 31.2 degrees) relative to the right hepatic vein. The landmarks indicating the position of the umbilical fissure showed marked variability. Only two of 10 subjects had three hepatic veins, with the left and middle veins sharing a common trunk. In the remaining eight subjects, nine accessory veins were present: three left, one middle, and five right. CONCLUSION: Planes of resection in liver surgery are largely determined by the precise position of tumor relative to the individual segmental anatomy. Consequently, localization of liver lesions and preoperative delineation of resection planes requires consideration of the significant anatomic variations in the segmental anatomy of the liver. These anatomic variations can be depicted on two- and three-dimensional displays of T1-weighted MR images of contiguous 4-mm sections.

Adult↗

PubMed1992

Integrated presentation of multimodal brain images.

This article discusses the fusion of brain images from multiple modalities as well as the presentation of the integrated image information. The paper has three parts. First, individual brain imaging modalities are compared as regards clinical appreciation, invasiveness, dimensionality, spatial resolution, temporal resolution, and cost. Next, methods to combine multiple images are briefly surveyed and collated by characteristics as accuracy, patient-friendliness, reproducibility, labour-extensiveness, feasibility of retrospective matching, and general applicability. Finally, techniques to display multimodal image information are outlined and examples of the various options for integrated presentation are shown.

Brain↗

PubMedDate not supplied

Registration, segmentation, and visualization of multimodal brain images.

This paper gives an overview of the studies performed at our institute over the last decade on the processing and visualization of brain images, in the context of international developments in the field. The focus is on multimodal image registration and multimodal visualization, while segmentation is touched upon as a preprocessing step for visualization. The state-of-the-art in these areas is discussed and suggestions for future research are given.

Brain↗